2014-12-24_REVISION - M2004051 (3)

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energize the lines. Envirocon continued excavation upstation until reaching approximate Station 60 +40 on April 19. On April 19, the crew reversed direction again in order to complete the slurry wall on the northeast part of the site. The crew continued downstation excavation from approximate Station 41 +10 through Station 0 +00 (on May 16) and continuing down station to station 94 +50 (on May 21) which was the closest point of approach of the slurry wall allowed on the south by PSCO. PSCO was not able to deenergize the lines at this point. Because the lines were not deenergized, Envirocon returned to approximate Station 60 +40 on May 29 and commenced excavation upstation until approximate Station 68 +20 on June 1. PSCO deenergized the lines on June 3 and Envirocon excavated below the lines from approximately Station 94 +50 to approximately 93 +00. On June 4, Envirocon was awaiting delivery of steel plates to protect the gas transmission line on the south side of the site. Envirocon returned to the north and excavated from approximate Station 68 +20 to 70 +30. After delivery of the steel plates, the crew returned to Station 93 +00 and excavated downstation through Station 70 +30 finishing the entire length of the wall on June 14. The trench continued past the finishing point providing 20 feet of overlap. As construction progressed, the mixing area was graded to provide an access road along the completed slurry wall and a protective soil cap was built over the slurry wall. At the end of construction personnel from Tetra Tech, Al, and Envirocon performed a final walk through. The purpose of the walk through was to observe the protective soil cap, the reclaimed slurry mixing pond, and other construction related items. 3.0 QUALITY CONTROL TESTING Engineering services provided by Tetra Tech included quality control testing on the slurry and the backfill, monitoring slurry wall key depth into bedrock materials, and the assimilation of as -built information. A summary of the quality control test results is presented in Appendix C. The material quality control program was followed throughout slurry wall construction. Test types, frequency, and specified test requirements are summarized on Table 1. In order to provide timely test results, a testing laboratory was set up on -site. Testing equipment included a mud balance, Marsh funnel, sand content kit, portable microwave oven, scale, portable sieve shaker, various sieves, #200 sieve wet washing apparatus, filter press, pH strips, and slump cone apparatus. In addition, six samples of backfill were obtained for laboratory permeabilities. These permeability tests were performed by a subcontract laboratory and are summarized on Table 2. Timely test results allowed for near real time adjustments to the various slurry trench parameters throughout the project. Testing conformed to industry standards, including the American Petroleum Institute - Specification 13A, the American Petroleum Institute Recommended Practice - Specification 13 -B -2, and ASTM C -143. - 3 - August 2013 PA23514 \133- 23514- 13003\Docs\ Reports\ Wattenberg _Construction_Report_2013.doc