The Schoolcraft aquifer is a large outwash fan in southwestern Kalamazoo and northwestern Kalamazoo and northwestern St. Joseph counties,Michigan. This very vulnerable aquifer is extensively used for irrigation and has been contaminated from a variety of sources. In general,groundwater flows from near the head of the fan southwesterly to its distal margins. Fifteen study sites consisting of a well or nest of wells were established across the fan to study the flow systems in the aquifer. Areal distribution of five chemical parameters were used to delineate probable recharge and discharge zones within the aquifer system. Zone 1is the extreme upgradient portion of the aquifer and appears to correspond to a chemically well-defined recharge area. Statistical analysis of the chemical constituents in Zone 2suggests that this area is hydrogeochemically distinct from the remainder of the aquifer. The vertical distribution of tritium concentrations supports the hydrogeological evidence that flow in the aquifer is stratified. The distribution of tritium concentrations among wells with an upward vertical gradient supports this same conclusion as wells screened at shallow depths,which display markedly higher values than deeper wells. Tritium concentrations from well clusters showing downward gradients indicate the rapid recharging of young water with older,less tritiated water representing a deeper flow system. Anthropogenic degradation of the Schoolcraft aquifer system in the form of nitrate and chloride species is extensive. Wetlands are an important element of the recharge-discharge system. These conclusions are supported by studies of water levels and water chemistry.
A steady state simulation of the regional groundwater flow system was developed in order to (1) better understand the data needs for an improved model and (2) provide an estimate of the impacts that groundwater withdrawals have on groundwater discharge to streams,wetlands and lakes in the Schoolcraft aquifer. A 2-D finite element model was utilized to simulate groundwater flow. Evapotranspiration from the wetlands was modeled as a linear function of water table elevation. The model was used to obtain a steady state solution prior to groundwater pumping. The modeling provided an excellent means for identifying additional data needs,which include data on the geology that influences flow at the boundaries of the modeled region and in the vicinity of wetlands. The model was run to obtain the impacts of groundwater withdrawals in order to provide a complete picture of the method of analysis and an estimate of the impacts that pumping has on streams and wetlands. Eighty nine pumping wells were incorporated into the model. Analysis of the simulation results showed that six wetlands in the study area were effected significantly by pumping. The simulation results also indicated that the reduction in groundwater flux to streams and lakes was higher than the reduction in groundwater flux to wetlands because of the distributions of the pumping wells. As more data become available on the geology and hydrology it will make sense to improve the description of model features and obtain an improved assessment.