ASSESSING GROUNDWATER VULNERABILITY ON THE PINE RIDGE RESERVATION IN SOUTHWESTERN SOUTH DAKOTA

Groundwater is used as a domestic water supply by about one-half of the US population (Alley and others, 1999). The U.S. Environmental Protection Agency (USEPA) requires assessment of groundwater vulnerability to contamination for all public water-supply systems as part of the Safe Drinking Water Act (1996).

Groundwater vulnerability assessment is a tool used to guide management and protection of water resources. Science objectives with regard to a vulnerability assessment involve objective approaches that provide data to administrators, regulators, and decision makers.

Assessment parameters include proximity of contaminants to the groundwater system, contaminant load, factors which could increase contaminant load, geochemical properties of contaminants, and fate/transport of contaminants in a groundwater system. Objective assessments combine statistical or process-based methods such as modeling, regression equations, and map overlay to determine relationships between explanatory variables or processes.

Most source water wells on the Pine Ridge Reservation are completed in the Arikaree aquifer. Aquifer characteristics have been investigated by the U.S. Geological Survey but as of this date, a comprehensive source-water assessment for the Pine Ridge Reservation has not been completed. The goal of this proposed vulnerability assessment is to produce scientifically defensible results that can be shared with stakeholders. A process-based model published by the US Geological Survey in 2014 will provide the basis for assessment. Contaminant and water quality data will be added to the model to complete the assessment. Combining a process-based model with measured water quality data and contaminant-specific parameters in a map-overlay process will produce source water assessment products with objective measures of aquifer vulnerability for the Pine Ridge Reservation.