A 3-year study in northwest Elkhart County, Indiana, was done to (1) de-fine the general flow and quality of water in the outwash aquifer system, (2) determine if a well field proposed for a site at the Elkhart Municipal Airport would draw leachate from the Himco landfill, and (3) define the areal extent of the ground water affected by the landfill and an east-side industrial-park area.

The outwash aquifers are mainly composed of sand and gravel and are separated by a silt and clay bed. The saturated thickness of these deposits averages 175 feet and ranges from 85 to 500 feet. Where present, the silt and clay bed confines the underlying aquifer. The confining bed is absent in the area underlying the landfill and part of the airport. Average hydraulic conductivities of the sand, and the sand and gravel, are 80 and 400 feet per day, respectively. Regional ground-water flow is toward the St. Joseph River.

A quasi-three-dimensional ground-water flow model, calibrated to match measured water levels and river seepages, was used to simulate proposed pumpings in the airport area. Drawdowns for simulated pumpings of 7.5-, 10-, and 20-million gallons per day were small percentages of the saturated thick-nesses of the unconfined aquifer underlying the airport area. Model-simulated streamflow reductions in Christiana Creek for these pumpings were 9, 12, and 23 percent of base flow, respectively. The model-simulated, steady-state water-level maps for the 7.5- and 10-million-gallons-per-day pumping experiments indicated that these pumpings would not draw water from the land-fill area to the pumping center at the airport. The simulated map for the 20-million-gallons-per-day pumping indicated that only a small part of the flow into the pumping center could come from the landfill area.

The general quality of ground water in the study area, defined by analyses of 68 water samples from 35 observation wells, included slightly basic pH (7-8), average hardness greater than 200 milligrams per liter as calcium carbonate, average alkalinity greater than 150 milligrams per liter as calcium carbonate, and, in more than 90 percent of the analyses, a calcium bicarbonate water type.

Eight volatile organic compounds were detected in water from 8 of 19 wells sampled in the industrial-park area. The health-effects advisory limit for chronic exposure to trichloroethylene was exceeded in samples from six of these wells. Areally, the results did not define a plume or a source of the volatile organic compounds.

Concentrations of dissolved solids, bicarbonate, bromide, chloride, sulfate, ammonia, calcium, magnesium, manganese, potassium, sodium, and dis-solved organic carbon in the leachate were at least five times their back-ground concentrations. Concentrations of bromide and dissolved solids were the best indicators of leachate. Bromide concentrations plotted areally indicated that the landfill was the source of the leachate, the leachate plume extended between 3,100 and 5,600 feet downgradient from the landfill, and the plume had not spread laterally much farther than the original width of the landfill. Bromide and dissolved-solids concentrations plotted in cross section indicated that the leachate plume was sinking as it spread downgradient in the shallow unconfined aquifer and the leachate was present in deep wells under and immediately downgradient from the landfill. All chemical constituents were attenuated within approximately 1 mile downgradient from the landfill.