LANDFILL HISTORY REVEALED THROUGH SITE CHARACTERIZATION FOR CSO UNDERGROUND STORAGE TANK, LAFAYETTE INDIANA

Lafayette Indiana, like many cities in the U.S., is actively involved in reducing combined sewer overflow problems under an edict by USEPA. In the past, sanitary effluent and storm water runoff were combined into a single sewer system which reaches full capacity during heavy rainfall events. To relieve pressure, overflow of the untreated water is dumped directly into rivers and lakes yielding contamination. In Lafayette, a 4.2 million gallon underground storage tank, roughly the size of a football field, is under construction. This storage will delay flow to the sewage treatment plant and reduce the CSO problem. Two of the nine overflow points into the river will be eliminated. The site, adjacent to the Wabash River, is a former municipal solid waste landfill that closed about 1970. Sand from the river was pumped to the site for daily cover and closure. Eleven exploratory borings 75 feet deep indicate a landfill thickness up to 28.5 feet and groundwater depth ranging from 20 to 38 feet. Below the fill, the soil consists of a fine to medium sand. About 18 million gallons per day is pumped from the construction site so the tank can be built in the dry. To build the tank approximately 100,000 cubic yards of solid waste and soil were excavated. Because of the high GWT, the tank was built to resist uplift pressure. Eight hundred and sixteen auger cast piles, 25 to 55 feet deep, were used to anchor the tank. Eight thousand cubic yards of concrete and 750 tons of rebar were used in the tank floor, walls and roof slab.