A Regional Tem Survey To Map Saline Water In The Cambrian-Ordovician Sandstone Aquifer Of Southeastern Wisconsin

The Cambrian-Ordovician aquifer is the major source of ground water for municipal and <br>industrial use in southeastern Wisconsin. Decades of over pumpage have created a regional cone of <br>depression centered in the western suburbs of Milwaukee. Total Dissolved solids levels in several <br>sandstone aquifer wells have more than doubled over the last ten to fifteen years. A time-domain <br>electromagnetic induction (TEM) survey was conducted to determine the cause of the rising TDS levels. <br>A total of 69 soundings were performed using a Geonics EM-57. The modeled soundings were <br>used to construct three geo-electrical cross sections across the survey area. The TEM survey indicated <br>that the rising salinity levels in the wells is related to vertical migration of saline water from the lower <br>aquifer in response to decades of over pumping. The findings are being used to evaluate future well <br>sites and rehabilitation options to reduce salinity levels in existing wells.