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Ge0bg1cal rechAks lnr Page 9 ' Groundwater Monitoring Report Project No 723 2 June 21,2006 displayed a decreasing trend until early 2004 and an increasing trend for the past two years The steep decline in the initial concentrations suggests that the contaminants I detected in the well were initially a drilling artifact The recent events suggest that the well intercepts the bottom of the plume o Oxidation-Reduction Potential (ORP) and Dissolved Oxygen (DO) measurements (Table 7) show that most of the wells monitored are screened in areas of the groundwater plume that are affected by the biodegradation reactions occurring within the plume The low to highly negative ORP values indicate that the wells are within the halo of reaction depleted water caused by biodegradation of the contaminants The low DO values of the wells also reflected this condition Several of the CMTrm wells had unusually high ORP values (both positive and negative) suggesting a methodology problem in the field ' 3.0 CONCLUSIONS & RECOMMENDATIONS Conclusions 1 Groundwater flow trends northeast to east The southerly flow direction recorded on December 4, 2000, appears to be anomalous The deepest set of CMTrm wells displayed a groundwater mound in the vicinity of MW-101 with divergence to the northwest and northeast It appears the deepest groundwater level monitored experiences periodic reversals from the easterly directions exhibited in the shallower levels Additional data is needed before reaching any definitive conclusions 2 High levels of BTEX and TPH-G are present in the groundwater of all six on-site shallow and intermediate monitoring wells (MW-1 through MW-6) 3 The main mass of contaminants has migrated to a depth of 45 to 70 ft bgs, indicating that the contaminants are mobile 4 Cross gradient deep well MW-207 has displayed an increase in contaminant concentrations since October 2004 (it was non-detect for TPH-G this event) This probably represents the edge of the advancing plume S Down gradient wells MW-8/108/208 contain moderate levels of TPH-G and BTEX as ' compared to the on-site wells 6 The groundwater contaminant plume was defined down gradient of the MW-8/108/208 well set with the advancement of the CPT borings in February 2006 ' 7 Well set MW-9/1091209 historically defines the lateral extent of the plume in an up gradient direction However, all three aquifer levels shallow, intermediate and deep ' (MW-9, MW-109 & MW-209) contained TPH-G during the three previous events The mechanism by which the contamination has mobilized up gradient may be related to a leaking water pipe on an adjacent sidewalk In late February 2006, a water leak was 1 noted on El Dorado Street next to the contamination site We notified the City water company (CWS) and requested that it be fixed ASAP A site inspection on March 9, 2006 noted that it had been fixed The influx of an unknown quantity of water onto the soil column may be responsible for spreading the contamination as evident by the new I