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3 . 2. 3 . 3 Monitoring Well Boring MW-6 <br /> Chemical analyses were performed on_ a soil sample taken at a <br /> depth of 21 feet below grade. TPHG was detected at a <br /> concentration of 3 ppm. BTEX constituents were detected at <br /> concentrations of 0 . 035 ppm, 0 . 020 ppm, 0 . 065 ppm, and 0. 675 ppm, <br /> respectively. <br /> 3 . 3 Groundwater Investigation <br /> ' The following sections discuss groundwater monitoring well <br /> construction, well development and sampling procedures, and <br /> results of chemical analyses. Appendices G, H, and I document <br /> TPE' s protocols relative to groundwater monitoroing well <br /> construction, development, and sampling procedures. <br /> 3 . 3 . 1 Monitoring Well Installation <br /> Monitoring well borings MW-4 , MW-5 and MW-6 were each drilled to <br /> ' a total depth of 31 . 5 feet below grade. Each boring was <br /> converted to a monitoring well. The wells are all similar in <br /> details of construction (see As-built Well Construction Diagrams <br /> presented in Appendix E) . The exact depth of each boring and <br /> ' screen length were determined by the geologic profile and the <br /> occurrence of groundwater in each boring. Groundwater was <br /> encountered in each boring at a depth of approximately 20 feet <br /> below ground surface. The borings for all of the wells were <br /> terminated approximately 10 feet into the uppermost aquifer. All � <br /> wells were constructed under the supervision of a TPE California <br /> Registered geologist. ' <br /> Monitoring Wells MW-4 through MW-6 were constructed using <br /> schedule 40, 4-inch diameter PVC well casing and screen. The <br /> proper lengths of screen and PVC casing were threaded together <br /> above ground and lowered inside the hollow-stem augers. The <br /> length of the slotted portion (screen) was designed to intersect <br /> the water table and account for seasonal variations (10 feet <br /> ' below and 10 feet above the water table) . No glue was used in <br /> this assembly. The well screen consists of . 01 machine-slotted <br /> schedule-40 PVC. A sand pack of # 2/12 filter sand was placed <br /> in the annular space from the bottom of the well boring to 2 feet <br /> above the top of the screened interval. The sand was slowly <br /> poured down the hollow-stem augers while the augers were slowly <br /> ' withdrawn. This method minimized the possiblity of bridging and <br /> helped assure that the filter sand would surround the well casing <br /> before the native materials could collapse into the borehole. <br /> After the screened portion of the well casing was backfilled with <br /> filter sand, , the holel,was sealed from possible surface, , I <br /> contamination with approximately 1. 5 feeti'of 3/8-inch bentonite <br /> pellets followed by a slurry of neat cement grout. A traffic <br /> rated, bolt-locked, vault box with a cover a ndi.cating " <br /> Monitoring Well " was set in concrete to protect each well <br /> 0` <br /> 5 <br /> I , E <br />