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WELL ABANDONMENT AND SOIL AND GROUNDWATER INVESTIGATION WORK PLAN US CAN-WELTY ROAD 1. INTRODUCTION At the request of Chevron Environmental Management Company(CEMC), Science Applications International Corporation(SAIC)presents this work plan for additional investigation at the US Can- Welty Road site(the site)in Vernalis,California(Figure 1). Former crude-oil facilities of Chevron's Old Valley Pipeline(OVP)and the Tidewater Associated Oil Company(TAOC)pipelines are located on the site,and past site investigations have documented the presence of total petroleum hydrocarbons(TPH) and polynuclear aromatic hydrocarbons(PAHs)in soil and groundwater. Although benzene,toluene, ethylbenzene,and total xylenes(BTEX)were minor constituents of crude oil,they are also constituents of concern(CDCs),as they are sometimes encountered at TAOC and OVP facilities. In the Soil and Groundwater Investigation Report and Second Quarter 2005 Monitoring and Sampling (SAIC,2005), SAIC concluded that the extent of affected soil and groundwater was not fully delineated and recommended additional investigation. The Central Valley Regional Water Quality Control Board (RWQCB)concurred with these conclusions and recommendations(RWQCB,2005). The RWQCB has also agreed with SAIC's recommendation that monitoring wells MW-3 and MW-4 be destroyed,because the wells do not yield adequate groundwater for sampling and analysis(RWQCB,2006). SAIC has subsequently evaluated historical groundwater sample analytical results against monitoring well destruction criteria(see Section 2.5 for more details). SAIC recommended the destruction of monitoring wells MW-3,MW-4, and MW-5,based on the evaluation,and the RWQCB agreed(RWQCB,2007), provided that the results of one additional groundwater sampling event satisfy the monitoring well destruction criteria. Therefore,this work plan proposes additional work to sample and abandon monitoring wells,as well as additional investigation to delineate the extent of soil and groundwater affected by crude oil. The investigation will be guided by the Technical Approach to Site Evaluation and Decision-Making, Historical Pipeline Portfolio, Central Valley Region(referred to as the"CTA";Geomatrix Consultants, Inc. [Geomatrix],2005). The CTA specifies Central Valley RWQCB Water Quality Objectives(WQOs) as the health-based and aesthetic criteria for determining whether groundwater is affected,delineating the extent of any affected groundwater,and assessing whether further groundwater characterization is appropriate. The CTA does not prescribe criteria by which affected soil is defined;therefore,U.S. Environmental Protection Agency(EPA)Region 9 Preliminary Remediation Goals(PRGs; EPA,2004) and San Francisco Bay RWQCB Environmental Screening Levels(ESLs;RWQCB,2005)will be used. Soil and groundwater analytical results will also be compared to ESLs,PRGs,and WQOs as a screening step to streamline the risk assessment process. The presence of a COC at a concentration above a screening level does not necessarily indicate risk to human health or the environment. It simply indicates that potential risk may exist and that additional evaluation may be warranted. Based on comparison of analytical results to the screening levels,the site may qualify for No Further Action Required status. 2. BACKGROUND 2.1 LOCATION AND SITE DESCRIPTION The site is located in San Joaquin County at 35275 Welty Road, Vernalis, California in a rural and light- industrial area. The site is situated at an approximate elevation of 103 to 105 feet above mean sea level and has a relatively flat topography that slopes gently downward to the northeast. The site is bordered by Welty Road on the east,Highway 33 on the north, and agricultural fields to the south and west. A paper insulation manufacturer,Insulair,Inc.,currently occupies the site. The site was formerly occupied by a �I"�I ate:• From Science to Solution