ARCHIVED REPORTS_XR0008229 - Laserfiche WebLink

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1 3 0 CONCLUSIONS, RECOMMENDATIONS AND PROJECT STATUS ' Between December 30, 2005 and March 15, 2006, the groundwater surface rose an average of ' 1 21 feet, the groundwater gradient decreased from 0 0152 to 0 0113 foot/foot, and the groundwater flow direction remained toward the northeast The groundwater table is at the highest recorded level, since the monitoring wells were installed in July 2002 Otherwise, the groundwater surface characteristics are consistent with historical and seasonal trends 1 Between December 30, 2005 and March 15, 2006, gasoline compounds in groundwater generally decreased in all three monitoring wells Concentrations of gasoline compounds in groundwater at MW-1 have declined significantly, since the monitoring wells were installed in July 2002, probably due to source removal efforts and natural attenuation processes Since March 2004, concentrations of MTBE have been detected in the perimeter wells (MW-2 and MW-3) During ' the first quarter of 2006, the MTBE concentrations detected in MW-2 and MW-3 were both below the state of California Secondary Maximum Contaminant Level (MCL) of 5 pg/1 ' On November 1, 2005, EHD met with representatives of the San Joaquin County Facilities Management Department In a letter summarizing the meeting dated November 17, 2005, EHD states that There is a sand lens at 35 feet bgs at this site that may be a migratory pathway for the ' MTBE contamination It was discussed that placement of soil borings up-gradient (southwest) and cross-gradient (southeast) of MW-9 and obtaining soil samples and grab water samples from 35 feet bgs may provide definition for the site If those samples are non detect then the site should be evaluated to see if further investigation is needed ' On February 17, 2006, Ramage Environmental submitted to EHD, Work Plan, Additional Site Investigation , which proposed the drilling and sampling of the two soil borings recommended by ' EHD The proposed soil boring locations are shown on Figure 3 On March 10, 2006, EHD approved the two proposed soil borings, and requested that two ' additional soil borings be added to the scope of work EHD requested that one boring should be drilled through the former UST source area to define the vertical extent of impacted groundwater, and one boring should be located approximately 60 feet north of the former UST in the downgradient direction, to define the lateral extent of impacted groundwater at the groundwater table Ramage Environmental agrees that these two additional soil borings may be required to ' fully define the extent of impacted groundwater, so that the case can be considered for closure • 7