Arsenic in Ground Water from the Maryland Coastal Plain Aquifers

WRD PROJECT #: MD166
PROJECT CHIEF: Bolton, David
BEGIN DATE: 01-July-2001
END DATE: 31-December-2003

Customers currently supporting the project:

Maryland Geological Survey
U.S. Geological Survey

Problem

This proposal describes a ground-water sampling project that will document the occurrence and distribution of arsenic in the major aquifers of the Maryland Coastal Plain. Arsenic concentrations in several public water-supply systems in the Aquia and Piney Point aquifers in the Maryland Coastal Plain exceed 10 micrograms per liter. However, there has been no systematic investigation of the occurrence and distribution of arsenic in ground water of the Maryland Coastal Plain. Because the U.S. Environmental Protection Agency is considering lowering the drinking-water standards, it is important to (1) identify parts of the ground-water system where elevated arsenic concentrations exist, and (2) determine the factors and processes that are associated with aquifers exhibiting high arsenic concentrations.

Objectives

1. Conduct a regional water-quality survey to determine the distribution of ground-water arsenic concentrations in the major aquifers of the Maryland Coastal Plain.
2. Identify geological and geochemical factors that are associated with arsenic concentrations greater then 10 micrograms per liter.
3. Determine whether there are any significant daily or seasonal variations in ground-water arsenic concentrations.
4. Write an interpretive report describing the occurrence and distribution of ground-water arsenic concentrations in the major aquifers of the Maryland Coastal Plain.

Approach

This project, which will be a cooperative project between the Maryland Geological Survey (MGS), the U.S. Geological Survey (USGS), the Maryland Department of the Environment (MDE), and the Maryland Department of Health and Mental Hygiene (DHMH), will he conducted in two phases. The first phase will be a reconnaissance survey of arsenic concentrations. The second phase involves analyzing high-arsenic ground water for a more comprehensive suite of chemical constituents. The following tasks are proposed:

1. Write a quality assurance (QA) project plan that describes procedures, sample transport, QA sampling and objectives, data reduction and validation, and corrective actions.
2. Purchase equipment and supplies.
3. Conduct field reconnaissance to locate suitable wells for sampling. Aquifers to be sampled will include the Potomac Group (Patuxent and Patapsco Formations), the Magothy, Aquia, and Piney Point Formations, the Chesapeake and Columbia Groups, and other aquifers as determined by the cooperating agencies. Meet with personnel from MDE, county health departments, and other appropriate agencies to identify possible wells. Coordinate reconnaissance activities with these personnel. Obtain permission to sample wells.
4. MDE will arrange for the Maryland DHMH laboratory to analyze water samples collected during the project.
5. Collect samples that will provide data on daily and seasonal variations of ground-water arsenic concentrations. Collect water samples at different times of the same day from two wells having previous arsenic detections. Collect quarterly samples from two wells. Filtered and unfiltered samples will be collected.
6. Collect water samples from approximately 250 wells. Samples will be analyzed for unfiltered arsenic and field parameters (specific conductance, pH, and dissolved oxygen).
7. Submit an interim report after the 250-well survey that identifies portions of aquifers with arsenic levels greater than 10 micrograms per liter.
8. Select and resample approximately 50 of the 250 original wells having more than 10 micrograms per liter arsenic. Samples will be analyzed for arsenic, major ions, nitrogen and phosphorus species, fluoride, iron, manganese and field parameters. Approximately 10 additional low-arsenic wells in the same aquifers will also be resampled and analyzed for these constituents in order to compare the low-arsenic and high-arsenic water concentrations.
9. Analyze water-quality data in relation to geologic and hydrologic data in order to identify factors and processes that are associated with elevated arsenic concentrations.
10. Write an interpretive report that discusses the occurrence and distribution of ground-water arsenic in the major aquifers of the Maryland Coastal Plain. It is anticipated that this report will he published as an MGS Report of Investigations.