Ground-water data were collected in northwestern Elkhart County, Indiana, from 1980 through 1989 to monitor hydrologic conditions and to provide information necessary for waterresources managers to evaluate the ground-water resources in this area. The area of study includes a closed industrial landfill and several areas of industrial and municipal pumping. Water levels were measured twice a year in 68 wells, and water samples were collected once a year from 32 wells. The wells were screened in unconsolidated glacial-outwash deposits primarily sand and gravel.

During the study, measured ground-water levels ranged from about 6 feet above ground level to about 29 feet below ground level. The average depth to water for all wells was 10 feet, and the average water-level fluctuation for the entire study period was 4.8 feet. In the study area, ground water flows toward the St. Joseph River. Water levels near the river are higher than the stage of the river, indicating that ground water is discharged to the river.

Water samples were collected and analyzed to determine concentrations of dissolved bromide. Onsite measurements of specific conductance, pH, water temperature, and concentrations of dissolved oxygen and alkalinity were made at the time of sampling. The water samples had a median specific conductance of 516 microsiemens per centimeter at 25 degrees Celsius, a median ph of 7.6, a median alkalinity of 216 milligrams per liter (as calcium carbonate), and a median dissolved-bromide concentration of 0.08 milligrams per liter.

Water-quality data were grouped according to the depth and position of the wells in the flow system with respect to the closed industrial landfill. Shallow wells are those less than 100 feet deep; deep wells are those more than 100 feet deep. Comparison among groups indicates that water from shallow wells downgradient from the landfill had larger values of specific conductance, larger concentrations of alkalinity and dissolved bromide, and smaller values of pH than did water from shallow wells upgradient from the landfill and water from deep wells throughout the study area.

Concentrations of dissolved bromide were used to estimate the extent of the landfill's effect on ground-water quality by plotting and contouring the concentration values on maps and hydrogeologic sections. The maps show a plume of bromide extending south of the landfill along the direction of groundwater flow. The hydrogeologic sections indicate that water containing bromide is moving vertically downward in the unconfined aquifer beneath and downgrfldient from the landfill. Maps and sections for different time periods were compared to determine how the distribution of bromide was changing. Although dissolved-bromide concentrations in water from individual wells were variable, the distribution of dissolved bromide did not change substantially during the study period.

The time of peak dissolved-bromide concentrations in water from shallow wells downgradient from the landfill was used to estimate a rate of horizontal flow of water in the unconfined aquifer. The average rate of flow between shallow wells downgradient from the landfill was estimated to be 1.2 feet per day. This rate is within the range of values for ground-water flow calculated according to Darcy's law.