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, ; r w 12 May 1998 AGE-NC Project No 95-0121 Page 4 of 5 l r -DISCUSSION AND CONCLUSIONS Based upon data collected during-the February 1998 monitoring, AGE concludes • Generally, ground water monitoring data collected at the site flows toward the northeast However, based on a low ground water elevation observed at MW-9, ground water in the ' southern portion of the site may be flowing towards the southeast } • The approximate distribution of dissolved TPH-g in wells MW-1 through MW-9 is depicted in Figure 4 Well screen intervals are listed in Table 1 • The ground water surface elevation at the site continues to remain above the slotted screened f - intervals in wells MW-1'through MW-9 Therefore, samples collected irons these wells may not be representative of dissolved petroleum hydrocarbon concentrations in shallow giound water i • From November 1997 to February 1998, a substantial increase of dissolved petroleum hydrocarbons was observed from MW-3 Conversely, substantial decreases «ere observed from wells MWA, MW-2, MW-4 and MW-7 The substantial decreases could be attributed to the observed increases in ground water elevation • Due to instrument complications, the laboratory reported that the sample holding tames for h the 8260 analysis expired prior to laboratory analysis • The greatest concentrations of dissolved petroleum hydrocarbons continues to be in the area of wells MW-1 througli,MW-4 and MW-7;near the `core" of hydrocarbon-impacted soil •` The laboratory reports for MW-1 through MW-9 indicated that detections by TPH-d analysis had non-diesel,chromatographic patterns and/or that the detections were probably the result of gasoline interference , i • Concentrations of benzene'detected in MW-I.through MW-4 and MW-7 were above the 'State of California Maximum Contaminant Lvels (MCLs) for drinking water'of 1 0 ppb The approximate distribution of dissolved benzene in wells MW-1 through MW-9 is depicted in'Figure 5 Well screen intervals are listed in Table l ' • , Concentrations of toluene exceeded the State of California MCLs of 150 ppb in wells MW-3 and MW-7, concentrations of ethylbenzene and xylenes exceeded MCLs of 700 ppb and 1750 ppb in well MW-3 ' ` Utilizing EPA methods 8020 and 8260, concentrations'of,MTBE were detected at concentrations greater than the State of California Action Limit of 35 ppb in ground water samples collected from MW-5 ` • Further assessment northeast of MW-4 and west to northwest of MW-7 will be necessary to A6anced CcoEmironmentat,Inc