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Map ID MAP FINDINGS Direction Distance EDR ID Number Elevation Site Database(s) EPA ID Number TRACY DEFENSE DEPOT(USARMY) (Continued) 1000182407 contamination exceeding cleanup standards at depths below the groundwater table because the ROD does not require excavation below the groundwater table. All excavation and confirmation soil sampling activities were completed on November 21,2002.Backfilling of the excavation and the hauling of waste off site were completed on December 18,2002.Over 17,000 cubic yards(more than double the quantity estimated in the ROD)of material were excavated,transported,and disposed of off site.Installation of the ROD specified new monitoring well (LMI7BAU)was completed downgradient of the excavation on February 24,2003. LM097AU,which was abandoned because of its location within the excavation area,was replaced with LM097AUA on February 24,2003. In response to confirmation sampling results,the excavation at SWMU 8 was expanded to more than double the design volume.Although soil concentrations exceeded the ROD cleanup standards,it was determined that all contaminant concentrations had been reduced to levels below risk-based cleanup levels identified in the ROD and were unlikely to pose a risk to the environment.This led to a decision to backfill the excavation prior to the onset of winter rains(rain pooling in the excavation might have increased the rate of residual contaminant migration). SWMU 20 SWMU 20 is the site of a former aboveground solvent tank that was located in Building 10.The site also included two sumps associated with discharge from Building 10 to the former industrial waste pipeline(SWMU 33).A variety of VOCs and SVOCs were detected in sludges collected from the sumps,floor drains,and soil samples at SWMU 20. Unexpected field conditions resulted in two phases of excavation at SWMU 20.The first phase occurred between September 1997 and July 1998.Sumps in the vicinity of manhole W-3 and a sump adjacent to SB204 near Building 10 were first pressure-washed to remove residual sludge and then demolished.A concrete slab discovered during the preoonstruction sampling effort for SB204 at 9 feet bgs turned out to be the foundation for a former underground storage tank.This tank was not identified during the RI/FS,but it significantly altered the approach to the remedy.Soil samples collected in the vicinity of SB204 below the concrete foundation had total petroleum hydrocarbon(TPH)concentrations between 15,000 and 100,000 microgram per kilogram(ug/kg),which exceed the cleanup standard.The remediation contractor installed sheet-pile shoring and proceeded to perform excavations at both SB204 and manhole W-3.Approximately 27 cubic yards of soil were removed during this phase of the excavation.Soil samples collected from the base of the SB204 excavation and sidewalls exceeded ROD cleanup standards for Dieldrin,trichloroethene(TCE),ethylbenzene,and TPH.The first phase of excavation was halted when further excavation could not be safely performed without a new shoring design.The excavation was filled with control density fill and the contractor demobilized. In June 1999,a second phase of excavation was performed at SWMU 20.An additional 305 cubic yards of soil were excavated at this time(resulting in a total excavation of approximately 332 cubic yards,over 30 times the 10-cubic-yard excavation anticipated in the ROD).Based on the results of confirmation sampling,soil containing contaminants of concern(COCl)at concentrations greater than cleanup standards still remains at SWMU 20.Other constituents have been removed to ROD cleanup standards. SWMU 33 In 1972,an existing pipeline and a storm drain were interconnected to form the industrial waste pipeline(IWPL) at SWMU 33.The IWPL is constructed of 4-inch to 7-inch-diameter pipe of varying composition and is buried to a depth of approximately two to four feet below grade.Eight manholes are located along the pipeline.The pipeline consists of two major segments that are referred to as the south industrial waste pipeline(SIWPL)and the east industrial waste pipeline(EIWPL).The total length of the SIWPL and its branches is approximately 1,200 lineal feet. The total length of the EIWPL and its branches is also approximately 1,200 lineal feet.Use of the IWPL has been discontinued.A removal action has already been performed to accomplish the excavation and pipe grouting TC3372962.1s Page40