DRINKING WATER SOURCE EXPLORATION: A CASE HISTORY FOR A SMALL PUBLIC COMMUNITY WATER SYSTEM IN VERMONT

A new bedrock well was located and drilled for a public community water system (the Dairy Center) near Enosburg Falls, Vermont. This public community water system serves seven mobile homes, a bowling alley, a restaurant, a motel, a banquet hall and a single family residence. The Enosburg area is in the western foothills of the Green Mountains, and is part of a belt of low-grade metamorphic rocks of Cambrian and Ordovician age. This belt is bounded on the west by the Champlain Thrust and to the east by the Green Mountain anticlinorium. The Dairy Center is located on a river terrace in the Missisquoi River Valley, which trends approximately east-west, with the Missisquoi River about 500 feet south of the site on the opposite side of Vermont Route 105. The new well was drilled into the Tibbit Hill formation, and generally consists of albite-actinolite-chlorite-epidote greenstone. Well logs in the vicinity of the project site indicated varying depths to bedrock, varying thickness of clay layers, and sand and silt deposits previously interpreted to be lake bottom sediments associated with Lake Vermont of about 10,000 years in age.

Geologic maps of the area showed numerous structural features trending approximately N 20° E. These features include structural and fracture trace linears, measured strikes of joints, rock cleavage and schistosity. Although these features cannot be seen beneath the river terrace deposits, the trends of these bedrock structural features were the target of well drilling activities. The new well was drilled to a depth of 205 feet. Bedrock was encountered at 34 feet, and there was approximately 21 feet of clay mixed with silt and angular rock fragments above the bedrock. The well driller’s yield was 40 gpm based on an air lift test.

The raw water passed all tests for primary and secondary drinking water standards with the exception of manganese at 0.443 mg/L and hardness at 168 mg/L (9.8 grains). The State required manganese treatment, and a water softener was installed to treat both manganese and hardness. The well has been completed, and improvements constructed including a new treatment building, booster pumping station, storage tanks, distribution lines, and a UIC permitted infiltration trench for water softener backwash. The Dairy Center Water System is now in compliance with State and Federal Regulations.