2001-05-22_REVISION - M2000158 - Laserfiche WebLink

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ENVIRONMENTS INC. MAY 22, 2001 PAGE 3 Attached are typical cross sections that will be used to design the bank armoring. They are from the Division of Minerals and Geol- ogy's Instream guidance document (Figure D-5, Figure D-7, and D-8). Proposed armoring plan Pickett Engineering used a D,o equal to 24 inches and the Divi- sion suggested the minimum thickness should be D,o x 2.0 for the pit banks and Dso x 1.75 to D,o x 3.0 on the river banks. These guidelines will be followed. If a change is necessary, revisions will be submit- ted to the Division for review and approval. Armoring will be doubled on each end of a reach whether in a lake or on the river, if it ends on a natural bank. Pit Slopes The pit slope armoring will be placed on slopes no steeper than 2.SH to lV as shown on the guidelines. The thickness will be calcu- lated by using D,o x 2.0 to determine the thickness. The applicant proposes using concrete rubble as riprap material. This material is readily available to Platte Sand ~ Gravel and has been proven effec- tive on other mines throughout Colorado. The concrete rubble is angular, durable, and non-slaking in nature, but physical testing and documentation showing that it meets the requirements and the gradation specification will be conducted on the material prior to use on each 500-foot section. Physical testing will include a slake test and an abrasion test to be sure the rubble is suitable for riprap. Any unsuitable material will be used as fill as explained in the permit application. The records of the test results will be kept in the corporate offices for review. Prior to placing the riprap the applicant will conduct at least one gradation test for each 500 linear feet of riprap installation to determine if the in situ material is suitable for the bedding. This will be done to demonstrate and document that the filter bedding is compatible with the riprap. This bedding will be a filter blanket of gravel, or sand and gravel that will prevent soil movement into or through the riprap. It is possible that the in situ materials will create suitable bedding, particularly on the pit slopes since pit run sand and gravel usually makes a good filter blanket. The armoring will cover a band from the existing ground surface to an elevation 3 feet below the river invert on any gives section and will be keyed in or doubled per the design specifications provided in the Division's guidance document. On the ends of the armored pit banks the depth