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W Ut c....;, ~) I l ;~j 2. Point Source - Stinking Spring (Onion Creek) Onion Creek drains Fisher Valley and is tributary to the Colorado River. The mouth of the creek is located 19 miles northeast of Moab, Utah. Base flow originates in the La Sa1 Mountains and is used for irrigation of hay fields in Fisher Valley. Base flow is approximately 2 cubic feet per second (cfs) and salt concentration is 800 mg/1 as the creek enters the "narrows" of Onion Creek Canyon. Stinking Spring discharges approximately 80 gpm into the creek from two major points; one yields 57 gpm at a concentration of 18,980 mg/1, the other discharges 23 gpm at a concentra- tion of 14,600 mg/1. These two combine to yield a total of 128 ac-ft of water and 3,084 tons of salt annually. Salinity of Onion Creek below Stinking Spring increases to 3,100 mg/1. If Stinking Spring water could be kept from entering the Colorado River, the salt concentration at Imperial Dam would be reduced by 0.24 mg/1. Figure 3 shows the possible location of a control structure and collector which would prevent saline spring water from entering Onion Creek and divert it into a pipeline. It also shows the pipeline location and the evaporation pond site. The pond would need to be lined to prevent brine seepage through sandy soil into the Colorado River. Day (15) provides a good manual on procedures to be followed in constructing brine ponds and installing liners to reduce seepage. The cost-effectiveness and benefits of the proposed project are computed as follows: a. Construction/Development and Replacement Costs (1) Collector System Barrier dam and gravel sump $ 20,000 :) . . . . . . . . . . 3-inch, rigid PVC pipeline, 5 miles @ $60,000/mi1e . . Air release valves. . . . . Amount set aside for periodic replacement of pipeline (assume a 25-year life) $310,000 x 0.22 (Sinking Fund Factor). . , . . . (2) Evaporation Pond Protective dike 20 feet high and hypa10n liner on inside face of dike, 3194 running feet of dike @ $68/ft .. ... $ 217,192 $ 300,000 $ 10,000 ,\ . . . . . . . $ 68,200 Protective dike 6 feet high and hypalon liner on inside face of dike, 2614 running feet of dike @ $12.40/ft. . $ 32,414 Pond liner of 20 mil PVC material (not covered), 64 acres or 309,760 sq. yds. 24 k_4- - =-, ','~,-,,,,, ~ -"", >g,-+~