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Updated Human Health Risk Assessment Natural Attenuation Analysis and Additional Site Investigation Work Plan California Tank Lines, Inc. Since 1954 3105 South El Dorado Street, Stockton, California 2.0 PROPOSED SCOPE WORK As part of the current investigation, El and Taber Consultants propose the following tasks: • Prepare revised HHRA using California Office of Environmental Health Hazard Assessment Toxicity Criteria Database; • Prepare Natural Attenuation Analysis; • Advance two (2) soil borings north and south of MW-4 to depths of 50-feet bgs; • Install absorbent socks in monitoring well MW-2; • Assess the level of silt in monitoring well MW-1. 2.1 Project Planning and Permitting Taber Consultants will obtain required boring permits from the SJEHD. Underground Service Alert (USA) will be notified at least 48 hours prior to field work to locate any on-Site utilities near planned boring locations. As a further precaution against encountering underground utilities during drilling, the soil boring locations will be hand-augered to five-foot bgs. El developed a site-specific health and safety plan (HASP) to support the field work--- (Appendix A). Prior to commencement of field activities, a site safety meeting will be held at an on-site staging area near the working area. Emergency procedures will be outlined at this 2 meeting. Also the hazards of known or suspected chemicals of interest will be reviewed. Level D personal protective equipment (PPE) is the anticipated maximum protection required. N 2.2 Updated Human Health Risk Assessment �c ,�JILO On behalf of California Tank Lines, Taber Consultants will complete an updated Human l r° Health Risk Assessment (HHRA) to evaluate potential,,risks to human health associated with } Ib petroleum hydrocarbons remaining beneath the Site.;The HHRA will be completed using the RISC4—Risk Integrated Software for Clean-ups (RISC4) software program developed by BP 1n� Oil International. Default chemical parameters will be adjusted as needed to comply with the Lt A b� California Office of Environmental Health Hazard Assessment (OEHHA) Toxicity Criteria Database. The Johnson and Ettinger model which is included in the RISC4 program will be Y applied to predict levels of contaminants of concern (COCs) in indoor air based upon site �„ �o specific parameters and COC concentrations detected in soil vapor. The RISC4 Model utilizes I f f the Domenico Model to simulate contaminant transport in groundwater. ,s�t/Y ,Al a 3� 2 Taber Project No. 051087