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CLOSURE REQUEST 5-31-94 . d) Certified laboratory, chain of custody procedures, sample preservation, holding times, sample preparation methods, and detection limits. All chain of custody procedures were met, along with sample preservation and holding time limits . Sample preparation methods, and detection limits were performed by DHS certified laboratories within required guidelines and limits. e) soil and/or groundwater analysis performed in accordance to Table 2 of Regional Board Staff Recommendations. Yes . For the gasoline underground storage tank and product line removals, over-excavation, excavated soil piles, aerated soil piles, soil borings and vapor recovery and ground water monitoring wells, Method 8015 for gasoline and diesel range hydrocarbons with extraction methods 5030 and 3550 used respectively, Method 8020 for Benzene, Toluene, Ethylbenzene and Xylenes, Method 7420 for Total Lead and DHS methods for Organic Lead and EDB, see Table 3 Also for excavated soil classification as a non-hazardous waste; Method 6010 TTLC/CAM Metals, 96 hour fish bioassay - flathead minnow were also ran, see PRELIMINARY ASSESSMENT REPORT, dated December 15, 1989 (Updated January 16, 1990) - Appendix E f) Method used to measure free product thickness No free floating product was ever observed in the borings or monitoring wells . g) Method used to measure groundwater elevations Depth to water is measured prior to purging and sampling a well with a product interface probe (Keck Instruments Model KIR-89) which has a calibrated tape in 0 01 foot intervals or a water interface resistivity probe (Solinst Model 101) which has a calibrated tape in 0 02 foot intervals . III . EXTENT OF SOIL AND GROUNDWATER POLLUTION. a) Vertical and lateral definition of soil contamination A soil and subsurface investigation designed specifically for the detection of gasoline contamination was initiated in the Work Plan dated October 19, 1989, ten days after the tank pull sampling had occurred. With the drilling and sampling of the initial sample borings (SB1 and SB2) and the installation of the initial ground water monitoring wells (MW1 . MW4) the vertical and lateral definitions had been established. This was confirmed with additional samples obtained from the over-excavations and the placement of additional ground water monitoring wells MW5, MW6 and MW7 . The placement and sampling of vapor extraction wells EX, P1, P3 , P3A, P3B, P3C, P3D, VSB3 , VSB5, VSB9, VSB11, VSB13 , VSB14, and VSB15 . And the sampling of soil borings SB4, pagel3