Wastewater Collection System Master Plan

(HAL Project No.: 429.01.100)

FINAL REPORT

JULY 2021

Mount Olympus Improvement District i Wastewater Collection System Master Plan

ACKNOWLEDGEMENTS

Successful completion of this master plan was made possible by the cooperation and assistance of many individuals, including the individuals listed below:

MOUNT OLYMPUS IMPROVEMENT DISTRICT

Board of Trustees

Ami Anderson Neff Giles Demke C. Kim Blair

General Manager

Kerry S. Eppich

District Staff

Dean Ayala, District Engineer Todd Perry, Superintendent

Mount Olympus Improvement District ii Wastewater Collection System Master Plan

TABLE OF CONTENTS

TITLE PAGE

ACKNOWLEDGEMENTS ........................................................................................................... i TABLE OF CONTENTS .............................................................................................................ii LIST OF TABLES ......................................................................................................................iv LIST OF FIGURES ....................................................................................................................iv

CHAPTER 1 INTRODUCTION ............................................................................................... 1-1 BACKGROUND AND PURPOSE ........................................................................................ 1-1 AUTHORIZATION ............................................................................................................... 1-1 SCOPE OF WORK .............................................................................................................. 1-1 PREVIOUS STUDIES.......................................................................................................... 1-2

CHAPTER 2 EXISTING WASTEWATER SYSTEM ................................................................ 2-1 SERVICE AREA .................................................................................................................. 2-1 EXISTING WASTEWATER SYSTEM .................................................................................. 2-1

Source of Data ................................................................................................................. 2-1 Collection Network ........................................................................................................... 2-1 Wastewater Treatment Plant ............................................................................................ 2-2 Lift Stations ...................................................................................................................... 2-2

CHAPTER 3 FLOW MONITORING ........................................................................................ 3-1 FLOW MONITORING .......................................................................................................... 3-1

Local Flow Monitoring ...................................................................................................... 3-1 CVWRF Flow Monitoring .................................................................................................. 3-1

CHAPTER 4 FLOW CHARACTERIZATION ........................................................................... 4-1 METHODOLOGY ................................................................................................................ 4-1 UNIT FLOWS ...................................................................................................................... 4-1 DAILY FLOW VARIATION ................................................................................................... 4-1

Peaking Factors ............................................................................................................... 4-2 WASTEWATER HYDROGRAPHS ...................................................................................... 4-4 CVWRF METER DATA ....................................................................................................... 4-4 ANNUAL FLOW VARIATION............................................................................................... 4-6

Infiltration ......................................................................................................................... 4-6 Inflow ............................................................................................................................... 4-7

LONG TERM FLOW VARIATION ........................................................................................ 4-8 EXTRAORDINARY FLOWS ................................................................................................ 4-8

CHAPTER 5 WASTEWATER FLOW PROJECTIONS ........................................................... 5-1 PLANNING PERIOD ........................................................................................................... 5-1 COLLECTION AREAS......................................................................................................... 5-1 GROWTH PROJECTIONS .................................................................................................. 5-1 FLOW PROJECTIONS ........................................................................................................ 5-2

10-Year Flows .................................................................................................................. 5-3 40-Year Flows .................................................................................................................. 5-3

CHAPTER 6 WASTEWATER COLLECTION SYSTEM EVALUATION .................................. 6-1 MODEL SELECTION........................................................................................................... 6-1 SYSTEM LAYOUT .............................................................................................................. 6-1 MODELING CRITERIA ........................................................................................................ 6-1

(TABLE OF CONTENTS - CONTINUED)

TITLE PAGE

Mount Olympus Improvement District iii Wastewater Collection System Master Plan

MODEL CALIBRATION ....................................................................................................... 6-2 MODEL SCENARIOS .......................................................................................................... 6-2 MODEL RESULTS .............................................................................................................. 6-3 EXISTING DEFICIENCIES .................................................................................................. 6-3 FUTURE IMPROVEMENTS ................................................................................................ 6-6

CHAPTER 7 OPERATIONS AND MAINTENANCE ALTERNATIVES................................... 7-1 SYSTEM AGING ................................................................................................................. 7-1 PIPELINE IMPROVEMENTS............................................................................................... 7-1

Cleaning ........................................................................................................................... 7-1 Replacement Sewers ....................................................................................................... 7-1 Bypass Sewers/Re-routing Flows ..................................................................................... 7-2 New Sewers ..................................................................................................................... 7-2 Alternative Construction Technologies ............................................................................. 7-2

COMPARISON OF IMPROVEMENT ALTERNATIVES ....................................................... 7-2 Sewers ............................................................................................................................. 7-2 Future Considerations ...................................................................................................... 7-2

CHAPTER 8 CAPITAL IMPROVEMENTS PLAN ................................................................... 8-1 PROJECT COST ESTIMATES ............................................................................................ 8-1 ACCURACY OF COST ESTIMATES ................................................................................... 8-1 RECOMMENDED IMPROVEMENT PROJECTS ................................................................. 8-2 ELIMINATE UNNECESSARY WASTEWATER ................................................................... 8-4

Direct Sewage .................................................................................................................. 8-4 SUMMARY OF CAPITAL FACILITY RECOMMENDATIONS .............................................. 8-4

REFERENCES ....................................................................................................................... R-1

APPENDICES

Appendix A Flow Study Results Appendix B Growth Projections and Projected ERUs Appendix C Cost Estimates

Mount Olympus Improvement District iv Wastewater Collection System Master Plan

LIST OF TABLES

TABLE TITLE PAGE

TABLE 2-1 LIFT STATION INVENTORY ................................................................................ 2-2 TABLE 5-1 SYSTEM ERU PROJECTIONS ............................................................................ 5-2 TABLE 5-2 EXISTING AND ASSUMED FUTURE ERU DENSITIES ....................................... 5-3 TABLE 5-3 SYSTEM FLOW PROJECTIONS.......................................................................... 5-4 TABLE 6-1 MODELING CRITERIA ......................................................................................... 6-1 TABLE 6-2 MODEL SCENARIOS ........................................................................................... 6-2 TABLE 6-3 EXISTING AND PREDICTED PEAK FLOWS ....................................................... 6-3 TABLE 6-4 EXISTING PIPE CAPACITY DEFICIENCIES AND SOLUTIONS .......................... 6-4 TABLE 6-5 FUTURE IMPROVEMENT PROJECTS ................................................................ 6-6 TABLE 8-1 EXISTING IMPROVEMENT PROJECT COST ESTIMATES ................................ 8-2 TABLE 8-2 FUTURE IMPROVEMENT PROJECT COST ESTIMATES................................... 8-3 TABLE 8-3 IMPROVEMENT PROJECT COST ESTIMATES SUMMARY ............................... 8-4

LIST OF FIGURES

FIGURE TITLE PAGE

FIGURE 2-1 EXISTING SYSTEM AND SERVICE AREA BOUNDARY .................... AFTER 2-1 FIGURE 2-2 MILES OF SEWER BY DIAMETER .................................................................... 2-1 FIGURE 3-1 FLOW MONITORING STATION LOCATIONS ....................................... AFTER 3-1 FIGURE 4-1 FLOW MONITORING RESIDENTIAL PATTERNS ............................................. 4-2 FIGURE 4-2 FLOW MONITORING COMMERCIAL PATTERNS ............................................ 4-3 FIGURE 4-3 FLOW MONITORING HIGH DENSITY RESIDENTIAL PATTERNS ................... 4-3 FIGURE 4-4 DIURNAL CURVES ............................................................................................ 4-4 FIGURE 4-5 COMBINED A AND I LINE FLOW TO CVWRF ................................................... 4-5 FIGURE 4-6 INDIVIDUAL A AND I LINE FLOW TO CVWRF .................................................. 4-6 FIGURE 4-7 A AND I LINE FLOW VS. PRECIPITATION ........................................................ 4-7 FIGURE 5-1 POPULATION AND ERU PROJECTIONS ..........................................................5-2 FIGURE 6-1 MODEL SYSTEM LAYOUT .................................................................... AFTER 6-1 FIGURE 6-2 EXISTING DEFICIENCY PROJECTS .................................................... AFTER 6-5 FIGURE 6-3 10-YEAR PROJECTS ............................................................................. AFTER 6-7 FIGURE 6-4 40-YEAR PROJECTS ............................................................................. AFTER 6-7 FIGURE A-1 FLOW MONITORING CALIBRATION GRAPHS .................. END OF APPENDIX A

Mount Olympus Improvement District 1-1 Wastewater Collection System Master Plan

CHAPTER 1

INTRODUCTION

BACKGROUND AND PURPOSE

Mount Olympus Improvement District (District) has a wastewater collection system that serves a population of approximately 103,400 with a service area that covers all or a portion of the following cities and townships: City of Holladay, Millcreek Township, City of South Salt Lake, Murray City, Cottonwood Heights City, and Salt Lake City. The District collects approximately 14 million gallons of wastewater per day on average and maintains over 366 miles of wastewater collection pipelines.

The area served by the District’s wastewater collection system is mostly developed. However, many of these areas are currently experiencing redevelopment projects where existing sewer loads are increasing due to higher development densities. These redevelopment projects are a concern for the District since they increase the amount of flow considerably. The increased loads resulting from redevelopment was evaluated as part of this master planning effort.

Recognizing the need for wastewater collection system planning, the District retained Hansen, Allen & Luce, Inc. (HAL) to prepare a wastewater collection system master plan. The purpose of the master plan is to 1) estimate wastewater flow values for the existing system, 2) evaluate the existing system’s ability to convey existing wastewater flows, 3) prepare growth projections, 4) predict growth areas with City and District input, 5) prepare future flow estimates based on growth,

6) evaluate future infrastructure needs and 7) recommend projects that will create the additional needed wastewater conveyance capacity.

The results of this study are limited by the accuracy of the development projections and other assumptions used in preparing the master plan. It is expected that the District will continue to review and update this master plan every 5-10 years, or more frequently if the assumptions included in this effort change significantly.

AUTHORIZATION

The District authorized HAL to prepare the wastewater collection system master plan.

SCOPE OF WORK

A summary of the scope of work is as follows:

1. Communication and coordination.

2. Stakeholder Engagement

3. Flow Monitoring

4. Flow Characterization

5. Inflow and Infiltration Study

6. Existing System Model Update and Identification of Deficiencies

7. Planning Future Facilities

Mount Olympus Improvement District 1-2 Wastewater Collection System Master Plan

8. Prepare Capital Facilities Plan

PREVIOUS STUDIES

This master plan is part of a long-term on-going planning effort by the District. The District has prepared master plans, as needed, in the past to ensure that the wastewater collection system facilities are adequate to meet the community needs.

Mount Olympus Improvement District 2-1 Wastewater Collection System Master Plan

CHAPTER 2

EXISTING WASTEWATER SYSTEM

SERVICE AREA

The service area of the District’s wastewater collection system is provided on Figure 2-1. It is not anticipated that the service area boundary will change in the future. However, as mentioned previously, loads are likely to increase with normal development and redevelopment activity.

Figure 2-1 EXISTING SYSTEM AND SERVICE AREA BOUNDARY

EXISTING WASTEWATER SYSTEM

This master plan evaluates the existing wastewater collection system. The existing wastewater system consists of gravity sewers, including laterals, collectors, interceptors and outfalls.

Source of Data

Data for the existing wastewater collection system sewers and manholes was provided by the District. This data includes the following:

· Existing computer hydraulic model from InfoWorks ICM.

· GIS files of manholes and gravity pipes.

Collection Network

The existing District wastewater collection system consists of nearly 367 miles of pipeline and over 9,200 manholes. The pipe sizes range from 6-inch diameter to 42-inch diameter pipe. The predominant diameter of the sewers in the system is 8 inches totaling nearly 300 miles of the system sewers. Figure 2-2 displays how many miles of each diameter pipe are found in the District’s system.

FIGURE 2-2 MILES OF SEWER BY DIAMETER

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MT OLYMPUS IMPROVEMENT DISTRICT

WASTEWATER COLLECTION SYSTEM MASTER PLAN

EXISTING WASTEWATER COLLECTION SYSTEM

AND SERVICE AREA BOUNDARY

FIGURE

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Legend Mt Olympus Improvement District Boundary

"/ Gravity Outfall

"/ Lift Station

Sewer Size (Inches Diameter)

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Central Valley Wastewater Treatment Plant

Mount Olympus Improvement District 2-2 Wastewater Collection System Master Plan

Wastewater Treatment Plant

The wastewater in the collection system flows to the Central Valley Water Reclamation Facility (CVWRF). CVWRF treats water from seven entities, including the District. These are:

Cottonwood Improvement District, Granger-Hunter Improvement District, Kearns Improvement District, Murray City, South Salt Lake City, and Taylorsville-Bennion Improvement District. The flows from the District arrive at CVWRF via two main gravity outfalls and a lift station force main.

Both the gravity outfalls are 42 inches in diameter. The I line generally receives flow from south of Big Cottonwood Creek and Spring Creek. The A line receives flows from areas north of these creeks. On average CVWRF treats approximately 50 MGD and has a permitted capacity of 75 MGD. The District’s current peak wastewater production is approximately 26.4 MGD.

Lift Stations

As a result of the fairly steep foothills and modest slope in the valley, most of the District’s service area flows by gravity to CVWRF. However, areas near the Jordan River are too low to flow by gravity to CVWRF and require pumping. The District uses one lift station to convey wastewater from this area to CVWRF. The location of the lift station is provided on Figure 2-1. Table 2-1 provides key characteristics for the District’s lift station.

TABLE 2-1 LIFT STATION INVENTORY

NAME ADDRESS

PUMP

CAPACITY

(GPM)

NO. OF

PUMPS

BACKUP

POWER

1100 West 1100 West 3000 South 800 Each 2 No

Mount Olympus Improvement District 3-1 Wastewater Collection System Master Plan

CHAPTER 3

FLOW MONITORING

FLOW MONITORING

Flow monitoring was performed as locations throughout the District’s service area. The purpose of flow monitoring is to obtain flowrate and time data at these locations to provide the basis for flow characterization, including flow peaking factors, construction of a model, and calibration of the model to real values.

Local Flow Monitoring

Flow monitoring was performed at various sites throughout the District by District and HAL personnel from April to July 2019. Each flow study location provided about two weeks of flow data.

Figure 3-1 shows the flow monitoring locations.

CVWRF Flow Monitoring

In addition to the flow monitoring performed by HAL and the District, CVWRF provided HAL with metered influent flow data for both the A line and I line from January 1, 2015 to July 1, 2019. The flows arriving at the treatment plant were analyzed in conjunction with precipitation data to assist in determining possible inflow and infiltration values. Graphs showing the recorded flow data are located in Appendix A.

Figure 3-1 FLOW MONITORING STATION LOCATIONS

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MT OLYMPUS IMPROVEMENT DISTRICT

WASTEWATER COLLECTION SYSTEM MASTER PLAN

FLOW MONITORING

STATION LOCATIONS

FIGURE

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Legend MTOID Boundary

Flow Monitoring Locations

Monitored By HAL

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Mount Olympus Improvement District 4-1 Wastewater Collection System Master Plan

CHAPTER 4

FLOW CHARACTERIZATION

METHODOLOGY

The purpose of flow characterization is to determine the flow patterns and variations that may be experienced by a wastewater system so that sewers, pump stations, and the treatment facility can be evaluated and sized appropriately. The flow characterization included evaluation of the following wastewater flow characteristics:

· Unit Flows

· Daily Flow Variation

· Annual Flow Variation

· Long Term Flow Variation

· Extraordinary Flows

UNIT FLOWS

Unit flows were estimated for the District and are expressed as Equivalent Residential Units (ERUs). An ERU is the average wastewater flow of residential units. The ERU is used to express all flows by the same unit. Commercial, industrial and other types of development flow can be expressed by the same unit as residences. For example, a commercial development that produces a flow of 5 times the average residence will be designated as having a 5 ERU flow.

When HAL received the current District wastewater collection system model, it was noted that the model contained high resolution information that identified the nearest manhole that received flow from each individual parcel. . Each parcel also estimated its Residential Equivalents (REs, which are the same as, and hereafter referred to as ERUs). To preserve the great and uncommon level of ERU detail, these parcels were used as the basis for assigning ERUs throughout the model.

The District informed HAL that 190 gpd/ERU was used to load the previous model. Areas that are predominately residential were evaluated to determine flow per ERU based on most recent flow monitoring data and the District’s ERU count within a monitored basin. The flow per ERU varied widely, but the average was around 200 gpd/ERU. Therefore, the following unit flowrate is identified:

Average Daily Flow / ERU = 200 gallons/day

DAILY FLOW VARIATION

Flow in a wastewater collection system varies continuously throughout the day. The available flow data were evaluated to determine the level and time of the variation. This evaluation included flow data from the two outfalls to CVWRF headworks. The data was on a 15-minute interval and occurred between January 2015 through June 2019. From the data, it may be observed that the minimum flow generally occurs during the early morning between 6:00 AM and 7:00 AM.

Mount Olympus Improvement District 4-2 Wastewater Collection System Master Plan

Maximum or peak flows typically occur around noon, between 11:30 AM and 12:30 PM, with a smaller peak occurring occasionally in the evening between 7:00 PM and 8:00 PM.

Peaking Factors

Peaking factors were developed for the District’s wastewater collection system. The peaking factor is the ratio between the peak instantaneous flow and the average daily flow. These peaking factors were calculated based on CVWRF flow data and on the local flow studies that were conducted by District and HAL personnel.

The flow monitoring data described in Chapter 3 was used to determine peaking factors and flow patterns. The peaking factors and flow pattern data were used to create a pattern in 15-minute increments. Based on this information, peaking factors were determined for the different land use types. As the flow data were evaluated, a representative curve for each of the following land use types was developed: residential, commercial, and high-density residential. Figure 4-1, Figure 4-2, and Figure 4-3 show the flow patterns at each of the monitoring site. The figures also show the composite patterns that were developed for each of these land use types and used in later modeling.

FIGURE 4-1 FLOW MONITORING RESIDENTIAL PATTERNS

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Mount Olympus Improvement District 4-3 Wastewater Collection System Master Plan

FIGURE 4-2 FLOW MONITORING COMMERCIAL PATTERNS

FIGURE 4-3 FLOW MONITORING HIGH DENSITY RESIDENTIAL PATTERNS

In Figure 4-1, Figure 4-2, and Figure 4-3 it may be observed that the flow meter data provides information with regard to patterns and peaking factor values. The residential, commercial, and high-density residential peaking factors of 1.65, 1.2, and 1.25 were derived from the flow studies.

In determining the shape of the diurnal curves for use in the model, the District’s recent and historic flow monitoring data were reviewed. The diurnal curves which were used in the model are provided in Figure 4-4.

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Mount Olympus Improvement District 4-4 Wastewater Collection System Master Plan

FIGURE 4-4 DIURNAL CURVES

WASTEWATER HYDROGRAPHS

Wastewater hydrographs were developed for the existing condition, the projected 10-year condition and the projected 40-year condition. In each condition, the wastewater hydrograph was developed using the hydraulic model. The predicted flows from throughout the District were converted to gallons per minute and added to the model at the appropriate flow loading locations.

A diurnal curve pattern was assigned to flow loading locations based on the loading type existing, the ERU allocations, and the predicted future ERU allocations. The model applies the flow based on the loads entered into the model and the associated pattern. The hydrographs are then routed through the system where flows combine and collect until they discharge at CVWRF.

CVWRF METER DATA

The District’s wastewater collection system discharges to CVWRF. Flow meter are located at both the east (A line) and south (I Line) outfalls to the treatment plant headworks. 15-minute flowrate data at these outfalls were obtained from January 2015 through June 2019. The District’s total flowrate to CVWRF from both outfalls is provided on Figure 4-5. Also, provided on the figure is the daily moving average wastewater flowrate (labeled as the 96 period moving average). This line on the figure shows the average flowrate for each day and helps with a comparison between peak, minimum and average flowrates.

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Mount Olympus Improvement District 4-5 Wastewater Collection System Master Plan

FIGURE 4-5 COMBINED A AND I LINE FLOW TO CVWRF

District flows to CVWRF are lowest October through December and highest March through June.

The typical highest month for flow to CVWRF is May with an average total outflow of 15.9 MGD and the typical lowest month for flow to CVWRF is November with an average total outflow of

11.2 MGD. This suggests an approximate flow increase of 40% due to inflow and infiltration, assuming no infiltration or inflow occurs in November. Of the five years of record provided, 2018 produced the least average flow to CVWRF at 12.3 MGD and 2017 produced the most average flow to CVWRF at 14.0 MGD. The average flow for the period of record is 13.6 MGD with only 1% of flows exceeding 20.8 MGD.

The average flow for the period of record can be used to confirm our assumed applied flow.

Dividing the average flow (13.6 MGD) to CVWRF by the number of existing ERUs (51,727) yields a average daily flow of 263 gpd/ERU. Infiltration will be discussed in more detail below; but it should be noted that an average value for infiltration based on the average in seasonal minimum flow variation from Figure 4-5 is approximately 3 MGD. Removing 3 MGD from the average daily flow of 13.6 MGD results in 10.6 MGD of average daily wastewater generation. 10.6 MGD divided by 51,727 ERUs yields a average daily flow of 200 gpd/ERU (rounded).

The flows were examined from each major outfall as well. The District’s flows are approximately evenly split; on average the A line discharges about 51.6% of the flow and the I line discharges

FL

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FLOWRATE TO CVWRF 96 per. Mov. Avg. (FLOWRATE TO CVWRF)

Mount Olympus Improvement District 4-6 Wastewater Collection System Master Plan the remaining 48.4% of the flow. Figure 4-6 shows the individual wastewater discharges from the A line and I line outfalls to CVWRF.

FIGURE 4-6 INDIVIDUAL A AND I LINE FLOW TO CVWRF

ANNUAL FLOW VARIATION

As seen in Figure 4-5 and Figure 4-6, wastewater systems can experience annual flow variation due to infiltration and other seasonal inflows such as irrigation or precipitation events.

Infiltration

Infiltration is defined as groundwater which enters a wastewater collection system through pipe joints, cracks in the pipe, and leaks in manholes or building connections. Infiltration may occur due to seasonal increases in groundwater level or may occur as the groundwater level increases due to a storm.

One indicator of infiltration is changes in the wastewater baseflow (minimum flow). In examining baseflow of the study data set, it appears that a maximum baseflow changes of about 6.2 MGD occurred in the flow record. These changes were discussed with the District, and it was decided that a flow of 6.2 MGD would be assumed for infiltration. The 6.2 MGD for infiltration was assigned

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Flows from A Line

Flows from I Line

Mount Olympus Improvement District 4-7 Wastewater Collection System Master Plan to manholes to calibrate the hydraulic model to observed monitored flows. This effort was concentrated in areas where the District expressed they believed infiltration was most predominate based on their observations during video inspections of the sewers.

Inflow

Inflow is defined as surface water that enters a wastewater collection system (including building connections) through rain gutters, foundation drains, area drains, cooling water discharges, manhole covers, cross connections from storm drains, culinary water discharges to the sewers and other direct discharges.

In order to estimate the amount of inflow, the flows from both the A line and I line near their respective CVWRF outfall locations were compared to precipitation data. It was observed that during medium to large storm events, CVWRF flows would increase during or shortly after a rainfall event. For example, a few of the larger events occurred during a week in March 2017.

The rainfall data and CVWRF flows were plotted together to observe the correlations. This comparison is found on Figure 4-7. Significant spikes in flows arriving at the treatment plant can be seen following the storm events. Based on a comparison of peaks before and during the storm, and removing the roughly 3 MGD of infiltration, it appears that a peak flow of approximately 3 MGD higher than normal occurred on the A line and a peak flow of 2 MGD higher than normal occurred on the I line due to the storms. Other storms showed similar results. It is possible that a larger storm event could cause a greater peak flow at CVWRF. This information was discussed with the District. It was decided that an inflow value of 6 MGD would be assumed, with 3 MGD spread throughout both the A line and I line drainage areas.

FIGURE 4-7 A AND I LINE FLOW VS. PRECIPITATION

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Mount Olympus Improvement District 4-8 Wastewater Collection System Master Plan

LONG TERM FLOW VARIATION

Average annual wastewater flows usually vary from year to year, although the variation between years is typically not extreme. The most predictable changes in average annual flows are typically associated with changes in population. Long term flow variations may also be caused by changes in weather patterns which may last several years.

Changes in weather patterns can result in changes in infiltration and water use patterns.

Decreased precipitation results in lower groundwater levels and less infiltration. Water conservation measures implemented during droughts may result in reduction in both indoor and outdoor water use. A reduction in indoor use results in less domestic wastewater generation. A reduction in outside use for watering lawns and gardens may lead to lowering of the groundwater table and less infiltration. Weather pattern changes are not expected to significantly impact the long-term flow rates of the District’s wastewater collection system.

Long term flow variations due to weather and planning density changes are difficult to predict.

However, HAL prepared flow projections based on the best available data for future growth conditions. Growth assumptions were prepared which included growth infill in areas not currently developed and included a degree of growth at higher densities.

EXTRAORDINARY FLOWS

Extraordinarily high flows may occasionally occur. These may be due to holidays or other events.

In the Salt Lake Valley, the Thanksgiving and Christmas Holidays are often days with high flows.

Aside from holidays, no specific high flow events have been identified. As discussed later, it is recommended that some excess capacity be included in the sewers for unexpected events.

Mount Olympus Improvement District 5-1 Wastewater Collection System Master Plan

CHAPTER 5

WASTEWATER FLOW PROJECTIONS

PLANNING PERIOD

The wastewater collection system master plan planning periods were established in consultation with the District. The periods that were modeled were the existing conditions, and projected loads through 2030 (10-year) and through 2060 (40-year). Growth areas and growth projections were developed in cooperation with District personnel and the District’s member cities. This enabled the identification of projects that are needed within the 0-10 year timeframe. Cost estimations were prepared for all projects needed within 10 years. Only projects needed within the next 10 years are eligible to include in the assessment of impact fees.

COLLECTION AREAS

A collection area is defined as a geographic area that contributes flow to a common point in the collection system. The District has established a labeling convention for the collection areas and main sewers. This labeling convention includes a letter and numbering system with are collection areas labeled with a letter and sewers labeled with a number. In the master plan analysis, the collection areas were typically split into smaller segments based on the incremental ERU count where the number of connections typically ranged between 400-600. This allowed the analysis to be performed with greater definition. The delineated collection areas are shown on Figure 2-1.

GROWTH PROJECTIONS

Population growth projections were prepared so that estimates of future wastewater production rates could be prepared. Population growth projections from the Wasatch Front Regional Council (WFRC) and the Kem C Gardner Policy Institute: 2020 Salt Lake County Projection (Gardner) were reviewed. The WFRC provided growth projections at the community level. The percent of each WFRC region which fell within the District was multiplied by that region’s population estimates and summed to get the total approximate District population. A similar technique was performed with the Gardner projections, which measures growth by county.

In consultation with the District, it was decided to model growth using the Gardner projection, as this was the more conservative of the two projections, in that it provided a higher growth rate. The average growth rate of the Gardner projection for the 40-year future is 0.84% per year. Figure 5-1 is a graph of both projections of the District’s estimated population and ERUs.

The existing population estimate from Gardner (103,378) was divided by the total number of existing ERUs (51,727) to come up with a conversion tool (1.97 people/ERU) to convert population to projected ERUs.

Mount Olympus Improvement District 5-2 Wastewater Collection System Master Plan

FIGURE 5-1 POPULATION AND ERU PROJECTIONS

ERU estimates for the existing wastewater collection system and growth projections have been prepared for the planning periods. These estimates and projections are summarized in Table 5-1.

A detailed list is provided in Appendix B.

TABLE 5-1 SYSTEM ERU PROJECTIONS

Approximate Year Cumulative Additional ERUs Total ERUs Description

2020 0 51,727 Existing System

2030 (10-Year) 5,550 57,277 10-Year Development

2060 (40-Year) 20,735 72,462 40-Year Development

It may be observed in Table 5-1 that the District is expected to experience significant sustained growth over the coming decades. The total number of ERUs after 40 years is expected to be about 40% more than existing.

FLOW PROJECTIONS

For the 2030 and 2060 planning periods, the new ERUs provided in Table 5-1 were distributed to collection areas throughout the District based on planning and zoning data received from the District’s member cities. The specific distribution of ERUs was based on workshops and discussions with District personnel.

50,000

55,000

60,000

65,000

70,000

75,000

100,000

105,000

110,000

115,000

120,000

125,000

130,000

135,000

140,000

145,000

150,000

2020 2025 2030 2035 2040 2045 2050 2055 2060

ER

U s

Po pu la tio n

WFRC Gardner

Mount Olympus Improvement District 5-3 Wastewater Collection System Master Plan

10-Year Flows

Generally, most of the growth in the first 10-years is expected to occur due to infill (construction in vacant/subdivided lots) or redevelopment in the Holladay Hills and Millcreek’s City Center areas, with other redevelopment occurring at locations throughout the District. The District indicated that many of the redevelopment requests which they are currently receiving are from existing residential units requesting to add an additional dwelling unit (ADU) to the same parcel.

To account for this type of growth, infill densities were assumed to be equal to the current land use zoning density plus 30%. Flow projections and ERU counts for Holladay Hills and Millcreek’s City Center were provided by the developers.

40-Year Flows

Beyond the 10-year population projection, growth is expected to be primarily redevelopment, and is expected to follow the densities assumed in the general land use plans of the District’s member cities. To forecast where growth will occur, the existing density of each land use polygon was calculated based on the spatial ERU data contained in the District’s previous water model. Each city’s zoning types were categorized into seven major zoning categories. Each of these categories was assigned a 40-year minimum density that would achieve the total number of projected ERUs.

Those areas with existing densities which exceeded the assumed minimum future density remained unchanged, while the areas which had less than the assumed threshold were assigned more ERUs. Table 5-2 provides a list of the major land use types and assumed minimum future densities.

TABLE 5-2 EXISTING AND ASSUMED FUTURE ERU DENSITIES

Land Use Type Range of Existing Densities

Assumed Minimum Future Land Use Density

ERUs/Acre High Density Residential 6.4 – 17.3 15

Medium Density Residential 3.6 – 9.2 10

Commercial 2.0 – 14.3 8

Industrial / Manufacturing 2.1 – 3.4 6

Mixed Use 2.6 – 12.7 6

Low Density Residential 0 – 4.0 2

Open Space 0 – 2.5 Existing

For future projections, the average daily flow established in Chapter 4 (200 gpd/ERU) was multiplied by the land use density (ERUs/acre) and the area (acres).

Table 5-3 shows the average wastewater generated based on the established average daily flow and ERU projections. The flows presented include the influence of inflow and infiltration but are not peaked.

Mount Olympus Improvement District 5-4 Wastewater Collection System Master Plan

TABLE 5-3 SYSTEM FLOW PROJECTIONS

Approximate Year Total ERUs Projected Peak Daily Flow*

(MGD)

2020 51,727 22.5

2030 (10-Year) 57,277 23.7

2060 (40-Year) 72,462 26.7 *Including flow from infiltration (2.4 MGD for A line, 3.8 MGD for I line) and inflow (3.0 MGD for A line, 3.0 MGD for I line).

Mount Olympus Improvement District 6-1 Wastewater Collection System Master Plan

CHAPTER 6

WASTEWATER COLLECTION SYSTEM EVALUATION

This section describes the steps involved in developing the model of the District’s wastewater collection system. The steps are as follows:

· Choosing the model software

· Establishing the System Layout in the model

· Developing the Design Criteria for the collection system

· Calibrating the model

· Creating different scenarios in the model

MODEL SELECTION

The District expressed an interest in possibly using a different software package than they had been using because of its high cost. HAL and District personnel discussed several software options and decided to use the Autodesk Storm and Sanitary Analysis (SSA) Model Software for the master plan hydraulic analysis. The software was selected because it is freely available with an AutoCAD license and uses the same computational engine as the software the District was using at the beginning of the project. SSA was also used because of the model’s ability to import GIS data, export models to EPA SWMM (free distribution), and because the model runs on an Autodesk platform, which the District uses

SYSTEM LAYOUT

The wastewater collection system layout was provided by District in a GIS data format. A copy of an exported SWMM model from previous efforts was also provided. A map of the existing District wastewater collection system, as well as wastewater and I&I model loading locations, as included in the model, is shown on Figure 6-1. Wastewater loading allocation within the model was performed using GIS and model data. Inflow and infiltration flows were determined using flow data from the wastewater treatment plant and precipitation data. During model creation, HAL and District personnel coordinated to correct identified errors or to add newly available data to the model.

Figure 6-1 MODEL SYSTEM LAYOUT

MODELING CRITERIA

A range of potential modeling criteria and values were suggested by HAL and reviewed by the District. The criteria and values adopted for this modeling effort are included in Table 6-1.

MT OLYMPUS IMPROVEMENT DISTRICT

WASTEWATER COLLECTION SYSTEM MASTER PLAN MODEL SYSTEM LAYOUT

FIGURE

6-1

Legend !( Model Loading Node

¡£ Inflow

") Baseflow

Sewer Size (Inches Diameter)

6 - 8

10 - 12

15 - 21

24 - 30

33 - 42

Tributary Basin A

B

C

D

E

F

H

I

J

K

L

N

P 0 3,500 7,0001,750 Feet

D oc um en t P at h:

H

:\P ro je ct s\

- M t O ly m pu s

ID

\0 1.

- S ew er M as te r P la n U pd at e\ G

IS

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/1 0/

Mount Olympus Improvement District 6-2 Wastewater Collection System Master Plan

TABLE 6-1 MODELING CRITERIA

CRITERIA VALUE OR ASSUMPTION

Average Daily Flow Existing average daily flow was developed based on a level of service (LOS) of 200 gpd per ERU. Future flow projects were developed based on growth projections and the LOS.

Daily Flow Variation Diurnal curves were developed from flow monitoring.

Peak Flow Peaking factors were developed with diurnal curves and peak flows were developed using the AutoCAD SSA model.

Inflow and Infiltration Inflow and infiltration values were determined by reviewing CVWRF data and precipitation values. Infiltration and inflow values were distributed throughout the District.

Future Planning Period Years 2030 and 2060.

Land Use & Population Projections

General land use plans were provided by each member cities. Population projections were based on the Kem C Gardner Policy Institute: 2020 Salt Lake County Projection.

Pipe Capacity (Depth/Diameter)

Roughness Coefficient = 0.013 Manning’s n District’s Selected Maximum d/D = 0.5 for all pipes 12 inches or smaller District’s Selected Maximum d/D = 0.75 for all pipes larger than 12 inches

MODEL CALIBRATION

Model calibration included comparing hydrographs generated by the model with actual flows collected during flow monitoring. Adjustments were made to I&I distribution and diurnal curves to better reflect measured flows. As discussed in Chapter 3, flow data observations from the flow monitoring stations and the wastewater treatment plant were used to calibrate the model. The peaked maximum design flow with inflow and infiltration for the A line was 13.2 MGD and the I line was 12.8 MGD. Observed and post-calibration model-computed hydrographs can be seen for all HAL-monitored flow locations on Figure A-1 in Appendix A. The post-calibration diurnal curves are those reflected in Figure 4-4.

MODEL SCENARIOS

Six modeling scenarios were developed and evaluated for the District’s wastewater collection system as shown in Table 6-2.

TABLE 6-2 MODEL SCENARIOS

SCENARIO DESCRIPTION

Existing The Existing scenario was used to identify deficiencies in the wastewater collection system, and to establish a baseline for evaluation of future conditions.

Existing Corrected The Corrected scenario reflects system improvements that resolve all existing deficiencies.

2030 The 2030 (10-Year) scenario was used to identify areas where the 10-Year projected flows exceed the existing (corrected) pipe capacity criteria.

Mount Olympus Improvement District 6-3 Wastewater Collection System Master Plan

SCENARIO DESCRIPTION

2030 Corrected The 2030 Corrected scenario reflects system improvements that resolve all 2030 (10-Year) projected capacity issues.

2060 The 2060 (40-Year) scenario was used to identify areas where the 40-Year projected flows exceed the existing (corrected) pipe capacity criteria.

2060 Corrected The Corrected scenario reflects system improvements that resolve all 2060 (40-Year) projected capacity issues.

MODEL RESULTS

The wastewater hydraulic models were run and the collection system was analyzed. The average flows discussed in Chapter 5 were placed into the hydraulic models at the manholes shown in Figure 6-1. The models applied peaking factors to generate peak flows at the CVWRF. All models included 6.2 MGD for infiltration and 6 MGD for inflow. The existing and future peak flows are provided in Table 6-3.

TABLE 6-3 EXISTING AND PREDICTED PEAK FLOWS

Planning Period A Line I Line Flows* Existing Conditions 13.2 12.8 26.4

2030 14.9 13.0 28.4 2060 16.7 14.4 31.7

*Including flow from 1100 West lift station and infiltration (2.4 MGD for A line, 3.8 MGD for I line) and inflow (3.0 MGD for A line, 3.0 MGD for I line).

In addition to evaluating the performance of the collection system, the flows predicted by the model to arrive at the lift station were evaluated. This was done to determine the remaining capacity of the lift station. The peak flow predicted during the 2060 (40-Year) model scenario was 410 gpm. Table 2-1 shows the lift station has a pumping capacity of 800 gpm with a second 800 gpm redundant pump. This mean the predicted flows do not exceed the lift station’s capacity and that the lift station is sized appropriately for the expected flows.

EXISTING DEFICIENCIES

The maximum depth ratio is the ratio between maximum depth in the pipe and the diameter of the pipe (d/D). Deficiencies were identified as pipes in the model that exceeded a d/D of 0.5 during peak flow conditions for pipes less than or equal to 12 inches. Deficiencies were also identified as pipes in the model that exceeded a d/D of 0.75 during peak flow conditions for pipes larger than 12 inches. Pipe capacity deficiencies identified in the Existing Scenario model are summarized in Table 6-4 along with the recommended solutions. Existing deficiencies are shown on Figure 6-2.

Figure 6-2 EXISTING DEFICIENCY PROJECTS

Mount Olympus Improvement District 6-4 Wastewater Collection System Master Plan

TABLE 6-4 EXISTING PIPE CAPACITY DEFICIENCIES AND SOLUTIONS

PROJECT

ID LOCATION ISSUE SOLUTION

E-1

Along West Temple between Silver Ave. and Angelo Ave.

Along 3300 South between Sue Street and West Temple

Pipe exceeds capacity because d/D > 0.5 (0.76)

Pipe exceeds capacity because d/D > 0.5 (0.67)

Remove and upgrade existing 10" and 12" gravity lines to 310 ft of 12" and 1,100 ft of 15" gravity line from A15-53 to A15.

Remove and upgrade existing 10" gravity line and 500 ft of 12" gravity line from A15-16 to A15-11.

E-2 Along 300 East between Lambourne Ave and Crestone Ave.

Pipe exceeds capacity because d/D > 0.5 (0.69)

Remove and upgrade existing 12" gravity line to 190 ft of 15" gravity line from A27-7 to A27.

E-3

Along 3680 South between 750 East and 700 East

Along 700 East between 3680 South and 3390 South

Pipe exceeds capacity because d/D > 0.5 (0.71)

Pipe exceeds capacity because d/D > 0.5 (0.61)

Remove and upgrade existing 8" gravity line to 2,740 ft of 10" gravity line from A42-99 to A42-25 and from A42-209 to A42-253.

E-4 Along 1000 East between Mansfield Ave. and 3300 South

Pipe exceeds capacity because d/D > 0.5 (0.55)

Remove and upgrade existing 10" gravity line to 1,050 ft of 12" gravity line from A53-5 to A53.

E-5 Along Imperial Street between Lahar Dr. and 3300 South

Pipe exceeds capacity because d/D > 0.5 (0.69)

Remove and upgrade existing 10" gravity line to 140 ft of 15" gravity line from A70-1 to A70.

E-6 Along 3300 South between Mill Creek Drive and 1885 East

Pipe exceeds capacity because d/D > 0.5 (0.53)

Remove and upgrade existing 10" gravity line to 390 ft of 15" gravity line from B1 to A77.

E-7 Along 3900 South between 1500 East and 1300 East

Pipe exceeds capacity because d/D > 0.75 (0.78)

Install 315 ft of parallel 10" gravity line next to existing 18" gravity line from C40A to C40.

E-8 Along Highland Drive between Siggard Drive and 3900 South

Pipe exceeds capacity because d/D > 0.5 (0.6)

Remove and upgrade existing 8" gravity line to 1,350 ft of 10" gravity line from C46-28 to C46.

E-9 Along 3900 South between Hillside Lane and 2000 East

Pipe exceeds capacity because d/D > 0.5 (0.58)

Remove and upgrade existing 10" gravity line to 4,020 ft of 12" gravity line from L17-63C71 to C56.

E-10 Along Craig Drive between 3140 East and 3100 East

Pipe exceeds capacity because d/D > 0.5 (0.54)

Remove and upgrade existing 8" gravity line to 85 ft of 10" gravity line…