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Ms. Lori Duncan August 31, 2005 Page 2 Project No.: 880-039.1A.01010000 Texaco Service Station. Based on data collected from subsurface investigations performed at the former ARCO Service Station, Chevron Station, and Texaco Station (located at the corners of Charter Way and Lincoln Street), residual and dissolved hydrocarbons have been detected beneath those facilities. Environmental investigation of the release began when the UST was removed in 1996. Soil Vapor Extraction (SVE) was conducted from February 2000 until October 2004 and has reduced the concentrations and mass of gasoline in the unsaturated zone. Groundwater monitoring and sampling continues to be performed on a quarterly basis. On June 29, 2005, Shaw submitted the Work Plan which proposed additional site investigation, installation of temporary wells, and performance of an air sparge test. The Work Plan was prompted by a review of site characterization and remedial data which suggest that an immobile mass of separate -phase gasoline hydrocarbon (SPH) may be present. The presence of submerged SPH would explain the ongoing concentrations of gasoline constituents in groundwater and the absence of SPH in site wells. The SJC/EHD responded to the Work Plan in a letter dated July 26, 2005. The following sections respond to the SJC/EHD's comments. ADDITIONAL SITE INVESTIGATION In response to the SJC/EHD's comments, Shaw has revised the number and location of proposed borings for the additional site investigation. Since the SJC/EHD accepted the analytical suite proposed in the Work Plan, Shaw does not propose to modify that portion of the scope of work. Shaw proposes to use Ultra -Violet Induced Fluorimetry Cone Penetration Testing (UVIF- CPT) in the five locations shown on Figure 1. These locations have been selected for UVIF-CPT because they are viewed as likely areas of submerged secondary sources of hydrocarbons based on their relationship to primary source areas formerly at the site. Shaw proposes to perform direct -push (e.g., "Geoprobe " or "HydroPuncho") methods (DP) in the twelve locations shown on Figure 1. These locations have been selected for soil and groundwater sampling in an effort to define the vertical and lateral extent of hydrocarbon impact. UVIF-CPT data will be synthesized with analytical laboratory data from the DP samples to develop a stratigraphic model that will include locations of residual masses of NAPROJECTSAT Group\Don Rodgers\work plan addendum.doc SHAW ENVIRONMENTAL, INC.