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September 2015 3-18 14-14979 3.3.2 Subsurface Hydrology 3.3.2.1 Subsurface Hydrologic Data for the Site Aquifers There are three major components to the subsurface hydrogeologic framework of southern Florida and the Site: the unconfined surficial aquifer; the confined FAS; and the nearly impermeable sediments of the Hawthorn Group,wluch separate the two aquifer units. Surficial Aquifer System Although the thickness of the surficial aquifer system is generally between 100 and 250 ft thick in Okeechobee County, it is expected to be approximately 100 ft thick in the vicinity of the Site. The surficial aquifer in the vicinity of the Site is unconfined and consists of layers of silt, clay, sand, and shell of the undifferentiated Holocene to Pliocene age sedimentary deposits. The yield from wells installed within the surficial aquifer in Okeechobee range between 10 and 400 gallons per minute (gpm) and the specific capacity(calculated from the South Florida Water Management District well completion reports)ranges from approximately 3 to 50 gpm/ft(Bradner, 1994). The higher yields are from wells that are installed deep enough within highly productive coarse sands and shell zones. Based on the SJRWMD East Central Florida Steady(ECFS)Model,the transmissivity of the surficial aquifer in the area of the site is approximately 1,703 ft2/day. Based on the characteristics of the soils at the depth of the water table(predominately fine sand),the specific yield is likely between 0.15 and 0.25. The surficial aquifer is recharged by rainfall and the downward percolation of irrigation water. The water table fluctuates in response to changes in seasonal precipitation amounts, evapotranspiration, and pumping. In Okeechobee County, the surficial aquifer water table ranges from land surface to 10 ft bls. Most of the domestic and public supply wells in Okeechobee County withdraw from the surficial aquifer(Bradner, 1994). Intermediate Confining Unit The intermediate confining unit(ICU)consists of the clay-rich,fine grained deposits of the Hawthorn Group. The clay-rich deposits form a confining unit that separates the Surficial Aquifer System from the deeper artesian FAS. The ICU is expected to be approximately 275 ft thick at the Site and extend to a depth of 400 ft bis (Scott T. M., 1988). The Hawthorn Group is frequently referred to as the Intermediate Aquifer; however, it is anticipated to have very limited productivity at the Site due to low permeability. The overall hydraulic conductivity of the Hawthorn Group is very low and provides good confinement for the underlying FAS. The calibrated ECFS groundwater flow model developed by the St. Johns River Water Management District uses a transmissivity of 1,938 feet squared per day [(ft)/day) for the layer representing the combined Intermediate Aquifer System (IAS) and ICU. The ground water flow model suggests a leakance coefficient of 6.8 x 10-6 feet per Attachment 1 b PQt_ 201