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Former Skips Service Station -2- <br />(AKA <br />2 - <br />(AKA H/S Auto Repair) <br />300 South California Street <br />Stockton, San Joaquin County <br />29 June 2018 <br />di -isopropyl ether (DIPE), ethyl tert butyl ether (ETBE), tert amyl methyl ether (TAME), tert butyl <br />alcohol (TBA), 1,2 -DCA, and ethylene dibromide (EDB), naphthalene, the leak detection <br />compound 1,1-difluoroethane (DFA), and percent oxygen. To assess shallow soil, Ground Zero <br />proposed advancing seven direct push borings to approximately 8 ft bgs, and to collect soil <br />samples for laboratory analysis at 4 ft bgs and 8 ft bgs. Ground Zero proposed analyzing soil <br />samples for TPH-G, BTEX, MTBE, DIPE, ETBE, TAME, TBA, and naphthalene. <br />Central Valley Water Board staff have the following comments: <br />1. The lateral extent of petroleum impact to groundwater is undefined to the north and west of <br />the Site. Grab groundwater samples collected from CPT borings CPT -3 in June 2000, from <br />CPT -4 through CPT -6 in March 2001, and from CPT -7 in December 2004 contained <br />petroleum hydrocarbons as presented in the table below: <br />Boring <br />ID <br />Sample <br />Depth <br />(ft bgs) <br />TPH-G <br />(ug/L) <br />Benzene <br />(ug/L) <br />MTBE <br />(ug/L) <br />1,2 -DCA <br />(ug/L) <br />CPT -3 <br />35 <br />ND <br />ND <br />73 <br />--- <br />55 <br />50,000 <br />5,200 <br />10 <br />--- <br />100 <br />ND <br />1 <br />ND <br />CPT -4 <br />33 <br />ND <br />ND <br />ND <br />--- <br />53 <br />65 <br />ND <br />ND <br />--- <br />125 <br />ND <br />ND <br />ND <br />--- <br />CPT-6 <br />33 <br />ND <br />ND <br />ND <br />--- <br />54 <br />31,300 <br />7,680 <br />ND <br />--- <br />CPT-7 <br />30 <br />No Water <br />40 <br />No Water <br />50 <br />859 <br />1.3 <br />1.2 <br />2.3 <br />82 <br />58.7 <br />ND <br />ND <br />22 <br />125 <br />ND <br />ND <br />ND <br />ND <br />Collection of current grab groundwater data to the north and east of the Site are needed to <br />define the lateral and vertical extent of the release. Therefore, by 30 August 2018, please <br />submit a work plan to complete groundwater delineation. <br />2. Ground Zero proposed installing temporary soil vapor probes. Central Valley Water Board <br />staff request that you install permanent soil gas wells to allow collection of repeatable <br />samples. At a minimum, at least two soil gas sampling events should be performed, <br />approximately 6 months apart. Please include in the Work Plan Addendum due <br />15 August 2018, a scope of work for installation of permanent soil gas wells. <br />3. Some of the proposed soil gas probe and soil boring locations are within the excavation <br />areas of the former USTs. Please ensure that soil samples are collected from native soil, <br />not backfill, and that soil gas probes are constructed in native soil. <br />