SEWER COLLECTION SYSTEM B UILD - OUT INFRASTRUCTURE PLAN P ROJECT U PDATE & R EVIEW D ECEMBER 3, 2019
SEWER COLLECTION SYSTEM BUILD-OUT INFRASTRUCTURE PLAN PROJECT GOALS 1. Forecast Total Sewer Flows from Build-Out Service Area(s): 2. Multi Step Process involving: • Evaluating Existing Sewer Flows • Evaluating Future Land Use and Development Patterns 3. Evaluate Performance of Existing Collection System Infrastructure. 4. Identify Future Capital Improvement Projects to Support Growth. 5. Develop Future Planning Level Capital Improvement Project Costs. Project Update & Review – December 3, 2019
SEWER COLLECTION SYSTEM BUILD-OUT INFRASTRUCTURE PLAN PROJECT DELIVERABLES OVERVIEW Technical Memo Subject Main Purpose (TM) • Develop Sewer User Class (SUC) Concept 1 Sewer User Class Unit Loads • Develop methodology for determining unit loads from existing data • Validation of existing collection system model 2 WWTP & Predicted Service Area Flows • Compare WWTP flows w/ model predictions using TM1’s SUC unit loads. • Develop methodology for assigning sewer loads to development parcels, current + future 3 Sewer Unit Loads for Vacant Parcels • Determine what unit loads are used for predicting service area build-out flows. • Review WWTP flow data for peak day and peak hour flows 4 Peaking Factors • Compare existing flows to climatological records to assign peaking factors • Develop Build-out flow projections for the service areas 5 Service Area Build-out Flow Projections • Basis - inputs from TM1-TM4 work • Evaluate the existing and future capacities of the Salida WWTP 6 Wastewater Treatment Plant Capacity • Time: Existing, Planned and Buildout • Model results showing capacity of various critical sewer lines under various growth scenarios • 7 Model Results and CIP Costs Recommended Improvements • Capital costs of recommended infrastructure improvements An Executive Summary was also developed for the combined TMs listed above. Project Update & Review – December 3, 2019
SEWER COLLECTION SYSTEM BUILD-OUT INFRASTRUCTURE PLAN TM 1: Identify Appropriate “Sewer User Class” Unit Loads 1. Four “Sewer User Class” unit loads were developed based on the water meter data: • Single-Family Class (SFC) • Multi-Family Class (MFC) • Commercial User Class (CUC) • Institutional User Class (IUC) 2. Average Sewage Flow from a “type” of Sewer User (SFC, MFC, Commercial). 3. Based on winter time water usage, 4 winters (2015-2018), for all water meter accounts. Average Daily Sewer Flow Municipality Sewer User Class (gpd) Single-Family Class 122 Multi-Family Class 91 City of Salida Institutional User Class Varies Commercial User Class 480 Residential Class 110 Town of Poncha Springs Commercial User Class 188 Project Update & Review – December 3, 2019
SEWER COLLECTION SYSTEM BUILD-OUT INFRASTRUCTURE PLAN TM 2: Compare Predicted Flows to Actual Flows 1. The metered sewer flows at the wastewater treatment plant (WWTP) were compared to the average annual daily flow (AADF). 2. The average WWTP Measured Flow from 2016-2018 was 0.59 MGD verses a Modeled Predicted Flow of 0.61 MGD. 3. The existing MMF at the WWTP is 1.30 MGD. Note: Graph units in MGD and the current Permitted Capacity for WWTP is 2.7 MGD Project Update & Review – December 3, 2019
SEWER COLLECTION SYSTEM BUILD-OUT INFRASTRUCTURE PLAN TM 3: Future Flow Predictions 1. Future undeveloped parcels in the sewer service areas classified as “planned” or “unknown”. 2. Future “Planned” parcel flows estimated using sewer user classes (SUC) and unit loads. 3. Future “Unknown” parcel flows were estimated using area unit loads. Average Daily Sewer Flow Municipality Sewer User Class (gpd/acre) Single-Family Class 516 City of Salida Multi-Family Class 1,392 Commercial User Class 552 Residential Class 524 Town of Poncha Springs Commercial User Class 96 Project Update & Review – December 3, 2019
SEWER COLLECTION SYSTEM BUILD-OUT INFRASTRUCTURE PLAN TM 3: Future Flow Predictions (Cont’d) - Salida Project Update & Review – December 3, 2019
SEWER COLLECTION SYSTEM BUILD-OUT INFRASTRUCTURE PLAN TM 3: Future Flow Predictions (Cont’d) – Poncha Springs Project Update & Review – December 3, 2019
SEWER COLLECTION SYSTEM BUILD-OUT INFRASTRUCTURE PLAN TM 4: Peaking Factors 1. Site-specific influent and effluent flow data (2014-2018) used to evaluate peak hour flow. 2. The peaking factor accounts for the overall variations of flow above the average flows. • This includes variable seasonal changes, use patterns, climatological impacts, etc. 3. A 3.4 peaking factor applied to collection system modeling for capital improvement planning. Project Update & Review – December 3, 2019
SEWER COLLECTION SYSTEM BUILD-OUT INFRASTRUCTURE PLAN TM 5: Build-Out Flow Projections 1. The average annual daily flow (AADF) was estimated for the Existing, Planned, and Unknown parcels for the buildout sewer service area. 2. The current AADF of 0.6 MGD is estimated to be approximately 1.6 MGD at buildout. Project Update & Review – December 3, 2019
SEWER COLLECTION SYSTEM BUILD-OUT INFRASTRUCTURE PLAN TM 6: Wastewater Treatment Plant Capacity Evaluation 1. The permitted hydraulic capacity of the existing WWTP of 2.7 MGD appears to be sufficient to treat flows for the existing and planned development scenarios. 2. Final buildout flows may require an increase in WWTP capacity. 3. Aging infrastructure and/or future effluent limitations for nutrients or other parameters will likely be the drivers for future WWTP upgrades / improvements. 0.67 1.30 48% Note: State of Colorado regulations require WWTP plant expansion planning to begin when the plant MMF reaches 80% of permitted capacity. Project Update & Review – December 3, 2019
SEWER COLLECTION SYSTEM BUILD-OUT INFRASTRUCTURE PLAN TM 7: Model Results and Capital Improvements 1. City provided recent additional survey and operational data to address previously identified data gaps. 2. The Existing, Planned, and Buildout scenarios were reevaluated. 3. No significant changes in model results were noted, but confidence in results gained. 4. Identified flow indicators at a “Controlling Segment”. Project Update & Review – December 3, 2019
SEWER COLLECTION SYSTEM BUILD-OUT INFRASTRUCTURE PLAN TM 7: Model Results and Capital Improvements 6. The Capital Improvement Plan (CIP) was developed through Buildout: • Planned scenario shows one segment of pipe slightly exceeding capacity (d/D = 0.81) criteria near Holman Avenue and HWY 50 (controlling segment). • Build-Out scenario will require upgrade to 15-inch diameter from east of Poncha Springs to the intersection of 14th Street and HWY 50. 7. Total estimated Costs to support the recommended CIP is $14.5 million. Project Update & Review – December 3, 2019
SEWER COLLECTION SYSTEM BUILD-OUT INFRASTRUCTURE PLAN TM 7: Model Results and Capital Improvements (Cont’d) Poncha Springs Interceptor Upsizing Project Update & Review – December 3, 2019
SEWER COLLECTION SYSTEM BUILD-OUT INFRASTRUCTURE PLAN CITY FINANCE DEPARTMENT CIP INPUT • Assume a revenue bond financing of the $14,500,000 project. • Interest conservatively at 3.8%. • Borrow for the debt service reserve, and earn 1.5% interest on it. • Accelerated net debt service – to track anticipated growth - would start around $600,000/year and grow over 30 years to $1,700,000. • Revenue Options: • The Sewer Fund is a TABOR enterprise that could issue revenue bonds. • Colorado Water and Power Development Authority makes low interest loans for projects such as this. • The USDA might have a loan option for the project. • The project would likely qualify for a DOLA grant, but would need to be limited to 10% of annual revenue. • Federal grants could be sought. Progress Update & Review – December 3, 2019
SEWER COLLECTION SYSTEM BUILD-OUT INFRASTRUCTURE PLAN Conclusions/Recommendations 1. Sewer Model well calibrated with the baseline data used in development. 2. There are concerns with the capacity of Sewer Interceptor based on projected growth. • Most recent flow data from the City indicates that the interceptor may be nearing capacity more quickly than anticipated. • This needs to be validated with continued and focused flow monitoring. 3. Recommended actions for Forecasting Future Flows: • Upgrade monitoring station at controlling segment and perform monthly monitoring. • Update and run the existing model based on new data at least once a year. • Perform additional condition assessments of the existing interceptor, identify any potential infiltration concerns, and take appropriate actions. 4. Begin planning for upgrade to the Sewer Interceptor for Build-Out conditions. Project Update & Review – December 3, 2019
SEWER COLLECTION SYSTEM BUILD-OUT INFRASTRUCTURE PLAN QUESTIONS QUESTIONS/DISCUSSION THANK YOU Project Update & Review – December 3, 2019
Recommend
More recommend
