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1 1� Working To Restore Nature Descriptions of soils encountered and monitoring well construction details were recorded on the boring/well log presented in Attachment 1 Soils encountered were monitored for organic vapors by placing a small amount of representative material in a sealed container, then measuring the concentration of volatiles collected in the head space of the container with a photoionization detector (PID) calibrated to the benzene molecule The values obtained at each measurement point were recorded on the boring logs --,0 evidence of soil"contamination was noted during drilling. ;Soil cuttings generated during the-drilling, process were contained on-site in a DOT approved 55-gallon drum Subsequent to installation, the monitoring well was developed using a pump and surge method Development water was contained in DOT 17H drums and is currently stored on site The well development log is included in Attachment 2 GROUNDWATER MONITORING Groundwater monitoring and sampling was conducted by RESNA personnel on September 20, 1993. Water level measurements were collected from each monitoring well prior to purging and sampling Water levels rose in wells MW3 and MW5 (nearest honker cut) and dropped in wells-' MW1, MW2 and MW4 since the last monitoring event in June 1993 (Table 1) A groundwater gradient map was created using the data collected on September 20, 1993 (Figure 3) Groundwater flows northeast, away from the slough, with a gradient of 0 067 feet/foot or approximately 354 feet per mile Subsequent to monitoring, each well was purged by extracting approximately 3 well casing volumes. While purging, the groundwater parameters (temperature, conductivity, and pH) were monitored and allowed to stabilize before water samples were collected Samples were collected using dedicated, disposable bailers with bottom emptying devices to reduce volatilization The samples were transported to and analyzed by state-certified Argon Mobile Labs in Ceres, California All purged groundwater was contained in DOT approved 55 gallon drums and remains on site pending appropriate disposal The well purge logs are included in Attachment 2 Samples were analyzed for benzene, toluene, ethylbenzene, and total xylenes (BTEX) using EPA Method 8020, and total petroleum hydrocarbons as gasoline (TPHg) and total petroleum, hydrocarbons as diesel (TPHd) using modified EPA Method 8015 Monitoring well MW4 did not contain enough water to collect a sample for TPHd analysis ; Monitoring Wells MW1, MW2, and MW3 did not contain detectable concentrations of the petroleum hydrocarbon constituents Newly installed well,MW6 contained only toluene at 38 parts per billion (ppb) Monitoring wells MW4 and MW5 contained low to moderate levels of benzene, xylenes and TPHg TPHd was not detected _in _any _sample ' The lapproximate extent of dissolved contaminants (benzene) is shown on Figure 4 Analytical results are summarized in Table 2 Laboratory reports with chain-of-custody documents are included in Attachment 3 jProj Disk13QR-1993 FNL} 2