Bedrock Wellhead Delineation Project Begins:

By Gail Lipfert, NEIWPCC/MGS

The Maine Department of Human Services, Division of Health Engineering, Drinking Water Program (DHE), the Department of Conservation, Bureau of Geology and Natural Areas, Maine Geological Survey (MGS), and New England Interstate Water Pollution Control Commission (NEIWPCC) are cooperating on a project to improve wellhead protection delineation for municipal supplies utilizing bedrock aquifers. This program is part of the work authorized by the 1996 Safe Drinking Water Act Amendments, and is funded by the US Environmental Protection Agency (EPA).

Ground-water contributing areas for 139 municipal wells utilizing sand and gravel aquifers have been successfully completed by the cooperative efforts of DHE, MGS, and NEIWPCC in support of the Source Water Assessment Program (SWAP). The goal of this project is to provide the same service to the 27 water districts utilizing bedrock aquifers. The current method of delineation for these bedrock aquifers is a fixed circle whose radius is based on the number of individuals served by the water district. The primary objective of this project is to develop more geologically defensible methods to delineate wellhead protection zones for well fields within fractured-bedrock systems. Gail Lipfert, a hydrogeologist, with a BS and MS from the University of Maine, has been hired by NEIWPCC and assigned to MGS for 18 months to complete this project. Ms Lipfert has concentrated her studies on the problems involved in understanding the movement of ground water through fractured-bedrock aquifers.

Delineating the area that contributes significant recharge in bedrock aquifers is more problematic than in sand and gravel aquifers. The passage of water through the non-porous rock in Maine is restricted to the openings provided by fractures. Given that the exact fracture network can never be known, methods for characterizing the fracturing must be used. Delineations will be performed using existing hydrogeologic, pump test, and operating data as well as field-measured fracture characterizations and photo-lineament analysis. The project will develop a methodology for establishing capture zones that takes into account the degree of uncertainty involved in predicting ground-water flow through fractured bedrock. The methodology is being tested on five pilot systems. Since the data for the delineations may be limited, the project will also identify data gaps so the water system could, if it chooses, improve the accuracy of the delineation in the future. Management plans, ordinances, or contingency plans based on the delineation will not be included, although water systems will be provided copies of the delineation for their use in developing such plans. For more information about the project, contact Andy Tolman at the Drinking Water Program at 287-6196.

DWP INFORMATION

Bedrock Wellhead Delineation Project Begins: