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Report of Secondary Investigation 6 Preeared for Barbara Drake,26485 Thornton Rd Thornton, CA May 4 1995 QA/QC standards for the laboratory method When questioned on the chemical makeup of the interferant,the laboratory noted that the chromatogram patterns indicate a heavier-end fuel pattern such as kerosene or diesel fuel Copies of laboratory analyses reports and chain-of-custody manifests for the soil samples collected February 16, 1995 are included in Appendix D 53 Analytical Results of Groundwater Samples Analytical results of groundwater samples obtained from 61 through B10 are summarized to Table 3 All groundwater samples collected were below laboratory reporting limits for BTEX and TPH-G with the exception of the sample from B3 which contained 0 51 pg/L ethylbenzene and 0 57 Pg/L total xylenes The detection limits were raised during the analysis of four (61, B2, B3, B9) of the 10 groundwater samples due to the presence of non-target analyte Interferences Laboratory analysts working on the project indicated that the chromatogram patterns resemble heavier-end fuels such as kerosene and/or diesel fuel Appendix D contains chromatograms for the daily method standards and each anomalous water sample Copies of laboratory analytical reports and chain-of-custody manifests for the groundwater samples collected February 16, 1995 are included in Appendix D 6.0 CONCLUSIONS AND RECOMMENDATIONS 61 Conclusions Sall samples collected by Groundwater Technology Indicate that shallow soils consist predominantly of varying mixtures of silt and clay Based on the data collected during previous environmental investigation, and data collected during January and February 1995, It appears that gasoline-range hydrocarbons in soil are concentrated in the area previously defined by Wallace-Kuhl (August 1994) However, it appears that other compounds not specified by the TPH-G analysis may be present in soil near sampling locations B4, B5, B8, B9 and 810 Boundanes of hydrocarbon-impacted groundwater have been refined by the results of this Investigation Gasoline-range petroleum hydrocarbons dissolved in groundwater are confined to the east by B2 and B10,to the south by B3 and B5,to the west by B4 and MW-1 to the north by B6 Impacted groundwater in MW-3 does not appear to be continuous with Impacted groundwater in the UST-pit area despite its downgradient location The abnormal chemistry noted in the samples appears to be widespread and recurring Abnormal chromatography has been noted in previous groundwater samples collected dunng quarterly groundwater sampling events The previous site owner has confirmed that no other fuel was stored in USTs at the site,therefore, the source of the abnormal chemistry must be naturally occurnng, an unknown UST, or a surface source D053EAR RPT GROUNDWATER ❑L�❑ TECHNOIACY