Figure 4.  Calculation of the residence timeof water in the Upper Glacial and Magothy aquifers north of the groundwater divide. Based on United States Geological Survey cross-sections (Buxton and Modica, 1992; Smolensky et al., 1989), natural recharge rates from Peterson [1987] and pumping rate for the Town of Huntington (SCDHS, 1987). The average porosity of sediments in the unsaturated zone is assumed to be 30% (Franke and McClymonds, 1972). Under natural conditions, flux is assumed to be equal to the natural recharge rate. Pumping is assumed to increase the flux of groundwater through the system by an amount equal to the amount withdrawn. Adjustments of the aquifer to the change in the flow regime are not taken into account.