ARCHIVED REPORTS XR0010859 - Laserfiche WebLink

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i` Ili! The resample of the well i!'n July 2001 showed that contaminants were not detected. In our opinion, this Well does not show contaminants from the M & M Buildings UST j sources. The one-time detection again leads Wright to the interpretation of self-oiling equipment as the source of,the "contaminants". Discussion Summary The verylow concentrations of TPH contaminants in groundwater show a very degraded dissolved plume has moved from the tank pit area slightly to the north. Residual contaminants are present in the soil in the immediate vicinity of the former tank pits, which are probably slowly desorbing into groundwater. Groundwater flow as plotted in wells shows a northwesterly flow. While very low TPHD dissolved concentrations were observed in B-6, contaminants were not detected in MW-1 groundwater samples. If Conclusions and Recommendations Eight borings were advanced for mapping the dissolved TPH plume, and 3 monitoring wells installed at M&M Builders. Previous assessment had revealed very low TPHD dissolved levels just north of the former tank pits. Soil and groundwater sampling for this work essentially confirms I'Isubsurface hydrogeology and has, in our opinion defined the extent of the dissolved plume. The highest observed dissolved concentrations of degraded TPHD and TPHG occur in the immediate vicinity of the former tank pits. The TPHG and TPHD data for MW-3 water samples did not match their laboratory standards, suggestive of a highly degraded fuel contaminant depleted in volatile content. A deep boring placed adjacent to Iithe irrigation water well showed that contaminants were not detected in soil/sediment or groundwater. A resample of this Water Well shows that TPHD-like contaminants were not detected. In our opinion, there is no contamination of the Water Well interpreted Ito arise from the former tank pit area. II� It is Wrights understanding that the water well has not been used for drinking water, and that this well is used for irrigation of concrete aggregate mixing. Wright recommends that a quarterlymonitoring program for TPHG TPHD and BTEX IgP g and MTBE and oxygenates be performed for the next four quarters. If concentrations continue to show very low, stable and/or none detected levels, Wright will request that site closure be considered Mer the fourth quarter. Limitations This report has been prepared specifically for M&M Builders site at 8111 West Eleventh Street in Tracy, CA and was done according to the State and local agency suggested guidance documents for I'I these investigations. The interpretations, conclusions and recommendations made herein are based on professional judgment of the data and analysis for the soil and water samples collected on-site and should be reviewed in the I� Page 7