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CHAPTER 10 - CONCLUSIO:\'S The estimated construction cost of the 3D-year alignment B plan is $3,498,500. The Federal and non.Federal share would be about $1,921,600 and $1.576.900, respec- tively. The plan would have annual net benefits of $64.600, annual costs of 5305,600, and aBiC ralioof 1.2. Floodcontrul lIlca.lureson Boxcldcr Crcekwould not beo:conomicaIly fcasible ,and the City of Fort Collins has delayed its plans for channel improvements on Boxeldcr Creek until revision of the 1981 drainageway plan is completed. Flood control improvements on Spring Creek from College Avenue to the BNRR were completed by the City in Decembcr 1990, and further flood control improvements arc planned for completion within2103 years. Flood control measures on the remaining portions of Spring Creek do notappcar to be economically feasible. , I , i i I i I I I There could be some environmental impacts associated with construction of the 30-yearchannel diversion. Thc Ute ladies' tresses, a proposed threatened species, and the Preble's meadow jumping mouse, a State species of special concern, could be affected by the alignment B plan. However, field surveys would be required to deter- mine if either of these species may be inhabiting in the area of the polential channel diversion. The sc1ected 30-year plan would resl.lltin the loss of I acre of riparian habitat along the Cache La Poudre River. which could possibly be mitigated by the reestablish- ment of riparian vegetation on a nearby tract of land in the riparian zone of the Cache La poudre River. During construction of the selected plan, sediments from disturbed areas could beearried south to the Cache La Poudre River and cause shorHerm, in- stream turbidity. negatively affecting the Johnny darter and common shiner. The sediments could plug the intergravcl spaces, leaving no room for fish eggs or food organisms. Sc<limelltcontrol mea.lureswould be required during lheconslrucliol\lIflhc selected plan in order to minimize runoffofscdiments from the construction arca, Average annual damages on Dry Creck are estimated to be $658,700. [t would be economically fca.lible 10 construct flood control mealureson Dry Crcck in tl1enorlhwest portion of Fort Collins. A 30-year level of protection channel diversion along align- ment B was selected as the reconnais~nce.level plan. A lOO-)'ear level of prokction challnel div"nion along alignmcnt B would not be f~sib!c. A channel civersion along alignment A would pass throl.lgh McMurry Park/Natural Area, which would have greater adverse environmental impacts than alignment R, and alignment A is not supported by Ihc.lponsor. The selected plan would (livert Dry Creek flows along alignment B from about 500 fect upslream from Larimer aJ1d Weld Canal to the Cache La POl.ldrc River. ThIS channel diversion wOl.lld be abollt 5,600 feet in length. The plan would redl.lce the EAD on Dry Creck fwm $658,700 to $28851)0, or a rc-dUClion of 56 percent. There ;, a potential for disturbing contarninatc-d soil near the midpoint of the alignment Bchannc1 diversion. rrrurthcrstudiesv.ould idcntify aa area whicheontains contaminated soil, the non-Federal sponsor WOllld be respoosiblc for the co,ts 10 re!1lOVC and properly dispose of contall1iTl<ltcd materials and soils. It is recommended that all necessary soil boring be completed at the beginning of the feasibility ~tudy in order to identif;' e<1r1y any UrlCxIl<.'cted costs from contaminated arcas. 10-1 10-2