TO: Mayor and City Council
THROUGH: Krishna Namburi, City Manager
FROM: Brian D. Martin, PE, Public Works Director
SUBJECT:
title
Update on the Pending Deep Drawdown of Detroit Reservoir Proposed this Fall and the Status of City Resiliency Measures.
Ward(s): All Wards
Councilor(s): All Councilors
Neighborhood(s): All Neighborhoods
Result Area(s): Safe, Reliable and Efficient Infrastructure
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SUMMARY:
summary
This report provides an update to City Council on ongoing activities related to the deep drawdown of Detroit Reservoir. The first drawdown is anticipated to occur late in 2026 with drawdowns expected every year thereafter. The City has continued to advance resiliency measures for the City’s water supply. These include ongoing development of new groundwater wells at Geren Island, accelerated maintenance of slow sand filters on Geren Island, and installing a temporary pump station at one of the interties with the City of Keizer. Additionally, public outreach through neighborhood presentations and the City’s website continue.
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ISSUE:
Information only.
RECOMMENDATION:
recommendation
Information only.
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FACTS AND FINDINGS:
Overview
On December 26, 2024, the National Marine Fisheries Service (NMFS) issued a Biological Opinion (BiOp) requiring the US Army Corps of Engineers (USACE) to conduct deep drawdown operations at Detroit Reservoir to improve fish passage for out-migrating spring Chinook and winter steelhead.
A deep drawdown at Detroit Reservoir will increase levels of suspended sediments and turbidity in the North Santiam River. The City of Salem draws water from the North Santiam River at its water treatment plant located on Geren Island, 27 miles downstream of Detroit Dam. Salem’s drinking water treatment system relies on slow sand filtration, which produces high volumes of clean and safe drinking water. For sustained operation, slow sand filtration requires the source water to have very low levels of turbidity.
City staff met multiple times with the USACE over the past year, including a site visit at the Geren Island Water Treatment Facility where the Portland District Commander and his team toured the facility and learned how slow sand filtration works.
Supplemental Environmental Impact Statement
In January 2026, the City of Salem submitted formal comments (Attachment 1) to the U.S. Army Corps of Engineers on its Draft Willamette Valley System Operations and Maintenance: Supplemental Environmental Impact Statement (Draft SEIS). The City expressed support for federal, state, tribal, and local efforts to improve fish passage and habitat for ESA-listed spring Chinook and winter steelhead and acknowledged that the Draft SEIS had incorporated several City concerns, including initiating drawdowns later in the year, implementing a stepwise drawdown approach over multiple years, and limiting the duration of drawdowns to two weeks. However, we reiterated to the USACE that annual deep drawdowns of Detroit Reservoir pose a significant and ongoing risk to regional drinking water supplies due to increased turbidity in the North Santiam River, the main source of drinking water for approximately 220,000 people served by the City’s water system.
The Draft SEIS addressed many of the concerns the City has expressed to the USACE over the past 12 months. Among the significant commitments made by the USACE in the Draft SEIS that are responsive to the City’s concerns are the following:
(1) The USACE will initiate the drawdown closer to late November or early December.
(2) The deep drawdown will be conducted in a stepwise manner over several years.
(3) The duration of the deep drawdown is limited to two weeks.
However, the City’s primary concern is the absence of enforceable turbidity triggers and action measures in the Draft SEIS. Based on operational experience and recent scientific testing, the City recommended that the Final SEIS include a firm turbidity trigger requiring the immediate cessation of drawdown operations if turbidity levels reach or exceed 10 NTU (see note below) for 12 consecutive hours at the USGS Niagara gauge. We concluded that such a trigger is necessary to protect public health, safeguard the City’s slow sand filtration treatment system, and provide regulatory consistency with the federal Clean Water Act, the federal Safe Drinking Water Act, and Oregon’s water quality standards. Without clear turbidity thresholds and response actions, the City believes the risks to drinking water reliability, emergency response capability, and long-term economic growth are unacceptably high, despite ongoing investments to increase system resiliency.
During the summer, the USACE indicated its intention to closely monitor levels of turbidity and to manage the drawdown operation in a way that is protective of the City’s water treatment facility. City staff believe it is necessary to include firm turbidity triggers in the Final SEIS.
Note: Nephelometric Turbidity Units (NTU) is a measure of the clarity of the water. Generally, water with turbidity of 10 NTU or less looks clear. Water with turbidity of 50 NTU looks cloudy. Water with turbidity exceeding 500 NTU looks muddy.
Update of Resiliency Measures
Even though the USACE is expected to employ protocols during the drawdown to reduce the risks to the City’s water system, turbidity levels in the North Santiam River are still expected to exceed 10 NTUs for at least a portion of the drawdown period. In the event of a temporary shutdown of the City’s slow sand filtration system, the City will implement a range of resiliency measures. These measures include drawing from groundwater wells on Geren Island, drawing from the Aquifer Storage and Recovery (ASR) system in South Salem, and opening interties with the City of Keizer’s water system. Additionally, maintenance of the slow sand filters has been accelerated to ensure optimum performance of the City’s water treatment system before and after the deep drawdown. City Council’s emergency declaration in July 2025, which streamlined contracting and procurement processes, has significantly enhanced the rate of progress on these actions. Recent accomplishments include:
Groundwater Development
Four wells have been drilled and partially developed as part of the well expansion project. However, the current groundwater production levels are lower than anticipated and desired. To address this issue, advanced development techniques will be implemented to improve groundwater extraction. Additionally, a comprehensive aquifer test will be conducted to collect critical additional data on the aquifer's capacity and sustainability. Pending those results, additional wells will be considered to further increase production capacity for resiliency in future years.
Keizer Intertie
There are two interties between the City of Salem’s and the City of Keizer’s water systems. One is located on Cherry Avenue NE and the other on Weissner Drive NE. There is an existing pump station at the Cherry Avenue intertie. As part of the emergency work, a temporary pump station was recently installed at the Weissner intertie. A test conducted in January verified our ability to receive an average of more than 8 million gallons of water per day through these two interties, which exceeded our preliminary expectations. Note that Keizer uses water drawn from wells, which will be unaffected by the drawdown of Detroit Reservoir.
Slow Sand Filter Maintenance
In anticipation of the upcoming drawdown, the schedule for re-sanding of our slow sand filters has been accelerated. This is a maintenance activity that is critical for ensuring optimal filtration performance. Recognizing the need for timely acquisition, a sand procurement contract has been awarded to ensure the necessary materials are readily available if needed. In addition, one of the City’s seven sand filters is scheduled for re-sanding this spring.
Aquifer Storage Recovery System
The City utilizes a natural underground storage aquifer in South Salem, mostly located under Woodmansee Park. The system is normally filled with water from Geren Island during low water demand months in the winter so that it is available for use during peak water demand months in the summer. The aquifer primarily serves the S-2 pressure zone in South Salem.
This past year City staff filled the aquifer to approximately 900 million gallons and tested the system to evaluate how well it can be utilized during winter months. While the system can provide approximately 5 million gallons of water per day, the winter demand in the S-2 pressure zone is less than that amount, which does not allow the City to fully utilize the system. Staff are evaluating upgrades to the water distribution system in the vicinity of the ASR to allow utilization of ASR water in more areas of the water system.
Overall System Expectations During a Deep Drawdown
Currently, with expansion of groundwater resources at Geren Island, the activation of an additional intertie with the City of Keizer, and increased storage volume in the ASR system, the City anticipates sufficient capacity to meet average wintertime demand of approximately 25 million gallons per day during the drawdowns. However, under this mode of operation there is limited redundancy in the system. Should a critical component of one or more of these alternative sources of drinking water fail, the City’s ability to supply water may fall below the demand. The shortened drawdown timeframe already acknowledged by the USACE, along with the City recommended turbidity triggers identified in our Draft SEIS comment letter, should significantly reduce the duration of turbidity threats to our water system.
Update on Grant Funding Requests
The City continues to engage with state, federal, and congressional partners to identify potential funding opportunities for additional buildout of water system resiliency projects. Most recently, the City submitted project authorization language titled “Water System Adaptation to USACE Reservoir Drawdown Operations” through Congresswoman Salinas for consideration in the 2026 Water Resources Development Act (WRDA). The project aims to advance resiliency measures at Geren Island, the Weissner intertie with the City of Keizer, and the ASR system. If successful, the legislation would authorize the project, though congressional appropriation would still be needed to secure funding.
Update on Public Outreach
Public outreach is ongoing.
(1) Every neighborhood association has been offered a presentation. To date, staff have visited 10 neighborhood association meetings.
(2) The City’s public website provides information on the drawdown at:
https://www.cityofsalem.net/community/household/water-utilities/salem-s-drinking-water#detroit-drawdown <https://www.cityofsalem.net/community/household/water-utilities/salem-s-drinking-water> and
<https://www.cityofsalem.net/community/household/water-utilities/salem-s-drinking-water>
BACKGROUND:
On December 26, 2024, the National Marine Fisheries Service (NMFS) issued a Biological Opinion (BiOp) requiring the US Army Corps of Engineers (USACE) to conduct deep drawdown operations at Detroit Reservoir to improve downstream fish passage. Drawdown operations at Detroit Dam can cause high levels of turbidity in the North Santiam River, the source of Salem’s drinking water. Elevated turbidity levels present a severe threat to the operation of the slow sand filter system at the City’s water treatment plant, which is the primary method for treating Salem’s drinking water supply. Deep drawdown operations are currently planned to begin late in 2026 and are projected to occur annually thereafter. On July 28, 2025, City Council approved an emergency declaration to procure necessary materials, equipment, and services to develop alternative water sources and build resiliency. In January 2026, the City of Salem submitted formal comments to the US Army Corps of Engineers on its Draft Willamette Valley System Operations and Maintenance: Supplemental Environmental Impact Statement.
Robert D. Chandler, PhD, PE
Assistant Public Works Director
Attachments:
1. City of Salem Comments - Draft SEIS 2026-01-13
2. City of Salem to USACE Attachment A to Comments
3. City of Salem to USACE Attachment B to Comments