The St. Peter-Prairie du Chien-Jordan Aquifer is overlain by glacial till. Exact thickness of this glacial on the proposed location of the Bridgewater plant is unknown. A broad range of several feet to several hundred feet can be given with certainty.
The saturated aquifer thickness is the thickness of a confined aquifer or the vertical distance between the water table and the base of an unconfined aquifer. In Bridgewater township, the St. Peter-Prairie du Chien-Jordan Aquifer has a saturated thickness between 200' and 300'. Saturated thickness increases towards the south. On the southern border of Rice County saturated thickness of the St. Peter-Prairie du Chien-Jordan Aquifer can exceed 500'. Just west of the Cannon river the St. Peter-Prairie du Chien-Jordan changes from being a confined aquifer (west) to an unconfined aquifer (east).
Recharge rates of Bridgewater township are fairly high. West of the boundary between confined and unconfined conditions, waters have tritium content greater than ten tritium units; on the boundary, tritium values are between ten and one indicating a slower recharge rate. Tritium values greater than ten indicate that waters have entered the subsurface since 1953 while values between ten and one indicate a mixture of both older waters, pre-1953, and younger waters, post-1953. Several miles to the southwest of Bridgewater township, 14C dating gives a range of 50-200 years before present for the groundwater.
Not surprisingly, the direction of ground-water movement is southeast towards the Cannon River.
Available drawdown for confined aquifers is the distance between the top of the aquifer and the potentiometric surface. Available drawdown represents the total amount of water available for use. However, any permanent decline in the potentiometric surface dewaters the confining beds above the aquifer and may be detrimental to the long-term use of the aquifer.