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RE: Clarification of comments on JBird drainage http: / /mail.aol.com/35478- 111 /aol- 6 /en -us /mail /PrintMessage.aspx <br />Tim Cazier, P.E. <br />Environmental Protection Specialist <br />Colorado Division of Reclamation, Mining and Safety <br />1313 Sherman Street, Room 215 <br />Denver, CO 80203 <br />ph: 303 - 866 -3567 x8169 <br />fax: 303-832-8106 <br />timcaziediestate.co.us <br />Rum: iamespirc (iiaol.com [mailto:jamcspirc(d)aol.coml <br />Sent: Tuesday. January 03, 2012 12:58 PM <br />To: Caner, Tim <br />Subject: Clarification of comments on JBird drainage <br />Mr. Cazier - <br />First I wish to thank you for providing the riprap sizing formula to be used in conjunction with the PAP 790 nprap design procedure. I also appreciate the <br />information as to the problems with the volumes derived with the WINTR -55 for small sites (interestingly, while doing further hydrology related investigation on <br />the web I cane across one slate that prohibits 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 penrnit application, I 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 the use of a granular filter specified. In <br />doing so it was stated that DRMS has seen a number of nprap failures due to the use of a geotextile and that this is corroborated by Frizell, et al in the riprap <br />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 a granular filter, this does not appear to <br />be correct. In the authors' conclusion it is stated that a geotextile filter should be used if there is no granular filter. If the discussion of the failure ofgeotxtile <br />filters is in another paper on this topic I would 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 accessed on the web allows the use of <br />geotextile as a supplement to or a replacement for granular filters. This correlates 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 use of the geotextile filter and it is <br />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 the flow velocities in the throats of the <br />spillways are under 2 fps, carrying a 16 -24 inch layer of riprap through the throat seems excessive. Therefore, the intent is to carry the geotextile filter through the <br />spillway and terminate it on the inside 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 performed extensive investigation (in <br />conjunction with the CSU civil engineering department - see attachment) into this topic. As a result of this investigation, the NRC has used sandstone extensively <br />at Uravan and other sites in the West. 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 impoundment it would be preferable not to have to <br />run the battery of lab tests to determine if the sandstone at the mine sites would meet those criteria. In reviewing the literature on riprap grading I came across a <br />decision chart for field testing 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 the use of sandstone as riprap. Locally <br />Montrose County road and bridge department uses quarry run sandstone for riprap with field inspection for suitability. <br />For the Prince Albert project, Rinrockprovided two specimens of die proposed sandstone last February for inspection as to it's suitability. After examination of <br />the specimens and determining the specific gravity of the material, the specimens were placed outside. After over 9 months of exposure to freeze /thaw cycles and <br />summer heat and precipitation (including being watered weekly when the lawn was watered), the larger specimen has lost Tess than 3 per cent of it's original <br />weight. There is some minor spatting developing along fractures that were not originally visible, but that would occur with any shot riprap. Corners are still <br />sharp and there was only a dusting of loose grains on tlx: bottom of the stone. <br />Finally, the ponds and spillways will be inspected during and after construction. They will also be inspected at least quarterly by the operator as well as after any <br />major precipitation event. In the event of significant deterioration of any of the stones, they would be replaced. Ultimately, DRMS can track the performance of <br />the riprap with it's annual inspections. <br />One further note - in reviewing the literature, it was noted that limestone is more susceptible to weathering than a silicified sandstone. hi a BUREC study it was <br />found that limestone nprap had failed at a 10 percent higher rate than sandstone used in similar circumstances for bank protection. <br />With the PAP 790 formula available for sizing the nprap and the inclusion in the formula of the specific gravity of the stone being used, the magnitude of the safety <br />factor will probably be reduced. Further thought will be taken on that matter. <br />Item four - as noted in the response to the comments on the first submittal for the JBird technical revision the potential discharge through the 100 year spillways <br />will occur after the flow has peaked. This raises a question on DRMS's criteria for for containment design - <br />2 of 3 2/9/2012 12:40 PM <br />