Relations that affect the probability and prediction of nitrate concentration in private wells in the glacial aquifer system in the United States

Abstract

The USGS aims to disseminate credible, timely, and relevant science information to address practical and effective water-resource management and strategies that protect and restore water quality. We hope this NAWQA publication will provide you with insights and information to meet your needs, and will foster increased citizen awareness and involvement in the protection and restoration of our Nation's waters. The USGS recognizes that a national assessment by a single program cannot address all waterresource issues of interest. External coordination at all levels is critical for cost-effective management, regulation, and conservation of our Nation's water resources. The NAWQA Program, therefore, depends on advice and information from other agencies-Federal, State, regional, interstate, Tribal, and local-as well as nongovernmental organizations, industry, academia, and other stakeholder groups. Your assistance and suggestions are greatly appreciated.

The quality of our Nation's waters: water quality in the glacial aquifer system, northern United States, 1993-2009

“…Two-thirds (66 percent) of domestic-supply wells are less than 100 ft deep, and some wells are as shallow as 12 ft. Fifty-eight percent of samples of shallow groundwater underlying agricultural areas contained nitrate concentrations greater than 1 mg/L as N, the background concentration for the glacial aquifer system. (55) Median concentrations of nitrate in groundwater were higher in shallow wells tapping groundwater underlying agricultural and urban areas than in groundwater from deeper drinking-water wells ( fig. 7-2).…”

“…All glacial aquifer system domestic-supply wells sampled in which nitrate concentrations exceeded 10 mg/L as N contained predominantly young, oxic groundwater. (25) Young groundwater tapped by shallow domestic-supply wells is more vulnerable to nitrate contamination than deeper groundwater because young groundwater is nearer to the land surface (where nitrate is applied) and often oxic. Some domestic-supply wells tap the deep groundwater that is farther from the source of nitrate and commonly is anoxic-as a result, nitrate, if detected at all in these wells, generally is at low concentrations.…”

“…The groundwater in mostly domestic-supply wells less than 50 ft deep was predominantly oxic and had the highest concentrations of nitrate. A statistical model developed to identify the vulnerability of domestic supplies to nitrate contamination demonstrated that the high concentrations of nitrate in domestic-supply wells depended on whether or not there was a source of nitrogen and on the characteristics of the domestic-supply well, such as diameter and depth of the well screen (55) (see sidebar, Large-diameter wells, p. 69). The highest concentrations of nitrate in drinking water were in wells that were shallower than 50 ft below land surface, where redox conditions mostly are oxic.…”

Tree-Based Modeling Methods to Predict Nitrate Exceedances in the Ogallala Aquifer in Texas

“…Intrinsic vulnerability methods do not account for chemical specific characteristics; therefore, approaches that account for existing pollution have also been proposed in the literature. In particular, logistic regression models have been extensively used, albeit with a mixed degree of success, to calculate the probability of the exceedance of a pre-defined nitrogen (or some other contaminant) threshold [12,[16][17][18][19][20][21][22][23][24][25][26][27].The main reasons for the popularity of logistic regression techniques for aquifer vulnerability assessment include its ability to deal with censored data and the availability of computer programs to perform the necessary calculations. Furthermore, the resulting equation can be easily embedded into a geographic information system (GIS) to develop aquifer vulnerability maps.…”

The simulated effects of wastewater-management actions on the hydrologic system and nitrogen-loading rates to wells and ecological receptors, Popponesset Bay Watershed, Cape Cod, Massachusetts

“…Anthropogenic sources of nitrogen include wastewater, fertilizers, and runoff from impervious surfaces. In groundwater in glacial aquifers that underlie agricultural areas, the primary source of nitrogen to pumped wells is nitrogen fertilizers (Warner and Arnold, 2010), and fertilizer application has resulted in the contamination of glacial aquifers in many areas of the United States (DeSimone and others, 2009). In urbanized, nonagricultural areas, such as Cape Cod, fertilizer application generally is limited to lawns and golf courses.…”