USGS Visual Identifier

Sensitivity of Ground Water to Contamination in Lawrence County, South Dakota

By Larry D. Putnam

U.S. GEOLOGICAL SURVEY
Water-Resources Investigations Report 00-4103

Prepared in cooperation with Lawrence County
and the City of Spearfish


Abstract

Ground-water supplies in Lawrence County, South Dakota, can be contaminated by agricultural, urban, suburban, commercial, and industrial land uses. To address this issue, the U.S. Geological Survey in cooperation with Lawrence County and the City of Spearfish mapped the sensitivity of ground water to contamination in Lawrence County.

Sensitivity of ground water to contamination was determined by delineating hydrogeologic settings with common hydrogeologic characteristics as described in the DRASTIC method, developed by the U.S. Environmental Protection Agency and the National Water Well Association. Within the framework of 11 hydrogeologic settings, sensitivity to contamination was ranked for six intrinsic hydrogeologic characteristics: (1) aquifer media, (2) unsaturated media (3) hydraulic conductivity, (4) recharge rate, (5) depth to water, and (6) land-surface slope. The rating conventions of DRASTIC were modified to provide a relative ranking of hydrogeologic characteristics without assignment of a combined numerical score. Soil characteristics were not included as a map layer because detailed digital data were not available; however, the general distribution of two soil characteristics were shown.

A total of 956 polygons were delineated and assigned a sensitivity-unit code that represented unique groups of sensitivity rank for the six intrinsic hydrogeologic characteristics. The polygons were created by overlaying and intersecting maps that describe the geology, precipitation, land-surface elevation, and depth to water using a geographic information system. Thirty drainage areas upstream from potential streamflow-loss zones were delineated to describe an additional mechanism of transport of potential contamination. The sensitivity of ground water to contamination was presented on a 1:100,000-scale map with code and label explanations. Limitations of the sensitivity map are described to facilitate appropriate use of the map as a screening tool to compare sensitivity to contamination.

Contents

Abstract

Introduction

Purpose and Scope

Description of Study Area

Method of Analysis

Ground-Water Regions and Hydrogeologic Settings

Sensitivity of Ground Water to Contamination

Hydrogeologic Units

Criteria for Delineation

Designated Units

Recharge Rate

Criteria for Delineation

Designated Units

Depth to Water

Criteria for Delineation

Designated Units

Land-Surface Slope

Criteria for Delineation

Designated Units

Streamflow Recharge

Criteria for Delineation

Designated Units

Use of Ground-Water Sensitivity Map

Relating Sensitivity Units to Hydrogeologic Information

Limitations of Sensitivity Map

Summary

Selected References

Supplemental Information



This report is available online in Portable Document Format (PDF). If you do not have the Adobe Acrobat PDF Reader, it is available for free download from Adobe Systems Incorporated.

Download the Report (PDF, 3.6MB).


Download plates: Plate 1 (3.8MB) and Plate 2 (1.3MB).

Document Accessibility: Adobe Systems Incorporated has information about PDFs and the visually impaired. This information provides tools to help make PDF files accessible. These tools convert Adobe PDF documents into HTML or ASCII text, which then can be read by a number of common screen-reading programs that synthesize text as audible speech. In addition, an accessible version of Acrobat Reader 5.0 for Windows (English only), which contains support for screen readers, is available. These tools and the accessible reader may be obtained free from Adobe at Adobe Access.

Send questions or comments about this report to the author, L.D. Putnam (605) 355-4560 ext. 212.

For more information about USGS activities in South Dakota, visit the USGS South Dakota District home page.




U.S. Department of the Interior, U.S. Geological Survey
Persistent URL: http://pubs.water.usgs.gov/wri004103
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Last modified: Thursday, September 01 2005, 04:54:57 PM
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