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Updated Human Health Risk Assessment Natural Attenuation Analysis and Additional Site Investigation Work Plan California Tank Lines , Inc. smc® 1.954 3105 South EI Dorado Street, Stockton , California 2.0 PROPOSED SCOPE WORK As part of the current investigation , EI 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 . EI developed a site-specific health and safety plan ( HASP) to support the field work �J (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 LJ 2.2 Updated Human Health Risk Assessment OcL On behalf of California Tank Lines, Taber Consultants will complete an updated Human l r ° 0 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� x0. Oil International . Default chemical parameters will be adjusted as needed to comply with the 6t lbs\ California Office of Environmental Health Hazard Assessment (OEHHA) Toxicity Criteria f �C Database . The Johnson and Ettinger model which is included in the RISC4 program will be Y � 5 6161 v applied to predict levels of contaminants of concern (CDCs) in indoor air based upon site t �o specific parameters and COC concentrations detected in soil vapor. The RISC4 Model utilizes I f the Domenico Model to simulate contaminant transport in groundwater. °' 6D LL 2 Taber Project No . 051087