2015 Issue

46 Figure 6. Alternative alignments for the Replacement of the East Layton Pipeline Because the existing pipeline can only be removed from service for 24 hour time periods, the District was interested in installing a parallel pipeline with the option to rehabilitate the existing pipeline in the future. Five separate pipeline alignments that provide a re- placement for the existing pipeline were identified and are shown in Figure 6. Each alignment was evaluated against the Districts objectives along with present worth costs and other engineering factors. Table 3 provides the advantages, disadvantages, and pres- ent worth cost estimate of each alternative. A brief description of each alternative is provided below. Alternatives 1 and 2. Alternatives 1 and 2 were selected because they avoided residential neighborhoods and follow the alignment of a major state highway and frontage road. Portions of these alignments are above the hydraulic grade line of the DNWTP and require a pump station to be built which greatly impacts the capital and long-term operation costs of these two alternatives. Alternative 3. Alternative 3 shares the alignment of Alternative 2, but includes tunneling to avoid the need for a pump station. Tunnel- ing represents a significant project risk and increased capital cost. Alternative 4. Alternative 4 follows the same corridor of the exist- ing pipeline. Because the existing easement is only 20 feet wide and significant development has occurred over and around the easement over the years, some segments of Alternative 4 would be tunneled to reduce the impact to local residents. This alternative includes significant challenges associated with the installation of a second pipeline parallel to the existing unrestrained and leaking pipeline, while keeping the existing pipeline in service. This pre- sented significant challenges and risks. Alternative 5. Alternative 5 was developed to provide an alignment that would eliminate construction in the backyards of residential neighborhoods and also allow gravity flow. This alternative requires construction of a large diameter pipeline in residential streets and disruption to the neighborhood. Alternative/PWC Advantages Disadvantages Alternative 1: - Limited disturbance in residential streets. - Pump station required Pumped Pipeline - Completely separate routing with high O&M Costs in Frontage Road from existing piping, limiting risk of - Future widening of Present Worth Cost : compromising existing pipe, and Highway 89 could require $9,300,000 stays away from residents. Highway 89 could require - Construction congestion on major commuter route Alternative 2: - Limited disturbance in residential streets. - Pump station required with Pumped Pipeline - Completely separate routing from high O&M Costs in Highway 89 existing piping, limiting risk of - Future widening of Highway Present Worth Cost : compromising existing pipe. 89 could require relocation $7,600,000 - New pipeline would be out of the of the pipeline. private backyards of resident - Construction congestion on major commuter route Alternative 3: - Gravity flow pipeline - Tunneling required with Gravity Pipe/Tunnel - Limited disturbance in public streets. significant amount of in Highway 89 - Completely separate routing from unknowns related to Present Worth Cost : existing piping, limiting risk of cost and constructability $8,300,000 compromising existing pipe. - Future widening of - New pipeline would be out of the Highway 89 could require private backyards of residents relocation of the pipeline in the future. - Increased visibility and congestion on major commuter route Alternative 4: - Gravity flow pipeline - Disturbance in public Gravity Pipe/Tunnel - Shorter than Alternatives 1, 2, and 3 streets and backyards in Existing Easement - Within the existing easement of residents. Present Worth Cost : - High risk of compromising $6,900,000 existing pipe through construction and soil disturbance. - Tunnelingwithsignificant amount of unknowns and risk Alternative 5: - Gravity flow pipeline - Disturbance to residential Gravity Pipe in - Lowest Cost Option streets. Westerly Streets - Pipeline located in existing - Construction challenges of Present Worth Cost : easements or public street utility crossings in public $5,900,000 rights of way. streets. - Impact to residential neighborhood and will require significant public involvement effort. Recommended Replacement and Rehabilitation Alternative Based on a qualitative comparison of the alternatives, as well as a comparison of the present worth cost estimates, Alternative 5 is the best available alternative for installation of a parallel pipeline in combination with rehabilitating the existing pipeline. Key factors that led to the selection of Alternative 5 as the preferred alterna- tive include a reduction of risk during construction by avoiding construction within Highway 89 which would likely require some of the pipe to be relocated when the highway is widened in the future, avoids tunneling, and provides the ability to operate the system through gravity flow (no pump station required). It was recommended that a 36-inch diameter pipeline be installed capable of delivering at least 10,000 gpm which will meet water demands for the next 10 to 15 years. This will allow the District to defer the cost of rehabilitation of the existing pipeline and provide additional time to take the existing pipeline out of service and further investigate rehabilitation options. CULINARY PIPELINE | continued from page 45 Advantages, Disadvantages, and Estimated Total Present Worth Costs of Alternatives 1 Through 5