**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the amount withdrawn.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.