COMPLIANCE INFO - Laserfiche WebLink

Home Browse Search

Geosyntec"' consultants Based on the data collected, the CVRWQCB approved shutdown of the on-site SVE system in August of 2013. Considering that the soil vapor concentrations remaining in on-Site soil did not represent an unacceptable risk to human health and were protective of groundwater quality, the RWQCB approved closure of the on-Site soil source areas and permanent decommissioning of the SVE and air/ozone sparging systems in 2013 (Cal/EPA RWQCB, 2014). 2.5 Recent Investigation Between August and September 2020, Geosyntec conducted VI investigation activities in accordance with the CVRWQCB-approved Pilot Study Work Plan (Geosyntec, 2020). Activities included installing and sampling two multi-depth soil vapor probes, SG-100 and SG-101 (Figure 2). SG-100 has probes installed at 6.5 feet bgs, 13 feet bgs, and 25 feet bgs and SG-101 has probes installed at 6 feet bgs and 13 feet bgs where relatively higher permeability soils were encountered. SG-100 had PCE reported at concentrations of 22,000 µg/m 3, 620 µg/m3, and 710 µg/m3, in the 6.5-foot, 13-foot and 25-foot probe respectively. PCE was reported in SG-101 at concentrations of 410 µg/m3 and 120 µg/m3 in the 6-foot and 17-foot probes, respectively. The results of the shallow probe at SG-100 (22,000 µg/m3)was unexpected based on the results of the confirmation soil vapor sampling conducted in 2013. The highest concentration of PCE reported during the 2013 sampling was 600 µg/m3, which was reported in a soil vapor probe located in the near vicinity of SG-100. The 13-foot probe(620 µg/m3)and 25-foot probe(710 µg/m3), were also slightly greater than the highest historical concentration reported during the 2013 sampling. The 6.5-foot probe at SG-100 was resampled on 21 September 2020 and PCE was reported at a similar concentration of 24,000 µg/m3. 2.6 Potential Data Gaps It is unclear why the soil vapor remedy implemented did not affect the SG-100 sample location and the source and extent of the elevated PCE reported in shallow soil vapor at SG-100 in 2020 is currently unknown. The sanitary sewer lateral located approximately 30 feet west of SG-100, which is connected to the former Village Cleaners suite,has previously been identified as a release mechanism of dry-cleaner solvents to the subsurface. Additionally, SG-100 is located in close proximity to a former hotspot identified during the 1999 RI and these shallow impacts may not have been adequately addressed by the SVE system that operated from 1999 to 2013 in this area. The former SVE wells at the Site (SVE-3, SVE-5, and SVE-7) were screened from 10 feet bgs to 30 feet bgs.The elevated concentration of PCE in newly installed SG-100 are at 6.5 feet bgs,above the screened interval of the former SVE wells. As described in Section 2.3, the geology of the Site is highly stratified with interbedded layers of fine to coarser grained material. Boring logs from the installation of the SVE wells were not available for review; however, during the installation of SG-100, a sandy clay layer was observed from 9 feet bgs to 15 feet bgs, followed by a clay layer from 15 feet bgs to 17.5 feet bgs. These interbedded layers may have impeded the flow induced by the SVE wells to lower strata. Therefore, additional data is necessary to confirm that the elevated PCE concentrations in shallow soil vapor in the vicinity of SG-100 are localized and do not represent a VI threat or require additional remedial action. 202012 Lincoln Center Soil Vapor Assessment Work Plan 4 December 2020