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LFR Inc. 5.1 Groundwater Sampling To address objective 1), LFR recommends collecting groundwater samples for VOC analysis from locations along the sanitary sewer pipeline that serves the building. The first phase of this investigation would include completion of a utility survey and mapping of the sewer line that services the dry cleaning facility. Approximately three sampling locations would then be selected based on the layout of that line. LFR would provide the sewer line layout, and the proposed groundwater sampling locations prior to collecting the groundwater samples. After receipt of concurrence from the RWQCB and after obtaining required permits from San Joaquin County, LFR would oversee the collection of grab groundwater samples from each of the three proposed locations using a direct push/hydropunch method. Collected groundwater samples would then be submitted to a State-Certified analytical laboratory for analysis for VOCs using EPA Method 8260. Soil samples also will be collected from each of the boreholes to assess for the presence of PCE in shallow soil near the sewer line. Boreholes advanced for this phase of the investigation would be abandoned in accordance with the requirements set forth by San Joaquin County. 5.2 Soil Vapor Pathway Assessment As described in Section 5.0, a site-specific sub-slab-to-indoor air attenuation factor is needed in order to more fully assess the potential human heath risk associated with PCE detected beneath the dry cleaning facility. Direct measurement of PCE in indoor air is not possible due to contribution of VOCs to indoor air from the current operations of the dry-cleaning facility. Therefore, LFR proposes to use radon measurements to evaluate VOC transport through the building foundation to indoor air. Radon has been shown to be useful in evaluating vapor intrusion impacts since radon is a naturally occurring compound in soil gas with vapor intrusion as the primarily transport mechanism. In addition, indoor sources generally do not contribute to indoor radon concentrations. LFR recommends collection of radon gas samples inside and outside the building to establish radon concentrations in indoor air and ambient air. This data will be used to establish a site-specific sub-slab to indoor air attenuation factor, which will then be used to calculate potential concentrations of PCE in indoor air. These calculated indoor air concentrations will be compared against applicable regulatory levels, including the CHHSL. 5.3 Reporting Results of the groundwater and vapor intrusion assessment activities will be presented in a report that will be submitted to the RWQCB. The report will include a description of the methods used to collect data, an interpretation of those data, and LFR's recommendations. Page 8 rpt-SoilGaslnv-RobinhoodPlz-09366 J=08.dm:lfr