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n ' <br /> proposed that the clearwell be completely re-designed, utilizing a construction method that <br /> was unproven for potable water storage reservoirs. Carollo provided a significant level of <br /> review assistance to the City. The alternative was rejected by the City, and the Contractor <br /> was able to revise the construction schedule to indicate that construction of the project in <br /> conformance with the contractual requirements was feasible. <br /> • Thrust Block Failure Evaluation. During the excavation of Clearwell No.2, the Contractor <br /> undermined the thrust block on the 84"diameter outlet pipeline from Clearwell No. 1, <br /> causing it to become dislodged. This pipeline had been retrofitted into Clearwell No. 1 in <br /> 1997. Review of the as-built drawings identified that no additional reinforcement had been <br /> added at the site of the penetration, leading to concerns that the unrestrained pipeline could <br /> lead to wall failure and subsequent plant shutdown. Carollo performed extensive finite- <br /> element computer modeling to evaluate the potential for failure, ultimately concluding that <br /> the chances of failure were relatively small. <br /> • Recovered Water Pump Station Evaluation. Preliminary investigations were performed to <br /> evaluate the upgrade of the City's RWPS to provide greater reliability and accommodation of <br /> future recovered water pumping requirements.This work was later placed on hold pending <br /> further analysis by City staff of anticipated future pumping needs. <br /> • CFDS Overflow Re-Design. The construction drawings reflected the City's direction to tie the <br /> CFDS overflow piping into the existing Clearwell No. 1 overflow, which discharges into the <br /> creek on the east side of the WFP in an overflow event. During the construction period, the <br /> City expressed concern that an overflow to the creek presented significant environmental <br /> impact, and directed Carollo to modify the design to divert overflow overland to the west, <br /> away from the creek. The CFDS structure and finished site grade were redesigned, and <br /> modified construction drawings were prepared and issued to reflect the change. <br /> H:\Client\Everett_SEA\Contracts\7094A10-Clearwell dsgn\Amend 2\Exhibit A A-7 <br />