VERIFICATION OF HYDRAULIC AND GEOPHYSICAL TESTING USING SEDIMENT CORES TO IDENTIFY HYDROGEOLOGIC LIMITATIONS OF WASTEWATER INFILTRATION LAND APPLICATION FACILITIES PRIOR TO CONSTRUCTION: LESSONS LEARNED WITHIN THE NEW JERSEY COASTAL PLAIN

Land application facilities designed to infiltrate treated wastewater have many benefits, including recharge to the water table, diminished impact to surface water systems, and supplemental treatment of effluent due to longer residence time in the unsaturated zone. The effectiveness of land application facilities is sensitive to subsurface hydrogeologic conditions, such as impermeable sedimentary units or a shallow water table, which can go undetected by typical surface-based tests of infiltration rates that yield only cursory subsurface information. Therefore, a more rigorous approach is necessary to properly evaluate the suitability of a site for land application. Operating land application facilities in Hammonton, New Jersey and Fort Dix, New Jersey experiencing less than desirable wastewater infiltration to the unconfined Kirkwood-Cohansey aquifer in the New Jersey Coastal Plain were investigated with a suite of hydraulic and geophysical testing methods corroborated with lithologic analyses of continuous sediment cores. Ferric ironstone concretions observed in cores at the Hammonton facility were identified as impermeable units on drive-point hydraulic profiling tests, but were not observed on natural gamma logs due to an absence of minerals containing gamma-emitters. At the Fort Dix facility, high gamma counts recorded at shallow depths were typical of impermeable clays, but cores consisted of fine sand with high concentrations of muscovite mica rich in gamma-radioactive potassium-40. Ground-penetrating radar transverses calibrated with measured water levels also indicated no perched water table was present. The coring of sediments at both facilities coupled with multiple testing techniques prevented incorrect interpretations of the cause of poor infiltration undetected by surface-based tests during site characterization. Planners and designers of future facilities can benefit both environmentally and economically from the results of these investigations when evaluating potential sites for land application. Local municipalities have incorporated many of these more detailed approaches into their feasibility studies before construction and found their planned sites were poorly suited for wastewater infiltration, thus avoiding expenditures of millions of taxpayer funds.