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URS Greiner Woodward Clyde Ms. Carol Oz, R.E.H.S. Page 2 LOP/Site Mitigation Unit San Joaquin County—Public Health Services Environmental Health Division March 13, 2000 Permitting SJCEHD requires that permits be obtained prior to the installation of soil borings. URSGWC will submit the appropriate permit application with fee to the SJCEHD prior to conducting field activities. Groundwater Monitoring Well Installation To assess the lateral extent of groundwater impact at the Site, URSGWC proposes drilling and installing three groundwater monitoring wells. One monitoring well is proposed for the current location of the UST. The other two monitoring wells are proposed to be situated for monitoring down-gradient of the UST location. The groundwater flow direction is anticipated to be in a north-north-west direction. A figure showing the proposed monitoring well locations is included as Attachment I. Underground Service Alert (USA) will be notified a minimum of 48-hours prior to commencement of field activities. The wells will be constructed in borings drilled using a truck-mounted,hollow stem auger(HSA) equipped drill rig. The borings will be drilled with 8.25-inch outside diameter(OD)augers to accommodate the installation of a 2-inch diameter groundwater monitoring well. The total depth of each boring will be approximately 15 feet bgs. To assess the lateral and vertical extent of the petroleum impacted soils, soil samples will be collected using a California-modified split spoon sampler at 5-foot intervals beginning at 1 foot below ground surface (bgs)and continue until groundwater is encounter; anticipated at approximately 5 to 7 feet below ground surface. A portion of each sample will be retained for field screening analysis. Based on the results of field screening, one soil sample from each of the borings will be submitted to Curtis & Tompkins, Limited (Curtis & Tompkins), a California State Certified Laboratory,for analysis of TPH-G by EPA method 8015 modified; and BTEX,MTBE, tert-butyl alcohol (TBA), di-isopropyl ether (DIPE), ethyl tert-butyl ether (ETB), and tert-amyl methyl ether (TAME)by EPA method 8260. The samples will be then sealed in plastic bags and stored in an ice-filled chest at approximately 4°C until delivery to the laboratory. Each soil sample will be delivered to the laboratory within the appropriate holding times and will be accompanied by the chain of custody(COC) documents. The monitoring wells will be constructed using 2-inch diameter (ID), schedule 40, flush-threaded polyvinyl chloride (PVC)well casing.Well installation will include up to 12 feet of screened casing and an above-ground, locking well monument. Twelve feet of well screen (0.020-inch machine-slotted) is proposed to allow for, seasonal fluctuations in groundwater levels(measured at between 5 and 7 feet bgs in March 1999).A Monterey No. 3 silica sand filter pack will be installed from the bottom of the boring to six-inches above the well screen. A 1-foot bentonite seal shall be placed above the sand pack and neat cement shall be used to seal the remaining annular space to the surface. The actual well completion details will be based upon groundwater conditions encountered in the field. Soil cuttings generated during the drilling activities will be placed in labeled 55-gallon Department of Transportation(DOT)-approved steel drums pending disposal. 1:13 4214102_Tracy\W orkp1 an.doc