FIELD DOCUMENTS - Laserfiche WebLink

Home Browse Search

375 West Larch Road,Tracy August 28, 2013 Page 3 The margins of the Basin act as recharge areas for groundwater. Deeper aquifers,occurring below approximately 250 feet, are regional producers of groundwater for agricultural and domestic purposes. Based on the regional topography the estimated groundwater flow direction is to the northwest. At 425 West Larch Road, a fuel leak site located approximately 400 feet to the east of the Property, the depth to water has been reported to be approximately 9.5 feet. According to their report the groundwater gradient was to the northwest to southwest with a very low gradient of approximately 0.0016 feet per foot(Ami Adini&Associates, 2012). Contamination under these conditions does not migrate great distances, rather remaining close to its source. FIELD WORK PERFORMED Prior to performing the field work, ERAS prepared and submitted a workplan describing the proposed work,dated August 9, 2013 to the SJCEHD. ERAS also obtained a drilling permit from the SJCEHD which is included as Attachment C. Prior to drilling, Scantech, a private utility locator, screened the area for the presence of any remaining UST's using a magnetometer. No UST's were found. Three 2.5-inch diameter soil borings were drilled using a hydraulic push sampling rig by ECA of Aptos, California on August 15, 2013. The locations of the borings are shown on Figure 2 in Attachment A. The locations were the most likely locations of the former fuel tanks based on the maps found by ERAS during the ESA investigation. Borings B-1 and B-3 were advanced at each end of the former fuel tank to a depth of 14 feet below ground surface (bgs). Boring B-2 was advanced in the location of the former fuel dispenser to a depth of 14 feet bgs. Soil was continuously collected for lithologic logging and monitored using an organic vapor meter(OVM)for indications of volatile organic content.The soil cores were logged by ERAS geologist Andrew Savage. Groundwater samples were retained for analysis from each boring. The Standard Operating Procedures for groundwater sampling with a direct-push sample rig are included as Attachment D. The subsurface vadose zone lithology consisted of silt clay to approximately 9.5-10.5 feet bgs. Groundwater was encountered at 9.5-10.5 feet bgs and the water bearing zone consisted of silty sand. No signs of contamination such as odor, discoloration or elevated OVM readings were observed during the drilling of the borings. Details of subsurface conditions are provided on the soil boring logs as Attachment E.