granular activated carbon system - wtad...feb 22, 2017 · cost estimates were developed for two...

Granular Activated Carbon System GAC System Preliminary Engineering Report

February 22, 2017

City of Hannibal, MO

City of Hannibal

GAC System Preliminary Engineering Report City of Hannibal

GAC System Preliminary Engineering Report

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Granular Activated Carbon System Preliminary Engineering Report

© Copyright 2017 Jacobs Engineering Group Inc. The concepts and information contained in this document are the property of Jacobs. Use or copying of this document in whole or in part without the written permission of Jacobs constitutes an infringement of copyright.

Limitation: This report has been prepared on behalf of, and for the exclusive use of Jacobs’ Client, and is subject to, and issued in accordance with, the

provisions of the contract between Jacobs and the Client. Jacobs accepts no liability or responsibility whatsoever for, or in respect of, any use of, or reliance

upon, this report by any third party.

Document history and status

Revision Date Description By Review Approved

0 01/23/17 First Draft – Issued to City of Hannibal Team Team MWM

1 02/22/17 Final – Issued to City of Hannibal Team Team MWM


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Contents

Executive Summary .............................................................................................................................................. 2

1. Introduction ............................................................................................................................................... 4

1.1 Background ........................................................................................................................................... 4

1.2 Objectives .............................................................................................................................................. 4

1.3 Scope and Limitations ........................................................................................................................... 4

2. Water Chemistry ....................................................................................................................................... 6

3. Regulatory Framework ............................................................................................................................. 8

3.1 Primary Drinking Water Standards........................................................................................................ 8

3.1.1 Stage 1 Disinfectants and Disinfection By-products Rule ........................................................... 8

3.1.2 Stage 2 Disinfectants and Disinfection By-products Rule ........................................................... 9

3.1.3 Interim Enhanced Surface Water Treatment Rule (IESWTR) ..................................................... 9

3.1.4 Long-Term (2) Enhanced Surface Water Treatment Rule .......................................................... 9

3.2 Secondary Drinking Water Standards ................................................................................................. 10

3.3 Future Drinking Water Regulations ..................................................................................................... 10

4. Existing WTP ........................................................................................................................................... 12

4.1 Existing Processes .............................................................................................................................. 13

4.2 Existing Operations ............................................................................................................................. 15

4.3 Disinfection Practices .......................................................................................................................... 16

5. Water Quantity and Quality .................................................................................................................... 18

5.1 Water Quantity .................................................................................................................................... 18

5.2 Raw Water Quality .............................................................................................................................. 19

5.3 Treated Water Quality Goals ............................................................................................................... 19

5.4 Finished Water Quality Analysis ......................................................................................................... 21

5.5 Disinfection By-Products ..................................................................................................................... 25

6. Control Measures to Minimize DBPs .................................................................................................... 36

6.1 Overview of Control Measures ............................................................................................................ 36

6.1.1 Alternative Source or Minimize Use of Source with Problematic Water Quality ....................... 36

6.1.2 Control DBP formation in the plant ............................................................................................ 36

6.1.3 Control DBPs in the distribution system. ................................................................................... 38

6.1.4 Summary ................................................................................................................................... 40

6.2 Granular Activated Carbon Treatment ................................................................................................ 40

6.3 Alternative 1: Retrofit GAC into Existing Filters .................................................................................. 41

6.3.1 Conceptual Design .................................................................................................................... 41

6.3.2 Process Flow Diagram .............................................................................................................. 44

6.4 Alternative 2: GAC Filters as Second Stage Filters ............................................................................ 46

6.4.1 Conceptual Design .................................................................................................................... 46

6.4.2 Process Flow Diagram .............................................................................................................. 50


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6.4.3 GAC Contactors Layout ............................................................................................................ 51

7. Alternatives Evaluation .......................................................................................................................... 52

7.1 Capital Cost Estimates ........................................................................................................................ 52

7.2 Operating Cost Estimates ................................................................................................................... 52

7.3 Net Present Value Estimates .............................................................................................................. 54

7.4 Impact to Customer Rates .................................................................................................................. 54

7.5 Preferred GAC Alternative .................................................................................................................. 55

7.5.1 Retrofit GAC into Existing Filters ............................................................................................... 55

7.5.2 GAC Filters as Second Stage Filters ......................................................................................... 55

7.5.3 Preferred Alternative ................................................................................................................. 56

8. Project Implementation .......................................................................................................................... 58

8.1 Treatability Studies .............................................................................................................................. 58

8.1.1 Optimized Coagulation .............................................................................................................. 58

8.1.2 GAC ........................................................................................................................................... 58

8.2 Distribution System Improvements ..................................................................................................... 61

8.3 Implementation Schedule .................................................................................................................... 61

9. References ............................................................................................................................................... 62

Appendix A. Engineers Opinion of Probable Cost

Appendix B. SRF Loan Payments and Fees

Figures

Figure 4-1 Hannibal Water Treatment Plant Process Diagram1 .......................................................................... 14 Figure 5-1 Production (Flow in MGD from January 2011 to September 2016) ................................................... 18 Figure 5-2 Raw Water Alkalinity, Temperature, and Finished Water Alkalinity ................................................... 21 Figure 5-3 Alum Dose and Raw Water Turbidity ................................................................................................. 22 Figure 5-4 Raw Water, Settled Water, and Finished Water Turbidity .................................................................. 23 Figure 5-5 Raw Water, Settled Water, and Finished Water pH ........................................................................... 24 Figure 5-6 Raw Water and Finished Water TOC ................................................................................................. 24 Figure 5-7 Applied Chlorine Dosages and Chlorine Demand of Finished Water ................................................ 25 Figure 5-8 DBP Monitoring Locations .................................................................................................................. 26 Figure 5-9 Locational Running Annual Average (LRAA) of TTHMs at HRH Location ......................................... 27 Figure 5-10 Locational Running Annual Average (LRAA) of HAAs at HRH Location ......................................... 28 Figure 5-11 Locational Running Annual Average (LRAA) of TTHMs at Industrial Location ................................ 29 Figure 5-12 Locational Running Annual Average (LRAA) of HAAs at Industrial Location .................................. 30 Figure 5-13 Locational Running Annual Average (LRAA) of TTHMs at WWTP Location ................................... 31 Figure 5-14 Locational Running Annual Average (LRAA) of HAAs at WWTP Location ...................................... 32 Figure 5-15 Locational Running Annual Average (LRAA) of TTHMs at SSBPS Location .................................. 33 Figure 5-16 Locational Running Annual Average (LRAA) of HHAs at SSBPS Location ..................................... 34 Figure 6-1 Low Profile Underdrain with IMS Cap................................................................................................. 43 Figure 6-2 Retrofit GAC in Existing Filters ........................................................................................................... 43 Figure 6-3 Retrofit GAC into Existing Filters Process Diagram (1 of 2 ) .............................................................. 45 Figure 6-4 Retrofit GAC into Existing Filters Process Diagram (2 of 2) ............................................................... 46 Figure 6-5 Carbon Exhaustion Profile .................................................................................................................. 48


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Figure 6-6 Series Contactors ............................................................................................................................... 48 Figure 6-7 GAC Filters as Second Stage Filters Process Diagram ..................................................................... 50 Figure 6-8 GAC Filters as Second Stage Filters Proposed Layout (3.5 MGD Case) .......................................... 51 Figure 8-1 Jar Test Apparatus ............................................................................................................................. 58 Figure 8-2 Laboratory Test................................................................................................................................... 59 Figure 8-3 Pilot Test Apparatus ........................................................................................................................... 60

Tables

Table 2-1 Summary of SUVA Values ..................................................................................................................... 7 Table 3-1 Stage 1 D/DBPR Maximum Contaminant Levels (MCLs) ..................................................................... 8 Table 3-2 Maximum Residual Disinfectant Levels (MRDLs) ................................................................................. 8 Table 3-3 Minimum TOC Removal Requirements under the Enhanced Coagulation Criteria of the Stage 1

D/DBP Rule .......................................................................................................................................... 9 Table 3-4 Log Removal Credits Filtration ............................................................................................................ 10 Table 3-5 Secondary Drinking Water Standards ................................................................................................. 10 Table 3-6 Health Advisories for Emerging Contaminants .................................................................................... 11 Table 4-1 Salient Features of Existing WTP ........................................................................................................ 12 Table 4-2 Existing Design and Operational Criteria for Unit Processes at WTP ................................................. 12 Table 4-3 Water Treatment Chemicals1 ............................................................................................................... 15 Table 4-4 Typical Chemical Use at the WTP ....................................................................................................... 15 Table 5-1 Water Quantity (January 2011-November 2016) ................................................................................. 18 Table 5-2 Raw Water Quality (January 2011-November 2016) ........................................................................... 19 Table 5-3 Finished Water Quality Goals .............................................................................................................. 19 Table 5-4 Finished Water Quality (January 2011-November 2016) .................................................................... 21 Table 5-5 Total Chlorine and Chlorine Demand (January 2011 - November 2016) ............................................ 25 Table 6-1 GAC Contact Time - Retrofit Existing Filters ....................................................................................... 44 Table 7-1 Total Project Cost for GAC Treatment Alternatives ............................................................................. 52 Table 7-2 Carbon Costs for Retrofit GAC into Existing Filters ............................................................................. 53 Table 7-3 Carbon Costs for GAC Filters as Second Stage Filters 2.7 MGD Case .............................................. 53 Table 7-4 Carbon Costs for GAC Filters as Second Stage Filters 3.5 MGD Case .............................................. 53 Table 7-5 Net Present Value ................................................................................................................................ 54 Table 7-6 Estimated Impact to Customer Rates .................................................................................................. 55 Table 8-1 Anticipated Implementation Schedule ................................................................................................. 61


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Executive Summary

Until mid-2015, the City of Hannibal Water Treatment Plant (WTP) disinfected treated water using chlorine as the primary disinfectant. However, the use of chlorine resulted in the formation of disinfection by-products (DBPs) in the water distribution system that reached levels in excess of regulatory limits. The City hired a Consultant to study the problem and make recommendations for a solution, which resulted in the replacement of chlorine as a primary disinfectant to ultraviolet (UV) as a primary disinfectant followed by chloramines (chlorine combined with ammonia) as a secondary disinfectant to minimize DBP formation and help maintain a persistent residual in the distribution system. The results of the change from chlorine to chloramines in September 2015 has resulted in substantial reductions in the DBP levels in the water distribution system and Hannibal has been in compliance with current regulations for DBPs.

Since this change, however, some residents have become concerned about the use of chloramines. A citizen group gathered sufficient signatures to place a referendum on the April 2017 ballot, which asks whether the City should be required to cease the addition of ammonia (to form chloramines) and revert to chlorine disinfection.

The City commissioned Jacobs to conduct this study to evaluate water treatment technologies required to facilitate the return to chlorine disinfection and to more fully understand the economic implications of that change.

In summary, the City will need to implement several strategies to minimize DBPs in the finished water if it reconverts from chloramine to chlorine as a secondary disinfectant. These include:

Optimizing Treatment Plant Operations

- Optimize Coagulation

- Optimize chlorine residual and pH

Install New Treatment Technologies

- Granular activated carbon (GAC)

Implement best management practices in the distribution system, which include

- Minimizing water age and flushing

- Mixers in storage tanks

The City should implement the above strategies to minimize the DBPs in the distribution system. In the event DBPs continue to be an issue, the City should evaluate decentralized treatment such as air stripping.

Cost estimates were developed for two approaches to adding GAC to the WTP; retrofitting the existing filters with GAC, and adding new GAC contactors as second stage filters after the existing filters. Two flow cases were considered for second stage filtration, 3.5 MGD for current average design capacity and 2.7 MGD, which reflects current average daily flow of 3.2 MGD less the amount of water (0.5 MGD) used by PWSD No. 1 of Ralls County. A total constructed cost estimate for each project alternative, including project management, engineering, construction support, and construction observation services were estimated to be:

Alternative Total Project Cost

1 – Retrofit GAC into Existing Filters $1,981,000

2 – GAC Filters as Second Stage Filters (2.7 MGD) $9,367,000



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Additionally, the impact of the debt service on the equipment and the added operating costs for carbon replacement on customer rates was estimated based on an average annual billing.

Annual Debt

Service

per 1000 gallons

Annual Operating Cost

per 1000 gallons

Annual Total cost

per 1000 gallons

Monthly Cost Increase for 5,000 gallon per month customer

1 – Retrofit GAC into Existing Filters $0.18 $0.61 $0.79 $3.96

2 – GAC Filters as Second Stage Filters (2.7 MGD)

$0.84 $0.48 $1.32 $6.58


$0.78 $0.49 $1.27 $6.34

These costs do not include costs for improvements in the distribution system because the need for and extent of such improvements is difficult to predict at this time.

Treatability studies will be necessary for predicting system performance, developing design criteria and validating the process. A small-scale pilot could help determine the effectiveness of the technology with respect to DBP reduction.

Assuming the referendum passes, the following table presents a schedule to implement the cessation of chloramines and return to chlorine disinfection:

Task Start Date End Date

1. Laboratory testing of selected alternative and initial planning coordination with MDNR

April 2017 January 2018

2. Pilot testing January 2018 August 2018

3. Preliminary Engineering Report for SRF application and MDNR plan approval

September 2018 November 2018

4. Final Design, MDNR review and permit approval December 2018 September 2019

5. Bid Phase October 2019 December 2019

6. Construction January 2020 January 2021

A rate increase would likely need to be in effect by January 2020 to support the new cost basis.


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1. Introduction

1.1 Background

Until September of 2015, the City of Hannibal Water Treatment Plant (WTP) disinfected treated water using sodium hypochlorite (chlorine) as a primary disinfectant. While using chlorine as a disinfectant, the City was confronted with an increase in disinfection by-products (DBPs) within their distribution system and the distribution system of their customer, Public Water Supply District No. 1 of Ralls County. The City hired a Consultant to study the issue of DBPs and make recommendations for achieving compliance with Stage 1 and Stage 2 of the Disinfectants Disinfection By-Products Rule (D/DBPR). The results of that study was the recommendation to use ultraviolet light (UV) as a primary disinfectant and use chloramine (combination of chlorine and ammonia) as secondary disinfectant to minimize DBP formation and help maintain a persistent residual in the distribution system.

The City completed these upgrades in September of 2015; at the present time the system has been in compliance with the requirements of the Stage II D/DBPR. In mid-2015, some residents began opposing the use of the current disinfection process, specifically the use chloramines as a secondary disinfectant. They have gathered sufficient signatures (10% of registered voters) to place this issue on the April 2017 referendum, which, if approved by voters, would require the City to discontinue using chloramines and revert to chlorine to meet disinfection requirements. As a result, the City contracted with Jacobs to evaluate alternatives to minimize DBPs, in the event it has to revert to chlorine as a secondary disinfectant. The City specifically wishes to evaluate the alternative of incorporating granular activated carbon (GAC) in the WTP to reduce the organics in the water; the organics are precursors to the formation of DBPs.

1.2 Objectives

The primary objective of this study is to evaluate alternatives to incorporate GAC into the existing WTP to comply with the existing Stage 2 D/DBPR and to develop conceptual designs capital and operating cost estimates of the alternatives. Other objectives include:

Review the issue of DBPs by evaluating operations and performance of the existing WTP.

Identify additional strategies to minimize DBP formation.

1.3 Scope and Limitations

This Report has been prepared by Jacobs for the City of Hannibal and may only be used and relied on by the City for the purpose agreed between Jacobs and the City.


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2. Water Chemistry

This section presents a brief description of water quality parameters that were evaluated as part of this study, and will be discussed throughout this report.

Natural organic matter (NOM): Natural Organic Matter (NOM), a precursor to Disinfection By-Products (DBPs), is a heterogeneous mixture of naturally occurring organic components consisting of humic substances (humic and fulvic acids), as well as various non-humic biochemicals such as proteins and carbohydrates. Adding further complexity is the fact that NOM varies significantly depending on its source. NOM is difficult to quantify due to its complexity. For practical purposes, organic matter is quantified by measuring organic carbon concentrations as total organic carbon (TOC), particulate organic carbon (POC), and dissolved organic carbon (DOC). It is also common to quantify NOM by measuring the amount of UV light it absorbs i.e. ultraviolet light absorbance at 254 nm (UV254).

NOM can be broken down into two subcategories:

a) High molecular weight, hydrophobic, aromatic NOM which is not only the most reactive (in terms of forming DBPs) but is also the most amenable to removal via coagulation. This type of NOM is also referred as the humic portion of NOM.

b) Low molecular weight, hydrophilic NOM which is much less amenable to removal by coagulation but is also less reactive with chlorine to form DBPs. This type of NOM is also referred as the non-humic portion of NOM.

Assuming optimized treatment, the residual NOM remaining after enhanced coagulation is primarily made up of low-MW and non-humic material. The latter NOM fractions represent the portion of the NOM that is resistant to removal by coagulation.

Total Organic Carbon (TOC): TOC is a measure of the total organic content of water which includes POC and DOC. This test provides a generic measurement of organic carbon content and it is not necessarily a consistent measure of DBP precursor concentrations. This is because the TOC analysis includes both the high and low molecular weight NOM. Also TOC does not provide an indication of the aromaticity, aliphatic nature, functional group chemistry, or chemical bonding associated with natural organic molecules all of which may affect DBP formation. The reactivity of chemical bonds and functional groups is likely to be a significant factor in explaining why different waters with the same TOC concentration will form different DBP concentrations under identical disinfection conditions. In addition to reducing the potential to form DBPs, enhancing existing treatment to reduce TOC levels also can result in added benefits that include reduced potential for bacterial regrowth in the distribution system, improved taste and odor, reduction in disinfectant demand, and reduced levels of unknown or unregulated DBPs.

Dissolved Organic Carbon (DOC): DOC is operationally defined as the organic carbon in water that has passed through a 0.45 micron filter. For many freshwaters, it has been reported that DOC represents 83% to 98% of the TOC (Owen et al, 1993). Most of the DOC in natural waters consists of non-biodegradable (or refractory) organic matter. A smaller portion of the DOC consists of biodegradable (or assimilable) organic matter (biodegradable dissolved organic carbon-BDOC), most of which can be removed by biological activity within filters.

Absorbance of ultraviolet light at 254 nanometers (UV254): UV absorbing constituents absorb UV light in proportion to their concentration. UV254 absorbance can be used as a surrogate for the concentration of organic molecules with aromatic groupings or extended conjugation and helps to predict the tendency of NOM to produce DBPs. The relationship between UV254 and TOC is unique for each raw water source. However, for a given raw water source, increases in either TOC or UV absorbance indicate increasing NOM concentrations. It is measured using water samples filtered through a 0.45 micron filter.


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Specific ultraviolet absorbance (SUVA): SUVA provides (in theory) an indication of the humic content of NOM, which is believed to be the more reactive portion when it comes to DBP formation. It is calculated as follows: SUVA = (UV254*100)/DOC. Table 2-1 summarizes the typical water treatment characteristics relative to the SUVA value. As shown in Table 2-1, SUVA < 2.0 low humic content-not amenable to enhanced coagulation; SUVA 2-4 moderate humic content amenable to enhanced coagulation; SUVA > 4.0 high humic content very amenable to enhanced coagulation. SUVA values of 4 to 5 L/mg-m are typical of waters containing primarily humic material. SUVA can be predictive of the removal capability of water treatment practices. Several studies reported that waters with a high SUVA value exhibited large reductions in SUVA and TOC as a result of enhanced coagulation, indicating an overall substantial removal of NOM. Waters with low SUVA values, however, exhibited relatively low reductions in SUVA and TOC, indicating an overall insignificant removal of NOM.

Table 2-1 Summary of SUVA Values

SUVA Value NOM Composition Coagulation Properties Anticipated DOC Removal

Greater than 4.0 Mostly aquatic humics, high hydrophobicity, high molecular weight

NOM has large impact on coagulation, good DOC removal possible

Greater than 50 percent for aluminum based coagulants

2.0 to 4.0 Mixture of aquatic humics and other NOM. NOM is a mix of hydrophobic and hydrophilic, varying molecular weights

NOM has some impact on coagulation, some DOC removal possible

25 to 50 percent for aluminum-based coagulants

Less than 2.0 Mostly non-humics. Mostly hydrophilic, lower molecular weights

NOM has low impact on coagulation, low DOC removal

Less than 25 percent for aluminum-based coagulants

* Source: Edzwald, James, K. Drinking Water Institute (2006).

Total Trihalomethanes (TTHMs): TTHMs are a group of four chemicals (chloroform, bromodichloromethane, dibromochloromethane, and bromoform) that are formed along with other DBPs when chlorine reacts with naturally occurring organic and inorganic matter in water.

Haloacetic Acids (HAAs): HAAs are a group of chemicals that are formed along with other DBPs when chlorine reacts with naturally occurring organic matter in water. The regulated haloacetic acids is for the sum of five HAAs known as HAA5, which include: monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid.


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3. Regulatory Framework

Finalized regulations promulgated by the United States Environmental Protection Agency (USEPA) include primary and secondary drinking water standards. Primary standards address contaminants that may affect health and secondary standards address contaminants that may affect the aesthetic and economic qualities of the water. Primary standards are enforceable and are enforced by state agencies having primacy, in this case the Missouri Department of Natural Resources (MDNR).

This section provides a summary of the current USEPA and MDNR drinking water regulations applicable to the improvements at the water treatment plant.

3.1 Primary Drinking Water Standards

3.1.1 Stage 1 Disinfectants and Disinfection By-products Rule

Stage 1 of the Disinfectants and Disinfection By-products Rule (Stage 1 D/DBPR) was the first of a staged set of rules that were created to reduce the allowable levels of disinfection byproducts (DBPs) in drinking water. The existing Maximum Contaminant Levels (MCLs) included in the Stage 1 D/DBPR (published in 1998) are contained in Table 3-1. The MCL for Stage 1 is based on a system-wide four-quarter running annual average (RAA).

Table 3-1 Stage 1 D/DBPR Maximum Contaminant Levels (MCLs)

Disinfection By-product Unit MCL

Total Trihalomethanes (TTHMs)

ppb or g/L 80

Haloacetic Acids (HAAs) ppb or g/L 60

Bromate ppb or g/L 10

The limits on disinfectants in the Stage 1 D/DBP Rule were finalized as Maximum Residual Disinfectant Levels (MRDLs) instead of MCLs. The final limits on disinfectants (MRDLs) are contained in Table 3-2. The City of Hannibal currently uses chloramines as the disinfectant in the distribution system.

Table 3-2 Maximum Residual Disinfectant Levels (MRDLs)

Disinfectant Unit MRDL

Chlorine ppm or mg/L 4.0

Chloramines ppm or mg/L 4.0

Under the final Stage 1 D/DBP rule, surface water systems (e.g. City of Hannibal) or groundwater under the influence of surface water systems operating with conventional treatment were required to install (unless systems meet exception criteria) and operate enhanced coagulation or enhanced softening for removal of TOC that will further reduce DBP formation.

Also, in the Stage 1 D/DBPR, USEPA added a requirement that all conventional filtration plants treating surface water reduce the concentration of TOC in their water by pre-determined amounts regardless of the TTHM and HAA levels they form. These requirements are shown in Table 3-3.


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Table 3-3 Minimum TOC Removal Requirements under the Enhanced Coagulation Criteria of the Stage 1 D/DBP Rule

Required TOC Percent Removal

Source Water

TOC (mg/L)

Source Water Alkalinity, mg/L as CaCO3

0-60 >60-120 >120

>2.0 to 4.0 35% 25% 15% >4.0 to 8.0 45% 35% 25%

> 8.0 50% 40% 30%

This Table essentially states that if a conventional filtration plant such as City of Hannibal WTP is treating a water source containing a TOC concentration higher than 2.0 mg/L but less than or equal to 4.0 mg/L, and an alkalinity greater than 120 mg/L as CaCO3, then the TOC removal required by enhanced coagulation at this plant is a minimum of 15%.

3.1.2 Stage 2 Disinfectants and Disinfection By-products Rule

The Stage 2 Disinfectants and Disinfection By-products Rule (Stage 2 D/DBPR) and the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) are a set of interrelated regulations that address risks from microbial pathogens and disinfectants/disinfection byproducts. Both the Stage 2 D/DBPR and the LT2ESWTR were promulgated simultaneously in January 2006 to address concerns about risk tradeoffs between pathogens and DBPs. The goal of the Stage 2 DBPR is to target the highest risk systems for changes beyond those required by Stage 1 DBPR.

DBPs as currently regulated under Stage 2 of the D/DBP rule, retain the same MCLs for DBPs from Stage 1, but also require that reporting of DBPs be site specific, based on locational running annual averages (LRAAs) instead of reporting running annual average values (RAAs). Sampling sites for the Stage 2 DBP Rule are selected through the Initial Distribution System Evaluation (IDSE) process as required by Stage 2 of the D/DBPR.

3.1.3 Interim Enhanced Surface Water Treatment Rule (IESWTR)

The Interim ESWTR applies to surface water (e.g. City of Hannibal) and groundwater under the direct influence of surface water systems serving over 10,000 people. The first draft of the Interim ESWTR was published in 1998 and requires that:

All surface water systems that filter and that serve a population of greater than10,000 people must achieve at least a 2-log removal of Cryptosporidium

Surface water systems that serve more than 10,000 people and use conventional treatment or direct filtration must achieve the following: (1) the turbidity level of a system’s combined filtered water must be less than or equal to 0.3 NTU in at least 95% of the measurements taken each month, and (2) the turbidity level of a system’s combined filtered water must at no time exceed 1 NTU.

3.1.4 Long-Term (2) Enhanced Surface Water Treatment Rule

The Long-Term (2) Enhanced Surface Water Treatment Rule (LT2ESWTR) was developed to reduce illness linked with the contaminant Cryptosporidium. Surface water systems serving greater than 10,000 people were required to conduct monitoring for Cryptosporidium (and E. coli) for 24 months to determine the source water concentration of Cryptosporidium for a given system. Subsequently the system would be placed in a source water classification threshold (“Bin”). Dependent upon the Bin Classification additional treatment for Cryptosporidium may be required. The rule specifies a minimum removal/inactivation of 4-log removal for viruses, 3-log removal for Giardia and 2-log removal of Cryptosporidium. Additional log removal for Cryptosporidium may be required, as per LT2ESWTR. Log credits can be given to well-operated filtration systems (e.g. City of Hannibal WTP) as per Table 3-4.


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Table 3-4 Log Removal Credits Filtration

Filtration Type Potential Log-Removal Credit for the Removal Of

Giardia lamblia Viruses Cryptosporidium

Conventional 2.5 2.0 2.0

Membrane Filtration1 2.5 2.0 2.0

Direct 2.0 1.0 2.0

Slow Sand 2.0 2.0 2.0

Diatomaceous Earth 2.0 1.0 2.0

Second Stage Filtration2 --- ---- 0.5

Notes: 1. Membrane filtration treatment technologies including either reverse osmosis, nanofiltration, or ultrafiltration are given a 2.0 log-removal credit for Cryptosporidium, a 2.0 log-removal credit for viruses, and a 2.5 log-removal credit for Giardia Lamblia if grab samples taken every four hours or continuous monitoring show turbidity levels equal to or less than 0.3 NTU 95% of the time and if all samples are equal to or less than 1 NTU. 2. To receive credit under LT2ESWTR, coagulation is required prior to first filter, both filtration steps need to treat 100% of the flow

3.2 Secondary Drinking Water Standards

Secondary standards are not enforced by the USEPA but are strongly recommended and may be enforced at the discretion of individual state primacy agencies. The Secondary Drinking Water Standards are summarized in Table 3-5.

Table 3-5 Secondary Drinking Water Standards

Parameter Standard Parameter Standard

Aluminum 0.05 to 0.2 mg/L Iron 0.3 mg/L

Chloride 250 mg/L Manganese 0.05 mg/L

Color (True) 15 color units Odor 3 threshold odor number

Copper 1.0 mg/L pH 6.5 to 8.5

Corrosivity Non-corrosive Silver 0.10 mg/L

Fluoride 2.0 mg/L Sulfate 250 mg/L

Foaming Agents 0.5 mg/L Total Dissolved Solids

500 mg/L

Zinc 5 mg/L Hardness none

3.3 Future Drinking Water Regulations

Currently there are no US EPA regulations for harmful, emerging contaminants such as cyanotoxins (algal toxins). Regulations addressing cyanotoxins, either as a group or individually, are likely at some point in the future. Cyanotoxins are listed on the Fourth Contaminant Candidate List (CCL4) and are also included in the Fourth Unregulated Contaminant Monitoring Rule (UCMR4) both published last year.


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USEPA has released health advisories for two emerging types of contaminants. These are:

Algal Toxins

Perfluorinated Compounds (PFCs)

The US EPA developed ten day health advisories for two key cyanotoxins of concern and lifetime health advisories for PFCs (Table 3-6).

Table 3-6 Health Advisories for Emerging Contaminants

Contaminant Unit Ten Day Health Advisory Lifetime Health Advisory

Microcystin ppb or g/L 0.3-for children younger than school age

1.6-for all age groups

-

Cylindrospermopsin ppb or g/L 0.7-for children younger than school age

3.0-for all age groups

-

Perfluorooctanoic acid (PFOA),

ppt or ng/L - 70-Individually or combined with PFOS

Perfluorooctane sulfonate (PFOS)

ppt or ng/L - 70-Individually or combined with PFOA

As part of the planning process for the City of Hannibal, treatment process options or operational improvements that would be required to reduce DBPs and also treat these emerging contaminants will be identified.


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4. Existing WTP

The City of Hannibal Board of Public Works currently operates and manages a conventional surface water treatment plant (WTP) with an average capacity of 3.5 million gallons per day (MGD). Approximately 0.5 MGD of treated water is purchased by the Ralls County PWSD and is considered as a “consecutive system”, whereas City of Hannibal, which produces and sells the water to Ralls County, is considered as a “wholesale system”. The WTP is comprised of a combination of structures built over 100 years ago and has undergone subsequent expansions and improvements over the years. Table 4-1 shows salient features of the WTP and associated water quality issues.

Table 4-1 Salient Features of Existing WTP

System Location Capacity Description Key Issues of

Concern

City of Hannibal Board of Public Works WTP

Riverview Park

3.5 MGD (average)

7.5 MGD

(peak)

Source: Mississippi River with intake structure Treatment: Conventional Population: 17,500 Number of Service Connections: 7,700

Algae, taste and odor, TOC, disinfection by-products (DBPs)

Table 4-2 shows various unit processes at the WTP and design and operational criteria.

Table 4-2 Existing Design and Operational Criteria for Unit Processes at WTP

Unit Process Description and Units Value

Intake Structure and Pump Station

One Pipe from Mississippi River to Intake Well (inches)

24

One Pipe from Intake Well to Pump House (inches)

30

3 Dry pit Pumps (gpm/min of each pump) 3500

Two pipes convey water to Pre-sedimentation Basin (inches)

14 & 20

Pre-sedimentation Basin

Number of Tanks 1

Side Water Depth (ft) 19.3

Capacity (MG) 3.5

Cleaning Frequency (1/year); Manual Cleaning

2

Hydraulic Retention Time (HRT) at Nominal Design Flow1 (hours)

24

HRT at Peak Design Flow Rate2 (hours) 10.3

Primary Flocculation and Sedimentation Basin

Number of Tanks 1


Capacity (MG) 2.5

HRT at Nominal Design Flow1 (hours) 17.3

HRT at Peak Design Flow Rate2 (hours) 8


13

Unit Process Description and Units Value

Secondary Sedimentation Basin

Number of Tanks 1

Capacity (MG) 1.0

HRT at Nominal Design Flow1 (hours) 6.8

HRT at Peak Design Flow Rate2 (hours) 3.25

Filter Feed Basins

Number of Tanks 2

Capacity of Each Tank (MG) 0.5

Width (feet) x Length (ft) of each Tank 45 x 90


HRT at Nominal Design Flow1, min 6.8

HRT at Peak Design Flow Rate2, min. 3.25

Filtration

Number of Filters 4

Width (feet) x Length (feet) of each filter Two cells per filter at

28.83 x 9.33

Filter Media (gravel, sand, anthracite); Depth of each media (feet)

1

Total area of Filters (sq. ft.) 2152

Surface Loading Rate at Nominal Design Flow Rate1 (gpm/sq.ft)

1.1

Surface Loading Rate at Peak Design Flow Rate2 (gpm/sq.ft)

2.4

UV Reactors (Medium Pressure)

Number of Trains 2.0

Maximum Flow Rate (MGD) 10

Average Flow Rate (MGD) 3.5

Log Cryptosporidium Inactivation 2.5

Transfer Pumps Number of Pumps 2

Rated Capacity of Each Pump (MGD) 10

Clearwell Storage Capacity (MG) 2.5

Dimensions (diameter x depth in feet) 120 x 30

Notes: 1. Nominal or Average Design Flow = 3.5 MGD; Peak Design Flow = 7.5 MGD 2. Design Parameters obtained from Horner and Shifrin Inc. Report titled “Disinfection By-Products Compliance Study” dated September, 2012

4.1 Existing Processes

Figure 4-1 shows the various processes located in the WTP. Treatment of the Mississippi river includes pre-sedimentation, coagulation with alum, primary sedimentation, secondary sedimentation with lime softening, filtration and primary disinfection achieved with ultraviolet (UV) light. The National Pollutant Discharge Elimination System (NPDES) permit allows waste streams (e.g. filter backwash) to be discharged back into the Mississippi river through two outfalls as shown in Figure 4-1.

Based on the source water testing for Cryptosporidum (LT2ESWTR requirement), the WTP was placed in “Bin 2”, which required an additional 1.0 Log removal/inactivation of Cryptosporidium. As such, the City decided to incorporate an UV disinfection system as the primary disinfectant in September of 2015, as the most effective and economical method to comply with the requirements of LT2ESWTR.


14

Chlorine is added prior to the filters to control algae and chloramines are used as a secondary disinfectant to meet disinfection requirements and maintain a chlorine residual in the distribution system. The City switched to chloramines in September of 2015, as a reliable and economical alternative to chlorine, to reduce the DBPs in their distribution system. Although chloramines are a weak disinfectant compared to chlorine, it is a longer lasting disinfectant, as their residuals persist longer in the distribution system.

Figure 4-1 Hannibal Water Treatment Plant Process Diagram1

NOTES: 1. At present, the WTP is using Polyaluminum Chlorosulfate as the coagulant, poly-dadmac as the raw polymer, DFLOC 3079 as filter aid polymer and wood based carbon from Aqua Nuchar


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4.2 Existing Operations

Chemicals used by the WTP and their point of addition in the WTP are summarized in Table 4-3.

Table 4-3 Water Treatment Chemicals1

Chemical Point of Addition Purpose

Polymer a) Intake Structure b) Pre-filtration

a) Control Zebra Mussels & reduce turbidity in the Pre-sedimentation Basin

b) Filter-aid to reduce turbidity

Sodium Permanganate Pre-sedimentation Basin Pre-oxidation

Copper Sulfate Pre-sedimentation Basin Control Algae

Alum a) Primary Flocculation b) Pre-filtration

Coagulant to reduce turbidity and TOC

Lime Secondary Settling Basin To adjust pH

Sodium hypochlorite Pre-filtration Control algae, meet disinfection requirements

Powdered Activated Carbon (PAC)

Primary flocculation and settling basin

Taste and Odor Compounds

Fluoride Pre-filtration To reduce tooth decay

Chloramines (Sodium hypochlorite with ammonium sulfate)

Post-Filtration in the Transfer Well and prior to Clearwell

Secondary disinfection and maintain a residual in the distribution system

Note: 1. “Disinfection By-Products Compliance Study” by Horner & Shiffrin Inc. dated September 2012 and site tour on 11/16/2016

Table 4-4 summarizes the chemical use at the WTP. The chemicals used at the WTP are included in the first column and the minimum, median, average, 90th percentile and maximum chemical usages are included in the subsequent columns. The 90th percentile is included in the Table to eliminate potential outliers that may exist in the ‘maximum’ column.

Table 4-4 Typical Chemical Use at the WTP

Daily Chemical Usage1

Parameters Units Average Maximum3 Minimum Median 90th

Percentile

Lime mg/L 23.2 93.0 0.25 25.2 43.1

Alum mg/L 114.8 442.8 1.9 79.7 241.2

Sodium Hypochlorite2 mg/L 46.6 172.1 6.4 41.3 75.0

Fluoride mg/L 3.7 18.4 0.07 3.6 5.2

Raw Polymer mg/L 1.3 5.3 0.06 1.1 2.4

Filter-aid Polymer mg/L 1.1 23.0 0.04 0.4 1.1

Powdered Activated Carbon mg/L 13.8 55.2 0.01 11.2 23.6

Notes: 1. Data from January 2011 - November 2016 2. Dosages for sodium hypochlorite are the total of feeding the chemical both pre-filtration and post-filtration. 3. Extreme values suggest that there was an error in collecting the data. 4. At present, the WTP is using Polyaluminum Chlorosulfate as the coagulant, poly-dadmac as the raw polymer, DFLOC 3079 as filter aid polymer and wood based carbon from Aqua Nuchar


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4.3 Disinfection Practices

A well operated filtration system, such as the Hannibal WTP, is awarded log credits for inactivation/removal for Giardia (2.5 Log) and viruses (2.0 Log) per Table 3-4 (Section 3). The primary disinfection process currently in place (UV) exceeds the required 0.5 log inactivation of Giardia while meeting the 2.5 Log inactivation of Cryptosporidium. No credit is offered to UV for virus inactivation. Currently, the WTP achieves the required 2.0 log inactivation of virus through a combination of pre-chlorination applied prior to the filters and chloramines applied prior to the clearwell. To meet the MDNR requirements for CT (residual disinfectant concentration x contact time), a chlorine residual of 0.5 mg/L is maintained in the WTP (post-filtration) prior to the application of chloramines in the clearwell.

USEPA Surface Water Treatment Rule (SWTR) requires that water systems such as the City of Hannibal that serve a population of more than 3,300 continuously monitor the disinfectant residual of the water that enters the distribution system. Whenever the residual drops below 0.2 mg/L, the water system must notify the State. Throughout the entire water distribution system, a detectable free chlorine residual must also be present to prevent harmful microbial re-growth that could affect public health (SWTR requirements). Per MDNR requirements, a minimum free chlorine residual of 0.2 mg/L or more has to be maintained at all locations in the distribution system at all times. As shown in Table 3-2 in Section 3, the MRDL is 4.0 mg/L as chlorine (3mg/L monchloramine equivalent), while using chlorine or chloramine as a disinfectant.

The WTP used chlorine prior to September 2015 and chloramines thereafter as a disinfectant. To maintain these levels, the chlorine residual level in the water leaving the WTP (post-filtration) must be higher to account for chlorine demands in the distribution system. To have a residual of 0.2 mg/L (plant goal) at the extremes of the distribution system, the finished water leaving the plant has to average 2.50 mg/L with levels ranging from 2.5 to 5.0 mg/L (Source: Daily Test Sheet, May 2016). In the month of May 2016, the average chlorine residual at the plant tap was 2.50 mg/L. Typical chloramine concentrations of 0.2-2 mg/L are found in drinking water supplies where monochloramine has been used as a disinfectant to provide a residual in the distribution system.


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5. Water Quantity and Quality

In this Section, an analysis of the raw water quantity and quality, finished water quality and disinfection by-products is presented. This analysis is based on an extensive review of the monthly operating reports (MORs), daily testing sheets, other reported documents (Disinfection By-products Compliance Study by Horner and Shifrin Inc., September, 2012) and from personal communications with plant operators and managers.

5.1 Water Quantity

The WTP has an average water production capacity of 3.5 MGD and a peak capacity of 7.5 MGD (Disinfection By-products Compliance Study by Horner and Shifrin Inc., September, 2012). A statistical analysis of the last 5 years of data showed that the average flow of treated water from the plant has reduced to 3.2 MGD (Table 5-1) with a 90th percentile of 3.7 MGD. The 90th percentile is included in the Table to eliminate potential outliers that may exist in the ‘maximum’ column. The maximum flow treated by the plant was 8.6 MGD on June 7, 2016, and 7.9 MGD on June 6, 2016 (Table 5-1 and Figure 5-1).

Peaking factors (maximum day/average day) were calculated based on the data in Table 5-1. Typical peaking factors range from 1.5-2.0. Additional design criteria for each alternative based on these flows is discussed in Section 6.

Table 5-1 Water Quantity (January 2011-November 2016)

Production in MGD

Average Maximum1 Minimum Median 90th

Percentile Peaking Factor2

Peaking Factor3

3.2 8.6 0.1 3.2 3.7 2.7 2.3 NOTES: 1. Maximum Flow on 6/7/2016 was 8.6 MGD; Maximum Flow on 6/6/2016 was 7.9 MGD 2. Peaking Factor based on Maximum Flow of 8.6 MGD 3. Peaking Factor based on Maximum Flow of 7.5 MGD

Figure 5-1 Production (Flow in MGD from January 2011 to September 2016)

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5.2 Raw Water Quality

It is our understanding that the City will continue to utilize the existing surface water supply, the Mississippi River, in the foreseeable future. Raw water quality information of the existing surface water source was presented in the Disinfection By-products Compliance Study by Horner and Shifrin Inc., dated September, 2012. Table 5-2 includes a summary of raw water quality measured daily from January 2011 to November 2016. The main water quality parameters are included in the rows and the minimum, median, average, 90th percentile and maximum levels are included in the columns. The 90th percentile is included in the Table to eliminate potential outliers that may exist in the ‘maximum’ column.

Table 5-2 Raw Water Quality (January 2011-November 2016)

Raw Water Quality

Water Quality Parameter

Units Average Maximum Minimum Median 90th Percentile

Turbidity NTU 21.2 407.3 1.9 9.0 50.0

Temperature degree F (0C) 54.3 (12.4) 96.4 (35.7) 1.0 (-17.2) 57.1 (13.9) 78.1 (25.6)

pH1 standard units 8.02 8.95 7.29 8.01 8.31

Alkalinity mg/L CaCO3 172 220 90 178 200

Total Organic Carbon (TOC)

mg/L 5.1 11.1 1.9 5.0 6.3

Hardness2 mg/L CaCO3 233 246 214 236 243 Notes: 1. pH data from daily test sheets (June 2014-May 2016) 2. Hardness data from daily test sheets (April 2016-May 2016)

The raw water can be characterized as neutral to alkaline pH, high alkalinity, hard water (hardness of 150-300 mg/L as CaCO3 is classified as hard water), with moderate to high turbidity and total organic carbon (TOC).

One significant water quality issue for the source water is total organic carbon (TOC) which is produced by allochthonous (decay of leaves and vegetation) and autochthonous (algae) sources. Algal blooms have been noticed in the Mississippi River (Disinfection By-products Compliance Study – Addendum 1 by Horner and Shifrin Inc., June, 2014). The raw water contains elevated levels of TOC (maximum TOC was 11.1 mg/L with a 90th percentile of 6.3 mg/L), which are direct precursors for the formation of disinfection by-products.

5.3 Treated Water Quality Goals

The water quality goals for full-scale treatment include compliance with all primary and secondary water quality standards (see Section 2) along with pathogen removal as per EPA’s Long-Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR). Table 5-3 summarizes the finished water quality goals relevant to this project.

Table 5-3 Finished Water Quality Goals


Significance Water Quality

Goal

Water Quality

Standard

Standard

Reference

Total Organic Carbon (TOC)

DBP precursors

Chlorine demand Stable water quality

Higher removals strongly recommended4

>15-30% removal

Stage 1 D/DBP Rule


20


Significance Water Quality

Goal

Water Quality

Standard

Standard

Reference

Turbidity

Filtration effectiveness

Indicator parameter for pathogens

< 0.1 NTU

<1 NTU at all times <0.3 NTU 95%

of all daily samples per month

NPDWR1 Treatment Technique IESWTR

pH Quantity of chemicals

DBP formation Concrete erosion,

calcification, corrosion potential

7.7-8.05 Between 6.5 – 8.5 NSDWR2

Conductivity

Lead and Copper uptake potential

<500 mg/L as Total Dissolved Solids

<500 mg/L as Total Dissolved Solids

NSDWR2

Iron Filter Clogging Color in finished

water

< 0.3 mg/L <0.3 mg/L NSDWR2

Manganese Filter Clogging Color in finished

water

< 0.05 mg/L < 0.05 mg/L NSDWR2

Color Aesthetic value indicator of organics

in the water which are DBP precursors

< 5 PtCo < 15 PtCo NSDWR2

Methyliosoborneol (MIB)

Taste and odor causing compound

<10 ng/L N/A Human Threshold

Geosmin Taste and odor causing compound

<5 ng/L N/A Human Threshold

TTHMs Disinfection By-products

<64 ppb or μg/L6 <80 ppb or μg/L

Stage 1 D/DBP Rule

HAAs Disinfection By-products

<48 ppb or μg/L6 <60 ppb or μg/L Stage 1 D/DBP Rule

Hardness Distribution System Scale buildup

120-150 mg/L as CaCO33

N/A N/A

Notes: 1. National Primary Drinking Water Regulation 2. National Secondary Drinking Water Regulations 3. If Softening is used, it is assumed that finished water target is 120 mg/L as CaCO3 4. Lower TOC levels in filtered water have additional benefits, such as a lower chlorine demand, less THM/HAA formation,

more stable chlorine/chloramines residual, and reduced risk of nitrification in the distribution system. 5. Finished water pH is partly dependent upon source and treatment process 6. Goal is set at 20% below the Standard.


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5.4 Finished Water Quality Analysis

The finished water quality for the WTP was reviewed using the MOR and daily test sheets which had manual entries for the past 5 years. Table 5-4 shows a statistical analysis of last 5 years of water quality data.

Table 5-4 Finished Water Quality (January 2011-November 2016)

Finished Water Quality


Units Average Maximum Minimum Median 90th Percentile

pH standard units

7.8 8.6 6.3 7.7 8.0

Alkalinity1 mg/L 163 216 86 166 190

Hardness2 mg/L 229 238 214 228 238

TOC mg/L 2.7 5.6 0.6 2.6 3.6

% Removal TOC % 52% 50% 30% 52% 57%

Notes: 1. Alkalinity data from daily test sheets (June 2014-May 2016) 2. Hardness data from daily test sheets (April 2016-May 2016)

The raw water temperature, raw water alkalinity and the finished water alkalinity are show in Figure 5-2. The raw water source for the WTP has high alkalinity, usually ranging between 90 and 220 mg/L as CaCO3 with an average value of 172 mg/L as CaCO3. The raw water temperature ranges from lows near -17.2 degrees C in the winter to around 35.7 degrees C in the summer with an average value of 12.4 degrees C (Table 5-2). The finished water alkalinity did not vary much from the raw water alkalinity as seen in Figure 5-2 and Tables 5-2 and 5-4. As lime is primarily used for pH adjustment and not for softening, the finished water hardness concentration was slightly lower than the raw water hardness (2-8 mg/L difference was observed; Table 5-4).

Figure 5-2 Raw Water Alkalinity, Temperature, and Finished Water Alkalinity

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Temp (deg C)

Alkalinity (m

g/L as CACO3)

Raw Alkalinity

Finished Alkalinity

Temp °C


22

Figure 5-3 shows the raw water turbidity and the coagulant (alum) dose. The average turbidity of the raw water is 21.0 NTU, 90th percentile was 50 NTU and had a maximum value close to 155 NTU (Table 4-2). Spikes in alum dose coincided with spikes in turbidity.

Figure 5-3 Alum Dose and Raw Water Turbidity

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Turbidity (NTU

)

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Alum


23

Finished, settled, and raw water turbidity is shown in Figure 5-4. The turbidity of the finished water was well below the US EPA IESWTR standard of less than 1.0 NTU 100% of the time and less than 0.3 NTU, 95% of the time.

Figure 5-4 Raw Water, Settled Water, and Finished Water Turbidity

Figure 5-5 shows the raw water, settled water and finished water pH. Raw water pH can be as high as 8.9. Algal blooms could be one of the reasons spikes in raw water pH are observed. This graph shows that coagulation pH is typically around 7.7 (90th percentile is 8.0; Table 5-4). There was no significant variation in settled and finished water pH. Operating at a coagulation pH of around 6.0 could optimize TOC removal. Coagulant doses and coagulant aids could be investigated to improve optimize TOC removal which would assist in lowering the DBPs.

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)

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Finished Water Turbidity


24

Figure 5-5 Raw Water, Settled Water, and Finished Water pH

Spikes in source water TOC, as shown in Figure 5-6, are typical in the summer months. Raw water TOC concentrations range from 1.9 to 11.1 mg/L with an average of 5.1 mg/L. Finished water from the WTP had an average TOC concentration of 2.7 mg/L, which represents an average TOC removal of 52% (Table 5-4). Per the Stage I D/DBPR, the WTP is in compliance of the TOC removal requirements, as it needs to remove TOC in the range of 15%-30%, depending on the incoming TOC and alkalinity in the source water (Table 3-3, Section 3).

Figure 5-6 Raw Water and Finished Water TOC

Table 5-5 shows the total chlorine and free chlorine obtained from the chlorine monitoring equipment at the clearwell (point of entry into the distribution system). The chlorine demand varied with an average chlorine demand of ~0.4 mg/L. Figure 5-7 shows the variation in total chlorine dosages and chlorine demand during different times of the year with the highest value observed in May 2016. Chlorine demand in general, increased during the summer months and decreased during the winter months.

6.0

6.5

7.0

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9.0

9.5Jun‐14

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pH

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Source Water TOC

Treated Water TOC


25

Table 5-5 Total Chlorine and Chlorine Demand (January 2011 - November 2016)

Chlorine Data at the Clearwell (Jan 2011 - Nov 2016)

Water Quality Parameter Units Average Maximum Minimum Median 90th Percentile

Residual Chlorine Free mg/L 1.40 4.30 0.09 1.23 2.31

Total Chlorine mg/L 1.82 12.43 0.63 1.70 2.45

Chlorine Demand (calculated) mg/L 0.42 8.13 0.54 0.47 Not Applicable

Figure 5-7 Applied Chlorine Dosages and Chlorine Demand of Finished Water

Around September of 2015, the WTP switched the secondary disinfectant from chlorine to chloramines. While using chlorine, booster chlorination was practiced in the distribution system to maintain free chlorine residuals (> 0.2 mg/L) to comply with the MDNR regulatory requirements. As seen from Figure 5-7, chloramine dosages (chlorine and ammonia) increased significantly after September 2015, as compared to chlorine dosages. Booster chlorination was discontinued after switching to chloramines. The increase in dosages may have been due to an increase in chlorine demand or operation staff trying to ensure that a free chlorine residual is maintained in the distribution system without booster chlorination.

5.5 Disinfection By-Products

One current regulation that has a significant impact on the required treatment at the WTP is the Stage 2 Disinfectant/Disinfection Byproduct Rule (Stage 2 D/DBPR), described in Section 2 earlier. Stage 2 D/DBPR requirements became effective for the City of Hannibal in October 2013, and retain the same MCLs for DBPs from Stage 1, but also require that reporting of DBPs be site specific, based on locational running annual averages (LRAAs) instead of reporting running annual average values (RAAs). Per Stage 2 D/DBPR requirements, the LRRA of TTHMs and HAAs at each of these locations has to be below 80 ppb (g/L) and 60 ppb (g/L) respectively.

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Free or total chlorine and Chlorine deman

d m

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Total Chlorine

Chlorine Demand


26

The City of Hannibal is required to measure TTHM and HAA quarterly in their finished water at four locations in the distribution system. These four locations are:

Hannibal Regional Hospital, 8503 Highway 36 (HRH)

#3 Industrial Loop (Industrial)

WWTP, 701 South Arch (WWTP)

Southside Booster Pump Station (SSBPS)

Figure 5-8 shows the monitoring locations in relation to the WTP along with the water storage tanks and the Ralls County PWSD No. 1 interconnects.

Figure 5-8 DBP Monitoring Locations

Figures 5-9 thorough 5-16 show the TTHM and HAA quarterly values (2013-2016) and their corresponding LRAAs. The graphs also show the prescribed MCLs and the water quality goals for TTHMs and HAAs (Table 5-3).


27

HRH

As seen from Figure 5-9, the quarterly values of TTHMs exceeded the MCL of 80 ppb from November 2013-August 2015, which was the time when the City was using chlorine as the primary disinfectant. Figure 5-10 shows that the MCL for HAAs were exceeded (MCL of 60 ppb) during May of 2014 and 2015, but were below the MCL during the rest of the year.

The City installed UV as the primary disinfectant and switched to chloramines as a secondary disinfectant during September of 2015. After switching to chloramines, the TTHMs were below MCL except in August 2016, when they were slightly higher than the MCL. After May 2016, the LRRAA of TTHMs was below the MCL. The LRAA of HAAs w well below the prescribed MCL of 60 ppb and is even below the water quality goal of 48 ppb (Table 5-3). Currently, the system is in compliance with Stage 2 of the D/DBPR requirements for TTHMs and HAAs at the HRH location.

Figure 5-9 Locational Running Annual Average (LRAA) of TTHMs at HRH Location

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Locational Running Annual Average TTHM Concentration at HRH (2013‐2016)

TTHM Limit (Recommended) TTHM Limit (Standards) Quarterly Value LRAA

Chlorine Chloramine


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Figure 5-10 Locational Running Annual Average (LRAA) of HAAs at HRH Location

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Locational Running Annual Average HAA Concentration at HRH (2013‐2016)

HAA Limit (Recommended) HAA Limit (Standards)

Quarterly Value Running Annual Average

Chlorine Chloramine


29

Industrial

Figure 5-11 shows that the quarterly values of TTHMs exceeded the MCL of 80 ppb from November 2013-August 2015, exhibiting similar trends as the HRH location. Figure 5-12 shows that the MCL for HAAs were exceeded (MCL of 60 ppb) during May of 2014 and 2015, but were below the MCL during the rest of the year.

After switching to chloramines, the TTHMs were below MCL except in August 2016, when they were slightly lower than the MCL. After May 2016, the LRRAA of TTHMs was below the MCL. The LRAA of HAAs was below the prescribed MCL of 60 ppb. Currently, the system is in compliance with Stage 2 of the D/DBPR requirements for TTHMs and HAAs at the Industrial location.

Figure 5-11 Locational Running Annual Average (LRAA) of TTHMs at Industrial Location

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Locational Running Annual Average TTHM Concentration at Industrial (2013‐2016)

TTHM Limit (Recommended) TTHM Limit (Standards) LRAA Quarterly Value

ChlorineChloramine


30

Figure 5-12 Locational Running Annual Average (LRAA) of HAAs at Industrial Location

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Locational Running Annual Average HAA Concentration at Industrial (2013‐2016)

HAA Limit (Recommended) HAA Limit (Standards) Quarterly Value LRAA

ChlorineChloramine


31

WWTP

As seen in Figure 5-13, the quarterly values of TTHMs exceeded the MCL of 80 ppb from November 2013-August 2015, exhibiting similar trends as the HRH and Industrial locations. Figure 5-14 shows that the MCL for HAAs were exceeded (MCL of 60 ppb) during May, August of 2014 and May, August of 2015 but were below the MCL during the rest of the year.

After switching to chloramines, the TTHMs were below MCL except in August 2016, when they were slightly lower than the MCL. After May 2016, the LRRAA of TTHMs was below the MCL. The LRAA of HAAs was below the prescribed MCL of 60 ppb after November 2015. Currently, the system is in compliance with Stage 2 of the D/DBPR requirements for TTHMs and HAAs at the WWTP location.

Figure 5-13 Locational Running Annual Average (LRAA) of TTHMs at WWTP Location

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Figure 5-14 Locational Running Annual Average (LRAA) of HAAs at WWTP Location

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As seen in Figure 5-15, the quarterly values of TTHMs exceeded the MCL of 80 ppb from November 2013-August 2015, exhibiting similar trends as the other locations. Figure 5-16 shows that the MCL for HAAs were exceeded (MCL of 60 ppb) during May, August of 2014 and May, August of 2015 but were below the MCL during the rest of the year.

After switching to chloramines, the TTHMs were below MCL except in August 2016, when they were slightly higher than the MCL (similar to the HRH location). After May 2016, the LRRAA of TTHMs was below the MCL. The LRAA of HAAs was below the prescribed MCL of 60 ppb after November 2015. Currently, the system is in compliance with Stage 2 of the D/DBPR requirements for TTHMs and HAAs at the WWTP location.

Figure 5-15 Locational Running Annual Average (LRAA) of TTHMs at SSBPS Location

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Figure 5-16 Locational Running Annual Average (LRAA) of HHAs at SSBPS Location

Summary

In summary, the highest TTHM and HAA concentrations are noticed during the months of May-August coinciding with high TOC and chlorine demand observed during these months. The HRH location had the highest TTHM and HAA concentrations while using chlorine as the primary disinfectant.

Since the incorporation of UV as the primary disinfectant and chloramine as the secondary disinfectant in September of 2015, the TTHM and HAA concentrations are below the prescribed MCL most of the time. In August of 2016, the TTHMs were above the MCL at two locations (HRH and SSBPS). During the same period, at the WWTP and Industrial locations, the TTHMs quarterly values were slightly below the MCL, but above the water quality goal of 64 ppb. The HAAs during this period at all locations were below the MCL of 60 ppb. However, at HRH and the Industrial locations, the HAAs were above the water quality goal of 48 ppb. At present, the City of Hannibal distribution system is in compliance with Stage 2 D/DBPR requirements for TTHMs and HAAs at all the four monitoring locations.

The monitoring data indicates that the conversion to chloramines as a secondary disinfectant has been an effective strategy in reducing the DBPs and achieving regulatory compliance. However, the chloramine dosages need to be optimized to meet the water quality goals set for TTHMs (64 ppb) and HAAs (48 ppb) at the sampling locations.

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6. Control Measures to Minimize DBPs

6.1 Overview of Control Measures

Disinfection by-product (DBP) formation is influenced by several factors such as total organic carbon (TOC) in the treated water, bromide, temperature, pH, chlorine residual and contact time, which are thus considered as the key parameters in controlling DBP formation. The water quality analysis in Section 5 showed that the primary factors that contributed to excessive TTHM formation in the distribution system when the City was using chlorine prior to September 2015 were (in order of importance):

TOC

Chlorine residual

The bromide content of the source water is not known at this time. The level of bromide in the raw water impacts the rate and amount of THM formation in the finished water (e.g. brominated DBPs such as bromoform).

Three basic control measures are available to minimize DBPs:

1) Use an alternative source, treat the source, or minimize using the raw water source with problematic water quality.

2) Control DBP formation in the treatment plant.

3) Control DBPs in the distribution system.

Each of these control measures is described briefly here.

6.1.1 Alternative Source or Minimize Use of Source with Problematic Water Quality

The City of Hannibal relies on the Mississippi river as its source water for drinking and is expected to continue using it in the foreseeable future. There are limited options for the City to use other sources (e.g. groundwater) or consider blending with a source that has better water quality. As such, the practical control measures available for the City include control measures in the treatment plant and the distribution system.

6.1.2 Control DBP formation in the plant

Copper sulfate is currently added at the pump house for algal control, on as needed basis. This can also can help in reducing the algogenic organic matter (AOM-which is considered as autocthonous NOM) that serves as the precursor to DBPs.

Several alternative disinfection technologies e.g. chlorine dioxide, chloramines, UV and ozone were evaluated by a previous consultant (Horner and Shifrin). The merits and demerits of these alternatives and associated life-cycle costs have been presented in a past report (Disinfection By-products Compliance Study by Horner and Shifrin Inc., September, 2012). Based on those evaluations and recommendations, the City incorporated UV disinfection and switched to chloramines as a secondary disinfectant in September of 2015.

Several alternatives are available in the treatment plant to reduce the DBP precursors and these include:


Installing New Treatment Technologies


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A review of previous reports and water quality indicates that two potential options for reducing the DBPs include:

Enhanced Coagulation

Optimizing Chlorine residual

Enhanced Coagulation

Enhanced coagulation is defined by US EPA as the addition of excess coagulant to improve removal of TOC. Enhanced coagulation with a coagulant (e.g. alum, ferric chloride, ferric sulfate, etc.) and polymer are very effective in reducing TTHM concentrations as they remove the DBP precursors (i.e. TOC, DOC, and color).

Bench-scale studies have been conducted in the past with various coagulants (Clarion A10, ferric sulfate, Clarion 4055) to evaluate TOC removal performance without altering the pH (Disinfection By-products Compliance Study by Horner and Shifrin Inc., September, 2012). The bench-testing results showed that Clarion 4055 removed 42%-58% more TOC than the coagulant the plant was currently using (Clarion A10). Based on turbidity, UV absorbance at 254 nm (UV254) and TOC, Clarion 4055 was the best performing coagulant. Clarion 4055 is an acidified alum based coagulant with an added polymer.

Further reduction of TOC is possible through optimized coagulation which in turn will help in reducing DBP formation, a primary concern for the City. Optimized coagulation is a condition where both pH level and coagulant dose are optimized for maximum organic carbon and particulate removal. This also results in lowered DBP production as compared to enhanced coagulation.

Previous bench-scale studies focused on testing the effectiveness of the various coagulants at pHs between 5.5-7.5 (Disinfection By-products Compliance Study by Horner and Shifrin Inc., September, 2012). The results showed that Clarion 4055 was the best performing coagulant at all pH values tested based on turbidity, UV254, and TOC. At a pH of 6.5, TOC removal by Clarion 4055 was double the amount removed by Clarion A10. The tests also revealed that the coagulant Clarion 4055 in combination with powdered activated carbon (Aqua Nuchar) produced the highest removal of DBP precursors as measured by UV254.

Based on these bench-scale study results, a recommendation was made to switch to Clarion 4055 as a coagulant and replacing the existing activated PAC with Aqua-Nuchar a wood based carbon (Disinfection By-products Compliance Study by Horner and Shifrin Inc., September, 2012).

The WTP is currently using PAC from Aqua-Nuchar, as noted in Section 5. However, the coagulant and polymer currently used at the plant are polyaluminum chlorosulfate and poly-dadmac respectively and not the Clarion 4055 as recommended by Horner and Shifrin (Disinfection By-products Compliance Study by Horner and Shifrin Inc., September, 2012).

Polyaluminum chlorosulfates are high basicity compounds and are generally suited to treat low alkalinity, low turbidity and low temperature waters. Currently, the WTP removes about 52% of the incoming TOC, satisfying the requirements of the Stage I D/DBPR which requires a TOC removal of 15%-30%.

For a source water such as the Mississippi river which has high alkalinity and high pH, an acidic coagulant such as Clarion 4055 that will drive the pH to ± 7.0 can be considered to promote further removal of TOC. At the WTP, the influent SUVA varies from 3.7-4.3 L/mg-m indicating that optimized coagulation is feasible to reduce the influent TOC (Table 2-1).


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Optimizing Chlorine Residual

As shown in Table 5-4 and Figure 5-5 (Section 5) chlorine residual varies significantly. Amongst other factors, DBP formation is influenced by pH, chlorine dose, chlorine residual and contact time. In general, THM formation increases as pH increases and HAA formation increases as pH decreases. As such, optimizing chlorine dosages and the finished water pH will be critical to control DBP formation in the distribution system. Such optimization in pH and treatment changes should also consider and evaluate the potential effects on the corrosivity of the treated water and the need for corrosion control.

Currently, the WTP is using chloramine, a weak disinfectant and achieves the required CT by applying chlorine prior to filtration. If the City reverts to chlorine as a secondary disinfectant (in lieu of chloramines), the chlorine application point could be relocated post-UV disinfection and prior to the clearwell to achieve the CT requirements for virus inactivation. This should significantly reduce the chlorine contact time in the plant and assist in lowering DBP formation.


The first step to take in reducing DBP formation is optimizing current treatment plant operations. However, the City will most likely need to install a treatment technology that will reduce TOC in the source water to minimize DBP formation.

Several treatment technologies such as magnetic ion exchange (MIEX), membranes (microfiltration/ultrafiltration, nanofiltration, reverse osmosis), granular activated carbon (GAC) and aeration, with their merits and demerits and associated life-cycle costs have been presented in a previous report (Disinfection By-products Compliance Study by Horner and Shifrin Inc., September, 2012).

One of the objectives of the current study was to evaluate the addition of a new treatment technology such as GAC (preferred alternative by the City) and assess its expected effectiveness in reducing organics and limiting the formation of DBPs. GAC is a proven advanced treatment technology that is effective for the removal of TOC, and also provides a treatment barrier for taste and odor compounds; synthetic and trace organics; and emerging contaminants such as algal toxins and PFCs (Table 3-6, Section 3). The next Sections, 6.2 through 6.4, focus on evaluating GAC to fulfill this objective.

In a general sense, MIEX and membranes have higher life-cycle costs than GAC (Disinfection By-products Compliance Study by Horner and Shifrin Inc., September, 2012). While high pressure membranes such as nanofiltration or reverse osmosis are the most effective method of removing TOC from water, membrane technology was not considered further in this study. Membranes, such as reverse osmosis or nanofiltration, would also require high-pressure pumps, adding significant electrical power costs and requiring additional electrical infrastructure to support the additional horsepower. In addition, membranes would produce a high salinity waste stream that would have to be disposed of. Finally, membrane operations require specialized skills and training that would add to plant operational costs. MIEX resin was also not considered further because the resin must be regenerated with salt brine. This produces a high salinity waste stream that would have to be disposed of. Should testing of GAC show that GAC is not as effective as anticipated or that GAC life is impractically short, MIEX resin, membranes, or other treatment options should be fully evaluated.

6.1.3 Control DBPs in the distribution system.

The combination of optimized coagulation and settling followed by GAC will provide for substantial reduction of DBP precursors (TOC) and thus reduce the formation of DBPs at the Hannibal WTP. However, some amount of TOC will remain in the finished water, and with the use of free chlorine as a disinfectant (in lieu of chloramines), DBPs will continue to form in the water distribution system as the remaining TOC reacts with the free chlorine.


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As noted earlier, DBP formation is influenced by several factors, such as TOC in the treated water, bromide, temperature, pH, and chlorine residual and contact time, which need to be optimized. Hence, optimizing DBPs can be a challenging for utilities, considering that there are several variables impacting DBP formation. Also, there is the need for utilities to simultaneously comply with multiple distribution system regulations. There are several best management practices (BMPs) recommended by the American Water Works Association (AWWA) in their publication BMPs for Maintaining Water Quality in the Distribution System, AWWA, 2001. BMPs include:

Minimizing water age

Flushing

Decentralized Treatment

Minimizing Water Age and Flushing

Water age refers to the time it takes for water to travel from source to consumers. Water age is a hydraulic parameter that depends on flow velocities and pipe lengths in the distribution system. Water age is also a general indicator of water quality. Excessive water age can reduce the residual disinfectant concentration as chlorine or reacts with organic material in the water and on the pipe walls. Lower water age indicates better water quality. The average water age in the City’s distribution system appears to be 3 days (Disinfection By-products Compliance Study by Horner and Shifrin Inc., Addendum 1, June, 2014). TTHM concentrations increase with water age. HAA5 concentrations increase with age to a certain level, after which biological activity lowers concentrations.

Reducing the water age in the City’s distribution system would reduce the concentration of DBPs observed at the various monitoring locations. Water age can be reduced by improved mixing and reducing the detention time in finished water storage tanks, eliminating dead ends with pipe looping, optimizing the water velocity in large pipe sections, and proper valve management. Unidirectional flushing as recommended by the AWWA and increasing the frequency of flushing helps in lowering the water age and can reduce DBPs

Long runs of pipe combined with low usage rates combine to extend water age in the distribution system. Since pipe lengths and usage rates are inherent characteristics of the system, these cannot typically be changed without excessive costs. However, water usage can be artificially accelerated by flushing the water lines on a routine basis at fire hydrants or blow-down valves. Areas of the distribution system that show elevated water age should be considered for routine flushing. Flushing is a maintenance activity and does not require the addition of capital equipment. Any flushing program must consider the flushing velocities imposed on the lines being flushed to ensure adequate velocity to remove not only old water but also accumulated sediment and rust, both of which can also contribute to the continued formation of DBPs.

Decentralized Treatment

Treatment options available in the distribution system are air stripping by aeration and installing mechanical mixers in finished water storage tanks. Aeration is an appropriate solution for localized TTHM reduction.

Mechanical mixing can be employed in the storage tanks to reduce DBPs. Several alternatives are available; bubble aerators, surface aerators and spray aerators. About 50%-60% reduction in 24 hours is possible with surface aerators when chloroform is the predominant form of TTHMs (>50%). Based on TTHM data, chloroform concentration is the predominant form of TTHMs in the City’s distribution system, approximately sixty percent (60%) of the total THMs (Disinfection By-products Compliance Study by Horner and Shifrin Inc., September, 2012). Hence, mechanical mixing will likely remove a significant portion of the TTHMs. Currently, the only tanks that have mixing are the Clinic Road Ground Storage Tank, which has a gridbee mixer, and the new Southside Storage Tank which has the tideflex mixing system. No data is available at this time to ascertain the effectiveness of these mixing systems.


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As an alternative to treating the entire flow at a centralized facility, many utilities are considering treating only a partial flow in the distribution system with air stripping to be in compliance with the Stage 2 D/DBPR requirements. Over the years, the cost of the centralized treatment (e.g. optimized coagulation, GAC, membranes) gets expensive and is not effective at reducing TTHM levels at distant locations within the water distribution system. Localized or decentralized treatment at the point of non-compliance is a cost-effective option as only the flow that is necessary is treated, to be in compliance with regulations.

Air strippers remove volatile organic chemicals (VOCs) from liquid (water) by providing contact between the liquid and gas (air). The gas (air) may then be released to the atmosphere or treated to remove the volatile organic compounds (VOCs) and subsequently released to the atmosphere. In general, the removal efficiency of air stripping for THMs is as follows:

Chloroform>Bromodichloromethane>Dibromochloromethane>Bromoform

As chloroform is the predominant form of the TTHMs in the City’s distribution system (> 60%), packed aeration towers will likely remove a significant portion of the TTHMs.

6.1.4 Summary

In summary, the City will need to implement several strategies to minimize DBPs in the finished water, if it reverts to chlorine as a secondary disinfectant. These include:


- Optimized Coagulation

- Optimizing chlorine residual and pH


- Evaluate the addition of GAC

Practicing BMPs in the distribution system

- Minimizing water age and flushing

- Mixers in storage tanks

The City should implement the above strategies to minimize the DBPs in the distribution system. In the event DBPs continue to be an issue, the City should evaluate decentralized treatment such as air stripping.

Regardless of the treatment option chosen, treatability studies will be necessary for predicting system performance, developing design criteria and validating the process. It is strongly recommended that the City pilot the chosen technology. A small-scale pilot could help determine the effectiveness of the technology with respect to DBP reduction.

6.2 Granular Activated Carbon Treatment

The formation of disinfection byproducts (DBPs) is reduced when the amount of organic compounds (TOC) in the water is reduced prior to the addition of free chlorine. While the practice of optimized coagulation can provide significant reduction in TOC (see Section 6.1), additional reduction of TOC will be needed to minimize DBP formation. Filtering the settled water through granular activated carbon (GAC), a highly porous material, will further reduce TOC via the process of filtration and adsorption. While the particulate fraction of the TOC will be removed by filtration, the dissolved fraction of the TOC – dissolved organic carbon (DOC) – is attracted to the surface of the carbon grains by the interactions of complex chemical forces. These forces bind the DOC to the pores in the carbon grains, effectively removing the DOC from the water. GAC also removes residual


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disinfectants (e.g. chlorine, chloramine) by catalytic reduction. Properly designed and operated GAC filters can remove 30%-90% of the incoming TOC in the water (USEPA, 2003).

GAC for drinking water is usually manufactured from bituminous coal by crushing and sizing, followed by processing at low temperatures and high temperature furnaces. This heating process is known as “activation” which results in the highly porous structure of the GAC particles. GAC can also be produced from lignite coal, peat, wood and from coconut shell. The micro pore structure allows for a very high unit surface area (surface area per unit weight).

It is important to note that GAC has a limited adsorption capacity. As DOC is adsorbed onto the surfaces of the carbon grains, the GAC eventually becomes saturated and that portion of the GAC bed is said to be “exhausted”. Once the entire GAC bed is exhausted, the GAC must be replaced.

GAC provides additional advantages beyond the reduction of TOC in the finished water to safe Stage 2 D/DBP Rule compliance levels. Other advantages include:

Removal of taste-and-odor causing compounds such as methyl-isoborneol (MIB) and geosmin

Removal of several pesticides, volatile organic compounds (VOCs), herbicides, algal toxins and perfluorinated compounds (PFCs)

Removal of trace and synthetic organic compounds, and some of the emerging contaminants such as endocrine disrupting compounds (EDCs), pharmaceutical and personal care products (PPCPs)

When used as a biologically active filter following ozonation it can remove assimilable organic carbon, enhancing overall TOC removal

Operation of GAC adsorbers is similar to filter operation so additional operator training is minimal.

However, the capital cost and annual operation and maintenance costs for GAC can be high. Depending on the influent water DOC and desired effluent DOC, the GAC can be exhausted in three months to a year. When exhausted, the GAC can be replaced with either new virgin GAC or with custom-regenerated GAC (by only using spent GAC from municipal facilities, and not mixing municipal and industrial spent GAC). This may increase the GAC regeneration cost slightly. Most GAC is not regenerated onsite, but is usually shipped to a central regeneration facility. Hence, transportation costs are added to the GAC regeneration costs which increases the overall cost.

At present, the Hannibal Water Treatment Plant (WTP) does not use GAC. The WTP can feed powdered activated carbon (PAC) and does so at certain times of the year to remove taste and odor causing compounds. PAC is fed ahead of the sedimentation basins and reacts within the basins. The PAC eventually settles out and is removed with the basin residuals (sludge). However, PAC is not generally effective at reduction of TOC to levels necessary to minimize DBP formation.

Filtration using GAC can be added to the Hannibal WTP treatment process by either retrofitting the existing filters (GAC filter media or GAC filter cap) or adding as second stage filtration (post-filter adsorbers). These two alternatives are discussed in the next two sections.

6.3 Alternative 1: Retrofit GAC into Existing Filters

6.3.1 Conceptual Design

The Hannibal WTP filters are gravity flow filters, consisting of a layer of anthracite over a layer of sand over a layer of gravel, all resting on clay tile underdrains in a concrete filter box. The anthracite and sand serve to filter out very small particles from the water. The gravel supports the sand and prevents it from being flushed out


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through the larger holes in the clay tile underdrains. The clay tile underdrains serve to collect the filtered water and convey it to a channel where it is collected and conveyed to the next steps in the WTP.

Anthracite is an inert, coal-based material used as a coarse filter but has no adsorptive characteristics. GAC is similar in size and density to anthracite and has very similar filtration properties. Thus, GAC could replace the anthracite in the filters.

The current filter profile at the Hannibal WTP is (top to bottom):

12” Anthracite

12” Sand

12” Gravel

12” Clay tile underdrain

Option 1

The least costly and least disruptive option is to replace the existing anthracite with GAC. This would provide for 12” of GAC and would not require any modification of the filter physical structure nor would it reduce the 12” depth of filter sand. The Missouri Department of Natural Resources (MDNR) – the body governing the design and operation of water treatment plants – calls for a minimum of 12” of filter sand.

Option 2

Under special conditions, the MDNR may allow for less than 12” of filter sand. In order to achieve such special permission, a filter study would have to be performed. If a filter study shows that Hannibal can filter effectively with 6” of sand, 18” of GAC could be installed over 6” of sand. This is also relatively inexpensive and not too disruptive to operations.

Option 3

A significant limitation to the depth of GAC than can be installed in the existing filters is the 12” of gravel and 12” of clay tile underdrain. In order to allow for a deeper GAC bed, the existing clay tile underdrains and gravel bed could be replaced with low profile PVC underdrains with a porous plastic cap (commonly referred to as an integrated media support (IMS) cap) – as illustrated in Figure 6-1. This underdrain and cap combination would be only 8” deep. When 12” of sand is placed on this low profile underdrain, 28” of GAC can be installed. However, this is a significant construction project. The existing anthracite, sand, and gravel would have to be removed and the clay tile underdrains would have to be demolished. The new underdrains would then be installed within the existing filter boxes.

Option 4

Option 4 is the same as Option 3 except that the sand layer is reduced to 6” allowing for a GAC depth of 34”. Reducing the sand depth to 6” will require MDNR approval as described under Option 2 above.

Figure 6-2 illustrates the retrofit of GAC into the existing filters. Note that support gravel is only required for Option 1 and Option 2.


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Figure 6-1 Low Profile Underdrain with IMS Cap

Figure 6-2 Retrofit GAC in Existing Filters

Empty Bed Contact Time Comparison and Options Feasibility

In order to be effective, GAC is designed to achieve a certain minimum empty bed contact time (EBCT). EBCT is defined as the gross volume taken up by the GAC bed divided by the volumetric flowrate through the filter . A GAC Contactor with 10 minutes of EBCT (GAC10) is considered a best available technology (BAT) for Stage 1D/DBPR. GAC20 (20 minutes of EBCT) and GAC10, combined with enhanced coagulation or softening are BATs for Stage 2 D/DBPR. Each filter has 538 sq. ft. of surface area.


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The Table 6-1 shows the EBCT achievable for each of the four options described above at three different WTP flows.

Table 6-1 GAC Contact Time - Retrofit Existing Filters

EBCT (MIN)

@ 3.5 MGD1

EBCT (MIN)

@ 7.5 MGD2

EBCT (MIN)

@ 10 MGD3

Option 1 6.6 3.1 2.3 Option 2 9.9 4.6 3.5 Option 3 15.5 7.2 5.4 Option 4 18.8 8.8 6.6

Notes: 1. 3.5 MGD = average flow 2. 7.5 MGD = plant design capacity 3. 10 MGD = plant hydraulic design capacity (per City future capacity plans) 4. Surface loading at 3.5 MGD = 1.1 gpm/sq ft 5. Surface loading at 7.5 MGD = 2.4 gpm/sq ft 6. Surface loading at 10 MGD = 3.2 gpm/sq ft

The Table clearly shows that only Options 3 and 4 approach 20 minutes EBCT at average plant flow, providing approximately 16 and 19 minutes of EBCT at 3.5 MGD. Options 1 and 2 are inadequate for TOC reduction and are not considered further.

There are additional drawbacks to installing GAC instead of anthracite in the dual media filters; the particulate loading on the GAC is higher than if the GAC is used as a second stage filter. This results in a risk of fouling – or blinding – of the GAC, diminishing its capacity. Moreover, the WTP filters would be backwashed many times more often than with GAC as a second stage filter. Backwash physically abrades the GAC, breaking up the grains, resulting in carbon fines that are washed from the filter. Over time, this reduces the volume of GAC, further reducing the capacity to adsorb TOC.

6.3.2 Process Flow Diagram

Figures 6-3 and 6-4 illustrate installing GAC in the existing filters by replacing the existing underdrains and gravel layer with a new, low profile underdrain and cap.


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Figure 6-3 Retrofit GAC into Existing Filters Process Diagram (1 of 2 )


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Figure 6-4 Retrofit GAC into Existing Filters Process Diagram (2 of 2)

6.4 Alternative 2: GAC Filters as Second Stage Filters

6.4.1 Conceptual Design

Second Stage Filtration

In order to increase the EBCT to a full 20 minutes and to protect the GAC by placing it after the dual media filters, new GAC Second Stage Filters (pressure contactors) sized for 20 minutes EBCT could be installed between the existing dual media filters and ultraviolet (UV) disinfection. Placing the GAC after the dual media filters protects the GAC from particulate loading and allows for a substantially reduced number of backwashes, leading to longer GAC life.

Currently, filtered water is pumped from a transfer well beneath the existing filters, through the UV to the large filtered water storage tank (2.5 million gallon clearwell). The filtered water pumps cannot produce adequate pressure to pass the filtered water through the GAC pressure contactors into the clearwell. These pumps would have to be replaced with larger pumps to support the addition of second stage GAC filters.

The ability of GAC to remove a wide variety of organic compounds makes it an attractive option as a final treatment step (after filtration). Placing the GAC ahead of the UV is essential because GAC reduces


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disinfectant residuals such as chlorine that will be present in the influent to the GAC. In the absence of a disinfectant residual GAC beds will provide a surface for bacteria to grow and proliferate. UV treatment following the GAC serves to inactivate any bacteria that slough off from the GAC. Another advantage of using the GAC as a secondary filter is that it improves UV transmittance and may qualify for 0.5 Log Cryptosporidum removal credit under LT2ESWTR (Table 3-4). To receive credit under LT2ESWTR, coagulation is required prior to first filter, both filtration steps need to treat 100% of the flow and the WTP would satisfy these requirements. These advantages will help reduce UV dose requirements for inactivation of Cryptosporidium, resulting in savings of O&M costs.

Contactor Design

Two criteria define the size of the GAC contactors, surface loading rate and EBCT. In addition, the maximum practical diameter of the GAC pressure vessels comes into play.

Diameter

A typical maximum pressure vessel diameter for shop-fabricated vessels is 12-feet. This is generally governed by the maximum width permitted on highways. While larger vessels up to 14-feet may be allowed on highways by special permit, most manufacturers limit their standard units to 12-foot diameter. Larger vessels can be fabricated on-site but this tends to be much more costly than shop fabricated vessels. Thus, 12-feet will be used as the contactor diameter.

Surface Loading Rate

The hydraulic capacity of a GAC filter is defined by the surface loading rate, which is the amount of flow per square foot of filter surface area and is described in gallons per minute per square foot (gpm/sq.ft.). For second stage filtration, surface loading rates can range from as little as 2 up to 10 gpm/sq.ft. For purposes of this report, a design surface loading rate of 6.2 gpm/sq.ft. was used, which is consistent with the standard design rate used by a major supplier of carbon and carbon treatment systems.

The hydraulic capacity of a 12-foot diameter vessel with a surface area of 113 sq.ft., operated at 6.2 gpm/sq.ft. would be 700 gpm (1 MGD).

EBCT

The GAC process capacity is based on achieving the design EBCT of 20 minutes and is achieved by providing sufficient carbon volume. Typically, the GAC system is designed to achieve the desired EBCT at an average flow, recognizing that at higher flows the EBCT would be proportionately less.

A standard, single 12-foot diameter GAC vessel commonly available from a major supplier contains a carbon volume of 5,106 gallons. At 20 minutes EBCT, such a vessel has a process capacity of 0.37 MGD. Two such vessels in series (doubling the carbon volume) would have a process capacity of 0.74 MGD at 20 minutes EBCT.

System Configuration

GAC contactors can be arranged in parallel or in series-parallel. In a parallel arrangement, each of the several parallel trains consists of a single GAC contactor. Each contactor provides for 20 minutes EBCT. In a series-parallel arrangement, each parallel train consists of two GAC contactors in series and each of the two contactors provides 10 minutes of EBCT, but a total EBCT of 20 minutes. Series-parallel configurations provide substantial advantages to drinking water plants. This is because carbon becomes exhausted (used up) from the inlet side first (see Figure 6-5).


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Figure 6-5 Carbon Exhaustion Profile

The cleanest carbon is at the end of the unit. In a series configuration, the first (lead) unit becomes progressively exhausted while the second (lag) unit remains relatively unused. Breakthrough occurs at the outlet of the first (lead) vessel in series and can be monitored by sampling between the vessels. Once the first (lead) vessel becomes exhausted, the pipe and valve arrangement allows the second (lag) vessel to become the first (lead) and the first (lead) vessel would be recharged with new carbon and become the second (lag) vessel. This allows for more complete usage of carbon and significantly reduces the risk of breakthrough into the finished water (see Figure 6-6).

Figure 6-6 Series Contactors

This report considers two design cases, 3.5 MGD, which reflects current average design capacity and 2.7 MGD, which reflects current average daily flow of 3.2 MGD less the amount of water (0.5 MGD) used by PWSD No. 1 of Ralls County.

Headspace

Virgin

Exhausted

Inlet Outlet


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System Backwash

GAC filters require periodic backwashing to remove accumulated solids but it is not possible to accurately estimate the backwash frequency without pilot testing. However, since the GAC contactors would follow the existing anthracite/sand filters, the particle loading would be very low, and backwash frequencies might typically range from every 2 weeks to every three months. Some systems are only backwashed at carbon change-out.

A major carbon provider lists the typical backwash rate for a single 12-foot diameter filter as 1,700 gpm for a duration of 15 minutes. This totals 25,500 gallons per vessel per backwash. The existing backwash tank has a capacity of 100,000 gallons. The backwash water consumption for one of the existing sand filters is 50,000 gallons and current practice is to backwash three of the filters each day for a daily backwash use of 150,000 gallons. Based on a comparison of the additional backwash requirements for new GAC filters to current practice, it appears at this time that improvements to the existing backwash system may not be required.

Backwash is typically initiated when the head loss becomes excessive and is easily monitored by a differential pressure gauge. Plant operations would also typically monitor the carbon outlet TOC and bacterial counts. Should either become “excessive”, backwash may be needed before it is initiated on head loss. Operating history is required to determine the backwash frequency over the long term.


50

6.4.2 Process Flow Diagram

Figure 6-7 illustrates the addition of GAC contactors into the WTP system.

Figure 6-7 GAC Filters as Second Stage Filters Process Diagram


51

6.4.3 GAC Contactors Layout

Figure 6-8 illustrates a possible layout of the GAC contactors on the Hannibal WTP site.

Figure 6-8 GAC Filters as Second Stage Filters Proposed Layout (3.5 MGD Case)


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7. Alternatives Evaluation

7.1 Capital Cost Estimates

A total constructed cost estimate for each project alternative, including project management, engineering, construction support, and construction observation services, is presented in Table 7-1. Option 4 was chosen for Alternative 1 as it was the closest of the four options to achieving the 20 minute EBCT. More detailed cost estimates are provided in Appendix A.

Table 7-1 Total Project Cost for GAC Treatment Alternatives

Alternative Total Project

Cost

1 – Retrofit GAC into Existing Filters $1,981,000



7.2 Operating Cost Estimates

As discussed in Section 6, GAC particles attract DOC to the surface of the carbon and bind the DOC in the pores, effectively removing the DOC from the water. After a period of time, the carbon becomes exhausted and loses its ability to remove DOC. Consequently, the carbon must be replaced periodically. Carbon replacement frequency (effective service life) is influenced by many factors, including temperature, pH, EBCT, type and concentration of organic compounds to be removed, and competitive adsorption by other contaminants. Typical service life ranges from 3 to 24 months, however it is extremely difficult to estimate the effective service life of GAC until pilot testing can be done. Carbon replacement costs for a range of service life values are presented in Table 7-2 and 7-3 below.

Carbon replacement costs are based on new carbon. Carbon can be regenerated and major suppliers can provide regenerated carbon used in municipal applications only or custom regenerate the carbon from the Hannibal facility. Purchasing regenerated carbon could potentially result in some savings, however the use of regenerated carbon would have to be approved by the MDNR and such approval has not been requested or granted at this time.

Note: The operating costs in this section and impacts to customer rates in Section 7.4 are presented on a cost per 1,000 gallons of billed water usage. In 2016, the City sold 871,023,111 gallons of water. In 2016, 155,918,000 gallons were sold to PWSD No. 1 of Ralls County. Since PWSD No. 1 of Ralls County will cease to buy water from Hannibal beginning in the near future, the total water billing will be reduced by approximately 155,918,000 gallons per year. Calculations of per gallon costs are therefore based on 715,105,000 gallons of water sales per year. The costs are assigned per the total gallons sold without differentiation between industrial and residential customers.

Alternative 1: Retrofit GAC into Existing Filters

At a carbon depth of 34 inches, each of the four existing filters would contain approximately 1,524 cu. ft. of carbon. At 30 lbs./cu. ft. density (backwashed and drained), each filter would contain 45,720 lbs. of carbon. Total carbon weight per filter carbon exchange would equal approximately 183,000 lbs.


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Table 7-2 Carbon Costs for Retrofit GAC into Existing Filters

Carbon Life (Months)

Annual Carbon Weight (Lbs.)

Carbon Cost

($/Lb.)

Annual Carbon Cost

($)

Carbon Cost Per 1,000 Gallon

($)

3 732,000 1.80 1,317,600 1.51

6 366,000 1.80 658,800 0.76

9 244,000 1.80 439,200 0.50

12 183,000 1.80 329,400 0.38

18 122,000 1.80 219,600 0.25

24 91,500 1.80 164,700 0.19Notes: 1. Carbon unit costs are estimates from Calgon for Filtrasorb 820 (for gravity filters) and are delivered and installed costs.

2. Shaded areas represent the most likely carbon life but testing is required to confirm.

Alternative 2: GAC Filters as Second Stage Filters

Each of the filters would contain 20,000 lbs. of carbon (redundant train not counted). Estimating a carbon life of 9 months, the total carbon weight per year would equal 266,667 lbs for the 3.5 MGD case and 213,333 lbs for the 2.7 MGD case.

Table 7-3 Carbon Costs for GAC Filters as Second Stage Filters 2.7 MGD Case



Carbon Cost

($/Lb.)

Annual Carbon Cost

($)


($)

3 640,000 1.60 1,024,000 1.43

6 320,000 1.60 512,000 0.729 213,333 1.60 341,333 0.48

12 160,000 1.60 256,000 0.36

18 106,667 1.60 170,667 0.2424 80,000 1.60 128,000 0.18

Notes: 1. Carbon unit costs are estimates from Calgon for Filtrasorb 400-M (for pressure filters in municipal applications) and are delivered and installed costs.

2. Shaded areas represent the most likely carbon life but testing is required to confirm.

Table 7-4 Carbon Costs for GAC Filters as Second Stage Filters 3.5 MGD Case



Carbon Cost

($/Lb.)

Annual Carbon Cost

($)


($)

3 800,000 1.60 1,280,000 1.796 400,000 1.60 640,000 0.89

9 266,667 1.60 426,667 0.60

12 200,000 1.60 320,000 0.4518 133,333 1.60 213,333 0.30

24 100,000 1.60 160,000 0.22Notes: 1. Carbon unit costs are estimates from Calgon for Filtrasorb 400-M (for pressure filters in municipal applications) and are

delivered and installed costs. 2. Shaded areas represent the most likely carbon life but testing is required to confirm.


54

For the net present value calculations in Section 7.3 and the impact to customer rates in Section 7.4, a 9-month effective service life is assumed.

7.3 Net Present Value Estimates

Net present value refers to a quantification of expenditures or values in terms of present dollars by considering the time value of money, and applying this concept to expenditures and credits incurred during the life expectancy of the improvements. The goal of a net present value analysis is to calculate the estimated life cycle costs associated with various alternatives. The net present value for each alternative is presented in Table 7-4 below.

Table 7-5 Net Present Value

Alternative Total Project

Cost

Annual Operating

Cost

Present Worth of Operating

Cost1

Net Present Value2

1 – Retrofit GAC into Existing Filters $1,981,000 $439,200 $6,861,000 $8,842,000


$9,367,000 $341,333 $5,332,000 $14,700,000


$10,578,000 $426,667 $6,665,000 $17,243,000

Notes: 1. Amortized at 25 year life, interest rate 4% 2. Net Present Value is the sum of Total Project Cost and Present Worth of Operating Cost

7.4 Impact to Customer Rates

The main two costs that will be passed on to the water customers will be the debt service on the total project cost and the cost to periodically replace the carbon in the filters.

Debt Service

The debt service calculation assumes that the project will be funded using bond to be paid back over a 25-year repayment period. Over the last five years, the average bond rate is 4.53%; this analysis uses a rate of 4.00%. A complete amortization table for each alternative is included in Appendix B.

Operating Cost

While there may be some increased electrical cost associated with necessary pump upgrades in Alternative 2, the main operating cost increase is due to the need to periodically replace the carbon. This cost will vary depending on the effective service life of the GAC. As discussed in Section 7.2, it is extremely difficult to estimate the effective service life of GAC until pilot testing can be done. For an initial estimate on the impact to customer rates, it is assumed that there is a 9-month effective service life for the carbon in both alternatives (see Table 7-2 and Table 7-3).

Estimated Impact to Customer Rates

Together, the estimated impact of the debt service and operating cost on customer rates is presented in Table 7-5. The debt service for the project was calculated using an average annual interest rate of 4% and a term of 25 years; based on general revenue bonds being issued for this project. The City should retain the services of a Public Financial Advisor to formally plan for the projected impact to customer rates. The cost per 1,000 gallons is based on average annual water sales of 715,105,000 gallons as noted in Section 7.2. The monthly cost for a


55

5,000 gallon per month customer is also calculated and included in the table. Actual rate increases will depend on final project and operating costs.

Table 7-6 Estimated Impact to Customer Rates

Alternative Annual Debt Service

per 1000 gallons

Annual Operating Cost

per 1000 gallons

Annual Total cost

per 1000 gallons

Monthly Cost Increase for 5,000 gallon per month

customer

1 – Retrofit GAC into Existing Filters

$0.18 $0.61 $0.79 $3.96


$0.84 $0.48 $1.32 $6.58


$0.95 $0.60 $1.54 $7.72

7.5 Preferred GAC Alternative

7.5.1 Retrofit GAC into Existing Filters

Advantages

Lower cost than post-filter adsorbers

Maximizes the use of existing assets

Requires no yard piping modifications

Can be phased in one filter at a time

Will not require modifications to the filtered water pumps

Does not require an additional building

Disadvantages

Obtaining regulatory approval by MDNR to reduce sand depth to 6” might be infeasible

EBCT of 20 minutes cannot be obtained without a pilot study (regulatory requirement)

A GAC exchange requires a filter to be off-line, reducing plant throughput capacity

GAC is exposed to high loads of turbidity (poor water quality), risking GAC fouling (blinding), which would reduce GAC effectiveness and potentially lead to premature GAC replacement

GAC is backwashed much more frequently, resulting in additional abrasive wear, reducing GAC life

Replacing anthracite with GAC will not qualify for Cryptosporidum credit under LT2ESWTR

7.5.2 GAC Filters as Second Stage Filters

Advantages

EBCT of 20 minutes can be attained, meeting the BAT under Stage D/DBPR for TOC reduction

A redundant train is provided, allowing for GAC exchange without diminishing plant capacity

Highest water quality is applied to the second stage filters which minimizes carbon usage and frequency of regeneration


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GAC is backwashed less frequently, reducing abrasive wear and extending GAC life

Provides for an efficient GAC design

Improves UV transmittance in filter effluent (UV influent)

May qualify for 0.5 Log Cryptosporidum removal credit under LT2ESWTR

Disadvantages

Higher cost than a filter retrofit

Requires a new building to house the contactors

Requires substantial changes to yard piping

Filtered water pumps might need to be replaced with larger pumps

7.5.3 Preferred Alternative

GAC pressure contactors as second stage filters following the existing dual media filters, is the preferred option. This allows for the complete 20 minutes of EBCT, providing for USEPA BACT treatment for TOC reduction. Since TOC reduction is the most critical criteria for this project, achieving 20 minutes EBCT was considered paramount. In this option, highest water quality is applied to the second stage filters which minimizes carbon usage and frequency of regeneration, providing for an efficient GAC design. Another advantage of using the GAC as a secondary filter is that it improves UV transmittance and may qualify for 0.5 Log Cryptosporidum removal credit under LT2ESWTR (Table 3-4). These advantages will help reduce UV dose requirements for inactivation of Cryptosporidium, resulting in savings of O&M costs. It is recognized that this is the higher cost option and the cost impact on the water users will need to be considered in any final decision.


57


58

8. Project Implementation

8.1 Treatability Studies

8.1.1 Optimized Coagulation

Optimized coagulation is a condition where both pH level and coagulant dose are optimized for a maximum organic carbon (measured as DOC) and particulate (measured as turbidity) removal. As noted earlier, limited bench-scale studies conducted in the past showed that at a pH of 6.5, Clarion 4055 was the best performing coagulant for turbidity and TOC removal (Disinfection By-products Compliance Study by Horner and Shifrin Inc., September, 2012). A recommendation was made by the study to switch to Clarion 4055 as a coagulant and replacing the existing activated PAC with Aqua-Nuchar a wood based carbon. The WTP is currently using PAC from Aqua-Nuchar. However, the coagulant and polymer currently used at the plant are polyaluminum chlorosulfate and poly-dadmac respectively and not the Clarion 4055 as recommended.

It is recommended that the City establish a rigorous jar-testing program to test a wide variety of coagulants and polymers at various doses and pH levels to confirm the findings of the previous study and apply the results to maximize TOC and turbidity removal at the full-scale plant. Figure 8-1 shows a typical jar test set up.

Figure 8-1 Jar Test Apparatus

8.1.2 GAC

Natural Organic Matter (NOM), a precursor to Disinfection By-Products (DBPs), is a heterogeneous mixture of naturally occurring organic components consisting of humic substances (humic and fulvic acids), as well as various non-humic biochemicals such as proteins and carbohydrates. Adding further complexity is the fact that NOM varies significantly depending on its source. NOM is produced by allochthonous (decay of leaves and vegetation) and autochthonous (algae) sources. The nature of NOM is highly variable from place to place and even at a single location, may vary throughout the year. Surface waters – such as the Mississippi River, which is the water source for the Hannibal WTP – are particularly subject to variability. Algal blooms have been noticed in the Mississippi River (Disinfection By-products Compliance Study – Addendum 1 by Horner and Shifrin Inc., June, 2014). In addition to the variability in water quality, different types of GAC, each with different


59

adsorptive characteristics are available for use in the water industry. GAC can be produced from bituminous coal, lignite coal, peat, wood and from coconut shell. Because of this, it is difficult or impossible to accurately select the appropriate GAC or to predict the long-term performance of GAC without performance testing. Performance testing accounts for the specific source water quality, the type of GAC, and the multiple impurities that compete for adsorption sites in the GAC. Performance testing assists in selecting the appropriate GAC media and treatment process, developing design criteria, and determining carbon usage for a given source water (e.g. Mississippi river) by estimating breakthrough and EBCT.

Performance testing of GAC generally takes two forms, laboratory scale testing and on-site pilot testing.

Laboratory Scale Testing

Isotherm testing and rapid small-scale column testing (RSSCT) can be conducted in a laboratory using ground GAC particles and using the actual source water being treated at the WTP (e.g. Mississippi river). These methods decrease the time necessary to determine the adsorptive behavior of carbon particles. The isotherm is a static, less sophisticated test that evaluates the adsorptive capacity of GAC under equilibrium. The RSSCT is a more dynamic and sophisticated test that provides data for adsorption capacity and kinetics. The RSSCT uses small scale columns in which similitude to the full-scale GAC contactor has been maintained

RSSCT testing involves collecting a sample of water in a container and transporting it to a laboratory. This sample is passed through a small column of GAC and the treated water is analyzed to determine the effectiveness of the GAC. Many different carbons can be tested and the design conditions – such as loading rate and EBCT – can be varied to establish the full-scale design criteria and to estimate GAC life.

Figure 8-2 Laboratory Test

Results from RSSCT testing provide information about adsorptive capacity and the kinetics of the breakthrough curve, which can be used to evaluate the effectiveness of the GAC and to estimate full-scale EBCT, use rate and breakthrough curves. While laboratory testing provides quick results – testing can be completed in a few weeks – its significant drawbacks are requiring larger volumes of water than isotherms, failure of DOC to behave as assumed in dimensionally scaling the columns, and not accounting for seasonal variability of the source water.


60

Pilot Testing

Pilot testing of GAC is a regulatory requirement imposed by the MDNR.. Pilot-scale columns utilize the same GAC and influent water as the full-scale system.

Pilot testing provides a more complete evaluation of GAC. Tests make it possible to determine the effects of influent water quality on treatability and refine carbon selection, EBCT and carbon use rates. A pilot test apparatus is set up at the WTP location and a side-stream of the source water is run through the GAC for an extended period to evaluate the GAC performance at actual on-site operating conditions. Multiple, parallel columns can be used to evaluate several different types of GAC and flows and hydraulic loading rates can be varied to establish the optimum design criteria. Figure 8-3 illustrates a typical pilot test apparatus.

Figure 8-3 Pilot Test Apparatus

The drawback to pilot testing is that it is generally run over an extended period, from several months to a year in order to fully evaluate GAC performance as the source water quality varies over time.

Test Plan For Hannibal

The actual plan for testing GAC for the Hannibal WTP will need to be negotiated between the City of Hannibal and the MDNR. It is likely that the testing would include both laboratory and pilot testing. Laboratory testing would be used to select the most effective GACs, and pilot testing would more fully evaluate these GACs to refine carbon selection, establish the final design criteria, and demonstrate the effectiveness of GAC treatment to the MDNR in order to obtain approval to install GAC at the Hannibal WTP. We anticipate that a pilot test (after laboratory testing) would need to run for a minimum of 3 months and potentially for up to 12 months in order to provide the necessary design criteria and provide adequate information to the MDNR.


61

8.2 Distribution System Improvements

The need for distribution system improvements – as discussed in Section 6.1.3 – should be evaluated through a computer hydraulic model analysis of the distribution system, which would show where long detention times could lead to DBP formation. The results of this modelling could discover areas of “dead-end” pipe (which should be abandoned or flushed), indicate where valves may have been left closed impeding system circulation, or identify areas where oversized water mains may be contributing to extended reaction times, or indicate where storage tank stratification may be occurring. Knowing the areas of extended reaction times could guide a flushing program, indicate areas where valve and/or pipe improvements need to be made, show where replacing or lining old and corroded lines or replacing oversized mains may be required, or indicate where tank mixing may be appropriate. A hydraulic model may also show where low chlorine residual may be expected to occur and aid in the design of chlorine booster systems. In the event DBPs continue to be an issue, the City should evaluate decentralized treatment such as air stripping.

8.3 Implementation Schedule

Table 8-1 Anticipated Implementation Schedule

Task Start Date End Date

7. Laboratory testing of selected alternative and initial planning coordination with MDNR

April 2017 January 2018

8. Pilot testing January 2018 August 2018

9. Preliminary Engineering Report for SRF application and MDNR plan approval

September 2018 November 2018

10. Final Design, MDNR review and permit approval December 2018 September 2019

11. Bid Phase October 2019 December 2019

12. Construction January 2020 January 2021

A rate increase would need to be in effect by January 2020.


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9. References

“Best Management Practices for Maintaining Water Quality in the Distribution System” Smith, D. Journal of AWWA, March (2001).

“Disinfection By-products Compliance Study” Horner and Shifrin Inc., September, (2012).

“Disinfection By-products Compliance Study” Horner and Shifrin Inc., Addendum 1, June, (2014).

Drinking Water Institute, Edzwald, James K. (2006).

“Characterization of Natural Organic Matter and its Relationship to Treatability” Owen, D.M.; Amy, G.L.; and Chowdhury, Z.K.. AWWA Research Foundation, Denver (1993).

“Technologies and Costs for control of Microbial Contaminants and Disinfection By-Products, Office of Groundwater and Drinking Water, Washington DC (2003)

“Water System Facility Plan” Horner and Shifrin Inc., March (2013)

“Water Treatment Plant Design” Randtke, S J.., Horsley,B. M AWWA, Editors, ASCE, Fifth Edition, Denver, Colorado (2012).


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Appendix A. Engineers Opinion of Probable Cost


City of Hannibal, MO GAC System Preliminary Engineering Report

Alternative 1 ‐ GAC Filter Retrofit

Cost Estimate

Item Description Qty.Unit Price

$Total

$1 Underdrains 1 390,000 390,0002 Initial Carbon Costs 1 330,000 330,0003 Construction Costs 1 210,000 210,000

930,000

Freight6 % of carbon and

underdrain cost 43,200Start-up support 3 % of underdrain cost 11,700

Contractor's mark-up10 % of carbon and

ujnderdrain cost 60,000

Subtotal Sub Total Direct Costs 1,044,900General conditions 10 % of subtotal 104,490

Contractors overhead and profit 20 % of subtotal cost 208,980

Total Construction Cost 1,358,370

Professional services(Project management, engineering,

construction support)

12 % of construction cost

163,004Construction observation services 6 % of construction cost 62,694

Total Installed Cost 1,584,068Project Contingency 25 % of TIC 396,017

Total Project Cost 1,981,000



Alternative 2 ‐ GAC Filters as Second Stage Filters ‐ 2.7 MGD Case

Cost Estimate


$Total

$

1Two Vessel GAC Contactor (with Carbon)

5 295,000 1,475,000

2 Upgraded Pumps 2 174,400 348,800

Bare Equipment Cost 1,823,800Freight 6 % of equipment cost 109,428

Start-up support 3 % of equipment cost 54,714Contractor's mark-up 10 % of equipment cost 182,380

Total Equipment Cost 2,170,322Mechanical installation 45 % of equipment cost 976,645

Electrical installation - power 15 % of mechanical cost 146,497Electrical installation - I&C 50 % of electrical cost 73,248

Concrete (includes foundations) 9 % of equipment cost 195,329Civil works 18 % of equipment cost 390,658

Building (6000 sq ft) 165 $/sq ft. 990,000

Sub Total Direct Costs 4,942,699General conditions 10 % of construction cost 494,270

Contractors overhead and profit 20 % of construction cost 988,540






Total Installed Cost 7,493,132Project Contingency 25 % of TIC 1,873,283


ASSUMPTIONS

1. Deep foundations are not required

2. Site is realtively flat (extensive earth moving not required)

3. Site access is unimpeded

4. Lay‐down area is readily available

5. Temporary utilities readily available

6. Building is CMU block building with heat and ventilation only

7. Equipment is skid mounted, pre‐piped and pre‐wired by the OEM



Alternative 2 ‐ GAC Filters as Second Stage Filters ‐ 3.5 MGD Case

Cost Estimate


$Total

$

1Two Vessel GAC Contactor (with Carbon)

6 295,000 1,770,000

2 Upgraded Pumps 2 174,400 348,800

Bare Equipment Cost 2,118,800Freight 6 % of equipment cost 127,128

Start-up support 3 % of equipment cost 63,564Contractor's mark-up 10 % of equipment cost 211,880

Total Equipment Cost 2,521,372Mechanical installation 45 % of equipment cost 1,134,617

Electrical installation - power 15 % of mechanical cost 170,193Electrical installation - I&C 50 % of electrical cost 85,096

Concrete (includes foundations) 9 % of equipment cost 226,923Civil works 18 % of equipment cost 453,847

Building (6000 sq ft) 165 $/sq ft. 990,000

Sub Total Direct Costs 5,582,049General conditions 10 % of construction cost 558,205

Contractors overhead and profit 20 % of construction cost 1,116,410






Total Installed Cost 8,462,386Project Contingency 25 % of TIC 2,115,596


ASSUMPTIONS

1. Deep foundations are not required

2. Site is realtively flat (extensive earth moving not required)

3. Site access is unimpeded

4. Lay‐down area is readily available

5. Temporary utilities readily available

6. Building is CMU block building with heat and ventilation only

7. Equipment is skid mounted, pre‐piped and pre‐wired by the OEM


Appendix B. Bond Payments and Fees


Alternative 1 ‐ Retrofit GAC into Existing Filters

Loan Amortization Schedule 5000 Gallon/Month

Year No. Payment Interest Principal Balance Total Payment

0 1,981,000$ Annual Cost Monthly Cost

1 126,808$ 79,240$ 47,568$ 1,933,432$ 126,808$ 0.18$ 0.61$ 0.79$ 47.47$ 3.96$

2 126,808$ 77,337$ 49,470$ 1,883,962$ 126,808$ 0.18$ 0.61$ 0.79$ 47.47$ 3.96$

3 126,808$ 75,358$ 51,449$ 1,832,513$ 126,808$ 0.18$ 0.61$ 0.79$ 47.47$ 3.96$

4 126,808$ 73,301$ 53,507$ 1,779,005$ 126,808$ 0.18$ 0.61$ 0.79$ 47.47$ 3.96$

5 126,808$ 71,160$ 55,647$ 1,723,358$ 126,808$ 0.18$ 0.61$ 0.79$ 47.47$ 3.96$

6 126,808$ 68,934$ 57,873$ 1,665,485$ 126,808$ 0.18$ 0.61$ 0.79$ 47.47$ 3.96$

7 126,808$ 66,619$ 60,188$ 1,605,296$ 126,808$ 0.18$ 0.61$ 0.79$ 47.47$ 3.96$

8 126,808$ 64,212$ 62,596$ 1,542,700$ 126,808$ 0.18$ 0.61$ 0.79$ 47.47$ 3.96$

9 126,808$ 61,708$ 65,100$ 1,477,601$ 126,808$ 0.18$ 0.61$ 0.79$ 47.47$ 3.96$

10 126,808$ 59,104$ 67,704$ 1,409,897$ 126,808$ 0.18$ 0.61$ 0.79$ 47.47$ 3.96$

11 126,808$ 56,396$ 70,412$ 1,339,485$ 126,808$ 0.18$ 0.61$ 0.79$ 47.47$ 3.96$

12 126,808$ 53,579$ 73,228$ 1,266,257$ 126,808$ 0.18$ 0.61$ 0.79$ 47.47$ 3.96$

13 126,808$ 50,650$ 76,157$ 1,190,100$ 126,808$ 0.18$ 0.61$ 0.79$ 47.47$ 3.96$

14 126,808$ 47,604$ 79,204$ 1,110,896$ 126,808$ 0.18$ 0.61$ 0.79$ 47.47$ 3.96$

15 126,808$ 44,436$ 82,372$ 1,028,524$ 126,808$ 0.18$ 0.61$ 0.79$ 47.47$ 3.96$

16 126,808$ 41,141$ 85,667$ 942,857$ 126,808$ 0.18$ 0.61$ 0.79$ 47.47$ 3.96$

17 126,808$ 37,714$ 89,093$ 853,764$ 126,808$ 0.18$ 0.61$ 0.79$ 47.47$ 3.96$

18 126,808$ 34,151$ 92,657$ 761,107$ 126,808$ 0.18$ 0.61$ 0.79$ 47.47$ 3.96$

19 126,808$ 30,444$ 96,363$ 664,743$ 126,808$ 0.18$ 0.61$ 0.79$ 47.47$ 3.96$

20 126,808$ 26,590$ 100,218$ 564,525$ 126,808$ 0.18$ 0.61$ 0.79$ 47.47$ 3.96$

21 126,808$ 22,581$ 104,227$ 460,299$ 126,808$

22 126,808$ 18,412$ 108,396$ 351,903$ 126,808$

23 126,808$ 14,076$ 112,732$ 239,171$ 126,808$

24 126,808$ 9,567$ 117,241$ 121,930$ 126,808$

25 126,808$ 4,877$ 121,930$ 0$ 126,808$

Average User

Amortization

Cost per

1000 Gal

Carbon Cost per

1000 gal

Total Cost per

1000 Gal


Alternative 2 ‐ GAC Filters as Second Stage Filters (2.7 MGD)




1 599,600$ 374,680$ 224,920$ 9,142,080$ 599,600$ 0.84$ 0.48$ 1.32$ 78.95$ 6.58$

2 599,600$ 365,683$ 233,917$ 8,908,163$ 599,600$ 0.84$ 0.48$ 1.32$ 78.95$ 6.58$

3 599,600$ 356,327$ 243,274$ 8,664,890$ 599,600$ 0.84$ 0.48$ 1.32$ 78.95$ 6.58$

4 599,600$ 346,596$ 253,004$ 8,411,885$ 599,600$ 0.84$ 0.48$ 1.32$ 78.95$ 6.58$

5 599,600$ 336,475$ 263,125$ 8,148,760$ 599,600$ 0.84$ 0.48$ 1.32$ 78.95$ 6.58$

6 599,600$ 325,950$ 273,650$ 7,875,111$ 599,600$ 0.84$ 0.48$ 1.32$ 78.95$ 6.58$

7 599,600$ 315,004$ 284,596$ 7,590,515$ 599,600$ 0.84$ 0.48$ 1.32$ 78.95$ 6.58$

8 599,600$ 303,621$ 295,979$ 7,294,536$ 599,600$ 0.84$ 0.48$ 1.32$ 78.95$ 6.58$

9 599,600$ 291,781$ 307,819$ 6,986,717$ 599,600$ 0.84$ 0.48$ 1.32$ 78.95$ 6.58$

10 599,600$ 279,469$ 320,131$ 6,666,586$ 599,600$ 0.84$ 0.48$ 1.32$ 78.95$ 6.58$

11 599,600$ 266,663$ 332,937$ 6,333,649$ 599,600$ 0.84$ 0.48$ 1.32$ 78.95$ 6.58$

12 599,600$ 253,346$ 346,254$ 5,987,395$ 599,600$ 0.84$ 0.48$ 1.32$ 78.95$ 6.58$

13 599,600$ 239,496$ 360,104$ 5,627,291$ 599,600$ 0.84$ 0.48$ 1.32$ 78.95$ 6.58$

14 599,600$ 225,092$ 374,508$ 5,252,782$ 599,600$ 0.84$ 0.48$ 1.32$ 78.95$ 6.58$

15 599,600$ 210,111$ 389,489$ 4,863,293$ 599,600$ 0.84$ 0.48$ 1.32$ 78.95$ 6.58$

16 599,600$ 194,532$ 405,068$ 4,458,225$ 599,600$ 0.84$ 0.48$ 1.32$ 78.95$ 6.58$

17 599,600$ 178,329$ 421,271$ 4,036,954$ 599,600$ 0.84$ 0.48$ 1.32$ 78.95$ 6.58$

18 599,600$ 161,478$ 438,122$ 3,598,832$ 599,600$ 0.84$ 0.48$ 1.32$ 78.95$ 6.58$

19 599,600$ 143,953$ 455,647$ 3,143,185$ 599,600$ 0.84$ 0.48$ 1.32$ 78.95$ 6.58$

20 599,600$ 125,727$ 473,873$ 2,669,313$ 599,600$ 0.84$ 0.48$ 1.32$ 78.95$ 6.58$

21 599,600$ 106,773$ 492,828$ 2,176,485$ 599,600$ 0.84$ 0.48$ 1.32$ 78.95$ 6.58$

22 599,600$ 87,059$ 512,541$ 1,663,945$ 599,600$ 0.84$ 0.48$ 1.32$ 78.95$ 6.58$

23 599,600$ 66,558$ 533,042$ 1,130,902$ 599,600$ 0.84$ 0.48$ 1.32$ 78.95$ 6.58$

24 599,600$ 45,236$ 554,364$ 576,538$ 599,600$ 0.84$ 0.48$ 1.32$ 78.95$ 6.58$

25 599,600$ 23,062$ 576,538$ ‐$ 599,600$ 0.84$ 0.48$ 1.32$ 78.95$ 6.58$

Average User

Amortization

Cost per

1000 Gal

Carbon Cost per

1000 gal

Total Cost per

1000 Gal


Alternative 2 ‐ GAC Filters as Second Stage Filters (3.5 MGD)




1 677,119$ 423,120$ 253,999$ 10,324,001$ 677,119$ 0.95$ 0.60$ 1.54$ 92.61$ 7.72$

2 677,119$ 412,960$ 264,158$ 10,059,843$ 677,119$ 0.95$ 0.60$ 1.54$ 92.61$ 7.72$

3 677,119$ 402,394$ 274,725$ 9,785,118$ 677,119$ 0.95$ 0.60$ 1.54$ 92.61$ 7.72$

4 677,119$ 391,405$ 285,714$ 9,499,404$ 677,119$ 0.95$ 0.60$ 1.54$ 92.61$ 7.72$

5 677,119$ 379,976$ 297,142$ 9,202,262$ 677,119$ 0.95$ 0.60$ 1.54$ 92.61$ 7.72$

6 677,119$ 368,090$ 309,028$ 8,893,234$ 677,119$ 0.95$ 0.60$ 1.54$ 92.61$ 7.72$

7 677,119$ 355,729$ 321,389$ 8,571,845$ 677,119$ 0.95$ 0.60$ 1.54$ 92.61$ 7.72$

8 677,119$ 342,874$ 334,245$ 8,237,600$ 677,119$ 0.95$ 0.60$ 1.54$ 92.61$ 7.72$

9 677,119$ 329,504$ 347,615$ 7,889,985$ 677,119$ 0.95$ 0.60$ 1.54$ 92.61$ 7.72$

10 677,119$ 315,599$ 361,519$ 7,528,466$ 677,119$ 0.95$ 0.60$ 1.54$ 92.61$ 7.72$

11 677,119$ 301,139$ 375,980$ 7,152,486$ 677,119$ 0.95$ 0.60$ 1.54$ 92.61$ 7.72$

12 677,119$ 286,099$ 391,019$ 6,761,467$ 677,119$ 0.95$ 0.60$ 1.54$ 92.61$ 7.72$

13 677,119$ 270,459$ 406,660$ 6,354,808$ 677,119$ 0.95$ 0.60$ 1.54$ 92.61$ 7.72$

14 677,119$ 254,192$ 422,926$ 5,931,881$ 677,119$ 0.95$ 0.60$ 1.54$ 92.61$ 7.72$

15 677,119$ 237,275$ 439,843$ 5,492,038$ 677,119$ 0.95$ 0.60$ 1.54$ 92.61$ 7.72$

16 677,119$ 219,682$ 457,437$ 5,034,601$ 677,119$ 0.95$ 0.60$ 1.54$ 92.61$ 7.72$

17 677,119$ 201,384$ 475,735$ 4,558,866$ 677,119$ 0.95$ 0.60$ 1.54$ 92.61$ 7.72$

18 677,119$ 182,355$ 494,764$ 4,064,103$ 677,119$ 0.95$ 0.60$ 1.54$ 92.61$ 7.72$

19 677,119$ 162,564$ 514,554$ 3,549,548$ 677,119$ 0.95$ 0.60$ 1.54$ 92.61$ 7.72$

20 677,119$ 141,982$ 535,137$ 3,014,412$ 677,119$ 0.95$ 0.60$ 1.54$ 92.61$ 7.72$

21 677,119$ 120,576$ 556,542$ 2,457,869$ 677,119$ 0.95$ 0.60$ 1.54$ 92.61$ 7.72$

22 677,119$ 98,315$ 578,804$ 1,879,066$ 677,119$ 0.95$ 0.60$ 1.54$ 92.61$ 7.72$

23 677,119$ 75,163$ 601,956$ 1,277,110$ 677,119$ 0.95$ 0.60$ 1.54$ 92.61$ 7.72$

24 677,119$ 51,084$ 626,034$ 651,076$ 677,119$ 0.95$ 0.60$ 1.54$ 92.61$ 7.72$

25 677,119$ 26,043$ 651,076$ 0$ 677,119$ 0.95$ 0.60$ 1.54$ 92.61$ 7.72$

Average User

Amortization

Cost per

1000 Gal

Carbon Cost per

1000 gal

Total Cost per

1000 Gal

granular activated carbon system - wtad...feb 22, 2017 · cost estimates were developed for two...

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