Occurrence and Distribution of Organic Chemicals, Nutrients, and Radium in Surficial Aquifer Drinking-Water Supplies in Delaware

WRD PROJECT #: MD138
PROJECT CHIEF: Ferrari, Matthew J.
BEGIN DATE: 01-July-2000
END DATE: 30-June-2001

Customers currently supporting the project:

Delaware Department of Natural Resources and Environmental Control
Delaware Geological Survey
U.S. Geological Survey

Problem

Over 400 public drinking-water supply wells are screened in unconfined parts of the surficial aquifer in the Coastal Plain of Delaware. This aquifer is comprised primarily of sands and gravels of fluvial and marginal marine origin and is largely unconfined, making it susceptible to contamination from applications or spills of chemicals on or near the aquifer surface. Land use surrounding the public supply wells in the Coastal Plain of Delaware primarily includes intensive agriculture, and urban and suburban areas associated with small towns and communities. Health officials and water-resource managers are concerned about the overall quality of this drinking-water resource. Of particular concern are the occurrence and distribution of commonly used pesticides and their metabolites, organic compounds associated with fuels and industrial uses, nutrients, and radium from natural sources in surficial aquifer ground water.

Previous studies have documented the occurrence and distribution of pesticides and nutrients from nonpoint sources in Delaware (Andres, 1993; Denver, 1993; Hamilton and others, 1991; and Koterba and others, 1993). Monitoring by State agencies has confirmed the presence of organic compounds associated with fuels and industrial sources, probably from nonpoint-source releases. Radium has not been sampled for in Delaware ground water, but it has been detected in both New Jersey and Maryland in areas with similar aquifer settings. These chemicals have not been sampled systematically or as a suite in the surficial aquifer.

Objectives

The objective of this study is to characterize the chemical quality of ground water in public water-supply wells from unconfined parts of the surficial aquifer in Delaware using a statistical sampling design.

Approach

This project is being coordinated with the USGS National Water-Quality Assessment (NAWQA) study unit on the Delmarva Peninsula. Protocols and procedures for network design, sampling, and quality assurance follow NAWQA guidelines. Ground-water-quality data will be collected from a subset of 30 randomly selected public-supply wells in unconfined aquifers of the Delaware Coastal Plain. Sites will be selected within a randomly located grid to ensure relatively even spatial distribution across the study area (Scott, 1990). Additional sites will be selected as replacements to be used in the event that any of the 30 primary sites cannot be sampled. Water temperature, specific conductance, pH, dissolved oxygen content, alkalinity, and (if possible) level below land surface will be measured at each well (Wilde and others, 1999). Water samples will be collected (Koterba and others, 1995) and analyzed for pesticides, pesticide metabolites, nutrients, major ions, dissolved organic carbon, volatile organic compounds (VOCs), and radon at USGS laboratories in Denver, Colorado and Lawrence, Kansas. Additionally, samples from 10 of the 30 wells will be analyzed for three isotopes of radium.

Quality-control samples will be collected to provide estimates of bias or variability in reported chemical concentrations. Field blanks will be collected and analyzed to identify bias or contamination from field processing or laboratory analyses. Duplicate samples will be collected and analyzed to estimate the variability of reported concentrations. Selected duplicate samples for pesticides and VOCs will be fortified with known concentrations of target analytes and analyzed to determine the percent recoveries of each compound (Koterba and others, 1995). Additional information about quality control at the USGS laboratory in Denver is available in Ludtke and Woodworth (1997).