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� r 6709iCA17CCIMICS1/u. Page 4 Dual Phase Extraction Pilot Test Work Plan Valentine(Castle Motors) 6w Project No.764.2 5ollowing September 8,2003The extraction well is proposed wi construction: Well ia. Screen Slot Sand Packtans. ea rout Seal �..� 4'�T60 - fl.U2U" san - -1 -sur ace This construction is proposed for the following reasons: ❑ A sand unit is present in the location of SB-B extending from approximately 20 to 35 feet bgs. (see Figure 4A) These sediments should exhibit a greater hydraulic conductivity then the clayey sediments predominant at the site. This location also has the highest levels of detected soil contamination in the investigation- select data 'aw from a previous consultant is included in Appendix F. ❑ The well screen extends to a depth of approximately 20 feet below the historical range of groundwater elevation at the site (groundwater depth 33 feet bgs June 2003). This will allow for continued vapor extraction if the well is de-watered during the test. 2.3 Soil Vapor Monitoring/Extraction Wells v The groundwater elevation has exceeded the screened intervals of all eight of the site's existing monitoring wells for the quarterly events completed since 1998. This will require the installation of at least two new monitoring wells to measure vacuum influence above the water table. GTI proposes installing two monitoring wells with screened intervals similar to the construction of well E - ewes a used as monitoring points during t e field es s Un-d can a so e used as Tuture soil vapor/groundwater extraction wells. The soil vapor monitoring/extraction wells are proposed with the following construction: Well a. creen of _Sand Pac Trans. Seal Grout Seal . sanTI8=5 - -sur ace "75 - sand - - I-5'-:sur ace Figure 6 includes a fence diagram of the subsurface as viewed from the east of the site. Proposed extraction wells EW-1, VEW-1 and VEW-2 are placed in the vicinity of MW-101 adjacent to the foriner dispenser island that is the presumed source of the gasoline release. The operation of the dual phase extraction system should indicate the effectiveness of the two technologies for the site. Initially, the vapor/water extraction will be from strata of higher conductivity but the vacuum influences will eventually permeate the lower conductivity clay units. As more fresh air is drawn into the soil, natural attenuation will be augmented through the introduction of oxygen to the anaerobic environment. 2.4 Dual Phase Extraction Test v GTI proposes conducting a 5-day pilot test utilizing proposed well EW-1. To optimize the pilot testing process, we propose to perform two separate tests using the dual phase equipment. The tests will include: 1. Vapor Extraction Test - measuring vacuum influence at surrounding monitoring wells to determine the effectiveness of soil vapor extraction for vadose zone remediation.