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4 <br /> 20 June 2005 <br /> AGE-NC Project No 05-1306 <br /> ' Page 3 of 8 <br /> ' surface grade using portland cement The procedures for well abandonment are presented in <br /> Section 4 1 The location of MW-2 is shown on Figure 2 <br /> Following excavation,monitoring well MW-2 will be replaced,the location of the replacement well <br /> will be just beyond the down-gradient limit of the excavation, either approximately 5 to 10 feet <br /> southwest of boring HA-9,or 10 feet south of boring SB-2 The replacement well will be constructed <br /> utilizing identical screen intervals and construction materials as the previous well The replacement <br /> well will be developed approximately 24 hours after installation <br /> 1 3 3 SOIL EXCAVATION <br /> ' The focus of alternative 1 in the H&H-prepared CAP-A was to remove all soils containing more than <br /> 500 mglkg of TPH,based upon the Environmental Screen Levels(ESLs)from the San Francisco Bay <br /> Regional Water Quality Control Board The area to be excavated is defined by both historic soil <br /> borings and soil samples collected in 2004 (Figure 3) Laterally, the area is defined by wells HA-8, <br /> HA-9 and MW-4 and a utility pole directly south of the proposed excavation Vertically, TPH-d <br /> concentrations up to 1,500 mg/kg extends to 30 feet bsg at the source area, however, EHD, with <br /> CVRWQCB concurrence, recommended a maximum excavation depth of 25 feet bsg at the source <br /> area The soil will be removed using an excavator The proposed lateral extent of soil excavation is <br /> ' depicted on Figure 3, a soil excavation profile is depicted on Figure 4 <br /> During excavation activities, soil will be screened for organic vapors (OVs)using an organic vapor <br /> meter(OVM) <br /> 34 SIDEWALL SHORING <br /> The depth of the excavation of up to 25 feet bsg relative to the excavation width of approximately 25 <br /> ' feet necessitates steep sidewalls that must be shored Shoring procedures are presented in <br /> Section 4 2 1 <br /> ' <br /> 35 DEWATERING <br /> Water within the excavation will be dewatered(extracted) at a rate of approximately 15 gallons per <br /> minute(GPM),piped to a treatment system consisting of one 2,000-pound carbon vessel,treated,and <br /> discharged to the City of Stockton sewer system pending approval of a temporary discharge permit <br /> ' Dewatering procedures are presented in Section 4 3 <br /> • <br /> ' Advanced GeoEnvaonmental,Inc <br /> 1 <br /> f <br />