LAND USE ASSESSMENT OF HIGH YIELD SAND AND GRAVEL AQUIFERS IN MAINE

This study assesses the cumulative impact of residential, commercial, and industrial development on 300 of the significant (>50 gpm) sand and gravel aquifers defined and mapped by the Maine Geological Survey. The method provides a relative comparison of the risk of adverse impact through the Aquifer Quantitative Use Assessment, or AQUA, Index. Non-point source risks due to population and travel corridors are treated as a function of the density of impervious surface in the aquifer polygon, by subtracting the total road covered or road salt influenced acreage (75 foot buffer from centerline) from the total number of acres of an individual aquifer. The balance of the remaining acreage was divided by a factor based on the presence and relative risk of petroleum tanks (underground/aboveground storage tanks (USTs or ASTs)), former tank locations (i.e. possible legacy of contamination) and potential or actual sources of contamination to groundwater (as derived from Environmental Geographic Analysis Database (EGAD) Site Data). The resulting number, still in units of acres, is divided by the original acreage to give the dimensionless AQUA index, which can also be expressed as a percent. An AQUA index of 1 or 100% means no impact. In general, larger overall acreage in combination with remoteness or other limits on development result in a higher AQUA index. This index may be used to assess the relative risk to future or present municipal, private, or commercial drinking water uses and to identify those aquifers most at risk from commercial/industrial development or residential pressures. Overall, 77 high yield aquifer locations (26%) are non-impacted (4,881 acres or 16% of total acres), 145 (48%) are less than 50% impacted (8,540 acres or 29% of total acres), and 78 (26%) are more than 50% impacted (13,325 acres or 55% of total acres (29,746)). Of the non-impacted high yield sand and gravel aquifers, 18% have public water supply wells. Of the aquifers with AQUA values between 1.0 and 0.5, 28% have public water supply wells, while of those with AQUA values less than 0.5, 38% have public water supply wells.