existing supply wells in fractured dolomite may lead to incorrect

interpretations of the configuration of the water table and the thickness of

the unsaturated zone. Vertical hydraulic gradients are relatively large.

Aquifer tests suggest that the aquifer is highly anisotropic at the piezometer

site, but tritium and 180 data indicate fairly rapid recharge and vertical

groundwater movement. Temperature logs appear to be particularly useful in

delineating zones of rapid groundwater movement in boreholes.


Purpose and Scope

     Dolomite of Silurian age forms an important aquifer in parts of central

 North America, including portions of the states of Wisconsin, Illinois,

 Indiana, Michigan, New York, and the Province of Ontario.    The Door Peninsula

 of northeastern Wisconsin, which lies between Lake Michigan and Green Bay, is

 an area of thin soils underlain by fractured Silurian dolomite (Figure 1) and

 is the focus of this paper.   This area (Door County) has a history of elevated

 nitrate, chloride, bacteria, and occasionally lead and arsenic levels in

 groundwater samples collected from private and public wells (Blanchard, 1988;
 Wiersma and others, 1984).   Such groundwater contamination is believed to be a

 direct result of agricultural and other land-use practices in areas where the

 fractured dolomite is overlain by thin soils. However, with the exception of

 Sherrill (1975; 1978) there has been little past research on the

 interrelationships between the fracture system, groundwater movement, and