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1 <br /> Treadvvell&Rollo <br /> • All nine on-site monitoring wells Four of these wells (MW-3, MW-6, MW-7 and MW-9 <br /> ' had the top of their screen below the groundwater table Four monitoring wells, MW-10, <br /> MW-16, MW-23 and MW-24, have had no or low, sporadic petroleum hydrocarbon <br /> detections and were previously removed from the sampling program Well MW-22 was <br /> removed because of site redevelopment plans <br /> ' Well SW-10 could not be located The 23 air sparging wells (made from 1-inch PVC tubing) <br /> were plumbed underground, without well boxes, and were not visible from the surface <br /> According to representatives of Advanced GeoEnvironmental, who installed the wells, and had a <br /> ' representative visit the site during the attempt to locate the wells, the well locations were never <br /> surveyed, and no as-built drawings of the well network was prepared Treadwell & Rollo used a <br /> ' backhoe to follow subsurface PVC piping from the old spargmg system location to the spargmg <br /> wells, and excavated the area around SW-10 During the planned subsurface demolition in April <br /> 2004, an additional attempt will be made to locate this well <br /> 6 0 PROPOSED REMEDIAL WORK <br /> The data indicate that high concentrations of gasoline, and possibly free product, are present in <br /> soil and groundwater around the former UST location From the early to mid 1990s, free product <br /> was consistently measured at a thickness greater than one foot in well MW-3 Since <br /> groundwater analyses began in MW-3 in 1996 (after the top of the well screen was submerged <br /> and product was no longer observed), the TPHg concentrations have not shown a significant <br /> change, and have averaged approximately 180,000 pg/L This is in spite of the fact that, for <br /> several years, in-situ remediation systems (air spargmg, vapor extraction and ozone spargmg) <br /> operated at the site During recent groundwater sampling, borings 16B-6b and 16B-8 had similar <br /> TPHg and benzene concentrations to MW-3, and a hydrocarbon sheen was observed on <br /> groundwater in these borings <br /> Soil sampling conducted during historic installation of wells around the former UST location, <br /> and during our investigation, identified high TPHg concentrations in soil above the water table <br /> 8 <br /> 25971014 DGD 7 April 2004 <br />