Laserfiche WebLink
DDRW-Tracy needs to provide more detailed and comprehensive <br /> description for establishing background levels of all <br /> constituents of concern. <br /> STLCs AND TTLCs VERSUS RISK-BASED ACTION LEVELS <br /> 10. In the discussions of contamination previously found in <br /> sample analysis results for various areas, comparisons are <br /> made with California's Soluble Threshold Limit <br /> Concentrations (STLCs) and Total Threshold Limit <br /> Concentrations (TTLCs) . While this may be the general <br /> practice, these numbers define hazardous wastes according to <br /> State guidelines and are not risk-based figures which are of <br /> importance in the Remedial Investigation/Feasibility Study <br /> (RI/FS) process. <br /> Proper figures to cite would be risk-based figures such as <br /> those presented in 40 CFR Part 264 , Subpart S, in the <br /> Federal Register dated July 27, 1990. This publication <br /> gives risk-based action levels (ALs) in soil, groundwater <br /> and air media for many contaminants, including metals, VOCs, <br /> SVOCs, and many pesticides. These ALs as listed in Subpart <br /> S represent "To-Be-Considereds" (TBCs) for the RI/FS process <br /> and will become applicable or relevant and appropriate <br /> requirements (ARARs) if and when the rule is promulgated. <br /> Table 1 is a direct comparison of TTLCs versus ALs. <br /> SOLID WASTE MANAGEMENT UNITS (SWMUs) <br /> 11. SWMU No. 3 , the present Industrial Waste Ponds (IWPs) , and <br /> SWMU No. 33 , the Industrial Waste Pipeline (IWPL) , are <br /> studied quite thoroughly in the AEPCO (1991) report <br /> referenced in this Work Plan. Extensive contaminants <br /> analyzed include all heavy metals, as well as some VOCs, <br /> SVOCs, reactive cyanides, sulfides, and organochlorine <br /> pesticides. (Analyses for other pesticides were not <br /> performed. ) Several of these constituents were discovered <br /> in downgradient wells (LM3 and LM15) in the August 1991 <br /> Monitoring Report. <br /> The EPA reviewers believe that these IWPs and the IWPL, as <br /> well as SWMU Nos. 7, 8 and 16 (potential or actual burn <br /> pits) , deserve special attention due to the potential wide <br /> range of contaminants involved at these sites which are of <br /> high probable risk to human health and/or to the <br /> environment. Some of the likely constituents that were <br /> utilized, destroyed or created (i.e. , at burn pits) at these <br /> sites are known or probable human carcinogens or teratogens, <br /> including arsenic, cadmium, chromium-VI, lead and dioxins. <br /> Metals, pesticides and VOCs have been detected downgradient <br /> from the IWPs and the IWPL, and the burn pits. The depth of <br /> the burn pits was reported to have been about two feet above <br /> I-3 <br />