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3.0 REMEDIAL INVESTIGATION ACTIVITIES 3.1 OVERVIEW Parsons was retained by PG&E to further assess the lateral and vertical extent of impacted soil, soil gas, and groundwater at the Site resulting from historical gas manufacturing and/or post- MGP operations associated with a former gasoline UST. Based on previous investigation results, the chemicals of concern at the Site include PAHs, TPH, VOCs and heavy metals. To develop the field investigation program, the United States Environmental Protection Agency (USEPA) Data Quality Objectives (DQO) process was utilized to facilitate the sampling approach design (USEPA, 2000). The DQO process is a seven-step iterative planning approach used to prepare plans for environmental data collection activities. It provides a systematic approach for defining the criteria that a data collection design should satisfy, including when, where, and how to collect samples or measurements; determination of tolerable decision error rates; and the number of samples or measurements that should be collected. DQOs define the purpose of the data collection effort, clarify what the data should represent to satisfy this purpose, and specify the performance requirements for the quality of information to be obtained from the data(USEPA, 2000). 3.2 FIELD INVESTIGATION PROGRAM Site investigation activities were conducted in July/August 2008 and April, 2009, which included the advancement and sampling of 15 soil borings; the installation and sampling of 22 soil gas probes; the sampling of five groundwater wells; and the collection of one grab groundwater sample. All field investigation activities were conducted in accordance with the Site-specific Health and Safety Plan (HASP) (Appendix D). Sample locations are presented on Figure 9, and the sampling program is summarized in Table 11. The field investigation consisted of three primary components: 1) biased soil sampling conducted in July/August 2008 and April 2009 to delineate areas where impacted soil was identified during previous investigations; 2) soil gas sampling conducted in July/August 2008 and April 2009 using a 100-foot by 100-foot systematic grid with additional biased sampling to delineate areas where impacts were identified in soil gas; and 3) groundwater sampling of five groundwater wells (TW-1 through TW-5) in August 2008, collection of one additional sample from TW-5 and the collection of one grab groundwater sample in April 2009. Soil borings were advanced to collect representative soil samples, at depth, for laboratory analysis and to allow for visual examination of subsurface materials and the identification of conspicuous MGP residual layers (such as lampblack). Soil gas samples were collected to identify the spatial distribution of VOCs in the subsurface and to assist with the assessment of potential vapor intrusion issues. Finally, groundwater samples were collected to determine if groundwater at the Site is impacted based on previous Site operations or by potential off-site sources. 3.2.1 Utility Survey/Geophysical Clearance Prior to intrusive investigation, proposed boring locations were clearly marked in the field with white paint. Underground utilities in the vicinity of marked boring locations were identified PARSONS 19 FINAL RI REPORT-FORMER TRACY MGP APRIL 2010