HomeMy WebLinkAbout2009-323A EXHIB I I " B "
Management Plan
IR44
Dredged Material Management Area
May 1999
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Management Plan
IR- 14
Dredged Material Management Area
Prepared for
FLORIDA INLAND NAVIGATION DISTRICT
by
R. Bruce Taylor, Ph .D ., P. E.
William F. McFetridge
Taylor Engineering, Inc .
9000 Cypress Green Drive, Suite 200
Jacksonville, Florida 32256
(904) 7314040
c
TABLE OF CONTENTS
LISTOF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
1 .0 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2.0 PRE DREDGING SITE PREPARATION AND DESIGN FEATURES . . . . . . . . . . . 9 8 . 0 0 5
2. 1 Site Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. 1 . 1 Containment Basin Capacity and Configuration Requirements . 5
2. 1. 2 Containment Basin Design . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . 9
2.2 Facility Construction . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . 9
2. 2. 1 Clearing and Grubbing . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . 11
2. 2. 2 Excavation and Grading . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . 11
2.3 Additional Design Features . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . 12
2. 3. 1 Inlet . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2. 3. 2 Weirs . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2. 3. 3 Ponding Depth and Basin Performance . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . 16
2. 3. 4 Interior Earthworks . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . 20
2. 3. 5 Ramps . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2. 3. 6 Perimeter Ditches . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . 21
2. 3. 7 Dike Erosion and vegetation . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . 23
2. 3. 8 Site Security . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.4 Groundwater Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . 24
2. 5 Migratory Bird Protection . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . 25
2.6 Cultural Resources . . . . . . . . . . . . : . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . 26
3 .0 OPERATIONAL CONSIDERATIONS DURING DREDGING . . . . . . . . . . . . . . . . . . . . .
. 27
3 . 1 Placement of Pipelines . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . 27
3.2 Inlet Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3. 2. 1 Monitoring Related to Inlet Operation . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . 29
3 .3 Weir Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.4 Effluent Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . 33
3.5 Groundwater Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . 34
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3 .6 MigratoryBird Protection . . . . . . . . . . . . . . . . . . . . 35
4 .0 POST=DREDGING SITE MANAGEMENT . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . 36
4. 1 Dewatering Operations . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . 0 36
4.2 Grading the Deposition Material . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . a 38
4. 2. 1 Control of Stormwater Runoff . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . a 38
4. 2. 2 Topographic Surveys . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . 39
4.3 Material Rehandling/Reuse . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . 39
4.4 Additional Environmental Considerations . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . 9 40
4. 4. 1 Biological Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . 0 40
4. 4. 2 Migratory Bird Protection . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . a 41
4. 4. 3 Groundwater Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . A 41
4. 4. 4 Mosquito Control . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . 0 41
4.5 Site Security . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . a 42
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
APPENDIX A
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LIST OF FIGURES
Figure 1 . 1 Location of IR- 14 Dredged Material Management Area, Indian River
County, Florida . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . 2
Figure 1 .2 Location of IRA4 , Within Reach III , Dredged Material Management Plan ,
•
Indian River County, Florida . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . 3
Figure 2 . 1 Site Plan, IR- 14 Dredged Material Management Area, Indian River County,
Florida . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . 6
Figure 2 .2 Land Use and Vegetation of IR- 14, Dredged Material Management
Area, Indian River County, Florida . . . . . . . . be be . be . . . be . . . . . . .
. . . . . 8
Figure 2 .3 Typical Dike and Ramp Sections, Vegetation Plan, Dredged Material
Management Area, Site IR- 14, Indian River County, Florida . . . . . . . . . . . 10
Figure 2 .4 Grain Size Distribution , ICWW Sediment, Reach III , likes 14 Dredged Material
Management Area, Indian River County, Florida . . . . . . . . . . . . . . . . . . . .
. . 18
Figure 2. 5 Zone Settling Velocity of Intracoastal Waterway Sediments (based on Taylor
and McFetridge, 1989) . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . 19
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1. 0 INTRODUCTION
Site IR. 14 (Figure 1 . 1 ), one of three sites in Indian River County, Florida, selected for development
as dredged material management facilities, will provide long-term capacity for the management of sediments
dredged from adjacent segments ofthe Intracoastal Waterway (ICWW) . The site-specific management plan
for the I11- 14 dredged material management facility, outlined in this report, provides guidance for the
development and operation of the material management area so that it efficiently processes, temporarily
stores, and ultimately transfers material dredged during scheduled channel maintenance operations.
To that end, this plan document addresses those facets of site design and operation which directly
influence site efficiency or reduce off-site conflicts. These include elements of site preparation and facility
construction, techniques ofdecantingand dewateringthe dredged material during and immediately following
maintenance operations, and guidelines for post-dredging site operation and maintenance. Throughout, the
goal of each phase of site management is to ensure that the site not only achieves its minimum 50-year design
service life, but that it also fulfills its potential as a permanent operating facility for the intermediate storage,
processing, and transfer of maintenance material dredged from the ICWW.
Site I1144 was selected as the primary site to serve that portion of the ICWW in Indian River County
defined in Taylor et al . ( 1997) as Reach III (Figure 1 .2). Reach III extends from a point near Vero Beach ' s
northern boundary, opposite the community of Gifford (Cut IR-24, station 28+00, ICWW mile 210 . 19)
southward 8 .27 miles to the Indian River/St. Lucie County line (Cut I11-35, station 31 +50, ICWW mile
218 .46).
A comprehensive evaluation ofJacksonville District Corps of Engineers ' archival records confirmed
that this segment of the Waterway has not been dredged since its 1959 deepening to the present 42-ft MLW
project depth . Nevertheless, the most recent examination survey ( 1996) documented a total in situ reach
shoal volume of 57,498 cubic yards (cy) within the authorized channel . The projected 50-year storage
requirement for Reach III — 162,658 cy — represents extrapolation of the documented in situ shoaling
volume multiplied by a bulking plus over-dredging factor of 2 . 15 . Thus, the IR- 14 containment basin must
provide a capacity of about 163 ,000 cy.
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Figure 1 .2 Celle
TAYLOR ENGINEERING INC.
• 1 : . CWress Green Drive Within Reach III
Florida0100000000 Dredged Material
nt Plan
•
WEEMEMENED Jacksonville, Florida 32256
Indian River • ,
i
The absence of a maintenance dredging history for Reach III precluded projecting the frequency of
future dredging operations . However, an assumed frequency of once every 5 to 10 years appears reasonable,
based on operational considerations such as scheduling and contract procedures, as well as present shoaling
patterns . Thus, depending on the interval between successive dredging operations, each maintenance
operation in Reach III should produce a bulked material volume between 16 ,300 cy and 32 ,600 cy for
placement in Site IR- 14 .
Beyond satisfying a minimum capacity requirement, the management objective forthe IR44 dredged
material management area is to process ( i .e . , decant and dewater) the dredged material efficiently and to
operate the facility so as to extend its usefulness beyond the design service life. The design and construction
of the containment facility establish the site ' s potential long-term efficiency, while its operating procedures
intend to ensure the realization of this potential. Specific elements of site design and operation during and
following dredging activities will be discussed in turn as they relate to site efficiency and local impacts.
Accordingly, Section 2 .0 begins the management plan with a discussion of site preparation and design .
Section 3 .0 presents operational considerations during dredging. Section 4.0 addresses post- dredging site
management.
4
2 .0 PRE-DREDGING SITE PREPARATION AND DESIGN FEATURES
2. 1 Site Design
The present discussion addresses only those aspects of site design which directly influence site
construction and operation as they relate to the facility' s long-term objectives . All other design elements (e .g. ,
construction details, materials, etc .) derive from specific information not yet available and thus are
necessarily deferred to the facility ' s final design phase.
2. 1. 1 Containment Basin Capacity and Configuration Requirements
The containment basin constructed within Site IRA4 (Figure 2 . 1 ) must satisfy four criteria : ( 1 )
provide sufficient material storage capacity for the projected 50-year material storage requirements of Reach
III of the ICWW in Indian River County, (2) provide adequate separation from adjacent properties , (3 )
minimally impact sensitive on- site habitats, most notably the wetlands that comprise most ofthe site ' s eastern
one-half, and (4) minimize the excavation depth required to obtain adequate dike material .
First, to repeat, Site IR- 14 is designated as the primary site to serve the maintenance needs of Reach
III of the Waterway in Indian River County . Thus, Site IR44 must provide adequate capacity for the
projected 50-year material storage requirements of Reach III. A comprehensive evaluation of Jacksonville
District Corps of Engineers ' archival records confirmed that this segment of the Waterway has not been
dredged since its 1959 deepening to the present - 12-ft MLW project depth . Nevertheless, the most recent
( 1996) examination survey documented a total in situ reach shoal volume of 57,498 cubic yards (cy) within
the authorized channel . The projected 50-year storage requirement for Reach III — 162,658 cy — derives
from this documented volume and includes a bulking plus over-dredging factor of 2 . 15 . Thus, the IR- 14
containment basin must provide a capacity of about 163 ,000 cy.
Second, the basin ' s placementon the site must provide adequate separation from adjacent properties.
As shown in Figure 2 . 1 , the containment dike' s outside toe lies 250 ft from the eastern right-of--way of Indian
River Boulevard on the site ' s western side, and 100 ft from a proposed wetland mitigation area to the north
and
5
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Pipeline Inlet p
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NOTES:
1 . Total Site Area : 53 . 39 Ac 4. Weirs : Three 8ft. Diameter CM Half— Pipes GRAPHIC SCALE
2 . Containment Area : With Removable Flash Boards Adjustable ° 150 J00
Within Outside Toe of Dike: 15. 54 Ac From + 1 . 8ft NGVD to + 12. 7ft NGVD .
Within Outside Toe of Dike: 10. 18 Ac
Capacity. 178, 051 cubic yards t INT
3 . Elevation Datum : NGVD of 1929 1 inch = 300 ft_
TAYLOR ENGINEERING INC . Site
Figure
lan , R- C9716
14 ^
9006 CYPRESS GREEN DRIVE Dredged Material Management Area
JACKSONVILt,.E. FLORIDA 32236 Indian River County, Florida ,April , 1999
from a passive-use county park to the south . Although less than the established 350-ft program optimum,
these setbacks provide adequate separation, given the intended uses of the adjacent properties .
Third , basin construction must minimally impact sensitive on -site habitats, most notably the wetlands
that comprise most of the site ' s eastern one-half. As shown in Figure 2 .2, the containment dike ' s outside toe
lies a minimum of 50 ft from the nearest wetland edge along the basin ' s eastern side and at its northeast
corner. However, establishing a similar setback was impossible in the central portion of the basin ' s western
side where construction will impact up to 0. 10 acres of disturbed wetland . Classified as a mixed
wetland/Brazilian pepper community, this former hammock area now qualifies as predominantly wetland,
based on hydric soils and periodic standing water. However, the dominant vegetation does not support this
classification as previous clearing has promoted a dense regrowth of Brazilian pepper. Within the disturbed
wetland, a formal wetland delineation would likely classify some isolated areas as upland. Avoiding this area
and providing an appropriate dike setback would unduly constrain the basin ' s total area. Notably, the
extensive mangrove impoundments within the site' s eastern one- half offer ample opportunity for on- site
mitigation .
Fourth , because of low upland elevations, the likelihood of a seasonally high water table, and the
possibility of a shallow limestone strata in portions of the site, basin construction must minimize the
excavation depth necessary to obtain the required dike material . Qualitative information presented in the
county soil survey (Wettstein et al . , 1987) provides the only available data describing soil and groundwater
conditions on site. Native soils include ( in order of decreasing areal coverage) McKee mucky clay loam ,
Riomar clay loam , Jupiter fine sand, Chobee loamy fine sand, and Perrin Variant loamy fine sand .
Characteristic of mangrove islands and swamps and thus confined to the wetlands within the site' s eastern
one-half, the McKee mucky clay loam and the Riomar clay loam soils avoid all construction impacts. The
site 's western one-half, predominantly upland and includingthose areas historically planted in citrus, contain
the remaining three soil associations . Typical of low, broad flats, depressions, or poorly-defined drainways,
all three upland soils are characterized as nearly level and poorly- drained to very poorly-drained . All three
soils typically maintain a water table within 10 in. of the soil surface from four to more than six months each
year. Because of the poorly-drained conditions, these soils become suitable for citrus production only if a
water control system (e . g., ditching and bedding) maintains the water table at a depth of 4 ft or greater. Relic
evidence of such water control methods remains in portions of the former grove areas of Site 1R- 14 . Notably,
7
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Impacted Wetlands
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Site Vegetation Legend
310 Herbaceous
1 1
Popper. 1 Ac 422 Brazilian
422 12 .2 Ac 1
611 Brazilian Pepper Wetland
• 11 1 . 1 Ac
Temperate425 7 . 6 Ac 425 • • • r -
437 7 . 3 Ac 437 Australian Pine
i
11 2 .4 Ac 11
Water
612 15 .3 Ac
612 Mangrove •
612/422 1 Ac
814
1 f it 11 i ( . Mangrove • Popper
Total Acreagen, 53.4 Ac 814 Roads and Highways
projed
Figure 2. 2 C9716
TAYLOR ENGINEERING INC.
Land Use and Vegetation of IR= 14 RmIslon
• 1 : • Cypress Green
Dredged Material Management
Jacksonville , Florida i
IndianCounty, Florida
e �
both the Jupiter fine sand and the Perrine Variant loamy fine sand typically possess a hard, continuous to
fractured limestone strata within 12 to 24 in . of the soil surface . If present, a shallow limestone strata could
require non- standard excavation methods for containment basin construction , could limit excavation depth,
and could dictate obtaining some dike construction material off site . However, inspection of the banks of the
large east-west ditch that bisects these soil groups failed to reveal the indicated limestone strata. A detailed
subsurface survey will provide more specific geotechnical information before final design and construction
of the containment basin. As shown , the basin' s preliminary design provides the maximum footprint within
the bounds set by the two preceding criteria and thus minimizes the excavation depth needed to provide the
required dike material .
2. 1. 2 Containment Basin Design
With the optimal basin footprint thus determined , the resulting containment basin design is specified
as follows . Within the 15 . 54-acre containment area, dikes will be constructed to a crest elevation of + 14 . 7
ft NGVD, or 11 . 0 ft above the existing mean site elevation of +3 . 7 ft NGVD (Figure 2 . 3 ). The dike cross"
sectional design, including side slopes of 1V : 3H and a dike crest width of 12 ft, will require 54,945 cy of
material for construction . Ramps to provide equipment access to the interior of the containment basin for
material dewatering and transfer will require an additional 1 ,667 cy of material. Excavating the basin interior
to a mean elevation of 4 . 4 ft NGVD — 4 . 1 ft below the existing mean grade elevation of the basin footprint
— will provide material for dike and ramp construction . An interior slope of approximately 0 . 2% will
provide drainage from the inlet point to the outlet structures. Thus the excavated grade within the basin will
range from +0 .4 ft NGVD at the inlet to - 1 .2 ft NGVD at the weirs . Excavation set back 20 ft from the inside
toe of the dikes will maintain the IV :3H side slope of the dikes. With the containment basin filled to
capacity, the surface of the deposition layer will tie a minimum of 4 ft below the dike crest, comprising 2 ft
of freeboard and 2 ft of ponding above the maximum deposition surface. The resulting basin capacity —
178,051 cy — exceeds the projected 50-year storage requirement for Reach III by 9. 5 %.
2.2 Facility Construction
Construction of the IR44 facility will occur in two phases. The first phase — to be completed as
soon as practical following site acquisition — will include clearing and grubbing all vegetation from within
9
BORROW FOR
PERIMETER DIM CONSTRUCTIMI
SEE NOTE aTOH. - ,2' + ,4.7 R NM
NOTES E SL OPES 3e ,
SDONCE HEIGHT ,, .0 R
Perim ter Di
2fr
20'
e tch :
.................................................... ::::::::::•::::::.::: ::::::•::::::•:::::::::::•:::•.-:.:::.:::. .. ...
Side Slopes 1 V: 2H 4.
— 4.
— 0.4 R NGW
Bottom Vidth 1 ft.
Mean Invert Elev. — 0. 5 ft. NGVD EIOSMG GRADE
Slope Bottom as Required for Section A-A'
Drainage
BORROW FOR
DIM CONSTRUCTION
PERIMEIER SIE NOTE OnGH' SIDE SLOPES 3e , ,2 .4+ ,4.7R, •ND
RAW , r DINE HEIGHT „ Aft
20r - -
.. .......................... .. .. ........ ... .. ..... .... .. ... .. .. ....... .. ... ... .......... ...... ..... .. .
... .. .............. ..... . ' ' -
'' ' 0.4 R NCVD
IRMA
E><ISTING GRADE
Section B-8'
PERNETER DITCH NAM GRASSES
PERNM R SERVICE
ROAD BORROW FOR
.. .... ...-- DNfE CONSTRUC71ON
20'
i
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ENS7W VEGETATION
IIIIIIIIw 100-255 R BUFFER
Dredged Material Management Area — Vegetation Plan
SECTIONS NOT TO SCALE
Figure 2. 3 9716low
�o�AcOR� ENGINEERINGRIVE* uINCoo Typical Dike and Ramp Sections, Vegetation Plan
J/►CKSONVILLB. FL.ofsIGA sxZsa Dredged Material Management Area , Site IR - 14
Indian River County, Florida
the planned basin footprint, construction of access roads, and installation of security fencing around the site ' s
upland perimeter. The second phase will include containment basin construction and related earthmoving
operations and the installation of outlet structures and other design features. This phase, subject to the
scheduling and budget priorities of the Jacksonville District Corps of Engineers, may not immediately follow
completion of the first phase. However, perimeter fencing and in- place security procedures will secure the
site before excavation , grading, and dike construction begin . The remainder of this section discusses each
site preparation element in more detail .
2. 2. ! Clearing and Grubbing
The first phase of facility construction begins with clearing and grubbing of site vegetation .
Although adding significantly to the initial facility construction cost, the removal of all woody vegetation
from the basin interior wiI l promote efficient settling within the basin . The trees and other woody vegetation
that dominate the upland areas of Site IR- 14 (Figure 2 .2), if allowed to remain , would constrict or channelize
flow through the containment basin . Cutting the trees, but allowing the roots to remain, would preclude the
uniform excavation and grading of the basin interior. Either omission would necessarily restrict the required
excavation to the perimeter of the basin interior and thereby result in short-circuiting, reduced retention times,
resuspension of sediment through increased flow velocities, and the deterioration of effluent quality.
Moreover, a failure to clear existing vegetation will make the periodic removal of the dewatered dredged
material more difficult. Therefore, clearing and grubbing the area within the containment basin footprint,
as well as the areas of the access and perimeter service roads (Section 2 . 3 . 5) and the perimeter ditch (Section
2 . 3 .6), should take place before construction .
2. 2. 2 Excavation and Grading
The second phase of site preparation includes all earthmoving operations required to construct the
containment dike and basin to the design geometry. Preliminary site design (Figure 2 . 1 ) specifies excavating
the containment basin interior to obtain the material required for initial dike and ramp construction .
Excavating to an average elevation of 44 ft NGVD, or 4. 1 ft below the existing mean grade elevation within
the basin footprint (+3 .7 R NGVD ; Figure 2 . 3) will provide the needed 56,612 cy. Excavation set back 20
ft from the interior toe of the dike will ensure dike foundation stability. Excavation of the perimeter ditch
11
(Section 2 .3 . 6) will produce an additional 7,200 cy of material. Should some material excavated from the
basin interior be unsuitable for dike construction, the ditch material can make up the deficit. Alternatively,
the material excavated from the ditch can contribute to the dike requirement to reduce the excavation depth
in the basin interior. The final excavation depth and distribution of material , determined in the final design
phase, will reflect the results of detailed subsurface investigation.
The interior of the containment basin must also be graded following excavation. Construction
efficiency may initially dictate taking dike material from a perimeter trench inside the containment dike.
However, before dredging operations begin, this trench must be eliminated and the site interior regraded to
avoid flow channelization and unacceptable effluent quality. If left ungraded , the irregular topography within
the basin will produce nonuniform flow and deposition patterns which, in turn, will result in isolated surface
water ponding. Ponding will inhibit drying of the deposition layer and make initial attempts at surface
trenching more difficult . For these reasons, a uniform grade with an adequate slope (about 0 .2%) must be
provided from inlet to weir as part of initial facility construction . Thus, although the basin interior will
maintain a mean excavated grade of -0.4 ft NGVD, the floor of the basin will slope uniformly downward
from approximately +0 .4 ft NGVD near the inlet to approximately - 1 .2 ft NGVD at the weir. Once dredging
operations begin , differential settling of varying grain size fractions ( i .e., rapid precipitation of the coarser
fractions nearer the inlet with increasingly finer sediments deposited nearer the outlet) will maintain a rough
downward slope from inlet to weir.
2.3 Additional Design Features
2. 3. 1 Inlet
The number and locations of the dredge slurry outfalls, or pipeline inlets, govern the pattern of
deposition within the containment basin . A single, moveable inlet offers several advantages over single or
multiple fixed designs. A single, fixed inlet would produce a mound of coarse material at the fixed inlet
point. If not mechanically redistributed, the mound would effectively reduce the basin ponding area. A
multiple inlet manifold could overcome this disadvantage. However, the infrequent maintenance projected
for this portion of the ICWW, once every 5 to 10 years, cannot justify the cost of a fixed, multiple inlet
manifold system for the IR- 14 containment basin . More cost effective, a single inlet, periodically
12
repositioned as dictated by the deposition pattern , can effectively distribute the coarse sediment over the basin
floor. A flow-splitter or a spoon to break the jet' s momentum will also help the single inlet distribute the
slurry. Regardless of the inlet design or operation , maintenance of optimal basin performance will require
regrading the dewatered sediment to reestablish the initial uniform slope of about 0 . 2% ( Section 2 .2 . 2) from
inlet to weir before each successive placement operation .
Preliminary analysis of the settling characteristics of the dredged material to be placed in the IR- 14
containment basin (Section 2 . 3 . 3 ) indicates that the available distance between inlet and weirs will afford
adequate solids retention. Moving the inlet for more even material distribution must not significantly reduce
this separation distance without additional precautions. To ensure continued compliance with water quality
standards, these additional precautions may include increasing the ponding depth or installing turbidity
screens surrounding the weirs .
2. 3. 2 Weirs
The IR- 14 facility will use weirs to control the release of the clarified surface layer of the water
ponded within the containment basin . Adjustment of weir height controls ponding depth within the
containment basin which in turn controls basin retention time. Weir height and ponding depth are discussed
in more detail in the next section . However, several additional aspects of weir design affect the flow of water
inside the basin and thereby strongly influence the efficiency of solids retention and the quality of effluent
released from the site . These include weir crest width, weir crest length , weir type, and the location of the
weir within the containment basin . Each of these design aspects and its effect on basin efficiency is discussed
in the following paragraphs .
The first two weir design parameters, weir crest width and weir crest length, affect weir
performance by determining its withdrawal depth. The withdrawal depth lithe depth at which gravity forces
on suspended sediment particles exceed the inertial forces associated with flow over the weir. It therefore
represents the depth of the surface layer of ponded water that is drawn over the weir crest and released from
the containment basin . Maintaining the withdrawal depth less than the ponding depth reduces the possibility
of resuspending sediment which has settled out of the upper water column . Moreover, since the
concentration of suspended sediment increases with depth, minimizing the depth of the withdrawal layer
13
maximizes the retention of suspended solids. Specific expected performance characteristics of the weir
system are discussed later in this section.
As mentioned above, the width of the weir crest affects withdrawal depth . Weirs typically employed
in dredged material containment facilities are described as sharp-crested or narrow-crested based on their
crest width relative to the static head over the weir. A weir is described as sharp- crested if the thickness (T)
of the weir crest is significantly less than the static head (H) over the weir, typically H/T > 1 . 5 . Under
specific conditions, sharp-crested weirs may result in a shallower withdrawal depth than weirs with a broader
crest, that is, for weirs with a value H/T s 1 . 5 (Walski and Schroeder, 1978 ). To withstand hydrostatic
pressure and reduce deformation and seepage the proposed weir design specifies the flashboards (discussed
below) to be nominal 6 in . X 6 in. timbers . The timbers ' finished dimension of 5 . 5 in ., combined with the
design static head over the weir of 4. 9 in . , yields H/T = 0 . 89, a ratio within the range of a narrow-, rather than
a sharp-crested weir system . However, in the present application, the use of a narrow-crested weir should
be adequate (Gallagher and Company, 1978).
The weir parameter that most directly influences withdrawal depth and effluent quality is weir crest
length. The Selective Withdrawal Model (Walski and Schroeder, 1978) developed by the U . S . Army
Engineer Waterways Experiment Station (WES) under the Dredged Material Research Program (DMRP)
relates weir crest length to withdrawal depth through the parameter ofweir loading. Weir loading is defined
as the ratio of the liquid discharge of the dredge (Q) to the effective weir crest length (B). Project planning
guidelines used by the Jacksonville District Corps of Engineers indicate that an 18- in. O.D. dredge will likely
be used for future channel maintenance in Reach III of Indian River County . Given typical design output
specifications for a 244n . dredge (discharge velocity of 16 ft/sec, a volumetric discharge of 3 , 560 cy/hr, and
a 20/80 solids/liquid slurry mix), the Selective Withdrawal Model indicates that a weir crest length of 24 ft
should produce a 2 . 0-ft withdrawal depth, based on a design weir loading (QB) of 0 . 89 ft'/ft- sec. As
discussed in the next section, this depth falls below the recommended minimum ponding depth at the weir
(2 . 8 ft) and thus should not result in the release of effluent with a high suspended sediment concentration .
Moreover, DMRP research indicates that under field conditions, the actual depth of withdrawal may fall
significantly below that predicted by the WES Selective Withdrawal Model . Therefore, the use of the WES
Selective Withdrawal Model provides a conservative containment basin design.
14
Three corrugated metal half-pipes, each with an 8-ft weir section , will provide the required 24- ft total
crest length . The three halUpipes connected by a common manifold will provide drainage from the
containment basin via a single culvert under the dike. During dredging and dewatering operations, the return
water pipeline will connect to this culvert and transport the clarified supernatant to the Indian River. Pipeline
placement and retrieval is discussed in Section 3 . 1 .
Removable flashboards will allow adjustment ofweir height over a range of 10. 9 ft - from the initial
elevation of ponded water within the basin following construction (estimated as + 1 . 8 ft NGVD) to a
maximum elevation of + 12 .7 ft NGVD . Setting the weirs at the minimum elevation permits the immediate
release of ponded water at the start of dredging operations. The maximum elevation provides a 2 ft mean
ponding depth and 2 ft of freeboard above the maximum deposition surface . The 5 . 5 in. X 5 . 5 in . flashboards
(finished dimension) provide an adjustment increment roughly equivalent to the projected depth of flow (4 .2
in . ) over the weir crest at the point the weir discharge approximately equals the liquid inflow to the
containment basin , a balance reflected by the design weir loading, Q/$ = 0. 89 ft'/ft-sec . This design provides
adequate adjustment resolution to maximize weir performance and effluent quality throughout the dredging
operation and subsequent release of ponded water.
The final weir design parameter considered is the location ofthe weirs within the containment basin .
First, to reduce the likelihood of flow constriction, sediment resuspension, and dike instability the weir crests
must be offset a minimum of 100 ft from the dike' s inside toe. Second , the weirs must be placed to maximize
their distance from the dredge pipe inlet and to minimize the return distance to the receiving waters.
Providing the maximum inlet weir separation also maximizes the basin ' s effective area and ensures that the
effluent released from the basin meets the weirs ' performance criteria. Hydraulic analysis (Section 2 . 3 . 3 )
indicates the 800-ft separation distance shown in Figure 2. 1 to be adequate. In addition, locating the weirs
to minimize the return distance from the weirs to the Indian River provides the most efficient effluent
transport from the containment basin . Gravity flow will be used to the greatest extent possible. However,
one or more dredging operations may be required to sufficiently raise the elevation of the basin interior such
that all ponded water will drain by gravity flow. Until that time, auxiliary pumping may be required .
Analysis ofweir performance based on nomograms developed at the Waterways Experiment Station
under the Dredged Material Research Program (Walski and Schroeder, 1978) indicates that the weir design
15
described above will produce an effluent suspended sediment concentration of less than 0 .45 g/l . Relating
suspended solids concentration to Florida effluent quality standards — based on the turbidity of the effluent
relative to the ambient turbidity of the receiving waters — is problematic since turbidity depends highly on
the physical characteristics and concentration ofthe suspended material . However, WES guidelines (Palermo
et al . , 1978 ; Walski and Schroeder, 1978) indicate that this 0 .45 g/1 falls well below typical standards for
effluent discharged into estuarine waters .
2. 3. 3 Ponding Depth and Basin Performance
Ponding depth refers to the height ofthe water column (with its suspended sediment load) maintained
above the depositional surface during dredging operations . It is regulated by the height of the weir crest and,
to a lesser extent, by dredge plant output. Given the initial slope of the basin interior (about 0 .2%), ponding
depth will vary within the basin . The ponded water, most shallow nearest the inlet, will increase to its
maximum depth nearest the weir. Conceptually, ponding depth is typically discussed in terms of its mean
value over the entire basin interior. However, as a practical operational criterion , ponding depth is more
usefully specified at the weir where it can be measured directly. At the weir, the excavated grade of the IR-
I4 basin is 4 .2 ft NGVD, or 0. 8 ft below the average basin depth. Therefore, ponding depth at the weir
exceeds the mean basin ponding depth by approximately 0. 8 ft. In the remainder of this report, ponding
depth will be given in terms of the mean depth over the basin and, where appropriate, related to the
corresponding depth at the weir.
Ponding should be maintained at the greatest possible depth during dredging operations. Increased
ponding depths produce increased retention times and decreased flow velocities through the containment
basin and therefore improved solids retention and effluent quality. The limiting consideration for increased
ponding depth is the amount of hydrostatic pressure the dike can withstand without loss ofstructural integrity.
Analysis of sediment settling characteristics established whether the 2 .0=ft minimum mean ponding
depth produces a basin retention time adequate for acceptable solids retention and effluent quality. The fine-
grained sediment component, because it requires the longest time to settle out of suspension, determines the
required basin retention time and therefore the required ponding depth .
16
Data characterizing channel sediments in Reach III were obtained in a program of sampling and
analysis conducted during the plan development phase . As documented in the Phase I report (Taylor et al . ,
1997 ), sediment samples were taken at nine locations within the Indian River segment of the ICWW channel
including three locations within Reach III . In an effort to sample worst case conditions, each sampling station
was located near a potential source of fine sediment. Analysis determined that sampling location IR-3 -2,
located at ICWW mile 213 .93 (Cut IR-30 , station 14+25 ) south of Vero Beach and opposite Prang Island near
channel marker R450 , produced the finest- grained sediment ofthe three locations within Reach III . Silt and
clay-sized particles (particles passing a #200 sieve, or with diameters less than 0 .074 mm ) comprised 80%
of the sample (Figure 2 . 4) .
Based on this conservative design criterion, an associated zone settling velocity was then determined
from an empirical relationship between the percentage of fine-grained material and settling behavior. This
relationship was developed from U . S. Army Corps of Engineers (COE) sediment data characterizing the silt
content of a variety of ICWW channel sediments and the corresponding settling behavior of slurry
concentrations similar to those typically encountered in dredging operations (Figure 2 . 5 , Taylor and
McFetridge, 1989). From these data the characteristic zone settling velocity for the sediment to be placed
in Site IR- 14 was determined to be 0. 25 cm/min, or 0.49 ft/hr. This settling velocity was then used to
determine the retention time needed to provide adequate sedimentation within the containment basin .
Retention time relates directly to the depth of ponded water maintained within the basin . The
preliminary design of the containment basin provides a minimum 2 .0-ft mean ponding depth above the
deposition surface. Analysis of the hydraulic characteristics of the proposed containment basin (Gallagher
and Company, 1978) indicates that a 2 . 0-ft mean ponding depth will provide a maximum retention time of
6 . 19 hours during which the flow over the weir balances the liquid discharge of the dredge. In comparison,
the time required for the sediment to settle out of the"2 .0-ft mean ponding depth is less than 4. 13 hours based
on the projected zone settling velocity of the Station IR-3 -2 material . However, research (Shields, Thackston
and Schroeder, 1987) by the WES under the DMRP indicates that the predicted settling time of the dredged
material should be multiplied by a correction factor of 2 .25 to account for field conditions . This yields an
adjusted required settling time of 9 .28 hours, a time which exceeds the maximum retention time of 6 . 19 hrs
produced by a 2 .0-ft mean ponding depth . Increasing the mean ponding depth to 4. 0 ft provides a maximum
retention time 12 .38 hrs, which exceeds the adjusted settling time required to maintain acceptable effluent
17
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10
CLASSIFICATION
GRADATION CURVES
Hydrometer and Grain Size
Analyses
X&A Project No . 95�1497
Figure 2 . 4
TAYLOR ENCINEERING INC .
Grain Size
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Percentage Finer than #200 Sieve (°/<0.074mm)
Figure 2.5 Zone Settling Velocity of Intracoastal Waterway Sediments (based on Taylor and McFetridge, 1999)
quality by a factor of 1 . 33 , and provides a margin of safety to ensure that the clarified supernatant released
from the IR- 14 containment basin will meet state water quality standards . Therefore, the IR- 14 containment
basin requires a 4 . 0-ft mean operational ponding depth .
However, care must be taken not to increase ponding depth above the 2 .0=ft minimum too quickly.
This may lead to dike saturation and promote dike instability. Operational experience has demonstrated that
dike permeability typically reduces with time as percolation filters and traps fine sediments. Thus, a
sufficiently slow increase in ponding depth will avoid piping, slumping, and other indicators of dike
saturation and instability. Restricting the operational ponding depth to 4 ft should also reduce the likelihood
of dike instability and provide an appropriate safety factor to ensure adequate solids removal .
Consideration of realistic field conditions further reinforce the IR- 14 containment basin ' s
conservative design . First, DMRP research indicates that under typical field conditions the actual depth of
withdrawal may be significantly less than the WES Selective Withdrawal Model predicts . Solids retention
should improve with decreased withdrawal depth. Second , field conditions may reduce dredge discharge
rates below the design criterion . The design dredge discharge (3 , 560 cy/hr) reflects a minimum separation
between the dredge plant and the placement site and thus a minimum discharge line length . Increasing the
discharge line length also increases frictional losses and correspondingly reduces dredge discharge and
extends basin retention time. The maximum pumping distance for Site IR- 14 to serve the extreme southern
end of Reach III is 4 . 97 miles. Thus, actual dredge discharge rates will likely fall well below the design
criterion and further improve basin solids retention .
2. 3. 4 Interior Earthworks
The IR- 14 containment basin design specifically excludes secondary interior dikes — e .g. , multiple
cells or spur dikes. Multiple cells are typically employed for continual or successive placement projects that
cannot provide adequate time for dewatering the previous deposition . The projected dredging frequency for
Reach III , once every 5 to 10 years, and the relatively small quantities anticipated with each operation, from
16 ,300 cy to 32,600 cy, do not warrant the use of multiple cells . Spur dikes are typically used in applications
where the basin ' s size or configuration cannot provide adequate retention time. However, hydraulic analysis
20
( Section 2 .3 .3 ) indicates the IR- 14 containment basin design provides sufficient retention time to allow
precipitation of the finest sediments anticipated in Reach III without recourse to spur dikes .
2. 3. 5 Ramps
An important goal of the Long-Range Dredged Material Management Program for Florida ' s ICWW
is to manage each dredged material management site as a permanent operating facility. This goal carries two
operational criteria. First, the material is to be actively worked to accelerate the drying process and thus
render the material suitable for removal and reuse as quickly as possible . Second, to restore the basin 's
capacity and thereby extend its service life, material must be removed from the basin at or before the point
at which the basin reaches its design capacity. As a result, ramps to provide heavy equipment access to the
containment basin interior have been integrated into the design of the containment dike (Figures 2 . 1 and 2 . 5 ).
Thus, the site is designed to function more as a material processing and rehandling station than as a
permanent storage facility. Although the design capacity ofthelR- 14containment basin ( 178,051 cy, Section
2 . 1 . 2) is adequate to receive the projected 50-year material storage requirement for Reach III, removing the
dewatered material off site can effectively expand its capacity. In this manner, the useful service life of the
site may extend indefinitely. In addition to providing for material removal, the ramps also allow easy entry
for equipment used in the dewatering process. This latter process is discussed in Section 4 . 1 .
The ramps will be positioned on the western and southern sides of the containment dike. An on-site
access road will connect the ramps to Indian River Boulevard (Figure 2. 1 ). Obliquely traversing the
containment dike, the ramps will maintain the same 1 V43H side slope as the dike. The road surface of the
ramps will be 12 R wide with an ascending/descending grade of 5%.
2. 3. 6 Perimeter Ditch
Saltwater seepage from the interior of the containment basin into the on- site shallow aquifer is not
expected to be a significant problem for several reasons. First, saltwater pumped from the ICWW (Indian
River) will remain ponded within the containment basin only during actual dredging operations and for a
short period immediately following dredging as the clarified effluent is released back to the ICWW. Such
periods are expected to last approximately 8 to 12 weeks, once every 5 to 10 years . Second, during the site ' s
21
first use and each subsequent use, percolation filters and traps fine sediments and thereby continually reduces
the permeability of the basin interior. Thus, although some minor seepage should be expected , particularly
during the basin ' s first use, the basin floor and dike walls are, within limits, self-sealing . Third, elements of
the facility design and its operational guidelines incorporate additional precautions against the off-site
migration of saltwater. Operational precautions, most notably the implementation of a groundwater
monitoring program , are discussed in Sections 2 .4 , 3 . 5 , and 4 . 5 . Design features to control the offsite
migration of basin seepage include a perimeter ditch, discussed below.
A perimeter ditch, constructed at a 20-ft setback from the outside toe of the containment dike and
surrounding the basin (Figure 2 . 1 ), will serve several purposes . First, as discussed above, the ditch must
interdict the lateral spread of saline seepage through the dike ' s side slopes and foundation. To accomplish
this purpose, the mean invert of the ditch must fall at or below the mean excavated grade elevation of the
basin interior. If inspection of the dike during dredging and decanting identifies excessive basin seepage,
its control may require that all water entering the perimeter ditch be continuously pumped back to the basin
until all ponded water is released over the weirs. Dike inspection requirements during dredging and
decanting are discussed in Sections 3 . 2 . and 3 . 3 . Additional design measures to control basin seepage (e.g. ,
underdrains) require site-specific geotechnical information not presently available, and thus must be deferred
to the facility ' s final design phase .
In addition to intercepting seepage from the basin , the perimeter ditch must serve two other functions .
First, the ditch must maintain the drainage and conveyance capacity provided by the east-west ditch that
presently bisects the site . Facility construction requires that this ditch be rerouted around the containment
basin . As shown in Figure 2 . 1 , the perimeter ditch will connect to the existing ditch on the basin ' s western
side, redirect the ditch ' s flow around the basin' s northern and southern sides, then reconnect to the existing
ditch on the basin ' s eastern side before continuing to the Indian River. Thus, the perimeter ditch must match
the existing ditch ' s invert elevation at both intersection points . By these criteria, the perimeter ditch ' s
preliminary design includes a mean invert elevation of approximately - 0 . 5 ft NGVD, or 4 .2 ft below the
existing mean grade elevation within the basin ' s footprint, I V : 2H side slopes and a bottom width of 3 ft, to
yield a mean top width of 20 ft. The slope of the existing ditch between the prescribed intersection points
dictates the mean slope within the perimeter ditch . Second , the perimeter ditch must control stormwater
runoff from the exterior face of the containment dike, the perimeter road, and portions of the buffer area .
22
Preliminary analysis indicates that the perimeter ditch will provide adequate conveyance for the 25-year
storm runoff. Control and conveyance of stormwater runoff from within the containment basin is discussed
in Section 4 . 2 . 1 .
2. 3. 7 Dike Erosion and Vegetation
The stability of the containment dike must also be ensured against erosion from rainfall runoff and
wind . Immediately following dike construction , native grasses will be planted on the exterior dike slopes and
crest (Figure 2.3 ) . While they quickly form soil binding mats, these grasses do not root so deeply as to
weaken the dike. An acceptable turf cover may be planted by approved techniques of sprigging, sodding,
or seeding (broadcast or hydroseeding), or a combination of these methods, as determined by the contractor.
Contract responsibilities shall include the maintenance of the vegetation until adequately established , as
certified by the COE or FIND' s designated representative. Vegetating the dike in this manner will also
improve the site ' s appearance.
2. 3. 8 Site Security
Site security provided for the project area will restrict access, prevent vandalism and damage to site
facilities, and ensure public safety. As stated in Section 2 .2, permanent security fencing will be erected
around the site' s upland perimeter (Figure 2 . 1 ). Locked gates will control access to this area . The FIND and
the Jacksonville District COE will hold the gate keys and distribute them on an as-needed basis to agents of
the COE, dredging contractors, and other authorized parties.
Site security is most critical during active dredging and dewatering operations. Therefore, a qualified
facility operator must remain at the site at all times during active dredging operations and decanting
procedures following a dredging event, as well as at any time when significant ponded water remains within
the containment basin . Among his other responsibilities, discussed further in Chapters 3 .0 and 4 .0 , the site
operator will ensure proper operation, adjustment, and maintenance of the weir and will prevent premature
release of effluent through unauthorized weir operation .
23
2 .4 Groundwater Monitoring
To ensure that the construction and operation of the IR- 14 containment facility does not adversely
affect local groundwater, a comprehensive groundwater monitoring program will be a key element of site
management. At present, data characterizing soil and groundwater conditions on site are limited . More
detailed information characterizing on-site soil conditions , to be obtained through comprehensive
subsurface investigation during the final design phase is required to assess the site' s potential to impact
local groundwater. Additional sediment data wi 11 be derived from core borings taken in channel shoals before
each scheduled maintenance operation. As discussed in Section 2 . 1 , excavation depth will be limited as much
as practical . Nevertheless, containment basin construction will still require excavation below the apparent
seasonal high water table. Material dredged from the ICWW will be discharged into the IR- 14 containment
basin as a slurry containing approximately 20% marine sediments and 80% saline water. Hydrostatic
pressure could potentially force saline water from the basin into the local shallow aquifer. However, two
factors limit the off-site movement of saline water. First, a system of perimeter ditches (discussed in Section
2 . 3 . 6) surrounding the containment basin will interdict the horizontal migration of basin seepage. Second,
ponded saline water should remain in the basin for relatively short periods (about 8 to 12 weeks) only once
every 5 to 10 years. Thus, the contamination of off-site groundwater by saline water seepage from the basin
appears unlikely .
Notwithstanding the above, an on-site groundwater monitoring program will be implemented to
detect any changes in local groundwater chemistry due to site operations. The program will begin before
facility construction and will remain in place throughout the life of the site. Preconstruction groundwater
monitoring activities are discussed below.
Implementation of the groundwater monitoring program requires the installation of shallow test
wells before site construction activities begin. Initially, three pairs of wells — one pair each on the
containment basin 's north, west, and south sides — will be sunk within the buffer area. Each pair will consist
of one shallow well (to 8 R below soil surface) and one deeper well (to 30 ft below the soil surface). Samples
from the test wells will be analyzed to document preconstruction groundwater elevations and chloride
concentrations. Analysis of the groundwater samples may also include additional chemical constituents if
present in the sediment to be dredged . Well monitoring data will be used to establish baseline groundwater
24
conditions before site development and to identify changes in groundwater elevation due to site development
or to changes in off-site groundwater demand . Additional wells may be installed if initial test results or
specific local concerns require an increased monitoring capability. Prescribed monitoring activities during
and between dredging operations are discussed in Sections 3 . 5 and 4 . 5 , respectively.
Though little change in groundwater conditions is anticipated before the first dredging operation,
groundwater monitoring should continue on a regular schedule . Samples should be taken monthly for the
first year after the wells are installed and quarterly thereafter until the containment facility' s first use .
2.5. Migratory Bird Protection
The Jacksonville District Corps of Engineers district-wide migratory bird protection policy (COE,
1993 ) will be followed to ensure that operation and construction of the dredged material disposal area will
not adversely impact migratory birds . The purpose of the migratory bird protection policy is to "provide
protection to nesting migratory bird species that commonly use the dredged material disposal sites within
the Jacksonville District while facilitating disposal of dredged material to meet the Federal standard for
navigation channel and harbor maintenance as authorized by Congress" (pg. 1 ) . Issues related to migratory
bird protection will be addressed during all phases of site operation . Specific actions taken to protect
migratory birds during pre-dredging site preparation are identified below.
Should construction activities at Site IR44 take place during the migratory bird nesting season.(April
1 through September 1 ), the site protection plan presented in Appendix I of the Migratory Bird Policy (COE,
1993 ) will be implemented. This plan provides for education of contractor personnel , daily monitoring for
nesting activity, steps to deter nesting in the construction area, avoidance of nests and, if necessary to protect
nesting birds, cessation of construction activities. Alternatives that may be considered to prevent impacts to
nesting birds include creation of undesirable habitat (e.g . , flagging construction area, placement of ground
cover, seeding or sodding exposed areas), dissuasion through noise or activity, or creation of alternative
nesting sites . A final, undesirable alternative — incidental take - should only be considered during a
documented emergency.
25
16 Cultural Resources
Inquiry to the Florida Department of State, Division of Historical Resources, revealed that the Florida
Master File records an archeological site ( 8IR835 ) near or within the boundaries of Site IR- 14 (letter from
G. W. Percy, State Historic Preservation Officer, dated January 14, 1998, Appendix A). Described as
inundated artifact scatter, this site lies east of the mangrove impoundments near the Indian River shoreline.
Given this location, facility construction will have no impact on the archeological site . However, the site lies
near the proposed pipeline routes (Section 3 . 1 ) and thus pipeline placement and retrieval may impact the site
Without appropriate protective measures . As recommended by the state Division of Historical Resources,
before any land clearing or construction activities, Site IR- 14 will " . . . be subjected to a systematic,
professional archeological and historical survey to locate and assess the significance of the recorded sites
and any as yet unrecorded historical sites in the project area . . . " The need for additional, more detailed
(Phase II) archeological survey work will be determined by the results of the initial (Phase 1 ) investigation .
26
3.0 OPERATIONAL CONSIDERATIONS DURING DREDGING
The primary objectives of site management during dredging operations are to maintain acceptable
effluent quality during the decanting process, to maximize the dewatering rate of the deposited material by
controlling the pattern of deposition , and to minimize the impact of the site on adjacent properties . To this
end, six elements of site management are discussed : ( 1 ) placement and handling of the dredge discharge and
return water pipelines, (2) operation and monitoring of the dredged slurry inlet, (3 ) operation and adjustment
of the weirs, (4) monitoring of the released effluent, ( 5 ) continued monitoring of local groundwater
conditions, and (6) compliance with the Jacksonville District' s Migratory Bird Policy.
3. 1 Pipeline Placement
The dredge (with additional boosters as necessary) will pump the dredged material as a slurry from
the dredging site to the containment basin via pipeline . Thus, each dredging operation over the design life
of Site IR- 14 will involve placing and retrieving both dredge discharge and return water pipelines . To
minimize impacts to the mangrove wetlands, the dredge discharge pipeline will follow an existing graded
road from near the Indian River shoreline to the road ' s intersection with the dike' s eastern side (Figure 2 . 1 ).
The pipeline will then follow the dike' s outside toe south and west to the basin ' s southwest corner and enter
the basin by passing over the dike crest. This route will temporarily impact only a narrow fringe of
mangroves at the Indian River shoreline. The return water pipeline will exit the basin near its northeastern
corner and follow the same graded road to the Indian River shoreline . The return water pipeline outfall will
be placed at or beyond the Indian River shoreline as necessary to minimize possible impacts to local seagrass
beds .
The pipelines will be placed immediately before dredging begins as part of the dredging contractor' s
mobilization procedures. The dredge discharge pipeline will remain in place only during active dredging
operations. The time required to complete this phase of operations will depend on the quantity and
distribution of the dredged material . As discussed previously, a 10-year dredging cycle is likely to produce
a bulked volume of approximately 32,600 cy of material . This volume corresponds to an in situ volume of
approximately 16,300 cy. Dredging this volume of material and transporting it to the containment basin,
combined with reasonable delays associated with dredging projects of this complexity, yields an estimated
27
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four to six weeks to complete each dredging operation . Immediately upon completion ofdredging, the dredge
discharge pipeline will be removed.
The return pipeline will remain in place to transport water decanted from the containment basin or
released by initial trenching procedures (Section 4. 1 ). After completion ofthis procedure, approximately four
to six weeks beyond the completion of dredging, the return pipeline will also be removed . Ponded
stormwater collected in the containment area will be subsequently removed via the weir system so that any
suspended sediment will be retained in the containment basin. However, unlike the clarified effluent removed
during dredging operations, stormwater will be routed to the on-site mangrove impoundment via the
perimeter ditch . The removal of runoff is discussed further in Section 4 .2 . 1 .
3 .2 Inlet Operation
The quality of the dredged sediment; specifically, the settling characteristics of the different gramn
size fractions, will primarily determine the operation of the inlet pipe. The coarsest fraction of the material
will settle out of suspension very rapidly and form a mound near the inlet. Successively finer fractions,
characterized by lower settling velocities, will be deposited closer to the outlet weir. Thus, absent an inlet
operation strategy, the dominant grain-size fraction will determine the distribution of sediment within the
basin. For example, if fine-grained sediments dominate, a relatively large volume of material may be
concentrated nearest the weirs . An extensive concentration of fine-grained sediment may require specialized
dewatering procedures to speed drying.
As discussed in Section 2. 3 . 3 , analysis of samples taken at three locations within Reach III suggests
that channel sediments in this reach contain significant fine-grained material . Mean grain diameters of
individual samples ranged between 0 . 104 mm (Station I11-3 -3 , categorized as fine sand) and 0.031 mm
(Station IR-3 -2, categorized as silt). The silt-sized fraction (i .e. , particles <0. 074 mm diameter) comprised
between 19 and 80% of the total . The one sample subjected to chemical analysis (Station IR- 1 - 1 ) yielded
an organic matter content of 3 % . Additional data characterizing specific channel shoal sediments will be
obtained before future dredging operations. These data will include, at a minimum, core boring logs
containing a qualitative categorization of each sediment strata ; laboratory data, including sediment size
28
distribution curves and/or Atterberg limits ; and suspended sediment-settling time curves representing the
finest-grained sample from each boring location .
The recommended inlet operation strategy, based on the sediment data presented above, reflects a
poorly graded mix of fine sand and silt-sized particles . This strategy makes no attempt to segregate material
grain-size fractions by inlet manipulation, although some segregation will occur naturally as a result of
differential settling behavioras described above . To minimize the mounding ofthe coarsest sediment fraction
and to distribute the deposited material more uniformly, the inlet pipeline should be repositioned during
dredging operations. This will require extending the pipeline and resting each extension on the sediment
mound formed at the previous position. A minimum distance of 100 ft must be maintained between the inlet
and the inside toe of the dike to preclude erosion or undercutting the interior dike slope. This strategy will
also reduce the concentration of the finest sediment nearest the weirs as each deposition mound captures a
portion of the silt- sized particles. (With a fixed discharge position , these particles would continually wash
from the mound . ) The resulting deposition pattern should maintain a consistent slope from inlet to weir,
should minimize dead zones and channelization, and should reduce the requirement for grading the deposited
material to reestablish the desired 0 . 2% slope between successive dredging operations .
3. 2. 1 Monitoring Related to Inlet Operation
During active dredging operations, several monitoring procedures related to inlet operations will be
required . Ponding depth , as previously mentioned , is a critical parameter for maintaining acceptable
containment basin performance. Increased ponding depth improves the basin 's solids retention performance
by increasing retention time. However, under saturated foundation conditions, unbalanced hydrostatic forces
resulting from too great a ponding depth can lead to slope instability, slumping, and the potential for dike
failure. Indications of impending dike instability" include evidence of seepage related to piping and
foundation saturation at the outer dike toe and small-scale slumping. Obviously, such conditions must be
avoided. Therefore, ponding depth should be increased above the 2-ft minimum mean depth only under close
monitoring by visual inspection of dike integrity. As discussed in Section 2 .2.2 , a 2-ft mean ponding depth
corresponds to a 2 . 8-ft depth at the weirs as a result of the initial slope of the basin interior. If no effluent
is released at the weir, the output of an 18- in . dredge (i . e. , 3 , 560 cy/hr slurry at a 20/80 solids/liquid mix, or
2,848 cy/hr liquid) will produce an increase in ponding depth of about 2 . 1 in ./hr and a rise in the water
29
surface (i . e . , deposition layer plus ponding) of less than 2 .6 in./hr. These rates are slow enough to allow close
continual monitoring of the entire dike perimeter. However, ponding depth should not be permitted to
increase beyond a maximum of 5 ft (5 . 8 ft at the weir) . Dike stability should be monitored continuously
during periods when ponding depth is maintained above the 2-ft minimum .
Optimal operating efficiency requires that flow through the containment basin approachs plug flow
to the greatest degree possible. Uneven flow distribution — evidenced by irregular sediment deposition,
channelization , and short-circuiting — increases flow velocities, reduces retention time, and promotes
sediment resuspension . If inspection reveals an irregular deposition pattern, the inlet pipe should be
repositioned to produce a more uniform depositional surface.
Last, the incoming slurry should be periodically monitored at the containment basin inlet to confirm
or refine dredge output specifications, including volumetric output and slurry solids content. These
parameters, in combination with the actual duration of dredging, can be used as an independent measure of
deposition volume to determine remaining site capacity. Additionally, the computed deposition volume can
be used with pre- and post-dredging bathymetric surveys of the channel and , following placement and
dewatering of the deposition layer, topographic surveys within the containment basin to refine the bulking
factor employed to translate in situ dredging volume to required storage volume. Also, within the same
monitoring program, the quality of dredged sediment should be established by laboratory analysis of grain
size distributions, settling velocities, specific gravity, and Atterberg limits .
3.3 Weir Operation
Weir operation — that is, controlling the ponding depth and flow rate over the weir by adjusting the
weir crest elevation -- is the procedure most critical to maintaining effluent quality during dredging and
decanting operations . Operational requirements extend to the period during and immediately after
containment basin construction . Initially, the weir crest elevation should be set as high as necessary to
prevent unwanted release of stormwater and groundwater seepage. Before the site ' s initial use, the site
operator will periodically release ponded stormwater and groundwater seepage during regularly scheduled
inspections.
30
f
Immediately before the first placement operation at Site IR44, the weir crest should be set to an
initial weir crest elevation of +3 . 6 ft NGVD to provide the recommended mean operational ponding depth
of 4 . 0 ft . Thus, the initial maximum ponded water elevation at the facility' s first use lies at or below the
existing mean elevation within the basin footprint. Given the initial 0 .2% bottom slope within the basin , a
4 . 0- ft mean ponding depth corresponds to a 4 . 8-ft depth at the weirs . The initial weir setting; prevents the
release of effluent until the ponded water reaches its recommended operational depth . During this initial
operational phase, the design dredge discharge (3 ,560 cy/hr) will increase the ponding depth at a rate of
approximately 2 . 1 in ./hr and increase the ponded water surface elevation (ponding depth plus deposition
layer) at a rate of approximately 2 .6 in ./hr. This relatively slow rise should allow for close continual
monitoring of the entire dike perimeter for indications of slope instability. Inspection is most critical during
periods when the ponded water surface elevation is allowed to rise above its previous maximum . Experience
has shown that as the ponded water percolates into the interior dike slope, the coarser dike material filters
the fine suspended sediment. This filtering reduces the dike permeability and thus decreases the dike' s
susceptibility to piping and saturation .
As stated above, no effluent should be released until the surface of the ponded water approaches the
weir crests' initial setting of +3 .6 ft NGVD . Notably, a flow control structure such as a weir cannot improve
effluent quality beyond that ofthe surface water immediately upstream . Thus, the decision to release effluent
over the weirs should be based on the analysis of water samples taken immediately upstream of the weir at
the maximum depth of withdrawal . For Site IR44, recommended WES procedures (Section 2 . 3 .2 )
determined this depth to be 2.0 ft, based on the design dredge discharge of 3 , 560 cy/hr and a design weir
loading of 0 . 89 ft'/ft- sec . If testing shows that the turbidity of the interior surface waters remains
unacceptably high, the release of effluent must be delayed by one of two methods : ( 1 ) raising the weir crests
by adding flashboards or (2) shutting down the dredge plant. Additional alternative measures may include
installing turbidity screens surrounding the weirs.
Once the weir has begun to release effluent that meets established performance criteria ( Section 2 .3 ),
the outflow over the weir must not exceed the design dredge discharge, or 0 . 89 ft'/ft- sec . As discussed
below, static head over the weir then becomes the most practical criterion to ensure that the flow over the
weir, and thereby the effluent quality, remains within the design limits.
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1
Static head represents the maximum elevation of the water surface above the elevation of the weir
crest as measured upstream of the weir at a point where velocities are low ( 1 to 2% of the velocity at the weir
crest) . The static head can be measured directly by a stage gauge located at least 40 to 50 ft upstream of the
weir. The water surface elevation can be read directly from the gauge, with the difference between the gauge
elevation and the weir crest elevation indicating the static head . An empirical relationship applicable to
narrow-crested weirs (Walski and Schroeder, 1978) indicates that a design weir loading of 0. 89 Oft-sec
corresponds to a static head 0. 41 ft (4.9 in .). Alternatively, the static head can be determined indirectly by
measuring the depth of flow over the weir. The ratio of depth of flow over the weir to static head, estimated
as 0 . 85 for narrow-crested weirs, yields a design flow depth for the IR- 14 facility of 0.35 ft or 4 .2 in. If the
head over the weir, as measured by either method, falls below these design values as a result of unsteady
dredge output or intermittent operation , effluent quality should increase. However, if the head exceeds these
values, the ponding depth should be increased by adding flashboards until the mean ponding depth reaches
its 5- ft recommended maximum . To safeguard dike stability, dredging should be temporarily halted rather
than allow the mean ponding depth to exceed the recommended 5-ft maximum .
At all times, each of the three weir sections must be maintained at the same elevation to prevent flow
concentration and a decrease in effluent quality related to an increase in weir loading. Preventing floating
debris from collecting in front of the weir sections is also important . An accumulation of debris at the weir
will reduce the effective weir crest length and thereby increase the withdrawal depth . This, in turn, may
increase the effluent suspended solids concentration .
To maintain the recommended 4. 0- ft mean ponding depth throughout the dredging operation, the weir
crest should be raised at approximately the same rate as the rise of the deposition layer. Based on the
projected bulked volume produced by the typical dredging operation within Reach III --- 16, 300 to 32,600
cy per event based on a 5- to 10-year maintenance interval — the average depth of deposition per event will
range from 1 . 0 ft to 2 . 0 ft. Thus, the typical maintenance operation will result in a final weir crest elevation
ranging from +4 . 6 ft to +5 . 6 ft NGVD at completion of the first dredging operation .
After dredging has been completed, the ponded water that remains within the basin must be slowly
released by gradually removing flashboards - a process known as decanting. Flow over the weir should
drop essentially to zero before the next flashboard is removed . Effluent monitoring must continue during the
32
decanting process. If at any time during this process effluent turbidity violates water quality standards, the
effluent must be retained until analysis of the interior surface waters shows the suspended solids
concentration to be within acceptable limits. Decanting then continues in this manner until all ponded water
is released over the weir. Subsequent dewatering techniques are discussed in Chapter 4 . 0 .
3.4 Effluent Monitoring
As discussed in the preceding section, effluent monitoring will be an integral part of facility
operation . The IR- 14 containment basin has been designed to produce effluent which meets water quality
standards for Class III waters asset forth in Chapter 62-302 ofthe Florida Administrative Code. These rules
require a comprehensive monitoring program to document permit compliance. The monitoring program
should therefore continue throughout active dredging and decanting operations . Effluent samples should be
taken and analyzed as often as practical . The minimum recommended sampling frequency is two times per
eight hour shift.
Although effluent turbidity is only 1 of 29 parameters addressed in Florida ' s state water quality
standards, compliance with these standards has been historically based on turbidity alone for several reasons.
First, turbidity is reliably measured in the field and is the only water quality parameter over which the site
operator may exercise direct control . Second, turbidity is a strong indicator of general effluent quality since
many contaminants, most notably metals, exhibit a strong affinity for fine particles . Thus, reducing turbidity
should result in an overall improvement in effluent quality.
However, the disturbance of contaminated sediments may result in the release of other pollutants
(predominantly nutrients and hydrocarbons) which do not necessarily associate with fine particles. If the in
situ sediments contain elevated levels of these contaminants, turbidity may be an inadequate indicator of
effluent quality. Shoal sediments should undergo comprehensive elutriate and dry analysis to determine the
presence ofthese contaminants . Additional testing under the effluent monitoring program , ifrequired , should
then focus on those contaminants documented by pre-dredging sediment analysis.
Because effluent turbidity is a primary water quality parameter for site operation, compliance with
turbidity standards will largely control both the dredge plant output and the release of effluent. However, the
33
prediction and interpretation of basin performance and effluent quality in terms of these standards can be
problematic . This situation arises from the incompatibility of established design and compliance criteria.
State standards for effluent turbidity are expressed in terms of optical clarity relative to ambient conditions
of the receiving waters . By comparison, containment area design guidelines published by the U .S . Army
Corps of Engineers Waterways Experiment Station (WES) under the Dredged Material Research Program
(DMRP) relate containment area performance to the suspended solids concentration of the effluent . The level
of turbidity produced by a specific suspended solids concentration depends highly on the physical
characteristics of the suspended material . Previous investigation (e .g. , Walski and Schroeder, 1978) could
not establish a method to effectively translate suspended solids concentration to optical clarity even for
sediments with well-defined physical characteristics. The design and operation of this and other similar sites
would greatly benefit from such a predictive relationship . A primary objective of the effluent monitoring
program should be to relate suspended solids concentration to the state performance criterion based on
turbidity for sediments typically encountered in the ICW W .
3 . 5 Groundwater Monitoring
As discussed in Section 2 .4, groundwater monitoring forms a key element of Site IR- 14 ' s long-term
management. Sampling and analysis of groundwater throughout the dredging and decanting operation
comprises an essential component of the monitoring program . The duration of this program component
should extend from the start of dredging to the completion of decanting, a period projected to last about 8 to
12 weeks.
The site ' s first use as a containment facility will likely be the most crucial period for monitoring the
potential seepage of saline water through the dike ' s side slopes and foundation . During this time, soils
forming the dike will be most porous due to their disturbance during site construction. Thus, the initial period
of each dredging operation requires frequent sampling and analysis of groundwater. During the site's initial
use, groundwater samples should be taken twice every 24 hours . This sampling regimen should begin at the
start of dredging and continue for a period equivalent to the theoretical transit time of saline water from the
basin to the furthermost sampling well . Maximum transit time should be estimated during the final site
design process, given adequate datato define soil permeability, stratification, and the governing groundwater
flow gradient . Such data should be obtained from core borings taken in association with monitoring well
34
installation . Following the estimated maximum transit time through the remainder of the decanting process,
sampling should occur a minimum of once every 24 hours . If at any time elevated chloride levels are
detected in the monitoring wells, pumping will be stopped and ponding depth will be reduced until additional
corrective measures can be taken . These may include the installation of a system of well points around the
dike to reverse groundwater flow. Operational experience has shown that dike permeability decreases as the
dike material filters and traps the finer fraction of dredged sediments. Thus, saline seepage from the
containment basin should become increasingly limited with each successive dredging operation .
3 .6 Migratory Bird Protection
Should dredging be necessary during the migratory bird nesting season (April 1 through September
1 ), procedures presented in Appendix I of the Migratory Bird Policy (COE, 1993 ) will be implemented .
These procedures include a variety of measures, summarized in Section 2. 5 , to ensure avoidance of impacts
to migratory birds during periods of active dredging operations.
35
� a
4. 0 POST-DREDGING SITE MANAGEMENT
The post-dredging phase of site operation begins following the completion of decanting and
continues until the start of the next planned dredging event. Post-dredging site management will be
accomplished through the joint efforts of the FIND and the Jacksonville District, COE, and will include, at
a minimum , quarterly site inspections . Additional post-dredging site management tasks are discussed in the
following section .
During the post-dredging phase, dredged material deposited within the containment basin is actively
managed to reduce its moisture content. Through this process, the material is made suitable for handling and
removal, should market conditions prove favorable . However, Site IR44' s intended use as a permanent
facility requires other management procedures between successive dredging operations. These include a
comprehensive monitoring and data collection effort, mosquito control, and site security. Each element of
post-dredging site management is discussed below .
4. 1 Dewatering Operations
Dewatering techniques to be used at Site IR- 14 depend on the physical characteristics of the dredged
material . As discussed in Section 2 .3 .3 , preliminary data indicate that the material to be placed in the IR44
containment basin may contain up to 80% silts and clays (i .e . , particles <0 . 074 mm in diameter), with
organics comprising up to 3 % . This fine-grained fraction will be the most resistant to drying. The relatively
thin deposition layer resulting from a typical dredging operation (<2. 0 ft, Section 3 . 3 ) suggests that the
coarser sediment fraction will likely dry through natural evaporation and percolation alone . However,
effectively lowering the moisture content of the fine-grained fraction will likely still require supplementary
dewatering techniques . The most appropriate dewatering techniques for this purpose include surface water
removal , progressive trenching to promote continued drainage, and progressive reworking or removal of the
dried surface layer. Each procedure and its specific application to the present situation are discussed below .
Decanting all ponded surface water is necessary before significant evaporative drying of the fine-
grained material can occur . Simply continuing to lower the weir crest will remove most of the ponded water
following the completion of dredging operations. However, the anticipated topography of the deposition
36
layer makes draining off all ponded water in this manner unlikely. As discussed, differential settling of the
various size fractions of the sediment results in partial segregation of the dredged material within the
containment basin . Coarser sand- and gravel- sized particles settle nearer the inlet, while finer particles
concentrate nearer the weir. The sand- sized fraction , concentrated nearer the inlet, should experience
relatively little consolidation because of its low initial water content. However, the fine material ' s greater
consolidation will likely form one or more depressions nearer the weirs . To remove the ponded water that
remains in these areas, a drainage trench must connect each depression to a sump excavated adjacent to one
or more weirs. During this phase of operations, the weir crest must be raised to prevent the premature release
of the ponded water which, as a result of the excavation, will likely contain a high concentration of suspended
solids. Clarified water can then be released over the weir as soon as effluent turbidity standards are met.
Following the removal of all remaining ponded water, evaporative drying will eventually form a
crust over the layer of fine-grained material nearer the weir. This crust will trap water beneath its surface
and retard continued evaporation . In addition, the desiccation cracks which quickly form in the crust will
hold rainwater and limit further drying. Therefore, complete drying will require additional trenching.
Initially, a perimeter trench can be excavated by dragline or clamshell operating from the crest of the
containment dike . More intensive trenching must wait until a crust of significant thickness (greater than 5
to 6 in .) has developed on the deposition surface. The crusted surface will allow the use of conventional low
ground pressure equipment. A network of radial or parallel trenches should then be constructed throughout
the area of fine sediment deposition . The depth of each trenching operation will be dictated by the slumping
resistance of the semiliquid layer beneath the crust. Based on the projected mean thickness of the deposition
to be placed in the IR44 containment basin (<2 . 0 ft, Section 3 . 3 ), adequate drying should require no more
than two successive trenching operations. As an alternative to intensive trenching, the dried surface crust can
be transferred to a more well-drained area of coarser material nearer the inlet. This would expose the wetter
under layers and restore a relatively high rate of evaporative drying.
The dewatering process will continue until the crust extends over the entire depth of the deposition
layer. The time required to complete this phase of site operation will depend on the physical characteristics
of the sediment, as well as climatic conditions (e .g. , rainfall, relative humidity, season , etc. ) . During the
entire dewatering phase of the site operation, the weir must be operated to control the release of residual
37
water and impounded stormwater. The clarified effluent will be routed to the perimeter ditch and drained
off site .
4.2 Grading the Deposition Material
Following the completion of dewatering, the dried sediment must be graded to prepare for the next
dredging operation . Grading — that is, distributing the mounded sand , shell , and gravel over the remainder
of the containment area — serves a number of necessary functions . These include reestablishing the initial
uniform 0 .2% slope from the inlet down to the weirs, restoring the effective plan area of the containment
basin, and improving subsequent dewatering ofthe fine-grained material by separating successive deposition
layers with a free-draining substrate. As discussed in the next section, grading also provides for sormwater
runoff control . Finally, a series of post-grading topographic surveys will assess material consolidation and
refine estimates of remaining storage capacity.
4. 2. 1 Control of Stormwater Runoff
As stated , grading the dewatered deposition layer provides the additional benefit of allowing the
control and release of sormwater that drains from the interior slopes of the containment dike as well as the
dewatered sediment. A shallow, uniform slope (0 .20/of, Section 2 . 1 .2) toward the weirs ensures adequate
drainage, eliminates ponding of runoff in irregular depressions, and minimizes flow velocities and the risk
of channelization and erosion . In compliance with regulatory policy, a sump or retention area of adequate
capacity should be constructed adjacent to the weirs (with the weir flashboards in place) to retain the runoff
from the first 1 in. of rainfall . For the IR- 14 containment basin interior area of 12. 87 acres (from the dike
crest centerline inward), a circular basin with a radius of 86 ft and an average depth of 2 ft will provide a
retention pond with the required minimum capacity- of approximately 46 ,700 W . A site operator would then
be responsible for the gradual release of the ponded runoff at intervals determined by local weather
conditions. Providing shallow trenches or swales from the center of the retention basin to one or more weir
sections may also be necessary to facilitate the rapid removal of runoff.
As discussed in Section 3 . 1 , the clarified runoff will be routed from the containment basin to the
perimeter ditch via the weir discharge culvert. The perimeter ditch, in turn, will drain to the on-site mangrove
38
impoundment through the existing drainage network and ultimately will discharge to the Indian River. Ditch
construction details such as required slope and stabilization will be deferred to the final design phase of site
development.
4. 2. 2 Topographic Surveys
Monitoring the containment area between successive dredging events will include two topographic
surveys of the deposition surface. Results from a post-dredging survey, performed as soon as possible after
grading of the dewatered material, will provide an independent check of the dredging pay volume derived
from pre- and post dredging bathymetric comparison . A second topographic survey should be performed
immediately before the start of the next dredging operation . Used in combination with the earlier post=
grading survey, this second survey will assess the degree of material consolidation and determine the
remaining site capacity.
4.3 Material Rehandling/Reuse
As discussed in Section 1 . 0, Site IR- 14 is one of three dredged material management areas being
developed to serve the long-term maintenance requirements of the ICW W within Indian River County. This
report, as well as the accompanying permit documentation, has emphasized that although each site has been
designed for a specific service life, each is also to be operated as a permanent facility for the intermediate
storage and rehandling of dredged material . To fulfill this intended use, at some point the dewatered material
must be removed off site . The ultimate use of this material is discussed in the following paragraphs .
Based on a comprehensive analysis of dredging records and survey data, the bulked material volume
projected for placement and temporary storage over the 50-year design service life of the three Indian River
County facilities exceeds 600,000 cy. Although relatively minor by the standards of some dredging
operations , this volume still represents a significant quantity of potentially valuable material . Even if the
possible return on the sale of this material were disregarded, the cost saving of permanent storage alone
would justify an effort to determine, through a formal market analysis, the potential demand for dewatered
dredged material .
39
, a
If such a determination reveals that material resale and/or reuse is practical, the properties of the
dredged material must then be demonstrated to satisfy the requirements of commercial interests . The coarsest
fraction of material (sand and gravel), having been partially segregated through differential settling, can likely
be used as is. However, the feasibility of compartmentalized segregation of material during dredging or
mechanical separation following dewatering should be explored if market conditions dictate. Portions of the
material determined to be unsuitable for fill or other construction purposes because of organic silt or clay
content might be used for landfill capping or agricultural purposes .
A determination that resale or reuse is unfeasible will dictate locating and developing a centralized
permanent storage facility. The appropriate location for such a facility would appear to be inland where
lower real estate values and development potential make permanent storage more economically feasible. The
optimal distance from the initial containment area to the permanent storage site would represent a
compromise between lower land costs and higher transportation costs .
4.4 Additional Environmental Considerations
4. 4. 1 Biological Monitoring
A primary consideration in the design and operational guidelines for Site IR- 14 is the intent to limit
adverse impacts to those directly related to construction of the dredged material management facility.
Notwithstanding the above, additional biological monitoring will be required within the buffer zone which
lies outside the containment area. A biological monitoring program , which may be extended to the proposed
pipeline route as well as the immediate vicinity of the site, may include the following elements. If required
to update existing information, an environmental survey of these areas will be performed before site
construction to establish current baseline habitat conditions and population densities . Periodic resurveys
should then continue throughout the service life of the site. Impacts to local habitat resulting from site
construction oroperation should be noted, corrective actions taken, and guidelines developed to avoid similar
consequences . Similarly, beneficial aspects of site management should be recognized and encouraged, and
the lessons learned should be applied to the future operation of this and other comparable dredged material
management areas .
40
4. 4. 2 Migratory Bird Protection
As discussed in Section 2 .4, migratory birds may nest on the sandy substrate left in the containment
basin following dewatering and grading. Should posvdredging site management activities be required during
the April 1 through September 1 nesting season, they will be carried out in accordance with the site protection
plan (COE, 1993 ) summarized in Section 2 .4 .
4. 4. 3 Groundwater Monitoring
As discussed in Sections 2 .4 and 3 .5 , a groundwater monitoring program will be implemented at Site
IR- 14 to detect possible saline water migration from the containment basin into local groundwater. Between
dredging events, sample collection and analysis will continue as part of the site operator's regular inspection
routine.
After the release of all ponded water remaining from the previous dredging operation, a period of
post-dredging sample collection will begin . During this period, groundwater samples will be collected and
analyzed monthly for the first year following the completion of decanting and quarterly thereafter unless
otherwise needed . More frequent sampling intervals may be required should conditions warrant. Should
elevated chloride levels be detected at any time, the source will be determined . If the containment basin is
the source, corrective actions will be taken . As discussed in Section 3 . 5, these may include the installation
of a system of well points around the dike to reverse groundwater flow. If chlorides originate from a source
external to the IR44 facility ( i . e. , intrusion caused by off-site groundwater demand), the proper authorities
will be notified.
4. 4. 4 Mosquito Control
The basic approach of the mosquito control program for Site IR- 14 will emphasize physical rather
than chemical control . The time during which standing water remains inside the containment area will be
kept to a minimum to reduce the potential for mosquito breeding. The operational phase most favorable for
mosquito breeding follows the completion of decanting when desiccation cracks form in the crust. Trenching
procedures (Section 4 . 1 ) will accelerate the dewatering process by allowing much of the moisture within the
41
cracks to drain to the weirs. However, adverse climatic conditions could delay the dewatering phase long
enough to result in successful breeding within the desiccation cracks . This would require a short-term spray
program coordinated through the Indian River County Mosquito Control District.
4.5 Site Security
Providing adequate site security will remain a key element in the proper management of IR44.
Unsecured dredged material containment areas typically host a variety of unauthorized activities including
illegal dumping, vandalism , hunting, and dike destruction through the use of off-road vehicles. As discussed
in Section 2 . 3 . 8, security fencing installed around the site ' s upland perimeter should preclude such activities
within the IR- 14 containment facility. Access to the area within the fence will be limited to agents and
representatives of the FIND and the Jacksonville District Corps of Engineers, and authorized contractor
personnel . Access gates will remain locked at all times exceptduring dredging and maintenance operations.
The presence of an on- site operator duing such operations should further discourage unauthorized entry to
the site and the occurrence of unsanctioned activities.
Between dredging operations the site operator will be responsible for carrying out regularly
scheduled inspections. The primary purpose of these inspections will be to perform routine operational
functions and to ensure that facility security is maintained . Breaches in site security will be identified and
appropriate actions will be taken as quickly as possible to restore the site to a fully operational standby
condition . Other responsibilities of the operator during these visits will include weir operation and
stormwater release, groundwater monitoring, and routine inspection of dike integrity and buffer area
conditions .
42
REFERENCES
Gallagher (Brian J.) and Company. 1978 . Investigation of Containment Area Design to Maximize Hydraulic
Efficiency. Technical Report D48- 12 . U . S . Army Engineer Waterways Experiment Station,
Vicksburg, MS .
Palermo, M . R. , Montgomery, R. L . , and Poindexter, M . E. 1978 . Guidelines for Designing, Operating,
and Managing Dredged Material Containment Areas. Technical Report DS-78 - 10 . U. S . Army
Corps of Engineers Waterways Experiment Station , Vicksburg, MS.
Shields, F. D., Jr. , Thackston , E. L. , and Schroeder, P. R. 1987 . Design and Management of Dredged
Material Containment Areas to Improve Hydraulic Performance. Technical Report 1)47-2 . U . S .
Army Corps of Engineers Waterways Experiment Station, Vicksburg, MS .
Taylor, R. B . and McFetridge, W. F. 1989 , Engineering Evaluation of Proposed Dredged Material
Transfer and Handling Operation. Taylor Engineering, Inc . , Jacksonville, FL.
Taylor, R. B . , McFetridge, W. F. , and Schropp, S . J. 1997 . Long-Range Dredged Material Management
Plan for the Intracoastal Waterway in Indian River County, Florida. Taylor Engineering, Inc .,
Jacksonville, FL,
U. S . Army Corps of Engineers (COE). 1993 . Draft Final Migratory Bird Protection Policy. U. S . Army
Corps of Engineers, Jacksonville District, Jacksonville, FL .
Walski, T. M ., and Schroeder, P. R. 1978, Weir Design to Maintain Effluent Quality from Dredged Material
Containment Areas . Technical Report D-7848 . U.S . Army Engineer Waterways Experiment
Station, Vicksburg, MS .
Wettstein, C . A . , Noble, C . V. , and Stabaugh, J. D . 1987 . Soil Survey of Indian River County, Florida. Soil
Conservation Service, U . S . Department of Agriculture, Washington, D .C .
43
APPENDIX A
• , .4
T " A Y L O R N G l N E E r I N G I N C
January 21 , 1998
Mr. David K. Roach
Assistant Executive Director
Florida Inland Navigation District
1314 Marcinski Road
Jupiter, FL 33477
Re: Response from the Department of State, Division of Tiistorical Resources, Concerning Proposed
FIND Sites in Indian River and St. Lucie Counties
Dear Mr. Roach:
Enclosed please find a copy of the letter we received from the Florida Department of State,
Division of Historic Resources, Bureau of Historic Preservation, in response to our December 3 , 1997,
letter of inquiry concerning the proposed FIND sites in Indian River and St. Lucie Counties. Also please
find a faxed copy of maps showing the recorded locations of the cultural resource sites . Please note that
the two cultural resource sites identified within the proposed FIND sites — archeological site 8IR849
in Site IM and archeological site 8IR835 in Site IR 14 — lie along the Indian River shoreline, east of
the mosquito impoundment, and would not be impacted by site construction.
If you have any questions or comments, please do not hesitate to call.
a
cFee
enclosures
o n R 6 C Y P R F S C G R E E N D R I A f K g O NV I It F F I 1 2 2 5 6
7 E l 9 0 4 7 1 1 7 n 4 0 F A X O n e 7 1 1 Q R 4
tWXMA DYPARTULYr OF STATE
Oftim of dw lewuly .ONIMDER OF THY noRIDA CABI.HIT
oai•c .s ratmaaonrl Ed�aoH Otvialaa of library & JLkm jonScyk,
Division of Adrnm nave sfzvk m 0*05 of Hislodw Ruowm
Divwoo olcarpont►oa Moues
Dtvidon otCul�urei Dmem of Licec
dvstoaot8teceonai
FLORIDA I)WARThSNT OF STATE
S*Adra Be Morthxm
Sacra of State
DIVISION OP MRICAL RESOURCES
BUREAU OF HISTORIC PRESERVATION
FACSIMILE TXMSMTTAL SHEET
TO FAX NUMBER;
NAME: Ir ! L 1. �t,� G r
COWANY: � N
SENDER $
DATE :
NUMPER OF PAGBS (Incluftg transmittal sheet):
From Phone (850) 4874333. -
Suncom 277.2333
Fax (850). 922690496
RA Gray Building • 500 South &oriou .. s op=
FAX: (830) 4WF33M • WWW Addre hjtph* vwwA0.State 01 -1480
O ARCHUSOLOCiICAL n3EA1tCH D HISTORIC PRESERVATION Q
(BSO) 487-2299 0FAFIISTORICAL MUSEUMS
FAX 4142207 (130) 487.2333 9 FAX: 9224u96 (350) 418.1484 6 PAX: 921 -2503
FUMDA DEF*% RTMENr OF STATE MEMBER OF THE FLORIDA CABINET
Office of the Secretary Division of Library & information Services
OtRce of International Relations Division of Historical Resources
Division of Administrative Services Ringling Museum of Art
Division of Corporations Division of Licensing
Division of Cultural Affairs Division of Elections
FLORIDA DEPARTMENT OF STATE
Sandia B . Mortham
Secretary of State
DIVISION OF HISTORICAL RESOURCES
January 14, 1998
Mr. William F . McFetridge In Reply Refer To :
Taylor Engineering, Inc. Frank J . Keel
9056 Cypress Green Drive Historic Preservation Planner
Jacksonville, Florida 32256 Project File No. 976476
RE : Cultural Resource Assessment Request
Florida Inland Navigation District Long-Range Dredged Material Management
Plan for the Intracoastal Waterway
Indian River and St. Lucie Counties, Florida
Dear Mr. McFetridge :
In accordance with the provisions contained in Chapter 267 . 061 , Florida Statutes, we have
reviewed the above referenced proJJ'ect(s) for possible impact to archaeological and historical sites
or properties listed, or eligible for listing, in the National Register of Historic Places, or
otherwise of historical or archaeological value.
A review of the Florida Site File indicates that two archaeological sites, SIR849 and IR835 are
recorded within the IR-2 and IR- 14 project areas, respectively. No formal assessment of
significance has been complete for either site. Archaeological site SIR849 is recorded as a
disturbed artifact scatter. Archaeological site 818835 is recorded as a partially inundated artifact
scatter. Both sites were recorded based only on surface inspection. It is, therefore, the
recommendation of this office that, prior to initiating any project related land clearing or ground
disturbing activities within the IR-2 and IR- 14 project areas, they should be subjected to a
systematic, professional archaeological and historical survey ,to located and assess the significance
of the recorded sites and any as yet unrecorded historic sites in the project areas.
It is also our recommendation that the IR- 12B, and M-8 project areas be subjected to a
systematic, professional survey. The purpose of these surveys will be to locate and assess the
significance of historic properties present. The results of the investigations will determine if
significant historic properties would be disturbed by this project. In addition, if significant
remains are located, the data described in the report and the archaeologist' s conclusions will assist
this office in determining measures that must be taken to avoid, minimize, or mitigate adverse
impacts to significant historic properties.
DIRECTOR'S OFFICE
R.A. Gray Building • 500 South Bronough Street • Tallahassee, Florida 32399-0250 • (850) 4884480
FAX: (850) 48&3353 • WW Address httpJ/www.dos. state-fl -us
O ARCHAEOLOGICAL RESEARCH d HISTORIC PRESERVATION O HISTORICAL MUSEUMS
(850) 487-2299 • FAX: 414=2207 (850) 487-2333 • FAX: 922-0496 (850) 488-1484 • FAX: 921 -2503
Mr. McFetridge
January 14, 1998
Page 2
Finally, a review of the Florida Site File indicates that no significant archaeological or historical
sites are recorded for or likely to be present within the proposed SL=2 and SL-26 project areas.
Therefore, it is the opinion of this office that these projects will have no effect on significant
historic properties.
Because this letter and its contents are a matter of public record, the applicant may be contacted
by consultants who have knowledge of our recommendations. This should in no way be
interpreted as an endorsement by this a0ency. The Society of Professional Archaeologists
(SOPA) is the national certifying organization for archaeologists. Upon request, our office can
supply a listing of archaeologists who are SOPA members living or working in Florida. In
addition, we can provide information on ordering their Directory of Certified Professional
Archaeologists from them.
If you have any questions concerning our comments, please do not hesitate to contact us. Your
interest ui protecting Florida's historic properties is appreciated.
Sincerely,
IVga� ec 4t%tol���
Geor$e W. Percy, Director
Division of Historical Resources
and
State Historic Preservation Officer
GWP/Kfk
xc : C . L . Irwin, FDOT
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TECHNICAL ADDENDUM
Weir Design Modifications and Operational Guidelines
Site IR- 14
Indian River County
Prepared for
FLORIDA INLAND NAVIGATION DISTRICT
by
R . Bruce Taylor, Ph . D., P.E .
William F. McFetridge
Taylor Engineering, Inca
10151 Deerwood Park Blvd .
Bldg, 300, Suite 300
Jacksonville, Florida 32256
(904) 731 - 7040
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15 0
ISO INTRODUCTION
This Technical Addendum to the existing Management Plan for the IR- 14 Dredged Material
Management Area (Taylor et al , May 1999) presents preliminary design revisions and operational
guidelines for the proposed weir system at FIND Site JR- 14 in Indian River County . It also presents
additional operational requirements contained in recently adopted Draft Environmental Resource Permit
(ERP) review criteria for dredged material containment facilities first proposed by the Florida Department
of Environmental Protection (FDEP) . The Florida Inland Navigation District (FIND), local sponsor of the
Intracoastal Waterway (1CMrW) and owner of Site IR- 14, contracted Taylor Engineering to develop this
addendum to improve weir performance and establish operational constraints on the dredging contractors '
use of all FIND dredged material placement sites. No schedule has been set for the final design and
construction of the IR- 14 facility. The design revisions and operational guidelines this addendum presents
assume that the IR44 facility 's final design and construction — in particular, the final design and
construction of its weir structure ---- remains consistent with its preliminary design first presented in the
site ' s Management Plan.
The FIND intends that both the site' s earlier Management Plan and the present addendum to that
plan be included as part of the bid package for the next dredging contract for maintenance of the ICWW,
Indian River County Reach III, not yet scheduled. The FIND also intends that both documents form
attachments to the contract for these dredging services . In all cases where the present Technical
Addendum conflicts with the earlier Management Plan, the Technical Addendum shall take precedence.
All design elements presented in these documents, including the weir design modifications
described in Chapter 2.0 of the present addendum, represent conceptual preliminary designs only. During
the project ' s Final Design Phase, it will remain the responsibility of the project 's Engineer of Record to
fully design and specify each of these conceptual designs elements for inclusion in the project's Final
Design and Construction Drawings and Technical Specifications .
Throughout, this Technical Appendix references the need for the Project Engineer to review and
approve contractor submittals. In each case, the Project Engineer refers to an authorized representative of
the contracting entity (USACE or the FIND) that assumes overall project responsibility for the dredging
project by authorizing and/or approving the project ' s final design, advertising the project for bid, selecting
the contractor, awarding the contract , administering the contract, and providing construction observation
f •
and/or inspection services, as required . Responsibility for the initial placement operation at Site IR- 14
remains to be determined.
The Addendum is organized as follows. Chapter 2 . 0 first outlines basic elements of the IR- 14
weir design as described in the site 's original Management Plan, then presents preliminary minor
revisions to the IR- 14 weir system that are intended to improve performance without requiring significant
alteration of the weirs ' basic structure. Chapter 3 .0 presents guidelines for operating the modified weir
system that the selected contractor must follow before, during, and immediately after dredging. Chapter
4 . 0 presents inspection criteria designed to ensure the stability and safety of the site' s containment dikes .
Chapter 5 . 0 presents additional criteria for maintaining a vegetative cover on the containment dikes to
facilitate the required inspections.
2. 0 WEIR DESIGN REVISIONS
2. 1 Elements of the Predominant Weir Design
This section presents the basic elements of the preliminary design for the IR- 14 weir structure. As
described in the site 's original Management Plan, the preliminary design for the IR- 14 weir structure
follows the predominant weir design now in use within the Jacksonville District, as well as the design
installed at almost all FIND containment facilities built since 1991 . This design features a parallel
arrangement of three to four pile-supported weir stacks, each stack formed by a corrugated metal half-
pipe. Removable flashboards key loosely into vertical 1-beam channels to form a vertical barrier across
the otherwise open side of each half-pipe. This face acts as a dam to retain water within the basin. Under
ideal conditions (that is, no leakage between the boards or around the boards ' ends), water may only exit
the basin by passing over the weir' s crest, that is, the top board in the stack. Adding or removing weir
boards allows the operator to maintain the crest elevation to just below the ponded water surface
elevation. In this manner, the weir maintains effluent quality by discharging only the clarified surface
layer from which almost all suspended sediment has already settled. The total weir crest length (that is,
the combined length of the weir crests of each weir stack) reflects the length needed to maintain the
withdrawal depth less than the minimum 2 . 0 -ft ponding depth (Section 3 . 3 . 1 ) . Withdrawal depth refers to
the theoretical depth of the surface layer of water selectively withdrawn over the weir crest . For the weir
to function as intended and maintain effluent turbidity within acceptable standards, the basin must provide
sufficient retention to allow the finest sediment component to settle from the weirs ' design withdrawal
depth. Given that the suspended sediment concentration within the ponded water increases with depth,
- 2 -
M •
decreasing the withdrawal depth should improve the basin' s solids retention performance and improve
effluent quality. Under most circumstances , maintaining the withdrawal depth less than the minimum
ponding depth should help ensure that the weirs release only the clarified surface layer that contains
relatively low concentrations of suspended sediment . The specified total weir crest length — 36 ft for the
four weir stack design and 24 ft for the three weir stack option — derives from nomographs developed
under the USACE 's Waterways Experiment Station (WES) Dredged Material Research Program (e . g . ,
Walski and Schoeder, 1978) . Based on the discharge of the design dredge plant, the 36 - 11 total length
assumes the output characteristics of a 24 -in . dredge, while the 24-ft length assumes an 18 -in. dredge. The
preliminary design for the IR- 14 weir structure recommends the three weir stack option.
This remainder of this chapter presents recommendations for minor design revisions to the weir
system proposed for installation at the IR44 containment facility. As discussed above, the basic
installation follows the predominant weir design now in use within the Jacksonville District, as well as the
design installed at almost all FIND containment facilities . The proposed revisions do not require
significant alteration of the weirs ' basic structure and can be installed as part of the dredging contractor's
site preparation responsibilities .
2 . 2 Deficiencies of the Predominant Weir Design
As part of our investigations into possible deficiencies in the predominant weir design currently
installed at existing FIND containment facilities , Taylor Engineering staff solicited information from two
groups : ( 1 ) USACE personnel presently or recently engaged in planning, designing, contracting, or
inspecting dredging/dredged material management operations at FIND dredged material containment
facilities and (2) dredging contractors that have recently used or are familiar with existing FIND facilities .
In addition to establishing typical weir operating procedures, these inquiries were intended to investigate
perceived deficiencies in the design and construction of the weir systems presently installed in FIND
dredged material containment facilities .
The discussions with representatives of both the USACE and private dredging contractors
focused on three basic concerns regarding present weir design : ( 1 ) the design 's failure to adequately
control leakage around the ends of the weir boards, where the boards key loosely into the vertical I-beam
channels; (2) its failure to adequately control leakage between the weir boards ; and (3) its failure to
adequately provide a means to safely access the weirs as required to add or remove weir boards and to
secure the boards in position. The discussions confirmed Taylor Engineering 's own observations that
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contractors typically use a combination of plastic sheeting, plywood, and roofing tar to address the first
two concerns — leakage around and between the weir boards — with varying degrees of success. The
discussions also confirmed that the third concern --- the difficulty of accessing the weirs and adjusting
and securing the weir boards — has forced contractors to resort to a variety of means, none of which
promote safe and efficient weir operations. Contractors typically use the limited access provided by the
existing fixed ladders to install or remove weir boards from above, and use a johnboat or similar small
vessel positioned directly in the discharge flow to install or remove weir boards from below . From these
precarious positions , the contractors then typically secure the boards by pounding in wooden wedges or
shims . The remainder of this section specifically addresses these three issues by presenting a conceptual
design for minor modifications to the weir system proposed for installation at the planned IR- 14
containment facility. All site-specific elements of the proposed modifications (e. g., elevations) refer to the
preliminary weir design as presented in the site ' s Management Plan (Taylor et at . , May 1999) .
2 . 3 Conceptual Weir Modifications
Figure 2 . 1 presents the basic elements of the proposed weir modifications . Notably, these
revisions require no dismantling, and only minor modification, of the weir system ' s basic structure. Each
of the proposed modifications is presented here as a preliminary conceptual design only. The Project
Engineer remains responsible to fully design, specify, and incorporate the proposed modifications into the
bid package for the site ' s first use. The selected contractor must then complete the proposed weir
modifications before the initiation of dredging as part of required site preparation activities .
As shown, the proposed modifications include three basic elements. First, to address the issue of
leakage around the ends of the weir boards, the modifications include wooden extensions, fabricated from
dimensional pressure-treated (PT) lumber, installed vertically against the inside (downstream) flange of
each vertical I-beam channel that holds the weir boards . These flange extensions will provide a smooth,
wide surface against which the downstream face of the weir boards will seat. Although providing an
imperfect seal, the width of these mating surfaces will greatly reduce the likelihood of leakage around the
ends of the weir boards. Equally important, the flange extensions will also provide a means to secure each
weir board in position without the use of wedges that can become dislodged by changes in water level .
Second, to address the issue of leakage between boards , the modifications also extend to the weir
boards themselves . The contractor must still supply all required weir boards, but with the boards modified
- 4 -
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BLDG, 300, SUITE 300 `"�`• 1 0( 1
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PRELIMINARY DRAWINGS; THESE DRAWINGS ARE NOT IN FINAL FORM, BUT ARE BEING TRANSMITTED FOR REVIEW.
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to accept a spline that ties each board to the adjoining boards above and below. The splines, constructed
from % -in . aluminum, 'h -in. marine plywood, or other appropriate material and supplemented by
appropriate sealants or lubricants (e.g. , beeswax or non-toxic grease) , will largely eliminate between-
board leakage while they also significantly strengthen each individual board by transferring to the
adjacent boards a portion of the bending moment produced by hydrostatic pressure.
Third, to address the issues of adjustability, the modifications include installing steel or wooden
cantilevered-beam hangers above each weir from which the contractor will hang commercially-available,
adjustable scaffolding similar to that used in commercial painting or window washing . The scaffolding
will provide the contractor 's designated weir operators a safe means to lower the weir boards from the
weir walkway to the correct level for installation . The scaffolding will also provide an adjustable work
platform, safely suspended above the discharge flow, from which the weir operators can efficiently place
and fasten the weir boards to the flange extensions. The remainder of this section discusses the concept of
the required modifications in more detail.
2. 3. 1. 1-Beam Channel Flange Extensions
As stated above, the I-beam channel flange extensions will serve two functions. First, they will
provide a wide and smooth surface against which the back (downstream) face of the weir boards will seat
to form an effective, although imperfect, seat . Although not completely water-tight, this seal will greatly
reduce the likelihood of significant leakage around the ends of the boards . Second, they will also provide
a means to connect and secure each weir board in position without resorting to wedges that may be
dislodged by changes in water level or pressure.
The contractor will fabricate the flange extensions from nominal 2x8 PT lumber (finished
dimensions — 1 %Z in. x 7 '/. in . ) and install the wooden extensions vertically against the inside face of the
downstream flange of each W8xl8 I-beam channel that holds the ends of the weir boards. Adjacent
vertical members restrict access and prevent bolting the flange extensions through the I-beam flange
itself. As a result, the flange extensions must be bolted through the flange of the adjacent C1503 . 9
channel , with a metal spacer or rubber bushing inserted between the outside face of the C-channel flange
and the wooden flange extension (Figure 2 . 1a). This length of the spacer or the compression applied to
the bushing must be adjusted to insure that the flange extension remains parallel to the I-beam flange
against which the flange extension must seat.
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The weir system proposed for installation at Site IR- 14 consists of three weir stacks with each
stack containing two single side channels and one double center channel for a total of four channels per
stack. As a result , the IR- 14 installation will require 12 separate 2x8 flange extensions . Each 2x8 flange
extension must be fabricated from a single board to extend the full 13 .9-ft range of adjustability required
by the IR- 14 facility, from - 1 .2 ft NGVD to at least + 12 . 7 ft NGVD. The first elevation corresponds to the
height of the base plate or sill of each weir stack. The second elevation corresponds to the maximum
allowable water level in the IR- 14 basin to maintain the required 2 ft freeboard below the + 14 . 7-ft
elevation of the dike crest .
The contractor will permanently attach each 2x8 flange extension to the I-beam flange as follows :
1 . Drill a series of holes, 2-11 on center and arranged vertically, through the center of the
C-channel flange (that is , I % in . from the flange' s edge) to accept 5l164n . x 3 -in.
stainless steel bolts .
2 . Chamfer one corner of each 2x8 flange extension to clear the filet of the I-beam
channel and thereby allow one edge of the 2x8 to seat against the I-beam' s web (Figure
2. 1a) .
3 . If necessary, plane one face of the 2x8 flange extension to match, as closely as
possible, the taper of the I-beam flange.
4 . With the 13 .9-ft+ base of the flange extension firmly seated on the weir base plate and
the edge of the flange extension firmly seated on the I-beam web, mark then drill
matching holes in the extension.
5 . On the upstream face of the flange extension, counter-sink the holes % in. to accept a
nut and washer.
6 . Begin installation of the flange extensions by placing a bed of roofing asphalt on the
weir base plate to receive and seal the bottom of the flange extension.
7. To improve the seal between the flange extension and the I-beam channel ' s bituminous
coating, wrap the mating surfaces (edge and face) of the flange extension with a
continuous gasket fabricated from rubber, neoprene, heavy roofing felt, or other
approved materials .
8 . Firmly seat the extensions against the weir base plate and the inner face and web of the
I-beam channels .
9. Align the holes with the pre-drilled holes in the C-channel flange.
- 7 -
a •
10 . Insert the 5/ 16-in . x 3-in. stainless steel bolts through the C-channel flange, the spacer
or bushing, and the flange extension and securely tighten into position with matching
washer and nut.
1 I . Following installation, ensure that the bolt does not project beyond the upstream face of
the flange extension and prevent the weir boards from seating firmly against the face of
the extension.
12 . Confirm that the face of the extension remains parallel to the axis of the weir crest to
maximize the mating surfaces and provide the optimal seal .
2. 3. 2 Weir Boards and Splines
The contractor will be responsible for providing and fabricating — from standard (PT)
dimensional lumber — all weir boards required for the minimum 13 .9 -ft range of weir adjustment for
each of the three weir stacks . To adequately resist the greater hydrostatic forces near the bottom of the
weir stack, the contractor must use (nominal) 6x6 boards (finished dimensions - 5 %: in. x 5 %: in.) within
the lowermost 4 ft of the weir stack (that is, below +2 . 8 ft NGVD) with (nominal) 4x6 boards (finished
dimensions - 3 '/ in . x 5 % in .) for only the upper 10 ft of the weir stack (that is, above +2. 8 ft NGVD) . In
addition to reducing cost and weight, using 4x6 weir boards (3 %s in. finished vertical dimension) above
+2 . 8 ft will improve the accuracy and resolution of the weir height adjustments . To further reduce cost
and weight the contractor may use (nominal) 4x4 weir boards (finished dimensions - 3 . 5 in. x 3 . 5 in .), but
only within the uppermost 3 ft of the weir stack (that is , above +9 . 7 ft NGVD) (Figure 2 . 1 b) .
To maximize the mating surface between the flange extension and the weir boards, each weir
board must be of sufficient length to extend to within 1 in . of the web of both opposing I-beam channels .
No weir boards can be used that when fully saturated would bind within the channels . For the Site IR- 14
installation, a weir board length of 52 in. should meet this requirement based on a 53 .5 -in. design
separation between opposing webs . However, the FIND cannot guarantee that the I-beam channels remain
plumb and parallel throughout their length. The contractor remains responsible to verify the actual field
dimensions and provide weir boards that will fall within the required tolerance throughout the full height
of the weir stack.
As stated earlier, to prevent between board leakage and to strengthen the weir stack, a spline will
tie each weir board to the adjacent members above and below. To provide a keyway for the spline, the
contractor must mill a matching dado or slot on opposite faces of each weir board, each slot set back I %:
- 8 -
• t
in . from the common, downstream face (Figure 2 . 1b) . For the spline itself, '/. -in . aluminum is the
recommended first-choice option, with ''/z -in. 5 -ply, marine-grade plywood (actual thickness — 12mm, or
15/32 in.) the lower-cost, second-choice alternative. Other materials, such as plastics or composites may
be acceptable, but must be submitted to the Project Engineer for review and approval . Each spline shall be
fabricated from the approved material , 2 -in . wide and of an equal length as the weir boards into which
each will be inserted.
Despite its greater cost compared to marine plywood, aluminum remains the preferred alternative.
Unlike marine plywood or other wood-based materials (e . g. , wood/plastic composites), aluminum will not
adsorb water, expand, and potentially lock the spline into the slot . As a result , the slot to accept the spline
can be milled to a closer tolerance. The addition of an approved , non-toxic lubricant will improve the
effectiveness of the seal , limit corrosion, and insure that the spline will not lock in place . Other non-wood
materials (e. g. , plastics) may also prove acceptable, but would likely require a thickness greater than ''/. in.
to provide sufficient shear strength. Marine plywood remains the second-choice alternative. Its primary
advantage, in addition to its relatively low cost, is that additional splines can be easily fabricated on-site
as needed . Milling the slot with sufficient tolerance to allow for the plywood' s inevitable expansion will
reduce the likelihood that the spline will lock into position. The addition of a non-toxic lubricant such as a
heavy coating of beeswax will reduce the plywood' s tendency to swell and lock itself into the slot.
2 .3 . 2. 1 Weir Board Installation
During dredging, each weir board will be added to the stack as follows . Because water typically
will flow over the weir crest , the weir operator must first divert the flow to the two remaining weir stacks
by driving a section of %z-in. marine-grade plywood between inner face of the upstream I-beam flange and
the weir boards . To adequately divert the flow, this section of plywood must span the full distance
between the webs of the opposing I-beam channels into which the weir board will be placed, and extend
sufficiently above the weir crest such that little or no flow continues over the weir. If necessary to prevent
hydrostatic pressure from bending the plywood, the operator may reinforce the plywood ' s upper edge by
securing a metal channel to its downstream face. The weir operator must then clear excess water from the
slot in the upper surface of the top board in the stack. (Note: the above procedure applies only during
active dredging as water flows over the weir crest. Obviously, diverting the flow will not be required
when the contractor prepares to start dredging and the weir operator initially installs weir boards to set
the initial ponding depth (Section 3. 2), or after the completion of decanting as he closes off the weirs as
part of his demobilization procedures (Section 3. 4). ] Next , the operator must apply a thick coating of the
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approved lubricant/sealant to the entire length of the spline and insert a spline into the slot . If necessary to
firmly seat the spline against the bottom of the slot, the weir operator may drive it into position by placing
a short length of 4x4 with a matching mortise over the spline and striking the 4x4 with a hammer until
lubricant extrudes from the joint on both sides of the spline. To prevent deformation of the spline, the
operator should not directly strike the spline under any circumstance. The operator then must align the
slot of the board to be added with the spline just inserted, and apply pressure to the added board until its
bottom face seats firmly against the upper face of the board below . Again, to preserve a smooth mating
surface, the operator must not strike the weir board directly with the hammer, but rather must first place
the short section of 4x4 on the board being added and then strike that section.
With the added weir board seated firmly against the board below, the final step in adding each
weir board requires that the weir operator secure the board in position as follows :
1 . If necessary to force the downstream face of the added board firmly against the flange
extension, temporarily drive a wooden shim between the inner surface of the upstream I-
beam channel flange and the plywood that temporarily diverts the flow.
2 . Working from the downstream (inner) side of the flange, drill a pilot hole through the
flange into the added board . The holes through the extension should then be enlarged
such that the lag screw that will attach the weir boards to the flange extension will not
bind in the hole .
3 . Insert a minimum 34n . lag screw through the extension hole, and drive it fully into the
pilot hole in the weir board until the screw head seats against the extension and draws the
downstream face of the weir board tightly against the flange extension.
4. After ensuring the added board remains firmly in position, remove the temporary
plywood that had been blocking the flow (and , if used, the additional shims) .
5 . Proceed to the next weir stack, continuing the process until all three weir stacks are set at
the same, higher elevation.
2 . 3 . 2 . 2 Weir Board Removal
Following the completion of dredging, the contractor must begin decanting the ponded water
within the basin by gradually removing the weir boards . Section 3 .4 describes the decanting process.
However, in removing the individual boards, the contractor must follow the procedures outlined below .
- 10 .
With the work platform of the scaffolding lowered into position near the weir crest , the weir
operator will remove the lag screws that have connected each board to the flange extension and remove
the top board with a pry bar. Through this process , the weir operator must take care to minimize damage
to the board and spline. All boards and splines removed intact and with minimal damage should then be
stacked neatly on a level surface with spacers separating each level to promote air-drying. The contractor
should use these boards and splines removed intact to close off the weirs following the completion of
decanting. However, if swelling of the board or spline prevents the operator from prying the top board
from the one beneath intact, the operator may remove the top board by cutting it into several sections with
a chain saw or cordless electric saw and knocking the sections loose with a sledge . All boards and splines
removed in such a manner must be discarded offsite in an approved manner.
2. 3. 3 Scaffolding/Ladders
To provide safe access to the weir boards and a secure working platform from which to perform
the now more complex weir board installation procedure, the contractor must provide an approved,
OSHA-compliant, moveable scaffolding system, similar to those in wide commercial use for painting or
window-washing. The scaffolding must be suspended by ropes or cables from contractor-installed,
wooden or steel cantilevered beams permanently fastened to the 3 " x 12 " bridging that supports the
walkway deck stringers, or to the wooden support piles themselves . The specific strength requirements
and fittings for the beams will depend on the requirements of the specific scaffolding system employed .
The scaffolding must provide access to the full span of the three stack weir system, either through the use
of a single scaffolding platform that may be moved from one stack to another or multiple platforms that
can provide access to all three stacks simultaneously. The contractor must use the scaffolding to lower the
weir boards to be installed from the weir walkway to a position near the weir crest from which the weir
operator may safely install additional weir boards .
Installation of the scaffolding will require removal of the existing ladder system that presently
extends from the walkway down the upstream face of each weir stack. This must be replaced with a
ladder system, either fixed or movable, on the inside of each weir stack that will allow the operator to
access the back (downstream) side of the weir boards, if necessary to install the weir boards and attach
each board to the flange extension.
- I1 -
2. 3. 4 Weir-Mounted Stage Gauge
Finally, to improve the contractor 's ability to monitor water levels and ponding depths within the
basin, the contractor must install a stage gauge, or staff, constructed of UV-resistant PVC or fiberglass, to
the front face of the weirs . Clearly marked in feet and tenths (as for a surveyor' s stadia rod) and leveled to
NGVD, this gauge will provide a means for the contractor (as well as inspectors, site operators, or other
personnel authorized to enter the IR- 14 facility) to directly read the water level within the basin from any
position around the basin ' s perimeter.
3 .0 WEIR OPERATIONAL GUIDELINES
3 . 1 Introduction
This section presents guidelines for operating the discharge weirs at FIND Site IR44 during all
phases of operations for which the selected dredging contractor will be responsible as part of his
contracted services. These guidelines are intended to supplement the guidelines contained in the site 's
Management Plan (Taylor et al . , April 1992). In those cases where the guidelines presented here conflict
with the guidelines presented in the Management Plan, the present guidelines supersede the guidelines
contained in the earlier plan document.
The remaining sections of this chapter are organized as follows . Section 3 .2 outlines requirements
for installing the required shut-off valve on the weir outflow pipe and modifying the existing weir system
consistent with the preliminary design modifications presented in Chapter 2 .0. Section 3 . 3 presents
guidelines for setting the initial weir elevation before the start of dredging operations and for operating
the weir system during dredging operations as required to control water level and ponding depths within
the basin and to maintain effluent quality consistent with permit requirements. Section 3 . 3 also presents
dike inspection requirements that may be triggered by excessive ponding depths within the basin. Section
3 . 4 presents guidelines for operating the weir system through the completion of decanting procedures, for
securing the weir system to prevent unauthorized discharges following the completion of decanting, and
for demobilizing from the site at the completion of contracted services.
- 12 -
s
3 . 2 Site Preparation and Pre-Dredging Operations
3. 2. 1 Installation of Shut- Off Valve
To ensure the ability to prevent any possible uncontrolled discharge from the weir system, the
contractor must install an approved shut-off valve on the discharge pipeline attached to the weir system .
The contractor must submit valve specifications for review and approval by the Project Engineer as an
element of his preconstruction submittals . The installation recently completed at 1711'41) Site SJ44
suggests that the installation at Site IR- 14 may require a ductile iron resilient wedge gate valve; however,
the contractor may submit other valve designs for review and approval by the Project Engineer.
Installation must conform to the valve manufacturer' s specifications, and must be completed before
performing the required system leak test . Closure of the shut-off valve at any time that water flows
through the valve must follow the valve manufacturer's recommendations for the pressures and flow
velocities at the time of the closure.
3. 2. 2 Installation of Effluent Discharge Pipeline
With the shut-off valve installed and fully closed, the contractor may begin to install the weir
discharge pipeline that will extend from the shut-off valve 850 f ± to the shoreline of the Indian River
(ICWW) . This pipeline will remain in place following the contractor 's demobilization from the site as
required to discharge stormwater and drainage from the basin. As a permanent installation, the pipeline 's
construction details (e. g. , buried vs. at grade, allowable slopes , etc.) must be addressed during the
project' s final design phase to reflect a topographic survey of the pipeline route . Section 3 .4 .2 discusses
the periodic release of stormwater following the contractor' s demobilization.
3. 2. 3 Installation of Required Weir Modifications
Simultaneous with or immediately following the installation of the shut-off valve, the contractor
must complete all required weir modifications including installation of the I-beam channel flange
extensions (Section 2 . 3 . 1 ), fabrication of all required weir boards (Section 2 . 3 .2), and installation of the
weir scaffolding and ladder system as required to access and install the weir boards (Section 2 . 3 . 3).
- 13 -
3 . 3 Weir Operating Procedures During Dredging
Once dredging begins and continuing though the completion of placement operations, the
contractor remains responsible for operating the weir system as required to maintain effluent turbidity
standards without compromising dike stability. The contractor achieves these objectives by adding weir
boards and raising the weir crest elevation as required to control water level and ponding depth, and
thereby retention time, within the basin . However, as described in Section 3 . 3 .2 , the contractor must not
allow the water level within the basin to increase too quickly or the ponding depth to increase beyond the
recommended maximum. Either condition could potentially lead to excessive seepage through the dikes,
slope instability and, under extreme conditions , dike failure. Obviously, avoiding these conditions
remains the one of the contractor ' s primary responsibilities .
The remainder of this section presents guidelines that the contractor must follow to complete the
required dredging and maintain effluent quality without compromising the integrity of the dike or the
weirs . The following basic principles of operation provide a necessary preface to that discussion:
• Throughout all phases of dredging operations, the contractor must maintain a qualified
operator at the containment facility. As part of the required pre-construction submittals,
the contractor must submit the specific qualifications of the designated operator(s) to
the Project Engineer for review and approval. Each operator shall remain in constant
radio contact with the dredge plant and shall possess the direct authority to shut down
the dredge if required . Each operator shall retain primary responsibility, either through
his direct action or through actions of others under his direct supervision, for adjusting
the weirs to maintain effluent quality and ensure dike integrity ( Section 3 . 3 . 1 ), for
performing all inspections related to dike integrity, for documenting the results of those
inspections ( Section 3 . 3 . 2), and for ensuring the security of the containment facility and
the safety . of all contractor personnel under his or her direct supervision.
• Throughout all phases of dredging operations, the contractor must ensure that all three
weir stacks remain fully operational . Closing off one or more weir stacks or weir
discharge pipelines by inserting bladders or other blockages is specifically prohibited.
• Throughout all phases of dredging operations except during short intervals white weir
boards are being added or removed from individual weir stacks, the contractor must
- ta -
ensure that all three weir crests remain at equal elevations, and that flow over all three
weirs (as measured by the depth of flow over the weir crests) remains essentially equal ,
within the limits of adjustment provided by the weir boards .
3. 3. 1 Operational Ponding Depths
Before dredging begins, the contractor must set the initial elevation of the weir crest . This initial
weir crest elevation corresponds to the minimum ponding depth at the weirs that must be reached before
the contractor releases any water from the basin. The minimum ponding depth reflects considerations of
the basin 's retention performance with respect to the settling characteristics of the dredged sediment. The
retention analysis presented in the IR- 14 Management Plan (Taylor et al . , March 1999) recommended a
minimum 4. 0-ft ponding depth based on a retention analysis that reflected available sediment data and the
performance characteristics of an 18-in . dredge . The analysis determined that for the 10 . 18-acre interior
plan area of the IR- 14 containment basin, a 2 .0-ft ponding depth provided a maximum retention time of
6 .2 hours. This time exceeds the 4 . 1 hours required for the finest fraction of sediment anticipated for
placement in the IR- 14 basin to settle out of the 2 .0-ft withdrawal depth, based on the projected settling
characteristics of the sediment to be dredged . However, consideration of actual field conditions suggests
that additional retention time may be required to provide adequate settling and further reduce effluent
turbidity levels . Given that retention time is directly related to' ponding depth, increasing ponding depth to
4 . 0 ft also increases the maximum retention time to 12.4 hours, or over three times the required settling
time . Experience with other similar FIND dredged material containment facilities has shown that
increasing the ponding depth to 4 .0 ft should not compromise dike stability. As a result, to ensure that the
DU- 8 facility produces acceptable effluent under all foreseeable conditions, the recommended mean
operational ponding depth is set at 4 .0 ft, with 5 .0 ft the recommended maximum ponding depth . Section
3 . 3 . 2 further discusses maximum ponding depth and related dike inspection requirements .
Based on a recommended 4.0-ft mean operational ponding depth, the contractor should set the
weir crest to an initial elevation of 4. 0 ft above the -0.4 ft NGVD mean elevation of the basin floor, or
+3 . 6 ft NGVD . Given the slope of the basin floor, this initial weir crest elevation also corresponds to 4 . 8
ft above the - 1 . 2 ft NGVD elevation of the weir base or sill . Lacking a bottom slot and spline to tie it to
the weir base plate, the bottom weir board should be set in a thick layer of roofing asphalt or other
approved sealant to minimize the potential for water to leak below the bottom board . Because the water
nearest the basin floor contains the highest concentration of suspended sediment, the contractor must take
particular care to seal the bottom weir board to the weir base plate as well as to the flange extension. All
- 15 -
remaining weir boards must be set according to the installation guidelines presented in Section 2 . 3 . 2 . In
addition, as also discussed in Section 2 . 3 . 2, the contractor must use weir boards fabricated from nominal
6x6 timbers (5 . 5 in. x 5 . 5 in. finished dimensions) for the lowermost 4 R of each weir stack.
As dredging progresses and the level of ponded water approaches the initial weir crest elevation,
the contractor must determine whether to begin the release of effluent . This decision must reflect the
results of turbidity testing of the upper 2 ft of the ponded water immediately upstream of the weirs . A
depth of 2 ft represents the estimated maximum depth of withdrawal, that is, the depth of the surface layer
released over the weirs .
3. 3. 2 Maximum Ponding Depths and Required Inspections
If testing determines that the ponded surface water at the weirs fails to meet permit requirements,
the contractor must provide additional retention time, either by raising the weir crest elevation or shutting
down the dredge until sufficient settling has occurred . If the contractor chooses to raise the weir crest by
adding additional weir boards, he must proceed with caution. Experience has shown that increasing the
water level too quickly or maintaining an excessive ponding depth can lead to excessive seepage through
the dike, a condition that increases the potential for slope instability and, under extreme circumstances,
dike failure.
Considerations of dike safety require that mean ponding depths at the IR- 14 containment facility
must not exceed 5 ft without notification and approval of the Project Engineer. Even with all required
approvals, the contractor must not exceed the 5 -ft maximum, even to meet required effluent standards,
without instituting a significantly more rigorous program of dike inspection. Chapter 4.0 outlines the
basic requirements for the dike inspection program as well as the critical conditions that would trigger
more intensive inspections. Inspections , conducted at least once a week under normal conditions, must
increase to at least once a day immediately upon discovery of a critical condition. However, increasing
the ponding depth (as measured at the weirs) beyond the recommended 5-ft operational maximum
requires that the contractor further increase the inspection frequency and provide close, continual
inspection of the entire dike perimeter at all times while ponding depths remain greater than the
recommended 5-ft maximum. All dike inspections must be performed by a qualified geotechnical
engineer or engineering technician experienced in the inspection of earthen dams, reservoirs, or dredged
material containment facilities . As part of the required preconstruction submittals, the contractor must
provide the qualifications of all designated inspectors to the Project Engineer for review and approval .
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Once the basin produces effluent that meets the required turbidity standards, the contractor should
then maintain the necessary ponding depth by increasing the weir crest elevation at about the same rate as
sediment builds within the basin. The contractor should install additional weir boards at the point the
depth of flow over the weir crest approaches the width of the boards to be added.
As the basin nears its design capacity, the contractor must reduce his operational ponding depth to
ensure that the elevation of the ponded water remains a minimum of Z ft below the elevation of the dike
crest, the minimum allowable freeboard for the IR- 14 containment facility. Continuing to meet effluent
standards may require that the contractor reduce the dredge output or operate the dredge intermittently to
provide the required retention time. During periods when the dredge remains idle, the contractor may also
find it necessary to grade and distribute the mounds of coarser material deposited nearer the dredge
discharge outlet to increase the plan area of the ponded water and thereby improve the basin ' s retention
performance and effluent quality. Under no circumstances shall the contractor allow the dredged material
to mound above the elevation of the dike crest .
3 .4 Weir Operations During Decanting
Following the completion of dredging operations, the contractor must continue to operate the weir
system and slowly release the clarified surface water that remains ponded within the basin over the weir
crest by incrementally removing weir boards . The process , known as decanting, continues until all
residual ponded water within the basin at the completion of dredging is released over the weirs. To
maintain effluent quality throughout the decanting process, the contractor should allow the flow over the
weirs to drop essentially to zero before removing another set of weir boards. The contractor may be
required to grade the deposited dredged material to drain isolated pockets of water so that this water may
also be released over the weirs. If at any time during the decanting process monitoring shows effluent
turbidity to exceed perniitted standards, the contractor must again add weir boards until testing of the
ponded water that remains within the basin confirms that turbidity has returned to acceptable limits .
While decanting proceeds, the contractor may begin to dismantle and remove the dredge pipeline.
Working from the site back toward the ICWW, the contractor must plan the operation to ensure that all
residual water contained within the pipeline drains to the ICWW.
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3. 4. 1 Project Close-out and Demobilization Procedures
Following the completion of decanting and the removal of all residual ponded water from the
basin via the weir discharge pipeline, the contractor must re-install the weir boards to a height sufficient
to ensure that no stormwater discharges over the weir crest . Stormwater thus retained must remain within
the basin until the FIND ' s designated site operator returns to perform a controlled release (Section 3 .4 . 2).
To this end, before the contractor demobilizes from the site, the Project Engineer will determine the weir
crest height required to ensure that no uncontrolled release of stormwater occurs following project close-
out . This determination will reflect information specific to each placement operation at the IR- 14 facility
including the bulked volume of the dredged material , the geometry of the deposition, and specific permit
requirements that may be imposed to govern the control and release of stormwater from the IR- 14 facility.
The contractor must then re-install the weir boards consistent with the procedures outlined in Section
2 . 3 . 2. 1 and set all weir stacks at or above this elevation. The earlier removal of weir boards to decant the
site may have resulted in some boards being destroyed (that is, cut out into sections or damaged such that
they cannot provide an adequate seal when re-installed consistent with the procedures outlined in Section
2 . 3 . 2 . 1 ) . The contractor should then fabricate additional weir boards sufficient to reach the required
elevation, plus additional boards to replace those that may become damaged during future stormwater
releases . The contractor must then close the facility' s weir discharge shut-off valve (Section 3 . 2 . 2), and
verify and certify to the FIND that the valve remains fully closed and free from leaks.
To facilitate the future release of stormwater from the basin, the contractor's final task is to
excavate a small sump immediately adjacent to one or more weir stacks . This sump will promote
stormwater drainage within the basin to the weirs so that removal of one or more weir boards will allow
the water to pass over the weir crest and continue to the ICWW, by gravity flow, through the permanent
weir discharge pipeline as discussed below .
3. 4. 2 Stormwater Control following the Contractor 's Demobilization
After the contractor completes his demobilization from the I1144 facility, responsibility for
continued management of stormwater within the basin, as well as all other continuing site maintenance
activities between successive dredging operations, resides with the FIND . To this end, the FIND 's
designated site operator will periodically return to the site to release stormwater as well
as the
accumulated drainage from the dredged material as it continues to consolidate under its own weight .
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To release this water, the site operator will first open the shut-off valve, then remove one or more
weir boards from a single stack as necessary to release the surface layer of the ponded water adjacent to
the weirs . To minimize the work required, the operator need only open one-half of a single weir stack
(that is, one column of boards) and only to the level to start water flowing over the lowered weir crest.
Removal of the weir boards should follow the procedures outlined in Section 2 . 3 . 2 .2 . Only when the flow
over the lowered weir crest approaches zero should the operator remove another board. This process
should continue one board at a time, until all ponded water drains from the site. The operator should then
replace the weir boards following the procedure outlined in Section 2 . 3 .2 . 1 , and close the weir discharge
shut-off valve.
4.0 DIKE INSPECTION REQUIREMENTS
As discussed in Chapter 3 .0, to comply with likely requirements of the Environmental Resource
Permit (ERP) for the operation of the IR- 14 facility, throughout all phases of dredging and dewatering the
contractor shall be responsible for additional inspections of the containment facility related to ensuring
the integrity and stability of the containment dikes. The remainder of this chapter details specific
inspection requirements.
4 . 1 Critical Inspections
The contractor shall perform periodic inspections of the containment dikes to check for certain
critical conditions that may require the implementation of remedial measures . As discussed in Chapter
3 . 0 , all inspections shall be conducted by a qualified geotechnical engineer or engineering technician with
specific training and experience in performing inspections of earthen dams, earthen reservoirs, or earthen
dredged material containment facilities . As part of his required preconstruction submittals, the contractor
must submit the qualifications of the designated dike inspector for review and approval of the FIND or its
authorized representative.
The contractor shall conduct inspections for the items listed below every week. Any of these
conditions shall be considered as indicating a critical condition that requires immediate investigation and
may require emergency remedial action. Immediately upon confirming the existence of a critical
condition, the contractor must inform the Project Engineer and increase the inspection frequency to a
minimum of once daily. The Project Engineer will then immediately notify the Florida Department of
Environmental Protection (FDEP) . Within 24 hours of confirming a critical condition, the contractor must
submit to the Project Engineer documentation of the inspections and implemented remedial actions . The
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Project Engineer will then submit to the FDEP a written report detailing the condition and
the
implemented remedial actions within seven (7) days of the confirmation of the critical condition . The
following items shall be considered as indicating a critical condition :
1 ) Seepage with boils, sand cones, or deltas on outer face of the dike or downstream from
the dike ' s outer toe;
2) Silt accumulations, boils, deltas, or cones in the drainage ditches at the dike ' s base;
3) Cracking of soil surface on the dike ' s crest or on either face of the dike;
4) Bulging of the downstream face of the dike;
5) Seepage, damp area , or boils in vicinity of or erosion around a conduit through the
dike; and
6) Any subsidence of the crest or faces .
4 . 2 Supplemental Inspections
During the critical inspections described above, the items listed below shall be considered
indicators of potential areas of concern that the contractor must then continue to monitor closely during
subsequent inspections and to perform repairs as necessary. Within 24 hours of confirming the presence
of an indicator of a potential area of concern, the contractor must also inform the Project Engineer of the
item and any required repairs undertaken. Indicators of potential areas of concern include the following:
1 ) Overgrowth patches of vegetation on the downstream face or close area downstream
from the toe;
2) Surface erosion, gullying, or wave erosion of the upstream face of the dike;
3 ) Surface erosion, gullying, or damp areas on the downstream face of the dike, including
the berm and the area downstream from the outside toe;
4) Erosion below any conduit exiting the dike; and
5) Wet areas or soggy soil in the downstream face of the dike or in the natural soil below
dike.
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5.0 ESTABLISHMENT AND MAINTENANCE OF VEGETATIVE COVER
Following construction of the containment facility, and again following each use of the facility to
receive and dewater dredged material, the FIND will remain responsible for establishing and maintaining
a vegetative cover on all exposed surfaces of the dike . To prevent the establishment of shrubs, trees , or
other woody vegetation, the dike ' s slopes and crest will be regularly mowed, and maintained sufficiently
short to allow visual inspection of the soil surfaces in critical areas such as
1 ) The condition of vegetation on the dike and in areas for 50 ft downstream from the
outside toe;
2) The condition of soil surfaces on the top and slopes of the dike and in areas for 50 ft
downstream from the outside toe;
3) The condition of drainage ditches in the area of the base of the dike;
4) The liquid surface elevation and amount of freeboard; and
5 ) The condition of spillways and water level control structures , including all conduits
exiting the dikes .
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