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1612 Hammer Lane Page 2 <br /> Should you decide to over-excavate, please note that soil samples should be collected every twenty feet from <br /> the bottom and sidewalls to characterize the extent of residual soil contamination, if any. Also, should you <br /> decide to backfill the tank excavation with the soil you are proposing to remove, rather than clean fill, your <br /> activities will require Central Valley Regional Water Quality Control Board approval per California Code of <br /> Regulations, Title 23, Division 3, Chapter 15 Discharges of Waste to Land. You should be aware that to <br /> backfill the proposed tank over-excavation to grade additional soil will be necessary and the work plan failed <br /> to indicate clearly the source of this additional soil . <br /> PHS/EHD also questions the ability of the proposed vapor extraction well, VWS, to remediate the suspected <br /> shallow soil contamination which may be observed (since soil samples are not currently proposed to be <br /> collected) in the soil proposed for subsequent backfill . No mention of the compaction of the proposed <br /> backfill was included. Please be aware that a City of Stockton grading permit should be obtained. In order <br /> to remediate soil contamination between 15 feet and 22 feet below grade, consideration should be given for <br /> the installation of additional vapor extraction wells. <br /> The soil removed from the waste oil tank excavation is proposed to be stored on site surrounded by visqueen <br /> plastic pending appropriate disposal . <br /> The soil removed from the gasoline tanks excavation is proposed to be used to backfill the former tank <br /> excavation . Treatment of this soil is proposed elsewhere in the work plan by inference that the soil <br /> contamination would be remediated using a vapor extraction well installed at 15 feet below grade. Please be <br /> informed that in order for the proposed vapor extraction system to be evaluated, PHS/EHD will require further <br /> characterization of the distribution of petroleum hydrocarbon contamination beneath the tanks which are <br /> proposed for removal . <br /> Tank Installation <br /> The work plan proposed to excavate soil in the area of the new tank excavation and to collect samples every <br /> 100 cubic yards to be composited by the laboratory. The ratio of field to lab composite samples was not <br /> indicated . Please be aware that should you wish to obtain permission to dispose of the soil in other than a <br /> Class II landfill , PHS/EHD requests a ratio of no more than 2 field to 1 lab sample. EMCON indicated that <br /> it would be unlikely that concentrations would exceed 50 ppm TPH-gas; but if concentrations did exceed 50 <br /> ppm soil aeration, under permit from the San Joaquin Valley Unified Air Pollution Control District, would <br /> occur and that confirmation sampling would be used to evaluate disposal options. <br /> In summary, please prepare a site map locating VW5 and a work plan addendum to characterize the <br /> distribution of contamination beneath the underground storage tanks proposed for removal . This information <br /> will be necessary for the preparation of a corrective action plan per Underground Storage Tank Regulations. <br /> If you have any questions, comments, or wish to schedule a site inspection, please contact Mary Meays at <br /> (209) 468-0337. <br /> Donna Henan, REHS, Director <br /> Environmental Health Division <br /> vV — , VCA <br /> Mary Meays, Senior REHS Diane M. Hinson, REHS <br /> Site Mitigation Unit Supervisor <br /> MM\1612HAM <br /> enclosure <br /> cc: Elizabeth Thayer, CVRWQCB (w/o enclosure) <br /> cc: Jay Johnson, EMCON (w/enclosure) <br />