cornhusker army ammunition plant

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The former Cornhusker Army Ammunition Plant (CHAAP) is located in the east part of Hall County, Nebraska, approximately three miles west of the City of Grand Island, and consisted of 12,042 acres. The former CHAAP was owned by the U.S. Army, but was operated by a contractor, making it a government-owned/contractor operated (GOCO) facility. The plant was built in 1942 to produce munitions and provide support functions during World War II, and produced bombs, artillery shells, boosters, mines and rockets. It has been in and out of production over the years. The plant consists of five main components: five major production areas where munitions were loaded, assembled, and packed; a fertilizer manufacturer; two major storage facilities; sanitary landfills; and burning grounds where materials contaminated with explosives were ignited. When the plant was active, staff disposed of wastewater contaminated with explosives into 56 earthen surface impoundments, which were located near the five production areas. Dried solids from the bottom of the pits periodically were scraped and ignited at the burning ground. The site was active intermittently from 1942 to 1973, producing munitions during World War II, the Korean War, and the Vietnam War. Between the wars, and after 1973, it was kept on standby status. During operation, the principal explosive compounds used during munitions production at CHAAP were 2,4,6-trinitrotoluene (TNT), cyclonite (RDX) and, to a lesser extent, cyclotetramethylenetetranitramine (HMX). Other chemical materials used to support munitions production included freon, p aints, grease, oil, and solvents. Solvents reportedly used at CHAAP included acetone, trichloroethylene (TCE), and 1,1,1-trichloroethane (1,1,1-TCA). During the CHAAP ammunitions production years, a total of five Load, Assemble, and Pack load lines (LL) were the major production areas and centers of operations. The ammunitions production required the use and disposal of large amounts of water. The explosives wastewater operations included: screening, melting and mixing, rod and pellet manufacturing, remelt and refill, and washing and laundry. The site received the explosives in flake form. It was screened and sifted for material handling purposes and was used to incorporate explosives (2,4,6-TNT and RDX) into munitions. The explosives wastes and residues associated with munitions loading, assembly and packing operations resulted in a ground water contamination plume that originated near the CHAAP load lines and extends northeastward toward Grand Island. One of the contamination pathways, wastewater, was generated by the ventilation systems where the explosive dust from the screening operations was collected and washed from the air with Schneible units (wet scrubbers). The water from the Schneible units ran through settling tanks and was recycled, leaving excess wastewater. Additional wastewater was also generated from periodic machinery and interior building surfaces wash-down. Some wastewater ran via interior building drains into a sack sump (concrete pit) where a filter bag (made of canvas-like material) was placed to collect the solid explosive particles. Then the wastewater was transferred via open concrete channels into circular earthen impoundments. The walls of the impoundment were masonry-lined, with the bottom open to the sand and gravel strata. One overflow channel was routed from the impoundment to the leaching pit that was designated to handle any water that did not filter into the bottom of the impoundment. This overflow occurred due to the limited filtering capacity of the sack sump to trap explosive p articles. The particles were periodically scraped from the bottom of both the earthen impoundments and leaching pits, and ignited at the burning grounds (CHAAP-005 OB/OD Area, OU5) located in the northwest section of CHAAP in tract 19. CHAAP has been on standby status since 1973, the operation leases land for agriculture, grazing, and wildlife management activities. During the time of site inactivity, some of the buildings on site may have been used for grain bin activities. On July 22, 1987, the CHAAP was listed on the National Priorities List ( NPL) due to ground water contamination resulting from site operations. As a consequence of common disposal practices during war time, ground water was impacted by explosives. Ground water containing explosive residue migrated from the cesspools and leach pits located in the center of the plant approximately two miles beyond the CHAAP boundary into the Grand Island City limits. The CHAAP was declared excess property and most maintenance ceased in 1989. At the time of the Interim Record of Decision (ROD) for Operable Unit 1 (OU1) in 1994, the affected ground water encompassed a disjointed area six miles long and one-half mile wide. Nitrates were also detected in ground water. However, these may have originated from other sources, including agricultural activities in the area. Geology & Hydrology – Grand Island Formation Aquifer The geology of the site consists of approximately 3 to 20 feet of loess deposit, which are underlain by 50 to 100 feet of Quaternary age sand and gravel. These deposits are the primary source of ground water in Hall County. The ground water flow direction from the site is towards the east-northeast. The depth of the ground water ranges from 5 to 35 feet beneath the ground surface at CHAAP. Shallow ground water underlying CHAAP occurs as an unconfined water table aquifer within the alluvial sands and gravels. Historically, the water table surface has generally been less than 10-feet below ground surface (BGS). Total thickness of the water table aquifer ranges from about 50 to 60 feet. Hydraulic conductivity values range up to 670 feet per day. T he predominant ground water flow direction with the water table aquifer near CHAAP is to the northeast toward the city of Grand Island. Regional horizontal gradients of 4 to 7-feet/mile have been measured in the area. The Grand Island formation aquifer is used regionally as a water supply source for irrigation and potable water. Locally, there are a number of irrigation wells in use east of CHAAP. However, in the vicinity of the existing explosives contaminated plume, all private, domestic water is being supplied by the City of Grand Island. The City’s municipal well field is located southeast of the city near the Platte River (approximately 10-miles southeast of CHAAP). Fullerton Formation Aquitard - The underlying Fullerton clay unit is a relatively low- permeability unit that appears to act as a barrier to ground water flow (i.e., aquitard). Holdrege Formation Aquifer. - The sands and gravels of the Holdrege Formation act as a confined aquifer unit (confined by the overlying Fullerton clay unit). Water level data from deep monitoring wells indicate that the general ground water flow direction appears to have a northeasterly component (similar to the overlying Grand Island Formation aquifer).