Depth-dependent Sample Collection for Perchlorate Isotopes

Science Center Objects

Chlorine and oxygen isotopic analyses of perchlorate have shown that perchlorate from agricultural and industrial (synthetic) sources is present in the Bunker Hill Groundwater Basin downgradient of the former Lockheed Propulsion Company (LPC) Site near Redlands, Calif., about 60 miles east of Los Angeles. Although agricultural and synthetic plumes merge in the central portion of the Bunker Hill Basin, better knowledge of how the plumes are distributed vertically within the aquifer, and how water containing perchlorate contributes to the quality of water yielded by wells in the area, is needed to better understand the perchlorate distribution

Map showing Location of study area and perchlorate plumes.

Location of study area and perchlorate plumes. From Sturchio and others, 2012.

(Public domain.)

The purpose of this study is to 1) characterize the vertical distribution of perchlorate from within the alluvial aquifer downgradient of the former LPC Site, and 2) to understand how water containing perchlorate from different sources contributes to the quality of water yielded by wells in areas where agricultural and synthetic plumes are present.

Coupled well-bore flow and depth-dependent sample collection will be done at three wells downgradient of the former LPC Site. Data collection has been divided into three tasks: 1) collection of borehole geophysical logs under unpumped conditions, 2) collection of borehole geophysical logs under pumped conditions, 3) collection of water-quality samples under pumped conditions. Borehole geophysical logs to be collected from wells include natural gamma, caliper, fluid resistivity, fluid temperature, and electromagnetic (EM) flow logs. Water-quality samples will be analyzed for the chlorine and oxygen isotopic composition of perchlorate. Analyses also will include field parameters, major-ions, selected minor ions, selected trace elements, nutrients, and the d18O and dD composition of water. Borehole geophysical logs and depth-dependent water-chemistry data will be evaluated to understand flow and potential redistribution of perchlorate through the wells under unpumped and pumped conditions. Data will be interpreted using the computer program Analyze-HOLE to estimate hydraulic properties of aquifer materials that yield water to sampled wells, and the effect of aquifer heterogeneity and well design on flow and contaminant movement to pumped wells.

This proposal will contribute to the U.S. Geological Survey's ability to "ensure adequate quantity and quality of water to meet human and ecological needs in the face of growing competition among domestic, industrial-commercial, agricultural, and environmental uses" as described in the U.S. Geological Survey Science Strategy (2007). The proposal is within the U.S. Geological Survey Water Resources Mission Areas to "define and better protect the quality of the Nation’s water resources".