2023 Archie Creek Fire Damage Oakland WTP Final Report.pdf

Horsley Witten Group Sustainable Environmental Solutions 90 Route 6A, Unit 1 • Sandwich, MA • 02563

Phone - 508-833-6600 • Fax - 508-833-3150 • www.horsleywitten.com

FINAL REPORT

Drinking Water and Watershed Evaluation City of Oakland, Oregon

June 21, 2023

Submitted to:

U.S. Environmental Protection Agency, Region 10 and U.S. EPA Office of Community Revitalization

Prepared by:

Horsley Witten Group, Inc.

www.horsleywitten.com

This document was funded by the US Federal Emergency Management Agency through Interagency Agreement #RW-07095974101-2 with the US Environmental Protection Agency

Region 10 under the US Environmental Protection Agency Office of Community Revitalization’s Disaster Resilience Blanket Purchase Agreement.

FINAL June 21, 2023 City of Oakland, Oregon Horsley Witten Group, Inc.

Drinking Water and Watershed Evaluation for the City of Oakland, Oregon

Table of Contents

1.0 Project Background

1.1. Project Goals

1.2. Project Team and Funding

2.0 Data Collection

3.0 Black Residue on WTP Optical Sensors

3.1. Water Quality Sampling and Analysis

3.2. Solids Sampling and Analyses

3.3. Chlorination Test

3.4. Conclusions

3.5. Recommendations

4.0 Diurnal Turbidity in Plant Finished Water

4.1. Background

4.2. Project Team Analysis

4.3. Recommendations

5.0 Evaluation of Future Conditions in the City’s Water Supply Watershed

5.1. Purpose

5.2. Climate Projections for the Region

6.0 Resilience Recommendations

7.0 Conclusions and Next Steps

8.0 References

9.0 Attachments (Attached as PDF)

FINAL 2 June 21, 2023

1.0 Project Background

The City of Oakland (herein, the City) has been experiencing water quality issues at its water treatment plant (WTP) that are believed to be the result of a recent nearby wildfire and drought conditions. The purpose of this project was to provide technical assistance to help the City further evaluate the impacts to its water supply source and develop potential solutions, either through changes in the operational practices at the plant or by incorporating new treatment technologies to improve water quality.

The City is located in Douglas County, Oregon, and had a population of 934 in 2020 (Center of Population Research and Census, Portland State University). The City derives its drinking water from Calapooya Creek, which is a tributary to the Umpqua River. The City’s water treatment plant was built in 2002 and the treatment process includes the use of aluminum coagulants with clarifiers, conventional filtration with mixed media, ultraviolet (UV) disinfection, and chlorine disinfection with a maximum design flow of 500 gallons per minute (gpm). During the winter, the City’s water treatment plant operates approximately 12 hours per day and the flow is approximately 150 gpm, with a residence time of 1.5 hours. During the summer, the plant operates 21 hours per day and the flow is approximately 250-300 gpm, with a residence time of

0.5 hours. The City has two 500,000-gallon storage tanks for treated water storage. The City also made improvements to its surface water intake on Calapooya Creek in 2020.

The City owns the oldest water rights on Calapooya Creek, providing the City 2.0 cubic feet per second (cfs), or 897.6 gpm, of water from the creek. This water certificate was issued to the City on September 27, 1909. The watershed upstream of the City’s water intake on Calapooya Creek, the drinking water source area, is approximately 122,240 acres as defined by Oregon Health Authority (OHA, 2019). The land use of the drinking water source area is identified as private industrial forest (46.8%), agricultural land (22.4%), private property (22.4%), and Bureau of Land Management land (8.3%). There are approximately 893 stream miles in the City’s drinking water source area, 880 miles of which flow through erodible soils (OHA, 2019).

The Archie Creek Fire burned from September 8, 2020, to November 16, 2020, in the North Umpqua River watershed in Douglas County, Oregon. It burned a total of 131,596 acres (FEMA, 2020). Approximately 19,309 acres (16%) of the City’s drinking water source area was burned by the Archie Creek Fire, including the Hinkle Creek, Gassy Creek, Gilbreath Creek, White Creek and South Fork subwatersheds to Calapooya Creek (Figure 1)1. Furthermore, the Archie Creek Fire was characterized by FEMA by higher burn severity compared to other recent fires in the watershed (FEMA, 2020). FEMA (2020) observed that fire-related impacts to the downstream City’s WTP could include increases in stream flows and increases in turbidity, sedimentation, and debris flow. Oregon’s Department of Environmental Quality (no date) analyzed samples

1 The Project Team was unable to obtain the Oregon Health Authority drinking water source area GIS data for Oakland, however, the Project Team was able to obtain this information from Douglas County. The Douglas County GIS information calculates the Oakland drinking water source area as approximately 119,438 acres.

FINAL 3 June 21, 2023 taken from the North Umpqua River (adjacent to the Calapooya Creek watershed) just after the fire and concluded that the following water quality parameters exceeded the 90th percentile range that had been observed over the prior 20 years: nitrate plus nitrite, ortho phosphate, total solids, total suspended solids, total organic carbon, and turbidity, which is consistent with other observations reported elsewhere (Hohner et. al., 2019).

Since the Archie Creek Fire, the operator has observed several changes at the WTP that required them to seek outside technical assistance. Optical sensors and other plant equipment including UV housing and tubing, started to be coated with black residue. Cleaning the equipment and sensors resulted in temporary relief before the black residue returned. In addition, the operator observed a trend of diurnal high turbidity in the WTP’s finished water that exceeded drinking water permit limitations during the peak summer months in 2021. It was unclear to the WTP operator if the diurnal high turbidity was related to black residue on the sensors and equipment related to the fire or was related to low-flow conditions in Calapooya Creek during drought conditions in peak summer months. These post-fire observations brought to the City’s attention the need to evaluate the resilience of the water supply and treatment plant to future anticipated conditions of droughts, wildfires, and a changing climate.

1.1. Project Goals

Using project background information provided by members of the Project Team, as well as information from the site visit conducted by HW and EPA in May 2022, this project was initiated to provide technical assistance to the City of Oakland to:

1. Identify the origin of and provide recommended treatment solutions to remove and prevent the black residue that appears to be precipitating out of solution in the water treatment plant and coating the plant’s equipment and optical sensors;

2. Evaluate the diurnal turbidity observed in the plant’s finished water during the summer months of 2021 and provide recommended solutions to manage periods of high turbidity; and,

3. Evaluate the future conditions for Calapooya Creek given climate change, future drought, and fire conditions, and provide recommendations for the City to consider in terms of water treatment, supply, and storage to improve the City’s resiliency.

This report documents HW’s research and findings into these three key issues. Further background information about each issue is provided below.

FINAL 4 June 21, 2023

Figure 1. Oakland Source Water Protection Area

FINAL 5 June 21, 2023

Black Residue On WTP Optical Sensors Since the September 2020 Archie Creek Fire, the WTP operator observed a black residue coating on optical sensors and equipment in the treatment process following the mixed-media filters. After cleaning of the equipment, including optical sensors and tubing, the black residue was reported to return within minutes, time after time. The operator did not test the black residue to identify its composition and possible origins prior to this project. However, the WTP Operator did inform municipal and state partners of the issue to solicit resources to support further investigation. One outcome of that effort was the initiation of this project funded by FEMA in coordination with EPA.

Water treated at the WTP passes through an ultraviolet (UV) light disinfection system (VIQUA Model Pro 50) to inactivate pathogens in the treated water prior to flowing through a chlorine contact tank for disinfection requirements. It then discharges into the distribution system, with the goal of maintaining a chlorine residual in the water to the furthest reaches of the system.

The City installed the UV system to conform with a permit condition imposed by the Oregon Health Authority (OHA) because of the extent of land in the City’s drinking water source area that is used for livestock ranching and the corresponding high loads of cryptosporidium in the watershed. When the UV system sleeve is coated with black residue, the UV light is unable to penetrate the glass tubing to inactivate microbial pathogens in the water passing through the system. As a result, since the WTP operator cannot attest to the UV system’s performance in support of its state reporting requirements, the WTP is out of compliance with its permit under the OHA Drinking Water Rules (Chapter 333, Division 061). OHA advised the City to issue a Boil Water Advisory to their customers whenever the UV system was not operating properly and there could be issues in the distribution system.

Other optical sensors in the WTP’s monitoring systems, such as for turbidity, pH, and free and total residual chlorine, as well as the temperature sensor, were also coated with the black residue and, therefore, the readings from these sensors were also unreliable. The WTP operator is not able to perform basic duties if the data he is receiving from the sensors is not accurate or trustworthy. Furthermore, other WTP functional problems or water quality problems not related to post-fire conditions (e.g., chemical spills or releases) are less likely to be detected or remedied by the WTP operator in the face of false or questionable readings.

Diurnal Turbidity in Plant Finished Water In July and August 2021, the operator noticed a pattern of diurnal turbidity fluctuations in the plant’s finished water, ranging from 0.01 to 0.4 NTU, as well as temperature fluctuations. This pattern was not detected in the raw water entering the plant. The highest turbidity readings observed in the plant’s finished water exceeded the plant’s permit limit of 0.3 NTU. During these two months of July and August 2021, Calapooya Creek experienced very low flows, and a flow of 1.32 cubic feet per second (cfs) (or 0.85 MGD) was recorded in July 2021 at the USGS Stream Gauge (ID 14320700) just downstream of the intake. The reason for the diurnal turbidity fluctuations was not evident to the operator, who surmised that the pattern could be

FINAL 6 June 21, 2023 related to post-fire impacts to Calapooya Creek and its watershed, turbidity sensors in the plant that had been rendered unreliable with the black residue coating, or something related to low-flow or drought conditions in Calapooya Creek.

Future Conditions and Recommendations for Increased Resilience The City’s management and the WTP Operator are concerned about their ability to provide safe and clean drinking water to their customers in the future, given projected climate change impacts resulting in more intense rainfall events and increased and prolonged drought and wildfire risk in the region. Both water quality and quantity issues may be observed due to climate-related impacts in the region. The summer of 2021 proved to City’s management that dangerously low flows in Calapooya Creek were a real possibility and prompted them to begin to consider other alternative sources of water.

The City of Oakland has the oldest water rights on Calapooya Creek, allowing the City to withdraw up to 2.0 cfs. While there are other legally permitted withdrawals from Calapooya Creek, there are also illegal users that potentially jeopardize the amount of water available for the City and other legal holders of water rights. Coordination by City officials with the Regional Water Master is critical to ensure sufficient supply is available to the City. Since the City has the oldest rights, the Regional Water Master will reduce the withdrawals of other users with less seniority of water rights to allow the City to withdrawal its full allowance as long as water is available in the creek.

1.2. Project Team and Funding

The Project Team consists of the U.S. Environmental Protection Agency (EPA), Federal Emergency Management Agency (FEMA), Oregon Department of Emergency Management (OEM), Horsley Witten Group, Inc. (HW) (contractor to EPA), University of Colorado Boulder (subcontractor to HW), and the City of Oakland. The City’s engineering contractors, Engineering Support Services, LLC and HBH Consulting Engineers, Inc., assisted with providing information to the Project Team. The technical assistance provided through this project to the City of Oakland was funded by the Federal Emergency Management Agency (FEMA) through an interagency cooperative agreement with EPA.

2.0 Data Collection

The Project Team conducted an in-person site visit to the City May 24-25, 2022. During the site visit, the Project Team collected information and data related to the issues observed at the City’s WTP. HW documented the data collected and findings from the site visit in a summary memorandum attached to this report. (Attachment A)

3.0 Black Residue on WTP Optical Sensors

The Project Team decided that the most critical issue to investigate first with the City of Oakland WTP operator was the black residue coating on the WTP’s optical sensors and

FINAL 7 June 21, 2023 equipment. The Project Team believed this issue to be critical and time-sensitive for two reasons: 1) the coating was causing the WTP to be out of compliance with OHA due to the inability of the City to confirm the UV system’s online monitoring performance, and 2) the coating impacted the accuracy of the readings from the optical sensors (e.g., pH, turbidity, temperature).

During the site visit, the Project Team discussed a theory that the black residue may be a result of iron or manganese captured in the plant’s filters and piping. Iron and manganese metal ions are present naturally in a clear and colorless form and they are typically naturally found in groundwater and groundwater-fed surface water systems, such as Calapooya Creek. Water percolating through soil and bedrock can dissolve the minerals containing iron and manganese and carry them to groundwater or surface waters (Extension Foundation, 2019). When iron and manganese are oxidized, the reaction creates ferrous oxide and manganese dioxide, both of which form visible particulates that are a blackish color in the water (MRWA; Zhou et al., 2020).

Both abiotic (via non-living physical and chemical factors) and biotic (via biological factors) oxidation of manganese can occur (Li et al., 2022; Sly et al., 1990). The presence of iron or manganese in the water can promote the growth of iron/manganese bacteria. This bacterium is non-pathogenic; it consumes the iron or manganese in the water to form ferric oxide and manganese dioxide and a resulting red-brown or black-brown slime (Extension Foundation, 2019). This manganese-oxidizing bacteria can live in areas of a WTP that do not maintain a sufficiently high chlorine or disinfectant residual concentration (Li et al., 2022). When the water is sufficiently disinfected, the biofilm can no longer thrive and therefore will not create manganese dioxide (Sly et al., 1990).

The City of Oakland staff reported to the Project Team that, to the best of their knowledge, they never observed a persistent presence of iron or manganese in their source water prior to the wildfire. The operator had never sampled the raw water at the intake for iron and manganese and therefore had no water quality data or online records with OHA that demonstrate evidence of iron or manganese. Just after the start of the 2020 Archie Creek Fire, the WTP operator analyzed the raw water for iron and manganese on September 19 and 20, 2020. Iron was detected in the raw water at 0.195 mg/L and manganese at 0.023 mg/L, both low concentrations and both below the OHA and US Environmental Protection Agency (EPA) Secondary Drinking Water Standards of 0.3 mg/L for iron and 0.05 mg/L for manganese2. No additional analyses for iron or manganese in the City’s raw water were performed during or after the 2020 fire. With just one data point within the timeframe following the Archie Creek Fire, it was difficult to confirm the magnitude of the metals’ concentrations in the raw water.

Since the black residue appeared in the City’s WTP following the start of the Archie Creek Fire, the WTP operator assumed it was a direct result of the fire. It is well documented that wildfires result in short- and long-term water quality changes for downstream waters. Physical changes

2 https://www.oregon.gov/oha/PH/HEALTHYENVIRONMENTS/DRINKINGWATER/RULES/Documents/61-0030.pdf https://www.oregon.gov/oha/PH/HEALTHYENVIRONMENTS/DRINKINGWATER/RULES/Documents/61-0030.pdf

FINAL 8 June 21, 2023 resulting from wildfires include changes in water yield, sediment loads, debris flow, and temperature. Chemical changes include changes in cations (e.g., calcium, magnesium, silica), nutrients, organic chemicals, and metals (Paul et al., 2022; HDR, 2014). Total iron and manganese, specifically, have been observed to increase in downstream water as a direct result of being mobilized by wildfires (Gill, 2004; Bitner, 2001). From the above-referenced wildfire studies, it is reasonable to assume that manganese was present in the source water during the high turbidity events.

During the Archie Creek Fire in September-November 2020, the City of Oakland continued to use and treat its source water from Calapooya Creek despite the challenge of addressing high turbidity in the water entering the WTP. The WTP operator provided anecdotal evidence that Calapooya Creek exhibited extremely high turbidity during and after rainfall events around the time of the fire. The FEMA post-fire incident documentation further noted that these rainfall events between September 18 and November 19, 2020 (FEMA, no date) washed ash into Calapooya Creek. When the City was withdrawing and treating highly turbid water, the WTP operator had difficulty maintaining the targeted chlorine residual concentrations in the finished water. To address this issue, the Operator kept the chlorine dose at 1.1 mg/L but raised the pre-chlorination dose in the water entering the plant and raised the dosage of aluminum coagulant (known as PassC) in the initial section of the WTP. The pre-chlorination dose of chlorine was typically set to zero prior to the fire but was raised as high as 10 mg/L after the fire to try to reduce turbidity, watercolor and maintain a minimum chlorine level of 0.3 mg/L at the furthest point in the system as required by OHA. For one week, the WTP operator elevated the pre-chlorination dose to 10 mg/L but found that chlorine reacted with the aluminum coagulant (Pass C), preventing the floc formation, so he reduced the dose back to zero.

Based on this information, the Project Team inferred that a significant amount of iron and manganese possibly was loaded onto the mixed-media filters when Calapooya Creek was highly turbid due to post-fire rain events. Further, the high dose of chlorine used in the pre-chlorination to address the highly turbid intake water may have caused the oxidation of the manganese, thus forming particulate manganese dioxide that settled on the filter media. The particulates, in theory, would be removed from the filters by the filter backwash operation unless the backwash was not functioning at 100% efficiency. In addition, the absence of chlorine residual in the water when the operator turned off the pre-chlorination dosing potentially allowed the later growth of a biofilm on the filters. It is highly likely that the biofilm contained manganese oxidizing bacteria as well as the oxidized manganese, resulting in an accumulation of manganese dioxide particulates throughout the WTP. The particulate manganese then likely began to slough off the filters and other areas where the biofilm grew, and eventually coated the WTP’s sensors and equipment. Given that there was no chlorine residual going through the filters, it is logical that the manganese came off in the biofilm. It is worth noting that the filter media used at the WTP was replaced earlier in 2020 before the fire because of its age and could be considered clean. Therefore, it is more likely that a significant

FINAL 9 June 21, 2023 accumulation of manganese on the filters occurred in the aftermath of the fire, and that the lack of chlorine residual through the filters caused the subsequent staining of the equipment.

It is also possible, although highly unlikely, that manganese could be an impurity in the aluminum coagulant (known as Pass C) used in the plant, as has been demonstrated for other coagulants, such as ferric chloride. However, no information on this potential source of contamination was obtained or confirmed, and given the new filter media, it is unlikely that the coagulant was the source of the manganese.

3.1. Water Quality Sampling and Analysis

The Project Team decided to take a first set of samples at different locations in the treatment process to understand where iron and manganese were present and at what concentrations. It was also important for the Project Team to try to determine if iron and manganese were still entering the plant from the raw water source in Calapooya Creek.

The WTP operator first sampled the plant’s raw water influent, mixed media filter effluent, and treated plant finished water for dissolved iron and manganese. In addition, the raw water influent was analyzed for a series of metals using EPA Method 200.7. The operator collected water samples on June 3, 2022, and Pace Analytical Laboratory in California performed the laboratory analysis for those samples. Sample results are included in Attachment B. A summary of the results is provided below in Table 1.

Table 1. Water Quality Sample Results (Collection date: June 3, 2022)

WTP Sample Location Parameter Analyzed Sample Result (µg/L) Raw water Dissolved Iron ND* Dissolved Manganese ND Total Recoverable Iron ND Total Recoverable Manganese ND Mixed media filter effluent Dissolved Iron ND Dissolved Manganese 11 Treated finished water Dissolved Iron ND Dissolved Manganese ND

* ND- non-detectable

The raw water results did indicate that there was no iron or manganese coming into the plant in the raw water on June 3, 2022, indicating that these metals may not be consistently found in the raw water. Dissolved manganese was detected in the mixed media filter effluent, revealing that there may be a legacy amount of manganese trapped in the mixed media filters.

The mixed media filter effluent and treated finished water samples were not analyzed for total recoverable iron and total recoverable manganese. Although the treated finished water did not contain dissolved concentrations of manganese and iron, it is possible that they contained particulate phase iron and manganese that would have been measured in the total recoverable

FINAL 10 June 21, 2023 analyses. This is one of the reasons that the actual black residue was sampled for iron and manganese (see Section 3.2).

Analyses for other metals in the raw water indicated minimal concentrations, except aluminum, which was detected above Oregon’s secondary contaminant levels3.

3.2. Solids Sampling and Analyses

Following the testing of the water within the treatment plant, the Project Team analyzed the black residue to evaluate its makeup and confirm whether it contained manganese. The Project Team also wanted to evaluate whether there was any indication of biological activity associated with the black residue, which could help identify whether iron/manganese bacteria was present in the WTP.

The WTP operator collected black residue samples from various elements of the WTP equipment (e.g., filter media from the mixed media filter, UV filter housings, tubing) and sent them for processing to the University of Colorado Boulder (UC Boulder). The UC Boulder laboratory conducted an elemental analysis of the following acid-leached samples collected:

1. Black residue material scraped from old UV filter housing that had recently been replaced in an attempt to minimize the impacts of the black residue;

2. Black residue material scraped from the newer UV filter housing in use at the plant at the time of the sampling;

3. Mixed media filter media; and

4. Tubing connecting to optical sensors.

Significant amounts of iron and manganese, greater than would be expected under normal plant operation conditions, were detected in the samples (Table 2). The high concentration of manganese in the acid leached sample from the “old UV filter housing” provides an assessment of how much manganese has accumulated over time. The laboratory report notes importantly, however, “Comparisons between sample types is not appropriate due to differences in the sample basis (media mass vs. scraping mass vs. tubing length). The filter housings recovered more manganese than iron and the opposite trend was observed for the filter media and tubing.”

Table 2. Elemental analysis of acid leached samples from WTP Elements (Collection date: July 2022)

Sample Concentration (µg/L) Manganese Iron

Filter Media 1,340 12,500 Old UV Filter Housing 26,600 410 New UV Filter Housing 8,640 <400 Tubing connecting to optical sensors 5,690 16,600

3 https://www.oregon.gov/oha/PH/HEALTHYENVIRONMENTS/DRINKINGWATER/RULES/Documents/61-0030.pdf https://www.oregon.gov/oha/PH/HEALTHYENVIRONMENTS/DRINKINGWATER/RULES/Documents/61-0030.pdf

FINAL 11 June 21, 2023

The University also analyzed the residue from the filter housings using phase-contrast microscopy with an Infinity Plan Phase Contrast Trinocular Microscope at 40X magnification to see if biological activity was present. The imaging indicated that there was biological material present but did not identify the type of biological cells. This suggests that there was indeed biological activity that was contributing to the formation and persistence of the residue. All results are presented in Attachment C.

3.3. Chlorination Test

With sample analyses confirming the presence of iron and manganese in the WTP, the Project Team looked toward developing a possible solution to the iron and manganese deposition problem. The Project Team theorized that the addition of chlorine to the water prior to the mixed media filters would create a disinfected environment with chlorine residual remaining in the water, which would inactivate the biofilm. This would result in a reduction or complete stop in the deposition of manganese dioxide. In order to test this theory, the Project Team requested that the WTP operator run an experiment in which he would add chlorine to the raw water and treatment process just prior to the filter media, in order to produce a chlorine residual that would be maintained throughout the WTP.

As a part of this experiment, the Project Team asked the operator to conduct additional sampling throughout the WTP so we could try to better understand the levels of manganese throughout the treatment processes. Samples were also tested for alkalinity to help evaluate the impacts of the added PassC aluminum coagulant. Before the experiment started, the WTP operator collected samples on September 8, 2022, of the raw water, backwash of both of the two mixed media filters in the WTP, combined effluent from the two mixed media filters, and plant finished water to analyze for dissolved manganese and alkalinity, and to further confirm that the raw water did not contain manganese (Table 3). Laboratory results are provided in Attachment D.

Table 3. Sample prior to pre-chlorination experiment (Collection date: September 8, 2022)

Sample Concentration

Manganese (µg/L)

Alkalinity (mg/L)

Raw water ND* 45.3 Backwash of Mixed Media Filter A 10 43.4 Backwash of Mixed Media Filter B 10 44.3 Combined Mixed Media Filter Effluent 10 51.2 Plant Finished Water ND 52.2

*ND- non-detectable

The Project Team recommended the operator dose chlorine as early in the treatment process as possible, to achieve a desired chlorine residual of 0.5 mg/L in the filter effluent water. This

FINAL 12 June 21, 2023 chlorine residual concentration is based on common best practices in the industry (Charlton et al., 2005; WRF, 2013). The Team suggested the operator add chlorine prior to rapid mixing in the chemical injection ports. The operator was concerned about possible interactions of the chlorine with the aluminum coagulant, Pass C, as he had observed earlier, so the operator installed a temporary chlorine dosing system directly on top of each mixed media filter, which is after the Pass C treatment. From September 13, 2022, to October 21, 2022, the operator dosed the mixed media filters with variable concentrations of chlorine, ranging from 0.4 to 2.5 mg/L.

During this experiment, the operator recorded the following measurements:

• Raw water turbidity;

• Raw water pH;

• Turbidity of the effluent from each mixed media filter;

• Turbidity at the combined effluent from the mixed media filters;

• Chlorine concentration in the combined effluent from the mixed media filters (using a pocket colorimeter);

• Finished water chlorine concentration (online monitor and pocket colorimeter); and

• Finished water pH.

Figure 2 presents the locations of the chlorine injection and the sample locations discussed above.

Table 4 provides the data collected by the WTP operator during the experiment. At the beginning of the experiment, there was a high chlorine demand from the biofilm within the mixed media filters. From September 13, 2022, to September 17, 2022, the biological demand for chlorine was high and the chlorine concentration therefore decreased as the water moved through the treatment process. During the experiment, the operator had to attend to other City obligations and was unable to monitor the experiment thoroughly, which resulted in certain gaps in the data collected. The data collected was not as comprehensive, consistent or conclusive as a formal scientific experiment, but still provided some additional information that the Project Team could use to inform our assessment. We did observe from this experiment that the addition of chlorine to the mixed media filter was able to limit the iron/magnesium bacteria growth. The data collected throughout the plant allowed the team and the WTP operator to monitor and react to any significant fluctuations in chlorine concentrations in the filter effluent and the finished water as the experiment proceeded.

FINAL 13 June 21, 2023

Figure 2. Flow Diagram of the WTP Treatment Process, with Chlorine Dosing Injections Locations and Sample Locations for 2022 Chlorine Injection Trial

During the experiment, on September 15, 2022, the WTP operator thoroughly cleaned all equipment, including the optical sensors. With the equipment cleaned, the operator would be able to inspect whether black residue was accumulating again on the equipment. The operator replaced the UV filter housing on September 22 when the ordered part was delivered to the WTP. Note this was the second time this filter housing was replaced since the fire occurred. In addition, the operator either replaced or cleaned the pH probes and turbidity meter parts4.

4 According to the WTP Operator, all six UV filter housings were cleaned and then replaced with new housings when materials were available. The pH probes were replaced with new Hach probes and the sample holder for the pH probe was replaced with a new clear acrylic inspection tube. All of the sensor connecting tubing was replaced.

All of the UV glassware inside the UV systems was replaced. All three turbidity sample cells were replaced and all

FINAL 14 June 21, 2023

During this experiment, the operator visually observed no accumulation of black residue on the WTP sensors or equipment that had been coated previously.

On September 15, 2022, during the experiment, the operator was required under the withdrawal permit by OHA to collect and analyze quarterly samples for disinfection byproducts5. The samples were collected on the day when the WTP’s dosage of chlorine was at its highest. The City’s samples indicated a violation above the maximum contaminant level for Haloacetic Acids (HAA56). Chlorine reacts with natural organic matter (NOM) to form disinfection byproducts, such as THMs (Trihalomethane) and HAAs (Haloacetic acids). The higher disinfectant dosage will likely yield higher disinfection byproducts. The five most common HHAs is called HHA5 (monochloroacetic acid (MCA), dichloroacetic acid (DCA), tricholoacetic acid (TCA), monobromoacetic acid (MBA) and dibromoacetic acid (DBA). The operator informed OHA of the experiment to explain the reason for the violation. Given this was a one-time violation (two consecutive violations trigger a formal notice of violation from OHA), the exceedance did not result in enforcement repercussions from OHA. The experiment for this assessment was completed and the WTP operator is working with the City’s WTP consulting engineers to adjust the current operations and WTP design. No further exceedances have been observed in Oakland’s quarterly testing for disinfection byproducts.

connecting tubes were replaced. The acrylic finish water sample inspection tube was removed but not replaced because it was not an OHA required component.

5 The HW Team was not aware that this OHA quarterly sampling was required on this date when the chlorine dosing experiment was initiated.

6 Haloacetic acids five (HAA5) are the five haloacetic acids regulated by federal standards, including monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid and dibromoacetic acid.

FINAL 15 June 21, 2023

Table 4. Data collected during pre-chlorination experiment (Collection dates: September 13 – October 21, 2022)

Parameter

9/

/2

9/

/2

9/

/2

AM

9/

/2

PM

/2

9/

/2

9/

/2

9/

/2

9/

/2

9/

/2

9/

/2

9/

/2

9/

/2

9/

/2

9/

/2

9/

/2

9/

/2

9/

/2

9/

/2

/1

/2

/2

/2

Turbidity, raw water

(NTU) 30 30 30 30 30 30 30 32 36 38 40 40 41 39 38

pH, raw water 6.77 6.78 6.85 6.66 6.67 6.67 6.67 6.67 6.67 6.67 6.67 6.67 6.67 6.67 6.67 Chlorine concentration, top of filters (mg/L)

0.9 1.5 2.5 2.00 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.60 0.60 0.60 0.60 0.60 0.60

Turbidity, Filter A effluent (NTU) 0.02 0.05 0.03 0.05 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.01 0.01 0.01 0.01 0.01 0.01

Turbidity, Filter B effluent (NTU) 0.02 0.05 0.03 0.05 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.01 0.01 0.01 0.01 0.01 0.01

Turbidity, Combined filter effluent (NTU) 0.02 0.05 0.05 0.05 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.01 0.01 0.01 0.01 0.01 0.01

Chlorine concentration using pocket colorimeter, combined filter effluent (mg/L)

0 0 1.01 0.88 0.86 0.86 0.05 0.05 0.05 0.05 0.05 0.05 0.04 0.02 0.02 0.12 0.13 0.11 0.12 0.1 0.13

Chlorine concentration using online monitor, finished water (mg/L)

1.34 1.01 1.87 1.71 2.00 2.00 1.41 1.39 1.44 1.46 1.41 1.42 1.59 0.91 1.01 1.51 1.51 1.01 1.42 1.41 1.41

Chlorine concentration using pocket colorimeter, finished water (mg/L)

1.34 0.98 1.86 1.68 2.00 2.00 1.4 1.38 1.4 1.4 1.39 1.38 1.55 0.90 1.43 pH, finished water 6.66 6.73 6.86 6.66 6.67 6.67 6.68 6.68 6.7 6.74 6.75 6.79 6.78 6.84 6.83 6.82 6.81 6.84 6.82 6.81 6.83

FINAL 16 June 21, 2023

Parameter

/3

/2

/4

/2

/5

/2

/6

/2

/7

/2

/8

/2

/9

/2

/1

0/

/1

1/

2/

3/

4/

5/

6/

7/

8/

/2

0/

/2

1/

Turbidity, raw water (NTU) 41 42 46 45 48 pH, raw water 6.94 6.95 7.00 7.00 7.00 Chlorine concentration, top of filters (mg/L) 0.60 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40

Turbidity, Filter A effluent (NTU) 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01

Turbidity, Filter B effluent (NTU) 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01

Turbidity, Combined filter effluent (NTU) 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01

Chlorine concentration using pocket colorimeter, combined filter effluent (mg/L)

0.12 0.05 0.04 0.06

Chlorine concentration using online monitor, finished water (mg/L)

1.43 1.56 1.13 1.01 1.26 1.24 1.22 1.31 1.31 1.31 1.31 1.31 1.31 1.31 1.41 1.34 1.31 1.31 1.31

Chlorine concentration using pocket colorimeter, finished water (mg/L) pH, finished water 6.81 6.9 6.82 6.84 6.84 6.84 6.84 6.84 6.84 6.84 6.84 6.84 6.84 6.84 ND ND ND ND 6.84

FINAL 17 June 21, 2023

3.4. Conclusions

The sampling results show that there is a significant amount of iron and manganese in the filter media. The black residue analysis also showed the presence of a biofilm in the City’s WTP. The Project Team suggests that this biofilm is likely iron/manganese bacteria and is the cause of microbial-mediated manganese oxidation and accumulation of manganese dioxide particulates throughout the treatment system downstream of the filters.

Based on the limited sampling conducted for this project, the Project Team has tentatively concluded that the iron and manganese likely was loaded into the WTP during the post-fire period when significant rainfall events washed ash, debris, and fire-impacted sediments down Calapooya Creek. The City’s pre-chlorination addition during an initial two-week period in 2020 likely contributed to some abiotic manganese oxidation and formation of manganese dioxide.

However, it is also likely that the absence of any chlorine residual in the WTP, especially in the filter media, prior to the chlorine contact chamber since fall 2020 has created an environment ripe for the iron/manganese oxidizing bacteria to grow and thrive. These bacteria have likely contributed to the long-term and more significant deposition of manganese dioxide particulates in the WTP.

The few raw water samples that were collected months after the wildfire indicate little to no iron and manganese in the raw water after the initial post-fire period. This further supports the idea that iron and manganese were loaded into the WTP during a brief period during and immediately following the Archie Creek Fire.

3.5. Recommendations

The Project Team makes the following recommendations.

1. The WTP operator should continue to gather additional data to verify whether the Project Team’s theory is correct. To do this, the Project Team recommends:

o The WTP operator should continue to monitor the raw water for iron and manganese (both dissolved and total) and for turbidity to ensure the raw water is not and does not become a continuous source of these pollutants and to verify they entered the WTP as a result of the Archie Creek Fire. Samples should be collected quarterly for the next two years. Since this Project Team suspects that iron and manganese entered the system during the high turbidity events during/after the Archie Creek fire, samples should also be collected and analyzed during any future high turbidity events (e.g., high or low Calapooya Creek flow) and any future wildfire events.

2. The WTP should provide iron and manganese control to prevent future equipment staining. To do this, the Project Team recommends:

FINAL 18 June 21, 2023 o The WTP operator should consider using sequestrant (such as sodium hexametaphosphate, sodium tripolyphosphate, and others) to keep the iron and manganese ions in solution if the iron concentration is less than 0.6 mg/L and the manganese is less than 0.1 mg/L.

o The WTP operator should continue to chlorinate the raw water prior to the mixed media filters (if existing filter media are in use) to maintain a sufficient chlorine residual (such as 0.5 mg/L) to further prevent the manganese oxidizing bacteria from growing and manganese dioxide particulates from depositing.

However, the WTP consulting engineers should design and install a permanent engineered pre-chlorination system that can be operated and monitored by the WTP’s SCADA (Supervisory Control and Data Acquisition) system. The WTP is already working with their water engineering consultant, HBH Consulting Engineers, Inc., to evaluate treatment options.

3. Once the Project Team’s theory has been further verified through data collection and analysis, and an engineered control for iron and manganese has been incorporated into the WTP system, the Project Team recommends:

o The WTP operator should replace the existing mixed filter media, which would eliminate any legacy iron and manganese deposits from the WTP filters altogether. This is a costly solution, but it could allow the WTP to cease pre-chlorination as a method to control the black residue issue. The WTP should only replace all filter media if it is confirmed, through regular sampling, that iron and manganese are not prevalent constituents in the City’s raw water. If the WTP operator does replace the mixed media filter, he should also thoroughly clean all equipment and replace consumables (e.g., tubing) to remove any traces of legacy iron and manganese throughout the system to the maximum extent possible.

o If the filter media were to be replaced, the WTP operator should send a sample of the existing filter media for laboratory analysis to determine the amount of iron and manganese in the filter media and identify the type of biofilm, if any, existing within the filter media.

o After the new filter media has operated for one year, the WTP operator should send a sample of the new filter media for analysis to determine the amount of iron and manganese in the filter media and identify any presence of biofilm.

o The WTP should test for impurities in the aluminum coagulant (Pass C) to eliminate this as a potential unintended source of iron and manganese.

FINAL 19 June 21, 2023

4.0 Diurnal Turbidity in Plant Finished Water

4.1. Background

In July and August 2021, the City’s WTP operator noticed a trend of diurnal turbidity spikes in the plant finished water, ranging from 0.01 to 0.4 NTU (Figure 3). The plant’s finished water turbidity limit is 0.3 NTU, so some of these high turbidity events exceeded the City’s permit limit. The operator also observed that the plant finished water temperature varied between 88 and 100 degrees Fahrenheit and plant finished water pH varied between 6 and 9 during the same time period (Figure 4). The operator did not see this obvious trend with the plant influent turbidity, because the influent turbidity meter measures 0 to 10,000 NTU and is much less precise than the plant finished water turbidity meter, which measures 0 to 1.0 NTU.

Fluctuations in the influent turbidity were more challenging to see on the chart recorder.

Figure 3. City’s WTP Chart Recorder data showing plant treated finished water turbidity over three consecutive weeks (7/5/21 to 7/28/21) with a daily turbidity range between 0.03 NTU and 0.30 NTU.

Image presented to demonstrate the format of chart recorder data. (Source: City of Oakland)

Figure 4. City’s WTP Chart Recorder data showing temperature, pH, and chlorine residual for plant treated finished water over three consecutive weeks. Image presented to demonstrate the format of chart recorder data. (7/5/21 to 7/28/21) (Source: City of Oakland)

FINAL 20 June 21, 2023

The Calapooya Creek streamflow during July and August 2021 shows a significant low flow between July 30th and August 5th below 2.0 cfs. Data from Oregon’s Water Resources Department Real Time Station #14320700, which is located on Calapooya Creek near Oakland, OR (Oregon Water Resources Department, 2023) (Figure 5) shows a low flow (<1.5 cfs) during the period between July 30 and August 5, 2021. In this same date range, the raw instantaneous water temperatures recorded at the gauge were above 85 degrees Fahrenheit.

Figure 5. Instantaneous Flow, Mean Daily Flow, Instantaneous Temperature and Mean Daily Temperature of Calapooya Creek between July 1-August 31, 2021 (Source: Oregon Water Resources Department, 2023)

FINAL 21 June 21, 2023

The summer 2021 seasonal streamflow average was 9.20 cfs compared to the average summer seasonal streamflow from 2018-2022 of 64.15 cfs (Table 5). In 2021, May, June, July and August monthly streamflow averages were below the monthly averages from 2018-2022.

Table 5. Seasonal and monthly streamflow averages (cfs) for Calapooya Creek 2018-2022 (Source:

Oregon Water Resources Department)

Year Spring Summer Fall Winter 2018 514.45 18.98 22.82 474.11 2019 711.24 16.08 42.69 703.35 2020 242.86 64.90 86.03 874.52 2021 209.23 9.20 93.24 915.19 2022 563.77 211.58 29.55 562.18

Average 448.31 64.15 54.87 705.87 Notes: For this analysis, spring season was defined by the date range between March-May, summer season is defined by the date range between June-August, fall season is defined by the date range between September-November, and winter season is defined by the date range between December-February.

FINAL 22 June 21, 2023

Year Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec

2018 703.60 406.99 832.34 593.40 117.60 41.87 10.01 5.06 4.46 15.16 48.85 311.74 2019 610.67 1318.65 867.86 1165.33 100.53 30.18 10.53 7.52 34.84 54.80 38.44 180.73 2020 1376.90 507.34 224.95 324.56 179.05 155.46 30.69 8.54 11.84 24.51 221.73 739.32 2021 960.59 1166.09 434.46 134.02 59.22 22.12 2.73 2.74 13.50 70.97 195.26 618.89 2022 1002.39 110.26 360.00 589.14 742.19 570.97 52.87 10.91 8.78 16.15 63.73 573.89

Average 930.83 701.87 543.92 561.29 239.72 164.12 21.37 6.96 14.68 36.32 113.60 484.91

During July and August 2021, the WTP operator attempted to control the diurnal turbidity spikes by adding chlorine early into the treatment process. The WTP operator considered that the cause of the turbidity could be algal growth, especially given the low streamflow and high temperatures in Calapooya Creek. This approach could have helped to kill and limit further algae growth in the treatment plant.

HBH Consulting Engineers, Inc. an engineering firm currently developing a draft Water Master Plan for the City of Oakland, looked at the varying water quality at the WTP post-fire to determine any potential impacts to the City’s wastewater treatment plant (HBH Consulting Engineers, 2021). One theory about the water quality issues was hypothesized as, “ the rapid drop in water levels coincided with significant rises in water temperature. It is believed the increase in water temperatures comes from the reduction in stream bank cover post fire. Also noted during the summer months were drastic fluctuations in pH. Nighttime pH levels stabilized at normal stream levels. As temperatures rose during the day, pH levels would spike to abnormally high levels. As water temperatures reached 95-100 degrees, pH levels would plummet and turbidity at the water plant would spike. It is believed this was caused by optimum growing conditions of blue green algae which decreased carbon dioxide levels. As carbon dioxide levels were lowered pH levels in the Calapooya would begin to rise. As water temperatures reached 95 degrees, algae began to die off; simultaneously increasing stream CO2 levels, decreasing the pH, and raising plant turbidity by the introduction of dead algae at the raw water intake. Water samples have not been taken to confirm this theory.”

In an attempt to test the algal growth theory given that no sampling had yet been conducted to confirm HBH Consulting Engineers’ theory, the WTP operator collected samples on August 4, 2021, to be analyzed for phytoplankton identification and enumeration. The operator collected two samples in the watershed close to the headwaters of Calapooya Creek (Hinkle Creek Bridge), two samples at the raw water intake (one at the raw water intake screen and one at the raw water intake holding basin), and one sample of the raw water once entered the plant.

The samples were analyzed by Aquatic Services and determined that algae of the major group Diatoms or Bacillariophyceae, Green Algae or Chlorphyta and Cyanbacteria were present. The enumeration process counted greater than 2000 cells per milliliter in all samples except one

FINAL 23 June 21, 2023 that was collected in the watershed at the Hinkle Creek bridge7. The results of this analysis are provided in Attachment D. The operator does not have any additional phytoplankton identification and enumeration results at these locations to be able to compare and assess these results.

4.2. Project Team Analysis

In 2022, when the Project Team was evaluating the black residue issue (see Section 3), the WTP operator did not observe a similar trend of diurnal turbidity spikes in the plant finished water.

The Project Team was unable to further evaluate this trend. Without the opportunity to investigate this issue further, the Project Team speculates that one or more of the following reasons may have contributed to this diurnal turbidity trend:

• It is possible that algal growth in Calapooya Creek during low flow and high temperature conditions in the summer season impacted the City’s treatment plant as described by HBH Consulting Engineers, especially if chlorine was not added early in the treatment train. Algae are buoyant and do not settle, so they can also clog filters and increase the formation of disinfection byproducts (Stantec, 2020). Algae in the finished water may have resulted in higher turbidity.

• The optical turbidity sensors may have been fouled due to the black residue issue and therefore, did not provide accurate readings. The operator found black residue in the sample tubing to some of the optical sensors. It is possible that the black residue interfered with the sample results of the turbidity optical sensor.