The Recharge Area and Water Quality of the Stevens Point Municipal Well Field

Abstract

Determining the area from which the City of Stevens Point Municipal Supply Wells draws recharge waters is important first step in protecting the city's water supply. In determining the recharge area, land uses that may affect the water quality of the aquifer may be discouraged. To determine the groundwater flow characteristics of the recharge area 9 piezometers and 12 water table observation wells were used to estimate to groundwater flow approaching the well field. Nested well systems were installed both east and west of the Plover River to determine the extent of the cone of depression and whether the cone extended to or beyond the Plover River. Water table observations revealed that the cone of depression extends beyond the Plover River during most of the year, indicating that water from the river and east of the river is drawn into the aquifer near the well field. Piezometers placed in the bed of the river verified that the river was recharging the aquifer near the well field. Observations from the nested well systems demonstrated that the groundwater flow approaching the city supply wells is predominately horizontal, suggesting that the groundwater flow is dominated by the pumpage from the city supply wells. The horizontal gradients east of the Plover River indicated that pumpage from the city wells was affecting groundwater flow east of the river, creating the potential for groundwater flow beneath the river bed. The aquifer water quality was examined through sampling all piezometers, monitoring wells, city supply wells, regional private water supply wells, and regional surface water bodies. All samples were analyzed for inorganic constituents to examine the aquifer water quality of the well field region and to use the specific constituents as natural traces of groundwater flow. The sampling revealed isolated high concentrations of many constituents. An area of impacted water was detected in the deeper aquifer adjacent to the well field east of the river. The elevated concentrations of nitrates, sulfates and chlorides suggested that the impacts were associated with agricultural fertilizers, animal wastes and septic systems. Impacted groundwater was also detected along Highway 66. Elevated concentrations of ammonia, sulfates, chloride, and to a lesser extent, nitrates are believed to be the result of roadsalt applications to the highway and septic system impacts. In each case however, the high values were significantly diluted as the city supply wells withdrew recharge water from the other regions with lower concentrations. The City is fortunate to have a relatively large undeveloped area near the well field to provide dilution of contaminates originating in the developed parts of the recharge area.