PHASE II INVESTIGATAIONS AND HUMAN HEALTH RISK ASSESSMENT FOR ARSENIC Santa Cruz Branch Line Santa Cruz and Monterey Counties, California

Regional Transportation Commission (SCCRTC) to evaluate environmental conditions along the rail line in support of the acquisition of the Branch Line right-of-way, between Watsonville Junction and Davenport. The Phase II investigations consisted of advancing soil borings to collect soil samples at targeted locations along the Branch Line identified in AMEC's 1996 Phase I environmental site assessment (Phase I; Geomatrix, 1997) and during site reconnaissance in 2005 and 2009, and at systematic sampling locations for general site coverage outside of the targeted sampling locations. The analytical results for soil samples collected were compared to screening level criteria to evaluate whether environmental impacts were present along the Branch Line corridor. As part of the evaluation a site-specific background concentration of arsenic in soil was calculated for the Branch Line in support of a human health risk assessment (HHRA) for arsenic. Summary of Work Performed In 1996, AMEC performed a Phase I environmental assessment for the Site on behalf of the SCCRTC. The Phase I assessment included a review of historical documents, site reconnaissance, and an environmental regulatory file review. The findings of the assessment identified features that potentially could affect environmental conditions on the Branch Line and were used to develop a Phase II investigation and sampling plan. The investigations included the completion of a site reconnaissance to observe updated conditions along the right-of-way, a geophysical survey to locate a potential underground storage tank (UST), and the collection of soil samples at targeted on-site features identified during the Phase I assessment and 2005 and 2009 site reconnaissance. AMEC also performed systematic soil sampling of six, 1-mile sections of the Branch Line to evaluate general site conditions and the presence of arsenic in soil; arsenic impacts could have occurred from the possible historical use of herbicides along the right-of-way. Data Evaluation Analytical data generated during the Phase II soil investigations were compared to health-based risk screening criteria, and were used to assess whether potential environmental impacts were present along the Branch Line and additional investigation or mitigation could be warranted. AMEC also evaluated data with regard to waste classification criteria in the event that soil potentially could be excavated and require off-site disposal. As discussed in this report, arsenic is naturally-occurring and typically is present at concentrations greater than risk-based screening criteria. As such, these screening criteria are not directly applicable, and it is appropriate to evaluate the presence of arsenic by estimating …