MSA Phase I Biosolids Improvements_PER_FINAL_to MSA_8.19.26.pdf

Hazen and Sawyer

210 Ridge McIntire Rd., Suite 400

Charlottesville, VA 22903

FINAL

Lexington-Rockbridge Regional WQCF –

Phase I Biosolids Improvements

Preliminary Engineering Report Maury Service Authority Task Order No.: HS-301 Hazen Project No.: 31742-001 August 2026

Maury Service Authority August 2026

LRRWQCF Phase I Biosolids Improvements

Preliminary Engineering Report FINAL

| Table of Contents i

Table of Contents

Executive Summary

1. Introduction ............................................................................................................ 1-1

1.1 LRRWQCF Background........................................................................................................... 1-2

1.2 Existing Flows and Loads ........................................................................................................ 1-3

1.3 Existing Solids Handling Facilities ........................................................................................... 1-4

1.3.1 Aerobic Digesters........................................................................................................ 1-4

1.3.2 Sludge Control Facility ................................................................................................ 1-5

1.3.3 Sludge Storage Tank and Mixing System .................................................................. 1-5

1.4 Condition Assessment ............................................................................................................. 1-6

2. Biosolids Improvements ......................................................................................... 2-1

2.1 Summary of Improvements ...................................................................................................... 2-1

2.1.1 Sludge Control Facility ................................................................................................ 2-1

2.1.2 Sludge Storage Tank .................................................................................................. 2-1

2.1.3 Additional Improvements ............................................................................................ 2-2

2.2 Mechanical/Process ................................................................................................................. 2-2

2.2.1 Sludge Control Facility ................................................................................................ 2-2

2.2.1.1 Thickened Waste Activated Sludge Pumps ........................................ 2-5

2.2.1.2 Shafted Screw Conveyors .................................................................. 2-6

2.2.2 Sludge Mixing Building ............................................................................................... 2-7

2.2.2.1 Alternative 1 – Repurposing of Existing SST Mixing System .............. 2-8

2.2.2.2 Alternative 2 – Installation of Pumps within Existing Sludge Mixing

Building 2-9

2.2.2.3 Alternative 3 – Installation of Pumps in New Sludge Transfer Building . 2-

2.2.3 Sludge Storage Tank ................................................................................................ 2-12

2.2.3.1 Glass-Lined Bolted Steel Tank ......................................................... 2-14

2.2.3.2 Rolled Steel Tank ............................................................................. 2-14

2.2.3.3 Pre-Stressed Concrete Tank ............................................................ 2-14

2.3 Structural ................................................................................................................................ 2-15

2.3.1 General Requirements .............................................................................................. 2-15

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2.3.1.1 Codes and Standards ...................................................................... 2-15

2.3.1.2 Dead Loads...................................................................................... 2-16

2.3.1.3 Live Loads ....................................................................................... 2-16

2.3.1.4 Equipment Loads ............................................................................. 2-16

2.3.1.5 Piping Loads .................................................................................... 2-16

2.3.1.6 Wind, Snow & Seismic Loads ........................................................... 2-17

2.3.1.7 Concrete Design .............................................................................. 2-17

2.3.2 Sludge Control Facility .............................................................................................. 2-18

2.3.3 Sludge Mixing Building ............................................................................................. 2-19

2.3.4 Sludge Storage Tank ................................................................................................ 2-19

2.4 Electrical ................................................................................................................................ 2-20

2.4.1.1 Existing Electrical System ................................................................ 2-20

2.4.2 Sludge Control Facility .............................................................................................. 2-25

2.4.3 Sludge Mixing Building ............................................................................................. 2-26

2.4.4 Sludge Storage Tank ................................................................................................ 2-26

2.5 HVAC ..................................................................................................................................... 2-26

2.5.1 Sludge Control Facility .............................................................................................. 2-26

2.5.1.1 Codes and Standards ...................................................................... 2-26

2.5.1.2 Design Concepts .............................................................................. 2-27

2.5.1.3 HVAC Design Overview ................................................................... 2-27

2.6 Instrumentation and Controls ................................................................................................. 2-27

2.6.1 Sludge Control Facility .............................................................................................. 2-27

2.6.2 Sludge Mixing Building ............................................................................................. 2-29

2.6.3 Sludge Storage Tank ................................................................................................ 2-29

3. Regulatory and Permitting Requirements .............................................................. 3-1

3.1 Virginia Department of Environmental Quality (DEQ) ............................................................. 3-1

3.2 Rockbridge County .................................................................................................................. 3-2

4. Summary of Recommendations ............................................................................. 4-1

5. Project Delivery ...................................................................................................... 5-1

6. Cost and Schedule ................................................................................................ 6-1

6.1 Preliminary Construction Costs ............................................................................................... 6-1

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6.2 Preliminary Design, Bidding, and Construction Schedules ..................................................... 6-1

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List of Tables

Table 1-1: WQCF Flows from the Assessment .......................................................................................... 1-3

Table 1-2: Solids Loading Rates (Post Digestion) ..................................................................................... 1-4

Table 1-3: Aerobic Digesters Design Criteria ............................................................................................. 1-4

Table 1-4: Existing GBT Design Criteria .................................................................................................... 1-5

Table 1-5: Existing SST Design Parameters ............................................................................................. 1-6

Table 1-6: Summary of Condition Assessment.......................................................................................... 1-6

Table 2-1: 3 BDP 3DP Thickening Mode Design Criteria .......................................................................... 2-3

Table 2-2: BDP 3DP Dewatering Mode Design Criteria ............................................................................ 2-4

Table 2-3: Proposed TWAS Pumping Design Criteria ............................................................................... 2-5

Table 2-4: Summary of Conveyor Type Evaluation ................................................................................... 2-6

Table 2-5: Shafted Screw Conveyor Design Criteria ................................................................................. 2-7

Table 2-6: Proposed Sludge Transfer Pump Design Criteria .................................................................... 2-8

Table 2-7: Proposed SST Design Criteria, Phase I Biosolids Improvements .......................................... 2-13

Table 2-8: Future SST Expansion Design Criteria ................................................................................... 2-13

Table 2-9: Summary of Live Loads .......................................................................................................... 2-16

Table 2-10: Summary of Concrete Design Properties ............................................................................. 2-17

Table 2-11: Existing vs. Proposed MCC Load Distribution ...................................................................... 2-25

Table 2-12: Indoor Design Conditions ..................................................................................................... 2-27

Table 2-13: Weather Design Criteria ....................................................................................................... 2-27

Table 6-1: Preliminary Construction Cost Estimate, Median ..................................................................... 6-1

List of Figures

Figure 2-1: Three-Belt Tower Style Combination GBT/BFP (Courtesy of BDP Industries) ....................... 2-3

Figure 2-2: Proposed Sludge Control Facility Equipment Layout .............................................................. 2-5

Figure 2-3: Alternative 1 – Repurposing of Existing SST Mixing System .................................................. 2-9

Figure 2-4: Alternative 2 – Installation of Pumps within Existing Sludge Mixing Building ....................... 2-10

Figure 2-5: Alternative 3 – Installation of Pumps in New Sludge Transfer Building ................................ 2-11

Figure 2-6: Proposed STFM Pipe Layout ................................................................................................ 2-12

Figure 2-7: Glass-Lined Bolted Steel Tank (Courtesy of Aquastore)....................................................... 2-14

Figure 2-8: Rolled Steel Tank (Courtesy of Lipp) .................................................................................... 2-14

Figure 2-9: Pre-Stressed Concrete Tank (Courtesy of CROM) ............................................................... 2-15

Figure 2-10: Utility Service Entrance ....................................................................................................... 2-20

Figure 2-11: Standby Generator in Generator Building ........................................................................... 2-20

Figure 2-12: Facility Main Switchboard .................................................................................................... 2-21

Figure 2-15: Panel PPS within SCF’s west Electrical Room ................................................................... 2-23

Figure 2-16: Panel PPSB1 Within East Electrical Room ......................................................................... 2-23

Figure 2-17: MCC-AD in Digester Building (Digesters 3 & 4) .................................................................. 2-24

Figure 2-18: PPSM1 located in Sludge Mixing Building .......................................................................... 2-24

Figure 2-19: Sludge Mixing Pump Starters in Sludge Mixer Building ...................................................... 2-24

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List of Appendices

Appendix A: Solids Process Flow Schematic

Appendix B: Network Architecture Drawing

Appendix C: Construction Cost Estimate

List of Acronyms

Abbreviation Definition

AA Average Annual

AACE American Association of Cost Estimators

AAF Average Annual Flows

ADF Average Daily Flow

ASHRAE American Society of Heating, Refrigerating and Air-Conditioning Engineers Standards

ASPE American Society of Plumbing Engineers Standards

Assessment Wastewater Collection and Treatment Facilities Assessment Study

BDP BDP Industries Manufacturers

BFP Belt Filter Press

BRRA Blue Ridge Resource Authority

CMAR Construction Manager At-Risk

CMU Concrete Masonry Unit

CTC Certificate-to-Construct

CTO Certificate-to-Operate

DB Design-Build

DBB Design-Bid-Build

DEQ Virginia Department of Environmental Quality

DX Direct Expansion

ENR Enhanced Nutrient Removal

GBT Gravity Belt Thickener gpm Gallons Per Minute

Hazen Hazen and Sawyer

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Abbreviation Definition

HP Horsepower

HVAC Heating, Ventilation, and Air Conditioning

IBC International Building Code kV Kilovolt

LP Lighting Panel

LRRWQCF Lexington-Rockbridge Water Quality Control Facility m meters

MCC Motor Control Center

MG Million Gallon

MGD Million Gallons Per Day

MIC Microbiologically Influenced Corrosion

MM Maximum Month

MOV Motor Operated Valve

MSA Maury Service Authority

NFPA National Fire Protection Association Standards

O&M Operation and Maintenance

PER Preliminary Engineering Report

PFAS Per- and Polyfluoroalkyl Substances

PFD Process Flow Diagram

PLC Programmable Logic Controller

PP Power Panel psf Pounds Per Square Foot

RVSS Reduced Voltage Soft Starters

SB Switchboard

SCADA Supervisory Control and Data Acquisition

SST Sludge Storage Tank

TN Total Nitrogen

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Abbreviation Definition

TP Total Phosphorous

TS Total Solids

TWAS Thickened Waste Activated Sludge

V Volts

VCWRLF Virginia Clean Water Revolving Loan Fund

VFD Variable Frequency Drive

VPA Virginia Pollution Abatement

WAS Waste Activated Sludge

Wet lb/hr Wet Pounds Per Hour

WQCF Water Quality Control Facility

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| Executive Summary 1

Executive Summary

The purpose of this Preliminary Engineering Report (PER) is to evaluate Phase I Biosolids Improvements for the Lexington-Rockbridge Water Quality Control Facility (WQCF). The project focuses on addressing critical asset renewal needs, improving operational resiliency, and providing Maury Service Authority

(MSA) with greater flexibility for future biosolids management while maintaining compliance with current and anticipated PFAS regulatory requirements.

The existing biosolids facilities include aerobic digesters, a gravity belt thickening system, and a 500,000-gallon sludge storage tank used to support land application of Class B biosolids. Several components of the existing system have reached or exceeded their useful life:

• Gravity Belt Thickener 1 (GBT-1) has been demolished and requires replacement.

• GBT-2 is aging and experiencing increased maintenance efforts.

• The existing 500,000-gallon sludge storage tank is nearing the end of its service life and has exhibited signs of structural deterioration. The existing storage capacity provides limited operational flexibility during periods when land application is restricted due to weather or other factors.

• The current biosolids operations and processing rely primarily on liquid biosolids land application. Emerging PFAS regulations and future disposal uncertainties underscore the need for additional biosolids management options.

Based on evaluation of available technologies, facility conditions, operational requirements, and lifecycle cost considerations, Hazen recommends the following Phase I improvements:

Sludge Thickening and Dewatering Improvements: Replace the demolished GBT-1 with a combination gravity belt thickener/belt filter press (GBT/BFP) unit. The proposed equipment will allow

MSA to:

• Continue producing liquid Class B biosolids when desired

• Produce dewatered cake biosolids for alternative disposal or land application options

• Improve operational flexibility and resiliency

• Restore redundancy and capability within the solids handling process.

Sludge Storage Improvements: Demolish and replace the existing 500,000-gallon sludge storage tank with a new 500,000-gallon storage tank. The replacement tank will:

• Address existing structural and reliability concerns

• Maintain current storage capacity

• Support future operational needs while reducing capital costs compared to a larger replacement tank

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| Executive Summary 1

• Allow future expansion if additional storage capacity becomes necessary.

Hazen recommends additional supporting infrastructure improvements including new thickened waste activated sludge (TWAS) pumps, sludge transfer pumps and piping, replacement of aged sludge mixing pumps, new polymer feed equipment, dewatered biosolids cake conveyance, cake storage facility, electrical, HVAC, structural, instrumentation and controls improvements.

The recommended Phase I improvements provide several significant benefits to the MSA including:

• Improved reliability through replacement of aging and deteriorated assets

• Greater operational flexibility by allowing both liquid and dewatered biosolids production

• Reduced dependence on a single biosolids management strategy

• Enhanced resiliency during adverse weather conditions or changing regulatory requirements

• Improved preparedness for future PFAS-related regulations and disposal constraints

• A phased approach that addresses immediate facility needs while preserving opportunities for future expansion as flows and biosolids production increase.

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| Introduction 1-1

1. Introduction

In 2022, the Maury Service Authority (MSA) contracted with a firm to complete, the “Wastewater

Collection and Treatment Facilities Assessment Study” (Assessment). The study determined the capacity and condition of the Lexington-Rockbridge Regional Water Quality Control Facility

(LRR[PY1.1][MW1.2]WQCF) and recommended improvements needed to maintain the plant’s 3.0-million gallons per day (MGD) average daily flow (ADF) rating. The Assessment noted that the potential of forthcoming regulations related to emerging contaminants, per- and polyfluoroalkyl substances (PFAS) specifically, may impact the MSA’s ability to land apply aerobically digested, Class B liquid biosolids in the future. The Assessment thus recommended the MSA conduct an additional study to further evaluate its biosolids processing and beneficial use or disposal options.

In 2023, the MSA applied for and received funding from the Virginia Department of Environmental

Quality (DEQ) through the Virginia Clean Water Revolving Loan Fund (VCWRLF) to complete an evaluation for biosolids processing options, including introduction of a new sludge dewatering process and emerging technologies for ultimate PFAS destruction. Hazen was contracted by the MSA in 2024 and completed an “Evaluation of PFAS Impacts on Biosolids Processing Options at the LRRWQCF”. This evaluation included results of PFAS sampling and testing a review of PFAS treatment technologies; a preliminary condition assessment of existing solids handling facilities; a summary of solids storage tanks, thickening, and dewatering technologies for consideration; and a biosolids strategy to guide the MSA in the following:

• Navigating the upgrade of existing process areas and installation of new process areas

• Assessing the available sludge storage, thickening, dewatering, and PFAS treatment (i.e., destruction) alternatives for major operations and maintenance considerations

• Estimating program costs, inclusive of design, capital, operations and maintenance (O&M), and 20-year lifecycle costs, of the potential Water Quality Control Facility (WQCF) improvements

• Developing conceptual site layouts and integration with the WQCF’s existing unit processes.

The report established a basis of design for future flow conditions as the plant approaches its permitted

3.0 MGD capacity and navigated an evolving regulatory landscape. Flow conditions beyond the permitted

3.0 MGD capacity were not evaluated.

This Preliminary Engineering Report (PER) summarizes assessments and recommendations for improvements to the biosolids treatment process. The PER focuses on addressing deferred maintenance of aged equipment and facilities and providing increased operational flexibility and resiliency with respect to sludge processing, storage and land application of Class B biosolids. The PER specifically evaluates alternatives for replacing one (1) gravity belt thickener with a combined sludge thickening and dewatering unit; replacement of the existing 0.5-million-gallon (MG) sludge storage tank; and the implementation of additional equipment and facilities to provide the capability to produce both liquid and cake Class B biosolids. The selected PER alternatives will serve as the scope for the design and construction of the

Phase I Biosolids Improvements Project.

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| Introduction 1-2

1.1 LRRWQCF Background

The LRRWQCF was first constructed in 1999. In 2011, the plant was upgraded with enhanced nutrient removal (ENR) to meet the water quality limits of the Chesapeake Bay Program. The plant’s permitted design capacity is 3.0 MGD, with average daily flows currently ranging from 0.8 to 1.0 MGD and peak hourly flows ranging between 9.6 and 12.3 and an average daily flow of 1.5 MGD during wet-weather events. The biosolids produced by the existing solids treatment process meet Class B requirements through aerobic digestion.

Upstream of solids handling, influent is screened, treated in an Orbel BNR oxidation ditch, and sent to a secondary clarifier, where waste activated sludge (WAS) is settled out and routed to aerobic digestion.

(Note: Since there are no primary clarifiers used at this facility, solids comprise WAS only.) The existing solids treatment process includes four aerobic digestion tanks, one operational gravity belt thickener

(GBT) and one out-of-service, inoperable, GBT, and one thickened biosolids sludge storage tank (SST) with a nominal 500,000-gallon bolted-steel tank.

MSA staff operate the four aerobic digestion tanks in series. WAS enters the first tank at 0.5-1.0% Total

Solids (TS) with staff having the ability to send WAS directly from the WAS pump station to the digester or following sludge thickening, and the contents of each digester are pumped manually to the next digester. Downstream of aerobic digestion, existing thickening equipment serves two purposes:

• One, the GBT[JC1.1][MW1.2] recuperatively thickens digestate from each digester for return into the digester tanks to achieve a solids concentration of 2.0-3.5% TS, and

• Two, the GBT thickens solids from the final digestion step to increase the solids concentration from 2.0-3.5% TS to 3.5%-4.0% TS as a part of the transfer step of thickened biosolids to the

SST.

Batch withdrawal from the series of digesters to the SST is performed once every 1 to 4 weeks as allowed by space available in the SST. The end use of the Class B biosolids is liquid land application on agriculture fields. MSA land applies liquid sludge every few months based on the farmers’ schedules.

Figure 1-1 provides a process flow diagram of the existing biosolids treatment facility from the

Assessment.

It should be noted that evaluation of the aerobic digesters is outside of the scope of this report.

| Introduction 1-3

Figure 1-1: Existing Solids Train Process Flow Diagram from the Assessment

1.2 Existing Flows and Loads

WQCF flow rates from the Assessment are detailed in Table 1-1. Hauled loads refer to liquid waste delivered to the WQCF by tanker trucks and includes landfill leachate and septage. Recycle streams refer to liquid waste produced from other processes at the WQCF, such as GBT filtrate and aerobic digester decant, that is returned to the plant headworks. The plant is permitted for total nitrogen (TN) and total phosphorous (TP) limits of 6.0 mg/L and 0.3 mg/L, respectively.

Table 1-1: WQCF Flows from the Assessment

Parameter Flow (MGD)

Average Daily Influent Flow 0.8-1.0

Max Average Daily Influent Flow 1.5

Average Hauled Loads (septage and leachate) 0.015

Average Recycle Streams (GBT filtrate and aerobic digester decant) 0.036

Peak Day Influent Flows 2.9-4.7

Peak Hourly Influent Flows 9.6-12.3

Average Annual (AA) and Maximum Month (MM) solids loading rates used for analysis of the facilities downstream of the aerobic digesters were determined using 24 months of GBT operations data (March

2022-March 2024). These solids loading rates are reflective of solids leaving the plant and are based on historical data. MSA provided 29 months of oxidation ditch, effluent, and solids loading data (November

2021-April 2024) which was processed to determine solids production within the WQCF and appropriate

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| Introduction 1-4 peaking factors. Additionally, the MSA provided 2025 (January 2025 – December 2025) solids production data from the GBT thickening operations for analysis.

The AA solids loading rate was calculated using the volume and solids concentration of the final biosolids product transferred from the GBT to the SST. Since solids transfer to the SST occurs periodically in batches, a peaking factor was calculated using daily loads from the WAS stream leaving the final clarifiers. The peaking factor was applied to the AA solids loading rate to produce the MM solids loading rate. Both the MM and AA loading rates will increase as the plant approaches its permitted capacity. This expected growth was considered when recommending changes to the existing solids handling facilities. The solids loading rates resulting from these calculations are provided in Table 1-2.

Table 1-2: Solids Loading Rates (Post Digestion)

Parameter

Value

Current AA Current MM Permitted AA

Design Flow (MGD) 1.0 1.3 3.0

Digested Solids Production (dry lb/MG) 2,170 - -

Solids Production (dry lb/day) 2,170 2,850 6,510

1.3 Existing Solids Handling Facilities

1.3.1 Aerobic Digesters

A detailed evaluation of the aerobic digesters was not included in the scope of this project, but background is provided herein, as aerobic digestion is central to the solids handling process. Two of the four aerobic digesters are from the plant’s original construction in 1998, while the other two were constructed in 2011. The digesters are aerated by three blowers and operated in series. Operation of the aerobic digesters is integrated with GBT operation. The GBT is operated periodically to increase the digestate concentration to 2-3% TS via recuperative thickening. Table 1-3 illustrates the existing Aerobic

Digester design criteria.

Table 1-3: Aerobic Digesters Design Criteria

Parameter

Value

Current AA Current MM Permitted AA

Design Flow (MGD) 1.0 1.3 3.0

Number of Digesters 4

Total Volume (gallons) 1,360,000

Solids Retention Time (days) 44

Solids Wasting Rate (gallons per day) 50,000

Solids Comcentration (%TS) 2

Digested Solids Production (dry lb/MG) 2,170 - -

Solids Production (dry lb/day) 2,170 2,850 6,510

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| Introduction 1-5

1.3.2 Sludge Control Facility

The existing sludge thickening system is located in the Sludge Control Facility (SCF) and includes two

GBTs, two polymer feed systems, and four thickened waste activated sludge pumps (two per GBT), with the sludge thickening system designed provide sludge thickening up to 3.0 MGD (AAF). GBT-1, and its associated appurtenances, is from the original plant construction, were demolished and has been out of service for over a decade. It’s original intent was to provide pre-thickening between the WAS pump station and the digesters and had a hydraulic capacity of 300 gallons per minute (gpm). Total replacement of GBT-1 is required to restore the MSA’s sludge thickening process to its original design intent. The

MSA has completed demolition of GBT-1 in anticipation of its replacement [Note: Because GBT-1 has been demolished, only one thickener is presently utilized for solids handling, as shown in

Figure 1-1.]

GBT-2 was installed in 2011 and has a hydraulic capacity of 500 gpm. GBT-2’s original design intent was to thicken digested sludge from the digesters, with TWAS pumps conveying the thickened sludge to the sludge storage tank for ultimate land application. With GBT-1 out of service, however, GBT-2 has the ability to pre-thicken WAS from the WAS pump station, and it thickens sludge from the four (4) digesters. Empirical information from MSA staff indicates that GBT-2 is beginning to require more frequent maintenance to keep it operational, likely due to its increased usage, and will require either significant repairs or replacement in the future. Table 1-4 illustrates the existing design criteria for the

Gravity Belt Thickeners.

Table 1-4: Existing GBT Design Criteria

Parameter

Value

Current AA Current MM Permitted AA

Design Flow (MGD) 1.0 1.3 3.0

Units Online 1

Capacity of Unit Online,GBT-2 (gpm) 500

Digested Solids Production (dry lb/MG) 2,170 - -

Solids Production (dry lb/day) 2,170 2,850 6,510

1.3.3 Sludge Storage Tank and Mixing System

The existing SST is a 500,000-gallon unlined, bolted-steel storage tank installed as part of the original 1998 construction. The tank is equipped with a continuous mixing system, with two (2) sludge mixing pumps installed in the Sludge Mixing Building. The mixing pumps are used to recirculate the tank’s contents and to load sludge trucks with Class B liquid biosolids for ultimate liquid land application.

Stored biosolids are maintained at 4% TS to accommodate truck loading, which reduces solids storage capacity. Table 1-5 presents the design parameters and capacities for biosolids storage at each flow condition. Due to the low percent solids of the stored biosolids, the storage capacity of the existing SST provides less than three (3) months’ storage capacity, which has historically been problematic for the

MSA, especially during extended periods of wet weather.

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| Introduction 1-6

Table 1-5: Existing SST Design Parameters

Design Parameter Value

Current AA

1 MGD

Current MM

1.3 MGD

Permitted AA

3.0 MGD

Total Capacity per tank (gallons) 500,000

Inner Diameter of existing tank (feet) 48

Solids Concentration (%TS) 4%

Design Flow (MGD) 1.0 1.3 3.0

Digested Solids Production (dry lb/MG) 2,170 2.850 6,510

Daily Volume to SST (gal/day) 6,510 8,550 19,520

Storage Duration (days) 77 58 26

Existing Mixing Continuous Pumped Mixing

Mixing Pump Type Horizontal Centrifugal Chopper

A 2006 Preliminary Engineering Report, completed by others, recommended rehabilitation of the existing

SST and construction of a second 0.5 MG SST to accommodate increased thickened sludge production up to the permitted influent flow of 3 MGD. The installation of a second SST did not occur during the

MSA’s 2011 WQCF Upgrades, despite the expected increase in solids generation and insufficient storage capacity; the existing SST was rehabilitated and retrofitted with a new sludge mixing system.

Over a decade later, the existing tank is at its end of life and in need of an upgrade based on the typical 20 to 30 year life span of unlined bolted-steel storage tanks. The MSA's staff has reported signs of continuing deterioration. Furthermore, a previous structural inspection revealed that the SST bolts were stressed, and the existing tank was at risk of failing.

1.4 Condition Assessment

In February 2026, Hazen and Sawyer (Hazen) conducted a site visit to assess the existing conditions of the MSA’s solids thickening and storage facilities at its WQCF. Table 1-6 provides a summary of site visit findings. The condition assessment, in conjunction with the prior Biosolids Assessment, served as a baseline for establishing the major improvements needed to increase operational flexibility and resiliency within the WQCF’s solids handling facilities.

Table 1-6: Summary of Condition Assessment

Equipment Units Size Condition Recommended Improvement

GBTs1 2 Designed for permitted capacity GBT-1: Demolished

GBT-2: Fair

Replace GBT-1 with combination unit Rehab or replace GBT-2 (future design phase, not considered in this PER)

TWAS Pumps

(GBT-1)1 2

Meets design pumping requirements Demolished

Install new TWAS pumps as part of GBT- 1 replacement.

SST 1

Undersized for liquid land application at 4% solids Poor

Replacement required. Evaluate need to expand storage capacity.

Sludge Mixing Pumps

Meets mixing design requirements Fair Existing pumps are nearing end of useful life. Consider in-kind replacement.

1 Existing Sludge Storage Facility.

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| Biosolids Improvements 2-1

2. Biosolids Improvements

2.1 Summary of Improvements

2.1.1 Sludge Control Facility

Several improvements to the existing Sludge Control Facility and SSTs were considered during a prior

Biosolids Processing Evaluation Study. During the Study and pertaining to the Sludge Control Facility, three sludge dewatering technologies were evaluated:

• Belt filter press (BFP)

• Dewatering centrifuge

• Screw press

Recommendations from the Study revealed that combination GBT and BFP units were the preferred technology, enabling the MSA to replace its obsolete GBT-1 within their existing Sludge Control Facility.

Replacing the existing GBT-1 with a combination GBT/BFP unit provides operational flexibility and redundancy for both thickening and dewatering processes, enabling the MSA to produce either liquid or cake biosolids, while maximizing the available footprint in the Sludge Control Facility.

Additional recommended improvements include:

• Replace two (2) existing thickened waste activated sludge (TWAS) pumps serving GBT-1

• Provide a new sludge transfer force main discharge connection, with actuated valving, to the combination GBT/BFP unit, to accommodate design solids production

• Provide a new polymer mixing and injection system to feed polymer to the GBT/BFP unit

• Provide a rolling access platform to allow MSA staff access to the GBT/BFP unit

• Provide a cake solids conveyor system, receiving cake from the discharge end of the GBT/BFP and discharging the cake to a new, covered sludge storage pad for ultimate land application or disposal

• Modify and improve electrical systems to accommodate the new equipment

• Modify structural supports in the Sludge Control Facility to accommodate the new solids conveyor

• Integrate instrumentation and controls for the new equipment.

2.1.2 Sludge Storage Tank

During the prior Biosolids Processing Alternatives Study, Hazen determined that replacement of the

MSA’s existing 0.5-MG sludge storage tank with a larger, 1.0 MG sludge storage tank, would be best to meet the MSA’s sludge storage and disposal needs. This recommendation was based on the MSA’s current permitted flow conditions and assumed liquid land application as the only method for biosolids

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| Biosolids Improvements 2-2 disposal from the WQCF. However, by expanding the MSA’s solids treatment train to include a sludge dewatering process, the new 1.0 MG sludge storage tank would be beneficial to MSA operations but not required. Therefore, in an effort to reduce the overall capital construction cost of this project, it is recommended that the new sludge storage tank be sized to match the existing tank (i.e., 0.5 MG of storage volume), coupled with an intentional plan to produce cake biosolids, as necessary, to maintain normal

WQCF operations.

2.1.3 Additional Improvements

Additional, recommended improvements in conjunction with replacement of GBT-1 and the SST include:

• Replace two (2) existing sludge mixing pumps in kind

• Install two (2) new sludge transfer pumps at the existing Sludge Mixing Building

• Install a dewatered cake storage pad adjacent to the existing Sludge Control Facility

• Construct a sludge transfer force main between the sludge transfer pumps (located at the

Sludge Mixing Building) and the Sludge Control Facility with a flow meter, pressure transmitter, and an actuated plug valve

• Modify and improve electrical systems to accommodate the new equipment

• Integrate instrumentation and controls for the new equipment.

Appendix A illustrates the proposed solids process flow schematic.

2.2 Mechanical/Process

2.2.1 Sludge Control Facility

Replacement of GBT-1 with a 2.0-meter (m) three-belt tower style filter press is recommended due to the operational flexibility of the system to operate in either dewatering or thickening mode. Additional benefits of the optimized configuration of combination units include:

• A gravity deck at waist-level for operator access (compared to the existing GBT-2 that is placed on a raised platform)

• MSA operator familiarity with belt filter press technology

• Polymer pumps can be selected with up to 10:1 turn down to accommodate the range of polymer dose requirements for thickening and dewatering modes

• Simple operator selection on a screen or SCADA system to switch between thickening mode and dewatering mode.

BDP Industries’ 3DP combination unit was used as Basis of Design for this evaluation; other manufacturers will be investigated during detailed design. Figure 2-1 depicts an example 3-belt combination GBT/BFP unit (3DP) by BDP Industries.

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Figure 2-1: Three-Belt Tower Style Combination GBT/BFP (Courtesy of BDP Industries)

The 3DP unit was evaluated and selected based on solids throughput of the system, 5% - 6% TS thickening output and operational hours. Table 2-1 provides 3DP thickening mode design criteria.

Table 2-1: 3 BDP 3DP Thickening Mode Design Criteria

Design Parameter

Value

Current

AA

1 MGD

Current

MM

1.3 MGD

Permitted

AA

3 MGD

Digested Solids Production at AA flow (dry lbs/day) 2,170 2,821 6,510

Digested Solids Production at MM flow (dry lbs/day)1 2,850 3,762 8,540 Belt Width (m) 2.0

Solids loading per meter (lbs. per hour per meter)2 996

Units Online 1

Sludge Feed Concentration (%) 0.5 – 3.0

Operating Schedule (hours per week)2 10 10 30

Hydraulic loading per GBT (gpm/ GBT) 133

Thickening Capture Efficiency (%) 95% for feed solids 1% or greater

90% for feed solids less than 1%

Sludge Output assuming 4% Thickened Sludge (wet lb/hr) 39,830

Polymer Usage (lbs of active polymer per year)2 4,142 5,385 12,427

Polymer Dilution Water (gpm) 5.0

Washwater usage (gpm) 35

Basis of Design BDP Industries

1The thickening portion of the BDP was evaluated based on MM solids production conditions.

2Vendor provided information

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The addition of a combination unit provides flexibility for the MSA to produce dewatered cake with options for disposal through land application or landfilling. The dewatering portion of the combination unit is expected to provide 95% capture efficiency and dewatering up to 16% TS. Dewatered cake will be conveyed from the BDP unit by using a shafted conveyor onto a storage pad located outside the Sludge

Control Facility as discussed in Section 2.2.1.

Table 2-2: BDP 3DP Dewatering Mode Design Criteria

Design Parameter

Value

AA

1 MGD

MM

1.3 MGD

Permitted AA

3 MGD

Dewatering Efficiency 95%

Dewatered Solids Cake Concentration (%TS) 16%

Solids Loading to combination unit (dry lbs/day)1 30,380 39,900 91,140

Wet Cake Produced2 (wet lbs/day) 180,380 236,910 541,100

Load onto conveyor3 (cf/day) 3,170 4,160 9,490

Number of Units Online 1 1 2

Operation hours per week 23 30 34

1. Assuming 14 days per month are needed for the aerobic digester duration

2. BDP unit assumed throughput = 8,000 wet lbs/hr. For a typical conveyor, assumed 50% of

16,000 wet lbs/hr Assumed dewatered cake density = 57 (lbs/cf)

Based on the MSA’s current solids production rate and estimated loading rate to the combination unit, the

2.0-meter unit is capable of meeting the MSA’s solids production needs for the current AA flow condition at 1 MGD and up to 100% cake production, without the need for sludge storage, which alleviates sludge storage duration concerns associated with the existing tank’s capacity, as discussed further in Section

2.2.3. As Average Annual Flows (AAFs) begin to approach the permitted capacity of 3.0 MGD, Hazen anticipates the need to install a second dewatering unit (e.g., GBT/BFP combination unit).

Additional proposed improvements within the Sludge Control Facility include replacement of existing

TWAS pumps with two new rotary lobe TWAS pumps to replace the aging existing pumps, a shafted screw conveyor to transfer dewatered cake to a storage pad outside the sludge control facility, polymer injection and mixing system, rolling access platform, booster pumps, a hydraulic power unit, hydropneumatic tank piping and associated appurtenances. Figure 2-2 provides the proposed sludge control facility equipment layout.

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Figure 2-2: Proposed Sludge Control Facility Equipment Layout

2.2.1.1 Thickened Waste Activated Sludge Pumps

Two new rotary lobe TWAS pumps will be provided to either transfer thickened sludge from the combination unit gravity deck to the aerobic digesters for recuperative thickening from 2.0 – 3.5% to 3.5

– 4.0% TS; or to transfer thickened sludge to the SST for ultimate land application. Hazen proposes replacing the TWAS pumps with rotary lobe pumps as they have a smaller footprint and are easier to maintain than the existing pumps. A summary of the TWAS pumps design criteria is shown in Table 2-3.

Table 2-3: Proposed TWAS Pumping Design Criteria

Parameter Value

Minimum Suction size (inches) 6 Minimum Discharge Size

(inches) 6

Design Flow rate (gpm) 50 – 150

Minimum Pump Speed (rpm) 150

Maximum Pump Speed (rpm) 250

Total Dynamic Head (psi) 60 at 3.5% TWAS

Basis of Design Netzch

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2.2.1.2 Shafted Screw Conveyors

Downstream of the combination unit, a conveyor is proposed to transfer dewatered cake from the discharge point of the combination units to a cake storage pad outside and adjacent to the Sludge Control

Facility. With the limitations of vertical space available in the existing Sludge Control Facility, three conveyor styles were evaluated including shafted screw conveyors, shaftless screw conveyors and belt conveyors. Table 2-4 provides a summary of preliminary conveyor type evaluation.

Table 2-4: Summary of Conveyor Type Evaluation

Conveyor Benefits/ Drawbacks

Shafted Screw Conveyor

Benefits

• Can run at higher rpms

• Can run dry without wear

• Staff familiarity

Drawbacks

• Lower trough fill rate required

• Intermediate hanger and end bearings required

• Not suited for stringy product

O&M needs: Grease hanger bearings every 10 -12 ft

Shaftless Screw Conveyor

Benefits

• Ideal for stringy, sticky, wet, product

• No non-drive end or intermediate hanger bearings

Drawbacks

• Liner replacement may be difficult in some applications (ceiling access)

• Long and/or high-volume applications require substantial spiral reinforcement O&M needs: Change out of UHMW PE liners

Belt Conveyor

Benefits

• No idler rollers

• Eliminates transfer points with continuous path conveying

• Staff familiarity

Drawbacks

• Occupies larger footprint

• Debris build up between the rollers and belt

• Wear and tear on the rollers and belt

• Likely requires sole- sourcing

O&M needs: Replacement of rollers, scarper blade adjustment

Basis of Design Shafted Conveyor by JMS Industries

All three conveyor types were evaluated for cost, ease of operations and maintenance, and their respective abilities to meet dimensional constraints within the existing Sludge Control Facility. Discussions with the

MSA revealed their preference for either a shafted screw conveyor, due to ease of operation and maintenance, or a belt conveyor, due to operational familiarity.

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Manufacturer representatives for both conveyor styles were contacted and dimensional drawings provided to verify sizing and confirm tolerances within the Sludge Control Facility. Upon review, it was confirmed that the belted conveyor is too wide to fit within the building’s available space, and therefore, shafted screw conveyors are recommended. Shafted screw conveyors are used as the basis of design within this

PER for subsequent equipment layouts and coordination with other trades (i.e., structural and electrical).

Design criteria for the screw conveyor is provided in Table 2-5.

Table 2-5: Shafted Screw Conveyor Design Criteria

Parameter Value

Conveyor Configuration Shafted

Size of Horizontal (inches) 12

Size of inclined conveyor screw (inches)

Incline (degrees) 25

Conveyor Capacity (wet lbs/hr) 16,800

Flow Condition (MGD) 1.0 3.0

Solids Production (wet lbs /day) 236,910 710,000

Operational Hours per week 30 44

Number of BDP units online 1 2

Basis of Design JMS Industries

2.2.2 Sludge Mixing Building

The Sludge Mixing Building currently houses two (2) existing sludge mixing pumps and associated suction and discharge piping from/to the existing sludge storage tank. Implementation of a new sludge dewatering process requires thickened sludge to be pumped from the Solids Storage Tank back to the

Sludge Control Facility, and ultimately to the new combination unit for sludge dewatering.

To allow for sludge dewatering, installation of two (2) new sludge transfer pumps is required, with connection of a new suction line to the sludge storage tank and a new sludge transfer force main installed from the transfer pumps to the GBT/BFP combination unit.

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Table 2-6: Proposed Sludge Transfer Pump Design Criteria

Parameter Value

Pump Type Rotary Lobe with VFD

Minimum Suction size (inches) 4

Minimum Discharge Size (inches)

Design Flow rate (gpm) 50 – 150

Minimum Pump Speed (rpm) 125

Maximum Pump Speed (rpm) 300

Total Dynamic Head (psi) 40 at 6% at low tank level

Power Requirement (hp) 10

Basis of Design Börger

Hazen evaluated several possible alternatives of pump styles and configurations available to transfer sludge to the Sludge Control Facility. The evaluation considered the cost saving benefits associated with re-purposing existing equipment and available space within the existing Sludge Mixing Building compared to the benefits (e.g., operational flexibility and future facility expansion) associated with locating the new sludge transfer pumps in a new, separate building.

2.2.2.1 Alternative 1 – Repurposing of Existing SST Mixing System

The first alternative utilizes the current SST mixing pumps to also provide sludge transfer capabilities to the new GBT/BFP unit. Currently, the mixing pumps recirculate the contents of the SST via mixing pumps. The discharge side of this alternative would require a new tee on the discharge header of the mixing system with a control valve as close to the existing mixing system as is practical, with a force main extending to the SCF and new combination unit.

This alternative (Figure 2-3) is the most cost-effective from a short-term, capital cost perspective, with the only cost being piping and valves. However, it is the most complex operationally. Centrifugal style pumps are not ideal for the application of feeding a BFP because the flowrate varies based on head conditions, which change as the tank drains and as the sludge quality varies.

The pumps are also oversized for the flow required. The minimum allowable flow rate for the mixing pump is 600 gpm, significantly higher than the design feed rate of the BFP. An actuated control valve would be required to throttle the flow in the discharge pipe to achieve proper operating flow at the BFP.

MSA would need to manually fine tune the valve to the percent open that achieves the necessary flow rate. Factors to consider during this process are the feeding rate of the BFP, which can vary depending on the desired output, the solids content of the sludge in the SST, and the changing head condition during the draining operation.

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Figure 2-3: Alternative 1 – Repurposing of Existing SST Mixing System

2.2.2.2 Alternative 2 – Installation of Pumps within Existing Sludge Mixing Building

The second alternative (Figure 2-4) includes purchasing two positive displacement style pumps, one duty and one standby, and installing them in the existing Mixing Building at the SST in place of the 'future mixing pump'. Positive displacement style pumps are ideal for this application because they provide a constant flow rate at a given pump speed regardless of the head condition. Hazen recommends rotary lobe pumps because of the ease of maintenance relative to other styles of positive displacement pumps. The suction side of the pumps would tie in at the existing blind flange meant for a 3rd mixing pump. The discharge side would be a new 4-inch line.

Alternative 2 balances short term savings and consistent operation. It utilizes existing infrastructure while upgrading pumping capability. The rotary lobe pumps will be sized proportionally to the feeding rate of the BFP. Preliminary pump sizing calculations result in an operating flow range between 50 and 150 gpm.

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Figure 2-4: Alternative 2 – Installation of Pumps within Existing Sludge Mixing Building

2.2.2.3 Alternative 3 – Installation of Pumps in New Sludge Transfer Building

The third alternative (Figure 2-5) requires constructing a dedicated Sludge Transfer Building to the north of the mixing building in the green space between the road and SST.