Chapter 8 - Taylor Water Treatment Plant

City of Corvallis Water Distribution and Treatment Facilities Master Plan

Chapter 8 TAYLOR WATER TREATMENT PLANT

DRAFT | June 2021

City of Corvallis Water Distribution and Treatment Facilities Master Plan

Chapter 8 TAYLOR WATER TREATMENT PLANT

DRAFT | June 2021

This document is released for the purpose of information exchange review and planning only under the authority of

Jude D. Grounds, June 25, 2021 State of Oregon, P.E. No. 74678.

CHAPTER 8 – TAYLOR WATER TREATMENT PLANT | WATER DISTRIBUTION AND TREATMENT FACILITIES MASTER PLAN | CITY OF CORVALLIS

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pw://Carollo/Documents/Client/OR/Corvallis/11194A00/Deliverables/WDTF Master Plan/Ch08 - Taylor WTP/Ch08

Contents Chapter 8 - Taylor Water Treatment Plant

8.1 Introduction 8-1

8.1.1 Background 8-1

8.1.2 Chapter Organization 8-1

8.2 Historical Water Quality and Regulatory Compliance 8-5

8.2.1 Raw Water 8-5

8.2.2 Finished Water Quality 8-9

8.2.3 Regulatory Compliance 8-12

8.2.4 Conclusion 8-12

8.3 Existing Facilities and Operational Performance 8-13

8.3.1 Introduction 8-13

8.3.2 Historical Performance and Process Capacity Evaluation 8-17

8.3.3 Operational Testing and Performance Optimization 8-53

8.4 Existing Infrastructure Condition Assessment 8-55

8.4.1 Repair and Replacement 8-55

8.4.2 Seismic and Life Safety 8-56

8.4.3 Resiliency and Redundancy 8-58

8.4.4 Energy Efficiency 8-58

8.4.5 Summary of Condition-Related Improvements 8-59

8.5 Capacity Expansion and Treatment Improvements 8-59

8.5.1 Treatment Process and Plant Capacity Improvements 8-59

8.5.2 Intake Improvements 8-64

8.6 20-Year Horizon Implementation Plan 8-64

Tables Table 8.1 Current OHA Regulatory Sampling Requirements at Taylor WTP 8-6

Table 8.2 Summary of Raw Water Quality 8-7

Table 8.3 Summary of Raw Water Microbial Detections 8-9

Table 8.4 Summary of Finished Water Quality 8-10

Table 8.5 Detected IOCs in Taylor Finished Water 8-11

Table 8.6 Plant Expansion and Modification History for Taylor WTP 8-13

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Table 8.7 Raw Water Pump Capacities 8-28

Table 8.8 Flocculation/Sedimentation Basins 1 – 3 Design Criteria 8-31

Table 8.9 Flocculation/Sedimentation Basins 4 Design Criteria 8-32

Table 8.10 Sedimentation Basin Settled Water Turbidities 8-32

Table 8.11 Filter Design Criteria 8-34

Table 8.12 Available Head for Solids Loading at Existing and Future Maximum Flow Rates 8-36

Table 8.13 Filter Backwash Design Criteria 8-36

Table 8.14 Available Head for Solids Accumulation for Current Plant Flow Rates 8-38

Table 8.15 High Service Pump Capacities and Configuration 8-43

Table 8.16 High Service Pumps Combined Capacity 8-45

Table 8.17 High Service Pumping Discharge Velocities 8-46

Table 8.18 Solids Handling Capacity Evaluation 8-47

Table 8.19 Alum Storage Capacity 8-49

Table 8.20 Soda Ash Storage Capacity 8-50

Table 8.21 Sodium Hypochlorite Storage Capacity 8-51

Table 8.22 Filter Aid Polymer Storage Capacity 8-52

Table 8.23 Sodium Silicofluoride Storage Capacity 8-53

Table 8.24 Taylor WTP Annual Repair and Replacement Program Costs (Project T-1) 8-56

Table 8.25 Taylor WTP Additional Repair and Replacement Project Costs 8-56

Table 8.26 Taylor WTP Seismic and Life Safety Projects 8-58

Table 8.27 Taylor WTP Condition-Related Improvements 8-59

Table 8.28 Taylor WTP Projects to Address Deficiencies in the 20-Year Planning Horizon 8-61

Table 8.29 Project Construction Durations for Taylor WTP Projects to Address Deficiencies in the 20-Year Planning Horizon 8-65

Table 8.30 20-Year Horizon Projects with Additional Permitting Considerations 8-67

Figures Figure 8.1 Taylor WTP Process Flow Diagram 8-3

Figure 8.2 Monthly Median Raw Water Turbidity (January 2008 to December 2017) 8-8

Figure 8.3 Taylor WTP Site Layout 8-15

Figure 8.4 Taylor WTP Average Monthly Energy Intensity 8-18

Figure 8.5 Taylor WTP Process Performance Summary 8-19


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Figure 8.6 Predicted Hydraulic Profile through Taylor WTP Flocculation/Sedimentation Basins 1 – 3 and Filters 1 – 4 at 21.6 mgd and 25 mgd 8-23

Figure 8.7 Predicted Hydraulic Profile through Taylor WTP Flocculation/Sedimentation Basin 4 and Filters 5 – 8 at 21.6 mgd and 25 mgd 8-25

Figure 8.8 Monthly Average Settled Water Turbidity by Basin 8-33

Figure 8.9 Taylor WTP Average Filter UFRVs (from 2018 filter backwash logs) 8-37

Figure 8.10 Filters 5 – 8 Effluent and Filter-to-Waste Piping Schematic 8-40

Figure 8.11 Required Chlorine Contact Basin Volume to Achieve CT Requirements at Different Water Temperatures (pH = 7.0 and Chlorine Residual = 1.0 mg/L) 8-42

Figure 8.12 High Service Pumps 1 – 4 Combined Pump Curve 8-44

Figure 8.13 High Service Pumps 5 – 8 Combined Pump Curve 8-44

Figure 8.14 Conceptual Layout for Selected Water Quality Process Improvement 8-60


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Abbreviations ° C Celsius

Carollo Carollo Engineers, Inc.

City City of Corvallis

CSMR Chloride-to-sulfate mass ratios

CT Contact time

ft. Feet

GAC Granular activated carbon

HGL hydraulic grade line

IOC Inorganic Contaminants

IOC Inorganic contaminants

kWh Kilowatt hours

LT2ESWTR Long Term 2 Enhanced Surface Water Monitoring Rule

MCL Maximum contaminant level

mg/L Milligrams per liter

mg/L Milligrams per liter

mgd Million gallons per day

MIB Methylisoborneol

NFMS National Marine Fisheries Service

ng/L Nanograms per liter

NTU Nephelometric turbidity units

OAR Oregon Administrative Rule

OHA Oregon Health Authority

PPCP pharmaceuticals and personal care products

SOC Synthetic Organic Contaminants

SOC Synthetic organic contaminants

TDH Total dynamic head

TOC Total Organic Carbon

UCMR Unregulated Contaminant Monitoring Rule

UFRV Unit filter run volumes

VFD Variable frequency drives

VOC Volatile Organic Contaminants

VOC volatile organic contaminants

WSE Water surface elevations

WTP Water treatment plant


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Chapter 8

TAYLOR WATER TREATMENT PLANT

8.1 Introduction

8.1.1 Background

The Taylor Water Treatment Plant (WTP) is one of two water treatment plants owned and operated by the City of Corvallis (City). The plant is located in southeast Corvallis along the Willamette River.

The Taylor WTP was constructed in 1949 as a conventional rapid sand filtration plant with a design capacity of 4 million gallons per day (mgd). An intake structure and pump station on the Willamette River supply raw water to the plant.

Major projects to increase plant capacity were completed in 1960 (plant expansion to 8 mgd), 1969 (modifications to bring capacity to 14 mgd), and 1996 (plant expansion to 21 mgd). Since then, additional modifications and improvements projects were completed to enhance WTP processes and meet water quality regulations. Figure 8.1 provides a process flow diagram for the Taylor WTP. Major plant components/processes are as follows:

• Raw water is collected at an intake structure with tee screens on the Willamette River. • Raw water is pumped from the intake structure to the main plant. • Pumped-injection rapid mixing. • Flocculation and sedimentation (with tube settlers and plate settlers). • Filtration using a dual-media configuration for Filters 1 – 4 (granular activated carbon

and sand) and tri-media configuration for Filters 5 – 8 (granular activated carbon, sand, and garnet).

• Chlorine contact basin for disinfection. • Two clearwells and high service pumps to pump water to the distribution system. • Concrete lagoons for solids thickening.

8.1.2 Chapter Organization

This chapter is organized into the following sections:

• Historical Water Quality and Regulatory Compliance. • Existing Facilities and Operational Performance. • Existing Infrastructure Condition Assessment. • Capacity Expansion and Treatment Improvements. • Implementation Plan.

Refer to Appendix R Part 1 for a list of studies, reports, and documents related to the Taylor WTP reviewed for this plan.


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Figure 8.1 Taylor WTP Process Flow Diagram


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8.2 Historical Water Quality and Regulatory Compliance

This section summarizes the Taylor WTP’s historical raw and finished water quality and its compliance with existing regulations. Appendix P Part 2 presents complete sampling data for all finished water quality parameters. Appendix P Part 3 and Part 4 present additional water quality discussions and background information, including a comparison between the Taylor WTP’s water quality with that of the Rock Creek WTP.

Data Sources

Data for raw and finished water was compiled from data that was reported to the Oregon Health Authority (OHA), gathered by field instruments, and monitored by plant staff. The complete list of data sources is provided in Appendix P Part 1.

Oregon Health Authority Required Sampling Schedule

The City is required to sample the Taylor WTP’s raw and finished water at the intervals listed in Table 8.1. This activity complies with Oregon Administrative Rule (OAR) Chapter 333, Division 061, which is reserved for regulations placed on public water systems.

8.2.1 Raw Water

8.2.1.1 General and Secondary Contaminants

Table 8.2 presents the combined data for the raw water quality entering the plant. The finished water maximum contaminant level (MCL) or secondary MCL indicates the threshold where removal or treatment is needed. Secondary MCLs are non-enforceable guidelines set for contaminants that may have aesthetic effects on the finished water.

The average alkalinity of the raw water was 24 milligrams per liter (mg/L), comparable with the typical low alkalinities seen in water sources of the Pacific Northwest.

The average turbidity of raw water coming into the plant was 8.1 nephelometric turbidity units (NTU), but was skewed by rare, high-turbidity events. The median turbidity was 4.8 NTU.


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Table 8.1 Current OHA Regulatory Sampling Requirements at Taylor WTP

Contaminant Group No. of Samples Sampling Interval Notes

Raw Water

Total Organic Carbon (TOC) 1 Quarterly

Alkalinity 1 Quarterly

Finished Water – Entry Point to the Distribution System

Arsenic 1 9 years

Inorganic Contaminants (IOCs) 1 9 years

Nitrate 1 Yearly

Nitrite 1 9 years

Radionuclides – Gross Alpha 1 6 years

Radionuclides – Radium 1 9 years

Radionuclides – Uranium 1 9 years

Synthetic Organic Contaminants (SOCs) 1 3 years Must be sampled for 2 consecutive quarters.

TOC 1 Quarterly

Volatile Organic Contaminants (VOCs) 1 Yearly

Turbidity 1 Daily


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Table 8.2 Summary of Raw Water Quality

Contaminant Unit Finished Water MCL / Secondary MCL No. of

Samples No. of

Detects Value Range Average Median

General

Alkalinity(1) mg/L as CaCO3 24.9(2) 1,383 1,383 20 – 30(6) 24.3 24.0

Geosmin(3) ng/L None 46 45 1.7 – 18.8 7.0

MIB(3) ng/L None 46 35 1.0 – 38.2 6.0

pH 7.0(2) 3,585 3,585 7.0 – 7.8 7.4 7.4

Temperature(1) °C None 3,586 3,586 6 – 20(6) 12.6 12.0

TOC(4) mg/L Dependent on raw water TOC and alkalinity. No removal required if running annual average raw water TOC <2.0 mg/L.

43 43 0.93 – 2 1.3 1.2

Turbidity(1) NTU Treatment technique. ≤0.3 NTU for 95 percent of samples. <1.0 at all times.

3,585 3,585 2.4 – 24.7(6) 8.1 4.8

Cyanotoxins(5)

Total Microcystins µg/L 0.3 7 0 - - -

Cylindrospermopsin µg/L 0.7 7 0 - - - Notes: (1) From City of Corvallis daily raw water summary data January 1, 2008 - December 31, 2017. (2) OHA set minimum finished water alkalinity level for both WTPs and in the distribution system on August 2, 2018, in addition to existing minimum pH requirements for corrosion control. Taylor

WTP minimum alkalinity increased from 24.9 mg/L to 25 mg/L by OHA in May 2021. (3) From summertime City bi-weekly sampling 2016-2018. (4) From sampling data reported to OHA from January 2008 - October 2018. (5) From 2018 temporary monitoring data reported to OHA. (6) Value range is 5th percentile - 95th percentile. Unless otherwise noted, other value ranges are minimum - maximum value.


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Figure 8.2 shows the monthly median turbidity with the error bars providing 5th and 95th percentile turbidity. Higher-turbidity responses in the raw water correspond with the high precipitation that occurs during the winter and the spring runoff season.

Figure 8.2 Monthly Median Raw Water Turbidity (January 2008 to December 2017)

On average, total organic carbon (TOC) in the raw water was 60 percent of the 2 mg/L level that requires removal for regulatory compliance. TOC in the raw water has not exceeded 2 mg/L. TOC is lowest during the summer months and highest at the beginning of the rainy winter months, which is consistent with the seasonal variations in turbidity.

Beginning in 2016, in response to customer concerns about the finished water’s taste and odor, raw water has been sampled for 2-methylisoborneol (MIB) and geosmin. MIB and geosmin are indicators of algal presence.

MIB was detected in 35 of 46 samples at an average concentration of 6 nanograms per liter (ng/L), which is higher than the human detection threshold of 5 ng/L. The highest detected concentration was 38.2 ng/L. Geosmin has also been regularly detected in the raw water (45 of 46 samples) at an average concentration of 7 ng/L, but not at a level higher than the human detection threshold of 30 ng/L. Raw water sampling results from the last three summers detected both contaminants, but there were no observable patterns or trends in MIB and geosmin detections.

Cyanotoxins have been historically detected in the Willamette River, and algal blooms have also been observed in the Willamette Basin and many of its reservoirs. In 2018, sampling did not detect total microcystins or cylindrospermopsin under OHA’s temporary cyanotoxin monitoring rule. As of April 2020, the City was not included in OHA’s list of public water systems susceptible to harmful algal blooms and was not required to monitor for cyanotoxins. Other public water systems (City of Creswell, Springfield Utility Board, City of Wilsonville) withdrawing water from the Willamette River are on the list of susceptible water systems.


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8.2.1.2 Microbial Contaminants

Weekly samples are collected to test for E. coli and total coliforms in the Taylor WTP’s raw water. During the most recent round of compliance sampling, the City also tested for cryptosporidium to comply with the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWR). Table 8.3 shows the results of the testing.

Table 8.3 Summary of Raw Water Microbial Detections

Contaminant Unit No. of

Samples No. of

Detects Value Range(1) Median

E. coli(2) count/100 mL 474 474 3 – 162 15

Total Coliforms(2) MPN/100 mL 466 466 205 – 2,419(3) 980(3

Cryptosporidium(4) Oocysts/ L 24 0 - - Notes: (1) Value range is 5th percentile – 95th percentile. (2) E. coli and total coliforms are tested in the raw water approximately weekly. From Taylor plant daily datasheets from

2008 to 2017. (3) Maximum value of 2,419 MPN/100 mL for the analysis method for total coliforms. Actual maximum value may be higher.

Median presented in this table is likely lower than actual median. (4) From LT2ESWTR sampling data reported to OHA from October 2015 – June 2017.

E. coli and total coliforms were detected in all the samples. Agricultural lands in the upstream watershed, combined with other human activity and discharge, likely contributed to this frequent detection of microbial contaminants.

The maximum total coliforms detected was 2,419 MPN/100 mL which is the upper detection limit for the analysis method so the actual number of total coliforms could be significantly higher.

The cryptosporidium sampling conducted to comply with the LT2ESWTR is used to classify utilities in bins. The bins determine if additional treatment for cryptosporidium is required. Cryptosporidium was not detected in the raw water at the plant, which places the Taylor WTP in the lowest classification, Bin 1, and no additional treatment for cryptosporidium is required.

8.2.2 Finished Water Quality

8.2.2.1 General and Secondary Contaminants

Table 8.4 summarizes the plant’s finished water quality.

Table 8.4 highlights a number key water quality parameters that are important in corrosion control: pH, alkalinity, chloride, sulfate, and the Langelier Index. The historical average CSMR in Taylor WTP’s finished water was 0.3, well below the threshold level for increased lead solder corrosion1.

1 Nguyen, Caroline K., Kendall R. Stone, and Marc A. Edwards. 2011. "Chloride-to-sulfate mass ratio: Practical studies in galvanic corrosion of lead solder." Journal AWWA 81-92.

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Table 8.4 Summary of Finished Water Quality

Contaminant Unit Finished Water MCL No. of

Samples No. of

Detects Value Range Average Median

General

Alkalinity(1) mg/L as CaCO3 24.9(2) 855 855 24 – 40(6) 32.3 32

Geosmin(3) ng/L None 24 11 1.0 – 2.86 1.7

MIB(3) ng/L None 24 8 1.1 – 5.9 2.5

pH 7.0(2) 3,585 3,585 7.0 – 7.2 7.1 7.0

Temperature(1) °C None 3,584 3,584 6 – 20(6) 12.5 12

TOC(4) mg/L Dependent on raw water TOC and alkalinity. No removal required if running annual average raw water TOC <2.0 mg/L.

43 43 0.5 – 1.09 0.65 0.62

Turbidity(1) NTU Treatment technique. ≤0.3 NTU for 95 percent of samples. <1.0 at all times.

3,585 3,585 0.02 – 0.04(6) 0.03 0.03

Secondary Contaminants(5)

Aluminum mg/L 0.05 – 2 9 2 0.044 – 0.072 0.1 0.058

Chloride mg/L 250 10 10 2.4 – 4.6 3.6 3.7

Iron mg/L 0.3 10 1 0.023

Langelier Index None 9 9 -2.9 – 0 -2.3 -2.7

Manganese mg/L 0.05 10 3 0.002 – 0.031 0.01 0.003

Sulfate mg/L 250 11 11 9.6 – 19.3 13.3 11.8 Notes: (1) From City of Corvallis’ daily finished water summary data January 1, 2008 - December 31, 2017. (2) OHA set minimum finished water alkalinity level for both WTPs and in the distribution system on August 2, 2018, in addition to existing minimum pH requirements for corrosion control. Taylor

WTP minimum alkalinity increased from 24.9 mg/L to 25 mg/L by OHA in May 2021. (3) From summertime City bi-weekly sampling 2016-2018. (4) From sampling data reported to OHA from January 2008 - October 2018. (5) From City of Corvallis secondary contaminant testing data from January 1, 2008 - August 27, 2018. (6) Value range is 5th percentile - 95th percentile. Unless otherwise noted, other value ranges are minimum - maximum value.


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The Langelier Index was negative, largely resulting from low calcium in the water; low calcium concentrations and the resulting negative Langelier Index are typical in the Pacific Northwest. Waters with low calcium and Langelier Indices are unlikely to result in scaling in the distribution system, even after pH and alkalinity adjustment.

For corrosion control, OHA established minimum alkalinity and pH levels for the City’s water system. The alkalinity of the Taylor WTP finished water must be at least 24.9 mg/L (raised to 25 mg/L by OHA in May 2021), and the alkalinity in the distribution system must be at least 29.8 mg/L (lowered to 28 mg/L by OHA in May 2021). Alkalinity in the distribution system varies depending on how much blending occurs between the Rock Creek and Taylor WTPs’ finished water.

The 10-year average of the Taylor WTP’s finished water alkalinity was 31.1 mg/L, which is above the OHA minimum. Alkalinity was below the minimum in 10 percent of weekly alkalinity tests with a low of 16 mg/L.

When combined, finished water from both of the City’s WTPs must meet the distribution system minimum. In 24 percent of historical samples the finished water alkalinity was below the distribution system minimum level. Section 8.2.3 discusses the challenge of meeting minimum alkalinity levels.

In the raw water, MIB was detected in over 75 percent of the samples since 2016 at an average concentration of 6.0 ng/L, and geosmin was detected in all but one raw water sample at an average concentration of 7 ng/L. In the finished water, only one-third of all finished water samples detected MIB (at an average concentration of 2.5 ng/L), and one-half of the samples detected geosmin (at an average concentration of 1.7 ng/L). The average removal of both at the plant is over 50 percent, indicating effective removal by the GAC filter media and treatment processes.

Manganese has been detected in 3 of 10 samples collected since 2008, with the highest concentration of 0.031 mg/L below the secondary MCL of 0.05 mg/L. Manganese concentrations above 0.02 mg/L can lead to colored water if not treated.

8.2.2.2 Inorganic Contaminants, Synthetic Organic Contaminants, Volatile Organic Contaminants

As shown in Table 8.1, grab samples are taken to test for inorganic contaminants (IOCs), synthetic organic contaminants (SOCs), and volatile organic contaminants (VOCs) in the finished water. None of the regulated SOCs or VOCs were detected.

Table 8.5 summarizes all detected IOCs in the finished water. All contaminants detected were well below their respective finished water MCLs or are not currently regulated.

Table 8.5 Detected IOCs in Taylor Finished Water

Contaminant Unit Finished

Water MCL No. of

Samples No. of

Detects Value Range

Median

Fluoride mg/L 4 7 7 0.58 – 0.92 0.73

Nitrate mg/L 10 12 7 0.18 – 0.41 0.35

Sodium mg/L None 2 2 17.6 – 18.1 17.85

Fluoride was the most frequently detected contaminant due to its addition to the finished water. The fluoride dose was 0.9 to 1.0 mg/L from 2008 to 2010 and was lowered to 0.7 mg/L in 2011.


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The current dose is consistent with the United States Public Health Service’s recommended fluoride level of 0.7 mg/L for community water supplies.

8.2.3 Regulatory Compliance

Taylor WTP is currently meeting or exceeding all of its regulatory requirements. Chapter 3 provides the complete list of regulations the City must comply with.

As discussed in Section 8.2.2.1, the biggest concern for existing regulatory compliance is maintaining the OHA-established minimum alkalinity levels at the plant and in the distribution system. To consistently meet the distribution system’s minimum, Taylor WTP must produce finished water with an alkalinity of 28 mg/L (lowered from previous minimum of 29.8 mg/L by OHA in 2021). To comply with the established minimum alkalinities the City has increased alkalinity in the finished water at Taylor WTP.

8.2.3.1 Contact Time Compliance

The chlorine contact basin provides the contact time (CT) to meet the regulatory requirement of 0.5-log inactivation downstream of filtration. The average inactivation ratio from 2008 to 2017 was 3.5. The 5th percentile inactivation ratio was 2.0. Meeting CT requirements has not been a concern, even during periods of low water temperatures or high flow rates.

8.2.3.2 Unregulated Contaminant Monitoring

No detected contaminants listed in Unregulated Contaminant Monitoring Rule (UCMR) 3 or UCMR4 exceeded reference concentrations during sampling. Metals detected during sampling for UCMR3 (strontium, vanadium, and chromium) are likely attributable to regional geology. Chlorate and haloacetic acids detected resulted from the use of sodium hypochlorite and disinfection with free chlorine, respectively. Appendix P Part 4 summarizes unregulated contaminant monitoring at the Taylor WTP in further detail.

8.2.3.3 Future Regulations

Future regulatory actions are not anticipated to significantly affect recommendations made for the plant’s treatment process. Additional regulation of cyanotoxins by the EPA is not anticipated to significantly affect the City as they are already regulated by OHA, however they are not currently identified as a susceptible source are not required to sample. The City’s current treatment processes would likely be challenged to handle any cyanotoxin event.

Appendix P Part 4 summarizes contaminants of emerging concern and potential future regulations that may affect Taylor WTP or Rock Creek WTP.

8.2.4 Conclusion

Historical water quality data shows that the plant consistently meets or exceeds regulatory requirements for finished water quality. All contaminants detected in the finished water were well below finished water MCLs.

Cyanotoxins are a growing concern for the region and the City’s sources may be regulated by OHA or the EPA in the future. Cyanotoxin events were considered when evaluating recommendations for treatment processes in this master plan.


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8.3 Existing Facilities and Operational Performance

8.3.1 Introduction

This section summarizes the Taylor WTP infrastructure and assesses historical performance. Evaluating the existing WTP components and processes sets a baseline for the plant’s current performance and identifies issues that may limit future operations. This section summarizes:

• Previous studies and documents used to support the analyses. • Existing treatment processes and facilities. • Process capacity evaluations for major treatment processes. • Evaluation of historical plant performance. • Hydraulic analysis, including hydraulic capacity restrictions. • Results of operational testing and performance optimization recommendations.

8.3.1.1 Data Sources

Historical plant performance and process performance analyses were conducted using plant operating performance data from January 2008 through December 2017.

The hydraulic model was built using information from available drawings:

• 1949 original construction as-built drawings. • 1960 expansion as-built drawings. • 1969 expansion as-built drawings. • 2008 filter modification and media replacement drawings. • 2013 mixing equipment improvement drawings.

Additional documents that were used to inform the analysis are listed in Appendix R Part 1.

8.3.1.2 Plant Overview

The Taylor WTP facilities and treatment processes were constructed in phases through multiple plant expansions (see Table 8.6). The original WTP was constructed in 1949 and consisted of the raw water intake and pump station, one flocculation/sedimentation basin, two filters, and one clearwell with high service pumps.

Table 8.6 Plant Expansion and Modification History for Taylor WTP

Year Plant

Capacity Details

1949 4 mgd

• Original plant construction: − Traveling screens and intake structure. − Raw water pump station. − Flocculation/sedimentations basins 1 and 2. − Filters 1 and 2. − Clearwell 1 and high service pumps. − Chemical facilities.

1960 8 mgd • Added filters 3 and 4. • Added flocculation/sedimentation basin 3. • Additional raw water and high service pumps.


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Year Plant

Capacity Details

1969 14 mgd • Earthen sludge lagoons 1 and 2. • Tube settlers added to sedimentation basins. • Clearwell 2 added.

1991 14 mgd • Additional high service pump addition. • High service pumping modifications.

1996 21.6 mgd

• Added treatment components: − Flocculation/sedimentation basin 4 with lamella plates. − Filters 5 – 8. − Chlorine contact basin. − Replaced earthen sludge lagoons with concrete sludge lagoons. − Additional raw water and high service pumps.

2004 21.6 mgd

• Added sludge lagoon 3. • Sludge lagoon basin infrastructure modifications. • Replaced traveling screens with tee intake screens. • Additional raw water pump.

2008 21.6 mgd

• Replaced surface wash system for filters 1 – 4 with air scour system. • Replaced filters 1 – 4 anthracite media with granular activated

carbon (GAC) media. • Replaced filters 1 – 4 underdrains and concrete troughs. • Replaced GAC filter media in filters 5 – 8.

2013 21.6 mgd • Replaced the in-line rapid mixer with pumped diffusion rapid mix. • Completed modifications to raw water piping to flocculation/

sedimentation basins 1 – 3 and flocculation/sedimentation basin 4.

Figure 8.3 shows the existing WTP site. Raw water is pumped from the raw water pumps on top of the intake structure on the Willamette River. The majority of plant processes and infrastructure from the 1949 original construction and 1960 expansion are located within the original WTP building or share common walls with this building. These processes/infrastructures are as follows:

• Flocculation/sedimentation basins 1 – 3. • Filters 1 – 4, clearwell 1. • High service pumps 1 – 4. • Backwash pumps. • Dry chemicals. • Administration/operation/laboratory spaces.


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Figure 8.3 Taylor WTP Site Layout

Clearwell 2 was constructed in 1969, west of filters 1 – 4, with the building above added in 1991. Infrastructure for the 1996 expansion was mostly constructed separate from the main operations and filters building.

Flocculation/sedimentation basin 4 was constructed as a standalone basin east of flocculation/sedimentation basins 1 – 3. Filters 5 – 8 were constructed as a standalone building, with the air scour blowers, filter controls, and one of the plant air compressors on the top level in the blower room and the pipe gallery on the lower level.

The bulk chemical building was connected to the northeast corner of the original operations and filter building. Rapid mix and liquid chemicals (alum and sodium hypochlorite) are located in the bulk chemical building.

Residuals handling facilities are located northeast of the main treatment buildings. The three concrete lagoons store backwash wastewater and provide sludge thickening.

8.3.1.3 Plant Capacity

Plant capacity is 21.6 mgd with all eight filters operating at their maximum allowed regulatory filtration rate. Capacity information for individual plant treatment processes is summarized in subsequent sections. Detailed capacity information for existing plant treatment components and processes is also provided in Appendix R Part 2.


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The Taylor WTP does not currently operate 24 hours per day. The plant is started and stopped each day, with operating times dependent on the time of year and water demands. During periods of high demand, the plant has operated up to 16 hours per day at flow rates close to 21.6 mgd. Maximum daily production for 2008 to 2017 was 16.8 MG.

8.3.1.4 Methods

Process Capacity and Performance Evaluations

Process capacity and performance evaluations are based on historical performance data and comparisons of process sizing and performance against typical design criteria (as presented in S. Kawamura, 2000 and MWH, 2003). The following WTP processes were evaluated:

• Flocculation/sedimentation. • Filtration. • Disinfection (chlorine contact basin). • Chemical systems (coagulant, pH adjustment, polymer, and disinfection). • Solids handling system.

Hydraulic Model Development

A hydraulic model of the Taylor WTP was developed using Hydraulix® software to compare water surface elevations (WSE) in the treatment plant at different flowrates. General notes and assumptions made for developing the hydraulic model are presented in Chapter 7.

The following assumptions were made when developing the hydraulic model:

• Elevations not found in previous drawings were taken from the hydraulic profile presented in the 1996 drawings.

• The flow split between filters 1 – 4 and filters 5 – 8 was assumed to be even, up to the maximum flow rate based on the maximum regulatory filtration rate for each set of filters. Flow splits for model verification were based on observed flow rates.

• Piping between flocculation/sedimentation basins 1 – 3 and flocculation/sedimentation basin 4 going to the filters was not modeled in detail. The filters are rate of flow controlled. Filter flow rate setpoints and WSEs control the hydraulic grade line (HGL) in the piping downstream of the flocculation/sedimentation basins. The HGL was determined only downstream of flocculation/sedimentation basins 1 and 2 based on the amount of flow sent to filters 1 – 4. For the point downstream of flocculation/sedimentation basin 4, where flow splits to the two sets of filters, the HGL for the portion going to filters 5 – 8 was determined based on the amount of flow being sent to filters 5 – 8.

• The WSE in the troughs for the flocculation/sedimentation basins was estimated using an assumed flow rate through each flocculation/sedimentation basin and the HGLs determined downstream of flocculation/sedimentation basins 1 and 2 and flocculation/sedimentation basin 4.

Hydraulic Model Verification

For comparison with the hydraulic profile from the 1996 drawings, the hydraulic model was first developed for 21.6 mgd. To verify the assumptions made in the hydraulic model, elevations of key hydraulic controls and WSEs were field measured in December 2019.

Measurements were made for plant operation at 11 mgd on December 4, 2019, and at 9 mgd on December 5, 2019. Note, filters 1 and 2 were out of service for GAC replacement at the time of


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testing. The field measurements were combined with operating values from SCADA to verify the hydraulic grade line (HGL) developed in the hydraulic model. All collected field measurements can be found in Appendix N.

While operating at 11 mgd on December 4, 2019, the following plant components were in service:

• One full lift raw water pump. • All four flocculation/sedimentation basins. • Filters 3 – 8. • High service pumps 3 and 8.

While operating at 9 mgd on December 5, 2019, flocculation/sedimentation basin 4 was taken out of service for cleaning and inspection and the following plant components were in-service:

• One full lift raw water pump. • Flocculation/sedimentation basins 1 – 3. • Filter 3 and filters 5 – 8. • High service pumps 3 and 8.

8.3.2 Historical Performance and Process Capacity Evaluation

8.3.2.1 Plant-wide Historical Performance

The Taylor WTP serves as a peaking plant to meet increased summer water demands so the average monthly productions varies throughout the year as water demands change.

Average finished water production ranged from 3.4 mgd to 9.0 mgd, with production highest in the summer months of July and August and lowest during the winter months from December through March. On average, Taylor WTP produced two-thirds of the City’s total water demands.

Average plant production efficiency (finished water produced divided by raw water taken in) ranged from 94 to 96 percent. Backwashes and other internal plant uses typically account for around 5 percent of total production.

Average production efficiency is relatively consistent year-round, with a slight decrease during the winter months when higher raw water turbidities require more frequent backwashing of filters.

Discrepancies between the raw and finished water flow rate measurements were previously observed by plant staff. This included concerns with the accuracy of individual flow meters within the plant. These differences between the raw and finished water flow rate were observed in December 2019 as part of plant testing; historical plant production efficiencies did not show a noticeable difference. Resolving discrepancies between flow meter measurements could change plant production efficiency ranges.

Historical daily plant energy use is dependent on the total volume of water pumped, with the raw water and finished water pumps using the most energy. Raw water is pumped from the Willamette River, then finished water is pumped into the distribution system.

Average daily energy use has ranged from 5,000 kilowatt hours (kWh) during the lowest production months (when average production is close 3 mgd) to 12,000 kWh during the peak production months of July and August.


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Historical average energy intensity was 1,540 kWh/MG. Average energy intensity at the Taylor WTP has been nearly five times that of the Rock Creek WTP. The large difference in energy use is attributed to the greater pumping needs at the Taylor WTP. Average monthly energy intensity is plotted in Figure 8.4. Overall energy use peaks in the summer, but average energy intensity decreases during that time due to increased production.

Figure 8.4 Taylor WTP Average Monthly Energy Intensity

Figure 8.5 summarizes key operational and water quality performance parameters for the Taylor WTP. Performance data is called out relative to its location in a simplified process flow diagram of the plant. The graphic summarizes the following parameters:

• Finished water production. • Plant production efficiency. • Turbidity throughout the plant treatment processes. • Disinfection performance. • Chemical usage.


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Figure 8.5 Taylor WTP Process Performance Summary


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8.3.2.2 Plant Hydraulic Capacity

Hydraulic Model Verification

The hydraulic model developed for the plant was verified by comparing modeled WSEs against measurements of WSEs collected in December 2019. In general, the modeled and measured WSEs were within 0.2 feet of each other, within the estimated 2 inches of error for field measurements. The developed model effectively predicted the HGL for the plant, allowing it to be used for hydraulic capacity evaluations at increased flow rates. Refer to Appendix R Part 3 for additional details on hydraulic model verification.

Key Hydraulic Controls

The following key components control hydraulics through Taylor WTP:

• Raw water pumps. - How the raw water pumps are operated determines the flow rate through the WTP. - Eight raw water pumps are located at the intake structure. - Two of them are full lift pumps with variable frequency drives (VFD); these pumps

are typically used. The remaining pumps are used for backup and require two-stage pumping to lift water to the plant.

• Raw water flow control valves. - The raw water pumps determine the flow rate entering the WTP, and the raw water

flow control valves determine the flow split between flocculation/sedimentation basins 1 – 3 and flocculation/sedimentation basin 4. The valve position is adjusted to direct additional flow to flocculation/sedimentation basin 4 if turbidities are increasing in flocculation/sedimentation basins 1 – 3.

- During the winter, typically both valves are 100 percent open, with flow passively split approximately evenly between flocculation/sedimentation basins 1 – 3 and flocculation/sedimentation basin 4.

- When plant flows are high in the summer, the valve positions are adjusted to limit the flow to flocculation/sedimentation basin 4 to approximately 9 mgd and to target equal settled water turbidities in the flocculation/sedimentation basins.

• Sedimentation basin effluent weirs. - The sedimentation basin effluent weirs maintain a consistent WSE in the

flocculation/sedimentation basins. • Filter operating WSE.

- The filter effluent valves are modulated to control the filter operating WSE. An operating WSE for the filters 5 – 8 filter influent channel is set.

- The filter effluent flow rate for a single filter is determined by dividing the total raw water flow rate by the number of filters online. Individual filter flow rate setpoints are then further adjusted by changing the “scale factor” setpoint for each filter to scale the amount of flow through a filter down from the value assigned for a single filter. This scale factor accounts for differences in the filter surface area between filters 1 – 4 and filters 5 – 8.

- The filter WSE controls the depth of water in the sedimentation basin weir troughs. The filters must be operated with a maximum WSE that still maintains a WSE at least 4 inches below the sedimentation basin weirs to ensure a free discharge from the weirs.


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• Chlorine contact basin stop log weir. - A stop log weir at the downstream end of the chlorine contact basin controls the

minimum WSE and the volume in the basin. Maintaining a consistent WSE ensures that a minimum, constant volume of water is maintained for contact time for disinfection.

- The weir elevation also controls the minimum HGL for the filters and ensures that the individual filter effluent pipes and the filter effluent valves remain submerged. This prevents partially full filter effluent piping and air from impacting filter effluent valve performance.

Hydraulic Profile at Maximum Plant Capacity

The flow through the Taylor WTP was modeled at the current maximum capacity of 21.6 mgd and the future plant capacity of 25 mgd. At 21.6 mgd, the model is based on all eight filters being online at their approved filtration rate. This is an instantaneous capacity, since the plant flow rate decreases when filters are backwashed.

For 25 mgd, it is assumed the existing filters would be uprated to a common filtration rate of 4.93 gpm/ft2, and one of filters 5 – 8 would be out of service for backwashing. This is a firm capacity of 25 mgd versus the current instantaneous capacity of 21.6 mgd.

Figure 8.6 and Figure 8.7 show the predicted HGL for at 21.6 mgd and 25 mgd. At 25 mgd, the modeled HGL remains below all overflow elevations, and no plant-wide hydraulic limitations are present. Specific hydraulic implications for operation at 25 mgd are detailed in Section 8.3.2.3 through Section 8.2.3.10 for individual processes.

Overflow Capacity

Taylor WTP has overflows in the following locations (most downstream to most upstream):

• Clearwells 1 and 2. • Filters 1 and 2 influent. • Flocculation/sedimentation basin 4 discharge channel. • Flocculation/sedimentation basins 1 – 3, downstream of stage 3 flocculation.

To avoid an uncontained overflow, the plant configuration requires processes upstream of each overflow to accommodate the WSE backing up to above the overflow elevation.

The following potential scenarios were evaluated at a future plant flow of 25 mgd:

• All high service pumps are off, leading to clearwell 1 and 2 overflow. • Chlorine contact basin discharge valve closed. • Filter effluent valves closed. • Filter influent or flocculation/sedimentation basin discharge valves closed.

In all scenarios, the WSE in the basins was checked to determine if an overflow would lead to water discharging over basin walls, surcharging of elevated slabs, or flooding in the plant. Based on the overflow elevations, there appears to be no concern with flooding or slab uplift.

Overflow water is directed to the lagoons through a series of pipes and manholes that are also used for backwash waste conveyance. The conveyance capacity of the overflow piping was evaluated to determine its ability to handle an overflow up to 25 mgd. Manholes were also evaluated to ensure they wouldn’t surcharge.


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Figure 8.6 Predicted Hydraulic Profile through Taylor WTP Flocculation/Sedimentation Basins 1 – 3 and Filters 1 – 4 at 21.6 mgd and 25 mgd


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Figure 8.7 Predicted Hydraulic Profile through Taylor WTP Flocculation/Sedimentation Basin 4 and Filters 5 – 8 at 21.6 mgd and 25 mgd


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A 25 mgd overflow would cause the majority of the overflow piping to surcharge.

Modeled HGL for steady state conditions indicates the WSE for manhole MH-9 in the 1996 drawings, located in the yard, would be at risk of surcharging if the chlorine contact basin overflowed due to a closed discharge valve.

Other manholes, both upstream and downstream of this manhole, are deeper and maintain a WSE at least 3 – 4 feet below the rim elevation.

For other overflow scenarios, there are no concerns for either the manholes nor the overflow piping have modeled concerns with surcharging.

8.3.2.3 Willamette River Intake Structure and Raw Water Pumps

The raw water intake structure is located on the Willamette River just east of the main WTP buildings. The original intake structure was constructed in 1949, and the most recent upgrade was completed in 2004. In 2004, the existing traveling screens were replaced with two Johnson tee screen assemblies (four screens total).

The tee screens are cylindrical stainless steel wedge wire 30-inch diameter static screens oriented in parallel with the river stream flow at the intake. They are protected by a galvanized steel frame structure.

The tee screens are cleaned with an airburst system that directs pressurized air to the screen interior to remove material collected on the screen. An air compressor and air receiver tank for the airburst system are located in a separate electrical building west of the intake structure.

Air is delivered to the intake structure via a 4-inch air pipeline, with individual 3-inch air pipelines off the main pipeline to provide an airburst for the individual screens. Airburst cleaning is automatically initiated based on a preset time schedule.

The original intake structure wet well contains four intermediate lift pumps. The intake structure was extended further into the river due to a historical change in the flow path of the Willamette River, with two low lift pumps housed in the added wet well. The six total low and intermediate lift pumps are not currently in use.

To use these pumps, the raw water has to be double pumped. The low lift pumps pump to the intermediate lift pumps wet well, then the intermediate lift pumps pump to the plant.

The intake extension addition has two full lift pumps (pumps 8 and 9) capable of pumping directly from the river to the plant. Both pumps are equipped with variable frequency drives (VFDs) that allow the raw water flow to be controlled by operator setpoint.

Each full lift pump discharges into its own 30-inch steel pipe that combines into a single 36-inch raw water pipeline to the plant. A 36-inch insertion-style magnetic flow meter, located in the raw water metering vault, measures flow entering the plant.

A sample line runs from the raw water metering vault upstream of chemical injection to monitor raw water turbidity, pH, temperature, and particle counts. Soda ash and sodium hypochlorite can be injected into the raw water pipeline in the raw water metering vault.

Design Criteria and Process Capacity

To meet National Marine Fisheries Service (NFMS) requirements for anadromous juvenile fish, each of the four intake screens has a maximum allowable approach velocity of 0.4 feet per


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seconds. This corresponds to a capacity of 10 mgd for each screen. The firm capacity of the screens (one screen offline for backwash or other reasons) is 30 mgd. This capacity is sufficient to meet current plant maximum production and the future maximum capacity of 25 mgd.

Table 8.7 summarizes the design capacities of the raw water pumps.

Table 8.7 Raw Water Pump Capacities

Pump Capacity (mgd)

Low Lift Pumps

Pump 1 and Pump 2 15 mgd at 12 ft Total Dynamic Head (TDH)

Intermediate Lift Pumps

Pump 3 4.3 mgd at 73 ft TDH




Full Lift Pumps

Pump 8 11 mgd at 70 ft TDH


Pumps 8 and 9 are each capable of pumping approximately half of the current plant maximum production. Pump 8 can produce up to a maximum of 13 mgd and pump 9 can produce up to a maximum 10.5 mgd, with pump capacity dependent on the river elevation. The firm capacity of the raw water pumps (capacity with largest pump offline) is approximately 10 mgd, since pumps 1 – 6 are not typically in service. If pumps 1 – 6 are placed in service, sufficient firm pumping capacity is available to meet the current plant maximum production.

To provide firm pumping capacity at the current plant maximum of 21.6 mgd, and for future expansion to 25 mgd, an additional full lift pump(s) with a similar capacity to pumps 8 and 9 is needed. Firm pumping capacity could also be provided with the use of the low and intermediate lift pumps.

Historical Performance

The current intake structure and intake screens have generally performed well, but gravel deposition near the intake is becoming a concern for screen performance. A large gravel island has formed about 300 feet downstream of the intake structure and has grown larger since forming in the late 1990s. As it has increased in size, the island has moved farther upstream so that it is now immediately east of the intake structure. When river levels are low in the summer, people can walk from the riverbank near the intake structure out to the island.

Because the river deposits large volumes of gravel during high flow winter/spring periods, the island continues to grow, causing additional gravel deposits to fill in and around the intake screens. As a result, the City has to remove the gravel near the intake every few years.

The Army Corps of Engineers has allowed the City to relocate, but not remove, up to 10,000 yd3 of gravel. As the river continues to deposit gravel and the island grows, gravel obstruction will hinder the performance and viability of the existing intake screens.


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The intake screens were originally designed to airburst based on a differential pressure, but the differential pressure instrumentation was installed improperly so the system cannot monitor differential pressure across the screens. As a result, the practice of initiating airbursts according to a set schedule is used and has been effective.

For raw water pumping, the existing full lift pumps perform well and provide sufficient capacity to meet current plant needs.

Hydraulic Capacity

Velocities in the combined 36-inch raw water pipeline from the raw water pumps are 4.73 and 5.47 ft/s at 21.6 mgd and 25 mgd, respectively. These values are within typical design criteria.

Velocities in the individual 30-inch pipelines are 4.10 ft/s at 13 mgd (maximum capacity for pump 8). Velocities remain less than 5 ft/s for flow rates up to 16 mgd in a single 30-inch raw water pipeline. The existing raw water pipe sizes and hydraulic capacity are sufficient up to 25 mgd as long as flows remain split relatively evenly between the two pipelines.

8.3.2.4 Rapid Mix

Rapid mix is a pumped-injection system where alum (primary coagulant) is injected into the raw water piping to instantly mix into the flow stream in the bulk chemical building. The rapid mix pump suctions raw water from the pipeline upstream of alum injection and pumps it back to the pipeline through a diffuser nozzle.

Sodium hypochlorite can be added at rapid mix for pre-chlorination, or upstream of rapid mix at the raw water metering vault.

The raw water is sampled for turbidity, pH, and temperature at the raw water metering vault. If pH adjustment is needed for coagulant optimization, soda ash is injected into the raw water pipe in the raw water metering vault upstream of rapid mix.

Streaming current, pH, and chlorine residual are measured just downstream of rapid mix. Streaming current measures the charge on particles in water and is used for coagulant optimization.


Rapid mix intensity is characterized by the amount of mixing provided. Velocity gradient (G) is a measure of the mixing provided, calculated as a ratio of the power applied to the volume mixed. This energy is applied for a period of mixing time (t). For pumped-injection rapid mix systems, typical G x t values are between 500 and 1,600. G x t values are influenced by the rapid mix pump flow rate and the flow characteristics of the rapid mix discharge.

The rapid mix has a 5-HP pump with a maximum capacity of 300 gpm at 47 feet total dynamic head (TDH). At 300 gpm, the rapid mix flow rate is 2 percent of a 21.6 mgd plant rate, within the typical design rate of 2 to 5 percent of plant flow. At 25 mgd flow rate, the rapid mix flow rate would be 1.7 percent of total plant flow, falling below the typical design range.

Estimated G x t values for the Taylor WTP are 610 at 21.6 mgd and 510 at 25 mgd, which are on the low end of the typical design range. The estimated G x t values assume that 20 percent of the pump motor horsepower (1.0 HP) is transferred to the water as mixing energy and all mixing occurs within one pipe diameter (36 inches) downstream of chemical injection. A larger rapid mix pump may be needed with plant expansion up to 25 mgd if insufficient mixing is observed.


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Mixing improvements were made in 2013 to remedy issues with alum mixing and different alum doses being delivered to flocculation/sedimentation basins 1 – 3 and flocculation/sedimentation basin 4. Improvements included moving the flow split point downstream, adding additional piping, and installing the pumped-injection rapid mix system. The rapid mix system has performed well since then, with no performance concerns.

Hydraulic Capacity

The rapid mix system has no identified hydraulic capacity concerns.

8.3.2.5 Flocculation/Sedimentation Basins

The Taylor WTP has a total of four flocculation/sedimentation basins. Coagulated water flow is split between flocculation/sedimentation basins 1 – 3 and flocculation/sedimentation basin 4. The flow split is controlled by raw water flow control valves in the bulk chemical building. Each flocculation/sedimentation basin is divided into three separate stages of flocculation (referred to as flocculation basins) and sedimentation (referred to as sedimentation basin).

Water flowing to flocculation/sedimentation basins 1 – 3 flows out of the bulk chemical building and into a combined influent channel. Each basin has downward opening gates that help distribute flow evenly among the basins.

To promote mixing for floc formation, flocculation/sedimentation basins 1 – 3 have three-stage tapered flocculation and are equipped with variable-speed vertical turbine and paddle wheel mixers.

Water flows from the flocculation basins in flocculation/sedimentation basins 1 – 3 horizontally through baffle walls and then enters the sedimentation basins. For solids removal, the sedimentation basins have tube settlers and chain and flight sludge collectors. Clarified water leaving the sedimentation basins flows over launder weirs into a combined discharge channel.

Water to flocculation/sedimentation basin 4 flows out of the bulk chemical building and discharges out of a pipe into the flocculation basin. Flocculation/sedimentation basin 4 also has three-stage tapered flocculation to promote mixing for floc formation, but uses horizontal paddle wheel flocculators.

Water leaving the flocculation basins in flocculation/sedimentation basin 4 follows a serpentine flow path around interior baffle walls before flowing into the sedimentation basin. The sedimentation basin is equipped with plate settlers and uses a Trac-vac system for sludge removal. Clarified water from the sedimentation basin flows over launder weirs into a combined discharge channel.

Water from the all of the flocculation/sedimentation basins is combined and flows to all filters. Because flocculation/sedimentation basin 4 and filters 5 – 8 are close together, it is hydraulically preferable for water to flow directly from basin 4 to filters 5 – 8. Similarly, it is hydraulically preferable for water from flocculation/sedimentation basins 1 – 3 to flow to filters 1 – 4.

The exact mixing from the different flocculation/sedimentation basins going to the filters depends on several factors: the flow rates through the individual flocculation/sedimentation basins, which filters are online, and the filter flow rate setpoints for individual filters.


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Filter aid polymer is dosed to the upstream end of the launder weir channels of flocculation/ sedimentation basins 1 – 3 and to the combined discharge channel at the downstream end of flocculation/sedimentation basin 4. Settled water turbidity is continuously monitored in each basin.


Table 8.8 and Table 8.9 compare key flocculation and sedimentation parameters with typical industry design criteria. Note that all criteria and capacity calculations assume an even 50/50 flow split between flocculation/sedimentation basins 1 – 3 and flocculation/sedimentation basin 4.

Flocculation/Sedimentation Basins 1 – 3

The detention time in flocculation basins 1 – 3 is 23 minutes at 11.3 mgd, half of plant maximum capacity of 21.6 mgd with all filters on-line. It is 19 minutes at 12.5 mgd, half of the future 25 mgd capacity, which would be just outside typical design criteria ranges.

The detention time in sedimentation basins 1 – 3 is between 1.3 and 1.5 hours, at 11.3 mgd and 12.5 mgd respectively. The design detention time for sedimentation basins with plates or tube settlers can be as low as 20 to 40 minutes.

Overflow rates for the projected tube area are within typical design ranges. The existing sedimentation basin capacity appears sufficient for increased plant flow rates.

Table 8.8 Flocculation/Sedimentation Basins 1 – 3 Design Criteria

Parameter Unit Typical Design

Criteria Flow Rate

11.3 mgd 12.5 mgd

Flocculation Basins

Total Detention Time min 20 – 40 23 19

Stage 1 G Value(1) sec-1 10 – 70 (tapered) 60



Sedimentation

Detention Time hr 1.5 – 4 1.5 1.3

Overflow Rate (tube projected area) gpm/ft2 2 -3.5 2.13 2.47 Notes: (1) G values taken from 2002 Facility Plan and 1996 drawings design criteria.

Flocculation/Sedimentation Basin 4

The detention time in flocculation basin 4 is between 26 minutes and 31 minutes for flow rates of 11.3 and 12.5 mgd, respectively. This time is within typical design values. The detention time in sedimentation basin 4 is between 20 minutes and 23 minutes, at 11.3 mgd and 12.5 mgd, respectively, which is on the low end of the design range for sedimentation with plates.

The overflow rates for the plate surface area are 0.36 and 0.41 gpm/ft2 for flow rates of 11.3 and 12.5 mgd, respectively, which exceed the original design criteria of 0.33 gpm/ft2. The design overflow rate of 0.33 gpm/ft2 was for the 10 mgd design capacity. Historically, the basin has occasionally been operated at flow rates as high as 12 mgd with limited observed process implications, but higher effluent turbidities are anticipated at increased flow rates.


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Based on these key process design parameters, there are few process capacity concerns for plant flow rates up to 25 mgd. Approval by OHA is required to increase the rated flow rates for the flocculation/sedimentation basins. OHA would conduct a Comprehensive Performance Evaluation as part of the approval process.

Table 8.9 Flocculation/Sedimentation Basins 4 Design Criteria

Parameter Unit Typical Design

Criteria Flow Rate

11.3 mgd 12.5 mgd

Flocculation Basins

Total Detention Time min 20 – 40 31 26




Sedimentation

Detention Time hr 1.5 – 4 0.4 0.3

Overflow Rate (plate area) gpm/ft2 0.36 0.41 Notes: (1) G values taken from 2002 Facility Plan and 1996 drawings design criteria.


In general, floc settling in the basins has not been a concern.

Sludge removal from basins 1 – 3 while the plant is operating has led to performance issues with the sedimentation basin with settled water turbidities increasing and causing carry-over of solids to the filters. As a result, sludge removal has been limited to once per day when the plant is shut down.

This practice does not allow continuous operations without performance implications. In the future, if continuous operations are required to keep up with demand, sludge removal improvements will be needed.

Basin 4 has different sludge removal equipment that can be operated while the basin is in service, but the equipment requires significantly more maintenance. In general basin 4 performs better than basins 1 – 3 with settled water turbidity being lowest of all four basins.

Table 8.10 compares the settled water turbidities of the four basins.

Table 8.10 Sedimentation Basin Settled Water Turbidities

Basin Average (NTU) Median (NTU) Range(1) (NTU)

1 0.7 0.6 0.3 – 1.3

2(2) 0.7 0.8 0.4 – 1.6

3(2) 0.8 0.8 0.3 – 1.6

4 0.6 0.5 0.3 – 1.2 Notes: (1) Range is 5th percentile to 95th percentile. (2) Settled water turbidities for basins 2 and 3 only available after October 2011.


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Figure 8.8 shows monthly settled water turbidity averages for each basin.

Figure 8.8 Monthly Average Settled Water Turbidity by Basin

On average the basins achieved 91 percent turbidity removal. The sedimentation basins perform very well, even during periods of high raw water turbidity, with 95th percentile turbidities less than 2 NTU for all four basins.

Hydraulic Capacity

The measured and modeled WSEs in flocculation/sedimentation basins 1 – 3 upstream of the overflow are within 0.5 to 3 inches of the overflow elevation. The WSE is controlled by the crest elevation of the v-notch weirs in the sedimentation basins. The overflow elevation is between 249.75 and 249.92 feet, depending on the drawing set reviewed, and overflow concrete observed in the field was uneven. Field measurements were unable to confirm the overflow elevation for all three basins.

Modeled WSEs remain largely unchanged even at flow rates up to 25 mgd because of the large weir length. The modeled WSE for flocculation/sedimentation basins 1 – 3 is close to the overflow, and well below the overflow for flocculation/sedimentation basin 4. Overflowing is not a concern for either basin, even at flow rates up to 25 mgd.

Assuming the filter operating WSE remains 248 feet, there is not a concern with submergence of the effluent weirs in any sedimentation basin up to 25 mgd, but at 248.75 feet the WSE in the weir troughs would be within 4 inches of the weir crest and would inhibit free discharge from the weirs.

8.3.2.6 Filters

The plant has two sets of four filters (eight total filters) with different dimensions, filtration rates, and media configurations. Individual filter effluent turbidity and particle counts are monitored. Combined filter effluent turbidity is measured entering the chlorine contact basin.


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Filters are backwashed based on a typical filter run time, effluent turbidity (0.1 NTU), or maximum head loss (7.5 feet), measured by filter differential pressure. All eight filters are backwashed with both air and water.

Backwash water is supplied from clearwell 1 to the filters by vertical turbine backwash pumps. The backwash header is also connected to the high service pump station discharge header, which provides additional flow. In the event the backwash pumps are out of service, the high service pump station discharge header is capable of supplying the required backwash flow rates. Backwashing solely from this header must be done manually.

Filters 1 – 4 were originally tri-media anthracite filters but were changed to dual-media with sand and GAC in 2008. Filters 5 – 8 are a tri-media configuration with garnet, sand, and GAC. Each of the eight filters is divided into two equally sized filter cells with a central filter gullet.

Water from the sedimentation basins can flow to either set of filters with the flow split dependent on plant hydraulics, such as which filters are on-line, filter flow rates, and the flow split between the flocculation/sedimentation basins.

Settled water flowing to filters 1 – 4 combines into a filter influent flume that runs beneath the filter gallery in the building. Filter inlet valves then distribute flow to the four filters.

Filtered water exits each filter cell and combines into a single filter effluent pipe leaving each filter. Filter effluent flows through a flow control valve and the individual pipes from each filter discharge into a combined filter effluent flume that exits the building and transitions to a 30-inch pipe. Filter effluent flow rate is measured with separate flow meters for each filter. During filter-to-waste cycles, filter effluent flows to the lagoons. As part of the media replacement project in 2008, air scour was added to filters 1 – 4.

For filters 5 – 8, water going to the filters flows through a single filter influent pipe and is split into two pipes outside the filter building. One pipe feeds the filter inlet channel for filters 5 and 7, with the other feeding filters 6 and 8. Filter inlet valves then distribute flow to the filters that are on-line.

The filtered water from filters 5 – 8 exits each filter cell and combines into a single filter effluent pipe from each filter. A 36-inch combined filter effluent pipe exits the building and combines with the combined filter effluent pipe from filters 1 – 4 upstream of the chemical injection vault. During filter-to-waste cycles, filtered water is directed to the lagoons.


Filter design criteria are summarized in Table 8.11.

The total filtration capacity with all eight filters operating is 21.6 mgd. The firm filtration capacity with one of filters 5 – 8 out of service for backwashing or resting is 18.4 mgd.

Table 8.11 Filter Design Criteria

Criteria Unit Filter Nos. 1-4 Filter Nos. 5-8

Number of Filters no. 4 4

Area per Filter ft2 484 528

Total Area ft2 1,936 2,112

Filtration Rate gpm/ft2 3.37 4.0


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Criteria Unit Filter Nos. 1-4 Filter Nos. 5-8

Capacity per Filter MGD 2.35 3.04

Total Capacity MGD 9.4 12.2

Media Type Dual Media Tri-Media

Granular Activated Carbon (GAC)

Depth in 34 42

Effective Size mm 1.0-1.2 1.0-1.2

Uniformity Coefficient <1.5 <1.5

Apparent Density 0.56 0.56

Silica Sand

Depth in 9 9

Effective Size mm 0.45 0.45

Uniformity Coefficient <1.5 <1.5

Specific Gravity 2.6 2.6

Garnet Sand/Gravel

Depth in NA 6

Support Gravel

Depth in NA 18

L/d Ratio (Media Depth/Effective Size) 1,290 1,475

To achieve filtration capacities above 21.6 mgd would require a significant increase in the maximum filtration rates. Increasing the approved maximum filtration rate for the existing filters requires OHA approval and potentially requires long-term testing to demonstrate the effluent water quality continues to meet regulatory requirements. In Oregon, newly constructed filters can be approved for filtration rates of 6 gpm/ft2 without a pilot study.

The 2017 filter evaluation indicated that filters 5 – 8 could support filtration rates as high as 6 gpm/ft2 by replacing the underdrains and gravel media and adding additional GAC media. The Filter Performance and Media Evaluation (Carollo, 2018) provides additional detail on media replacement possibilities for filters 5 – 8. Filters 1 – 4 are smaller with a shallower media configuration that is not as conducive to increased filtration rates.

While higher filtration rates may be allowable for new filters or with modifications to the media for filters 5 – 8, they are not feasible for the existing filters due to hydraulic limitations. Table 8.12 summarizes the available head for solids loading for the existing filters operating at their current maximum filtration rates and if all filters were uprated evenly to 4.93 gpm/ft2, as used for the plant-wide hydraulic analysis at 25 mgd.


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Table 8.12 Available Head for Solids Loading at Existing and Future Maximum Flow Rates

Scenario

Filters 1 – 4 Filters 5 – 8

Filtration Rate

(gpm/ft2)

Individual Filter

Capacity (mgd)

Available Head for

Solids Accumulation

(ft)(1)

Filtration Rate

(gpm/ft2)

Individual Filter

Capacity (mgd)

Available Head for

Solids Accumulation

(ft)(1)

Existing(2) 3.37 2.35 5.3 – 5.7 4.0 3.05 3.5 – 4.0

Uprate All Filters Evenly(3)

4.93 3.44 2.6 – 3.3 4.93 3.75 1.6 – 2.1

Notes: (1) Range presented for water temperatures of 5 degrees Celsius to 20 degrees Celsius. (2) All 8 filters online and total capacity of 21.6 mgd. (3) Firm capacity of 25 mgd with one of filters 5 – 8 online. Filters 5 – 8 have greater capacity for these scenarios.

Available head for solids loading is limited, particularly for filters 5 – 8. Increasing the maximum filtration rate would further reduce available head for solids loading and would require frequent backwashing. Additional evaluation of media selection and piping configurations could identify ways to increase available head for solids loading but achieving higher filtration rates to meet the future capacity of 25 mgd is unlikely with the existing filters.

Table 8.13 summarizes filter backwash design criteria. The larger of the two backwash pumps can supply 6,500 gpm and is supplemented with flow from the high service pump discharge header. The backwash protocol for filters 1 – 4 has a maximum flow rate of around 5,000 gpm. The backwash protocol for filters 5 – 8 is to backwash at a maximum flow rate of 6,500 gpm in the winter and 7,200 gpm in the summer, or 24.6 and 27.3 gpm/ft2. These backwash rates are at the upper end of what is typically required to achieve necessary bed expansion.

Table 8.13 Filter Backwash Design Criteria

Criteria Unit Typical Design Criteria Filter Nos. 1-4 Filter Nos. 5-8

Air Scour Rate scfm/ft2 2 – 4 4.4 4

Backwash Rate gpm/ft2 16 – 24 20.7 27.3(1) Notes: (1) At maximum summer backwash flow rate of 7,200 gpm.

If the larger backwash pump alone were used to backwash filters 5 – 8 at 6,500 gpm, the backwash rate would be 24.6 gpm/ft2. Although sufficient pumping capacity is available from the larger pump to provide backwash rates within typical design criteria, the smaller backwash pump is unable to supply the desired backwash flow rates for filters 5 – 8.

In 2017, filter bed expansion was evaluated for filters 5 and 6 and showed the backwash flow rate could likely be reduced without diminished backwash performance. Different filter backwash flow rates were tested during Area Wide Optimization efforts in 2010 and 2011, but no changes were made as the current backwash protocol has worked well. Further analysis and testing of the filter backwash protocol could evaluate backwash performance at lower flow rates for further optimization.

There is not currently redundant capacity for the filter backwash system. The smaller backwash pump cannot provide desired backwash flow rates for filters 5 – 8. Also, no redundant supply of


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backwash water exists if clearwell 1 is offline; both the backwash pumps and the connection to high service pumps 1 – 4 discharge header rely on water from clearwell 1.

Air scour blowers are sized to provide 4.4 scfm/ft2 and 4 scfm/ft2 for filters 1 – 4 and filters 5 – 8, respectively. The air scour rates are within typical design criteria.


Filter backwashes are generally initiated based on filter run time or head loss, not effluent turbidity. Individual filter effluent turbidities were generally between 0.01 and 0.03 NTU.

Overall filter historical performance has been excellent, meeting the regulatory requirements for effluent turbidity. Combined filter effluent turbidity and finished water turbidity have consistently been between 0.02 and 0.04 NTU, with an average of 0.03 NTU. The maximum recorded finished water turbidity was 0.10 NTU, well below regulatory limits.

Filter performance was also evaluated for January – March 2018 and June 2018 – July 2018 by estimating unit filter run volumes (UFRVs) from backwash logs. UFRVs provide the volume of water filtered per square foot of media area during a filter run. This normalizes filter production and allows for performance to be evaluated across a spectrum of plant flows and water quality conditions. To estimate UFRVs, the following assumptions were made:

• One filter was out of service, and the seven remaining filters were in operation at all times.

• Flow rates were based on raw water flow rates recorded in backwash logs at the time of the backwash.

• Flow was evenly distributed among all seven filters, with the scale factor applied for filters 1 – 4.

Figure 8.9 shows the average estimated UFRV for each filter at Taylor WTP.

Figure 8.9 Taylor WTP Average Filter UFRVs (from 2018 filter backwash logs)


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UFRVs were typically between 5,500 and 6,500 gal/ft2 for the February and March period and between 6,000 and 8,000 gal/ft2 for the June and July period. These values were generally consistent with UFRVs estimated for filters 5 – 8 during the 2017 evaluations. As a comparison, top-performing filters at newer WTPs can achieve UFRVs of 10,000 gal/ft2.

Filter run times vary seasonally, from as low as 35 hours (2 – 4 backwashes per day) during the summer to 50 – 60 hours (1 filter backwash per day) during the winter. While there may be an opportunity to increase UFRVs with longer filter run times, filter operation appears to be highly efficient. Filter production efficiencies were estimated to be 97 to 98 percent for the current backwash protocols.

The 2017 performance evaluation identified the following key conclusions for filters 5 – 8 performance:

• The filters generally performed well. An observed degradation in the effective size of the GAC media could have been limiting floc penetration and the depth of the filter used for solids removal.

• Filter backwash protocol was effective for filters 5 – 8. Additional optimization of backwash protocol and flow rates could lessen backwash water requirements.

• A lack of pressure relief on the backwash header puts the underdrains at risk if a plug or flow restriction were to occur in the underdrains.

As discussed, there are redundancy concerns with the filter backwash system. The connection with the high service discharge pump header will only provide complete redundancy for the backwash pumps if pressure relief on the backwash supply piping is provided. No redundant backwash supply exists if clearwell 1 is out of service.

While the filters perform well, there have been numerous issues with leaking valves introducing air into the filter piping. The air relief valves have been changed, but air in the pipelines has caused false turbidity readings and disturbance of the filter media in filters 5 – 8. To-date, replacement of valves and troubleshooting efforts have been unable to resolve these issues.

Hydraulic Capacity

Table 8.14 summarizes available head for solids accumulation under current plant flow rates during different seasons.

Table 8.14 Available Head for Solids Accumulation for Current Plant Flow Rates

Flow Rate Filters 1 – 4 Available

Head for Solids Accumulation (ft)(1)

Filters 5 – 8 Available Head for Solids

Accumulation (ft)(1)

8 – 12 mgd (typical wintertime flows)(2) 7.6 – 8.7 6.5 – 7.7

18 – 20 mgd (summertime peak flows)(3)(4) 5.2 – 6.0 4.5 – 5.3 Notes: (1) Range presented to account for either 3 or 4 filters online. Modeled head losses are for 7 filters online. (2) Water temperature of 5 degrees Celsius assumed for modeled head loss. (3) Water temperature of 20 degrees Celsius assumed for modeled head loss. (4) All filters assumed to be online when operating at 20 mgd.


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At current plant flow rates, the available head for solids accumulation generally falls between the typical design values of 4 to 6 ft for shallow filters and well below the 10 to 12 ft for deep bed media filters. At high summertime flow rates, available head for solids accumulation in filters 5 – 8 is at the low end of this design range. The higher modeled head loss between filters 1 – 4 and filters 5 – 8 is because of smaller diameter effluent piping in filters 5 – 8.

During summertime high flows, the available head for solids accumulation is reduced by 30 percent requiring more frequent filter backwashing. Operating all eight filters at the same time lowers the flow rates through each filter creating additional available head for solids loading. Limited available head for solids accumulation is a hydraulic capacity limitation for the filters.

Figure 8.10 provides a schematic of the filter effluent and filter-to-waste piping for filters 5 – 8.

The hydraulics of the filter effluent and filter-to-waste piping are challenging when draining a filter for maintenance or prior to backwashing. Currently, the filter effluent flows to either the chlorine contact basin (CCB) or through the filter-to-waste piping to an air gap manhole.

When the CCB and filters 5 – 8 were first constructed, the water level in the CCB prevented the filters from being drained down for backwash. The stop log weir had to be lowered to allow the filters to drain for backwashing. Even with the lowered stop log weir, the hydraulics do not allow the filters to be drained quickly prior to backwashing.

Draining to the filter-to-waste piping does not allow the filters to be fully drained because the filter-to-waste piping must have an air gap. The discharge elevation of the air gap allows for draining to a minimum of 241.2 feet which is within the range of CCB operating levels. To drain the filters below these levels, a drain valve must be opened on the effluent piping downstream of the check valve, which discharges water directly onto the filter gallery floor.


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Figure 8.10 Filters 5 – 8 Effluent and Filter-to-Waste Piping Schematic

CHAPTER 8 – TAYLOR WATER TREATMENT PLANT | WATER DISTRIBUTION AND TREATMENT FACILITES MASTER PLAN | CITY OF CORVALLIS

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8.3.2.7 Disinfection

For disinfection, combined filter effluent flows from the filters to the CCB by gravity. The CCB is baffled and provides contact time for disinfection with free chlorine.

Sodium hypochlorite is injected upstream of the CCB in the chemical injection vault. Fluoride is added at the upstream end of the basin, and soda ash is added at the downstream end of the basin to adjust the pH and alkalinity of the finished water.

The stop log weir at the downstream end of the CCB maintains a minimum water depth and volume in the basin. The hydraulic profile for the CCB in the 1996 drawings shows the stop log weir was designed to maintain a basin depth of approximately 10.5 feet and a volume of 600,000 gallons. At the maximum depth of 12.5 feet, the CCB can hold up to 700,000 gallons. As discussed in Section 8.3.2.6, the stop log weir and water level in the CCB had to be lowered to allow filters 5 – 8 to be backwashed.

December 2019 measurements of WSEs indicate the stop log weir is at an elevation of 237 feet, resulting in a minimum water depth of 8 feet and a minimum volume of 450,000 gallons. The most recent tracer study, completed in 2007, determined a baffling factor of 0.97 for the CCB at a plant flow rate of 22 mgd. This baffling factor exceeds the typical baffling factors for well-baffled serpentine basins.

As a conventional treatment plant, Taylor WTP is required to achieve 3-log inactivation of Giardia and 4-log inactivation of viruses. Giardia inactivation governs the required contact time (CT) because it is more resistant to inactivation than viruses with chlorine. OAR requires the Taylor WTP to achieve a minimum of 0.5-log inactivation of Giardia and 2.0-log inactivation of virus in the CCB.

In the 2016 sanitary survey, OHA expressed the following concerns with the CCB overflow and drain piping:

• A lack of a flap valve or screen that protects the pipes from access by outside organisms. • A lack of an approved air gap on the discharge piping.


The CCB has a volume of 450,000 gallons, based on the current stop log weir elevation. This volume has historically been sufficient to meet CT requirements. Figure 8.11 shows the CCB volume required to meet CT requirements for a range of water temperatures assuming the following:

• Baffling factor of 0.97. • pH of 7.0 (OHA minimum pH requirement). • Chlorine residual of 1.0 mg/L (historical average from 2008 to 2017).


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Figure 8.11 Required Chlorine Contact Basin Volume to Achieve CT Requirements at Different Water Temperatures (pH = 7.0 and Chlorine Residual = 1.0 mg/L)

The existing CCB volume of 450,000 gallons is shown with a red line. At water temperatures 5 degrees Celsius and greater, the existing volume is sufficient to meet CT requirements for the current and future capacities of 21.6 mgd and 25 mgd. When water temperatures are coldest, existing volume does not appear adequate for the future 25 mgd, but the periods of coldest water in the winter do not coincide with periods of maximum water demands in the summer.

The above analysis only considers the volume of the CCB with the stop log weir at an elevation of 237, a water depth of 8 feet. Adjusting the stop log weir elevation to increase the water depth and volume would provide additional CT. However, it would also reduce solids accumulation capacity in the filters by an equivalent amount further restricting the existing limited solids accumulation capacity in the filters.

If the CT in the piping from the CCB and the CT in the clearwells are combined, meeting CT requirements appears achievable for temperatures as cold as 5 degrees Celsius.

Note, if the baffling factor for the CCB were to be more comparable to typical values for a well-baffled, serpentine basin with similar dimensions, between 0.7 and 0.8, the CT achieved through the CCB would be 20 to 30 percent lower. A corresponding increase in disinfection volume would be needed to achieve a similar CT value assuming chlorine residual is unchanged.


The plant has had no problems meeting disinfection requirements for 0.5-log inactivation of Giardia. The disinfection achieved was greater than 2.0 times the regulatory required amount 95 percent of the time.

Hydraulic Capacity

No operational hydraulic capacity concerns were identified for the CCB for flow rates up to 25 mgd. With the stop log weir at 237 feet, the WSE in the basin remains well below the overflow


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elevation at 25 mgd. The CCB is currently operated at depths well below the maximum operating depth, and overflow is not a concern.

While there are no specific hydraulic capacity concerns for the CCB, the hydraulics of the filters and the CCB pose multiple challenges for filter operation, as discussed in Section 8.3.2.6.

8.3.2.8 High Service Pumping and Clearwells

Disinfected water from the CCB flows to clearwell 1 and clearwell 2. Clearwell 1 was built during the original plant construction and is located below the floor of the original operations and filter building structure. Clearwell 2 and the additional high service pumping were added during the 1969 plant expansion. Clearwell 2 is located in a separate building that was constructed in 1991, beneath high service pumps 5 - 8.

The clearwells have a combined volume of 350,000 gallons. High service pumps are operated to maintain a consistent water level of 9 feet in the clearwells, a volume of 300,000 gallons.

Seven high service pumps deliver finished water from the clearwells to the distribution system. A list of suction sources and discharge connections for the clearwells is shown in Table 8.15.

Discharge pressures in the finished water pipelines generally range from 70 – 80 psi depending on distribution system reservoir levels and water demands. During high demand periods pressures can approach 90 psi.

Finished water turbidity, chlorine residual, fluoride residual, and pH are measured from a sample pulled from clearwell 2, with the ability to manually sample from the discharge header for high service pumps 5 – 8 as well.

In the 2016 sanitary survey, OHA expressed the following concerns with the overflow and drain piping for the clearwells:

• A lack of a flap valve or screen that protects from access by outside organisms for clearwell 1.

• A lack of an approved air gap on the discharge of overflow/drain piping from clearwells 1 and 2.


Table 8.15 summarizes the design capacities of the high service pumps.

Table 8.15 High Service Pump Capacities and Configuration

Pump Capacity Source Discharge

Pump 1 2.7 mgd at 210 ft TDH Clearwell 1 20” Main


Pump 3(1) 4.3 mgd at 160 ft TDH Clearwell 1 20” Main




Pump 7 Out of Service Clearwell 2 36” Main

Pump 8(1) 7.2 mgd at 220 ft TDH Clearwell 2 36” Main Notes: (1) Pumps 3 and 8 are equipped with VFDs.


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Figure 8.12 and Figure 8.13 show the combined capacity of high service pumps 1 – 4 and pumps 5 – 8.

Figure 8.12 High Service Pumps 1 – 4 Combined Pump Curve

Figure 8.13 High Service Pumps 5 – 8 Combined Pump Curve


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The minimum and maximum system head curves were developed using the following assumptions:

• High service pumps continue to perform according to their original pump curves. • Clearwell level operating range of 8 to 9 feet. • Distribution system pressures control pump discharge pressures. The anticipated

operating discharge pressure range for the pumps is 65 to 95 psi (discharge pressure can be monitored on discharge piping from high service pumps 1 – 4 and pumps 5 – 8).

• The crossover valve between the 20-inch and 36-inch discharge pipes is closed. The high service pumps 1 – 4 discharge to the distribution system only through the 20-inch main, and the high service pumps 5 – 8 discharge only through the 36-inch main.

• The maximum system head curve coincides with the minimum clearwell level and the maximum distribution system pressure. The minimum system head curve coincides with the maximum clearwell level and the minimum distribution system pressure.

• The maximum and minimum system head curves define a wide range of potential operating points; this range may be outside the pump manufacturer’s recommended operating range.

Table 8.16 presents the combined total capacity and the firm capacity (capacity with the largest pump out of service) for pumps 1 – 4 and pumps 5 – 8.

Table 8.16 High Service Pumps Combined Capacity

Pumps Total Capacity Range (mgd)(1) Firm Capacity Range (mgd)

1 – 4 12.6 – 17.0 8.1 – 11.6

5 – 8(2) 22.6 – 28.6 13.3 – 17.1

Total 35.2 – 45.6 21.4 – 28.7 Notes: (1) Capacity range represents capacity of pumps alone. More detailed hydraulic evaluation should be performed to confirm

pump and clearwell hydraulics are in compliance with Hydraulic Institute standards. (2) Pump 7 is out of service and is not included in total or firm capacity for pumps 5 – 8.

The total combined capacity range for high service pumps 1 – 8 exceeds the future maximum capacity of 25 mgd. Depending on pressures in the distribution system, the firm capacity may drop below 25 mgd. For additional firm capacity, a new high service pump 7 could be installed.


Of the eight high service pumps, only pumps 3 and 8 have VFDs allowing variable pumping rates. Replacing pump 7 that is currently out of service with a new pump and VFD would provide additional operational flexibility.

High service pump 3 was installed in 2018 and has a rated total dynamic head of 160 feet, well below the rated head for the other high service pumps. During the winter, when lower system demands reduce discharge pressures leaving Taylor WTP, the lower rated head does not pose operational concerns. However, during the summer, pressures leaving the plant can exceed 80 psi and the pump cannot operate at its rated capacity.


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Hydraulic Capacity

Table 8.17 compares velocities in the finished water pipelines with typical design values for a range of flow rates and flow splits.

Table 8.17 High Service Pumping Discharge Velocities

Total Flow Rate and Flow Split Between Clearwell 1 and Clearwell 2

Typical Design Criteria

(ft/s)

Velocity in 20-inch Finished Water from

Clearwell 1 (ft/s)

Velocity in 36-inch Finished Water form

Clearwell 2 (ft/s)

21.6 mgd (33/67 flow split)

5

5.0 3.2

21.6 mgd (50/50 flow split) 7.7 2.4

21.6 mgd (clearwell 2 offline) 15.3

21.6 mgd (clearwell 1 offline) 4.7

25 mgd (50/50 flow split) 8.9 2.7

25 mgd (clearwell 2 offline) 17.7

25 mgd (clearwell 1 offline) 5.5

Velocities in the 20-inch finished water pipeline from clearwell 1 are below 5 ft/s for current maximum plant flow rates, as long as the percentage of flow being pumped from clearwell 1 is less than 33 percent. If clearwell 2 were taken offline during high flows, velocities would significantly exceed 5 ft/s, resulting in much greater head loss.

Upsizing the clearwell 1 pipe would be required to operate the plant at flow rates higher than 12.5 mgd with clearwell 2 and high service pumps 5 – 8 offline for an extended period of time. The existing finished water pipe size for clearwell 2 appears to have sufficient hydraulic capacity for future maximum plant flow rates.

8.3.2.9 Solids Handling

Taylor WTP has three identically sized concrete lagoons that provide storage for filter-to-waste water, backwash water, and sedimentation basin sludge. Each lagoon has a projected surface area of 7,200 ft2 (120 feet x 60 feet) and a total depth of 8 feet.

The concrete lagoons replaced the plant’s previous two earthen lagoons. Two of the concrete lagoons were constructed in the 1996 expansion, and the third was added in 2004.

The concrete lagoons have an influent distribution structure with gates that allow for isolating individual lagoons. The WSE in the lagoons is controlled by aluminum plate gates.

The lagoon floors are sloped to a sump along the wall at the lagoon’s halfway point. The sumps are equipped with submersible sludge pumps that can pump sludge to a sludge fill station or between the lagoons for sludge consolidation. Sludge pumps can be used to pump sludge between lagoons 1 and 2 and into lagoon 2 from lagoon 3.

The concrete lagoons are filled with backwash water from the filters, filter-to-waste water, and sludge from the sedimentation basins. Water is decanted to the Willamette River. To reduce chlorine residual prior to discharge to the river, calcium thiosulfate and carrier water are sprayed from a spray bar at the discharge of each lagoon. Each lagoon has a level sensor to trigger calcium thiosulfate spraying when water is being decanted.


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Filter aid polymer is pumped to the lagoons to improve sludge thickening. A chemical metering pump automatically feeds the polymer when the sludge removal system in flocculation/sedimentation basin 4 or a filter backwash cycle is running.

During normal operation, all three lagoons are in service and decanting to the river. When a sufficient amount of sludge has built up in lagoon 2, it is taken offline for a few weeks to thicken and consolidate sludge as much as possible.

After this initial sludge thickening in lagoon 2, lagoons 1 and 3 are taken offline periodically (for no more than a day at a time) and sludge is pumped to lagoon 2. Eventually, the sludge depth in lagoon 2 reaches a point where turbidity carry-over to the river is a concern, and the lagoon is taken offline. When lagoon 2 is full and offline, and sludge begins to build up in lagoons 1 and 3, plans are made for sludge removal.

The City hauls sludge in sludge tanker trucks. Sludge is typically removed twice a year, once in May/June and once in October/November. Hauling is typically coordinated with bio-solids hauling from the City’s wastewater reclamation plant; sludge is typically hauled before and after the window for bio-solids hauling. In total, sludge removal takes between 4 and 6 weeks annually.


Based on historical plant flow, raw water turbidities, and chemical doses the estimated solids production rate was 163 dry lbs/MG. The higher raw water turbidities and higher alum doses at the Taylor WTP result in an estimated solids production rate over 2.5 times greater than at the Rock Creek WTP.

At the average (2008 – 2017) production of 5.2 mgd estimated annual solids loading rate to the lagoons was 14.3 dry lb/ft2.

As the lagoons are operated for thickening only, the lagoon solids loading rates were compared to the typical loading rate for gravity thickening of alum sludge, 10 lb/ft2/day. Based on the average solids production of 163 dry lbs/MG and an average flow rate of 5.2 mgd, the existing three lagoons are loaded at a rate of 0.04 lb/ft2/day, well below the typical design value for gravity thickening. Sufficient surface area is available with the existing lagoons for solids thickening.

Table 8.18 summarizes the solids and sludge production for current and future flow rates, assuming the sludge is 3 percent solids by weight.

Table 8.18 Solids Handling Capacity Evaluation

Percent Solids in Lagoons

Average Flow Rate (mgd)

Annual Solids Production (dry tons)

Annual Sludge Production (gal)

Existing

3% 5.2 310,000 1,214,000

Future

3% 8.5 310,000 1,984,000

At a future average flow rate of 8.5 mgd, annual solids production is anticipated to increase by 60 percent. If solids continue to be removed twice per year and the sludge remains around 3 percent solids by weight, increased sludge depth may lead to solids carry-over and potential


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discharge permit violations. Additional lagoon volume or more frequent sludge removal will likely be required to continue the existing operational protocols for the lagoons.


In general, the lagoons perform well, but there are multiple operational challenges:

• The low percent solids of the thickened sludge in the lagoons drives the hauling requirements. Hauling currently takes 4 to 6 weeks per year and requires significant City staff time, which will increase as solids production increases.

• The process of consolidating sludge from lagoons 1 and 3 into lagoon 2 is time consuming for plant staff.

• Once lagoon 2 has been taken offline, transferring sludge from either lagoon 1 or 3 leaves only lagoon in service. Operating with only one lagoon online is challenging, particularly during the summer when backwash frequency increases.

• Backwashing of new installed GAC media in the filters sends GAC fines to the lagoons that are difficult to settle and raise the pH of decant from the lagoons, both of which can create compliance challenges with existing discharge permit limits for the lagoons. Plant staff currently dose alum to the backwash water to mitigate these issues.

Adding a fourth lagoon would have several benefits, improving operational flexibility and allowing solids consolidation in two lagoons at a time. The additional storage would allow greater flexibility to manage the GAC fines and allow filters to be brought back in service earlier.

Further study is recommended to identify opportunities to optimize existing operations and reduce hauling requirements to address some of these existing operational challenges.

8.3.2.10 Chemical Facilities

Taylor WTP has chemical storage and feed equipment for the following liquid and dry treatment chemicals:

• Aluminum sulfate (alum). • Sodium hypochlorite. • Soda ash. • Filter aid polymer. • Sodium silicofluoride. • Calcium thiosulfate.

Alum and sodium hypochlorite bulk storage tanks and feed equipment are located in the bulk chemical building. A chemical fill station with spill containment for alum and sodium hypochlorite is located on the north face of the bulk chemical building.

Soda ash is stored in a 60-ton silo at the western boundary of the site near the power distribution equipment. Filter aid polymer and sodium silicofluoride are delivered and stored in 50-lb bags in the original operations building. Calcium thiosulfate is delivered on-site in 55-gallon drums. One drum is stored in a shed at the discharge of the lagoons with additional drums stored on a pallet in the bulk chemical building.

The plant also has storage and feed equipment for liquid potassium permanganate, but this system is not used. The potassium permanganate system was installed in response to taste and odor events. Sodium permanganate replaced potassium permanganate, but it was not effective.


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Existing chemical facilities were evaluated against the following typical design chemical storage criteria for current and future demands:

• Fourteen days of storage at average dose and maximum flow. • Fourteen days of storage at maximum dose and average flow. • Thirty days of storage at average dose and average flow.

Storage evaluations for existing production were based on the following:

• A current average day flow of 5.2 mgd. • A current maximum day flow of 21.6 mgd. • A future average day flow of 8.5 mgd. • A future maximum day flow of 25 mgd.

Aluminum Sulfate (Coagulant)

Alum is used to coagulate suspended solids and dissolved organic carbon in the raw water. The alum system consists of the following:

• Two 5,000-gallon polyethylene tanks in the bulk chemical building, storing 49 percent liquid alum solution.

• Two diaphragm metering pumps to dose alum from the storage tanks to rapid mix.

The metering pump speed is automatically controlled for flow-pacing based on the raw water flow rate. Adjustments are made to the target alum dose based on the streaming current, pH, and pilot filter performance.

Based on daily plant data from 2008 to 2017, alum doses (as dry alum) are:

• Fifth percentile: 15.6 mg/L. • Average: 28.3 mg/L. • Ninety-fifth percentile: 50.4 mg/L.

Table 8.19 summarizes the evaluation of existing alum storage capacity under multiple conditions for current and future plant demands. While the existing alum storage does not meet the goal of 14 days storage at maximum plant flow and average dose, the plant does not typically operate at flow rates higher than 20 mgd continuously, and there are no concerns meeting the chemical storage goals for current operation.

Table 8.19 Alum Storage Capacity

Condition Storage Goal Current(1) Future(2)

Average Flow and Average Dose(3) 30 days 44 days 27 days

Average Flow and Maximum Dose(3)(4) 14 days 25 days 15 days

Maximum Flow and Average Dose(3) 14 days 11 days 9 days Notes: (1) Current raw water average flow of 5.2 mgd is from the Taylor WTP’s daily operating data (2008 to 2017). Current

maximum flow assumed to be 21.6 mgd, total plant filtration capacity with all filters on-line. (2) Future average flow assumed to be 8.5 mgd. Assumes the Rock Creek WTP will produce 5 mgd and the Taylor WTP will

meet the remainder of the 13.5 mgd ADD. Future maximum flow rate assumed to be 25 mgd. Assumes the Rock Creek WTP will produce 5 mgd and the Taylor WTP will meet the remainder of the 30 mgd MDD.

(3) Average and maximum chemical doses were calculated from daily plant data (2008 to 2017). (4) Maximum chemical dose was calculated as the 95th percentile.


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For expansion to 25 mgd, additional storage is needed. The existing storage is insufficient to meet the 30-day goal for average flow and average dose and the 14-day goal for maximum flow and average dose.

No known performance issues exist for the alum system.

Soda Ash (pH Adjustment)

Soda ash is used for pH adjustment and alkalinity addition to the raw water and finished water. Up to 60 tons of bulk soda ash can be stored in an on-site silo. Separate feed systems are located in the bottom of the silo, one for pre-soda ash and one for post-soda ash, with each feed system consisting of a single dry hopper, feeder, mixing tank, and centrifugal pump.

Pre-soda ash is injected to the raw water pipe in the raw water flow metering vault. Post-soda ash is added at the end of the chlorine contact basin. The dose is adjusted to meet the desired pH, which sets the feeder speed.

As shown in Figure 8.5, pre-soda was used consistently between November and May for coagulation optimization. These months coincide with the highest average alum doses. Since alum consumes alkalinity and lowers the pH, more soda ash is needed to counteract the effects of the higher alum doses. During good water quality months (June through October), pre-soda ash was used sparsely or not at all. When pre-soda ash was used consistently, doses ranged from 7.8 mg/L to 41.6 mg/L, with an average of 23.6 mg/L.

Post-soda ash has been used consistently year-round to meet the minimum finished water pH required by OHA. Doses were highest when pre-soda ash was not used daily (June – October), with typical doses ranging from 10 to 12 mg/L. For the entire period of available data between 2008 and 2017, doses ranged from 5.2 mg/L to 16.8 mg/L, with an average of 9.8 mg/L.

As discussed in Chapter 7 and Section 8.2.3, additional alkalinity may be required to meet OHA minimum alkalinity requirements. This could increase soda ash usage, but this potential change was not quantified for this plan.

Table 8.20 shows the soda ash storage required to meet typical storage goals under current and future plant demands. The soda ash storage evaluation considers the storage requirements for months when both pre- and post-soda ash are used consistently (November through May). Combined soda ash doses for these months were between 15.9 mg/L and 50.8 mg/L, with an average of 31.9 mg/L. During the summer when pre-soda ash is used less frequently, less on-site storage will be required.

Table 8.20 Soda Ash Storage Capacity


Average Flow and Average Dose(3) 30 days 87 days 53 days Average Flow and Maximum Dose(3)(4) 14 days 54 days 33 days Maximum Flow and Average Dose(3) 14 days 21 days 18 days

Notes: (1) Current raw water average flow of 5.2 mgd is from Taylor WTP’s daily operating data (2008 to 2017). Current maximum

flow assumed to be 21.6 mgd, total plant filtration capacity with all filters on-line. (2) Future average flow assumed to be 8.5 mgd. Assumes the Rock Creek WTP will produce 5 mgd and the Taylor WTP will


(3) Average and maximum chemical doses calculated from daily plant data (2008 to 2017). Chemical dose data from November through May was used for average and maximum doses.

(4) Maximum chemical dose calculated as the 95th percentile of combined soda ash doses for November to May.


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The existing chemical storage is sufficient to meet chemical storage goals even with expanded future plant capacity.

However, the current soda ash system presents multiple performance and operation concerns:

• When water temperatures are low, dissolving soda ash into solution has been challenging.

• The pumps and piping require frequent maintenance and cleaning to prevent clogging. • The length of pre-soda ash piping from silo to the distant dosing point presents

additional challenges for maintenance. • The soda ash solution mixing tank must be turned over to effectively change the dose,

creating a lag time during dosing changes.

Sodium Hypochlorite (Disinfection)

Sodium hypochlorite is used as a pre-oxidant upstream of filtration (pre-chlorination) and for free chlorine disinfection following filtration (post-chlorination). For pre-chlorination, sodium hypochlorite is added to the raw water at the rapid mix pump, and to the combined filter effluent at the chemical injection vault prior to entering the chlorine contact basin for post-chlorination.

Sodium hypochlorite is delivered to the plant as 12.5 percent solution and is stored in two 5,000-gallon storage tanks. There are three diaphragm metering pumps, all of which can be configured to pump sodium hypochlorite for pre-chlorination or post-chlorination.

To control algae growth in the flocculation/sedimentation basins and the filters, pre-chlorine has typically been adjusted to maintain a maximum chlorine residual of 0.1 mg/L at the filters. Post chlorine has been dosed to achieve a finished water chlorine residual of 0.9 mg/L to 1.2 mg/L.

Combined sodium hypochlorite doses as chlorine have ranged from 1.8 mg/L to 3.3 mg/L, with an average of 2.5 mg/L. Sodium hypochlorite metering pumps can be flow-paced to provide a desired chemical dose. Chlorine residual is continuously monitored at rapid mix, in the chlorine contact basin influent, in the chlorine contact basin effluent, and in the finished water leaving clearwell 2 prior to entering the distribution system.

The sodium hypochlorite system has no known performance issues.

Table 8.21 summarizes the evaluation of the existing sodium hypochlorite storage capacity under multiple conditions for current and future plant demands. The existing sodium hypochlorite storage volume of 10,000 gallons is adequate to meet typical chemical storage goals for current plant operation and anticipated future plant capacity.

Table 8.21 Sodium Hypochlorite Storage Capacity


Average Flow and Average Dose(3) 30 days 91 days 55 days Average Flow and Maximum Dose(3)(4) 14 days 70 days 43 days Maximum Flow and Average Dose(3) 14 days 22 days 19 days

Notes: (1) Current raw water average flow of 5.2 mgd is from the Taylor WTP’s daily operating data (2008 to 2017). Current

maximum flow assumed to be 21.6 mgd, total plant filtration capacity with all filters on-line. (2) Future average flow assumed to be 8.5 mgd. Assumes the Rock Creek WTP will produce 5 mgd and the Taylor WTP will




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Filter Aid Polymer

Filter aid polymer is added at the upstream end of the effluent weirs for sedimentation basins 1 – 3 and to the combined discharge channel for sedimentation basin 4 to improve filter performance. Polymer is also pumped to the sludge lagoons for solids thickening.

Dry nonionic polymer is stored in 50-lb bags in the polymer room adjacent to the polymer mixing unit. The dry polymer is batched into a dilute solution using a dry chemical feed system that consists of a dry hopper, mixing tank, and aging tank.

Two diaphragm metering pumps pump the polymer solution to the sedimentation basin feed points. A third dosing pump pumps polymer to the sludge lagoons during sludge removal from sedimentation basin 4 and during filter backwashes.

The pumps are flow-paced and adjusted to provide a desired dose based on observations of filter head loss, filter effluent turbidity, and filter effluent particle counts. When called to run, the dosing pump for the lagoons runs at a constant speed set by plant staff.

Filter aid polymer doses have been very low:

• Fifth percentile: 0.004 mg/L. • Average: 0.016 mg/L. • Ninety-fifth percentile: 0.027 mg/L.

No known performance issues were identified for the filter aid polymer system.

Table 8.22 summarizes the evaluation of the required dry polymer storage capacity. For the low polymer doses, storage requirements are minimal; the existing plant currently has sufficient storage space for the polymer.

Table 8.22 Filter Aid Polymer Storage Capacity

Condition Storage Goal Required Current

Storage(1) Required Future

Storage(2)

Average Flow and Average Dose(3) 30 days 10 lbs / 0.2 bags 16 lbs / 0.3 bags

Average Flow and Maximum Dose(3)(4) 14 days 16 lbs / 0.3 bags 27 lbs / 0.5 bags

Maximum Flow and Average Dose(3) 14 days 40 lbs / 0.8 bags 46 lbs / 0.9 bags Notes: (1) Current raw water average flow of 5.2 mgd is from Taylor WTP’s daily operating data (2008 to 2017). Current maximum




Sodium Silicofluoride

Sodium silicofluoride is added at the upstream end of the chlorine contact basin to maintain a fluoride residual in the finished water for dental health. A volumetric feeder adds dry silicofluoride via a stream of carrier water.

Since 2011, the average fluoride residual (analogous to dose for fluoride) has been 0.7 mg/L, consistent with the US Public Health Service’s recommended fluoride level for community water supplies.


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No known performance issues were identified for the sodium silicofluoride system, but the storage area is very open and fluoride dust is hard to contain. Enclosing the fluoride system and chemical storage to contain the dust would be beneficial.

Table 8.23 summarizes the evaluation of the dry sodium silicofluoride storage capacity. Typically, three to four pallets (150 to 200 bags) of sodium silicofluoride are stored on-site, which is sufficient to meet current and future storage needs.

Table 8.23 Sodium Silicofluoride Storage Capacity

Condition Storage Goal Required Current

Storage(1) Required Future

Storage(2)

Average Flow and Average Dose(3) 30 days 448 lbs / 15 bags 733 lbs / 24 bags

Maximum Flow and Average Dose(3) 14 days 1,860 lbs / 61 bags 2,155 lbs / 71 bags Notes: (1) Current raw water average flow of 5.2 mgd is from Taylor WTP’s daily operating data (2008 to 2017). Current maximum



(3) Average chemical doses was calculated from daily plant data (2008 to 2017).

Calcium Thiosulfate (Dechlorination)

Calcium thiosulfate neutralizes any remaining chlorine residual in the decant liquid from the lagoons. Liquid twenty four percent calcium thiosulfate is stored in a 55-gallon drum in a shed at the east side of the lagoons.

Prior to discharge to the Willamette River, one peristaltic pump doses calcium thiosulfate and carrier water to spray bars at the discharge of each of the lagoons. A chlorine residual analyzer located in the shed detects any remaining chlorine residual going to the Willamette River. No performance issues were identified with the calcium thiosulfate system.

Average calcium thiosulfate dose is not monitored in daily plant data. The total weight of calcium thiosulfate solution is recorded when the drum is changed out.

The estimated daily calcium thiosulfate usage was 14.7 lb/days (as bulk solution), which would require 2 drums of calcium thiosulfate to meet chemical storage goals. Currently, storage of two to six additional drums is maintained in the bulk chemical building. Additional calcium thiosulfate storage space is not anticipated with increased plant production.

8.3.3 Operational Testing and Performance Optimization

Operational testing was conducted at the Taylor WTP in December 2019 to evaluate opportunities to optimize operational performance and chemical usage. Testing involved:

• Coagulant/polymer testing. • Hydraulic and process capacity confirmation. • Automation review.

Complete operational testing results are provided in Appendix N and summarized in this section. Note, results from the hydraulic and process capacity confirmation are discussed in Section 8.3.2. Results of the coagulant/polymer testing and automation review are summarized below.


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8.3.3.1 Coagulant/Polymer Testing

Coagulant/polymer testing consisted of jar tests to investigate the following:

• Aluminum chlorohydrate (ACH) as an alternative primary coagulant. • The impact of coagulant aid polymer addition. • The impact of flocculation aid polymer addition.

Prior to jar testing, zeta potential measurements were used to characterize the different coagulants and polymers used for testing. Based on the results of the zeta potential evaluations, coagulant and polymer doses were selected for jar testing. Jar testing was then used to evaluate the impacts of different coagulants and polymers on settleability for the Taylor WTP raw water.

Alternative Coagulant Testing

ACH was evaluated as an alternative primary coagulant because it provides more charge neutralization than alum. No discernible difference was observed between jars tested with alum or ACH without polymer addition. Jar tests with either coagulant alone did not lower settled water turbidities.

While there was no observed performance benefit associated with the use of ACH, switching to ACH could provide savings in chemical costs predominantly from a reduction in the use of soda ash for alkalinity adjustment. However, switching from alum to ACH would also require additional Lead and Copper Rule compliance monitoring which would lessen the short-term cost savings from switching to ACH.

Coagulation Aid Polymer Testing

Cationic polymer addition as a coagulant aid improved settling performance with both coagulants tested. With 1 mg/L of coagulant aid polymer, alum doses less than half the dose at the time of testing produced the most effective settling performance. The costs of adding an additional coagulant aid polymer feed system and dosing cationic polymer at 1 mg/L were estimated to increase treatment costs even with the observed reduction in alum dose.

Nonionic polymer provided no observed improvements in settled water turbidity as a coagulant aid.

Flocculation Aid Polymer Testing

The addition of a flocculation aid polymer improved settleability, most noticeably when used in conjunction with ACH as a primary coagulant. For the water quality at the time of testing, an anionic flocculation aid polymer in conjunction with ACH produced the lowest settled water turbidity of all tests. Coagulant doses were not reduced with the addition of flocculation aid polymer and no coagulant cost savings were estimated. The costs of adding a separate flocculation aid polymer feed system were anticipated to increase treatment costs at the Taylor WTP.

8.3.3.2 Automation Opportunities

The majority of the automation opportunities identified were associated with improved monitoring and control of the residuals handling system and chemical systems. Select automation opportunities are listed below with the full list provided in Appendix N:

• Install actuators on sludge blowdown valves for flocculation/sedimentation basins 1 -3 to allow for automated sludge blowdown.


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• Install online pH and chlorine residual analyzer on supernatant from the lagoons. • Improve monitoring and control of lagoon supernatant quality during GAC installation

and backwashing. • Update soda ash and sodium hypochlorite feed system controls to trim chemical dose

setpoints based to target a pH or chlorine residual setpoint.

8.4 Existing Infrastructure Condition Assessment

This section summarizes the capital improvements recommended to address condition deficiencies identified at the Taylor WTP. Condition-related capital improvements were broken into four categories:

• Repair and replacement. • Seismic and life safety. • Resiliency and redundancy. • Energy efficiency.

8.4.1 Repair and Replacement

Repair and replacement improvements cover the costs to maintain, repair, rehabilitate, and replace equipment and infrastructure at the plant and ensure continued viability of the treatment processes.

8.4.1.1 Annual Repair and Replacement Program

Annual repair and replacement costs were developed using the City’s existing asset management database, which contains information for all assets at the Taylor WTP including:

• Installation date. • Useful life. • Replacement cost.

Repair and replacement costs were developed for inclusion in the 20-year capital improvement plan (CIP), detailed further in Chapter 9. The costs address only those assets whose useful life will expire within the period of the 20-year CIP, from 2022 to 2041. The costs to replace assets were assigned to the following three time periods, based on when the assets are expected to exceed their useful life:

• Near-term (2022 to 2026). • Mid-term (2027 to 2036). • Long-term (2037 to 2041).

Table 8.24 summarizes the estimated annual repair and replacement costs associated with each time period. Note that the first period from 2022 to 2026 includes costs for assets that will exceed their useful life prior to 2022 and have not yet been repaired or replaced.


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Table 8.24 Taylor WTP Annual Repair and Replacement Program Costs (Project T-1)

Time Period Total Repair and Replacement

Cost ($) Annual Repair and

Replacement Cost ($)(1)

2022 – 2026 $4,982,0000(2) $996,400

2027 – 2036 $1,789,000 $178,900

2037 – 2041 $424,000 $84,800

Total $7,195,000 $359,750 Notes: (1) All costs are from the City’s asset management database as of December 2018. Costs are not escalated and are shown in

present-day dollars. (2) Cost includes $2,754,000 backlog of items that exceed their useful life prior to 2022 and $2,228,000 for items exceeding

their useful life between 2022 and 2026.

8.4.1.2 Additional Repair and Replacement Projects

Table 8.25 summarizes additional repair and replacement projects identified to address condition-related deficiencies which are not reflected in the City’s asset management database. Appendix S further details each project.

Table 8.25 Taylor WTP Additional Repair and Replacement Project Costs

Project Number

Name Description Cost ($)(1)

T-2 Concrete Repairs

in Clearwell 1

Repair locations in clearwell 1 where concrete has broken loose and exposed reinforcing steel. Concrete repairs must cure for four weeks, requiring clearwell 1 to be taken off-line for

four to six weeks. A redundant backwash supply must be

established before proceeding with this project.

$9,000 (per repair

location)

T-3 Annual GAC Filter

Media Replacement

Annually replace GAC filter media in two filters. $150,000

(annual cost)

T-4 Filters 5 – 8

Influent Valve Replacement

Replace the existing electric actuators with pneumatic actuators comparable to those used

for the majority of the plant’s filter valves. $90,000

Notes: (1) Project costs in 2020 dollars.

8.4.2 Seismic and Life Safety

As detailed in Chapter 3, the City selected a magnitude 9.0 Cascadia Subduction Zone (CSZ) earthquake as the designated seismic hazard for this planning effort. Chapter 3 also summarizes the level of service goals and performance objectives that the City set for water system infrastructure if it does suffer this seismic event. Detailed geotechnical and structural seismic evaluations were conducted on the intake structure, plant site, and plant structures to evaluate their seismic performance and identify any deficiencies that would prevent achieving the established level of service goals.


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8.4.2.1 Geotechnical Seismic Hazard Summary

A geotechnical seismic hazards evaluation was conducted consisting of field explorations with five exploratory borings, laboratory testing, a data review, and a seismic hazard analysis. The evaluation assessed the risk of strong ground shaking, liquefaction settlement, lateral spreading, and seismic-induced landslides on plant infrastructure. Appendix I details the complete geotechnical seismic hazards evaluation.

The evaluation found the majority of the plant site is stable with a low risk of lateral spreading or liquefaction. The only facilities potentially at risk for these hazards are those close to the riverbank, which include the lagoons and the intake structure:

• There is a high risk of significant ground deformation (multiple feet) due to lateral spreading that could extend up to 200 feet from the intake structure.

• Additionally, there is a high risk of seismic landslides and large ground deformation due to liquefaction-induced loss of strength in the silty sand present in the vicinity of the riverbank and intake structure.

Seismic resilience improvements to the intake structure are discussed further in Section 8.5.2; no other specific mitigation measures to existing facilities are recommended to address geotechnical seismic hazards at this time.

8.4.2.2 Seismic and Life Safety Evaluation

The Taylor WTP’s seismic and life safety evaluations assessed seismic performance vulnerabilities and deficiencies in existing structures, structure connections, equipment and tank anchors, and other ancillary non-structural components. The seismic evaluations used the following performance objectives:

• Immediate occupancy for structural performance. • Position retention for non-structural performance.

The plant building structures were evaluated using American Society of Civil Engineers (ASCE) 41-17 while water-bearing structures were evaluated using American Concrete Institute (ACI) 350.3-06. Appendix K presents the complete seismic and life safety evaluations including vulnerabilities, mitigation measures, and estimated costs.

The evaluation identified the following structural vulnerabilities in the plant:

• Insufficient shear capacity in the second-floor diaphragm of the operations building dry chemical storage room and in the roof diaphragm of the clearwell 2 building.

• Drag connections in the roof diaphragms of the operations building high service pump room and the bulk chemical building lack the capacity to transfer roof seismic loads.

• Insufficient roof deck welds for the filters 5 – 8 building. • Sloshing over the tops of the perimeter walls of the flocculation/sedimentation basins. • Insufficient flexural capacity for the baffle walls in flocculation/sedimentation basin 4. • Lack of anchorage to the intake structure and to the bridge abutment for the access

bridge to the intake structure.

The following non-structural vulnerabilities were identified:

• Insufficient anchorage for the electrical equipment in the operations building, bulk chemical building, filters 5–8 building, and electrical buildings for the raw water pumps.


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• Lack of lateral pipe bracing in the bulk chemical building, filter galleries, and clearwell 2 building.

• Lack of flexible couplings on fire sprinkler and natural gas piping in the operations building and bulk chemical building.

• Lack of flexible joints on the raw water pipes on the intake structure access bridge. • Lack of bracing on the vertical suction pipe columns inside the intake structure.

8.4.2.3 Seismic and Life Safety Projects

Table 8.26 summarizes costs to mitigate the identified structural and non-structural seismic hazards. Mitigation efforts to these vulnerabilities for core treatment processes are combined into a single project, T-5. Mitigation efforts for the intake are combined into a single project, T-24.

Table 8.26 Taylor WTP Seismic and Life Safety Projects

Project Number Component Cost

T-5 Structural Seismic Vulnerability Mitigations $696,000

T-5 Non-structural Seismic Vulnerability Mitigations $195,000

T-24 Intake Structural Seismic Vulnerability Mitigations $15,000

T-24 Intake Non-structural Seismic Vulnerability Mitigations $250,000

8.4.3 Resiliency and Redundancy

The Dependencies, Emergency Response Planning, and Continuity of Operations Planning TM, provided in Appendix V, and the Seismic Resiliency and Redundancy TM, provided in Appendix L, identified systemwide deficiencies that could impact the City’s ability to meet the established LOS goals. See Chapter 7 for a summary of the recommendations and systemwide resilience projects to be incorporated into the CIP.

These evaluations identified a lack of backup power as a significant resiliency and redundancy deficiency for the Taylor WTP. The plant currently has a 150-kW generator that can operate lights and computers, but no process equipment. In the event of a power failure post-earthquake, the plant cannot supply water and the City will be unable to meet the desired 8.5 mgd of supply capacity.

To mitigate this deficiency, a 1.5-megawatt (MW) diesel power generator and ancillary equipment is recommended (project T-21). Note this generator size accommodates anticipated electrical loads for pre-ozone (project T-15). Refer to Appendix L for additional details on generator sizing and power supply evaluation. Estimated cost for this project is $1,919,000.

8.4.4 Energy Efficiency

The City values sustainability and energy efficiency and participated in the Energy Trust of Oregon’s Core Strategic Energy Management program to identify and develop projects to reduce energy use. The City has completed many energy efficiency projects and will continue to identify energy savings opportunities and select high-efficiency equipment when replacing assets. No CIP projects have been identified solely based on improving energy efficiency.


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8.4.5 Summary of Condition-Related Improvements

Table 8.27 summarizes the total costs for condition-related improvements at the Taylor WTP.

Table 8.27 Taylor WTP Condition-Related Improvements

Category Cost(1)

Repair and Replacement $10,330,000(1)(2)(3)(4)

Seismic and Life Safety $1,156,000

Resiliency and Redundancy $1,919,000 Notes: (1) Costs in 2020 dollars. (2) Includes total 20-year repair and replacement program costs. (3) Assumes 20 years of annual GAC replacement. (4) Costs may vary depending on the number of locations in clearwell 1 that must be repaired. Five repairs were assumed to be

included in the cost estimate.

8.5 Capacity Expansion and Treatment Improvements

This section summarizes improvement projects identified to address capacity and treatment deficiencies.

Appendix S presents a complete evaluation of all capacity and treatment improvement alternatives being considered for the plant. Appendix O details all improvements being considered for the intake.

8.5.1 Treatment Process and Plant Capacity Improvements

This master plan covers a 20-year and a 50-year planning horizon. Process and capacity improvements were identified for both.

8.5.1.1 20-Year Horizon Treatment Process Improvements

Two alternatives were considered to address water quality challenges posed by algal toxin events and pharmaceutical and personal care products (PPCPs) in the 20-year horizon. Appendix S provides a detailed evaluation of the treatment process alternatives.

The alternative selected to improve the finished water quality for both the 20-year and 50-year planning horizons includes construction of an ozone generation facility and ozone contactors that will be incorporated upstream of the existing rapid mix process. This alternative is estimated to cost $19.6 million. Figure 8.14 provides a conceptual site layout of the selected alternative.


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Figure 8.14 Conceptual Layout for Selected Water Quality Process Improvement

8.5.1.2 Projects to Address 20-Year Horizon Deficiencies

Table 8.28 summarizes projects developed to address deficiencies in the 20-year planning horizon for the plant. Appendix S details each of the projects. Projects shown in Table 8.28 were classified according to their driver for improvement:

• Aging infrastructure: Existing infrastructure and equipment that exceed their useful life. - Useful life of concrete was assumed to be 100 years. - Useful life of pipes of any materials was assumed to be 80 years. - Useful life of plant equipment was taken from the City’s asset management

database. • Capacity: Capacity limitations of existing treatment processes. • Water quality: Treatment processes to address water quality challenges.

- Water quality challenges for the Taylor WTP considered for this plan are harmful algal blooms and algal toxin events as well as pharmaceuticals and personal care products.

• Resilience: Meet the City’s level of service goals for seismic resilience. • O&M: Existing challenges that affect the current operation of the plant.


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Table 8.28 Taylor WTP Projects to Address Deficiencies in the 20-Year Planning Horizon

Project Number

Project Name Drivers Deficiency Addressed Discussion Reference Cost(1)

T-1 Annual Repair and Replacement Program Aging Infrastructure Infrastructure exceeding useful life during the 20-year planning horizon. Section 8.4.1 $7,195,000(2)(1)

T-2 Clearwell 1 Concrete Repairs Aging Infrastructure Concrete spalling and corrosion of reinforcing steel in clearwell 1. Section 8.4.1 $9,000

(per repair location)

T-3 Annual GAC Filter Media Replacement Aging Infrastructure,

Water Quality Diminished GAC adsorption capacity. Section 8.4.1 $150,000(3)

T-4 Filters 5 – 8 Influent Valve Actuator Replacement O&M Failure of existing electric actuators for filters 5 through 8’s influent valves. Section 8.4.1 $90,000

T-5 Seismic Vulnerability Mitigation Resilience Seismic vulnerabilities identified in the seismic and life-safety evaluation. Section 8.4.2 $891,000

T-6 Filters 5 – 8 Drain Pipe Modifications O&M Challenges fully draining filters for maintenance or media replacement. Section 8.3.2.6 $20,000

T-7 Backwash System Pressure Relief O&M Lack of pressure relief on backwash piping. Section 8.3.2.6 $255,000

T-8 Backwash System Study O&M Presence of air in backwash piping. Section 8.3.2.6 $50,000

T-9 Sedimentation Basins 1 – 3 Sludge Removal Improvements

O&M, Capacity Lack of automated sludge blowdown. Limitations on plant capacity because sludge can only be removed when the plant is shut down without causing solids carry-over to the filters.

Section 8.3.2.5 $1,079,000

T-10 Additional Alum Tank Capacity Alum storage capacity. Section 8.3.2.10 $96,000

T-11 Additional Solids Handling Lagoon O&M, Capacity Frequency of sludge hauling required with existing lagoons. Challenges managing washout of GAC fines and pH of lagoon decant when changing out filter media.

Section 8.3.2.9 $1,443,000

T-12 Additional Raw Water Full Lift Pump Capacity Lack of redundant raw water full lift pumping capacity. Section 8.3.2.3 $844,000

T-13 Backwash Pumping Redundant Capacity Capacity Capacity limitations for existing backwash pumps. Section 8.3.2.6 $1,624,000

T-14 Redundant Backwash Pump Supply Resilience Inability to supply backwash water from either clearwell. Section 8.3.2.6 $1,045,000

T-15 Pre-Ozone Water Quality Lack of treatment barrier against identified water quality challenges from algal byproducts and PPCPs. Section 8.5.2.1. $19,571,000

T-16 Tube Settler Replacement O&M Existing maintenance challenges with tube settlers and poorer settling performance in basins 1 through 3 when compared to basin 4.

Appendix F (Facility Fact Sheets) $1,190,000

T-17 Solids Hauling Operation Optimization Study O&M, Capacity Substantial hauling requirements and time spent hauling sludge for existing solids handling. Section 8.3.2.9 $150,000

T-18 Raw Water Isolation Valves O&M Inability to isolate the two raw water pipes leaving the raw water pumps. Appendix F (Facility Fact Sheets) $61,000

T-19 Additional Operator Workspace O&M Limited operator workspace within existing plant. Appendix F (Facility Fact Sheets) $397,000

T-20 HVAC Control System Replacement O&M Poor HVAC system performance. Appendix F (Facility Fact Sheets) $300,000

T-21 New Backup Generator Resilience, Capacity Existing lack of generator capacity to power plant equipment. Backup power required to meet near- and long-term emergency power needs.

Section 8.4.3 $1,919,000

T-22 Overflow Piping Modifications Water Quality Issues raised by Oregon Health Authority in most recent sanitary survey. Section 8.3.2.8 $178,000

T-23A Automation Improvements – Filter Backwash Programming

O&M Limited control over automated backwash cycle. Section 8.3.3 $15,000

T-23B Automation Improvements – Lagoon Decant Monitoring

O&M Limited monitoring of lagoon decant pH and chlorine residual. Section 8.3.3 $39,000

T-23C Automation Improvements – New Lagoon Waste Water Chemical Feed

O&M Operational challenges for the lagoons during GAC filter media replacement. Section 8.3.3 $93,000

T-23D Automation Improvements – Chemical System Programming and Monitoring Upgrades

O&M Control system discrepancies with the soda ash dose. Lack of trim control for soda ash and chlorine doses. Section 8.3.3 $29,000

T-24 Seismic Vulnerability Mitigation – Intake Structure Resilience Seismic vulnerabilities identified in the seismic and life-safety evaluation. Section 8.4.2 $265,000

T-25 Intake Structure Jet Grouting Resilience Seismic vulnerabilities of the river bank near the intake structure identified in the geotechnical seismic hazards evaluation.

Section 8.5.2 $2,625,000

T-26 Intake Structure Replacement Aging Infrastructure,

Resilience, O&M Operation and maintenance challenges associated with gravel infringement and identified geotechnical seismic vulnerabilities near the existing intake structure.

Section 8.5.2 $25,000,000

Notes: (1) All project costs are in 2020 dollars. (2) Total 20-year program cost. (3) Annual cost for replacement of GAC media in two filters per year. GAC replacement is likely not needed after ozone installation.


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8.5.1.3 Planning for the 50-Year Horizon

To meet the required treatment capacity target of 25 mgd in the City’s long-term water supply strategy, the Taylor WTP treatment processes must be expanded. In addition, portions of the existing treatment process infrastructure will exceed their useful life during the 50-year planning horizon and require replacement.

Three treatment process alternatives were developed to address: • Aging infrastructure: Infrastructure that will exceed its useful life during the 50-year

planning horizon. This includes all infrastructure installed during the plant’s original construction in 1949 and subsequent expansions in 1960 and 1969. This includes: - Intake structure. - Flocculation/sedimentation basins 1 – 3. - Filters 1 – 4. - Clearwells 1 and 2 and associated high service pump stations. - Operations and filter building.

• Capacity: Process infrastructure to increase the plant’s treatment capacity to 25 mgd. • Resilience: At least 8.5 mgd of treatment infrastructure is fully seismically resilient to

meet the City’s established level of service goals. • O&M: The plant’s existing operational challenges.

The selection of pre-ozone as a process improvement in the 20-year horizon reduced the three process alternatives for the 50-year horizon to two viable alternatives which can be explored in future master planning efforts, closer to the time of implementation, before a preferred alternative is constructed.

Expanding the treatment processes to meet the capacity target will also require expanding the solids handling processes. The City decided to continue using the existing lagoons for thickening and pumping and to add a fourth lagoon.

Appendix S offers full details on the evaluation of all treatment process alternatives and solids handling alternatives.

Both alternatives replace and expand a number of the same processes and structures. To allow for a comparison of these alternatives, detailed capital cost estimates for the water quality and pretreatment components were developed. This comparison and these costs are presented in Appendix S.

Total costs for process expansion and infrastructure replacement in the 50-year planning horizon are estimated to be as much as $70M; intake replacement costs are discussed in Section 8.5.2. With the exception of the expense to install pre-ozone, this cost estimate does not include costs for projects completed within the 20-year planning horizon.

Implementing improvements identified in both the 20-year and 50-year planning horizons will require complex sequencing and timing. Additional planning for selecting a process strategy to meet the long-term water supply strategy requirements should be performed prior to constructing any significant facility projects in the 20-year CIP planning horizon to ensure these projects are consistent with the City’s long-term vision for the utility.


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8.5.2 Intake Improvements

The primary concerns for the existing intake structure discussed in Section 8.2.3, Section 8.4.2, and Appendix O are gravel deposition, geotechnical seismic vulnerabilities, and a lack of firm full-lift pumping capacity.

No improvement projects are recommended in the 20-year horizon to address gravel deposition beyond the City’s current dredging and gravel relocation efforts. An additional full lift pump (project T-12) is recommended to increase the firm capacity of the full lift pumps. Installing a third full lift pump would also facilitate future removal of the other six pumps that require double pumping of water to the plant.

A number of potential mitigation measures are discussed in Appendix I to address the potential for lateral spreading and flow failure to cause tilting and structural damage to the intake after a CSZ event. Ground improvement through jet grouting is recommended to encompass a zone approximately 50 feet by 100 feet beneath the intake access bridge to target the silty sand layer 20 to 40 feet below ground surface to address these geotechnical seismic hazards (Project T-25). Estimated cost for these ground improvements is $2.6 million; refer to Appendix I for additional details on the recommended improvements.

The existing intake can meet the City’s long-term water supply strategy needs from the Taylor WTP of 25 mgd, however the original core of the structure will exceed its useful life in 2049 and require replacement. Six intake improvement alternatives were developed to address the following drivers:

• Aging infrastructure: The existing intake structure will exceed its useful life during the 50-year planning horizon and must be replaced.

• Resilience: The intake structure must be fully seismically resilient to meet the City’s established level of service goals.

• O&M: The ongoing gravel deposition impacting intake operation must be mitigated.

The selected alternative 5 includes:

• A new intake approximately 500 to 800 feet upstream of the existing intake with new in-river cylindrical screens along the west bank.

• A new raw water pump station south side of the WTP site. • New piping from the new raw water pump station to the plant’s treatment processes.

The implementation of this alternative is estimated to cost as much as $25 million. Appendix O details the evaluation of the intake improvement alternatives. Given the significant seismic vulnerabilities and gravel deposition concerns with the existing intake structure, replacement of the intake structure could be accelerated and considered within the 20-year planning horizon and is included as Project T-26 in Table 8.28. No seismic improvements are recommended (projects T-24 or T-25) in the 20-year CIP as these seismic vulnerabilities will be mitigated by full intake structure replacement.

8.6 20-Year Horizon Implementation Plan

Project durations were estimated for all 20-year horizon projects to facilitate project sequencing for the CIP and are shown in Table 8.29. These durations indicate construction efforts alone and additional time will be required for design and permitting. Design, permitting, and construction


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of larger projects may need to be sequenced over several years. Multiple projects recommended for a single process should be considered for combining into a single project.

Table 8.29 Project Construction Durations for Taylor WTP Projects to Address Deficiencies in the 20-Year Planning Horizon

Project Number Project Name Project Duration

T-1 Annual Repair and Replacement Program Ongoing(1)

T-2 Clearwell 1 Concrete Repairs <6 months

T-3 Annual GAC Filter Media Replacement <6 months

T-4 Filters 5–8 Influent Valve Actuator Replacement <6 months

T-5 Seismic Vulnerability Mitigation Varies(2)

T-6 Filters 5–8 Drain Pipe Modifications <6 months

T-7 Backwash System Pressure Relief <6 months

T-8 Backwash System Study <6 months

T-9 Sedimentation Basins 1 – 3 Sludge Removal Improvements <1 year

T-10 Additional Alum Tank <6 months

T-11 Additional Solids Handling Lagoon <1 year

T-12 Additional Raw Water Full Lift Pump <1 year

T-13 Backwash Pumping Redundant Capacity <1 year

T-14 Redundant Backwash Pump Supply <1 year

T-15 Pre-Ozone >1 year

T-16 Tube Settler Replacement <1 year

T-17 Solids Hauling Operation Optimization Study <6 months

T-18 Raw Water Isolation Valves <6 months

T-19 Additional Operator Workspace <6 months

T-20 HVAC Control System Replacement <6 months

T-21 New Backup Generator <1 year

T-22 Overflow Piping Modifications <6 months(3)

T-23 Automation Improvements <6 months

T-24 Intake Seismic Mitigations <1 year

T-25 Intake Structure Jet Grouting <1 year

T-26 Intake Replacement >1 year Notes: (1) Annual program for replacement of equipment. Project durations will depend on equipment slated to be replaced in a

given year. (2) Includes all identified individual seismic mitigations. Project duration varies for individual mitigation projects. (3) Project timing dependent on extent of modifications required. Duration to protect clearwell and CCB overflow/drain from

outside intrusion anticipated to be <6 months.


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Chapter 9 details the final project prioritization and sequencing in the CIP.

The following projects will require full or partial plant shutdown and must be carefully sequenced, to ensure the City continues to meet customer water demands:

• T-2: Without a redundant backwash supply source, repairs to clearwell 1 will require full plant shutdown. Repairs may take one to two weeks with an additional four weeks needed for concrete curing.

• T-9: Sludge removal improvements may require filling in the sludge collection sumps in the sedimentation basins with concrete, which requires a cure time of four weeks. Individual basins must be offline for over four weeks to complete the improvements.

• T-16: Flocculation/sedimentation basins 1 through 3 must be taken out of service to have their tube settlers replaced with new plate settlers.

• T-18: Raw water pumps will need to be taken out of service while isolation valves are installed.

The majority of the identified projects are for the plant’s existing structures or equipment and, are not anticipated to have significant permitting requirements. However, permitting requirements are likely to be much more substantive for the projects T-11, T-15, and T-26 that construct new structures or complete in-water work for the intake.

Table 8.30 summarizes the land use and natural hazards designations that will require additional consideration for permitting during project development. Coordination with the relevant agencies and interested parties in permitting for these projects should be initiated as early as possible in project development. Appendix T provides additional detail on permitting challenges and requirements for the Taylor WTP.


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Table 8.30 20-Year Horizon Projects with Additional Permitting Considerations

Project Number

Project Name Permitting Considerations

T-11 Additional Solids Handling Lagoon

• The proposed location for the new lagoon is within the following land use overlays: - Natural Resources Overlay Highly Protected Riparian

Corridor. - Natural Resources Overlay Highly Protected

Significant Vegetation. - Willamette River Greenway Overlay.

• The new lagoon’s proposed location is within the 500-year floodplain.

• This project is anticipated to trigger complex land use permitting processes.

T-15 Pre-Ozone

• The proposed location for the ozone contactor is within the following land use overlays: - Natural Resources Overlay Highly Protected Riparian

Corridor. - Natural Resources Overlay Highly Protected

Significant Vegetation. - Willamette River Greenway Overlay.


T-26 Intake

Replacement

• The proposed location for a new intake structure is within the following land use overlays: - Natural Resources Overlay Highly Protected Riparian

Corridor. - Willamette River Greenway Overlay.

• A Locally Protected Locally Significant Wetland on the southeast corner of the Taylor WTP site.

• The proposed location for the intake structure is within the 100-year floodplain.

• In-water construction will take place within the waters of the United States.

• This project will require construction within a floodway and a floodplain development permit.


• This project is anticipated to trigger state and federal environmental permitting through the Oregon Department of State Lands and US Army Corps of Engineers.

• State permitting efforts may take up to two years.


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