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c) Verify that the air flows are balanced if multiple spargmg wells are used <br /> d) Verify that air injection pressures are low enough to avoid fracturing the soil <br /> e) Verify that the contaminant concentrations are sampled and analyzed in accordance with a sampling and analysis <br /> plan designed to assess the system performance Determme if any additional monitoring is needed to evaluate the <br /> operating conditions <br /> f) Are groundwater samples being collected at proper locations(e g, at points at some distance from sparging <br /> wells yet still within the target zone) <br /> 7) Typical Performance Problems <br /> a) Is there evidence of short-circuiting along the well casing,through nearby utility corridors, or through soil <br /> fractures or other subsurface features) This may be due to poor well installation,preferential air flow paths and may <br /> require well replacement or relocation <br /> b) Have contaminant concentrations been declining in most of the target zone9 If concentrations are not declining <br /> significantly,consider the possible existence of additional source zones that may require remedial action,the <br /> likelihood of inadequate air distribution, or preferential air flow paths These conditions may require that additional <br /> wells be installed, air flow rates be increased,efforts be made to verify air flow paths, that ISAS be augmented with <br /> other treatment processes, or that ISAS be replaced by an alternate technology <br /> c) Did concentrations rebound following cessation of sparging? This may be due to short circuiting of air through <br /> the monitoring points(i e ,monitoring well concentrations do not reflect aquifer concentrations), inadequate air <br /> distribution, or ongoing sources Consider replacing monitoring points, increasing sparging well density,increasmg <br /> air flow to each well, or other source removal alternatives <br /> d) Is there good evidence for adequate air distribution in three dimensions based on relatively reliable indicators9 <br /> e) Are the air flows unevenly distributed among the various wells in a multi-well system?Determine if this may be <br /> due to incorrect flow control valve settm2s differences in de>7th to water in various wells, clogging of the wells, <br /> inconsistent well construction,or significantly different pressure drops in certain piping legs <br /> f) Has there been unexpected contamination found outside the target zone or any indication of an unknown source? <br /> (An investigation into another source may be warranted) <br /> 06/07/99 <br /> Page 4 of 6 <br />