2006-07-05_REVISION - M1982015 (2)

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In response, the applicant has provided assurances that the slurry wall will be keyed into a competent layer or ryuivalent using excavations and grouting if necessary, and indicates that a geotechnical engineer will be onsite to detcm~ine when adeyuate key material were penetrated. Please commit to providing the Division with a copy of the QaQc Specifications f>r the Sluny 1WaH Installation currently being prepared by Terraa>n. Also, there are certain locations of the slurry wall installation where underground utilities run along or ntn perpendicular to the slurry wall. Has there been an analysis of what the impacts of the slurry wall installation will have on these underground utilities? Will the presence of the utilities impact the structural integrity of the slung wall'? Are there risks to the utilities during the installation of the slurry wall? What steps will be taken to ensure problems from occumng. Please respond. 3. Please address the following concerns with respect to the Groundwater Monitoring Plan recommended by the Applegate Group. a. Commitment - Camta has committed to implementation of a groundwater monitoring plan to assess changes in water level elevations due to the slurry wall installation. At this time, Camta is not yet the operator. Therefore, the current applicanVOperator (Siegrist Conswction Co.) will need to provide a definite commitment that the operator of the site will implement the proposed groundwater monitoring plan. b. Revised Map - fhe applicant will need to provide a revised copy of the Tab 14 Map ("Lake Rcrlamation Exhibit") which shows the locations of proposed groundwater monitoring stations, and the location(s) of wficre mitigation measures such as perimeter drains will be installed. c. Baseline Uata The applicant has proposed to use the existing lake water levels as a baseline water elevation. Please provide existing lake water surface data and a discussion of how the applicant will collect a set of baseline water levels, prior to slurry wall installation, that are representative of the existing groundwater levels in the area. Such determination will need to be representative of either a "worst case" scenario or the full range of natural groundwater (luchrations expected during the course of a 12 month period. d. Trigger Criteria The applicant has proposed a "trigger" ofthrec j3) fact beyond natural baseline elevations tier determining when mitigation measures will be implemented. Please discuss how this criteria was determined, and whether this criteria is adcyuate to ensure nu adverse impacts to structures to the west of the slurry wall, such as the C'DOT bridge foundations. ("Che Division rcyuests that the applicant use a trigger criteria that provides enough sensiti+ity to determine when adverse groundwater conditions may be occurring at or near a nearby, permanent man-made structure). c. Mitigation The proposed mitigation measures appear to be adequate to minimize impacts to structures to the west and north of the slurry wall installation.