U.S. Geological Survey
National Water-Quality Assessment Program
USGS Internal Access Only
Water-Quality Issues
Because the NACPAS is used extensively as a source of potable water supplies, and, in some areas, is a sole-source, the chemical quality of ground water is a major concern for those who use the water and for water managers and health officials responsible for ensuring a safe drinking-water supply. Contamination in the NACPAS was documented as early as the 1940s when fertilizers and detergent compounds were detected in samples of shallow ground water underlying the heavily developed areas of
Water-quality studies conducted in the 1980s and 1990s indicate that the concentration of nitrate in samples of shallow ground water underlying agricultural areas across much of the NACP and agricultural and urban areas on Long Island frequently exceed drinking-water guidelines (Ayers and others, 2000; Shedlock and others, 1999; Spruill and others, 1998; Eckhardt and Stackelberg, 1995). Pesticide compounds are frequently detected in shallow ground water underlying agricultural and urban areas, and VOCs in shallow ground water underlying urban areas, throughout much of the NACP (Ayers and others, 2000; Shedlock and others, 1999; Spruill and others, 1998). Concentrations of pesticides and VOCs in shallow ground water are generally low; however, and rarely exceed drinking-water guidelines. Nonetheless, elevated nitrate concentrations and the frequent detection of pesticides and VOCs in water samples from unconfined aquifers throughout much of the NACP indicate that these aquifers are vulnerable to chemicals used in agricultural and urban areas. The use of (1) pesticides, nitrogen-based fertilizers, and manure to support crop production, (2) septic systems for disposal of domestic wastewaters, and (3) common products such as fuels and solvents that contain VOCs, combined with the presence of well-drained and well-aerated soils across much of the NACP, favor the formation of nitrate and the movement of nitrate and organic contaminants such as pesticides and VOCs to ground water.
Although human activities associated with agricultural and urban land uses are the principal sources of contaminants in ground water, factors other than land use can affect ground-water quality. These factors include hydrogeologic conditions, chemical degradation, naturally-occurring contaminants, and the time period when ground water recharge occurred. For example, in agricultural areas of the outer Coastal Plain (surficial hydrogeologic subregion I), nitrate concentrations in shallow ground water are significantly lower than in similar settings of the middle and inner Coastal Plain. Low nitrate concentrations in shallow ground water of the outer Coastal Plain are due to denitrification and nitrate-reduction processes resulting from the large amounts of organic carbon in these poorly drained soils and sediments (Spruill and others, 1998; Ator and others, 2000). Additionally, some extensively used pesticides are not detected in ground water because they degrade readily or are not mobile (Ayers and others, 2000). Some constituents, such as radium and phosphorous, were detected in ground water where surficial sediments or aquifer materials are known to contain these elements (Ayers and others, 2000; Spruill and others, 1998). Finally, samples of water from confined aquifer systems generally are not affected by agricultural and urban activities at land surface because most water in these confined aquifer systems predates urban and agricultural activities (Shedlock and others, 1999).
Several water-quality issues of emerging concern in the NACPAS have only recently been identified including the occurrence of pesticide metabolites, select radionuclides, and organic contaminants associated with wastewater effluent. The occurrence of pesticides in ground water underlying agricultural and urban settings across the NACP is well documented, however, the occurrence of metabolite compounds has only recently been identified as an important water-quality concern. When analyzed for, metabolites of heavily used pesticides such as metolachlor, alachlor, and atrazine are commonly found at concentrations an order of magnitude or more than the parent compounds (Kalkhoff and others, 1998; Ferrari, 2001); thus, to fully assess the fate of pesticides and their influence on drinking-water resources pesticide metabolites must also be considered.
Recent National and Statewide reconnaissance surveys of selected radionuclides in public ground-water supplies (Focazio and others, 2001; Szabo and others, 2002) indicate that concentrations of Ra-224 are significantly elevated in water from parts of the Coastal Plain aquifer systems. Preliminary interpretations indicate that the combination of aquifer characteristics (permeable, coarse grained, quartzose), geochemistry (acidic), and land use (agricultural with nitrogen bearing leachate that increases acidification) affects the concentration of radium isotopes such as Ra-224 in unconfined Coastal Plain aquifers in New Jersey (Szabo and others, 2002). To fully assess the chemical quality of ground-water drinking supplies in the NACP, the occurrence, concentration, and source of these naturally occurring radionuclides must also be assessed.
Organic compounds that are likely derived from domestic, industrial, and (or) agricultural wastewaters including antibiotics and other prescription drugs, nonprescription drugs, fragrances, flame-retardants, plasticizers, plant and animal steroids, detergent metabolites, byproducts of oil use and combustion, and other extensively used chemicals have recently been found to occur extensively in surface- and ground-water resources and drinking-water supplies (Kolpin and others, 2002; Buser and others, 1998a, 1998b, and 1999; Herberer and Stan, 1997; Halling-Sorensen and others, 1998). These compounds form an important, yet previously under-evaluated, class of contaminants that should be considered when fully assessing the chemical quality of drinking-water supplies.
