Pilot Study of Water Quality in Drinking Water Wells, Anne Arundel County, Maryland

WRD PROJECT #: MD170
PROJECT CHIEF: Hayes, Martha A.
BEGIN DATE: 01-April-1997
END DATE: 30-September-1999

Customers currently supporting the project:

Maryland Department of the Environment
Maryland Geological Survey
U.S. Geological Survey

Problem

Health officials and water resource managers are concerned about the distribution and concentrations of carcinogens in ground water that supplies drinking-water wells in Anne Arundel County, Md. Many carcinogens are industrial chemicals whose presence in ground water is usually associated with localized or "point" sources of contamination such as leaking underground storage tanks or accidental spills. Other carcinogens such as water-soluble pesticides and radionuclides may have both point and nonpoint sources.

Objectives

A study of well-water quality in Anne Arundel County has been requested by the Environmental Risks Subcommittee (ERS) of the Anne Arundel County Advisory Task Force on Cancer Control. Discussions between members of the ERS, Anne Arundel County Health Department (CHD), U.S. Environmental Protection Agency (USEPA), U.S. Geological Survey (USGS), and Maryland Geological Survey (MGS) led to the decision that a pilot study should be conducted. The purpose of the pilot study is to acquire water-quality data from water samples taken from a limited number of existing wells in the major aquifers in Anne Arundel County. If carcinogenic compounds are detected at concentrations and frequencies that suggest that drinking-water quality has been compromised, a more comprehensive study will be required. If concentrations are low or sparsely distributed, the ERS will not require further study of ground-water supplies in the county at this time.

Approach

This project has been planned and will be conducted by the USGS in cooperation with MGS, EPA, and CHD. The design of this pilot study is based on the hydrogeologic conditions in Anne Arundel County; the expected chemical behavior of carcinogens in ground water; water-quality data from previous studies; and the logistical requirements of ground-water-quality investigations.

Three common groups of carcinogens--volatile organic carbons (VOCs), selected pesticides, and radionuclides--will be studied during this project. Sampling wells will be selected separately for each group of carcinogens. A stratified random design will be used for VOCs and pesticides: commercial, industrial, and agriculturally affected areas will be delineated, and a random selection process used within the areas outlined. Targeting these potentially affected areas will maximize the likelihood of detecting systematic contamination by these two groups of carcinogens. A county-wide random selection will be made of wells for sampling for radon and other radionuclides. There is relatively little data on radionuclides in ground water in the Coastal Plain aquifers in Maryland; therefore, no assumptions about relative likelihood of contamination can be made so that a smaller target area can be used.

The candidate population of wells in each targeted area will consist of all private water-supply wells currently in use. This includes dug wells and wells with and without construction documentation. Public-supply wells will be excluded because they are already tested for contaminants. Non-water-supply wells such as monitoring wells at known contaminated sites will not be sampled. All wells will be analyzed for major ions, VOC's, and selected nutrients, trace elements, pesticides, and radionuclides. Major-ion concentrations will be used to define hydrochemical facies within the principal aquifers in the county. Nitrate (Cancer Group classification under review) is included because there is some evidence that nitrate in drinking water is related to stomach cancer and other cancers (Hill, Hawksworth, and Tattersall, 1973).

MGS will direct the study and supply the materials for analysis of pesticide content in water samples. USGS will supply personnel support in the areas of Geographic Information Systems (GIS), field work, data management and interpretation, and report writing; laboratory analyses of water samples for major ions, trace elements, and radionuclides (including radon) and quality-assurance testing for pesticides will be performed at the USGS National Water-Quality Laboratory. USEPA will provide laboratory analyses of the samples for volatile organic carbon content. CHD will provide laboratory analyses of nitrate, ammonia, and bacteria content of water samples and measure indoor radon concentrations in air.