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hand auger. The results and discussion of these investigation activities were reported in the 2004
<br /> OffSite Assessment Report(SECOR, 2005a).
<br /> • Between July 12 and 14, 2005 28 offsite soil borings (A-6, A-8, B-8, B-9, B-10, B-11, C-3.5, C-6, C-8,
<br /> D-9, D-10, D-11, D-12, D-13, F-9, F-10, H-9, H-10, H-11, H-12, H-13, J-8, J-9, K-8, K-10, P-7, P-9,
<br /> and R-7) were advanced using a hand auger. The results of this investigation were reported in the 2005
<br /> OffSite Assessment Report(SECOR, 2005b).
<br /> 2.3 UST Site Assessment
<br /> The purpose of the UST site assessment was to evaluate soil and groundwater quality in the area surrounding the
<br /> former transmix UST. The transmix tank was a 1,000 gallon fiberglass, double-walled UST with a Veeder-Root
<br /> leak detection system and was previously used as a flow-through tank during removal and treatment of
<br /> condensate water which accumulated at the bottom of the onsite ASTs. Gasoline/water or diesel/water mixtures
<br /> were pumped through the UST to another onsite treatment area for separation on a monthly basis until 2000. In
<br /> 2000, alternate piping was installed to transfer water and fuel mixtures directly to the onsite treatment area and
<br /> the transmix UST was discontinued. The UST was removed on March 5, 2003 under oversight of the Tracy Fire
<br /> Department. The UST measured 4 feet wide by 11 feet long and had no visible damage or holes. Soil
<br /> surrounding the UST appeared to be stained and visibly impacted. Aboveground piping leading from the tank
<br /> was abandoned during the UST removal (SECOR 2004d).
<br /> After the UST was removed, soil samples TS-1, TS-2, and TS-3 were collected from the excavation sidewalls at
<br /> approximately 8 feet bgs. On September 2, 2003, soil borings USB-1 and USB-2 were advanced to 10 feet bgs
<br /> to evaluate soil and groundwater quality approximately 160 feet north and 150 feet northeast of the former
<br /> transmix UST, respectively. Also, monitoring well MW-67UA was installed to 15 feet bgs northeast of the
<br /> former transmix UST. On December 11, 2003, boring MW-68A (the soil sample was referred to as UST) was
<br /> advanced at the location of the former transmix UST to 41 feet bgs, and a well was installed in the boring to 26
<br /> feet bgs. Results of soil sample analysis collected from each boring during borehole advancement are
<br /> summarized in Table 6. The results of this previous assessment were summarized in the UST Site Assessment
<br /> Report(SECOR, 2004b).
<br /> On December 1, 2004, groundwater monitoring well MW-69UA was advanced to a total depth of 14 feet bgs
<br /> with slotted screen from 4 feet bgs to 14 feet bgs. On December 13, 2004, the groundwater monitoring well
<br /> MW-65B was advanced to a total depth of 60 feet bgs with slotted screen from 55 feet bgs to 60 feet bgs. Each
<br /> boring location was hand-cleared using an air-knife tool to a depth of approximately 8 feet bgs. Select soil
<br /> samples were collected from each boring and submitted for chemical analysis.
<br /> On April 19, 2004, extraction well EW-1 was installed approximately 100 feet northeast of the former transmix
<br /> UST. EW-1 was installed as part of the proposed Non-aqueous Extraction Treatment (NETTM) system to
<br /> remove SPH and mitigate hydrocarbon mass from the source area between AST #131 and AST # 139. EW-1
<br /> was monitored and sampled during all four quarters of 2005. Free product was not detected in the well during
<br /> installation;therefore the NETTM system was not installed. Assessment activity findings are summarized below.
<br /> 2.3.1 Subsurface Lithology
<br /> Field observations and boring logs indicate that the top 5 feet of soil consisted primarily of sandy silt. From
<br /> approximately 5 to 10 feet bgs silt and sandy silt was encountered. Beyond 10 feet bgs, the sands, silts, and
<br /> BLASLAND,BOUCK &LEE, INC.
<br /> 7124106 engineers,scientists,economists 2-5
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