Ammon Foothill MPC_WWTrtImpactStdy_JUB_2021-9-29FINAL
BCP DEVELOPMENT, INC.
Wastewater Treatment Impact Study
for Ammon Foothill Master Planned Community
Ammon, ID
September 2021
J-U-B ENGINEERS, Inc.
275 S. 5th Avenue, Suite 220
Pocatello, ID 83201
208-232-1313
Ammon WW Treatment Impact Study iii
Table of Contents
Overview .......................................................................................................................................... 1-1
Background ........................................................................................................................... 1-1
Objective of Treatment Impact Study ................................................................................... 1-2
Flow Projections .............................................................................................................................. 2-1
Summary of Impacts to WRF ........................................................................................................... 3-1
Summary of Impacts ............................................................................................................. 3-1
List of Tables
Table 2-1 – Projected Flows vs. WRF Capacity Table ................................................................................. 2-2
Figure 2-2 – Projected Flows vs. WRF Capacity Graph .............................................................................. 2-3
List of Figures
Figure 1-1 – EIRWWA Approximate Service Area and Oxbow WRF Location ........................................... 1-1
Ammon WW Treatment Impact Study 1-1
Overview
Background
The Eastern Idaho Regional Wastewater Authority (EIRWWA) provides regional conveyance to, and
treatment at, the Oxbow Water Reclamation Facility (WRF) which is located west of Shelley, Idaho. The
service area for the Oxbow WRF includes the cities of Ammon and Shelley, and portions of Bingham and
Bonneville Counties as shown in Figure 1-1. The facility currently discharges to the Snake River under a
National Pollutant Discharge Elimination System (NDPES) permit that became effective on June 1, 2014.
Figure 1-1 – EIRWWA Approximate Service Area and Oxbow WRF Location
Note: Not all areas and communities in the service area contribute to the EIRWWA Oxbow facility.
The Ammon Foothill Master Planned Community (AFMPC) will discharge wastewater to the City of
Ammon’s collection system which will convey the flow to EIRWWA’s “East” sewer interceptor. This
interceptor will convey the flow to EIRWWA’s Oxbow WRF.
The 2018 Facility Plan completed by J-U-B for EIRWWA included a Capital Improvement Plan (CIP) that
outlined a series of improvements for EIRWWA to undertake at the Oxbow WRF over the ensuing 20
years. In 2020, the existing membranes were replaced, and construction for a chemical addition project
is currently underway. The chemical addition project also included an emergency repair to the facility’s
outfall, which had been undercut by erosion and damaged, increasing the pipe size from 15 inches to 30
inches.
Ammon WW Treatment Impact Study 1-2
Continued growth has resulted in maximum month flows approaching 85 percent of the facility’s
nominal capacity of 2 mgd and is highlighting the need to prioritize capacity-related improvements
identified in both the “0 to 5 Years” and “5 to 10 Years” categories described in the 2018 Facility Plan.
Therefore, EIRWWA is currently completing a Preliminary Engineering Report (PER) for a Capacity
Upgrade project to address the needed improvements.
Objective of Treatment Impact Study
This Treatment Impact Study for the AFMPC will address anticipated impacts to Ammon’s wastewater
treatment system (i.e., EIRWWA’s Oxbow WRF). The study will document how the wastewater flows
projected from the development are included in the flow projections for the Capacity Upgrade project
and the associated impacts from the development’s flows on the Oxbow WRF will be addressed in the
PER for the project.
It should be noted that the impacts of AFMPC on the collection system of Ammon and the EIRWWA
interceptor are not addressed in this study but will be addressed in a separate “Collection System
Impact Study”.
Ammon WW Treatment Impact Study 2-1
Flow Projections
Table 2-1 summarizes projected flows versus the treatment capacity of the WRF. As indicated in the
table, growth from a “planned community” (i.e., the AFMPC) is included in the flow projections. The
analysis includes the following assumptions:
• 757 ERUs have been pre-purchased from EIRWWA but currently not connected. It is assumed
these ERUs will connect over the course of the next 5 years.
• EIRWWA has issued “will-serve” letters to approximately 1,122 ERUs that are currently not
connected. It is assumed these ERUs will connect over the course of the next 5 years.
• 3,300 ERUs for the planned community development are assumed with connections starting in
2023 and occurring linearly over a period 15 years.
• Flows from growth resulting from other contributors within EIRWWA service area are included.
Because much of the growth in the service area in the next 5 years is assumed to occur from the
ERUs that have been pre-purchased or issued “will-serve” letters or in the planned community,
the assumed growth rate for this contribution is assumed to be low for the next 5 years.
The assumptions made in this analysis result in an overall annual growth rate of 8.0% for the next 5
years declining to 2.5% by the end of the 20 year planning period. The average overall annual growth
rate for the 20 year planning period is 5.6% which is conservatively high relative to the historical average
growth rates that have been observed in this region and the future growth rates of 0.8 to 2.2% that are
projected in the Comprehensive Plans for the cities and counties. The average annual growth rate for
the service area over the entire 20 year planning period, not including the growth that is assumed to
occur within the AFMPC, is approximately 2.3%.
Figure 2-1 summarizes this information graphically. The treatment capacity of the WRF is shown as a
nominal 2.0 million gallons per day (mgd) until 2025 when the Capacity Upgrades project is anticipated
to be complete which will increase the capacity to a nominal 4.0 mgd (maximum month flow). The table
and graph also show data for “85% of nominal capacity” which is the trigger level when DEQ requires
the initiation of a project to increase capacity.
The analysis shows that the planned capacity increase will be sufficient to accommodate flows from the
AFMPC in addition to growth from other contributors throughout EIRWWA’s service area.
The wastewater generated from the AFMPC is assumed to be residential strength. Therefore, the
pollutant loadings from the AFMPC should be captured within EIRWWA’s assumed loadings per ERU for
residential units, and additional loading analysis specific to the development was not performed.
Ammon WW Treatment Impact Study 2-2
Table 2-1 – Projected Flows vs. WRF Capacity Table
ERUs from
Currently Pre-
Purchased but
Not
Connected
ERUs from
Currently
Committed
with a "Will-
Serve" but Not
Purchased or
Connected
ERUs from
Planned
Community
Assumed
Growth Rate
for "Other"
Future Growth
ERUs from
"Other"
Future Growth
Total
Cumulative
Added ERUs
from All
Projected
Growth
Resulting
Overall
Annual
Growth Rate
Resulting
ERU's
Connected
Resulting
Influent Max
Month Flow
(mgd)
Nominal
WRF
Capacity
(mgd)
85% of
Nominal
WRF
Capacity
(mgd)
# of ERUs 757 1,122 3,300 8,809
Years to
Build-Out 5 5 15
Year
2021 0 0 0 0 0 8,030 1.61 2.00 1.7
2022 151 224 0 3.3%265 641 8.0%8,671 1.73 2.00 1.7
2023 303 449 220 0.6%313 1,285 8.0%9,315 1.86 2.00 1.7
2024 454 673 440 0.6%361 1,929 8.0%9,959 1.99 2.00 1.7
2025 606 898 660 0.6%410 2,573 8.0%10,603 2.12 4.00 3.4
2026 757 1,122 880 0.6%458 3,217 8.0%11,247 2.25 4.00 3.4
2027 757 1,122 1,100 3.0%699 3,678 5.7%11,708 2.34 4.00 3.4
2028 757 1,122 1,320 3.0%940 4,139 5.7%12,169 2.43 4.00 3.4
2029 757 1,122 1,540 3.0%1,180 4,599 5.7%12,629 2.53 4.00 3.4
2030 757 1,122 1,760 3.0%1,421 5,060 5.7%13,090 2.62 4.00 3.4
2031 757 1,122 1,980 3.0%1,662 5,521 5.7%13,551 2.71 4.00 3.4
2032 757 1,122 2,200 3.0%1,903 5,982 5.7%14,012 2.80 4.00 3.4
2033 757 1,122 2,420 2.3%2,088 6,387 5.0%14,417 2.88 4.00 3.4
2034 757 1,122 2,640 2.3%2,272 6,791 5.0%14,821 2.96 4.00 3.4
2035 757 1,122 2,860 2.3%2,457 7,196 5.0%15,226 3.05 4.00 3.4
2036 757 1,122 3,080 2.3%2,642 7,601 5.0%15,631 3.13 4.00 3.4
2037 757 1,122 3,300 2.3%2,827 8,006 5.0%16,036 3.21 4.00 3.4
2038 757 1,122 3,300 2.5%3,027 8,206 2.5%16,236 3.25 4.00 3.4
2039 757 1,122 3,300 2.5%3,228 8,407 2.5%16,437 3.29 4.00 3.4
2040 757 1,122 3,300 2.5%3,429 8,608 2.5%16,638 3.33 4.00 3.4
2041 757 1,122 3,300 2.5%3,630 8,809 2.5%16,839 3.37 4.00 3.4
Ammon WW Treatment Impact Study 2-3
Figure 2-2 – Projected Flows vs. WRF Capacity Graph
Ammon WW Treatment Impact Study 3-1
Summary of Impacts to WRF
Summary of Impacts
At build-out, AFMPC will use a little over 1/3 of the 2.0 mgd of capacity added by the Capacity Upgrades
project. As noted earlier, a PER is being prepared for the Capacity Upgrades project to detail the impacts
on the Oxbow WRF of future flows and loadings from the EIRWWA service area (including the AFMPC)
and identify needed improvements to address the impacts. A summary of the impacts and
improvements, as understood at this time, is provided below:
• River Bend Lift Station: This lift station receives flow from the collection interceptors and
conveys it to the WRF for treatment. Two additional pumps are needed to accommodate the
projected peak influent flows, with one pump reserved for standby operation.
• Headworks: The headworks facility includes manually-cleaned bar racks, grit removal, and fine
screening. The capacity of the existing bar racks is adequate for the projected flows. The
addition of a second grit removal system and a third fine screen with associated washer /
compactor will be needed to treat the peak design flows with one unit reserved for standby
operation.
• Primary Lift Station: This lift station receives flow from the headworks facility and conveys it to
the downstream facilities for treatment. Two additional 40 Hp pumps are needed to
accommodate the peak design flows, with one pump reserved for standby operation.
• Biological Treatment: The biological treatment basins receive screened influent and return
activated sludge. The contents are mixed and aerated to provide an environment where
microorganisms in the wastewater grow and feed on the pollutants. To provide capacity for
design flows, a second biological basin is needed along with increased blower capacity. In
addition, the capacity of the pump station which conveys flow from the biological basin to the
downstream membrane basins needs to be doubled.
• Chemical Addition: A chemical addition upgrade is currently under construction to provide
storage tanks and feed pumps needed to inject alum into the wastewater which will react with
phosphorus (P) to form a precipitate that can be removed in the membranes, thereby, reducing
phosphorus in the effluent. Additional flows will necessitate a lower P limit, which will increase
chemical addition. Also, EIRWWA is waiting for renewal of its discharge permit by DEQ which
may result in lower P limits necessitating increased chemical addition. Since P removal is non-
linear (i.e., lower effluent limits require higher molar concentrations), the alum usage may have
to increase considerably. Due to all these variables, the exact timing of further chemical addition
improvement is difficult to estimate at this time. The chemical addition project was designed for
a future second storage tank to theoretically be installed within 10 years, the expected life of
the current tank. At that time, one new tank plus a replacement tank would be installed.
• Membranes: The existing two membrane basins contain hollow fiber membrane modules which
separate solids from the wastewater. Associated systems include chemical storage tanks and
feed pumps for membrane cleaning, permeate pumps, blowers and wasting pumps. To
Ammon WW Treatment Impact Study 3-2
accommodate design flows, two additional membrane basins with associated systems are
needed.
• Ultraviolet (UV) Disinfection: The UV disinfection system is a closed vessel system which doses
the membrane permeate with UV light for inactivation of viruses and bacteria. Provided
EIRWWA continues discharging to the Snake River (not a Class B or A reuse system), the UV
modules have capacity to deliver a sufficient UV dose for the projected flows. No major
expansion of capacity is anticipated to be necessary.
• Biosolids Management: Biosolids wasted from the biological treatment process are pumped to
the Solids Handling Building where a belt filter press dewaters the biosolids. The dewatered
biosolids are hauled to a landfill for disposal and the pressate is returned to the head of the
plant for treatment. The 2018 Facility Plan noted that a second belt filter press would be
required in the “10 to 20 Year” horizon (see Table 7-3). The timing of that project will be
accelerated based on the projected additional loading to the facility from AFMPC.
• Outfall: The effluent pipe and outfall to the Snake River was recently replaced and upsized in
2021. The upgraded capacity of the outfall is 9.1 mgd based on the design point when the water
level in the non-potable wet well inside the process building is approximately 1-foot from
overflowing (water elevation 4,600 feet). Based on peak hour peaking factor of 2.4 (from the
2018 Facility Plan), this capacity would be sufficient for average daily flows of 3.8 mgd which
should be adequate for the projected 20-year design flows.
• Other Items: The Capacity Upgrades project may also include other items which are not directly
related to address capacity impacts such as:
o A drying bed for storing and drying vactor truck solids
o A new primary access road to the WRF
o Improvements to adjacent property to accommodate Class A reuse