2011 Issue

23 S INCE THE NINETEEN forties, munitions and explosive were produced for military, mining and other uses fol- lowing World War II, at the Trojan explosives plant at the mouth of Spanish Fork Canyon [Figure 1]. The facility previ- ously was owned and operated by Cytec Industries of Delaware and Mallinckrodt Inc. ofMissouri. In theeighties, theEnsign- Bickford Company purchased the plant and operated until shutdown in 2006. In the past, wastewater frommanufactur- ing operations was usually discharged to open trenches and unlined ponds for evaporation and percolation to the ground, until the advent of rules for water pollution control. In themid 1980s, waste- water disposal practice was upgraded to a discharge to a two-cell lagoon with synthetic liner in the hope of preventing groundwater contamination. In 1986, the lagoon began leaking excessively, result- ing in release of over one million gallons of concentrated fluids that containedboth nitric acid as well as explosives constitu- ents such as: RDX – the British research department explosive hexahydro-1, 3, 5-trinitro-1, 3, 5-triazine; HMX — octo- gen, a powerful and relatively insensitive nitroamine high explosive, chemically related to RDX, variously listed as High Melting eXplosive, Her Majesty’s eXplo- sive, High-velocity Military eXplosive, or High-Molecular-weight rdX, octahydro-1, 3, 5,7-tetranitro-1, 3, 5, 7-tetrazocine; PETN — pentaerythritol tetranitrate, a nitrate ester of pentaerythritol, a polyol; and other explosive constituents. These compounds ultimately found their way into the groundwater. As a result of this liner failure, the plant ended discharg- ing wastewater to the failed lagoon, and began conveying it to the Spanish Fork wastewater treatment plant. The stratigraphy of the valley fill com- prises alternating Quaternary Lake Bonneville laccustrine and alluvial fan deposits. The impact on groundwater occurs below a clay layer creating confined aquifer conditions, also referred to as the re- gional aquifer. This clay layer thins eastward, and is not present be- low the source, thus allowing fluids to travel and become trapped under the confining layer. Groundwater flow in the region of impact is primarily to the north, influenced both by fa- cies changes, geologic structure, as well as groundwater flow de- rived from the losing flow of Spanish Fork River as the river enters Groundwater Remediation: A Case Study Keith Eagan, P. G. Kiran L. Bhayani, P. E., D. EE., F. ASCE Explosive constituent concentrations may take decades to achieve cleanup criteria of two micrograms per liter for RDX based on the current the US Environmental Protection Agency’s health advisory in the regional aquifer. the valley fill just south of the facility, and numerous ephemeral streams coming off the adjacent Wasatch Mountains. Initial investigations focused on a nitrate plume that originated fromthe reactionof nitric acid and carbonate substrate. Early in 1990, the investigation was extended further for off-site tracking of the nitrate plume. By 1992, it became apparent that geologic structure and facies — a regime dictated by sedimentation, reflecting a particular process or environment — were the controlling factors for dispers- ing the contamination. Facies along the Wasatch Mountain front rapidly change from coarse to fine in a westerly dipping direction concurrent with the Wasatch Fault. This geologic fabric and structure directed fluids to the north rather than to thewest, as wouldbe predictedbased on regional groundwater flow. In 1994, offsite discovery of explosive constituents were detected in two moni- toring wells and one public water supply well [Figure 2]. The impacted public water supplywell,MapletonNo. 1, is nearly three miles away fromthe source. TheMapleton No. 1 well is not supplying water to the drinking water system of Mapleton City. With the discovery of explosive constitu- ents in the drinkingwater well, a forty-two monitoring well network was established to ascertain the extent of contamination. This network consistedmostly of installed monitoringwells, but also included several private wells. The planning for remediation measures involved the analyses of several available methods of treatment. A pump and treat approach incorporating the granular activated carbon treatment technology began removal of contaminants from groundwater in 1998. The impacted area Figure 1. Location.