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%/ r.I TETRA TECH,INC. 3.0 DATA QUALITY OBJECTIVES Data Quality Objectives(DQOs)provide strategic scientific planning,which define systematic criteria on the type, quality, and quantity of data needed to characterize a site and make remediation decisions. DQOs are formulated by considering the problems that may be encountered during the sampling effort, determining what data will be needed to make future decisions, and using the data needs of the project to drive the data collection process. This process focuses the work and resources for maximum efficiency. DQOs were originally developed by the U.S. Environmental Protection Agency (EPA) to provide a planning tool for remedial investigations ate at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) sites. CERCLA human health risk assessments are typically based on comparing a measured environmental contaminant concentration to a regulatory action level or a remedial action goal. In this sampling effort,measured environmental concentrations of COCs will be compared to 2013 San Francisco Bay Regional Water Quality Control Board Tier 1 Environmental Screening Levels (ESLs; SFBRWQCB 2013). This sampling effort is not intended as a full-scale study of the nature and extent of potential contamination. The purpose of this sampling effort is to evaluate the rate of natural attenuation of CDCs in groundwater and soil at the Site,and the potential presence of COCs in soil gas. The seven steps of the DQO process for the investigation of the Site are presented below. 3.1 STEP 1: STATE THE PROBLEM 3.1.1 The Problem Tetra Tech must determine the rate of natural attenuation of COCs in groundwater and soil at the Site,and the potential presence of COCs in soil gas. 3.1.2 Conceptual Model The conceptual model involves impacts to soil, soil gas, and groundwater due to releases from OVP leaks at and adjacent to the south of the Site. During previous Site investigations, groundwater was encountered between depths of 8 and 10 feet bgs. Based on regional information, groundwater flow is north-northeast. Groundwater is not used for any purpose at the Site(Geomatrix 1999a). 3.1.3 Available Resources,Constraints,and Deadlines No environmental concerns other than those identified in Section 1.3 will be addressed under the scope of this work plan. The study area is limited to the groundwater, soil, and soil gas in the southern portion of the Site. COCs are limited to TPH, VOCs, and SVOCs. No other environmental concerns will be addressed during this sampling effort. Subcontractors will be used for drilling services and laboratory analysis(see Section 1.6). Permit requirements are described in Section 1.5. 3.2 STEP 2: IDENTIFY THE GOALS OF THE STUDY 3.2.1 The Primary Question What is the rate of natural attenuation of COCs in groundwater and soil at the Site,and are COCs present in soil gas? Sampling Effort Work Plan Page 3-1 Tracy Mansfield Property