EndPoint was recently retained by a developer in Massachusetts to handle the discovery of dissolved arsenic in ground water that is within a Zone II of a potable water supply well field. What makes this condition unique is that the arsenic source is naturally occurring from shallow bedrock underlying the developed property. The first task for EndPoint was to identify the nature of dissolved arsenic detected in ground water. It was concluded that the most probable source of arsenic was from the shallow bedrock and not associated with any arsenic release at the property. The mechanism for the release of arsenic from bedrock to ground water was through a process called reductive dissolution. This process is typically found at petroleum release sites and landfills where a substantial organic carbon source is introduced to ground water. The technical literature on this topic indicates that naturally-occurring bacteria within the aquifer matrix will consume the organic carbon and available oxygen, reducing iron-oxides to ferrous iron, causing reducing conditions in the aquifer. This condition releases the arsenic from the aquifer matrix into ground water, resulting in a spike in dissolved arsenic concentrations in the immediate area of the organic carbon source. Possible organic carbon sources at this site are an upgradient gas station and a former commercial septic leach field located on the developers property.
The second task was to evaluate if the presence of dissolved arsenic was considered a reportable condition under the Massachusetts environmental regulations (i.e., the Massachusetts Contingency Plan or MCP). We found it difficult to believe that the Massachusetts Department of Environmental Protection (MassDEP) would want to regulate this type of condition, given the substantial number of commercial leach fields in Massachusetts and the financial effect this may have on businesses. We initially argued on behalf of our client that the release of arsenic met the definition of background (naturally occurring conditions) and attributable to geologic conditions, which is exempt from reporting under the MCP. However, this condition is exempt only if the arsenic was not mobilized, transferred to another environmental medium, or increased in concentration as a result of man-made activities, which was not the case at this site. We subsequently argued that the release was discharged from a point source that was operated under a valid permit, and did not result in an Imminent Hazard as defined in the MCP.  Based on the MCP, this type of release also does not require reporting to the MassDEP. However, it was eventually concluded by MassDEP that the discovery of arsenic was a reportable condition.
The third task was to evaluate the magnitude and extent of the dissolved arsenic, to assess risk in accordance with the MCP, and to evaluate if there is a contribution from the upgradient gas station release. This task is currently ongoing and includes a ground water monitoring program that focuses on evaluation of spatial and temporal trend in dissolved arsenic, ferrous iron, dissolved oxygen and oxidation-reduction potential in ground water. The developer has terminated the use of the leach field, thus cutting off the organic carbon supply utilized by microbes in the environment. It is likely that by eliminating the organic carbon supply, the arsenic concentration trend will be reversed, eventually reaching drinking water standards that will allow for the filing of a Class A Response Action Outcome (RAO) Statement, thus completing MCP Response Actions for this condition.