WORK PLANS - Laserfiche WebLink

Home Browse Search

Mr.James Barton,RWQCB May 14,2008 Work Plan for Additional Site Assessment Former Dolly Madison Bakery,Stockton,California Page 7 GRO (92 µg/L) and 1,2-DCA were.also detected in the MW-14 sample. The lateral extent of GRO impacted groundwater is not fully assessed south, southeast, north, and west of wells MW-9 and MW-14. Minimal petroleum hydrocarbon impact was observed at well MW-8. Deep Interval Groundwater Impact GRO, benzene, and MTBE iso-concentration .contour maps for the deep water bearing interval are presented as, Figures 15 through 17, respectively. The distribution of groundwater contaminants in the deeper water bearing interval (monitored at the site by wells MW-10 through MW-13) ,appears anomalous relative to the distribution of contaminants in the shallow .and mid-depth well network. Lower concentrations of GRO (68 µg/L and 69 µg/L) and MTBE (1.0 µg/L and 1.8 µg/L) were detected in wells.MW-10 and MW-13 (located near the western portion of the site and closest to the former UST location) than the.GRO (3.40 µg/L and 1,500 µg/L) and MTBE (16 µg/L and 21 µg/L) concentrations observed in wells MW-11 and MW-12, located east and northeast of the former USTs. GRO concentrations at well MW-11, located approximately 170 feet from the USTs (near the eastern property line) are higher than concentrations observed at shallow monitoring wells MW-1 through MW-7 and each of the mid-depth monitoring wells. Based on the information available, the majority of the petroleum hydrocarbon impact observed in the deeper,water bearing interval has likely originated from an off-site source. The predominant south and southeast groundwater flow direction observed in the `B" zone by a consultant representing Texaco between 2002 and 2007, would place the site downgradient of the Texaco, Chevron, and former Colombo Bakery sites. Although a northeast flow direction was noted at the site during the first quarter 2008 in the deeper zone using measurements at wells MW-10 through MW-13, the six years of monitoring completed on behalf of Texaco at this interval of the subsurface may be more representative of the predominant long-term groundwater flow direction in the site vicinity. PROJECT APPROACH GRO (260 µg/L) is currently present at well MW-1, located at the southern boundary of the shallow well network. Stratus is therefore proposing to install an additional shallow screened well (MW-15)- approximately 40 feet south of MW-1 to allow for further characterization of petroleum hydrocarbon impact in this area. Stratus is also proposing to install an additional monitoring well (MW-16) east-southeast (generally downgradient) of MW-5, which is impacted with MTBE(21 µg/L). . Petroleum hydrocarbon impact to the mid zone wells appears to extend.predominately east, southeast, and south of the former UST area. In order to more fully constrain the extent of KATimothy Kone PronertyMork Plans\Kong-may08workPlan.doc