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procedure. I also appreciate the information as to the problems with the volumes derived with the WINTR -55 for small <br />sites (interestingly, while doing further hydrology related investigation on the web I came across one state that prohibits <br />it's use for sites less than one acre in size). <br />Prior to resubmitting either the drainage for the JBird 110d technical revision or the Prince Albert 110d permit application, I <br />would like to clarify several items. <br />Item one - In the comments on the latest drainage resubmittal for the JBird, the use of a geotextile filter was ruled out and <br />the use of a granular filter specified. In doing so it was stated that DRMS has seen a number of riprap failures due to the <br />use of a geotextile and that this is corroborated by Frizell, et al in the riprap design guide being used for these projects. <br />However, when reviewing PAP 790 for it's conclusions on the use of a geotextile filter as a supplement or replacement for <br />a granular filter, this does not appear to be correct. In the authors' conclusion it is stated that a geotextile filter should be <br />used if there is no granular filter. If the discussion of the failure of geotxtile filters is in another paper on this topic I would <br />be interested in seeing it. <br />Additionally, in researching this, it was found that nearly every Federal, State, or local entity with criteria that can be <br />accessed on the web allows the use of geotextile as a supplement to or a replacement for granular filters. This correlates <br />with Ten Cate's usage suggestions for their Mirafi line of products <br />Therefore, unless there are other circumstances that would contraindicate this usage, it would be preferable to retain the <br />use of the geotextile filter and it is requested that DRMS reconsider this comment. <br />Item two - Related to item one is the configuration of the 100 yr discharge spillways for the proposed retention ponds. As <br />the flow velocities in the throats of the spillways are under 2 fps, carrying a 16 -24 inch layer of riprap through the throat <br />seems excessive. Therefore, the intent is to carry the geotextile filter through the spillway and terminate it on the inside <br />face of the pond one foot (vertically) below the break. This should act to prevent flow beneath the filter. A 1 -2 inch thick <br />layer of sand /gravel is to be placed over the fabric to protect the geotextile from exposure (primarily as a UV screen). <br />Item three - As to the suitability of sandstone as riprap. The NRC at the time of the Uravan mill decommissioning <br />performed extensive investigation (in conjunction with the CSU civil engineering department - see attachment) into this <br />topic. As a result of this investigation, the NRC has used sandstone extensively at Uravan and other sites in the West. <br />This also resulted in the development of criteria for determining the suitability of specific deposits of sandstone. As the <br />JBird and Prince Albert ponds are not being designed to meet the NRC's 1000 year criteria for uranium tailings <br />impoundment it would be preferable not to have to run the battery of lab tests to determine if the sandstone at the mine <br />sites would meet those cnteria. In reviewing the literature on riprap grading I came across a decision chart for field testing <br />limestone (Riprap design criteria, recommended specifications, and quality control, modified from Office of Surface Mining <br />- 1982) that would appear to work equally well for the sandstone that is proposed for these projects. <br />There are several other entities (Nebraska DOT, Pennsylvania DOT, among others) that allow or have specific criteria for <br />the use of sandstone as riprap. Locally Montrose County road and bridge department uses quarry run sandstone for <br />riprap with field inspection for suitability. <br />For the Prince Albert project, Rimrock provided two specimens of the proposed sandstone last February for inspection as <br />to it's suitability. After examination of the specimens and determining the specific gravity of the material, the specimens <br />were placed outside. After over 9 months of exposure to freeze /thaw cycles and summer heat and precipitation (including <br />being watered weekly when the lawn was watered), the larger specimen has lost less than 3 per cent of it's original <br />weight. There is some minor spalling developing along fractures that were not originally visible, but that would occur with <br />any shot riprap. Corners are still sharp and there was only a dusting of loose grains on the bottom of the stone. <br />Finally, the ponds and spillways will be inspected during and after construction. They will also be inspected at least <br />quarterly by the operator as well as after any major precipitation event. In the event of significant deterioration of any of <br />the stones, they would be replaced. Ultimately, DRMS can track the performance of the riprap with it's annual <br />inspections. <br />3 <br />