C150295 Feasibility Study - Laserfiche WebLink

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2.1.1 Introduction The Town of Dillon, Summit County Government, and the Town of Silverthorne have agreed under an inteYgovernmental agreement to enlarge Old Dillon Reservoir (ODR) to store addirional water and serve watex needs in their respecrive juxisdicrions. In order for the Town of Dillon to paYticipate in the enlargement, the Town is Yequesting a loan in the amount of $1,500,000. Construction of ODR and the Dillon Ditch by the Town of Dillon began in 1936 and was completed in 1939 to pxovide domestic water supply to the Town at its original location prior to construction of Denver's Dillon Reservoir. The xeservoir was constructed with a north and south dam, and a diversion and ditch to convey water from Salt Lick Gulch (SLG) located north of ODR. An oudet pipe in the south dam conveyed water to the Town. After 1963 when the Town of Dillon was relocated for the construcrion of Denver's Dillon Reservoir, the Town has not been able to deliveY water from ODR direcdy into the Town's water supply system. The Town continues to maintain the reservoir and diversion to Dillon Ditch since 1963. The Dillon Ditch conveys water from SLG noxth of I-70, through an invexted siphon under I-70, and south of I-70 to ODR. Currently, an outlet pipe in the north dam and channel conveys water back to SLG approxirnately 0.9 miles downstream of the divexsion. The outlet works in the south dam which conveyed water to the Town of Dillon is still visible in the reservoir but is not functional. In the spring of 2008, the culvert conveying retutn flows fxom ODR back to SLG failed under the west bound lanes of I-70 creating a hole in the highway. The ColoYado Depaxtment of Transportation replaced the culvert under the west bound lanes and lined in place the culve~t under the east bound lanes. On July 17, 2008, the ColoYado Division of Water ResouYCes issued an order to the Town of Dillon to dYain the reservoir due to concerns oveY safety of the noYth dam (fee Zero Storage Be.rtriction, Exhibit A and Engineer'.c In.c-pection I~eport, Exhibit B). The Town drained the xeservoir shordy afteY, and it will Yemain drained until eitheY the proposed enlaYgement is approved, ox if the enlaYgement is not appYOVed, the Town will reconstruct the noYth dam in accordance with curxent dam ,safety standards and continue to operate the reservoir at the current size. The existing reservoit has a surface area of about 9.006 acres and is impounded by two embankments of about 5 to 7 feet high in a saddle on an east-west t.xending ridge; and, wateY is supplied by the Dillon Ditch via a diversion fxom Salt Lick Gulch, located appxo~cimately 1 mile noxth of the xeservoir. The ditch flow is conveyed under Interstate 70 (I-70) in an invexted siphon. Salt Lick Gulch is tributary to the Blue River. CuYrently, flows axe diverted to ODR and retuYned to Salt Lick Gulch appxoximately 0.9 miles downstYeam of the diversion via an outlet channel and culvert under I-70. Suintnit County Government and the Towns of Dillon and Silverthorne have identified the need for additional wateY supplies to meet future water demands within their service areas ([JPCO UppeY ColoYado RiveY Basin Study 1998). Each entity requires the increased water storage capacity and water supply security. The purpose of this project is to provide additional wateY storage capacity and water supply security to meet e~sting and future domestic water supply needs. Additionally, the Town of Dillon's cuYxent water supply fxom Sttaight Creek is susceptible to contamination from several sources, including potential wildfire due to massive pine beetle kill and potential contamination from hazardous matexial spills on I-70 in the watershed, xequiring an identified 1