Background

In October 2003, wells supplying ground water to the Chapel Point Woods community near La Plata, Maryland showed gross alpha-particle activity (GAPA) exceeding the U.S. Environmental Protection Agency’s Maximum Contaminant Level (MCL) of 15 picocuries per liter (pCi/L) in Wells 1 and 2 for the first time since they were drilled in the 1970s. More specific radionuclide testing performed by the National Institute for Standards and Technology (NIST) with correspondence to Maryland Department of the Environment (MDE) indicated that polonium-210 was the main alpha radiation emitter in Well 1, while Well 2 (a back-up supply well) was not tested further. Since then other communities in the area such as Mount Carmel Woods and Clifton on the Potomac were found to have high gross alpha radiation concentrations as well (Figure 1). These wells are not in use, either having been abandoned, taken off-line, or re-drilled and re-tested.

Polonium-210 is fairly volatile and has a half life of approximately 138 days (International Atomic Energy Agency, 2012). One plausible reason why test results before 2003 had not indicated elevated radiation levels is that testing of the water samples might not have occurred until months after the samples were collected; the polonium may have disintegrated too quickly for the tests to discover high radiation amounts. Adverse health effects from Po-210 result from ingestion, so being able to predict its presence in water sources would be of high importance to public health.

To date, there has been no systematic evaluation of the extent of polonium, GAPA, or GBPA in ground water in Charles County. The proposed study described in this scope of work seeks to determine the stratigraphic intervals that contain elevated polonium and/or GAPA and GBPA, whether there are wells that may be at risk of elevated radioactivity, and what areas may warrant additional testing. Additional well testing would not be part of this study, although it may be recommended as a result of the study findings.

Objective

This study’s purpose would be to (1) identify (to the extent possible) the specific hydrostratigraphic sections in which elevated levels of radioactivity (including polonium-210) have been detected, and (2) locate other areas where water wells (especially private wells) may be at risk for elevated gross alpha radiation based on the hydrostratigraphic zone that the wells are screened in. If wells are determined to be at risk, subsequent studies may be proposed that examine the water quality associated with these wells.

Approach

Evaluate existing polonium and other radioactivity data from water wells in known affected areas (including Chapel Point Woods, Mt. Carmel Woods, Clifton on the Potomac, and the St. Paul well in Waldorf).

• Gather existing test data on polonium-210, gross alpha-particle and gross beta-particle activity.
• Acquire data on well-construction characteristics of wells having elevated radioactivity.
• Evaluate detections in relation to screen depths, aquifers/parts of aquifers and geologic features (basement faults, etc.).
• Determine to the extent possible what aquifers/parts of aquifers where polonium or elevated GAPA is located. This would include using Maryland’s Aquifer Information System and past Reports of Investigation for Charles County to identify where in the aquifer(s) these wells are screened.

Evaluate potential for elevated polonium/GAPA elsewhere in Charles County.

• Determine well-depth distribution of other water wells in the region surrounding the high-polonium area. This would be done using the approach outlined in Drummond (2007), which evaluated private water-well distributions in southern Maryland based on Maryland’s grid coordinate locations in the Maryland Department of the Environment’s “Source Table” (which consists of almost all well permits and driller’s log information in Maryland).
• Identify which areas and wells may be at risk, including stratigraphically equivalent zones updip of the affected area, areas possibly influenced by basement faults, or other areas.

Write a report documenting the findings of the study

• A report summarizing the distribution of radioactivity in the study area will be prepared and submitted to the funding agency. The report will include recommendations for future work such as additional sample collection.