SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

Preferred Remedial Alternative DOE/LLNL, U.S. EPA, RWQCB, and (i.e.,5 ppb forTCE)are reached in both DTSC believe that Alternative 3b is the best the regional and shallow aquifers. remedial alternative,considering the CERCLA Modeling predicts that ground water evaluation criteria. extraction will reduce ground water In summary, the preferred remedial alter- VOC concentrations in the central GSA native 3b includes the following components: and eastern GSA debris burial trenches • Monitoring to be conducted throughout area to MCLs within 55 years and 10 the predicted 55 years of remediation years, respectively. plus 5 years of post-remediation moni- The estimated 60-year present-worth cost toringfor the preferred alternative 3b is$19,750,000. • Contingency point-of-use treatment us- Alternative 3b is protective of human health ing aqueous-phase carbon adsorption for and the environment. The risk reduction com- three off-site water-supply wells. ponents of this alternative are readily imple- • Restrictions on access and procedures mentable with modifications to the existing for construction in the area. ground water and soil vapor extraction and • Soil vapor extraction and treatment by treatment systems. Figures 9 and 10 show sche- carbon adsorption in the central GSA dry matic drawings of the proposed soil vapor and/ well source area. Soil vapor extraction or ground water extraction and treatment sys- will be conducted to reduce VOC con- tems in the central and eastern GSA, respec- centrations in soil vapor to levels pro- tively. tective of ground water(i.e.,MCLs)and Ground water and soil vapor extraction and to mitigate VOC inhalation risk inside treatment are established remedial technologies Building 875. Modeling indicates that and,since functioning treatment systems are al- the remediation goal of 360 ppbV/V will ready in place, they will readily fulfill the re- be reached within 10 years. The evalu- quirements of the evaluation criteria. ation criteria for reaching the soil vapor However, other more innovative technolo- gies will continue to be considered for applica- extraction remediation goal will be dis- cussed in detail in the ROD. tion to the GSA throughout the process of re- Extraction and treatment of ground wa- mediation. These technologies may be intro- ter by air stripping and/or carbon adsorp- duced into the process if site conditions change tion in the central GSA dry well area and or technology development and testing indicate the eastern GSA debris burial trenches a potential for cost-effective and expedited re- area until MCL drinking water standards mediation. 14