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tht�r� i V SAN JOSE, CA 9512` -. kC'#H SERV 106*Z INC. (408) 995•663.) SAM- PEING METHODOLOGIES FOR TYPICAL SOIL SAMPLLNvG PROJE=CTS Standard RWQCB Interface Samples: Samples taken immediately following a tank removal are required to conform to criteria established by the Regional Water Quality Control Boards. Interpretation of these criteria is usually entrusted to the discretion of the local implementing agency inspector, but are widely known and confortr:ance with these criteria is expected even when no regulatory agency personnel are present to direct the procedures. Accordingly, "Standar Interface samples" are those which have been taken in accordance with the standard protocol for obtaining interface samples.These samples fall into the category of samples which are known to be of primary concern to the interested regulatory agencies for determining if additional action will be tequired at a site and the methodology has been closely defined in stat- and RWQCB publications, supplements, and pmscntauons. These specify both the acceptable depth and lateral situation of sample collection points. In accordance Aith these specifications, sample collection is executed as close as possible to the center line tlongitu(Enai axis)of the tank and on a vertical axis with the fill pipe. A corresponding location is also found at the opposite end of the tank when- ever standard interface samples are being collected Briefly, the method consists of d gging up native soil from directly klow, the fill pipe and. the corresponding opposite end of the tank and obtaining a sample. front the bacldill/native soil interface or a short distance below the interface. A short distance has boon defined by Region 2 Board engineers as not greater than r enty-four inches below the backfill/native soil interface and is generally tal _n to be one foot below he backfill/native sc l interface. This soil is brought up in the bac Li oe buck-t. A shovel of trowel is used to cut away surface soil and backfill material �hieh rna j have been included in the bucket, and the sample is taken by pushing or driMsig a brass sample liner into the newly exposed soil from the designated depth and location. Add;conal clarifications by F:cg on 2 Board engineers have indicated that wh_n there L an obvious difference in the relative contami- nation of soil biought up from tl:e interface depth, then it is the relatively more contami- nated soil that should be selected for inclusion to the sample, Elective Exploratory Samples: —his tyre c` samp!ing employs the same sample collec- tion and handling procedures as a:e uscd m -..=dard RWQCB interface sampling, but soil is typically obtained at a Brearer depth cr 'rc."• e position that is laterally offset from the interface location. Elective ConfirrningSamplQs F A!Oving Additional Excavation; Ir, c es v:hnrc, as a precaution, excavation is continGed in on'er ce remove soil which tray be contaminated, it is customary to obtain rrn: or nic-- sampoes c' tiro soil at the furthest eKtznL of excavation. These samples provide informati.:.t oa thc. cc diuon of the sniff rcmaining ufivr tl.e excava- tion effort was completed