Geologic, hydrologic, and water-quality data were collected at the Julietta and Tibbs-Banta landfills in Marion County. Both landfills were closed in the mid-1970's, and sewage sludge mixed with dirt was spread on the landfills in the mid-1980's as part of a revegetation project.
The landfills were constructed in unconsolidated glacial sediments that consist of sand, gravel, silt, and clay. The maximum thickness of the sediments is 180 feet at Julietta and 100 feet at Tibbs-Banta. Both landfills are underlain by sand and gravel aquifers and are adjacent to gaining streams. Ground water flows toward and into the streams at each study area. Two sand and gravel aquifers were mapped at Julietta and four were mapped at TibbsBanta. The aquifers are separated in places by discontinuous clay layers.
Ground-water-flow models, calibrated to simulate steady-state low-flow conditions, indicate that about 19,000 gallons of water per day move through the refuse at Julietta and 42,000 gallons per day move through the refuse at Tibbs-Banta. The Julietta model also indicates that recharge through the surface of the landfill is less than in the surrounding natural areas, probably because of the addition and compaction of the sludge/soil mixture.
Concentrations of dissolved inorganic substances in ground-water samples indicate that leachate from both landfills is reaching the shallow aquifers. The effect on deeper aquifers is small because of the predominance of horizontal ground-water flow and discharge to the streams. Increases in almost all dissolved constituents were observed in shallow wells that are screened beneath and downgradient from the landfills. Several analyses, especially those for bromide, dissolved solids, and ammonia, were useful in delineating the plume of leachate at both landfills.
