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TETRA TECH RMC Ms. Madoline Wallace January 5, 2004 Page 3 5) Hydraulic analysis of the proposed new ditch segment. This is required to provide evidence of the capacity to convey 20 cfs of flow with one (1) foot of residua] freeboard. The capacity and freeboard requirements have been previously conveyed to Lafarge's consultant. 6) A formal easement description for the relocated Smith & Emmons Ditch across the former Duckworth property. 7) A commitment to maintain delivery of at least a portion of its water in the Smith & Emmons Ditch as ditch seepage compensation to the remaining users. Unless presented with evidence to the contrary, 25 percent is recommended as compensation. 8) A commitment to allow access to the Smith & Emmons Ditch by Ditch Company representatives at all times. Design Co~isiderations To provide guidance to Lafarge in preparing these items we offer the following suggestions: 1) It appears from the submittal that the relocated ditch segment will be constntcted once that area has been mined and backfifled. It is imperative that the new ditch segment not suffer from excessive seepage, excessive erosion, or excessive settlement in order to be able to deliver the water required for downstream irrigators. Therefore, only overburden material, no bedrock, slrould be used as backfill in the area to contain the relocated ditch. The backfill should be placed in horizontal layers, moisture conditioned to within 2 percent of optimum, and compacted to 95 percent or better standard Proctor density. Backfill material to be located within five (5) feet of the relocated ditch (either horizontally from the banks or vertically from the bottom) shall contain at least 50 percent 5nes passing a #200 sieve, have a plasticity index equal to or greater than 15, and be classified as CH, CL or CL-SC. The fill should be brought up to the full final bank height and then the new ditch section should be excavated. 2) Lafarge should carefully examine the existing portions of the ditch system to determine required tie-in elevations that will need to be maintained for the proper delivery of water. It is conceivable that the northwest corner of the property may have to be raised to allow continued deliveries to the east lateral. 3) As mentioned previously the. Ditch relocation should be designed to accommodate 20 cfs with one (1) foot of residual freeboard. 4) Velocities should be maintained that provide for flow conditions that neither scour nor deposit materials in the ditch.