Groundwater

The groundwater system in the region is determined by the underlying geologic resources. Rocks of the Stockton Formation form a complex, heterogeneous, multi-aquifer system. Water occupies most of the open space in the rock formations below the water table. These spaces occupied by water constitute the groundwater reservoir (USGS 1996).

The USGS has monitoring wells installed across the country to monitor groundwater levels. The monitoring well in Montgomery County reported groundwater levels from August 1997 through October 2001. The average depth of water below the ground surface was 10.37 feet. A similar monitoring well exists in Chester County. This well reported data from September 1996 through October 2001. The initial reading at the well was 9.96 feet below the surface. This measurement ranged as deep as 12.12 feet and as shallow as 7.67 feet during the reported monitoring (USGS 2003).

Issues associated with groundwater relate to both water quantity and water quality. Like surface waters and floodplains, groundwater quality has been affected by human activity. Historic water quality concerns documented for groundwater in the area include contamination by organic chemicals from industrial spill; storage tank leakage; leachate contamination; and discharge from septic systems, lagoons, and waste disposal sites. Recent groundwater sampling within the park by the USGS and EPA has detected contaminants from these sources surrounding the park; however, the levels are below the EPA maximum level concentration.

Groundwater quantity is affected by the increase in impervious surface area, water withdrawals, and precipitation. With the increase in impervious surface area throughout the watershed, the ability of precipitation to recharge groundwater reserves has been reduced. In Pennsylvania, about 30% of annual precipitation on average infiltrates the ground surface to recharge groundwater aquifers (Fleeger 1999). According to previous studies, groundwater is also lost by infiltration into the regional Valley Forge sewage system. Another source of groundwater depletion may be from two high-capacity wells in the watershed (NPS 1996). In 1980, the Delaware River Basin Commission recommended that the entire Valley Creek watershed be designated as a groundwater protected area. Under this designation, the commission limits the quantity of water that can be withdrawn on a daily basis.