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Project No 58100-06-11A June 29, 1995 30 INVESTIGATIVE METHODS ' 3 1 DRILLING AND SAMPLING t31 1 Rationale for Boring/Well Placement Soil borings were advanced to a maximum depth of 23 5 meters (77 feet) bgs to an attempt to define the vertical and lateral extent of residual petroleum hydrocarbons in soil Groundwater monitoring wells were ' constructed in each boring to evaluate the groundwater flow direction and gradient, to evaluate the groundwater quality in the project area, and to attempt to define the lateral limits of the dissolved phase petroleum hydrocarbon groundwater impacts The placement of the monitoring wells was based upon the location of the existing monitoring wells and the historical groundwater data In addition, a soil boring was located within the former UST excavation to aid in determining the maximum TPHg and TPHd concentrations in the vadose zone soil in the central portion of the plume and for the subsequent ' installation of a vapor extraction well (VW-1) The locations of the vapor and monitoring wells are depicted on the Site Plan, Figure 2 ' 3 1 2 Sample Collection Soil samples were collected from the borings at approximate 1 5 meter (five-foot) vertical intervals utilizing a 50 8-mm (two-inch) diameter split spoon sampler equipped with 152 4-mm-long by 50 8-mm (six-inch-long by two-inch)diameter stainless steel sample tubes to facilitate sample handling and storage The borings were logged under the supervision of a California Certified Engineering Geologist utilizing the Unified Soil Classification System The sample tubes were capped, labeled and chilled pending transport to an analytical laboratory Soil samples were field screened with a flame-ionization detector (FID) to assess possible qualitative indicators of volatile organic compounds The soil sample locations and FID readings are recorded on the boring/well logs presented in Appendix B Quality assurance/quality control procedures provided during the field exploration activities included Q h' q �' cleansing/rinsing of the sampling equipment and steam cleaning the augers prior to and between borings ' Cleansing/rinsing of the sampling equipment was performed prior to the collection of each soil sample by washing the equipment with a trisodium phosphate solution followed by subsequent tap water and deionized water rinses ' 3 1 3 Laboratory Analytical Methods ' Soil samples were delivered to Excelchem following chain-of-custody procedures Soil samples were submitted for the analyses of TPHg and TPHd following EPA Test Method 8015 modified and BTEX following EPA Test Method 8020 5 1