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Lined Pit Guide 13 September ?000 <br />Post Construction Testing <br />Typically, post construction testing will be conducted in accordance with the "State Engineer <br />Guidelines for Lining Criteria for Gravel Pits," August 1999, section 3.1. This document is available <br />from the Office of the State Engineer or online at http://water.state.co.us/pits.htm. Once an Operator <br />can document that the State Engineer has determined the lined pit meets performance standards, the <br />Division of Minerals and Geology can release the portion of the bond that covers clay liner installation <br />PERMITTING OPTIONS <br />Frequeritly, the process of permitting a gravel pit and lined reservoir project precedes the design phase <br />making it difficult and costly to prepare and application that will qualify for [he regulated construction <br />option and the reduced bond amount. The following list describes permitting mechanisms [hat may be <br />employed to allow application approval prior to design and specification preparation and preserve the <br />option to post the reduced bond amount available under the regulated construction option. <br />• An application could include a general description of the clay liner or slurry wall installation, <br />similar to what would be sufficient under the 100 percent performance bonding option. The applicatiot <br />would be approved with a commitment stating that a liner or slurry wall design, specifications, and <br />quality assurance plan would be submitted as a technical revision and the revision would be approved <br />prior [o the exposure of ground water in the pit. <br />• . An applicant may find it difficult to design a clay liner mix and specifications for gradation and <br />plasticity until after a pit has been opened up and representative samples of overburden and underlying <br />bedrock can be collected. In order to permit and bond for a clay liner when the liner soil specifications <br />have not yet been developed, an Applicant may include in the bond a cost for mixing bentonite into the <br />liner scil. This will assure that a low permeability material can be created from virtually any fine <br />;rained overburden, even if the overburden is non-plastic. The amount of bond dedicated to adding and <br />mixing in of bentonite may be released once the pit soils have been tested and demonstrated to be <br />suitable for lining. <br />• There are circumstances where an Applicant proposes to install a sluiry wall prior to initial <br />excavation in the pit. This method has the advantage minimizing water inflows and dewatering costs <br />during minim. If an Applicant commits to complete installation of the slurry wall prior to exposing <br />ground water in the pit, and can demonstrate that the slurry wall performs up the standards established <br />by the State Engineer, bonding for the slurry wall may be waived. However, it may be difficult to <br />demonstrate that the slurry wall is performing up to standard until after the pit has been excavated and <br />the rate of any inflows can be measured over time. If an Operator can provide the Division with a <br />construction report and engineer's certification of the slurry wall prior to the exposure of ground water, <br />and the Division accepts that the report and certification demonstrate that the slurry wall will function <br />up to standard, then the operation would be eligible for the reduced (20 percent of replacement cost) <br />slurry wall bond. <br />