Groundwater contamination potential in northern Nevada from mining, associated communities, and agriculture as forecasted by two vulnerability methods

Two methodologies, DRASTIC and the NDEP method, were used to compare the groundwater vulnerability of mining, associated towns, and agricultural areas in northern Nevada. The DRASTIC and NDEP methods were compared to determine which method produces a more accurate depiction of vulnerability. Vulnerability maps were created using the United States Environmental Protection Agency's (USEPA) DRASTIC and Nevada Department of Environmental Protection (NDEP) methodologies. The DRASTIC map uses seven aspect layers of geologic and hydrologic information with assigned values and weights that are applied to a mathematical equation. The NDEP method uses field data collection for potential contaminant sources and well construction, well geological and hydrological information, and water quality data to create a vulnerability map. The map was created by applying values and weights to each aspect influencing the vulnerability and applied to a mathematical equation.;To compare the two methods, a correlation was performed using historic water quality data for naturally occurring and anthropogenic contaminants. The DRASTIC and the NDEP method indicated that the vulnerability to groundwater contamination of mining areas and towns are similar with mining in regions of low to moderate and towns in regions of moderate to high. Agricultural regions were ranked differently by each method. DRASTIC indicated that agricultural areas were in regions of high vulnerability whereas the NDEP method indicated that it was in regions of very low to low vulnerability.;It can be concluded from the results that the NDEP method can forecast expected contamination with naturally occurring contaminants (e.g. arsenic, fluoride and radionuclides) better than DRASTIC. Both methods could not forecast very well expected contamination with anthropogenic nitrate. The NDEP method uses historic water quality data as a parameter which may account for the better forecasting ability. It appears that the NDEP method is sensitive to the number of contaminant sources present around a well. The NDEP method requires extensive field survey data whereas the DRASTIC method uses data that is widely available. Therefore, the cost to implement the NDEP method is much higher and time consuming compared to the DRASTIC method.