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Monitoring Well Installation Report - Chevron Station #9-5775, Lodi, CA
<br />April 7, 2000
<br />Hydrocarbons as gasoline (TPHg), 84 ppm of benzene and 56 ppm of methyl tert-butyl ether (MtBE)
<br />Based on field screening data, the area beneath the eastern end of the middle gasoline UST was excavated
<br />from 14 5 to 16 feet bgs, and a second sample was collected This sample contained 880 ppm of TPHg
<br />and 11 ppm of MtBE Benzene was not detected in this sample
<br />The area beneath the eastern end of the middle gasoline UST was overexcavated from 16 to 22 5 feet bgs
<br />on August 31, 1998 Soil samples were collected from the base and the eastern wall of this excavated
<br />area The base sample contained 2,300 ppm of TPHg, 4 1 ppm of benzene and 330 ppm of MtBE The
<br />wall sample, collected at 18 5 feet bgs, contained 290 ppm of TPHg, 0 35 ppm of benzene and 22 ppm of
<br />MtBE
<br />On January 25 through 27, 1999, five soil borings were drilled at the subject site, with four of the borings
<br />completed as monitoring wells The four monitoring wells (MW -1 through MW -4) were completed to 65
<br />feet bgs Soil samples collected form the borings contained detectable concentrations of TPHg (up to
<br />1,200 ppm), benzene (up to 0 81 ppm), and MtBE (up to 110 ppm) Ethyl tert-butyl ether (ETBE) (up to
<br />1 3 ppm) and tert-amyl methyl ether (TAME) (0 34 ppm) were also detected in soil samples Groundwater
<br />samples contained concentrations of TPHg (up to 11,000 parts per billion, or ppb), benzene (up to 6,800
<br />ppb), MtBE (up to 62,000 ppb), ETBE (2,400 ppb), and TAME (780 ppb)
<br />In a recent groundwater monitoring and sampling event on December 3, 1999, wells MW -1, MW -3 and
<br />MW -4 had detectable concentrations of TPHg (up to 3,130 ppb), benzene (up to 996 ppb), MtBE (up to
<br />• 14,400 ppb), and ETBE (up to 1,120 ppb) Wells MW -1 and MW -4 had detectable concentrations of
<br />TAME of 161 and 274 ppb, respectively Well MW -2 was nondetect for TPHg, benzene, toluene,
<br />ethylbenzene, and xylenes (BTEX), MtBE, ETBE, and TAME Ethanol, tert-butyl alcohol (TBA), or
<br />di -isopropyl ether (DIPS) were not detected in any of the wells Groundwater flow direction was to the
<br />east at a gradient of approximately 0 007 ft/ft Depth to water ranged from 56 45 to 57 15 feet below top
<br />of casing (btoc) Historically, groundwater in the immediate vicinity of the Chevron station has ranged
<br />from 56 33 to 69 35 feet btoc
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<br />FIELD ACTIVITIES
<br />Recent monitoring data suggest a west -southwesterly flow component in the groundwater beneath the
<br />site Due to the presence of MtBE in groundwater beneath the site, and due to the close proximity
<br />municipal well #12 southwest of the site, two groundwater monitoring wells (MW -5 and MW -6) were
<br />installed at the southwest corner of the site and three groundwater monitoring wells (MW -7 through
<br />MW -9) were installed west and south of the subject site In preparation for remedial activities, one
<br />groundwater extraction well (EX -1) and four vapor extraction wells (VE -1 through VE -4) were installed
<br />in the vicinity of the former gasoline USTs Two soil borings (SB -2 and SB -3) were drilled in the
<br />vicinity of the former USTs for soil characterization Field work was performed in accordance with GR's
<br />Site Safety Plan #346408 06, dated December 15, 1999 GR Field Methods and Procedures are included
<br />in Appendix A Underground Service Alert was notified prior to beginning site activities, and a private
<br />subsurface utility locating service was contracted to locate subsurface utilities at the boring locations
<br />The soil borings and wells were installed by V&W Drilling (C57 #720904) under SJCEHD permits
<br />#018004, #0021673, and #0021674, City of Lodi encroachment permit 499208, and Caltrans
<br />encroachment permit #I099-6SV-1069 Copies of the permits are included in Appendix B
<br />34640806-1
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