SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

Mithael Oliphant -4 - 18 October 2012 NFAR- Former Vernalis Pump Sta concentrations of 9,000 to just under 18,000 mg/kg at depths of 11 feet to over 30 feet bgs; visually affected soil was observed in soil at those depths. Analytical results for some samples from other nearby borings at depths between about 11 to 69 feet bgs were ND for TPH compounds. Threat to Groundwater: The historical OVP pipelines and pump station facility were removed from service more than 40 years ago. The lateral and vertical extent of affected groundwater overlaps, and is larger than the affected soil area. It occurs within/beneath the location of the historical crude oil pipelines, pump station, State Highway 33 and UPRR easements, and some adjacent agricultural land downgradient to the east. Investigations for the downgradient Vernalis Offsite project were previously completed and the case was closed in September 2010. i According to a Department of Water Resources (DWR) well.records search in 2010, the wells identified are upgradient or crossgradient of affected soil/groundwater. In addition, depth'to onsite groundwater is about 30 to 40 feet bgs. The DWR wells identified are screened to depths greater than the vertical extent of affected soil/groundwater. Due to the distance and direction up/cross gradient locations, it is unlikely conditions at the Site will affect these wells. Considering the present Site uses, it is not likely a water supply well would be completed onsite, within the railroad, highway, or pipeline easements. Threat to Human Health: Dermal contact is possible by future maintenance/trench excavation workers within the area of affected shallow soil at the Site. Based on the applicable environmental screening levels and the risk screening evaluation using residential exposure scenario (considered very conservative), the concentrations of residual crude oil present in soil should not result in an unacceptable health risk for an adult or child resident. The non-cancer health hazard is below the de minimus level of 1, which is a conservative estimate of risk. However, avoiding development of the known affected areas on the Site by future excavations could reduce/minimize potential human contact with residual TPH compounds. Summary: Based on the investigative findings, and a health risk screening evaluation, it is anticipated that the residual crude oil remaining would not present an unacceptable threat for the residential exposure scenario that was considered. The concentrations of residual crude oil compounds detected in soil and groundwater are highly immobile, limited in extent, and will continue to naturally degrade with time, likely over several years. Consistent with SWRCB Resolution No. 92-049, an evaluation of alternative cleanup technologies other than natural attenuation are ineffective, not easily implemented, and/or disproportionally costly in comparison to benefits. The site specific SGMP acts as a management reference designating Chevron as the responsible party if any affected soil or groundwater confirmed to be related to the historical pipelines is encountered during future construction/utility maintenance work. A copy of the SGMP was provided to the owners of property determined to overlie the areas of affected soil/groundwater. The Site groundwater monitoring wells were properly destroyed in 2009. One upgradient domestic water supply well is not anticipated to be affected by Site conditions. A threat to sensitive ecological wildlife receptors do not appear to exist within a one-mile radius of the Site. Comments received from a representative for a nearby property owner during the 30-day public notice period were addressed by Chevron and Central Valley Water Board staff. No further comments or follow-up response from the.representative was provided.