Hydrogeological and Hydrogeochemical Characterization and Implications for Consumptive Groundwater Use of a Large Glacial-Drift Aquifer System in Southwest Michigan. Part 1.

摘要

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 1 is 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 2 suggests 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.