WORK PLANS - Laserfiche WebLink

Home Browse Search

with regulatory agency approval. The sampling locations should include biased 8. An assessment of the adequacy of the current CSM and a subsequently sampling locations to optimize detecting and delineating VOCs. Selection of revised CSM; appropriate number,locations and sampling depths are site-specific,and should 9. Data gaps identified based on revised CSM;and be based on the CSM and the project DOOs. 10.Conclusions and recommendations: Sample Depth Soil gas sample depths should be chosen to minimize the effects of changes in All engineering or geologic work(e.g.,logging continuous soil cores,soil barometric pressure,temperature,or breakthrough of ambient air from the description)should be performed or supervised by a California Registered surface and to ensure that representative samples are collected. Consideration Professional in accordance with the Business and Professions Code, should be given to source location,types of chemicals of concern,and the Chapters 7 and 12.5,and the California Code of Regulations,Title 16, lithology encountered. Chapters 5 and 29. Vapor monitoring wells should be installed at a minimumoftwo sample depths, at approximately five(5)feet below ground surface(bgs).and 10 to 15 it bgs. 2.3 Soil Gas Sampling Location and Sampling Wells/Probes Installation Variation of sample depths and the need for deeper sample locations will be evaluated based on site specific characteristics. Lithology For shallow contaminant sources of less than 10 feet bgs,collect soil gas samples immediately above the source. Samples collected at less than 5 feet Use site soil or lithologic information to select appropriate locations and depths bgs may be subject to barometric pressure effects and are more prone to for soil vapor monitoring wells. If on-site lithologic information is not available ambient air breakthrough. For deep contaminant sources,collect soil gas prior to conducting the soil gasinvestigation,at least one(1)continuously cored samples starting at 10-15 feet bgs. boring to the proposed greatest depth of the soil gas investigation should be - installed at the first sampling location,unless specifically waived or deferred by When evaluating vapor intrusion,obtain soil gas samples at appropriate depths the regulating agency. Depending on site conditions,additional continuously so that risk to human exposure can be adequately quantified. Empirical studies cored borings may be necessary. If the soil gas data are to be used for human indicate that shallow soil gas measurements at 5 feet bgs may not be indicative health risk assessment or vapor intrusion assessment,the lithology/geology of soil gas concentrations under buildings(Hers et al.,2006;DiGiulio and Cody, should be understood and documented in an appropriate level of detail. 2006). These studiessuggest that soil gas samples collected at depth of 10 to Geotechnical information required to be collected for vapor intrusion risk 15 feet are a better indicator of vapor intrusion risk than samples collected at 5 assessment purposes can be found in the DTSC Vapor Intrusion Guidance feet bgs when the source depth is greater than 15 feet bgs. Numerical modeling (Cal/EPA;-2005,Appendix H). A statistically sufficient number of geotechnical also suggests this relationship(Abreu and Johnson,2005;Abreu et al,2006). samples should be collected for vapor intrusion(i.e.,Johnson&Ettinger) Hence,risk quantified with shallow soil gas measurements(5 feet bgs)using the modeling used for the risk assessment. Johnson and Ettinger(1991)model may yield estimates that are biased low if the Prepare lithologic logs prepared for all borings,soil matrix sampling,and soil gas is from a deep source, geotechnical sampling. Information gathered from the continuously cored For vapor intrusion evaluations,soil gas sample depth is dependent on the depth borings may include soil physical parameters,geotechnical data and contaminant of the contaminants. Deeper sampling would be needed when evaluating data. Use information collected from borings to modify the CSM. Provide all buildings with basements(Abreu or al.,2006). - boring logs to the agency. Sample Spacing Vertical Profiling Vertical profiling is achieved by collecting soil gas samples at varying depths in a Sample spacing should be in accordance with the study design rationale single location,or by using closely spaced vapor monitoring wells installed at provided in the workplan,and may be modified based on site-specific conditions varying depths. Use vertical profiling in areas where significant contaminant concentrations are identified.The objectives of vertical profiling are to: 3/3/2010 -17- 3/3/2010 -18-