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Lined Pit Guide 13 Sentember 2000 Post Construction Testing Typically, post construction testing will be conducted in accordance with the "State Engineer Guidelines for Lining Criteria for Gravel Pits," August 1999, section 3.1. This document is available from the Office of the State Engineer or online at http://water.state.co.us/pits.htm. Once an Operator can document that the State Engineer has determined the lined pit meets performance standards, the Division of Minerals and Geology can release the portion of the bond that covers clay liner installation PERMITTING OPTIONS Frequently, the process of permitting a gravel pit and lined reservoir project precedes the design phase making it difficult and costly to prepaze and application that will qualify for the regulated construction option and the reduced bond amount. The following list describes permitting mechanisms that may be employed to allow application approval prior to design and specification preparation and preserve the option to post the reduced bond amount available under the regulated construction option. • An application could include a general description of the clay liner or slurry wall installation, similaz to what would be sufficient under the 100 percent performance bonding option. The application would be approved with a commitment stating that a liner or slurry wall design, specifications, and quality assurance plan would be submitted as a technical revision and the revision would be approved prior to the exposure of ground water in the pit. • An applicant may find it difficult to design a clay liner mix and specifications for gradation and plasticity until after a pit has been opened up and representative samples of overburden and underlying bedrock can be collected. In order to permit and bond for a clay liner when the liner soil specifications have not yet been developed, an Applicant may include in the bond a cost for mixing bentonite into the liner soil. This will assure that a low permeability material can be created from virtually any fine grained overburden, even if the overburden is non-plastic. The amount of bond dedicated to adding and mixing in of bentonite may be released once the pit soils have been tested and demonstrated to be suitable for lining. • There are circumstances where an Applicant proposes to install a slurry wall prior to initial excavation in the pit. This method has the advantage minimizing water inflows and dewatering costs during mining. If an Applicant commits to complete installation of the slurry wall prior to exposing ground water in the pit, and can demonstrate that the slurry wall performs up the standards established by the State Engineer, bonding for the slurry wall maybe waived. However, it may be difficult to demonstrate that the slurry wall is performing up to standard until after the pi[ has been excavated and the rate of any inflows can be measured over time. If an Operator can provide the Division with a construction report and engineer's certification of the slurry wall prior to the exposure of ground water, and the Division accepts that the report and certification demonstrate that the slurry wall will function up to standazd, then the operation would be eligible for the reduced (20 percent of replacement cost) slurry wall bond.