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Ivlr. Mike Applegate, P.E. October 24, 2003 Page 2 demonstrate that the contractor's proposed plan will provide for the proper construction of the dam embanlonent over the top of the slurry wall. The written plan and construction of the test section should be approved by this office in writing prior to the commencement of the construction of this project. A re-submittal of all of the construction drawings and specifications addressing the above items is not required. Nevertheless, documentation addressing these items should be submitted to our office for our review and acceptance prior to the commencement of the construction of this project, as noted in the above text. Rule S.A.(5)(b)(X) of the State of Colorado's "Rules and Regulations for Dam Safety and Dam Construction" requires that all new dams have a minimum of five feet of freeboard, unless a lesser freeboazd standazd can be considered acceptable for good clause shown. Based on information and calculations contained in the Design Report, it has been shown that three feet of freeboazd is adequate for this project site. Therefore, a waiver of the aforementioned Rule is granted and a minimum of three feet of freeboazd is considered to be acceptable for this dam. Rule S.A.(6)(g) 5 of the Rules and Regulations requires that the placement of dam embankment materials results in a minimum compacted density of 95 percent of the maximum dry density as determined in accordance with the requirements of ASTM D-698. The interior slopes of the Tigers Reservoir were constructed prior to any application for the construction of this new dam being submitted to this office for our review and approval. The slopes were also constructed without the benefit of construction observation and control typically employed for the construction of a dam. Investigations of the in-situ materials identified some materials with low in-place densities and strengths. The in-situ densities of the materials were found to be less than the minimum 95 percent of the maximum dry density. Nevertheless, the slope stability analysis revealed that even with the low density and low strength materials, the interior slopes of the reservoir meet the minimum factors of safety for slope stability as presented in Rule S.A.(6) of the Rules and Regulations. Based on the results of the investigation of the in-situ materials and the slope stability analysis as presented in the Geotechnical Design Report, a waiver of the aforementioned Rule is granted and the construction of the interior slopes of the reservoir aze considered to be acceptable. The waiver of this Rule does not imply that substandazd construction and the placement of dam embanlmrent materials at lower than minimum densities will be accepted on future construction project. Rule S.A.(7)(C) of the Rules and Regulations requires that all new dams have riprap protection over the entire upstream face of the embankment. The proposed design of this dam shows the upstream riprap slope protection extending from the crest of the dam down to approximately five feet below the maximum water surface elevation, which is approximately eight feet below the dam crest. At this elevation, it is our understanding that the riprap coverage is below the original natural ground surface at the maximum section of the dam. With the reservoir water surface at lower elevations, the water surface is protected from wind action by the reservoir rim, and in combination with a small reservoir fetch length results in relatively small wind generated wave heights. Design calculations show that with the reservoir at the maximum water surface elevation and with 100 mile per hour winds, the wave run-up on the dam slopes should be less than three feet. This office has also received of a letter dated October 14, 2003 from the City of Thornton committing to the performance of the long-term maintenance of the upstream slope and riprap protection for the dam embankment.. This maintenance will be required to be performed in a timely manner if wave erosion damage threatens the safety of the dam. Based on information and calculations contained in the Design Report and the aforementioned commitment of the City of Thornton, a waiver of the aforementioned Rule is granted and the proposecL*+,t ~;n,T*n couera~.o€apmp:slope=-P?ntection:isconsideFechtobe~acceptab}~for.3hisedam_prajeet:and... for a Class 3 dam.