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CLEARWATER <br /> G R O U P, 1 N C. <br /> €n iranmenta! Services <br /> Clearwater respectfully requests that PHS/EHD reconsider the conceptual design as <br /> submitted. Data that support this assertion were presented in the Remedial Action <br /> Plan (RAP) and are amplified below: <br /> • While air sparging was demonstrated as feasible, data presented in the RAP <br /> indicates that this approach is second tier, and should only be initiated following <br /> the removal of a significant fraction of the contaminant mass, including the <br /> floating product. The recommendation to implement air sparging as a second <br /> tier remedial application is associated with the fact that the Ruiz residence is <br /> within the identified area of soil and groundwater contamination, and the forced <br /> volatilization of hydrocarbons in the immediate vicinity of their living space <br /> may result in unacceptable exposure of the Ruiz family to potentially harmful <br /> vapors. <br /> • As indicated by the information provided in the PAR, the purpose of extracting <br /> both groundwater and soil vapor from a single extraction point is to aggressively <br /> address the hydrocarbons adsorbed to soil beneath the surface of the existing <br /> water table, not simply to extend the radius of system influence. Water levels at <br /> this site fluctuate significantly between the wet and dry seasons, and as such, <br /> contaminants are periodically trapped beneath the surface of the water table. Soil <br /> vapor extraction without dewatering would not remove these trapped <br /> hydrocarbons. <br /> Additionally, as you are likely aware, the application of vacuum to vapor <br /> extraction wells completed in fine-grained materials typically results in an <br /> upwelling of groundwater in the extraction wells, often occluding the very area <br /> that the extraction system is attempting to address. Given the fact that a <br /> significant fraction of soil contamination evidenced at this site is located within <br /> the capillary fringe, it is very likely that wells completed in the contaminated <br /> zone would experience this problem. For this reason, the installation of <br /> additional vapor extraction wells in exchange for the elimination of the <br /> groundwater extraction component of the remedial process appears <br /> inappropriate. <br /> I have enclosed copies of two papers presented in May at the National Ground <br /> Water Association Outdoor Action Conference. As the papers state, multi-phase <br /> extraction is neither new nor unproven. I hope this information is useful in <br /> your re-evaluation of Ruiz site data. <br /> • Extraction of contaminants from multiple wells has been demonstrated to <br /> significantly reduce the remedial time period, as the contaminants are removed <br /> from the surface much more quickly than would be possible using a single <br /> extraction point. As site conditions dictate the use of dual-phase recovery <br />