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I4 <br /> 5.3.3 General biological treatment procedure: ij <br /> ii <br /> 1. Drill through the concrete cap above the tank site. ' <br /> 2. Introduce the treatment mixture into the pea gravel mass. <br /> 3. Introduce bioventing if warranted. <br /> 4• Allow a minimum.of 30 days for biological action. <br /> 5. Evaluate the treatment progress. <br /> 6. Re-sample and retest within the contamination zone at a point where the highest <br /> levels of contaminants have been observed <br /> 7. If results exceed action levels,evaluate additional`treatment or extending treatment <br /> time an additional 30 days. <br /> 8. If results are below action levels,perform Idditional verification sampling. <br /> 9. When sampling indicates the contamination zone is below action levels request <br /> closure. <br /> 5.3.4 Discussion of Strengths and Weaknesses of Method <br /> : i� <br />{I Bioremediation potentially could be the method of)east cost,and would allow the native soils <br /> to remain in place. There are two draw backs. This method requires significant time for <br /> completion and would necessitate re-sampling to prove efficacy- <br /> 5.4 Excavation With Bucket Auger <br />' 5.4.1 Background <br /> A large Bucket Auger excavation follows the same rational as traditional excavation. The <br /> auger method allows removal without shoring. Shoring is avoided by making multiple small <br /> excavations with the auger and backfilling as the a'ger moves to the next borhole. <br /> i' <br /> The lateral extent soil investigation I� <br /> ga suggests the contamination is localized directly under the <br /> location of the gasoline tank. The bucket auger technique for remediation would be to <br /> excavate the soil directly beneath the tank location i to a depth of 28 feet. <br /> 5.4.2 General Procedure <br /> 1. The cap slab will be cut with a concrete sawl at a width slightly larger than 30 inches, <br /> k and a section of slab 30 by 72 inches removed. <br /> 2. Remove backfill material, (pea gravel), from the 30 by 72 inch section. <br /> 3. Remove native soils to a <br /> depth of 2$ feet, by multiple auger excavation. <br /> 4. Move the drill rig to clear another section.!, <br /> S. Backfill individual excavations. �# <br /> 6. Saw cut another 30 b 72 inch section and remove the slab section. <br /> Y � <br /> 7. Repeat steps 2.through 5.until the soils directly beneath the tank location have been <br /> removed. The cap slab dimensions are approximately 6 feet by 12 feet. <br /> 8. Excavated native soils will be transported to licensed soil remediation firm. <br /> Page 7 <br /> ill <br /> ji <br /> E <br />