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ORIGINAL RESEARCH PAPERS

Spatial Variability of Groundwater Recharge and its Effect on Shallow Groundwater Quality in Southern New Jersey

^a U.S. Geological Survey, 413 National Center, Reston, VA 20192
^b U.S. Geological Survey, West Trenton, NJ
^* Corresponding author (btnolan{at}usgs.gov).

Received 27 November 2002.

Point estimates of groundwater recharge at 48 sediment-coring locations vary substantially (-18.5–1840 cm yr^-1) in a 930-km² area of southern New Jersey. Darcian estimates of steady, long-term recharge made at depth in the unsaturated zone were estimated using pedotransfer functions of soil texture and interpolated (mapped) with nonparametric methods to assess aquifer vulnerability in the area. The probability of exceeding the median recharge (29.1 cm yr^-1) is low in the southwestern and northeastern portions of the study area and high in the eastern and southeastern portions. Estimated recharge is inversely related to measured percentage clay and positively related to the percentage of well-drained soils near wells. Spatial patterns of recharge estimates, exceedance probabilities, and clay content indicate that sediment texture controls recharge in the study area. Relations with land elevation and a topographic wetness index were statistically insignificant. Nitrate concentration and atrazine (6-chloro-N²-ethyl-N⁴-isopropyl-1,3,5-triazine-2,4-diamine) percentage detection in samples of shallow groundwater (typically <10 m) are higher for low recharge sites (29.1 cm yr^-1) than for high recharge sites (>29.1 cm yr^-1) in agricultural and urban areas. Differences between high and low recharge sites in these areas are highly significant for NO₃ concentration, but not for atrazine concentration.

Abbreviations: CCDF, conditional cumulative distribution function • DEM, digital elevation model • DO, dissolved oxygen • GIS, geographic information system • IGF, Indicative Goodness of Fit • IK, indicator kriging • KED, Kriging with external drift • MLR, multiple linear regression • PTF, pedotransfer function