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Home My WebLink AboutDRC-2010-007687 - 0901a0688027eb94Geosyntec consultants •.yv cy I to j ^-^ \ y\ y y-^ yy <?J^ y;y 10875 Rancho Bernardo Road Suite 200 San Diego. CA 92127 PH 858.674.6559 FAX 858.674.6586 www.geosyntec.com 21 December 2010 David Rupp, P.E. Division of Radiation Control Utah Department of Environmental Quality 195 North 1950 West PO Box 144850 Salt Lake City, Utah 84114-4850 Oxnard, CA 93030 Subject: Response to Construction Deficiencies Letter Dated 9 December 2010 White Mesa Mill - Cell 4B Blanding, Utah Dear Mr. Rupp, Geosyntec Consultants, Inc. (Geosyntec) has prepared this letter on behalf of Denison Mines (USA) Corp. (DMC) in response to the Utah Department of Environmental Quality, Division of Radiation Control's (DRC's) letter of Construction Deficiencies dated 9 December 2010. For ease of review, the DRC's comments are summarized below in italics with DMCs responses following each comment. 1. The Slimes Drain Windrow Header a. Improper Exterior Geotextile. See Photo No. 1. This photo shows a portion ofthe slimes drain header. Cushion or non-woven geotextile is shown as the exterior cover of the slimes drain header. Conversely, woven geotextile is the required exterior fabric for the slimes drain header, per drawnng sheet 6 of 8, Section B-7. DRC's photo no. 1 shows a cushion geotextile "rub sheet" used during installation of the strip drains south of the header pipe. The cushion geotextile was used to protect the underlying woven geotextile from potential damage while the installer crossed over the header pipe at this location. Photo nos. 1 and 2 in the attached photo log (Attachment 1) show the woven geotextile as the exterior material. The cushion geotextile "rub sheet" has been removed from the exterior of the slimes drain header. SC0349.4B - RTCdatedl2-9-2010.20101210.doc engineers I scientists I innovators David Rupp, P.E. 21 December 2010 Page 2 b. Inadequate Lateral Ballast on Slimes Drain Header. See Photo No. 5 in the attached photos. The side flaps of the geotextile materials are not sand bag ballasted adequately because the sand bags are not placed over the entire flap width, as required by drawing sheet 6 of 8, Section B-7. Note the contrast in the windrow header balasting with this and with Photo 1. Photo I shows the geotextile laying flat on the upper FML. Please fix these situations as illustrated in Photo 5, by adjusting sand bag placement and/or adding additional sand bag ballasting as needed. Section B-7 on Drawing 6 of 8 indicates a minimum of one foot of the woven geotextile should be anchored by the sand bag and the note states the sandbags should be spaced at a minimum of one per ten feet on both sides of the header. However, Part l.H.l 1 of the Ground Water Discharge Permit (GWDP) states the following: "7 7. Corrections to Engineering Drawing Sheet 6 of 8 - prior to construction of Cell 4B, the Permittee shall revise Cross-section B-7 presented in Engineering Drawing Sheet 6 of 8 and any related technical specifications, to reflect the following changes: (a) Both cushion geotextile material flaps must be extended at least 1-foot laterally beyond the sewn seam at the right (north) side of toe of the drainage aggregate windrow, and (b) Sandbags placed on both the right (north) and left (south) side of the drainage aggregate windrow, must be placed and abutted continuously along the length of the windrow." The cushion geotextile flap (sewn seam) can be placed on either side of the header pipe as it is a feature not related to the performance of the filter geotextile other than to seal the edge. The cushion geotextile and overlying woven geotextile conform to the intent of the design drawings and the additional requirements outlined in the permit. The sand bags have been rearranged to provide continuous coverage (end to end) along both the woven geotextile flaps (north and south sides of header pipe). Photo nos. 1 and 2 in the attached photo log (Attachment 1) show the completed sand bag rearrangement. SC0349.4B - RTCdatedl2-9-2010.20101210.doc engineers I scientists I innovators David Rupp, P.E. 21 December 2010 Page 3 2. Slimes Drain Sandbags in Cell 4B a. Using Larger Bags to Seal-off the Voids Created fi^om the Piggy-backing of Smaller Bags. See Photos 3, 4, and 6. Mr. Carlson of Geosyntec proposed to Mr. Goble of DRC, that the larger bags could be used to seal off voids, created from the use ofpiggy-backing method used during installation of the smaller bags. This proposal conflicts with the approved plans and specifications and DUSA's letter of October 8, 2010 regarding the correction of sand bag placement errors, committing that, "All sandbags will be in full compliance with the thickness and strip composite coverage requirements outlined in the approved plans and specifications upon completion of the liner installation. " If DUSA wishes to pursue DRC acceptance of this method, DUSA must submit a demonstration, for approval, that this method would be effective. Mr. Goble discussed this issue with Mr. Snyder on November 30, 2010. b. Piggy-backing of Larger Bags. Photo No. 6 shows a longitudinal view of a strip- drain, which shows piggy-backing of larger bags onto smaller bags clearly. Also see Photo Nos. 3 and 4. Not^'ithstanding the issues discussed above, these photos show that many of the larger bags being places are actually being piggy-backed onto the existing smaller piggy-backed bags, preserving the void pathways to the slimes drains. The bags were arranged to be in accordance with the original design as shown in Section C on Drawing 6 of 8 (i.e. sand bags are no longer placed along the sides of previously frozen, unmovable bags, which have now been rearranged to comply with coverage and thickness requirements). Photo nos. 3 through 7 in the attached photo log (Attachment 1) show the rearranged bags. In a previous DRC letter, dated November 24, 2010, it was mentioned that each individual line of strip-drain and sandbag cover will be reviewed, corrected as needed, and separately documented by Geosyntec. Further, that an individual record for each strip drain will be made by Geosyntec in the as-built report, or as an addendum thereto. This element will be critical to obtain final DRC approval of the strip-drain/sand bag system. SC0349.4B - RTCdatedl2-9-2010.20101210.doc engineers I scientists I innovators David Rupp, P.E. 21 December 2010 Page 4 Appendix M in the CQA Report dated 30 November 2010 contained the referenced strip- drain and sandbag documentation. Appendix M of the CQA Report is supplemented by the photos attached to this letter (Attachment 1). If you have any additional questions please feel free to contact me at (858) 716-2905. Sincerely Attachment: 1 - Photo Log Copies to: Harold Roberts, DMC iregb/y T. Corcoran, PE Principal Engineer SC0349.4B - RTCdatedl2-9-2010.20101210.doc engineers I scientists I innovators Attachment 1 - Photo log Photo 1 Direction: Southeast Date: 12/21/10 Description: Slimes drain header pipe looking southeast. Photo 2 Direction: Southeast Date: 12/21/10 Description: Slimes drain header pipe looking southeast from approximate midpoint of cell. Photo 3 Direction: N/A Date: 12/17/10 Description: Rearranged sand bags. Red markings on primary geomembrane indicate issues that were previously addressed using additional sand bags placed adjacent to previously frozen bags in accordance v^ith DCN-6. Since thawing, bags have been rearranged to maintain compliance with original design intent. Attachment 1 - Photo log Photo 4 Direction: Northeast Date: 12/17/10 Description: Rearranged sandbags along strip drain lateral. Photo 5 Direction: South Date: 12/17/10 Description: Rearranged sandbags along strip drain laterals. Photo 6 Direction: N/A Date: 12/17/10 Description: Rearranged sandbags along strip drain lateral - Slime Drain row #15. Attachment 1 - Photo log Photo 7 Direction: Southeast Date: 12/17/10 Description: Rearranged sandbags along strip drain laterals.