In 1941, limestone was excavated from a quarry four miles south of the Weldon Spring Site to construct the roads and building foundations for the Weldon Spring Ordnance Works (WSOW). From 1942 to 1969, the quarry was used to dump the debris generated from the cleanup efforts of the WSOW and various U.S. Department of Army and U.S. Atomic Energy Commission operations.
The nine-acre quarry site was placed on the National Priorities List as a Superfund Site in 1987 due to the perceived threat to drinking water wells that were located less than a mile away. In 1989, the U.S. Environmental Protection Agency expanded the National Priorities List designation to include the chemical plant area. This combined listing was designated as the Weldon Spring Site.
Dewatering the Weldon Spring Quarry was the first step in the cleanup of the quarry. In May 1989, the U.S. DOE obtained a National Pollutant Discharge Elimination System (NPDES) permit issued by the Missouri Department of Natural Resources to treat and release the impounded water at the quarry. Water pumped from the quarry was treated to remove its chemical and radiological contaminants, tested to confirm compliance with permits, and released through a pipeline to the Missouri River. The Quarry Water Treatment Plant began treating the contaminated water in 1992. Over 70 million gallons of water were treated at the plant during operations between 1992 and 2001.
The next step in the cleanup of the quarry was to remove the bulk waste. The U.S. Environmental Protection Agency and the U.S. Department of Energy signed a Record of Decision (ROD) in March 1991 approving the removal of the bulk waste at the quarry. Bulk waste removal was completed in 1995 after more than 120,000 cubic yards of contaminated soil, metal, rock and building rubble was removed from the quarry.
In September 1998, a second Quarry ROD was approved. This ROD addressed residual contamination in the groundwater under and immediately south of the quarry. The decision provided for long-term monitoring to ensure that conditions at the quarry and the well field will remain protective of human health and the environment.
The final phase of cleanup at the Weldon Spring Quarry was restoration of the quarry site. Restoration was completed in 2002.
The quarry bulk waste was excavated from the quarry and transported to the Chemical Plant site. The four-mile haul road from the Weldon Spring Quarry to the Chemical Plant was dedicated solely to bulk waste hauling, thus eliminating any traffic on state Highway 94. The waste was then placed on an engineered lay down pad within the Chemical Plant boundary.
The temporary storage area was an engineered storage facility for sorting, characterizing and temporarily storing bulk waste excavated from the quarry. The 11-acre storage area, located near the southwest corner of the chemical plant, was designed and constructed to meet the substantive requirements for a Resource Conservation and Recovery Act (RCRA) waste pile. Separate subareas were constructed to store segregated wastes, and a double-lined surface impoundment collected rainfall runoff and leachate generated from the stored wastes. The water collected at the temporary storage area was treated at the Site Water Treatment Plant.
The Record of Decision for Quarry Residuals outlined the performance of field studies to support the selected action of long-term monitoring. These field studies consisted of installing a groundwater collection system (interceptor trench) and operating it for two years. The groundwater collected in the trench was sampled, analyzed, pumped to a collection basin, treated and discharged to the Missouri River.
Restoration of the quarry included backfilling the quarry and dismantling the Quarry Water Treatment Plant. Backfilling of the quarry reduced the physical hazards associated with excavated areas such as rock benches, open fractures, ponded water, and potential instability in the high wall. Converting the haul road to a hiking and biking path and final grading of the quarry was the last phase of restoration. The final grade minimizes erosion and returned the area as near as possible to its natural state.
