WORK PLANS_FILE 1 - Laserfiche WebLink

Home Browse Search

GeologtcaI Uckala Inc. Page 5 Bioventing/B iosparging Pilot Test Work Plan Project No.770.2 June 9,2006 r being in a down gradient direction of the former UST location for the monitoring events completed to date by GTI. The reason for this anomaly remains an enigma. None of the deep .. wells contained laboratory contaminants concentrations above the laboratory reporting limits and therefore a contour map was not developed. However, the discrete CPT groundwater samples indicate that the high concentrations noted in MW-5 (42,000 ug/1) attenuate very rapidly with depth. The groundwater sample from CPIP@ 73 feet bgs was obtained just five feet from and three feet below the screen of MW-5. his sample contained only 310 ug/1 TPH-D. 3.0 PILOT TEST OBJECTIVES The site presents challenges for the selection of a clean up alternative. Assuming an approximate depth of 15 feet bgs for the bottom of the former UST excavation, a vertical r column of 49 feet of impacted soil remains above the water table at 64 feet bgs (March — 2006). Soil layers of variable permeability are present to inhibit the vertical migration of diesel fuel and cause lateral migration or pooling of the contaminant. This case is demonstrated in the apparent NAPL present at 45 feet bgs in MW-7 where a fine to coarse- grained sand unit lies above a silt unit. In addition, veins and/or fractures in the soil structure has been identified that facilitate vertical migration of contaminants. Removing the contamination from this higher permeability zones would be relatively easy using soil vapor extraction (SVE) if the contaminant were gasoline, however, diesel fuel is much less volatile �.. than gasoline. _ In GTI's September 17, 2003 "Pilot Test for Soil Vapor Extraction" work plan we proposed a pilot test utilizing high vacuum (>25 inch Hg) soil vapor extraction (SVE). In an April 27, 2004 letter the SJC PHS/EHD denied the work plan on the basis that SVE was not applicable to diesel contamination and directed that a SCM be developed. GTI staff subsequently met with SJC PHS/EHD staff on June 3, 2004 to discuss the site. The challenge of remediating diesel contamination in low permeability soils was discussed at the meeting. It was agreed that our SVE work plan and additional site characterization would be set in abeyance while SJC PHS/EHD would contact the RWQCB for guidance on remedial technologies. In a June 17, 2004 email correspondence, SJC PHS/EHD stated that RWQCB staff proffered that bioventing technology was utilized by the Air Force to address diesel releases. The email `r also included links to relevant technology websites. Upon review of the relevant data and updating the SCM with the October 2005 CPT .r investigation, GTI recommends that a pilot test be pe.46ffwd for evaluating a combination of bioventing with low flow biosparging be performed at the site. This would involve injecting air into the subsurface to stimulate aerobic biodegradation of the petroleum hydrocarbons. The test would involve the installation of injection wells with associated infrastructure to blow air into the subsurface and monitor air flow rates, pressure, vacuum and other r