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Ms. Mary Meays San Joaquin County December 6, 1994 Page 2 On 30 April 1993, hydropunch groundwater samples were collected adjacent to the four sides of the former limits of the excavation (this hydropunch sampling was documented in a report prepared by Treadwell & Rollo, Inc. dated 17 ,lune 1993 and titled "Report, Groundwater Sampling, 4110 Industrial Way, Tracy, California". This data was duplicated in the subsequent report, titled "Monitoring Well Installation, 4110 Industrial Way, Tracy, California", presented in Attachment D). Diesel was detected in the two samples from the north and west sides of the excavation at 0.2 and 0.4 parts per million (ppm), respectively_ Toluene was detected in a single sample at 0.0005 ppm. No other BTXE nor extractable (diesel) hydrocarbon constituents were detected. In a letter dated 10 August 1993, the San Joaquin County Health Services Agency (Agency), the local enforcement agency, requested additional work at the site including the installation and sampling of three shallow groundwater monitoring wells. In a phone conversation on 17 August 1993, the Agency agreed to a reduced scope of work which included the installation and sampling of a single well downgradient from the former excavation, as indicated by the results from the hydropunch sampling. On 29 September 1993, monitoring well MW-1 was drilled and installed, in accordance with conventional protocols, to a depth of approximately 21 feet within about five feet and north and west of the former limits of the excavation (Figure 2). The well construction and sampling of the soil and groundwater were documented in a report prepared by Treadwell & Rollo, Inc. dated 18 November 1993 and titled "Monitoring Well Installation, 4110 Industrial Way, Tracy, California" (Attachment D). No extractable hydrocarbons (diesel) nor BTXE were detected in a soil sample collected at the groundwater interface and only a trace level of diesel, (0.1 ppm) and no BTXE, were detected in the groundwater sample. This well was the focus of the subsequent quarterly monitoring discussed in greater detail in other sections of this report. Groundwater Monitoring - On September 29, 1994, our sampling technician purged and sampled the monitoring well following the methodologies described in greater detail in Attachment A, Protocol for Groundwater Sampling. A factory-cleaned, disposable, polyethylene bailer was used to both purge and sample the well_ The field parameters measured during sampling were recorded on a field data sheet which is duplicated and presented in Attachment B, Field Data. The groundwater sample was decanted into sample containers prepared and provided by a contracted analytical laboratory. These containers were labeled, placed into an ice-cooled chest, and transported to American Environmental Network (AEN), a California Environmental Protection Agency certified laboratory in Pleasant Hill, California. AEN also performed the chemical analyses for the samples collected during monitoring for the previous three quarters. The groundwater sample was analyzed for total petroleum hydrocarbons as diesel (GCFID 3510), benzene, toluene, xylenes-total, and ethylbenzene (BTXE) (EPA 8020). A trip blank was also analyzed for BTXE constituents. A copy of the laboratory analytical reports for these analyses and the chain-of-custody record are attached (Attachment Q.