2005-136 - Laserfiche WebLink

Home Browse Search

basin extension, the salinity of the Indian River Lagoon is affected by large-scale freshwater discharges during the wet season. Additionally, in the IRFWCD basin the agricultural and urban land uses have increased the historic contribution of nutrients, suspended solids, and other pollutants to the Indian River Lagoon. In the Status and Trends Summary of the Indian River Lagoon (IRLNEP(d), 1994) the effects of the discharges of the IRFWCD are documented. Salinity values in the Lagoon drop to an annual average of about 26 ppt near the IRFWCD outfalls . The discharges cause an increase in the color values in the Lagoon during the wet season by a factor of about 3 . Color is an important optical parameter that has been shown to inhibit the health of seagrasses. Additionally, total phosphorous values are substantially higher in the IRL around the IRFWCD discharges than in other areas of the Lagoon. Total Kjeldahl Nitrogen concentrations are also elevated. In the Loadings Assessment of the Indian River Lagoon , (IRLNEP(c) 1994) total annual loads for nitrogen, phosphorous, suspended solids, BOD, zinc, and lead are presented for the entire IRFWCD . These total loads were used to estimate the existing loads contributed by the drainage basins of the Main and South Canals (totaling 37 ,500 acres) — these are the two IRFWCD drainage basins predominately affected by the Lateral C Canal discharges . The combined Main and South Canal loadings are estimated to be : Total Nitrogen: 99 ,412 kg = 110 tons Total Phosphorous : 13 , 598 kg = 15 tons Total Suspended Solids : 2 ,277,715 kg = 2 ,500 tons BOD : 295 , 347 kg = 325 tons Zinc : 2,337 kg = 2 . 5 tons Lead: 3 , 141 kg = 3 . 5 tons . Flows from the Main and South Canals are 78 and 39 cubic feet per second (cfs), respectively, on an annual basis . The maximum monthly discharge for the Main Canal is 465 cfs, and for the South Canal is 292 cfs (IRLNEP(b), 1994) . To address the problems of the IRFWCD , in the spring of 2001 , Indian River County awarded a contract to prepare a stormwater management master plan for the 37, 500 acre area of IRFWCD that drains into the Main and South Canals, approximately 75 % of the total IRFWCD drainage basin. In early 2002 , the contract was amended to include the North Relief Canal drainage basin in the study, thus making the study encompass the entire IRFWCD drainage basin. As part of this effort, Indian River County identified managed aquatic plant systems as a potential structural BMP in the agricultural areas of the IRFWCD basin. Less intensively managed aquatic plant systems have also been identified as a possible option for stormwater park areas with enough acreage to accommodate them. Indian River County has developed this proposed project because it will remove huge quantities of pollutants from the IRFWCD canal system. It will demonstrate the effectiveness of a managed aquatic plant based treatment system to both agricultural and urban stakeholders. Because this is a "full-scale" system, permanent water quality benefits will be achieved as part of the effort to affect a 50% to 60% reduction of nutrient and suspended solids loads to the IRL . Additionally, construction of a fully operational system will allow Indian River County to obtain real-rime data about operation and maintenance costs for a managed aquatic plant system. In the Master Plan, a County- owned parcel of land was identified for potential use for treatment of water from the IRFWCD canal system. This site is called the Southwest Industrial Stormwater Park in the Master Plan and has been renamed the Egret Marsh Regional Stormwater Park (Egret Marsh) . The site is a 35 -acre parcel at the southeast corner of 74"' Avenue and 4`h Street. A preliminary engineering report has been completed for this site, recommending a design flow rate of 10 MGD to be withdrawn from the Lateral C Canal for treatment. Canal flow averages 24 MGD with nutrient-rich contributions from a 9, 000-acre drainage basin ( 80% agricultural, 20% urban) . As discussed in the "Estimated Pollutant Load Reduction" section, a treatment-train approach using multiple BMPs is recommended for this site . To recap, 10 MGD of canal water will pass first through a pre-treatment pond, then through an algal turf scrubber system, and finally through a polishing pond. Some of the effluent from the polishing pond will flow through a manmade wetland for further treatment. Finally, the treated water will flow back into the IRFWCD canal system, and it will ultimately discharge into the IRL. DEP Agreement No. G0143 , Attachment A, Page 5 of 9