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aLHL- a-m7e15 Claw laws ,ar,an „m Evans Us,subo,caat Iss,2017 3) Extracting and treating VOCs in Easmrn USA ground water to reduse VOC cnnecntralions to meet ground water cleanup standards. 'Ile remedial objective was to reduce VOC concentrations In meet cleanup standards in all impacted ground water. 'Ile cleanup standards for ground water in the GSA OU were set at MCLs (Table 1). The ROIL indicated that when V0C concentrations In ground water were reduced m MCL cleanup standards, the ground water extraction and treatment system could be shut OR and placedonsfndley. Ground water was to he monitored fur a period of five years following system shutdown to verify that contaminant concentrations remained below cleanup standards. 2.5. Remedial Design for the Eastern GSA Ground Water Extraction and Treatment System Following remedy selection in the 1997 GSA ROD, the Remedial Design forthe GSA OU was issued in 1999. Because the ground water saturation and treatment remedy that was used during the Eastern GSA removal action was retained as the long-term remedial action, the Remedial Design report documented and updated design specifications, performance standards, and conards and safrguards. It also included requirements for close out based on the cleanup standards selected in Me ROD. Remedial action cnnsWction completion for the entire GSA OU was inspected by EPA and documented in 2005. The Eastern GSA second water extraction and treatment system was designed to pump ground water from Three extraction wells brand dovmmadient of the debris burial trench area at a combined now rate of45 gallons per minute (gpm). VOCs were removed from catrected ground water by throe I ,t if-pound aqueous-phase granular activated carbon units mmosecorimseries. The effluent from the Cameo GSA treatment system was discharged (a Corral Hollow Creek under a National political Discharge Elimination System pounih. and later Substantive Requirements issued by the R WQCB. Details of the design of the motem GSA ground water extraction and treatment system can be found in the Remedial Design far the GSA OU (Rueth et al, 1998). 2.6, Cleanup Activities Performed in the Eastern GSA Ground water extraction and treatment in Me Eastern GSA to remove TCE and other VOCs began as a non-tune-critical removal action in 1991 and continued as a remedial action after the GSA ROD was signed in 1997. In addition On ground water extraction and treatment, monitoring of ground water was conducted to evaluate the effectiveness of Me remedy in achieving cleanup standards, and to ensure there is an impact to downgradient water-supply wells. 3fie treatment facility influent and effluent were monitored to ensure compliance will Me treatment facility effluent discharge limits. The effluent receiving surface water in Corral Hollow Creek was also monitored m evaluate potential surface waterquality impacts. Figure 3 presents the Eastern GSA OU site map showing monitor, extraction, and water supply wells, and the former ground water extraction and treatment facility. A Risk and NBrard Management Program, including i otitutiona land use controls, was also implemented to prevem human expomrc to contamination and to prolect the integrity of the remedy. As discussed in Section 2.3. the only unacceptable risk identified in Me baseline human health risk assessment for the Eastern GSA was associated with Me proadid ingestion of Wound water ping VOCs at concentrations exceeding drinking water MCLs (cleanup standards). Because Me MCI, cleanup standards am protective under a residential and unrestricted land use,