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t28 June 1995 <br /> AGE-NC-95-0112 <br /> Page 3 of 4 <br />' container, and transported under chain-of-custody to Alpha Analytical Laboratories(AAL) in Ukiah, <br /> California. All samples were analyzed for TPH-g and BTE&X in accordance with EPA methods <br /> 5030/8015m and 602, respectively. <br />' 4.0. FINDINGS <br /> 4.1. GROUND WATER ELEVATION AND FLOW DIRECTION <br />' The relative elevation of ground water in each well was calculated by subtracting the ground water <br /> depth from the surveyed casing elevation (Table 1). Ground water elevation has risen an average of <br /> 2.00 feet since the January 1995 monitoring event. <br /> Ground water flow continues to slope to the southwest at the site (Figure 3). The overall gradient <br />' is similiar to that of previous calculations. However, unlike previous calculations, the gradient <br /> steepens significantly between MW-1 and MW-3. <br /> 4.2. LABORATORY ANALYSIS OF GROUND WATER SAMPLES <br />' TPH g was detected in samples from MW-1, MW-3, MW-4 and MW-5 at concentrations of 3 7,000 <br /> pg/l(parts per billion: ppb),20,000 ppb, 260 ppb and 180 ppb, respectively. BTE&X were detected <br /> in samples from MW-1, MW-3 and MW-4 at concentrations ranging from 0.53 ppb (ethyl benzene, <br />' MW4)to 6,900 ppb (benzene,MW-1). Petroleum hydrocarbons were not detected in samples from <br /> MW-6,MW-7 or MW-8. The analytical results of all water samples are summarized in Table 2. The <br /> laboratory report and chain-of-custody are included in Appendix B. <br /> 5.0. CONCLUSIONS & RECOMMENDATIONS <br />' 5.1. HYDROCARBON-RvIPACTED GROUND WATER <br />' Petroleum hydrocarbon concentrations continue to fluctuate at the site. However, hydrocarbon <br /> impacted ground water continues to be centered near MW-1. Wells MW-6, MW-7 and MW-8 define <br /> the up-gradient portion of the dissolved hydrocarbon plume; MW-5 remains near the down-gradient <br /> extent of the plume. <br />' Since installation in 1993, petroleum hydrocarbons have not been detected in wells MW-6 or MW-8. <br /> Therefore, we recommend reducing the sampling frequency of MW-6 and MW-8 to twice-yearly. The <br /> next quarterly ground water monitoring at the site should be scheduled for July 1995. <br /> 1 <br />