FIELD DOCUMENTS_CASE 4 - Laserfiche WebLink

Home Browse Search

(I TLC) value of 1,000 mg/kg. The TTLC value, 'per Title 22 of the California Code of Regulations (CCR), is the concentration of a solubilized, extractable and .nonextractable bioaccumulative or persistent toxic substance which, if equaled or exceeded in a waste, renders the waste hazardous.' . 4.3 PRELEW NARY RISK ASSESSMENT The concentration of MTBE detected in groundwater in boring B1-2 (120 µglf) exceeds the US EPA Region IX Preliminary Remediation Goal (May 1998) of 201cg/I (for tap water) and the recommended US EPA drinking water health advisory for MTBE of 20 to 40 µgl f. These 1 levels are recommended concentrations that would likely avoid objectionable/unpleasant taste R and odor effects in drinking water. Health risks have been evaluated by Cal/EPA's Office of Environmental Health Hazard Assessment (OEHHA), who have proposed a public health goal of 14. parts per billion in drinking water based on their findings of potential cancer risk associated with MTBE exposure (OEHHA, 1998). The primary risks caused by the presence of-MTBE in groundwater at this site appear to be: 1) impairment of beneficial uses of groundwater in the immediate area; and 2) risks to the health and safety of sensitive receptors through exposure to MTBE. Beneficial uses of groundwater.in the area are identified in the Regional Water Quality Control Board Basin Pian as municipal, agricultural or industrial supply.- Sensitive receptors in the area are people who work in the vicinity'of the site, and possibly aquatic biota in the deep water channel located about 350 feet north of the site. Reasonable potential exposure pathways/scenarios for human contact with-the MTBE include inhalation of vapors, ingestion, or dermal contact. Scenarios for aquatic biota include ingestion.or external contact with potentially sensitive tissue. The following factors have been identified regarding the likelihood.of MTBE contact associated with these exposure scenarios: o Assuming that the MTBE found in the B1-2water sample was introduced by a ,_1 leak from the former tank at Site 1, the removal of the tank and the absence of MTBE (or any other petroleum constituents) in soils in the vicinity of the tank constitutes source removal. As such, remaining MTBE in groundwater will eventually be reduced to concentrations below action levels through natural attenuation and dilution through mixing with groundwater, thus reducing potential exposure. o Ingestion of MTBE is only likely to occur if the MTBE is transported by groundwater flow to an active municipal supply well used for drinking water. B&R contacted California Water Service, the municipal water supplier in the 6 98111AINVRPTs1S1USTINV.RPT