REMEDIATION OF A MANUFACTURED GAS PLANT SITE IN PRESCOTT, ARIZONA

摘要

From the early 1800’s through the middle of the 20th Century, manufactured gas plantsrn(MGPs) generated gas from coal or oil to fuel lighting and heating throughout the United States.rnMGP sites vary in the types and quantities of wastes remaining, based on the feedstock andrnmanufacturing processes used. Inorganics, metals, VOCs, and polynuclear aromatic compoundsrn(PAHs) may be found at MGP sites. Last year Arizona Public Service Company (APS)rnremediated an MGP site in Prescott, Arizona, which operated from 1909 until 1949.rnSince 1992, APS conducted a series of investigations to characterize soil, groundwater,rnand surface water impacts from the former MGP operations and to evaluate the groundwatersurfacernwater interaction at the Site. Investigations found elevated concentrations of PAHs,rntotal petroleum hydrocarbons (TPH), benzene, cyanide, and lead in soil. Cyanide,rn(benzo(a)pyrene, and nitrate, were detected in groundwater collected from Site monitoringrnwells above applicable Aquifer Water Quality Standards (AWQS). In addition dense nonaqueousrnphase liquid was found in one groundwater monitor well and subsequently found inrnthe fractured bedrock beneath a portion of the facility. Groundwater impacts were veryrnlocalized. Water samples collected from Miller Creek occasionally have shown slightly elevatedrncyanide concentrations.rnIn 1999, APS developed and submitted a Remedial Action Plan (RAP) to the ArizonarnDepartment of Environmental Quality (ADEQ) Voluntary Remediation Program (VRP). AfterrnADEQ approval of the RAP, remediation began at the Site in late 1999 and was completed inrnJanuary 2001. The goal of the RAP was to remediate soil impacted by MGP-related compoundsrnto levels that are protective of human health and water quality to the maximum extentrnpracticable. A total of 101,000 tons of soil were excavated and treated. A total of 819,000 gallonsrnof water were treated and discharged to the sanitary sewer. Remediation activities wererncomplicated by several factors including: maintaining operations at an active substation andrnconstruction yard; installation of shoring around the substation; location near a residentialrnneighborhood; re-routing and restoring of Miller Creek; and, relocating and excavating aroundrnactive utilities, sewer lines, water lines and fiber-optic cables.