SITE INFORMATION AND CORRESPONDENCE

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Ernesto Renteria, Jr. March 12, 2015 Pimentel Property Page 3 of 4 1650 S. EI Dorado Street Stockton, CA 95219 uncertainty that the one vapor point sampled in the former dry cleaning area was near the point most likely to have been at a release point; the EHD is of the opinion that this uncertainty can be reduced by identifying the location(s) of the former dry cleaning equipment or increasing the number of sampling points in the former dry cleaning facility building footprint. It seems a bit surprising that the one soil gas sample not to contain detectable concentrations of PCE was the one collected within the suspected footprint of the former facility building. The EHD also recommends sampling along the former sewer line if it still exists and its location can be determined; the CVRWQCB also recommends videotaping the sewer line interior to identify potential release points to guide the selection of sampling points. The CVRWQCB thought the sample with a high leak-detector concentration should be resampled, with which the EHD concurs. The CVRWQCB also thought the three-foot soil gas sampling depth needed to be justified or the samples collected from the more commonly utilized five-foot sampling depth, which the EHD also recommends; the deeper, standard depth may help minimize the potential compromising of sample integrity by leakage of atmospheric air. Any additional soil gas sampling should incorporate a methodology for quantifying the effects of atmospheric leakage, if detected, on the analytical results. The soil and groundwater data collected from boring B3 shows that there was a release in the area of the suspected former UST system and the soil discoloration, odor and analytical data demonstrated that the boring was located in or near the point of release. The lack of detectable BTEX in the B3 soil samples is consistent with an aged, biodegraded petroleum fuel release, as is the lack of benzene and minimal toluene, ethylbenzene and xylenes in the B3 groundwater sample. However, the sample does show that groundwater was impacted by the release. As groundwater has been impacted, current practice is to determine the depth of the impact as well as the lateral extent. The depth, or vertical extent, of impacted groundwater has not been demonstrated, however, if it can be shown that the groundwater samples collected from B1, B2 and/or B7 are downgradient of B3 and are from the sandy interval encountered at 35 feet below surface grade (bsg) in B7, and deeper contamination is not encountered, the EHD will consider the lateral extent of impacted groundwater to be adequately demonstrated at this time. The EHD cannot issue a letter stating that the investigation of possible UST and dry cleaning releases is complete, poses minimal environmental or human health risks, and that further investigation is not necessary until the following items have been adequately demonstrated: • All data QA/QC elements have been reported and are satisfactory, • The soil gas sampling density in the former dry cleaning facility building footprint is sufficient for reasonable confidence that any releases from the equipment or plumbing have been detected; • The vertical and lateral extent groundwater impacted by the suspected UST release has been delineated; and • Currently known and any additional contamination encountered on the site does not pose a significant threat to human health or the environment. To address the items noted above, please submit a work plan to acquire the data needed to complete the site characterization. The EHD will review the work plan for adequacy and comment on it. Please include the analytical results for PCE on all tables of relevant data in future reports.