Hydrogeology & Hydrology Program
Arsenic Study	contact: David Bolton (dbolton@mgs.md.gov)

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 geologic and geochemical factors that are associated with arsenic concentrations greater than 10 µg/L.
3. Write an interpretive report describing the occurrence and distribution of ground-water arsenic concentrations in the major aquifers of the Maryland Coastal Plain.

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This ground-water sampling project will document the occurrence and distribution of arsenic in 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 (µg/L), which is the new drinking-water standard for arsenic (J. Grace, Maryland Department of the Environment, written commun., 2000). There has been no systematic investigation of the occurrence and distribution of arsenic in ground water of the Maryland Coastal Plain. In light of the new drinking-water standard, it is important to (1) identify those parts of the ground-water system where arsenic concentrations often exceed the new standard, and (2) determine the factors and processes that are associated with aquifers exhibiting high arsenic concentrations.

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This project, which will be a cooperative project between the Maryland Geological Survey (MGS), the U.S. Geological Survey (USGS), and the Maryland Department of the Environment (MDE), will be 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 sampling 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. Collect water samples from approximately 250 wells. Samples will be analyzed for arsenic and field parameters (specific conductance, pH, and dissolved oxygen).
5. Using the data from the 250 samples obtained in Task #4, select and resample approximately 50 of the 250 original wells that had more than 10 µg/L arsenic. Samples will be analyzed for arsenic, major ions, nitrogen and phosphorus species, fluoride, iron, manganese, and field parameters (table 1). Approximately 10 additional low-arsenic (less than 10 µg/L) 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 chemistry.
6. 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.
7. 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 be published as an MGS Report of Investigations.

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A quality-assurance (QA) project plan will be written that describes all aspects of the project, including a project description, sampling procedures, QA objectives, analytical procedures, QA samples, and corrective action to be taken. QA samples will be collected in order to (1) ensure there is no sample contamination from sampling equipment; (2) document the effectiveness of decontamination procedures; and (3) document analytical precision. QA samples may include trip blanks, equipment blanks, and field duplicates. Data from the QA samples will be analyzed immediately in order to take any corrective actions that may be necessary. Other QA activities will include (1) comparison of field and laboratory values of pH, alkalinity, and specific conductance; (2) comparison of analytical values of total dissolved solids to residue-on-evaporation; and (3) evaluation of charge-balance errors and selected parameter ratios.

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Table 1. Proposed water-quality constituents to be analyzed in the Maryland Coastal Plain arsenic study.

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