Pagosa Springs San Juan/Delores River Div 7 Response Letter

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Gunnison, the Arkansas River in Salida, the Yampa River in Steamboat Springs and Boulder Creek in Boulder. Mr. Dorsey's letter also implies that the grout used is a toxin—which it is but only in the un-cured state. Cured concrete is inert. All grouting work done on this project occurred behind coffer darns as required. There was no lime released to the San Juan River and no fish were killed. We recommend that we continue this best practice standard during Phase 1, Lime in "live" concrete,sharply increases pH High pH can kill aquatic life, e.g., aquatic invertebrates,fish Answered above. 2. Concrete grout used to stabilize rocks in the river is considered an illegal discharge if pi-1>RO results Answered above 3, Hardening of river banks and ins/ream structures with concrete grout impairs the natural fitnetion of the river. Riparian and jloodplain development is inhibited, reducing the overall biological productivity of the river system and exacerbating the risk of downstream flooding and bank damage. The changes made to the river do not result in a more"natural"condition for the river. Mr. Dorsey has offered no substantiation for this claim, The U-structure replaced two W-structures that already',spanned the river with hardened material. The river itself is already within a confined floodplain at the work-site and was both significantly denuded and littered with debris. There was a positive effect on the Riparian and floodplain functions as the U-structure will maintain the existing floodplain. Additionally, removal of debris from the banks and a significant bankside replanting project is planned in the next phase. Mr. Dorsey's suggestion that the improvements will exacerbate downstream flooding and bank damage is also unfounded, The hydraulic at the base of the structure is a natural energy dinser that will decrease downstream current velocities. In fact, the sort of erosion that Mr. Dorsey's letter references are typically associated with uniform flaodways much like the previous condition of this streambed. Inspection of this new structure during this spring's high flow confirms the integrity of the structure and flood carrying capacity or the river in this reach. 4. Benthic interstitial spaces are lost by grouting. Feeding resting, hiding places for small trout and native fishes like mottled sculpins are destroyed by grouting, As,mentioned previously,the net amount of interstitial spaces has dramatically increased and will continue to increase as this project progresses. The grout in the drop structures is "held back"such that interstitial spaces on the structure,on the