SITE INFORMATION AND CORRESPONDENCE

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• • Y Mr. Phillip Fitzwater - 2 - 18 August 2005 4. OxyChem should submit a formal review of the remediation program every five years. This review should include results of the five-year soil gas surveys and an assessment of whether the health of residents of Bridgeport Trails are protected. 5. OxyChem should submit a soil and groundwater management plan that will be in force for the life of the remediation, a statement of the funding mechanism for the maintenance of the phytoremediation program, a plan for regular inspections and maintenance, a means to restrict future uses of the site that might interfere with remediation, and a plan to adandon the monitoring wells at Bridgeport Trails when the remediation is completed. Residents of Bridgeport Trails do not have access to shallow groundwater,which ranges from about five to ten feet below ground surface. In OEHHA's 29 May 2002 review of the 2001 Health Risk Assessment for Bridgeport Trails, OEHHA found that the Health Risk Assessment was overly conservative and concurred with the conclusion that the groundwater pollutants did not pose a risk to overlying residents. In late 2001, after the Health Risk Assessment for Bridgeport Trails was prepared, OxyChem excavated and treated about 2,900 tons of contaminated soil. The soil was excavated adjacent to the common boundary with Bridgeport Trails. By 2004, significant reductions in the concentration of groundwater pollutants, including volatile organic compounds,was observed in the downgradient monitoring wells located in the Bridgeport Trails development. As long as the constituent concentrations beneath Bridgeport Trails do not increase to the point that they significantly exceed the concentrations identified in the HRA, overlying residents are not expected to be exposed to harmful concentrations of constituents. Iris Environmental is concerned that soil vapor samples have not been obtained beneath the Bridgeport Trails development. The San Francisco Bay Regional Water Quality Control Board, in collaboration with the Central Valley Regional Board,has prepared a document of Environmental Screening Levels (Screening For Environmental Concerns at Sites With Contaminated Soil and Groundwater, Interim Final - February 2005)that conservatively estimates concentrations of specific constituents in various media that could pose risks to the environment or human health. For vapor phase transport of volatile compounds, the Environmental Screening Levels identify a 1,000-fold reduction between a volatile compound concentration in indoor air and its concentration in soil gas, assuming permeable soil extending about five feet below grade. An additional concentration reduction occurs as volatile compounds migrate to soil gas from groundwater. For the volatile compound 1,2-dichloropropane, the Environmental Screening Levels identify a threshold concentration of 280 ug/1 in groundwater (within five feet of ground surface, assuming permeable soils). If the 1,2-DCP concentration exceeds this value, then additional investigation, such as evaluation of soil gas, is warranted. The maximum concentration of 1,2-dichloropropane detected beneath the Bridgeport Trails development was 150 ug/1 in 2002, which is less than the screening threshold of 280 ug/1. At the present time, the Environmental Screening Levels do not identify threshold concentrations for 1,2,3-trichloropropane,the other volatile constituent of concern at this site. The maximum concentration of 1,2,3-trichloropropane detected beneath Bridgeport Trails was 2.9 ug/1 in 2003, and the concentration of 1,2,3-trichloropropane was 0.5 ug/1 in 2005. Regional Board staff has directed OxyChem to revise its Contingency Plan to include threshold concentrations for volatile organic compounds in groundwater that would be protective of human health via the vapor inhalation exposure pathway and to include an action plan should that threshold be exceeded.