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EPP t Coca-Cola Enterprises - West Job No. 90054 3.5 GROUNDWATER ELEVATION MEASUREMENTS Groundwater monitoring was performed in all groundwater monitoring wells on September 17, 1990. The free product was checked and the depth to water was measured in each well to the nearest 0.1-inch using a calibrated electronic interface probe (Photograph No. 5). Prior to monitoring each well, the interface probe was decontaminated using an Alconoxm detergent wash followed by a distilled water rinse,an isopropyl alcohol rinse,and a final rinse of distilled water. The depth to groundwater measurements and the water table elevation data are presented in Table 2. Groundwater elevation data is based on a well head s,irvey conducted by Mid-Valley Engineering, Inc., Modesto, California. The well elevat;ons were established from level circuits carried from the City of Stockton Benchmark No. 77. The accuracy of this survey was plus or minus 0.02 feet. The groundwater elevation results are discussed in Section 6.5. 3.7 GROUNDWATER SAMPLING - Groundwater samples were collected from groundwater monitoring wells MW-1 through MW- 3 in August, 1990,and from wells MW-4 and MW-5 in September, 1990. In order to minimize the potential for cross-contamination during the sampling process,work proceeded in order from the wells with the least reported or suspected contamination to wells with increasingly contaminated water. All items used within the well (including the bailer and electronic interface probe) were decontaminated between each sample in accordance with the procedures outline in f.a Section 3.10. ' 3 3.8 SOIL VAPOR A40NITORING Soil vapors were monitored in each boring with an HNU model PI 101 photoionization detector f ' (PID) equipped with a 10.2 electron volt(eV) lamp. For each sample interval,the lower sample retainer was promptly removed from the drive sampler barrel and transferred to a labeled F , "ziplock" style plastic bag (Photograph No. 4). The sample was then disaggregated and allowed to stabilize under ambient conditions for a minimum of fifteen minutes. The HNU probe was then inserted through the seal of the plastic bag into the "headspace" above the soil } sample. The highest HNU readings were.then recorded in parts per million (ppm) on the a.:J .