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�- Cleo bgkat Technics inc. %`'1 %11/ Pace 4 Interim Remedial Action Plan b Project No.622.2 March 28,2005 V� 2.0 PURPOSE AND GOALS OF REMEDIAL ACTION The purpose of this plan is to propose an interim remedial plan to address the gasoline contamination that continues to source the MTBE groundwater plume. The goals of this corrective action are: 1. To remove the high concentration of contaminants located in the soil and groundwater La in the source area beneath the former UST excavation. 2. To prevent the further migration of groundwater away from the source area by inducing a capture zone through groundwater extraction. 3. To obtain additional groundwater pumping characteristics to complete the Site Conceptual Model (SCM) and to develop a final Corrective Action Plan (CAP). GTI plans on operating the system for a one year period to achieve these objectives. 3.0 INTERIM SOIL & GROUNDWATER REMEDIATION The following sections outline GTI's proposal for achieving the above listed goals. 3.1 Source Removal ` The core of the contamination plume is located beneath the former UST area. It will continue to source the groundwater MTBE plume that extends to the east to the location of MW-7. The dual phase extraction pilot test performed on wells EW-1 and EW-2 demonstrated that the source area was amenable to soil vapor extraction and groundwater extraction technologies. Removing this contamination will cut off the migrating groundwater MTBE plume. 3.1.1 Extraction Well EW-2 Extraction well EW-2 was completed with a screen length that penetrated the water table so the well could be used for both vapor and groundwater extraction. Well EW-2's construction details are included in the following table: w Well No. DiamJTD Screen Slot Sand Pack Transition Grout Seal (in/ft) Interval (ft) (in) (ft) Seal (ft) (ft) EW-2 4"132' 22—32' 0.010 20— 32' 18 -20' 18'-surface The pressure necessary for demonstrating vacuum influence is generally regarded as at least ;. 0.1 inches of water ("How to Evaluate Alternative Cleanup Technologies for Underground Storage Tank Sites", USEPA, May, 1995). The influence detected in monitoring wells MW- 1, MW-2 and MW-3 during extraction from EW-2 achieved an average minimum of 0.46 �. inches water vacuum during the December 2004 pilot test. Well MW-2 is located approximately 58 feet from EW-2 and this distance is used as a conservative estimate as the