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6. TERMINOLOGY <br /> Asymptotic Stabilization - describes the function where an expression containing a <br /> variable tends to infinity when a given value is approached; for the SVE systems, VOC <br /> concentrations are anticipated to stabilize after a rapid decline in concentrations is <br /> observed. <br /> Capillary zone - the zone immediately above the water table, where water is drawn <br /> upward by capillary attraction. <br /> Clean closure - (see definition for closure below); specifically refers to closure meeting <br /> both performance criteria, (i.e. stabilization of VOC concentrations and achieving specified <br /> soil gas cleanup goals). Clean closure requires no further action other than a closure <br /> report. If soil gas cleanup goals are not achieved, closure can proceed with residual VOCs <br /> left in soil. <br /> Closure - closure in this memorandum refers to completion of SVE system operation in <br /> accordance with the procedures described in this memorandum and the achievement of <br /> one or both performance criteria established to assess the effectiveness of the SVE <br /> system. Completion of the procedures and meeting one or both criteria indicates that the <br /> SVE system has been operated to its limit to control sources of VOCs in the soil. Closure <br /> in this case may entail a risk assessment and/or possible site restrictions. <br /> Mass removal rate - the VOC mass removed instantaneously or cumulatively can be <br /> calculated using vapor concentration and flow rate measurements. Remedial progress can <br /> be evaluated using mass removal rate determinations over time as an indicator of the SVE <br /> system's relative effectiveness. <br /> Pulsing - the periodic shutdown and startup operation of the SVE system to allow the <br /> subsurface environment to come to equilibrium (shutdown) and then begin extracting <br /> vapors again (startup). <br /> Rebound - VOC concentration rebound is defined in this memorandum as occurring if <br /> static VOC vapor concentrations exceed 200% of the vapor concentrations measured at <br /> the end of the final stabilization period. <br /> Soil gas cleanup goals - DTSC has specified performance goals for soil remediation <br /> based on the application of the Los Angeles Regional Water Quality Control Board "Interim <br /> Guidance for Remediation of VOC Impacted Sites." Due to the volatile nature of the <br /> chemicals of greatest concern, ( i.e., PCE and TCE) DTSC has published preliminary <br /> performance goals for soil gas rather than soil. <br /> Stabilization period - defined for the performance criteria presented in this memorandum <br />