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} <br /> of residual constituents of concern in soil or and groundwater at the former wards <br /> • site <br /> g Verify that the concentrations are sampled and analyzed in accordance <br /> with the sampling and analysis plan designed to assess the system <br /> performance Determine if any additional monitoring is needed to evaluate <br /> the operating conditions Quarterly groundwater sampling is used to <br /> deternnine the combined in-situ AS/SVE system's effectiveness in treating <br /> dissolved concentrations of petroleum hydrocarbons beneath the site Monthly <br /> vapor samples collected on the influent and effluent sides of the SVE air stream <br /> are used to monitor the AS/SVE system's ability to extract hydrocarbons from soil <br /> beneath the site <br /> 7 Typical Performance Problems <br /> a Is there evidence of too much air flow through the soil such that travel <br /> times are too small, or that diffusion limitations hamper the effectiveness <br /> of the high extraction rates? (if extracting air at higher rates does not <br /> increase the mass removal rate, the system may be moving more air than <br /> necessary.) There does not appear to be any evidence to indicate that the SVE <br /> system is being limited by diffusion <br /> b Is there evidence of short-circuiting along the well casing, through nearby <br /> utility corridors, or through soil fractures or other subsurface features? <br /> Consider well replacement or relocation There does not appear to be any <br /> evidence to indicate that the SVE system is being limited by short-circuiting <br /> c Have the VOC concentrations in the extracted gas (in combined influent or <br /> from most wells) approached an asymptotic concentration value? This <br /> may be cause by diffusion limitations, continuing source, or poor well <br /> placement Consider whether reduced flows, system pulsing, additional <br /> wells, thermally enhanced SVE, or bioventing might remove additional <br /> contaminant mass Concentrations of VOCs in extraction wells have not been <br /> evaluated since October 2004 due the unplanned system outage on <br /> November 30, 2004 The influent vapor sample concentrations of VOC's for <br /> September 2004 were 132 parts per million (ppmv) The October 2004 influent <br /> vapor sample concentration for VOC's were 39 ppmv No sample was collected <br /> in November 2004 <br /> d Are there portions of the target zone in which contaminant concentrations <br /> have failed to decline in response to SVE? This may be due to inadequate <br /> air flout in that nnrfinn of the tarriat -ynna� rliffiocion hrnitatinnr� hinh enil <br /> moisture content perhaps due to surface irrigation, or a continued source <br /> of contaminants in that area Consider increasing air extraction rates from <br /> certain wells or the entire system, adding wells in areas of inadequate <br /> extraction, limiting irrigation, or excavating hot spot soils There is not <br /> enough information to evaluate the effect of the SVE since it was restarted in <br /> . September 2004 However, early indications are that the SVE system, in <br /> combination with the in-situ AS, has been effective in removing petroleum <br />