1-River Well 1 Technical Memorandum - November 2025.pdf

W212229OR.00 • November 2025 • City of Bend River Well #1 • 1

Technical Memorandum Date: November 6, 2025

Project: W242229OR.00

To: Nick McAteer City of Bend

From: Heather Pina, PE Consor

Reviewed By: David Stangel, PE Nathan Nutter, PE Consor

Re: River Well #1 Rehabilitation Options

Executive Summary Project Overview River Well #1, constructed in 1972, is one of the City of Bend’s (City’s) longest-operating and highest-producing wells, providing critical redundancy and backup capacity within the City’s water system. Its central location near the Deschutes River enables operational flexibility during peak demands and surface water outages, making its long-term reliability essential to the City’s 108,000 residents and overall supply resiliency strategy.

The City retained Consor, with hydrogeologic support from GSI Water Solutions, to evaluate rehabilitation and replacement strategies for River Well #1. The assessment included review of historical construction data, structural and geotechnical evaluations, downhole video and alignment surveys, and comprehensive water quality testing. Together, these efforts established a technical foundation for identifying deficiencies and recommending improvements to sustain reliable operation of this key source.

Key Findings Structural and Geotechnical Condition The existing wellhouse, built in the early 1970s, exhibits significant structural distress including approximately 3.5 inches of differential settlement and widespread cracking caused by weak, organic-rich soils and compressible volcanic tuff beneath the site. Geotechnical investigations confirmed that continued settlement is likely, making repair or retrofit infeasible. Replacement of the wellhouse is therefore required under all improvement scenarios.

Well Condition The 53-year-old, 16-inch steel well casing is in generally fair condition but shows evidence of deterioration and multiple small leaks at welded joints, primarily between 357 and 480 feet below ground surface (bgs).

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While these leaks do not appear to reflect surface water intrusion, they do indicate aging weld integrity and the need for full sealing to maintain long-term reliability.

Water Quality Water quality testing identified elevated manganese concentrations exceeding Oregon Health Authority (OHA) infant advisory levels (300 µg/L) during initial sampling. However, extended flushing for approximately four hours reduced manganese levels below the advisory threshold, suggesting that operational strategies may effectively manage water quality without requiring full treatment. No evidence of surface water influence was detected, and total coliform (TC) detections at the pre-chlorination point were successfully managed through existing chlorination practices.

Alternatives Evaluation Three primary alternatives were evaluated to address the structural and hydrogeologic deficiencies at the River Well #1 site.

Option 1A – Internal 14-Inch Liner: Install a removable 14-inch liner inside the existing casing to maintain capacity but without full sealing.

Option 1B – Internal 14-Inch Casing: Install a new 14-inch steel casing inside the existing casing, sealed with cement grout to fully address leaks and restore well integrity.

Option 2 – New Replacement Well: Construct a new production well at the existing site, including full permitting, OHA site plan review, and potential land use approvals.

Each option includes wellhouse replacement, new pump and motor, conversion to onsite sodium hypochlorite generation (OSG), and enhanced site security. Cost estimates ranged from approximately $3.8 million to $5.2 million, with an additional $3.5 million for optional manganese treatment if required in the future.

Preferred Alternative Option 1B – Internal 14-Inch Casing has been identified as the preferred alternative. This approach offers the best balance of cost, constructability, regulatory feasibility, and long-term reliability. It provides a complete seal of all casing leaks, is fully permissible under Oregon Water Resources Department (OWRD) standards and maintains the well’s existing 1,930 gallons per minute (gpm) pumping capacity. Compared to a new well, this option avoids extensive permitting and land use constraints while delivering comparable operational benefits.

Post-rehabilitation monitoring and sampling will confirm whether manganese levels can be managed through operational flushing. If necessary, the City retains the option to implement a modular manganese treatment system at a later phase.

Implementation and Next Steps The project is anticipated to span approximately 2.5 years, including about 10 months for design and permitting, 3 months for bidding, and 14 months for construction. River Well #1 will be offline for at least one peak-demand season. Early coordination with regulatory agencies and pre-purchasing of long-lead equipment will be key to minimizing service disruptions.

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Closing Statement Rehabilitating River Well #1 through the preferred re-casing alternative will restore a vital component of the City’s groundwater system, extending its service life by several decades. This investment strengthens the City’s capacity to meet future demands, enhances supply reliability during surface water interruptions, and supports long-term operational resiliency across the municipal water system.

1. Introduction & Existing Conditions

1.1 Project Background and Purpose

The City operates and maintains a total of 20 water supply wells located in the regional aquifer that, along with surface water, deliver reliable drinking water to the majority of the City’s population of 108,000.

Constructed between 1972 and 1974, River Well #1 is one of the City’s longest-operating and highest-producing wells but has recently been determined to need significant improvements for long term use. It is a critical well, relied upon to serve demands when surface water is restricted or not available and its central location in the water system provides significant flexibility for conveying water to much of the service area.

The City has engaged Consor with support from GSI Water Solutions (GSI) to complete an alternatives analysis to evaluate strategies for maintaining River Well #1 in reliable long-term service. The analysis includes an assessment of the existing wellhouse’s condition and identification of potential improvements to support continued operation over a 20-year plus planning horizon.

At the start of this project, the City discussed abandoning River Well #1, however elected to continue operating it under emergency conditions to maintain system reliability during peak-demand periods while long-term rehabilitation and replacement strategies were evaluated. This temporary use allows the well to remain available as a supplemental source, recognizing that it is operating in its existing condition until permanent improvements are implemented.

As noted, Consor’s project team (Project Team) includes GSI as hydrogeologist, providing well construction and rehabilitation expertise. GSI’s primary role was to evaluate the hydrogeologic and physical characteristics of the well and to provide technical guidance on potential rehabilitation or replacement options. Their work included coordination with a licensed water well driller to assess feasibility, constructability, and considerations related to rehabilitation/alteration of the existing well and drilling a new well at the existing River Well #1 site.

This technical memorandum presents the findings of the condition assessment, which was informed by field observations, historical documentation, and City input. Based on the identified deficiencies and anticipated future needs, it outlines recommended improvements to support continued operation and long-term reliability of the River Well #1 site.

1.2 Document Structure

The structure of this document is organized to reflect the major tasks completed as part of the River Well #1 Alternative Analysis. The sections are structured as follows.

Remainder of Section 1 – provides an overview of the data collected, River Well #1 site characteristics, property ownership, access, and River Well #1 existing site and specific wellhouse conditions to establish the basis for the alternatives analysis.

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Section 2 – Well Condition and Source Water Evaluation: Summarizes the investigation into the general condition of River Well #1 and origin of water entering the well, including well video reviews and surveys, development of a sampling protocol, and coordination with the City for water quality testing.

Section 3 – Scenario Analysis and Risk Assessment: Provides a scenario analysis of the existing well casing, potential treatment needs based on water quality, and regulatory constraints. It also identifies any fatal flaws that would preclude future reinvestment in the River Well #1 site.

Section 4 – Mitigation Rehabilitation Strategies: Develops and defines the full range of mitigation strategies for River Well #1 site, drawing on the condition assessment, water quality results, and property/regulatory constraints documented earlier. This section translates the findings into specific conceptual strategies, rehabilitation of the existing well and wellhouse, drilling of a new well, or other supporting improvements, and provides associated cost estimates, structural considerations, and an implementation timeline.

Section 5 – Final Recommendation and Next Steps for Preferred Alternative: Compiles key findings and presents the recommended path forward based on the alternative analysis.

1.3 Data Collection

As part of this project, existing data and documentation were collected and reviewed to develop an understanding of the current condition and operation of the River Well #1 site. This review supported the assessment of condition and informed the development of potential improvement strategies. The key sources of information included:

DOWL Structural Assessment of River Well #1 Wellhouse, September 2023

Wallace Group Geotechnical Exploration Summary – Update, November 2024

River Wells Water Operational Narrative for River Wells Assets #WAWL00RW1 and WAWL00RW2, Updated December 12, 2016 (River Wells Operational Narrative)

City of Bend Well Maintenance Plan, April 2024, Version 1.0

Status of Record Title Report

Oregon Water Resource Department Logs for River Well #1 (DESC 5577) & River Well #2 (DESC 5578)

This document review was supplemented with a site visit conducted July 8, 2025 by Consor and GSI team members, as well as regular coordination with City staff through biweekly project meetings. These discussions provided valuable context, confirmed assumptions, and supported timely decision-making throughout the alternative analysis.

1.4 Property Ownership, Access, and Regulatory Constraints

The River Well #1 site is located at 341 SW Shevlin Hixon Drive in Bend, Oregon, within the City’s Mixed Riverfront (MR) zoning district on a 0.23 acre leased parcel, tax lot no. 181205B001100, also known as Tract B. The lease expires on October 31, 2070, unless it is extended by both parties. The existing River Well #1 site is 105 feet, 9 inches by 95 feet, 2 inches parcel and is centrally situated within the City’s water

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As part of the existing conditions review, Consor evaluated a title report for the River Well #1 site to identify any constraints that may impact future improvements or long-term operation of the site. The review included ownership, easements, and other property records provided by the City. Findings are summarized below and are intended to inform the feasibility of upgrades and site access constraints.

Ownership: The River Well #1 site is owned by River Bend Limited Partnership, with a lease that allows the City to use the property for “the development and production of well water to supplement the City’s water [system].”

o The River Well #1 site Lease was granted to the City on November 1, 1971 under Instrument No. 16-936 from Brooks-Scanlon with amendments in 1986, in which the locations of River Well #1 and #2 sites were specified. The lease expires on October 31, 2070.

o A Pipeline Easement granted to the City on December 3, 1971, with the intended purpose “to serve wells developed on the grantor’s property according to terms and conditions of [the] Wellsite Lease.”

o Additional easements recorded in 1997 and 1998 (Instrument Nos. 468-1683 and 507-0332) may affect property access or placement of new infrastructure. All designs for improvements must be approved by the River Bend Limited Partnership Design Review Committee and construction of any building must be completed within 18 months after beginning construction.

Land Use & Zoning: The River Well #1 site is zoned MR within the City’s Urban Growth Boundary

(UGB).

o Items to confirm: Need to confirm with City planning department if upgrades are allowed or if conditional use permitting is required under MR zoning. City has indicated that they will be confirming the appropriate process.

Covenants, Conditions, and Restrictions (CC&Rs):

o Multiple recorded CC&Rs between 1995 and 2021 under Instrument Nos. 370-778, 499-2948, 2007-23852, 2021-70995.

• Old Mill District CC&R Type Review is required. Based on coordination, traditional split-face construction is acceptable for new structures; no additional special architectural requirements or landscaping are identified.

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Setback and Site Constraints: No explicit building setbacks are noted in the record title documents or MR district zoning regulations.

Solar Ordinance: The River Well #1 site is subject to Bend Development Code § 3.5.400 (“Solar Standards”), which includes requirements for shade point height and limits on building or structure height to avoid shading neighboring properties, especially with respect to solar access periods. The proposed improvements may need to comply with those height/shade point restrictions. Verify with the Bend Planning Department whether the planned filter building or other structures exceed local solar shade or height limits.

1.5 River Well #1 Site Overview

The following subsections provide a high-level overview of the existing River Well #1 site, including property constraints, improvements, and current physical and operational characteristics.

1.5.1 Site Configuration and Infrastructure

The River Well #1 site consists of a 16-inch diameter production well, associated pumping and discharge piping system, and wellhouse. The well was completed in April 1972 to a total depth of 900 feet, as described in further detail in the OWRD well log (DESC 5577) provided in Appendix A.

Site piping ranges from 8 to 16 inches in diameter and includes a meter and meter vault directly downstream of the wellhouse, a fire hydrant, irrigation waterlines and an irrigation meter. Minimal landscaping is provided on the River Well #1 site, consisting of a lawn and a couple trees, as depicted in Figure 2. There are no existing storm or sewer lines on the River Well #1 site but an existing sewer main is located within SW Shevlin Hixon Drive, located adjacent to the northern and eastern margins of the site.

The River Well #1 site is fully fenced with a single access point off SW Shevlin Hixon Drive. There is an existing transformer in the southwest corner of the site. The wellhouse operates on 3-phase, 480V power and there is currently no backup power supply.

The original wellhouse was constructed with a submersible pump but was converted to a vertical turbine pump in 1996, at which time the pump, motor, and major electrical components were replaced. No other upgrades have been completed since. During the July 8, 2025 site visit, the well pump was not operating but the operator reported no performance concerns during past operations. The wellhouse is equipped with basic heating, ventilation, and air conditioning (HVAC), consisting of an exhaust fan, louver, and unit heater. City personnel have noted that the wellhouse can become hot during operation, highlighting limitations of the current HVAC and ventilation systems. No issues have been observed with electrical components overheating. A section of metal roof tin panels can be removed to allow access to the pump motor, though it is not a dedicated hatch.

Additional operational details include:

The entire River Well #1 well pump is manually operated, with City personnel responsible for initiating pump cycles and managing all disinfection activities.

Pump-to-waste system: An 8-inch diameter line tees off the pump discharge header through a control valve and discharges to the Deschutes River. A pump-to-waste cycle is operated each time the pump starts, with duration manually set by City personnel

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Air line: A previous airline was removed due to unreliable readouts and is not planned for reinstallation. No other level measurement equipment is installed.

Chlorination system: Chlorination at River Well #1 and #2 sites are manually controlled rather than flow-paced. If both wells are running and one shuts down, City personal must manually adjust chlorine dosing. A redundant chlorination system is in place, with chlorine stored at River Well #2 in a separate building. Chlorine injection occurs downstream of the River Well #1 and #2 connection, near the River Well #2 wellhouse, via a manhole/vault. Refer to the Start-Up standard operating procedure (SOP) for additional details on manual chlorination operations.

Table 1 provides a summary of the well and pumping system infrastructure. Figure 3 and Figure 4 are selected photos from the July 8, 2025 site visit.

Table 1 | River Well #1 Existing Infrastructure Summary

Attribute Description

Pump Type Vertical Turbine

Pump Characteristics

Design Point 1930 gpm at 630 ft total dynamic head Model/Stage: American Turbine #14-M-270, 15 stage Pump Column Size: 10-inch diameter low-carbon steel (LCS) Installed: 1996

Motor Characteristics 500 HP, 460 volt (V), 3 phase (ph), 1775 revolutions per minute (RPM) US Electrical Motors, model unknown Installed: Early 1996

Well Depth Drilled 900 ft

Well Construction

24-inch diameter borehole from 0 to 232 feet bgs 20-inch diameter borehole from 232 to 637 feet bgs 12-inch diameter borehole from 637 to 900 feet bgs 16-inch diameter LCS blank casing from ground surface to 637 feet bgs Open borehole from 637 to 900 feet bgs Seal intervals: 0 – 50’; 96 - 112’; 232 – 262’; and 600 – 637’ bgs.

Remaining sections filled with drill cuttings and crushed rock.

Refer to well log (DESC 5577) and well schematics in Appendix A.

Static Water Level1 569.5 ft bgs (as measured March 2023) Pump Intake Level 593 ft bgs Air Level (Not Used) Airline Bubbler, installed to 625 ft bgs Lubrication Water Chlorination Gas, manually controlled Discharge Piping Size 10-inch diameter

Pump-to-Waste Cla-Val; 8-inch; Cat No. CSM11-A2-2 From wellhouse discharges to the Deschutes River.

Existing Electrical Component Summary MCC/Switchgear, VFD, breaker panel, etc. replaced in 1996 Notes:

1. Minor discrepancies were observed between historical and recent measurements of the static water level at River Well #1. Differences are likely due to seasonal variation or measurement methods. The current static and pumping water levels should be confirmed during final design to verify pump setting and hydraulic conditions.

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Figure 3 | River Well #1 Wellhouse: Motor & Discharge Piping

Figure 4 | River Well #1 Wellhouse Exterior

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1.5.2 Operational Summary

River Well #1 in conjunction with River Well #2 primarily supply water to Awbrey Reservoir, serve Pressure Zone 5 directly, and are typically operated to satisfy summer peak demands or to help replace the partial or total loss of surface water. Once the River Wells are turned on for the season they are typically utilized for as long as possible due to the electrical demand charges incurred when they are turned on.

Although the wellhouse is equipped with a programmable logic controller (PLC) connected to the City’s supervisory control and data acquisition (SCADA) system for monitoring, all major operations remain manual. City personal are responsible for turning the pump on and off, initiating pump-to-waste cycles (which discharge to the Deschutes River), and controlling chlorine addition and feed adjustments as system conditions change. The River Well #1 SOP can be found in the River Wells Operational Narrative.

1.5.3 Existing Wellhouse Condition and Geotechnical Summary

The existing River Well #1 wellhouse was evaluated by DOWL in a 2023 condition assessment, supported by a geotechnical exploration effort. The structure, originally constructed in the early 1970s, shows clear signs of differential settlement and structural distress, attributed primarily to underlying soil conditions.

Observations from the structural assessment include widespread wall and plaster cracking. The south wall was also measured to be out of plumb by approximately 2.5 inches. Inside the wellhouse, the concrete slab exhibited extensive cracking, particularly near pipe penetrations and construction joints. The surface of the slab appeared uneven and sloped from southeast to northwest, with visible signs of water ponding in the northwest corner. These conditions suggest long-term movement and separation between the slab and foundation elements. Additionally, two interior wall cracks were identified on the east side of the structure, likely resulting from differential foundation movement.

A follow-up geotechnical investigation was conducted in 2024 by Wallace Group and included two soil borings near the wellhouse perimeter. The investigation found that soils beneath the River Well #1 site consist of undocumented fill, organic-rich materials (the site was formerly a raw log processing business), alluvial sands and gravels, and a thick layer of decomposed tuff with low bearing strength. At greater depths, the subsurface profile transitions to dense alluvial gravel. Laboratory testing indicates the potential for total settlement in the range of 14 to 25 inches, with at least 3.5 inches of differential settlement already observed. The ongoing consolidation is primarily attributed to the decomposition of organic materials and the compressibility of the tuff layer. Additionally, it was noted that soils adjacent to the well casing may impose downdraw forces as settlement progresses.

Based on the combined structural and geotechnical findings, DOWL recommends replacing the existing wellhouse rather than attempting a structural retrofit. Although repair strategies such as installation of helical piers and slab replacement are technically feasible, the cost is comparable to full replacement and would not significantly extend the wellhouse’s useful life. DOWL recommended interim measures such as patching visible cracks and conducting biannual monitoring, but those measures were noted as not being completed at the time of this report generation.

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2. Well Condition and Source Water Evaluation

2.1 Introduction

This section summarizes the investigation into the general condition of River Well #1 and the origin of water entering the well, including well video reviews and surveys, development of a sampling protocol, and coordination with the City on water quality testing and results review.

2.2 Well Video and Drift Survey Findings

The Project Team reviewed a City-supplied down-hole well video completed in January 2025. However, due to limited video quality another down-hole camera survey was conducted in June 2025. The June 2025 work also included a plumbness and alignment (aka, drift) survey completed in accordance with American Water Works Association (AWWA) A100-15 methodology to assess deviation of the original well bore, for purposes of evaluating potential new well locations. Specific aspects of the down-hole well video are illustrated on a well diagram provided in Appendix B.

Findings from the video and drift surveys are summarized below:

Approximately 30 feet of accumulated material was observed at the bottom of the open-hole portion of the well, indicating long-term sedimentation or collapse of formation material over time.

It is recommended that this material be removed during rehabilitation work on the existing well.

The existing 16-inch diameter casing showed general signs of corrosion and aging, consistent with its age.

The camera survey revealed water leaking into the casing at several depths above the SWL; many of which appeared to align with casing weld joints. Casing leaks evident in the June 2025 video survey were noted at the following approximate depths (above the static water level), and include rough flow estimates based on general visual observation:

o 357 ft bgs (approximately 0.5 gpm) o 381ft bgs (approximately 1 gpm) o 400 ft bgs (approximately 0.5 gpm; two small leaks) o 480 ft bgs (approximately 5 gpm, most significant leak)

Based on a review of the original well construction and camera survey observations, the casing leaks are located at depths where the space between the 16-inch casing and the borehole is filled with permeable material (drill cuttings and crushed rock)1 and approximately align with casing weld joints (see Appendix B). While the casing leaks observation indicates potential issues regarding the casing weld joint integrity, it is not interpreted to reflect surface water intrusion into the well. Based on GSI’s review, the observed casing leaks are interpreted to reflect groundwater derived from shallower intervals within the basalt aquifer formation as the production interval of the well. This concept is supported by a review of the hydrogeologic setting and presence of a continuous cement seal from ground surface to 50 feet bgs; which extends below alluvial deposits and into the basalt aquifer – thereby sealing off shallower groundwater and surface waters. It was determined

1 The original well log (DESC 5577) included in Appendix A includes documentation regarding annular seal construction that was approved by OWRD at the time of drilling.

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The well meets AWWA standards for plumbness, it is still suitable for re-use with a properly aligned column pipe and pump. The drift survey also indicated no restrictions with regard to new well locations intersecting the existing well bore. Directional drift and drift tolerance graphs are provided in Appendix C.

These findings directly inform the well casing condition discussion in Section 3.2 and the mitigation strategies evaluated in Section 4.1.

2.3 Water Quality Testing & Results

The City, in conjunction with the project team, developed a sampling protocol to evaluate water quality (WQ) at River Wells #1 and #2 with the intent to understand if the observed water cascading into River Well #1 was surface water from the nearby Deschutes River. River Well #2 sampling was conducted to establish baseline WQ data for comparison to the potentially compromised River Well #1 WQ. The sampling protocol (provided in Appendix D) identifies sampling locations, timing, and a comprehensive list of constituents for laboratory analysis. While historical data for the Deschutes River was available and sufficient for comparison, no new surface water samples were collected as part of this study.

After the initial round of sampling indicated manganese levels at River Well #1 in excess of an OHA health advisory for infants, the City conducted a second round of sampling after flushing the well for approximately 20 hours to confirm elevated manganese concentrations. The sampling plan was then expanded for a third round to include more detailed testing on the impact of flushing the well on constituent concentrations over time. For the third round, operators took grab samples at three points in the system for approximately 30 hours. The three points in the system, upstream to downstream, were:

1. River Well #1 Pre-Chlorination

2. River Well #1 & River Well #2 Combined Entry Point

3. First Hydrant in System

The findings from the three sampling events completed in summer 2025 are summarized in Table 2. The full water quality reports are provided in Appendix E.

The results from the sampling events overall did not show clear indication that River Well #1 is under the influence of the nearby surface water at the Deschutes River. Turbidity and manganese levels were noted as significantly high for a groundwater source, and a low total suspended solids (TSS) reading indicates that particles causing the high turbidity are colloidal. However, low total organic carbon (TOC) indicates that particles are most likely inorganic, which is typical of groundwater and not of surface water.

Pre-chlorination samples at River Well #1 did not find present TC or E. coli in the first round of sampling;

however, a present TC test (absent E. coli) was returned in the second round. In response to the present TC test, the City conducted two more tests at the pre-chlorination point that returned one additional present TC result and one absent TC result. Results were shared with OHA.

The presence of TC at the pre-chlorination point for River Well #1 is not concerning as long as the City is able to maintain existing chlorination practices to deactivate microbiologicals in the source water before entry into the distribution system. However, OHA has indicated that persistent source water TC positive results could lead to further scrutiny. OHA would need to confirm that chlorination to eliminate TC in the

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Manganese levels at River Well #1 were found to be consistently higher than the OHA infant advisory level of 300 micrograms per liter (ug/L). Flushing the well did show significant benefit in reducing levels of all tested constituents at River Well #1, and preliminary conclusions suggest that flushing for at least 4 hours may reduce manganese levels to below 300 ug/L and eliminate the need for well treatment. These results (shown in Figure 5) should be confirmed with additional sampling but suggest operational protocols may be an option to positively influence water quality outcomes at River Well #1. Figure 5 shows the results of manganese concentrations over time at the Combined Entry Point sampling location, but all sampling locations followed the same trend, including samples taken at the Pre-Chlorination point.

Figure 5 | Manganese Concentrations Over Time at Combined Entry Point

Declining manganese concentrations over time at the pre-chlorination sample location, roughly matching those shown in Figure 5, indicates that the decrease in manganese is not occurring as a result of manganese oxidation and precipitation after the chlorine dose point. The Deschutes Brewery confirmed issues with filter clogging on the same day as the flushing exercise, which may indicate that the solids in their filters are supplied by operation of River Well #1. The Brewery also sent their samples in for analysis and confirmed they are high in iron and manganese content. These findings further support the theory that iron and manganese are not precipitating out post-chlorination but might be built up at the bottom of the well casing, which get sent out to the system at high concentrations at well startup and then decline over time as River Well #1 operates.

The City has expressed concerns for requiring a 4-hour flushing period before they can bring their emergency wells online. If re-casing the well does not resolve the manganese issues at River Well #1 and the City does not want to implement an operational protocol to flush the well for a given amount of time before sending flow to the distribution system, treatment is another potential solution. Section 3.3 discusses potential treatment requirements as part of mitigation strategies.

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The City also tested calcium, hardness, iron, magnesium, and aluminum as part of their sampling while flushing the well. All other constituents mirrored the same trend of declining concentration over time with the exception of iron. Iron levels roughly matched the trends of the others but also showed some unexpected fluctuations of higher iron levels than expected over time at the 1st Hydrant sample location.

These results are shown in Figure 6 and could be indicative of stagnant water at this location or dislodged iron deposits as a result of the flushing exercise. Recommendations for investigating this further are included in Section 3.3. .

Figure 6 | Iron Concentrations Over Time at First Hydrant

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Table 2 | WQ Sampling Results – Summer 2025

Event No.

Date Locations Key Results Notes

1 June 30, 2025 (Pre-chlorination)

RW1 & RW2 Both Wells: Coliform & E. coli non-detect

RW1:

Turbidity: 4.1 NTU (Very High) Manganese 634 µg/L (Very High) Iron 216 µg/L (Slightly Elevated) Calcium 1,700 µg/L Hardness 66.7 mg/L (Slightly Elevated) TOC = 0.35 mg/L (Low)

RW2:

Manganese 160 µg/L (Slightly Elevated) Hardness 47.1 mg/L (Slightly Elevated) TOC = 0.18 mg/L (Low)

Turbidity was high for groundwater in RW1. Low TSS and TOC indicate inorganic colloids (clay) as possible cause of high turbidity and apparent color. No clear indication that RW1 is under the influence of surface water. High Fe/Mn content could be treated by oxidation + filtration with manganese dioxide media.

Oxidation of iron and/or manganese post-chlorination may explain filter issues at Deschutes Brewery.

Manganese exceeded EPA secondary MCL of 50 µg/L at both wells and OHA (Oregon Health Advisory) of 300 µg/L at RW1.

2 August 6, 2025 (Follow-up, multiple locations)

RW1, RW2, Combined System Entry Point, 1st

Hydrant

RW1:

Manganese 257 µg/L Iron 96 µg/L Pre-chlorination: two present coliform tests; E. coli non-detect IOC/VOC/SOC results: no regulated contaminants detected; sodium at RW1 = 9.9 mg/L

RW2:

Manganese 0.122 µg/L Coliform & E. coli non-detect IOC/VOC/SOC results: no regulated contaminants detected; nitrate at RW2 = 0.45 mg/L; sodium at RW2 = 10.3 mg/L

Demonstrates flushing reduces Mn/Fe.

Coliform hits at RW1 pre-chlorination are not abnormal for this source water. Three rounds of sampling with first two rounds present; third test absent. No existing concerns with treating via chlorination.

EPA advisory level for sodium is 20 mg/L. Sodium ~10 mg/L typical for aquifer.

3 September 4, 2025 (Extended flushing sequence)

RW1, Combined System Entry Point, 1st

Hydrant

RW1:

Manganese: Pre-chlorination concentration started at 539 µg/L, dropped <300 ug/L

(OHA) at 4 hours flushing Iron: Pre-chlorination concentration started at 510 ug/L, dropped <300 ug/L (EPA

SMCL) at 2.5 hours flushing Hardness, calcium, magnesium follow similar patterns of decrease to stable levels around 13 hours of flushing

Indicates all tested constituent concentrations reduce with flushing.

Manganese pre-chlorination reduces to below OHA advisory levels at approx. 4 hours of flushing.

Iron pre-chlorination reduces to below EPA SMCL at approx. 2.5 hours flushing.

Iron levels at 1st hydrant show some volatility, possibly indicating fluctuations as iron precipitates post-chlorination or an additional source of iron. Iron levels do not drop significantly between post-chlorination and 1st hydrant, indicating precipitation of iron and manganese out of the water after oxidation is not likely occurring. Iron and manganese solids may be built up at the bottom of the well casing and flushed out when the well is turned on.

Deschutes Brewery noted filter clogging on September 4th and sampled solids showed high iron and manganese levels.

Notes:

1. River Well #1 = RW1, River Well #2 = RW2

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2.4 Future Sampling Recommendations

During the video surveys, water was observed entering the well casing at several depths above the SWL as noted in Section 2.2. An effort to collect samples for water quality testing at these cascading leak points was not performed as part of this project due to the expected difficulty in confirming a sample containing only the water entering the casing at the leaks; the possibility of a false positive for TC given that the sampling equipment would contact the interior wall of the casing at numerous and indeterminable depths;

and the expectation that the issue may go away after the City selects an option to repair the well source.

The priority for water quality testing was to confirm River Well #1 was not under the influence of surface water and was safe for use, which was accomplished via testing at the more accessible pre-chlorination, combination system entry, and 1st hydrant sampling points. Future sampling of the intruding water for other analytes of interest to the City could be accomplished if appropriate sampling equipment or methods are identified.

The options of drilling a new well or a new sealed casing within the existing well should effectively seal the entire cased interval and address the leaking casing waters. However, if the City elects to retain the existing casing, either by leaving the well as is or selecting an option that does not fully seal the leak points, such as a removable liner, it is recommended that targeted sampling be conducted to evaluate the general water quality characteristics and potential origin of these inflows. This would help determine whether leaks are introducing water from other and/or distinct water-bearing zones within the aquifer formation and whether additional treatment (e.g., disinfection or filtration) may be required for long-term operation.

3. Scenario Evaluation and Risk Assessment

3.1 Introduction

The purpose of this task is to evaluate the long-term viability of the River Well #1 wellhouse by assessing condition of the well casing and potential treatment needs based on water quality results as discussed in Section 2 that may impact mitigation strategies that are discussed in Section 4. This scenario-based evaluation is intended to identify any fatal flaws that would preclude future reinvestment in the River Well #1 site and to determine whether rehabilitation is feasible.

The assessment draws on information developed under previous tasks, including the video inspection, water quality sampling, and field investigations. The Project Team conducted a targeted review of the well structure and surrounding conditions. In parallel, the City is evaluating land ownership and long-term control options for the River Well #1 site.

The scenario analysis includes the following components.

A review of the existing well casing and initial consultation with OWRD regarding rehabilitation/alteration options.

Treatment needs assessment.

A summary of findings and recommendations to guide City decision-making regarding well rehabilitation.

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3.2 Casing Condition of Well

As part of the condition assessment, GSI and their drilling contractor partner, Schneider Water Services (SWS) completed a well video survey, discussed in Section 2.2, and evaluated the general condition of River Well #1 casing. The review focused on identifying issues or deficiencies that could impact long-term well operations, operational performance, or rehabilitation potential.

Observations from the video and drift surveys (discussed in Section 2.2) indicated water leaking into the casing at several depths; many of which appeared to align with welded casing joints. Casing leaks evident in the June 2025 video survey were noted at depths of approximately 357, 381, 400 and 480 feet bgs with flow rates visually estimated between less than 1 gpm to about 5 gpm.

No fatal flaws were identified during the video and drift surveys and based on current findings, the existing well casing/borehole remains a viable candidate for rehabilitation, though targeted improvements will be necessary to extend the useful life of the well casing and also address existing casing leakage.

Due to the age of the well (53+ years old) and the observed leaks, this well is approaching the end of its useful life. Three rehabilitation strategies to address the degrading well have been identified and vetted with OWRD, summarized below. Appendix F includes sketches depicting elements of the first two options below.

Strategy 1: Install Internal 14-Inch “Liner”: Install a new section of 14-inch diameter steel liner inside the full length of the existing 16-inch steel casing. The bottom of the new 14-inch liner would rest on the rock ledge where the borehole transitions from the existing 16-inch casing into the lower 12-inch open borehole (aka “step-down” location). To be considered a liner, the OWRD indicated that the 14-inch liner cannot be cemented or grouted in place. (i.e. must be removable).

However, a backfill material like a sand pack or pea gravel could be installed between the 14-inch and 16-inch casings. This rehabilitation strategy is unlikely to fully seal off the cascading water.

o The existing 1930 gpm pumping capacity from the well can be maintained with this strategy.

Strategy 2: Install Internal 14-Inch “Casing”: Install a new section of 14-inch steel casing inside the full length of the existing 16-inch steel casing. The OWRD indicated that, to be considered a "casing", the following would need to be completed:

o Using a 16-inch diameter drill bit, penetrate at least 5 ft below the base of the existing 16-inch casing currently located at 637 ft bgs (i.e. drill out the current 12-inch diameter open borehole from 637 ft to at a minimum of 642 ft bgs with a 16-inch bit). This will create the required minimum 5 feet of consolidated formation that the 14-inch casing can be set and sealed into with cement grout.

o The new 14-inch casing would then extend to the surface. The annular space between the new 14-inch casing and the existing 16-inch casing would then be pressure-grouted with cement.

Per correspondence with OWRD, the existing 16-inch casing would not need to be perforated during this process.

o The existing 1,930 gpm pumping capacity from the well can be maintained with this strategy.

Strategy 3: Install Internal 12-inch “Casing” or “Liner”: This approach is similar to the options described above, however would use a smaller 12-inch liner or casing. It was initially considered in case OWRD required additional clearance between the existing casing and the new casing or liner.

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However, OWRD confirmed that a 14-inch size would be acceptable. Because the 12-inch option would likely reduce pump size and limit overall pumping capacity, this strategy was not evaluated further.

Re-drilling a new well is another strategy that is further identified in Section 4.

3.3 Treatment Strategy Assessment

The results of the water quality sampling as described in Section 2.3 indicate elevated manganese and iron concentrations at River Well #1. While it was discussed that these concentrations may be influenced by existing casing leaks or accumulated sediment at the bottom of the well, no data was collected to confirm or eliminate whether either issue might be a source of these metals prior to reinstalling the pump. The future well rehabilitation efforts target elimination of the cascading water and sediment in the base of the well; however, those actions may not resolve the iron and manganese issue. Therefore, the City may need to consider treatment options if elevated concentrations persist, particularly of elevated manganese in exceedance of the OHA health advisory for infants. The City has expressed a preference to rely on operational strategies, such as pumping-to-waste for extended periods of time, to eliminate the need for treatment.

After repair or replacement of River Well #1 is completed, the City should sample again to understand if the work has positively impacted (i.e., decreased) manganese levels in the source water. If levels are still elevated above 300 ug/L, the City should flush the well and take samples again to confirm flushing sufficiently reduces manganese concentrations and establish an operational protocol for the duration of flushing that should be completed at each startup of River Well #1. The operational protocol should also include a protocol for sampling manganese levels to confirm sub-300 ug/L concentrations after flushing, as well as trigger points for public notification if required.

If post-rehabilitation water quality does not consistently meet standards even with operational flushing strategies in place, dedicated treatment may be required.

Key assumptions for planning a treatment strategy include the following:

Treatment Approach: Pressure filtration using ATEC manganese filters.

Design Capacity: Sized for River Well #1 at 1,930 gpm maximum capacity, consistent with the existing pumping capacity.

Disinfection: Chlorine dosing assumed upstream of ATEC filter influent. Transition from gas chlorine to OSG is identified in Section 4. Pilot testing should be completed to confirm if chlorine will need to be re-dosed downstream of ATEC filters.

Backwash Wastewater: The City confirmed that 250 gpm of backwash water can be discharged to the existing sewer system. Coordination will still be required to verify available capacity and minimize or eliminate the need for on-site backwash storage, particularly if the City chooses to proceed with sewer discharge.

Treatment Building Footprint: See Appendix G for a preliminary layout for a treatment building.

o The ATEC filters are housed in a separate treatment building rather than the wellhouse, providing cost flexibility and avoiding oversizing the wellhouse if treatment is ultimately not required.

River Well #1 • 20 A:\_V-W\Projects\OR\Bend\2024\W242229OR.00\5 Documentation\1-River Well 1 TM - Final_Nov.2025.docx o Conceptual footprint developed based on similar facilities and vendor supply assumptions.

o Sized to accommodate four parallel filter trains: 42-inch diameter vessels, 20 units typical.

The planning level cost for this treatment strategy is further defined in Section 4.3.2. While implementation is not preferred by the City, documenting this contingency option supports preparedness should future water quality conditions warrant treatment.

4. Mitigation Rehabilitation Strategies The purpose of this section is to build on the previous findings by defining the mitigation strategies for River Well #1 that are necessary to ensure reliable long-term operation. The strategies are categorized based on the type of well work, as this is the primary distinction between alternatives. While these options differ in how they address long-term capacity and reliability, many supporting improvements, such as wellhouse replacement, treatment contingencies, and site upgrade, are consistent across all strategies and therefore discussed following the well rehabilitation and replacement strategies discussion. The section ends with a discussion of planning-level cost estimates and overall implementation timeline. A full mitigation matrix can be found in Appendix H, which is a comparative analysis of the mitigation strategies to provide the City with a clear basis for decision-making.

This section serves as the foundation for selecting the preferred strategy in Section 5.

4.1 Well Rehabilitation and Replacement Strategies

Three potential well strategies were identified during the scenario evaluation in Section 3:

1. installing an internal, floating 14-inch steel “liner” within the existing 16-inch well casing

2. installing an internal, cement-sealed 14-inch “casing”

3. drilling a new replacement well at the site.

While Section 3 provided an overview of these concepts in the context of well casing condition and OWRD requirements, this section develops them further into mitigation strategies.