WORK PLANS_FILE 1 - Laserfiche WebLink

Home Browse Search

Geological Techda Inc. Page 2 Bioventing/Biosparging Pilot Test Work Plan Project No.770.2 June 9,2006 r • 1992 to 1998—intermittent monitoring/sampling of wells MW-1 through MW-4. • 2000 to present - quarterly groundwater monitoring & sampling of all site monitoring wells. *Pre-2001 data from Wm. J. Hunter& Associates documentation. The data compiled during the course of this investigation indicate that the soil and groundwater were impacted with diesel range petroleum hydrocarbons. 2.0 SITE CONCEPTUAL MODEL A Site Conceptual Model (SCM) dated August 23, 2004 was developed and submitted for regulatory review. In accordance with the SJC PHS/EHD directives the SCM was updated to reflect new data obtained from additional field investigation. GTI submitted our April 20, 2006 "Site Conceptual Model (March 2006 Revision)" to reflect the new information obtained by the installation of eleven CPT borings on October 28 —November 3, 2005. The ,r following sections summarize the geology, hydrogeology and contaminant distribution at the _ site. 2.1 Geology • The geology of the site consists primarily of alternating layers, lenses and interstratified beds of clays, silts and sands. Units containing gravels are less frequent. Fine grained sediments dominate over course grained sediments. • Figures 4 and 5 provide a geologic interpretation of the units observed in the borehole logs. Note: The cross sections were developed using data gathered by different individuals utilizing different methodologies. Therefore, they need to be looked at as one of several possible interpretations of actual site conditions.) The cross sections include lithologies divided into fine grained units (slits and clays) or coarse grained units (sands and gravels). See Figure 3 for cross section locations. • Figure 4: Geologic Cross-Section A - A' illustrates the subsurface from the southwest to northeast sections of the subject area. The section displays the predominantly fine grained soils at the site. A significant sand layer is present in the location of wells MW-4 & MW-7 at a depth of 40— 45 feet bgs but no sand layer appears as laterally continuous across the site. • Figure 5: Geologic Cross-Section B - B' illustrates the subsurface from the northwest to southeast sections of the subject area. The section also displays the predominantly fine grained soils at the site as in Cross-Section A—A'. • The sand layer identified at a depth of 40 - 45 feet bgs in MW-7 was further defined during the November 2005 CPT investigation. The CPT investigation revealed that the sand layer appears to be a channel (?) deposit with a southwest-northeast trend as depicted in Figure 6. The sand/gravelly layer is present at depths ranging from as shallow