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Musco Family Olive Com - 2 - 27 July 2006 <br /> ¶(b)(1)(B)1. and ¶(b)(1)(B)2., to provide the best assurance of the earliest possible <br /> detection of a release from the Unit; <br /> • (B)4. a sufficient number of Monitoring Points and Background Monitoring Points <br /> installed at appropriate locations and depths to yield ground water samples from zones <br /> of perched water to provide the best assurance of the earliest possible detection of a <br /> release from the Unit; and <br /> • (B)5. Monitoring Point locations and depths that include the zone(s) of highest hydraulic <br /> conductivity in each ground water body monitored pursuant to this subsection [i.e. <br /> under¶(b), inclusive]. <br /> Based upon a review of the current wells utilized to monitor the upper water bearing zone, it is <br /> staffs professional judgment that wells W-2 (dry), MW-11 (dry), and MW-17 are inadequate to <br /> monitor the shallow groundwater beneath the surface impoundments. Wells MW-12 and <br /> MW-18 are inadequate to monitor the deep groundwater beneath the surface impoundments, <br /> and the current monitoring well network (W-2, MW-11, MW-12, MW-17, and MW-18) is <br /> inadequate for monitoring the highest hydraulic conductivity zone beneath the surface <br /> impoundments. To evaluate the well system, Board staff reviewed the boring logs for shallow <br /> wells W-2, MW-11 and MW-17, and deep wells MW-12 and MW-18. In addition, boring logs <br /> of W-1 and W-3 were also reviewed. <br /> Monitoring Well W-2 <br /> Well W-2's boring log lacks detail from approximately 30 feet below ground surface (bgs) to 50 <br /> feet bgs or the total depth drilled. First encountered water in boring W-2 was detected on 13 <br /> May 1985, at 29 feet bgs. According to the Kleinfelder Report dated 7 June 1985, boring W-2 <br /> was drilled with a 6-inch diameter continuous flight auger and constructed using 4-inch <br /> diameter PVC well casing fitted with 30 feet of slotted casing. The filter pack was backfilled <br /> one foot over the screened interval to 19 feet bgs, followed by a five foot thick bentonite <br /> transition seal to 14 feet bgs, and a sanitary seal to ground surface. Neither slot size nor sand <br /> pack can be determined from the report nor boring log. Based on this information the <br /> following standards where not complied with when constructing well W-2: <br /> • According to ASTM D5092— Standard Practice for Design and Installation of Ground <br /> Water Monitoring Wells in Aquifers, Section 6, subsection 6.6.2: The diameter of the <br /> casing for filter packed wells should be selected so that a minimum annular space of <br /> 2-inches (50 mm) is maintained between the inside diameter of the casing and outside <br /> diameter of the riser. <br /> • According to Department of Water Resources (DWR) California Well Standards Bulletin <br /> 74-90, Part 11 Monitoring Well Construction, Section 9, A: Minimum Depth of Annular <br /> Seal: Water quality monitoring wells and monitoring wells constructed in areas of known <br /> or suspected pollution or contamination. The annular space shall be sealed from the top <br /> of the filter pack or monitoring zone to ground surface, unless otherwise approved by <br /> the enforcing agency. The top of the filter pack or monitoring zone shall not extend into <br /> another water-bearing unit above the single water-bearing unit being monitored unless <br /> otherwise approved by the enforcing agency. The filter pack or monitoring zone shall <br />