The Silurian dolomite aquifer in the Lannon-Sussex area of southeastern Wisconsin is overlain by glacial deposits, but is within 8 ft of the land surface over 15% of the study area. The proximity of the dolomite aquifer to the land surface makes it susceptible to contamination from man 's activities. Water from the aquifer was analyzed and several characteristics were monitored in a 30-sq-mi area of Waukesha County, including: water temperature, calcium, magnesium, potassium, strontium, alkalinity, chlorides, fluorides, sulfates, nitrites, nitrates, nitrogen, iron, manganese, hardness, and pH.
The water is hard, commonly having a hardness of more than 350 mg/L as CaCO3, and high in iron, commonly containing more than 0.3 mg/L. However, nutrient concentrations are not high; nitrogen, greater than 8 mg/L; phosphorus, none detected; and potassium, greater than 4 mg/L. The chloride content of the water averages more than 50 mg/L indicating contamination probably from septic systems. The water quality varies over a time. High concentrations of chloride and, occasionally, of bacteria correlate with periods of groundwater recharge over a period of 17 months. Chloride concentrations were highest in water from wells where housing density is high.
An attempt was made to relate water quality changes with depth to beds of cherty dolomite that are identified in geologic logs; it was postulated that these zones might be confining beds. Although the beds appear to extend over the area, no evidence was found that they are confining beds, other than reports of a few artesian wells. Water quality, indicated by chloride content, showed no significant relation to well bottom altitudes, casing bottom altitude, or well depth.
