2010 Utility Plan Amendment Boxelder Sanitation District

Transcription

1 2010 Utility Plan Amendment Boxelder Sanitation District For inclusion of the Harmony Ridge Development November 7, Specht Point Rd. Ste. 105 Fort Collins, Colorado p f

2 1612 Specht Point Road, Suite 105 Fort Collins, CO p f w.com November 6, 2014 North Front Range Water Quality Planning Association Civic Center 500 E. Third Street Loveland, CO Attn: Re: Mr. Warren Mesloh P.E., Manager Boxelder Sanitation District Request to Modify the 2010 Utility Plan to Accept the Harmony Ridge Development into its sewer service area. Dear Warren: On behalf of the Boxelder Sanitation District and the Town of Windsor, we have prepared the attached Amendment to the 2010 Utility Plan for the Harmony Ridge Development. The proposed amendment changes the 2010 Utility Plan to allow Boxelder Sanitation District to permanently serve the proposed development instead of the Town of Windsor, as the existing 2010 Utility Plan is written. If any questions arise, or if any additional information is needed to review and approve this amendment, please do not hesitate to contact Brian Zick or me. Thanks in advance for your assistance in this matter. Sincerely, FARNSWORTH GROUP, INC. Thomas Renner P.E. Encl. cc: Karen Reynolds, General Manager Pat Mathena, Assistant Manager and Controller Brian Zick P.E., Farnsworth Group ENGINEERS ARCHITECTS SURVEYORS SCIENTISTS

3 I. INTRODUCTION A. Background This report serves as an amendment of the approved 2010 Utility Plan for the Boxelder Sanitation District (District). The District is a quasi-public entity under the laws of Colorado. Presently, the District s service area encompasses roughly 78 Square miles. The District s service area is shown on Figure I-1. The area is comprised of five (5) interceptor basins and encompasses portions of the growth management areas of: the City of Fort Collins, Wellington, Timnath, Severance, and Windsor. Additionally, the service area covers properties in Larimer and Weld Counties. The 2010 Utility Plan projected the growth within the District with the following table. Table I-1 Boxelder Equivalent Tap and Population Projection Total Taps Year (SFE's) Population ,640 9, ,640 11, ,640 14, ,640 16, ,640 19,406 This Utility Plan amendment is to incorporate an additional 450 acres (Harmony Ridge Subdivision) of zoned residential mixed use area into the District boundary. The land will be subdivided planned for 1650 residential units, 43 acres of non-residential development including commercial, a school and a park. See Figure I-2 showing the location and project boundary of the Harmony Ridge Subdivision relative to the existing District boundary. The Harmony Ridge Subdivision is currently located in the Town of Windsor Wastewater Treatment Plant service area. The 5 mile radius map is shown in Figure I-3.

4 Boxelder Sanitation District Figure I Plan Boundary Amendmnet AB Boxelder 208 Harmony Ridge Windsor Miles Sources: Esri, DeLorme, NAVTEQ, USGS, Intermap, ipc, NRCAN, Esri Japan, METI, Esri China (Hong Kong), Esri (Thailand), TomTom, 2013

5 208 Plan Existing Boundary AB Boxelder 208 Windsor Miles Sources: Esri, DeLorme, NAVTEQ, USGS, Intermap, ipc, NRCAN, Esri Japan, METI, Esri China (Hong Kong), Esri (Thailand), TomTom, 2013

6 Figure I-3 Harmony Ridge Development Five Mile Radius Map Mulberry Drake Boxelder WWTP Proposed LS S Fort Collins Legend Other WWTP Windsor Lift Station Lift Station 5-Mile Radius Sources: Esri, DeLorme, NAVTEQ, TomTom, Intermap, increment P Corp., GEBCO, USGS, FAO, NPS, NRCAN, GeoBase, IGN, Kadaster NL, Ordnance Survey, Esri Japan, METI, Esri China (Hong Kong), swisstopo, and the GIS User Community Miles Date: 10/29/2014

7 B. Town of Windsor, Concurrent Review and IGA In order to clearly demonstrate the changes in service area for the District and the Town of Windsor WWTP and to expedite the review process, the Town of Windsor is submitting an amendment of their Utility Plan concurrently. The District and Town of Windsor governing boards have recently terminated their Intergovernmental Agreement. The District will agree to service the Harmony Ridge Subdivision for the foreseeable future. In addition the District governing board has agreed to incorporate the subdivision into its service area. See Appendix B for supporting documentation including the legal description of the Harmony Ridge Subdivision, the terminated intergovernmental agreement between the District and the Town of Windsor, and the incorporation of the Harmony Ridge Subdivision into the District s service area.

8 II. Project Overview A. Harmony Ridge Subdivision Harmony Ridge is a proposed 1650 unit subdivision, including 43 acres of non-residential development, (commercial, a school and a park) that will be located on 3/4 of Section 31 bounded by Weld County Road 13 on the West, and Harmony Road on the South. Harmony Ridge lies in the Town of Windsor WWTP service area, but cannot be served by the Town due to the lack of infrastructure to reach the Town s WWTP. The Boxelder Sanitation District (District) has agreed to serve Harmony Ridge for the foreseeable future. As described, below, the District has treatment capacity and will have the necessary infrastructure constructed to service the Harmony Ridge Subdivision. B. Feasibility Study In 2013, the District commissioned a study to evaluate the feasible alternatives for servicing the Harmony Ridge subdivision by maximizing the use of its existing infrastructure, coupled with additional infrastructure required to connect to the subdivision (See the feasibility study in Appendix C). The alternatives developed include opinions of costs, and timing to complete improvements identified in the study. Two alternative sewerage scenarios were identified: Alternative A Walker Manufacturing Lift Station Alternative comprised of: 1. 7,700 lineal feet of gravity sewer along Harmony Road from Harmony Ridge connecting to an existing collection system manhole upstream of the Walker Manufacturing Lift Station (WMLS). 2. WMLS required upgrades including: new submersible pumps, piping, controls, emergency generator and new 6-inch, 7,000 foot long parallel force main to the Rest Area Lift Station (RALS). 3. RALS required upgrades including: new submersible pump station, all piping, controls, emergency generator and two (2) new 8-inch, 6,500 foot long force mains. Alternative B Timnath Reservoir Lift Station Alternative comprised of: 1. New Harmony Ridge Lift Station located at the southwest corner of Harmony Ridge 2. Parallel 6-inch forcemains 4,300 feet north along Weld County Road 13 (WCR 13) to a high point, then gravity via 15-inch sewer 5,800 feet north along WCR 13 to the Timnath reservoir Lift Station (TRLS). 3. Piping Improvements to the TRLS. The conclusion of the feasibility study was that either alternative would be acceptable to service the Harmony Ridge Subdivision. The District along with the subdivision developer have agreed to construct Alternative B.

9 C. Population, Flow and Loading Projections The Boxelder Utility and Master Plans developed in 2010 dictated the following criteria for new developments: Residential Flow Generation: 75 gallons per day, per capita (GPCD) Density: 2.54 capita per unit (persons per dwelling unit) Peak Factor: PF = / (Population equivalent) Non-residential Flow Generation: 500 gallons per day per acre State Code requires that a minimum peak factor of 2.5 be used for residential flows, and 1500 gallons per day per acre for non-residential flow. Lacking any recent data on new developments in the District, the more conservative non-residential State Code flow and residential flow peaking factors will be used for this development and the lift station design. Proposed Harmony Ridge Population The developer has estimated that the build out of the 1650 residential units will be over a 14 year period for the Harmony Ridge Subdivision. Using the criteria above, Harmony Ridge Subdivision could contribute 117 taps to the District s service area and an approximate population 300 persons per year. The additional taps could affect the 20-year population growth projections as outlined in Table II-1, below. Table II-1 Boxelder Equivalent Tap and Population Projection With Harmony Ridge Year Total Taps Population (SFE s) Proposed Harmony Ridge Flows and Loadings The historical influent flow and biological oxygen demand (BOD) for the District WWTP is provided in Appendix D. The current monthly average flow for the WWTP is approximately 2.1 MGD and the current monthly average BOD loadings to the District is approximately 2500 lbs./day. The design average flow of the WWTP is 3.0 MGD and the design BOD loading is 3881 lbs./day. The WWTP is currently at 70% of its flow capacity and at 65% of its BOD capacity.

10 The build out of the Harmony Subdivision will contribute an additional daily average flow of 0.38 MGD and daily BOD loading of 899 lbs./day to the District s WWTP. Over the 14 year subdivision build out the yearly flow increase would be MGD and 64 lbs. BOD/day per day. The additional flow to the District s WWTP would increase flows to 80% of the rated capacity over the next 11 years. The additional loading to the Districts WWTP would increase BOD loadings to 80% of capacity over 9-10 years. At full buildout, WWTP flows will increase to 2.48 MGD, which is 83% of the WWTP s hydraulic capacity. BOD loading will increase to 3399# BOD/day, which is 88% of the plant organic capacity. The Boxelder Sanitation District currently has a program for inflow and infiltration (I&I) reduction. Budget is allotted to I&I reduction yearly. With their current program the District will create conditions necessary to reduce WWTP influent flow and free additional capacity. Description of Proposed Conveyance Facilities Harmony Ridge Lift Station, forcemain and gravity sewer: Using the State Code flow factors, the list station design capacity should be 0.34 MGD average day flow, and 0.85 MGD peak wet weather flow. The lift station will consist of an 8 foot diameter precast concrete wetwell equipped with two 590 GPM submersible sewage pumps, an 8 foot diameter valve manhole, a 6 foot diameter flow metering manhole, and a small building housing an emergency power generator, pump controls and an automatic power transfer switch. The pumps will discharge into two parallel 6 inch diameter, 5,400 feet long forcemains that will convey the flow to the 15 inch gravity sewer. Note that the force main length has changed compared to the length estimated in the Feasibility Study. This change has resulted when the lift station site location was finalized. The gravity sewer will convey the sewage flows approximately 4,000 feet to the north to the existing Timnath Reservoir Lift Station. The lift station facility will also include an emergency pumping connection to the discharge forcemains to allow sewage to be pumped from the wetwell directly into the discharge forcemains using a trailer-mounted engine driven pump. Existing Timnath Reservoir Lift Station: In the Feasibility Study to Evaluate Sanitary Sewer Service Alternatives to Harmony Ridge Subdivision, it was determined that modifications to the existing Timnath Reservoir Lift Station (minor changes to the lift station discharge piping and changing the operating speed of the belt driven sewage pumps) would increase its capacity to 910 GPM. This capacity was determined to be sufficient to service full buildout sewage flows of the original Timnath Reservoir service area and the Harmony Ridge Subdivision. That analysis was based on the adopted Utility Plan flow factors of 2.54 PE/unit, 75 Gallons/Capita-Day, and a peaking factor of 2.0. Using the currently recommended 2.5 peaking factor for the existing Timnath Reservoir service area as well as for the Harmony Ridge Subdivision, the peak hourly flows to the lift station at full buildout of both service area will be: a. Timnath Reservoir: 1200 units x 2.54 PE/unit x 75 GPD/cap x 2.5 PF = 571,500 GPD, or 400 GPM. b. Harmony Ridge Subdivision: 590 GPM.

11 The combined peak hourly flow for the two service area will be 990 GPM, which is 80 GPM in excess of the 910 GPM upgraded capacity of the Timnath Reservoir lift station. To accommodate this future full buildout peak flow, the existing Timnath Reservoir Lift Station will have to be upgraded in the future as the service areas approach 90% of full buildout by either further increasing the speed of the existing pumps, or replacing the pumps with new pumps of higher capacity. By the time these two service areas approach 90% of full buildout, it is likely that the existing sewage pumps will require replacement in any case due to wear and age. The Timnath Reservoir Lift Station currently discharges into one 6 inch and one 8 inch parallel forcemains. Operating in parallel, the friction losses in the two pipes will match. At the future design condition, the 6 inch forcemain will convey approximately 300 GPM, operating with a flow velocity of 3.5 feet per second, and the 8 inch pipe will convey approximately 700 GPM, operating at a flow velocity of 4.5 feet per second. Thus both pipes will operate at acceptable flow velocities. D. Financing Future Improvements Once the District s WWTP reaches 80% capacity they will start the planning process to increase capacity through capital improvements. Tap fees will be a significant financial contribution towards these improvements. The current fee for the District is $6,176 per tap. The Harmony Ridge Subdivision will have 1650 residential taps, which could amount to $10,190,000 in reserve capacity revenue over the 14 year build out period.

12 III. Conclusions This amendment to the District s existing 208 Plan will serve as a permanent increase to the District s service area to incorporate the Harmony Ridge Subdivision. The build out of the subdivision over the next 14 years will have a minor impact to capacity of the District s WWTP as described above, bringing it to 80% capacity in the next years. However, capacity impacts may be offset by the continuance of the District s inflow and infiltration reduction program and with slowing of other developments within the District s service area. Collection of tap fees from the Harmony Ridge subdivision will be set aside for future improvements to the District s WWTP. The District will provide service to the Harmony Ridge subdivision with the construction of a new lift station, two parallel 6-inch forcemains, a 15-inch gravity sewer connecting to the Timnath Reservoir Lift Station and improvements to the Timnath Reservoir Lift Station. These improvements will be funded by the District through agreements with the subdivision s developer.

13 APPENDIX A Existing Intergovernmental Agreement Town of Windsor

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19 APPENDIX B Agreement to Terminate Intergovernmental Agreement Boxelder Agreement to Service Harmony Ridge Subdivision Harmony Ridge Subdivision Legal Description

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32 APPENDIX C 2013 Feasibility Study

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62 APPENDIX D Boxelder Sanitation District WWTP Influent Flow and Loading

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