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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 transferwill require an additional 1 , 667 cy of material . Excavating the basin interior to a mean elevation of - 0 . 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 lie 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 IR- 14 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