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2.2 Soil Gas Sampling Probe Installation <br /> 2.2.1 Lithology: Site soil or lithologic information should be used to select <br /> appropriate locations and depths for soil gas probes. If onsite <br /> Iithologic information is not available prior to conducting the soil gas <br /> investigation, at least one(1) continuously cored boring to the <br /> proposed greatest depth of the soil gas investigation should be <br /> installed at the first sampling location, unless specifically waived or <br /> deferred by Agency. Depending on site conditions, additional <br /> continuously cored borings may be necessary. <br /> A Lithologic logs should be prepared for all borings(e.g., <br /> continuously cored borings, soil matrix sampling, geotechnical <br /> sampling, etc.). Note: This does not apply to direct-push soil gas <br /> probe installations. <br /> B. Information gathered from the continuously cored borings may <br /> include soil physical parameters, geotechnical data and <br /> contaminant data. <br /> C. If low-flow or no-flow conditions(e.g., fine-grained soil, clay, soil <br /> with vacuum readings that exceed approximately 10 inches of <br /> mercury or 136 inches of water) are encountered, soil matrix <br /> sampling using EPA Method 5035A should be conducted in these <br /> specific areas. Also see Section 4 of LARWQCB's"General <br /> Laboratory Testing Requirements for Petroleum Hydrocarbon <br /> Impacted Sites"on use of EPA Method 5035A. <br /> D. If the bottom five (5)feet of a continuously cored boring is <br /> composed of clay or soil with a vacuum exceeding approximately <br /> 10 inches of mercury or 136 inches of water, the continuously <br /> cored boring should be extended an additional five(5) feet to <br /> identify permeable zones. If the extended boring is also composed <br /> entirely of clay, the boring may be terminated. Special <br /> consideration should always be given to advancing borings and <br /> ensuring that a contaminant pathway is not being created through <br /> a low permeability zone. <br /> 2.2.2 Sample Spacing: A scaled site plan depicting potential or known areas <br /> of concern (e.g., existing or former sumps, trenches, drains, sewer <br /> lines, clarifiers, septic systems, piping, underground storage tanks <br /> [USTs], chemical or waste management units) should be provided in <br /> the project workplan. Sample spacing should be in accordance with <br /> the most current ASGI and may be modified based on site-specific <br /> conditions with Agency approval. To optimize detecting and <br /> delineating VOCs, the grid spacing should be modified to include <br /> biased sampling locations. <br /> 01/28/2003 -4- <br />