John M. Peckenham

Background Mercury Concentrations in River Water in Maine, U.S.A.

Mercury concentrations in 58 rivers in Maine was measured to range from below detection up to 7.01 ng L-1 and averaged 1.80±1.29 ng L-1. The concentration gradient for mercury in rivers across the state was not uniform. Mercury strongly correlated with dissolved organic carbon (DOC) and aluminum, and less strongly with copper, lead, and zinc. Mercuryexhibited significant differences in correlations with chemical variables and local geology when partitioned by flow state (high or low). Mercury concentrations were greatest in rivers flowingacross either wacke-type bedrock at low metamorphic grade, or glacial-till deposits. Elevated concentrations of mercury formed a locus in northern Maine under both high and low-flow states while in southwestern Maine a locus formed only during high-flowstates. These regional differences were statistically significantwhen compared by geographical location. We suggest that there is a bedrock source of mercury in northeastern Maine that is dilutedduring periods of high runoff. The elevated concentrations detected under high-flow states, as noted in southwestern Maine, may reflect mercury released from storage in association withDOC during periods of high runoff. The association of mercury with flow state indicates that watershed processes and local geology can modulate the concentration of mercury in rivers.

Maine’s Experiment with Gasoline Policy to Manage Mtbe in Groundwater

The gasoline additive MtBE has become one of the most commonly detected contaminants in groundwater nationwide and has caused much concern in the state of Maine. In 1998 the Maine Department of Human Services conducted a statewide survey of groundwater wells and MtBE was detected in 16% of private and public wells tested. These findings resulted in the state regulatory agencies deciding to opt out of the reformulated gasoline (RFG) program in 1999. Subsequently, the average concentration of MtBE in gasoline dropped from ∼15% to 2% by volume to protect water resources. This major policy change provided a microcosm to study the economic and environmental effects of this gasoline additive. In order to test the effect of this policy on water quality, groundwater samples were analyzed over a period of six years (1998–2003) from 19 wells distributed across a sand and gravel aquifer in Windham, Maine. MtBE continues to occur in detectable concentrations in 30 to 40% of the study wells despite Maine’s decision to opt out of the RFG program in 1999. Although recent detected concentrations are lower than in previous years, this study confirms MtBE’s temporal and spatial persistence in the environment. Reducing MtBE concentrations in gasoline may not be sufficient to eliminate its occurrence in groundwater. The economic perspective is that MtBE increases the cost of groundwater remediation, as compared to MtBE-free gasoline. Economic data for spills are being analyzed to assess if reducing MtBE concentration in gasoline has affected remediation cost. Preliminary results suggest that MtBE increases costs, even when present in low concentrations in gasoline.