Research about Kirkwood-Cohansey aquifer system

USGS2010

Variability of mercury concentrations in domestic well water, New Jersey Coastal Plain

Concentrations of total (unfiltered) mercury (Hg) exceed the Maximum Contaminant Level (2 µg/L) in the acidic water withdrawn by more than 700 domestic wells from the areally extensive unconfined Kirkwood-Cohansey aquifer system. Background concentrations of Hg generally are <0.01 µg/L. The source of the Hg contamination has been hypothesized to arise from Hg of pesticide-application, atmospheric, and geologic origin being mobilized by some component(s) of septic-system effluent or urban leachates in unsewered residential areas. Initial results at many affected wells were not reproducible upon later resampling despite rigorous quality assurance, prompting concerns that duration of well flushing could affect the Hg concentrations. A cooperative study by the U.S. Geological Survey and the New Jersey Department of Environmental Protection examined variability in Hg results during the flushing of domestic wells. Samples were collected at regular intervals (about 10 minutes) during flushing for eight domestic wells, until stabilization criteria was met for field-measured parameters; the Hg concentrations in the final samples ranged from about 0.0005 to 11 µg/L. Unfiltered Hg concentrations in samples collected during purging varied slightly, but particulate Hg concentration (unfiltered – filtered (0.45 micron capsule) concentration) typically was highly variable for each well, with no consistent pattern of increase or decrease in concentration. Surges of particulates probably were associated with pump cycling. Pre-pumping samples from the holding tanks generally had the lowest Hg concentrations among the samples collected at the well that day. Comparing the newly obtained results at each well to results from previous sampling indicated that Hg concentrations in water from the Hg-contaminated areas were generally greater among samples collected on different dates (long-term variations, months to years) than among samples collected on the same day (short-term variations, minutes to hours). The long-term variations likely are caused by changes in local pumping regimes and time-varying capture of slugs of Hg-contaminated water moving on flowpaths.

New Jersey↗

USGS2000

Comparison of nitrate, pesticides, and volatile organic compounds in samples from monitoring and public-supply wells, Kirkwood-Cohansey aquifer system, southern New Jersey

The number and total concentration of volatile organic compounds (VOCs) per sample were significantly greater in water from public-supply wells than in water from shallow and moderate-depth monitoring wells in the surficial Kirkwood-Cohansey aquifer system in the Glassboro area of southern New Jersey. In contrast, concentrations of nitrate (as nitrogen) and the number and total concentration of pesticides per sample were statistically similar in samples from shallow and moderate-depth monitoring wells and those from public-supply wells. VOCs in ground water typically are derived from point sources, which commonly exist in urban areas and which result in spatially variable contaminant concentrations near the water table. Because larger volumes of water are withdrawn from public-supply wells than from monitoring wells, their contributing areas are larger and, therefore, they are more likely to intercept water flowing from VOC point sources. Additionally, public-supply wells intercept flow paths that span a large temporal interval. Public-supply wells in the Glassboro study area withdraw water flowing along short paths, which contains VOCs that recently entered the aquifer system, and water flowing along relatively long paths, which contains VOCs that originated from the degradation of parent compounds or that are associated with past land uses. Because the volume of water withdrawn from monitoring wells is small and because shallow monitoring wells are screened near the water table, they generally intercept only relatively short flow paths. Therefore, samples from these wells represent relatively recent, discrete time intervals and contain both fewer VOCs and a lower total VOC concentration than samples from public-supply wells. Nitrate and pesticides in ground water typically are derived from nonpoint sources, which commonly are found in both agricultural and urban areas and typically result in lowlevel, relatively uniform concentrations near the water table. Because nonpoint sources are diffuse and because processes such as degradation or sorption/dispersion do not occur at rates sufficient to prevent detection of these constituents in parts of the aquifer used for domestic and public supply in the study area, concentrations of nitrate and pesticides and numbers of pesticide compounds are likely to be similar in samples from shallow monitoring wells and samples from public-supply wells. Results of a comparison of (1) the general characteristics of, and water-quality data from, public-supply wells in the Glassboro study area to available data from public-supply wells screened in the Kirkwood-Cohansey aquifer system outside the study area, and (2) land-use settings, soil characteristics, and aquifer properties in and outside the study area indicate that the findings of this study likely are applicable to the entire extent of the Kirkwood- Cohansey aquifer system in southern New Jersey.

New Jersey↗