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4 <br />2 REVISED SUBSURFACE INVESTIGATION LOCATIONS AND PROCEDURES <br />Based on EHD comments regarding sample locations and depths, PSC proposed to <br />S.. use a membrane interface probe (MIP) to vertically delineate hydrocarbon impact <br />beneath the site. This exploration tool will collect semi -quantitative data on <br />` concentrations of contaminants of concern (COC), as well as, soil conductivity to <br />L profile impact and lithology for the full depth of exploration. In addition, PSC has <br />agreed to move sample locations to laterally delineate hydrocarbon impact. <br />f <br />L <br />2.1 Revised Locations <br />, <br />6' PSC and their subcontractor will advance four Cone Penetration Test (CPT) <br />borings to depths of approximately 100 feet below ground surface (bgs). The <br />revised locations, as agreed upon by PSC and EHD, are shown on the attached <br />L Revised Figure 10, Site Map Showing Proposed CPT Sampling Locations. <br />2.2 Revised Drilling/Sampling Procedures for CPT Borings <br />L CPT technology allows collection of various soil parameters to assess <br />lithology and the subsurface environment. Based on EHD request for more <br />data on COC concentrations in addition to the lithology data, PSC will use <br />L MIP technology to assess COC concentrations for the full depth of <br />exploration. Since the objectives of the investigation will be focused on the <br />permeable zones in the subsurface, PSC has chosen to connect the <br />conductivity sensor in the MIP rather than connecting the tip, skin resistance <br />and additional sensors of the Cone Penetrometer. Conductivity measurements <br />are a better indication of permeability of the subsurface. <br />MIP technology involves the advancement of a 1.5 -inch diameter, 12 -inch <br />i long probe into the subsurface at a rate of approximately one foot -per -minute. <br />a The probe has a dipole conductivity sensor at the tip that measures soil <br />conductivity. Readings from the probe are transmitted to the surface for <br />evaluation and analysis. Generally, soil conductivity is higher for clays and <br />L_ silts and lower for sands and gravels. Conversely, soil conductivity logs can <br />be used to indicate relative permeability of the subsurface strata. These logs, <br />when correlated with logs of historic soil boring logs, will provide a valuable <br />assessment of lithology and the subsurface strata. <br />The probe, which is heated between 80° to 125°C, also contains a membrane - <br />covered chamber with a carrier gas connected to the surface by inert tubing. <br />When the probe is advanced, volatile organic compounds (VOCs) in the <br />t. Site Conceptual Model and Work Plan for Remedial Investigation - Addendum <br />Prepared for. Sara Lee Bakery Group Inc. Prepared by: Philip Environmental Services Corporation <br />Airport Way12008_01_24 - SCM and Work Plan for RI Addendum.doc January 24, 2008 <br />Page 2 <br />