[an error occurred while processing this directive] GW Background and Perspective

Part 1: Summary text below. | Part 2: Table listing of previous investigations

The water quality in aquifer systems of the LINJ has been extensively investigated. The areal extent and number of these investigations, however, varies across the study unit. The fractured bedrock and valley-fill aquifers of the Piedmont and New England provinces in northern NJ have been the subject of fewer and more site-specific investigations, whereas, the unconsolidated sand and gravel aquifers of the Coastal Plain of LI and NJ have been the subject of numerous site-specific and regional water-quality investigations. Consequently, more is known about the geohydrology and water quality of the Coastal Plain aquifers.

Numerous ground-water quality investigations undertaken as part of the Toxic Substances Hydrology Program in the Coastal Plain examined relations between land use and shallow ground-water quality in regionally extensive areas of LI and NJ (Barton and others, 1987; Eckhardt and others, 1989; Stackelberg, 1995; Eckhardt and Stackelberg, 1995; and Vowinkel and Battaglin, 1995). Eckhardt and others (1989) evaluated the relation between land use and ground-water quality in the surficial aquifer system of Nassau and Suffolk Counties on LI examining over 14,000 chemical analyses of samples from 903 wells collected between 1978-84. Results indicate that contamination from human activities has affected water quality in the surficial aquifer system. The occurrence of volatile organic compounds and pesticides was confirmed and statistically significant correlations between land use and these and other contaminants were established.

In a later investigation, Eckhardt and Stackelberg (1995), water-quality data from 90 monitoring wells screened near the water table beneath five areas of differing land use were compared. Results indicate that samples from undeveloped areas had the lowest and smallest range in concentrations of most human-derived constituents such as nitrate, boron, VOCs, and pesticides. Concentrations of these constituents in samples from three suburban areas and an agricultural area generally were intermediate to high and had the widest variation. Equations predicting the occurrence of contaminants near the water table were developed using logistic regression analyses of explanatory variables that characterize the type of land use and population density within a 1/4-mile radius of each of the 90 wells.

Vowinkel and Battaglin (in press) evaluated the effects of nonpoint sources of contamination on the quality of water in aquifers of the Coastal Plain in New Jersey. Water-quality data from over 1,000 wells sampled between 1980-89 for major ions, nutrients, trace elements, and organic constituents including dissolved organic carbon, phenols, volatile organic compounds, and pesticides were examined. Results indicate that nonpoint sources of contamination significantly affect the quality of shallow ground water in aquifers of the Coastal Plain in New Jersey and that the distribution of contaminants are significantly related to patterns of land use.

The vulnerability of water withdrawn from public-supply wells to contamination by pesticides and volatile organic compounds has also been statistically and deterministically evaluated for aquifers in the Coastal Plain (Navoy, 1993; Vowinkel and others, 1994). Navoy (1993) utilized a finely discretized ground-water-flow model and flow-path simulation to demonstrate the vulnerability of Coastal Plain aquifers to non-point sources of contamination. Navoy (1993) applied a quantitative understanding of the ground-water flow system of the Potomac-Raritan-Magothy aquifer system in Gloucester County, NJ, to identify public-supply wells where contamination by VOCs was likely. Results from this analysis were consistent with available water-quality data and indicate that wells currently unaffected by contamination probably will be affected by contamination in the future and that the concentrations of VOCs in water from affected wells is likely to increase. The method of investigation utilized by Navoy (1993) demonstrates the (1) utility of a quantitative approach to understanding water-quality issues in water-supply aquifers, and (2) transferability of such methods to other locales where a finely discretized ground-water flow model and high-resolution land-use data are available.

Beginning in 1995, Safe Drinking Water Act regulations required the 626 large community water systems in New Jersey to monitor their 2,600 wells quarterly for 23 pesticides. As part of a 3-year study that began in October 1992, the USGS, in cooperation with the New Jersey Department of Environmental Protection (NJDEP), developed a geographic information system (GIS) data base to provide data on the vulnerability of water from public supply wells to contamination by pesticides (Vowinkel and others, 1994). Vulnerability was determined by using a numerical rating method based on information in the GIS data base. The information will be used by the State to determine the level of monitoring as a function of the vulnerability rating and to give waivers if a well is not vulnerable. The vulnerability of a well to contamination by pesticides is defined by (1) the sensitivity of the aquifer to contamination and (2) the intensity of pesticide use in areas where the aquifer is sensitive. Three variables were used to predict aquifer sensitivity: (1) location of a well relative to the outcrop area, (2) soil organic matter content, and (3) depth from the land surface to the top of the open interval of the well (top of screen for wells in unconsolidated sediments and top of the open hole for bedrock aquifers). Three variables were used to predict pesticide-use intensity near wells that are sensitive to contamination: (1) predominant land use near the well, (2) distance from the nearest agricultural area, and (3) distance from the nearest golf course.

Where information was available, well-construction characteristics and location were determined for 2,100 of the 2,600 public supply wells in New Jersey. These wells are located in three different aquifer types: (1) Coastal Plain unconsolidated sand and gravel deposits, (2) unconsolidated glacial-deposit sediments, and (3) fractured bedrock. Using the numerical rating method, each well was assigned to one of 9 vulnerability groups on the basis of its sensitivity and intensity ratings. It was determined that about 26 percent of all public supply wells are not vulnerable to contamination from human activities. All wells in this low vulnerability group are in the confined parts of Coastal Plain aquifers. About 4 percent of public supply wells are ranked in the high sensitivity and high intensity group. These wells belong to the high vulnerability group, are located within the unconfined parts of aquifers and are within or adjacent to agricultural land. The remaining 70 percent of wells were determined to be moderately vulnerable to contamination from human activities and are largely unconfined and within or adjacent to residential or agricultural land.

Predicted model results were validated by analyzing water samples for pesticides and nitrate from a subset of 90 public supply wells throughout New Jersey. Wells were chosen from each combination of vulnerability category and aquifer category. Pesticides were detected in 6 of the 90 wells sampled. Three of these wells were rated in the high sensitivity and high intensity group. The other three wells were rated as having either high sensitivity or high intensity. None of the six wells were rated as having low sensitivity to contamination by pesticides.

Ground-water studies like those for predicting nitrate and VOC contamination of ground water on Long Island using regression analysis and for predicting pesticide contamination of ground water in New Jersey using the vulnerability rating method benefit everyone. The NJDEP estimated that monitoring waivers for pesticides granted for wells will save taxpayers almost $5 million annually for a one-time cost of $0.7 million. In addition, consulting firms, other Federal, State, and county agencies, universities and the general public make requests daily for the water-use, water-quality, and hydrogeologic data resulting from these and similar studies.

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