Passive Soil Vapor Extraction - GSI Environmental Inc.

SRNL-STI-2009-00571Rev. 14.2 Miscellaneous Chemical Basin (MCB)4.2.1 Site DescriptionThe MCB waste unit is located in the northwest portion of the Savannah River Site. Limitedinformation is available concerning historic releases within the MCB, but it is thought that thebasin received mixed solvent waste, used oil, and partially full drums until 1974. Thesehistoric releases led to vadose zone soil impacts and the development of a soil gas plume(with the center of the plume not corresponding to the former location of the basin due toregrading). Twenty-five vadose zone wells were installed across the source area of the MCBin 1996 (Figure 4.2) and Baroball TM devices were installed at the surface of each well casingon each well casing to facilitate passive soil vapor extraction due to natural barometricpressure changes. Monitoring of well vapor concentrations (PCE and TCE) began in April1996 as part of a treatability study that extended for a period of approximately 1 year. Basedon the success of this initial study, the system was left in place and continues to operatethrough present day. An active soil vapor extraction system was also operated betweenOctober 2001 and December 2002.Site characteristics that contributed to the selection of PSVE:• Vadose zone source is well-defined and present in deep, lithologically isolated strata• Need for cost-effective, low-maintenance treatment that protects the groundwater4.2.2 Results/Performance MetricsComprehensive performance data for the MCB is available from the treatability study (Rihaand Rossabi, 1997) and includes temporal concentration trends, mass removal rates, plumesize, cumulative mass removal, and estimation of remediation timeframe, as summarized inTable 4.2. It should be noted that the operation of an ASVE system at the MCB influencedthe performance of the PSVE after this period, such that subsequent data would notnecessarily be reflective of long-term performance of a stand-alone PSVE system.28 Enhanced Attenuation TechnologiesPassive Soil Vapor Extraction