Ground water in the upper Winooski River basin, Vermont, occurs in bedrock and in overlying unconsolidated deposits of glacial origin. Bedrock in the area is composed of a series of metamorphic and igneous rocks. Median yield for 126 wells in four different bedrock formations ranges from 5 to 6 gallons per minute, and median depth ranges from 130 to 200 feet. Lineaments, interpreted as fracture of breakage zones in bedrock, were mapped to identify zones where well yields are expected to be higher than average.
Unconsolidated deposits in the upper Winooski River basin include unsorted till, water-sorted clay, silt, sand, and gravel. Properly constructed wells in saturated deposits of sand or gravel having high permeability can yield large quantities of water. Twenty-six domestic wells in these unconsolidated deposits have a median yield of 18 gallons per minute and a median depth of 58 feet.
Chemical analysis of water from six wells indicate a median hardness of 120 milligrams per liter, (as CaCO3), which is moderately hard. Iron and manganese are common constituents of ground water in the area, and several analyses show concentrations of these elements which exceed recommended National Academy of Sciences and National Academy of Engineering (1973) limits for public drinking water supplies.
