RISK EVALUATION: BACKFILLING A GRAVEL PIT WITH ROAD CONSTRUCTION DEBRIS, NEAR RESIDENTIAL AREAS, LAFAYETTE, TIPPECANOE CO., IN

The Crider Pit, is located on a sandy terrace of the Wabash River sluiceway, Tippecanoe County, IN., with a water table depth of 50 to 60 feet in the unconfined aquifer containing individual wells in several adjacent housing areas. Wells are highly productive (>30gpm), with hydraulic conductivity = 10^-2 cm/sec and a hydraulic gradient of about 0.01 yielding a groundwater average velocity of about 100 ft/yr. toward the neighboring houses and a travel time for the 0.5 mile separation of about 13 years. The pit measures about 16 acres, 25 feet deep and the gravel was excavated to provide fill for new construction of State Road 25. Crider Construction Co. plans to backfill the pit with road construction material including broken concrete and asphalt pavement from a US 52 widening project. Asphalt milling material and concrete blocks in a soil mixture comprise the anticipated backfill. Under the Indiana solid waste regulations, road construction debris can be placed in a so called “clean fill” with none of the common requirements, such as monitoring wells , liner, landfill cap, or daily cover. The local citizens contend that backfilling the pit with road construction debris will create a threat to their water well supplies. Another concern is that other construction/demolition materials such as metal products, painted wood, plastic and paper products would also be deposited which could lead to groundwater contamination. Crider improperly placed some of this material in the pit previously and had to remove it. Approval to backfill road construction material was granted by the local planning board with an understanding that careful monitoring of backfilled materials would be conducted by the state and by local residents. Concern still exists that organic contamination from the milled asphalt will impact the water supply.