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I � <br /> I Updated Human Health Risk Assessment <br /> Natural Attenuation Analysis and Additional Site Investigation Work Plan <br /> California Tank Lines , Inc. since 1954 <br /> �I 3105 South EI Dorado Street, Stockton , California <br /> The updated HHRA will include an evaluation of the following potential exposure pathways . <br /> • On-Site ingestion of surface soil ; <br /> t � t , . A, <br /> • On-Site dermal contact with surface soil ; - , •. , <br /> • Off-Site ingestion of groundwater; vj�' J b �V <br /> • Off-Site dermal contact with groundwater: and <br /> • On-Site inhalation of indoor air. <br /> An adult worker and child resident will be selected as potential receptors. A cumulative <br /> carcinogenic risk will be calculated for each receptor to account for potential risks from all <br /> potential exposure pathways . In the similar manner, a cumulative hazard quotient will be <br /> r calculated for each receptor. <br /> The HHRA will be updated in conformance with the June 16 , 2009 Interim Guidance , <br /> Evaluating Human Health Risks from Total Petroleum Hydrocarbons (TPH), Human and <br /> f Ecological Risk Division , California Department of Toxic Substances Control , <br /> 2.3 Natural Attenuation Assessment <br /> Taber Consultants will prepare an assessment of the potential for natural attenuation to <br /> effectively degrade impacted ground water in the vicinity of MW-4. This assessment will use <br /> soil and groundwater analytical results from samples secured in the CPT study in September <br /> 2008 . \ WCL. yd e i v Dlif a -sem <br /> rGprr r , r <br /> 2.4 Soil Borings i1 ,.[.y4 <br /> Taber Consultants propose to advance two (2) Geoprobe® borings to an approximate ' n "za e <br /> depth of 50-feet bgs, in the locations shown on Figure 3 . Borings will be advanced to the north <br /> and south of monitoring well MW-4 to further delineate the extent of groundwater impacts in <br /> o .`' <br /> these areas . i :6/ /�� .., <br /> To provide a preliminary indication of petroleum hydrocarbons in the borings, a portable <br /> photo-ionization detector ( PID) will be used to monitor for the presence of organic vapors in drill <br /> cuttings collected from the boring at five-foot intervals. This field screening method will consist <br /> of filling a sealable plastic bag to about one-third capacity with soil and sealing the container. <br /> After allowing sufficient time for the soil vapor to equilibrate with the container's headspace, the <br /> bag will be slightly opened or pierced to allow for the insertion of the PID probe. The <br /> concentrations of organic vapors detected by the PID will be recorded on the boring log . Field <br /> screening will also include documenting visual indications for the presence of petroleum <br /> hydrocarbon impacts, such as staining , discoloration , and/or chemical sheens . Soil lithology will <br /> be logged using the Unified Soils Classification System ( USCS) method . <br /> 3 Taber Project No . 051087 <br /> I <br />