MEMORANDUM 7/7/2016 TO: BOARD OF DIRECTORS, CRWCD ENTERPRISE ERIC KUHN, GENERAL MANAGER PETER FLEMING, ESQ. FROM: JOHN CURRIER, P.E. CHIEF ENGINEER SUBJECT: RITSCHARD DAM INVESTIGATIONS OF UNUSUAL DEFORMATION No Action Requested; for Board information and discussion. We would like to provide a brief update on activity since the April Board meeting. Review and Summary At your April 2016 Board meeting we reported: • The conclusion of the PFMA/RA (Probable Failure Modes / Risk Analysis) workshop held in February was that the risk of a deformation-related dam failure occurring in any given year is two orders of magnitude lower (1X10-8, or 1 in 100 million) than the normally acceptable risk of a probable maximum flood causing failure due to overtopping the dam (1X10-6, or 1 in a million). Thus, the deformation-related public risk is much lower than other, normally acceptable dam-related risks. • From a risk-based perspective there is no compelling reason to proceed with remediation of the dam now or in the foreseeable future. The dam is functioning properly, and has a very high probability of continuing to function properly even if deformation continues at the historical rate for many more years. • Normal reservoir operation along with continued reasonable monitoring is appropriate. While operating the reservoir 10 ft. down slows deformation, it just prolongs the time it takes to complete the deformation. • A reasonable monitoring program will provide extensive advanced notice of any impending dam safety concern. With extensive advanced notice, an appropriate response can be implemented. An appropriate response might range from intensified observation and monitoring up to implementing an embankment remediation plan. Page 2 of 2 7/7/2016 RITSCHARD DAM INVESTIGATIONS OF UNUSUAL DEFORMATION Update since the April Board meeting: • One additional inclinometer was installed near the toe of downstream embankment as recommended by the Consultant Review Board. This was installed before runoff to capture any deformation that might occur during the reservoir fill cycle. • Staff worked with Bill McCormick, Chief of the Dam Safety Branch, on a 2016 Reservoir Operating Plan that allows normal (full pool) reservoir operations. • We are still working to schedule a workshop with our Engineer AECOM, the Dam Safety Branch and our Consultant Review Board to: o Evaluate and develop a long-term monitoring plan that sets forth the frequency of data collection. o Develop behavior thresholds (e.g. core pore pressure excursions, deformation acceleration, etc.) and potential responses, that might range from do nothing to implementing a remediation plan. We expect to finalize this in a workshop setting with the Dam Safety Branch as an active participant. o Further investigate and fine-tune realistic remediation alternatives and identify a plan that can be implemented should remediation ultimately be required. Questions to answer include; efficacy at remediating deformation, cost, implementation issues and risks, probable reduction of the dam failure risk probability as determined by a quantitative risk analysis, and others. • We received the attached letter from Robert Mahoney, P.E., Director of Engineering for Denver Water in response to the memorandum that was in the April board packet. I have discussed the letter with Bob Mahoney and we will be sending a short response clarifying a few matters and inviting Denver’s continued involvement and expertise in the deformation issues. Attachment: 5/2/2016 Letter Regarding 4/4/2016 Memorandum. RECEIVED MAY 05 2015 $223.?322?552312412 COLORADO RIVER WATER 303 628 6000 DENVER WATER CONSERVATION DISTRICT denverwmer 0?9 Sent Via US. Mail 8: Email May 2, 2016 Mr. John Currier Chief Engineer Colorado River Water Conservation District PO BOX 1120 Glenwood Springs, Colorado 81602 Re: April 7, 2014 Memorandum, Ritschard Dam Investigations of Unusual Deformation Dear John, I am sending this letter to you in response to the April 7, 2016 Memorandum (?Memorandum?) regarding Ritschard Dam Investigations of Unusual Deformation prepared by you for your Board. The primary purpose of this letter is to clarify incorrect statements characterizing Denver Water?s role as a ?risk estimator? and a ?participant? at the February 23-25 Probable Failure Modes/Risk Analysis workshop. Similar characterization also recently appeared in an April 17, 2016 article published in the Grand Junction Sentinel titled ?Risk 9? of Failure at Wolford dam ?Very remote . First, I want to let you know that Denver Water sends this letter to you reluctantly, as we would prefer to avoid an exchange of letters as I am sure you do as well. However, with the Memorandum now public, and incorrect statements being made in the news media about Denver Water?s role at the workshop, we feel compelled to send this letter to clarify Denver Water?s role at the workshop. In the Memorandum, you characterize Denver Water as a ?risk estimator? and an active participant during the workshop. Denver Water takes exception to these characterizations. At no time did Denver Water participate in the workshop as a risk estimator, nor was it ever invited to participate as a risk estimator on the panel. The only voting risk estimators participating at the workshop were yourself, Larry Von Thun and John Smart both formerly with the Bureau of Reclamation, Dick Davidson of AECOM, and a representative of the State Engineer?s of?ce. Denver Water also disagrees with characterizations in the Memorandum implying that Denver Water was an active participant and that we concluded and agreed with the findings of the risk estimators. Page 1 of 2 Letter Regarding 4/7/2016 Memorandum May 2, 2016 Denver Water?s role in attending the workshop was that of a concerned observer. Based on our observations, the workshop and your Memorandum only addressed the probability of a dam failure consequence. While the probability of a dam failure appears low, dam failure is not the only potential adverse impact of concern to Denver Water. The probability of cracking in the core of the dam, which could reduce storage capacity, has a much greater range of uncertainty. According to Mr. Dick Davidson, cracking of the core has a 50 percent annual probability of occurrence starting in 20 years (the time criteria set for the workshop and probability estimation). Given this uncertainty, it would be bene?cial to develop plans now to remediate Ritschard Dam in the event of a crack. Further, based on the information presented at the workshop, Denver Water does not agree that Ritschard Dam is functioning as designed because no dam is designed to function with the degree of movement observed at Ritschard Dam to date. As addressed in the April 27, 2016 letter from Bill McCormick, Chief of the Dam Safety Branch of the State Engineer?s Office, Ritschard Dam is in the category ?of dams with significant issues? and is on ?an abnormal trend.? Our Dam Safety Engineers have the understanding that the River District would be sharing a draft of notes from the workshop with them for review and comment, which is one reason that the public reports prior to that review were surprising to us. When these are available to review, please let us know. In closing, it may be helpful to meet to further discuss our concerns, the River District?s plan to remediate Ritschard dam, and the extent of liability and responsibility for these repairs. If this is something you would be interested in, please let me know. If you have any questions regarding this letter, please do not hesitate to contact me to discuss further. Sincerely, ?g Robert Mah ney, P. . Director of Engineering Page 2 of 2