Sustainable Water Sources

SSC’s Review of the Guiding Documents for Water Use in Silverton, Oregon

- January 1, 2026

The two guiding documents we reviewed related to the City of Silverton’s water source management are:

• 2018 Updated Source Water Assessment (SWA) (Oregon DEQ/OHA) (https://www.silverton.or.us/media/7806)  – identifies upstream water quality risks surrounding the Abiqua and Silver Creeks.

• 2021 Water Master Plan (WMP) (City of Silverton) (https://www.silverton.or.us/media/7576) – provides a plan for infrastructure capacity, treatment reliability, and seismic resilience, which Silverton has been faithfully implementing.

The 2018 SWA identifies watershed vulnerabilities. The 2021 WMP addresses infrastructure resilience. Together, these documents define:

• Where Silverton’s drinking water comes from (Abiqua Creek & Silver Creek),

• What threatens it (erosion, landslides, spills, agricultural and transportation risks),

• How the City plans to meet future demand (infrastructure, treatment, storage, seismic resilience).

Our review revealed the absence of governance-level watershed protection. We considered that the next step would be aligning our infrastructure investments with the upstream watershed governance tools and conservation strategies already identified in the 2018 SWA, as well as identifying gaps in the 2018 SWA. Our observations flowed into the following “pools,” if you will. 

1. Conservation & Ensuring Sufficient Stream Levels (aka “Sharing with the Fish”)

What We Know

• Silverton relies entirely on surface water (Abiqua & Silver Creek).

• The WMP projects increasing demand through 2041–2055.

• Climate trends suggest longer, drier summers and greater baseflow stress.

Current Approach

• Infrastructure expansion and reliability planning.

• Demand forecasting and supply buffering strategies (e.g., ASR feasibility).

Opportunities for increased Sustainability and Resiliency

• Commission an ecological flow study (summer baseflow modeling under climate-adjusted demand + fish thresholds)

• Voluntary irrigation efficiency and reduction incentives.

• Coordinated instream considerations during drought response planning (consider how much water must remain in the creek for fish, habitat, temperature control, and ecosystem function — not only how much the City can legally divert).

In cooperation with:

• City Council and City Public Works & Planning

• Oregon Water Resources Department

• Pudding watershed council

• SSC (education + advocacy)

The WMP focuses primarily on ensuring reliable supply to residents through 2041 and beyond. It includes demand projections to 2055 and capital improvements to meet peak demand. The SWA frames the watershed primarily as a risk exposure area rather than as an ecological system requiring flow protection. 

NEITHER document provides a robust ecological flow analysis addressing summer low-flow conditions, climate-driven extended dry seasons, fish habitat thresholds, or instream water rights coordination. Neither document provides essential information on ecological minimum flow thresholds, drought contingency impacts on fish habitat, long-term climate-adjusted hydrology modeling.

Silverton relies entirely on surface water (Abiqua & Silver Creek). Demand is projected to increase. Summer irrigation demand is historically high (per WMP demand analysis). A complete response must encourage conservation and incorporate source protection into planning. 

What has been done? Infrastructure upgrades for reliability. ASR feasibility study exploration. Demand forecasting and curtailment planning (operational resilience).

We could advocate for: Explicit ecological flow-sharing framework. Instream habitat coordination. Climate-adjusted baseflow modeling. Specifically:

• Commission an ecological flow study (summer baseflow + fish thresholds).

• Institute demand reduction incentives (irrigation efficiency, landscape conversion).

2. Health & Contamination (Erosion, Pollutants, Fire Response)

The SWA identifies significant erosion potential (99% erosion potential over 389 streamside miles), landslide-prone terrain, and agricultural runoff risk and fuel storage sites upstream of Silverton’s intakes. 

The WMP addresses contamination only through infrastructure: treatment plant capacity and operational monitoring; disinfection byproduct compliance reporting; infrastructure resilience. It does not establish a watershed-scale erosion control or spill response framework.

What has been done? New intake and transmission infrastructure (resilience). Treatment upgrades. Seismic mitigation planning.

What the SWA Identified

• High, extensive erosion potential and landslide-prone areas upstream.

• Agricultural and transportation-related contaminant risks.

• Rapid exposure potential within 8-hour time-of-travel zones.

Current Approach

• Treatment plant capacity and compliance monitoring.

• Seismic and intake resilience projects.

Opportunities for increased Sustainability and Resiliency

The SWA recommends voluntary and regulatory protection tools, including:

• Public/landowner outreach,

• Formal interagency spill response plan,

• Technical assistance partnerships (SWCD/Extension),

• Hazardous waste reduction efforts,

• Land use overlay or performance standards.

• Structured erosion mitigation partnerships. 

• Conservation easements program. 

• Fire-driven sediment pulse preparedness plan. 

• Drinking Water Source Protection Plan and Overlay District building off SWA.

• Organize hazardous waste amnesty events targeted to protection area residents.

• Eric - amnesty aged out chemical disposal; 

• Cory - does SWCMD do much around this? 

• Develop wildfire sediment contingency plan.

• Cory - agrees this would be critical

In cooperation with: 

• City Council 

• City Public Works & Planning

• Marion SWCD

• OSU Extension

• Oregon Dept. of Forestry

• Republic waste?

• DEQ Drinking Water Protection Program

• Fire Districts

• SWCD & landowners

• SSC (convener + public education + policy advocate)

3. Sustainable Growth & Watershed Impacts

The WMP includes population projections and demand scenarios through 2055, but the growth analysis is engineering-based (capacity, storage, treatment, distribution); there is no ecological carrying capacity analysis. The reports also do not model things like: cumulative withdrawal impacts on summer baseflows; increased erosion risk from expanded rural development; and land use change effects within the source area. Growth is treated as a demand forecasting challenge, not a watershed sustainability question.

What has been done? Storage and treatment capacity planning. Distribution upgrades. Seismic redundancy.

What We Know

• Growth scenarios are modeled for system capacity.

• Growth impacts on watershed sediment loading, runoff, and stream levels are not modeled.

Opportunities for increased Sustainability and Resiliency

• Watershed-scale growth impact analysis. What can be supported by our water sources?

• Integrate SWA source-area maps into land use and development review processes; Erosion-risk overlay triggered by development.

• Evaluate whether targeted erosion control or performance standards are warranted in protection areas.

• Incorporate wildfire sediment contingency planning.

• Formal coordination mechanism between planning and watershed protection.

• Conditional use standards for high-risk land uses.

• Green infrastructure, low-impact development, and Integrative Pest Management standards.

In cooperation with: 

• City Council

• Planning Commission

• SSC

4. Ecological Assessment of Treatment Process & Chemicals

Both plants use conventional filtration and chlorine (generated on-site) for water treatment. Chlorine reacts with dissolved organic carbon to form carcinogenic disinfection by-products (DBPs): Total Trihalomethanes (TTHM) and Haloacetic Acids (HAA5). Monitoring results since 2018 showed average values well below regulatory limits (TTHM: 0.080 mg/L / 3.6% of MCL; HAA5: 0.060 mg/L / 13.6% of MCL). 

What has been done? The 2021 WMP shows active TOC monitoring, enhanced coagulation to remove organic acids, and good operational control to prevent DBP formation. 

Consider if there are better/healthier ways to treat water (without creating carcinogenic DBPs). This an area we do not know enough about at this time to evaluate usefully.

5. Earthquake Risk & Seismic Vulnerability

The WMP includes a formal seismic risk assessment, as required by Oregon Health Authority and identifies the critical facilities:

• Abiqua Creek Dam & Intake

• Silver Creek Intake

• Both raw water transmission mains

• Treatment Plants 1 & 2

• Reservoirs

• Pump stations

• Silver Creek crossings

The plan finds the following vulnerabilities:

Abiqua Creek Intake - Built in 1940s, not to current seismic code. A major quake could severely damage the dam and transmission main.

Silver Creek Intake - Built in 1973. Better performance is expected, but it is still vulnerable.

Treatment Plants & Reservoirs - 1927 reservoir and Plant 1 most susceptible.

Silver Creek Crossings - Only three distribution crossings and no seismic restraints. If they fail, all west-side customers lose water.

Our Strategic Risk Profile finds the following strengths: Dual surface water sources, conservative demand planning, DBP levels far below regulatory limits, formal seismic mitigation strategy, and new treatment plant plans. If finds the following key vulnerabilities: Surface water dependency in changing climate, Silver Creek crossings limited and infrastructure is all on one side of the creek, aging dam and intake infrastructure, no explicit modeling of long-term hydrologic climate impacts.

What has been done? The City has been implementing the Capital Improvement Program’s mitigation plan, which is based around redundant sources, seismically resilient intakes, transmission main upgrades, the Silver Creek intake replacement and a new seismic-flexible transmission main. If completed, the system becomes “fairly resilient.”

What We Know

• The WMP seismic risk assessment finds our Strategic Risk Profile includes some strengths, and some key vulnerabilities: 

  • Surface water dependency in changing climate, 

  • Silver Creek crossings limited and infrastructure is all on one side of the creek, 

  • Aging dam and intake infrastructure

  • No explicit modeling of long-term hydrologic climate impacts.

• The City has been implementing the Capital Improvement Program’s mitigation plan, which, if completed, will bring the system to “fairly resilient.”

• Ware in a “seismic pocket” because of the Mt. Angel fault line

Opportunities for increased Sustainability and Resiliency

• Earthquake emergency education and resources, especially for areas on the West side of Silver Creek.

SSC recommends the following near-term actions:

1. Develop a Drinking Water Source Protection Work Plan aligned with the 2018 SWA.

2. Establish a formal spill response coordination protocol for upstream incidents.

3. Incorporate SWA maps into planning and development review procedures.

4. Bring to the SUTAB; discuss convening a watershed protection roundtable (City, SWCD, ODF, ODOT, fire district, nonprofit partners).

5. Mobilize volunteers and landowners within a coordinated stewardship program