Wastewater Report 1.2
Wastewater System
Impact Study
for
Ammon Village
Master Plan
December 2021
Prepared for the City of Ammon
Civil Engineering:
2295 N Yellowstone Hwy, Unit 6
Idaho Falls, Idaho 83401
208.881.0081
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Table of Contents
Introduction .............................................................................................................................................. 3
1.1 Purpose ................................................................................................................................ 3
1.2 Scope of Analysis ................................................................................................................ 3
1.3 Significant Assumption ....................................................................................................... 3
AVMPC Location .................................................................................................................................... 4
EIRWWA Existing System ..................................................................................................................... 5
3.1 Location and Description of Existing System .................................................................... 5
3.2 Existing Depth of Flow in d/D ........................................................................................... 5
3.2.1 Existing Flow ....................................................................................................................... 5
3.2.1 Reserve Capacity ...................................................................................................... 5
3.3 Existing Model Conclusions .............................................................................................. 5
AVMPC Future System .......................................................................................................................... 6
4.1 Future Flows ....................................................................................................................... 6
4.2 Future Flow Analysis ......................................................................................................... 7
4.2.1 Growth ...................................................................................................................... 7
4.2.2 Future Discharge of the City of Ammon & S30” with and without AVMPC ................. 7
Summary .................................................................................................................................................. 9
5.1 Total Flow Analysis ............................................................................................................ 9
5.2 Needed Improvements ........................................................................................................ 9
Appendix A ............................................................................................................................................. 10
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List of Figures and Tables
Figure 1. Aerial and Boundary of Ammon Village Master Planned Community ............................. 4
Figure 2. Manning’s Equation, trial-and-error method of partially full 42” pipe ............................ 5
Figure 3. Population growth of the City of Ammon from 2020-2105 ......................................................... 6
Figure 4. Ammon Projection of Qmax in the year 2062 without AVMPC ............................................. 7
Figure 5. Ammon Projection of Qmax in the year 2058 with AVMPC .................................................. 7
Figure 6. S30” Projection of Qmax in the year 2098without AVMPC .................................................... 8
Figure 7. S30” Projection of Qmax in the year 2094 with AVMPC ........................................................ 8
Table 1. Table 1, Current Depth-Flow-Capacity ...................................................................................... 5
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Introduction
1.1.1 Purpose
The Ammon Village Master Planned Community (AVMPC) will discharge wastewater to the Eastern Idaho
Regional Wastewater Authority (EIRRWA). EIRWWA will convey the wastewater to the Oxbow Treatment
Facility.
1.1.2 Scope of Analysis
Connect Engineering completed the scope of analysis in two parts. First is the analysis of the AVMPC. The
study of the AVMPC is to gain a full accounting of expected peak flows that will impact the existing utilities.
The second is analyzing the existing Eastern Idaho Regional Wastewater Authority’s system. The impact of the
AVMPC on the current collection system. Analysis of the Oxbow WRF facility capacity or available
connections.
1.1.3 Significant Assumptions
The significant assumptions include straight grading, minimum pipe slopes, no surcharging or negative capacity
within trunk pipes, population growth rates remaining the same as current rates, the total unit load of AVMPC,
and the unit occupancy rate of AVMPC.
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AVMPC Location
Figure 1. Aerial and Boundary of Ammon Village Master Planned Community.
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EIRWWA Existing System
3.1 Location and Description of Existing System
The applicable existing system that was analyzed is the 30” trunk pipe located south of Township Road, west of
Ammon Road, east of S 25th E, and north of E 65th S, and the 42” trunk pipe flowing to Oxbow Facility. Flows
were provided by EIRWWA.
3.2 Existing Depth of Flow d/D
3.2.1 Existing Flow
EIRWWA current average flows of 1.1 MGD or 1.70 cfs with a metered peak flow of 2.85 MGD or 4.41cfs.
The 30” pipe west of AVMPC carries most of the flow at 1 MGD. The remaining 0.1 MGD flow is transported
in the 30” southern (S30”) pipe that runs through the AVMPC. AVMPC plans to connect directly to pipe S30”.
Using manning’s equation, we can calculate the depth of the flow. The average depth of flow for Ammon in the
42” trunk is 0.675ft and a peak flow depth of 1.07ft. 75% capacity being the full operational capacity, the
current average flows are at 26% capacity and peak flows 41% of operational capacity using depth over
diameter d/D. See Table 1. The current average flows in S30” are at 09% capacity and peak flows 22% of
operational capacity using depth over diameter d/D.
Table 1, Current Depth-Flow-Capacity
Depth (ft) Flow (cfs) Capacity d/D% Reserve Capacity d/D%
S30” Qavg 0.225 0.140 09% 91%
S30” QPeak 0.408 0.536 22% 78%
Ammon Qavg 0.675 1.700 26% 74%
Ammon QPeak 1.070 4.410 41% 59%
The depth calculations were developed using the trial-and-error method of manning’s equation, see Figure 2.
𝑃=1.49
𝑛𝐴𝑃2∕3𝑃1∕2
0.155𝑐𝑓𝑠=1.49
0.01[
1.252 ⋅(2 𝑎𝑐𝑛𝑠(1.25 −𝑦
1.25 ))−𝑠𝑖𝑛(2 𝑎𝑐𝑛𝑠(1.25 −𝑦
1.25 ))
2 ]⋅
[
[
1.252 ⋅(2 𝑎𝑐𝑛𝑠(1.25 −𝑦
1.25 ))−𝑠𝑖𝑛(2 𝑎𝑐𝑛𝑠(1.25 ⋅𝑦
1.25 1)
2 ]
1.25 ⋅2𝑎𝑐𝑛𝑠(1.25 −𝑦
1.25 )
]
2
3
⋅√0.0005
Figure 2. Manning’s Equation, trial-and-error method, for partially full 30” pipe
3.2.2 Reserve Capacity
The reserve capacity for Ammon is as follows: The peak d/D for Ammon is 41% of full operational capacity.
For the City of Ammon in the 42” trunk pipe the reserve capacity at peak flow is currently 59%.
The reserve capacity for S30” is as follows: The peak d/D for d/D is 22% of full operational capacity. For the
S30” pipe the reserve capacity at peak flow is currently 78%.
3.3 Existing Model Conclusions
The maximum operational flow for the 42” pipe is 21.47cfs at max operational d/D capacity, and current flows
as stated above are 4.41 peak hourly flow. The current peak flow is 20.5% of a max operational flow for the 42”
trunk pipe. The peak flow for S30” is 10.62cfs and current peak use is at 5% of the Qmax.
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AVMPC Future System
4.1 Future System Expected Flows
The AVMPC is expected to have a unit load of 716 units. With the current Ammon in-home occupancy of 2.96
persons per home, the higher 3.3 people per home were used in the possibility of higher unit loads of the final
design of the AVMPC. The daily usage per home is 325 gallons per day per home totaling 0.2327 MGD.
The peaking factor (Pf) of 3.53 was developed with the Harmon Method shown below.
𝑃𝑓=1 +14
4 + √𝑃𝑟�𝑙𝑟𝑟𝑎𝑙𝑑𝑟
The expected flows for the AVMPC are the discharge Q in MGD multiplied by the peaking factor 3.53.
The discharge (Q) comes out to a total of 0.8214 MGD or 1.52 cfs.
4.2 Future Flow Analysis
4.2.1 Growth
The growth within the AVMPC will be complete at the unit load of 716, and the assumed occupancy of 3.3
persons per unit, a total of 2363 residents at maximum occupancy. The growth of the city of Ammon must be
considered. The current growth rate is 3.95% and will be used to analyze the future impact.
Figure 3. Population growth of the City of Ammon from 2020-2105 @ 3.95%
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4.2.2 Future Discharge of the City of Ammon & S30” with and without AVMPC
Figure 4, Projection of Qmax in year 2062 without AVMPC
Figure 5, Projection of Qmax in year 2058 with AVMPC
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Figure 6, S30” Projection of Qmax in year 2098 without AVMPC
Figure 7, S30” Projection of Qmax in year 2094 with AVMPC
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Summary
5.1 Total Flow Analysis
The flow of the AVMPC into the current EIRWWA Ammon to 42” trunk pipe to Oxbow Treatment Facility
will have an insignificant immediate impact on the existing system. It will however shorten the length of
expected operation of the existing pipe by 4 years reaching the maximum discharge of 21.47 cfs in the 2058,
and without AVMCP Qmax is predicted to be achieved in the year 2062. The 42” trunk pipe is the limiting
factor due to the projection of the S30” not reaching maximum operational capacity with AVMPC until the year
2094.
Calculations for Qmax with respect to Time: 𝑃(1 +𝑃𝑙𝑙𝑙𝑟𝑙𝑎𝑟�ℎ𝑙𝑙 𝑓𝑟𝑙𝑤𝑟�)𝑇=𝑃𝑙𝑎𝑤, T is in years.
5.2 Needed Improvements
There is no immediate need for improvements to the existing system to accommodate the development of the
AVMPC.
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Appendix A: Engineering Drawings
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