ARCHIVED REPORTS XR0009294 - Laserfiche WebLink

Home Browse Search

' CW10g&A1 r AKi"tfir Page 3 Site Characterization Report ' Project No 724 2 . May 9,2006 ' • On November 20 -- 26, 2003, GTI supervised the installation of three continuous multi- chambered tubing (CMTrm) wells (MW-7, MW-8 and MW-9, respectively) Each ' CMTTM well was constructed with three discretely screened intervals with the bottom cap comprising an integral fourth screen at the terminal depth The MW-7 CMTTM well borehole was installed across E Castle Street approximately 120 feet northwest of the ' location of the former dispenser island The MW-8 CMTrM well borehole was placed across N El Dorado Street approximately 140 feet east of the location of the former dispenser island in the predominant down gradient groundwater direction The MW-9 ' CMTTM well borehole was placed in an up gradient location on W Adams Street approximately 220 feet from the former dispenser island • In our September 8, 2003 work plan, GTI proposed a pilot test to evaluate the use of dual ' phase extraction technology to clean up the soil and groundwater plumes Dual phase extraction involves the use of both soil vapor extraction and groundwater extraction ' technologies simultaneously from one well Extracting groundwater induces a cone of depression that exposes more impacted soil to vapor extraction The SJC/EHD approved the work plan in their November 15, 2003 letter correspondence Three new extraction ' wells (EW-1, VEW-1 and VEW-2) were installed at the site on July 7, 2004 and the pilot was performed on July 26 — 31, 2004 The results of the dual phase extraction pilot test were detailed in GTI's November 5, 2004 "Dual Phase Pilot Test" report and submitted to the SJC/EHD • An additional extraction well, EW-2, was installed at the site on September 28, 2005 for a pending groundwater treatment system ' The "Conclusions & Recommendations" section of GTP s "Dual Phase Pilot Test" report contained the following points the five foot sampling methodology utilized at this site may ' have failed to intercept lithologic units of greater hydraulic conductivity, and that the plume remains undefined down gradient of the MW-8/-1081-208 well cluster These concerns indicated that additional site characterization was warranted In our March 15, 2005 "Soil and Groundwater Investigation" work plan, GTI proposed using Cone Penetrometer Testing (CPT) in order to define the down gradient extent of the gasoline impacted groundwater and address the above concerns The following sections detail the completion of three CPT borings (CPT 1 — 3) to the northeast of the subject site in February 2006 ' 2.4 SOIL & GROUNDWATER INVESTIGATION 2.1 Cone Penetrometer Testing ' Cone penetrometer testing (CPT) uses specialized technology to determine subsurface lithology It consists of using a large truck to apply massive force to drive a cone at the head of rods through the subsurface Friction, pore water pressure and tip resistance are measured