WBS-Based Cost Models for Drinking Water Treatment Technologies
EPA
United States
Environmental Protection
Agency
Work Breakdown Structure-Based Cost Models
for Drinking Water Treatment Technologies
Office of Water (4607M)
EPA815-B-14-007
May 2014
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WBS-Based Cost Models for Drinking Water Treatment Technologies
Table of Contents
1. Introduction 1
1.1 Background 1
1.2 Objectives 1
1.3 Organization of the Report 2
1.4 List of Abbreviations and Symbols in this Chapter 2
1.5 References 2
2. WBS Model Overview 3
2.1 Model Structure 3
2.2 The WBS Approach 8
2.3 Model Use 10
2.3.1 Input Sheet Structure and Use 10
2.3.2 Common Inputs 13
2.3.3 Input Sheet Examples 14
2.3.4 Output Sheet Structure and Use 16
2.3.5 Critical Design Assumptions Sheet Structure and Use 17
2.3.6 Index Sheet Structure and Use 19
2.4 General Cost Assumptions 20
2.4.1 Building Costs 21
2.4.2 Residuals Management Costs 22
2.4.3 Indirect Capital Costs 22
2.4.4 Add-on Costs 23
2.4.5 Annual O&M Costs 25
2.4.6 Total Annualized Cost 25
2.4.7 Updating and Adjusting Costs 26
2.5 List of Abbreviations and Symbols in this Chapter 27
2.6 References 27
3. Granular Activated Carbon Model 28
3.1 Overview of the Treatment Process 28
3.2 Input Sheet 31
3.3 Model Assumptions Sheets 42
3.4 Contactor Constraints Sheet 44
3.5 Backwash and Regeneration Sheet 44
3.6 Retrofit Sheet 45
3.7 Pumps, Pipe and Structure Sheet 46
3.8 Instrumentation and Control Sheet 47
3.9 Residuals Management Sheet 47
3.10 O&M and HVAC Sheets 47
3.11 Indirect Sheet 49
3.12 Output Sheet 49
3.13 Ancillary and Reference Model Components 49
3.14 List of Abbreviations and Symbols in this Chapter 50
3.15 References 50
4. Packed Tower Aeration Model 52
4.1 Overview of the PTA Treatment Process 52
4.2 Input Sheet 53
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WBS-Based Cost Models for Drinking Water Treatment Technologies
4.3 Model Assumptions Sheets 59
4.4 Tower Design Sheets 61
4.5 Retrofit Sheet 63
4.6 Chemical Use Sheet 64
4.7 Off-Gas Sheet 64
4.8 Pumps, Pipe and Structure Sheet 64
4.9 Instrumentation and Control Sheet 65
4.10 O&M and HVAC Sheets 65
4.11 Indirect Sheet 66
4.12 Output Sheet 66
4.13 Ancillary and Reference Model Components 66
4.14 List of Abbreviations and Symbols in this Chapter 67
4.15 References 67
5. Multi-Stage Bubble Aeration Model 69
5.1 Overview of the MSB A Treatment Process 69
5.2 Input Sheet 71
5.3 Model Assumptions Sheets 75
5.4 Basin Constraints Sheet 77
5.5 Off-Gas Sheet 77
5.6 Pumps, Pipe and Structure Sheet 78
5.7 Instrumentation and Control Sheet 79
5.8 O&M and HVAC Sheets 79
5.9 Indirect Sheet 79
5.10 Output Sheet 80
5.11 Ancillary Model Components 80
5.12 List of Abbreviations and Symbols in this Chapter 80
5.13 References 81
Appendix A. Valves, Instrumentation and System Controls 82
Appendix B. Building Construction Costs 88
Appendix C. Residuals Management Costs 97
Appendix D. Indirect Capital Costs 107
Appendix E. General Assumptions for Operating and Maintenance Costs 130
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WBS-Based Cost Models for Drinking Water Treatment Technologies
1. Introduction
This report describes cost models for the drinking water treatment technologies listed in the table
of contents. Most of these technologies are used in drinking water systems to remove or destroy
pollutants such as arsenic, radon, disinfection byproducts, sulfates, hardness and waterborne
pathogens. In addition, several of these technologies can be used as add-on technologies to
existing treatment systems. For example, some of the technologies can be installed to provide
pre-oxidation to improve contaminant removal efficiency by subsequent treatment processes.
1.1 Background
The Safe Drinking Water Act Amendments of 1996, as well as a number of other statutes and
executive orders, require that the U.S. Environmental Protection Agency (EPA or the Agency)
estimate regulatory compliance cost as part of its rulemaking process. The compliance cost
models described in this document differ from the drinking water cost models previously used by
the Agency in that the new models are based on a work breakdown structure (WBS) approach to
developing cost estimates. In general, the WBS approach involves breaking a process down into
discrete components for the purpose of estimating unit costs. EPA pursued this approach as part
of an effort to address recommendations made by the Technology Design Panel, which convened
in 1997 to review the Agency's methods for estimating drinking water compliance costs (U.S.
EPA, 1997).1
1.2 Objectives
In developing WBS-based models for estimating drinking water treatment system costs, EPA
had the following objectives:
• Transparency of process design and cost
• Defensibility of design criteria and assumptions
• Ease of use and updating
• Modularity of components for use with centralized cost database.
The Agency determined that the best way to meet these goals was to develop spreadsheet-based
engineering models drawing from a central database of component unit costs. Each engineering
model contains the work breakdown for a particular treatment process and preprogrammed
engineering criteria and equations that estimate equipment requirements for user-specified design
requirements (e.g., system size and influent water quality). Each model also provides unit and
total cost information by component (e.g., individual items of capital equipment) and totals the
individual component costs to obtain a direct capital cost. Additionally, the models estimate add-
on costs (permits, pilot study and land acquisition costs for each technology), indirect capital
costs and annual operating and maintenance (O&M) costs, thereby producing a complete
compliance cost estimate.
1 The panel consisted of nationally recognized drinking water experts from U.S. EPA, water treatment consulting
companies, public and private water utilities, suppliers, equipment vendors, and Federal and state regulators in
addition to cost estimating professionals.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
1.3 Organization of the Report
This report is organized as follows:
• Chapter 2 provides an overview of the general model components and the methods used
in these components to estimate treatment system costs.
• Subsequent chapters describe the individual models, design criteria and assumptions for
the selected treatment technologies.
• Appendices provide additional information on methods EPA used to estimate design
requirements and costs for specific components, such as buildings, system controls,
indirect capital costs and annual O&M costs.
1.4 List of Abbreviations and Symbols in this Chapter
EPA U.S. Environmental Protection Agency
O&M operating and maintenance
WBS work breakdown structure
1.5 References
U.S. Environmental Protection Agency (U.S. EPA). 1997. Discussion Summary: EPA
Technology Design Workshop. Washington, D.C.: U.S. EPA, Office of Groundwater and
Drinking Water.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
2. WBS Model Overview
This chapter includes the following sections:
• An overview of how the models are structured (Section 2.1)
• A description of how this structure was developed using the work breakdown structure
(WBS) approach (Section 2.2)
• A brief users guide describing how to operate the models (Section 2.3), including
documentation of general design assumptions
• Documentation of the general cost assumptions incorporated in all of the models (Section
2.4).
2.1 Model Structure
The WBS-based engineering models integrate the following structural features to generate
treatment cost estimates:
• Treatment component selection, design and cost output based on a WBS approach
• Process design based on state-of-the-art techniques and generally recommended
engineering practices (GREPs)
• A centralized reference database containing unit costs for components and reference
tables for component sizing and chemical properties.
Exhibit 2-1 shows how these features are integrated in a series of spreadsheets that include an
Excel workbook for each technology and a central cost and engineering reference database (the
WBS cost database), which is in a separate Excel workbook. An input sheet allows the user to
define treatment requirements such as system design and average flows, target contaminant and
raw water quality. Exhibit 2-2 provides an example of an input spreadsheet. The information
provided via the input sheet interacts with three critical design assumptions sheets (one each for
process design, operating and maintenance [O&M] and indirect capital costs) to generate inputs
to the engineering design sheets. Although the critical design assumption values are based on
GREPs and can be used without modification, the user can also revise these values to reflect site-
specific requirements. Each model also has a predetermined list of treatment equipment needs
(e.g., tanks, vessels and instrumentation) identified using the WBS approach. The engineering
design sheets calculate equipment quantity and size requirements based on the treatment needs
and critical design assumptions. The technology chapters of this report describe technology-
specific content and function of each sheet. General design and cost assumptions are described in
Sections 2.3.5 and 2.4.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
Exhibit 2-1. Structure of the WBS Models
User Input Required
User Input Optional
L
Input Sheet
(user-defined design
parameters such as flow
rates, raw water quality,
bed depth)
Reference Sheets
(applicable only for some
models; includes guidance
on setting input
parameters and critical
design assumptions)
I
Critical Design
Assumptions Sheets
(includes key design criteria,
e.g., loading rate, bed
expansion; O&M and indirect
assumptions)
WBS Engineering
Analysis
WBS Component
List
(applicable components
such as tanks, vessels,
piping, instrumentation,
and building)
Engineering Design Sheets
(design of applicable components
and systems, e.g., vessels, tanks,
membranes, backwash, pumps,
pipes, valves; structure design;
chemical and media requirements)
Cost Equations
(component functions)
Output Sheet
Process Capital Costs
Useful Life Data
Indirect Costs
Add-on Costs
O&M Costs
Total Annualized Cost
WBS System Cost
Analysis
WBS Cost Database
(documented cost and useful
life estimates by component
type and size; some
engineering reference data)
O&M and Indirect
Sheets
Annual O&M
requirements
Some indirect costs
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WBS-Based Cost Models for Drinking Water Treatment Technologies
Exhibit 2-2. Sample of Input Spreadsheet
MULTI-STAGE BUBBLE AERATION SYSTEM DESIGN AND COST INPUT
STEP 1
Select On
STEP 3.:
Select one of the eight standard designs at right
OR
Select "CLEAR FOR MANUAL ENTRY"
_rj For VQCs, default designc available up to 1 MGD only, because information oh using MSB,4, for these '.cT.taminants in larger systems if limile<
Enter or change values in the
under "Manual Inputs"
and > cells belo1
0.030 mgd standard design <- U;ing tLi=- d
0.124 mgd standard design
0.305 mgd standard design
O.T40 mgd standard design
2.152 mgd standard design |
7.365 mgd standard design I
22.6U mgd standard design
75.072 mgd standard design
CLEAR FOR MANUAL ENTRY
(•p«t Complete — Results Ready
Results arc ready f no need to click button1)
Generate Results
See model documentation For more information on standard designs
HAHUAt INPUTS
Direct Capita! Cost: J1DT.797
Total Capital Cost: (158,337
Annual OftM Cost: J7.232
aliMd Cost: 123.623 f.16.3 u«,rs at 7M
Optimize Numbci
of Basins
Desiq* Flow
Aweraqe Flo
For uf or«ttoB
Treatment system design flo
Bypass design flo
0.030 MGD
0 (JOT MGD
0.030 *i<3iJ
O.OOD TuJL-
Theoretical Percent Removal
Number of Basins (including redundancy)
Basin Length (including quiescent chamber)
Basin Width
Basin Height (including freeboard)
Dif f ustrs per stage
Total diffuses
30.OII
1 units
4 feet
2.5 Feet
I Feet
1 units
VOC release at wkick air polUtio* control
sTft«> is iccdcd
ber of booster piBps
For icf or»at JOB: tt of boostci pumps f
ber of blowers
For iftforaatioft: tt of blowers (including r
ber of redikda>t ba;»f to be added •
For tmf orBatio*: Redundant basins
po»e»t level
tcH avtoHatio*
Fof iBfom*tio>: Component level r
Mtomatiorir
Current bypass percentage is OS. Go to Critical Design Assumptions to change this value.
Vendor packages include abovecjround stainless steel, plastic, or fiberglass basins and typically are used
by small systems
Guidance: For VOCs. typical air to water ratios are between 10:1 and 300:1
Guidance: VOCs require no more than 2 to 3 feet water depth, biuond this depth no significant gain is
realised I Lo-.vry peer review comments')
Guidance: for VOCs. minimum of & stages, maximum of 12 stages, vendor uses 3 stages for most
applications fLowry peer review comments)
Estimate only, based o
number of stages
Adjust diff user access space requirements
Used only to determine whether air pollution control might be required; not part of system design
Using theoretical removal from above
CMRP (2000) states this is the maximum emission level for all VOCs for California South Coast AGMD,
but other districts may require different emissions standards based on location of the site and regional
ambient air quality.
Enter 0 to exclude booster pumps (i.e.. use existing pumps). Clear cell to accept model defaults (included
for all sices in this technology)
Designs should always include at least one blower. Leave blank to accept model default cakulatioi
Adjust number of redundant blowers
Leave blank to accept redundancy specified in critical design assumptions
Leave blank to use low cost components
Leave blank to allow model to pick based or. component level
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WBS-Based Cost Models for Drinking Water Treatment Technologies
Exhibit 2-3 shows an example of an output spreadsheet. The output sheet summarizes the results
of the calculations performed by the engineering design sheets, listing size and quantity required
for each item of equipment and the corresponding unit cost from the database. The output sheet
multiplies unit cost by quantity to determine total component cost for each WBS component. The
output sheet also lists the estimated useful life of every WBS component. The models use the
component useful lives in estimating total annualized cost (see Section 2.4.6).
For many of the components, there are optional materials, all of which are illustrated on the
output worksheet. For example, pressure vessels can be constructed with different types of body
material (stainless steel or carbon steel) and different types of internal materials (stainless steel or
plastic). Where there are optional materials, the output sheet selects from among these materials.
The specific selections are determined by input values and documented in the "use?" column of
the output worksheet. Direct capital cost is the sum of the selected component costs.
The output sheet also contains sections that calculate add-on costs, indirect capital costs, annual
O&M costs and total annualized cost. Annual O&M costs are based on the annual requirements
calculated on the O&M sheet. Indirect capital costs for certain items (standby power,
geotechnical, site work and yard piping) are based on calculations performed by the indirect
sheet. Other indirect capital costs and add-on costs are based on assumptions described in
Sections 2.4.3 and 2.4.4. Section 2.4.6 describes the calculation of total annualized cost.
The output sheet obtains unit costs (both capital and O&M) either from the central WBS cost
database or from estimated equipment cost curves. All of the treatment technology models use
information from the WBS cost database, which consists of a series of lookup tables that contain
costs by equipment or O&M element type and size. The database also provides useful life
estimates and documents the source of information. The central WBS cost database also contains
several tables that are used by the engineering design sheets of each model. For example, these
tables include information used in selecting pipe diameters, footprint for pumps and chemical
properties.
The WBS cost database itself is not provided along with the publicly released WBS models.
Instead, for ease of review and to maintain vendor confidentiality, relevant cost and engineering
data have been extracted from the database and included directly in the WBS model workbooks.
Thus, users can review (and adjust, if needed) the information from the central cost database in
the same manner as other WBS model inputs and assumptions.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
Exhibit 2-3. Sample of Output Spreadsheet
OUTPUT SUMMARY
Ts-ihnolDix
Contaminant Tj-po
System Size Catenary
DttianFlau
AueraotFlBU
Humttr af Bonn/
Numtarof£t.n|«-ptrB.irin
BvinLtnqth
Bwir, Width
BarinHeiaht
Sf^S2«™.
Dirtct Capital Cart
AiH-nnCart
Indirect Capital Cart
T.t.lC.»it.lC«t
A»»l 0 *M Cut
A»..liz»J Cut (1*-$ T»*rj *t TX}
f«l» U»tr
MSBA
TCE
j-m-ill
0.03 M'sDu-K-il-j-Ji-rt-yp-i/jflnu'l
O.QQ7 IISDfL-Kcl'jdiM-t-yp-ifrflaLil
1 unitr
* Jtflaw
4 f stt
2.5 f »*t
5 fstt
1 unitr
10T.T9T Eituk
1.033 D.^iir
50,162 POoilr
1SS.33T D>tJiir
T.232 Gjrtjiif
23.623 Gstaitr
J(V AlAA/AllUV
.2.1 Pl«rt!e
f wt, AH AH AM
cy AH AH AM
ey AH AH AM
- ,rt AM AM AM
i lutftr AV ^^ -fj-V ^w1 f £$¥ff f XSfJif
1 «!tr 374 *.! 374 4.] f 2.114 f 2.114
/ iM/tr JBV »«/ '.WV »«/ *' Ayft f 2Z*f#
* «itr 14 cf> 14 «f« * 4t f 345
ADDITIONAL WBS COMPONENTS NOT SHOWN
Kt.t Atflrfi™^ AM AM AM AM
jftjjUjMMTW
Add-on Cost Details f£iv.!.->ifos.rtiKrv.vff-t->iy*r-rji,fjqin<-£
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WBS-Based Cost Models for Drinking Water Treatment Technologies
2.2 The WBS Approach
These models represent improvements over past cost estimating methods by increasing
comprehensiveness, flexibility and transparency. By adopting a WBS-based approach to identify
the components that should be included in a cost analysis, the models produce a more
comprehensive assessment of the capital requirements for a treatment system. The models are
flexible in that users can change certain design parameters; warning messages indicate when user
inputs violate GREPs or logical functions. The transparent structure of each model allows users
to see how costs are built up from component unit costs to total treatment costs, which enables
users to identify cost drivers and determine whether the input assumptions generate a cost-
effective treatment design. Users also can perform sensitivity analyses showing how changes in
water quality parameters, chemical feed doses and equipment configuration affect cost.
Unlike prior EPA models, which used a variety of cost build-up methods, the WBS-based
engineering models have been developed using a consistent framework. Exhibit 2-4 shows this
framework. For each technology, the result is an engineering spreadsheet model that combines
user-identified inputs with pre-programmed engineering criteria and equations to generate
appropriate treatment design and equipment requirements. The models also result in a system-
level cost estimate for regulatory cost analysis.
Exhibit 2-4. Framework for Developing the WBS-Based Models
Step 1: Identify the treatment requirements based on the contaminant requiring removal, the flow for which treatment is
required, the influent water quality and treated water quality requirement, and then select a treatment technology
or combination of technologies capable of meeting the requirements.
Step 2: Develop the general design assumptions that apply to all the technologies (e.g., chemical storage capacity).
Step 3: Develop site- and technology-specific design assumptions that might affect treatment performance and, thereby,
design requirements (e.g., assumptions related to influent water constituents such as alkalinity or water quality
parameters such as pH).
Step 4: Construct a typical process flow diagram or P&ID showing the main unit processes for the technology and
identify equipment requirements.
Step 5: Calculate the equipment requirements, including dimensions and quantities, for the core elements of each unit
process. At each component (or group) level, identify choices of material (e.g., stainless steel or PVC pipe
material).
Step 6: Link the treatment equipment requirements to a database that contains unit costs by equipment type, size and
material. Multiplying the unit costs by the dimension and quantity requirements developed in Step 5 provides the
component-level design costs.
Step 7: Tally the costs of the selected components to determine direct capital cost.
Step 8: Develop and add indirect and add-on costs to determine total system capital cost.
Step 9: Develop operation and maintenance cost estimates.
The WBS approach provides EPA with a consistent method for identifying components to
include in a cost estimate. For each technology, the WBS approach develops a piping and
instrumentation drawing (P&ID) or a typical schematic layout showing the main unit processes
needed to achieve the contaminant removal goals. Exhibit 2-5 provides examples of several
classes of components that can be included in a P&ID. The models often include further
breakdown for alternative materials of construction for each component, because costs can differ
substantially across materials. For example, most pipes can be constructed of stainless steel,
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WBS-Based Cost Models for Drinking Water Treatment Technologies
steel, polyvinyl chloride (PVC) or chlorinated PVC. Stainless steel piping can cost twice as much
as PVC.
Exhibit 2-5. Component Classes Included in the WBS Inventory
Component Classes
Vessels
Tanks/basins
Pipes
Valves (see Appendix A for further details)
Pumps
Mixers
Instrumentation (see Appendix A for further details)
System controls (see Appendix A for further details)
Chemicals
Treatment media
Building (see Appendix B for further details)
Example Components
Pressure vessels
Storage
Backwash
Mixing
Contact
Flocculation
Sedimentation
Filtration
Process
Backwash
Chemical
Inlet/outlet
Bypass
Check (one-way)
Motor- or air-operated
Manual
Booster
Backwash
High-pressure (for membrane systems)
Chemical metering
Rapid
Flocculation
Inline static
Pressure gauge
Level switch/alarm
Chlorine residual analyzer
Flow meter
pH meter
Air monitor/alarm
High/low pressure alarm
Gas flow meters— rotameters
Scales
Programmable logic control units
Operator interface equipment
Controls software
Acids
Bases
Coagulants and coagulant aids
Antiscalants
Corrosion control
Oxidants and disinfectants
Activated alumina
Activated carbon
Membranes
Sand
Resins
Structure
Heating and air conditioning systems
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WBS-Based Cost Models for Drinking Water Treatment Technologies
Exhibit 2-5. Component Classes Included in the WBS Inventory
Component Classes
Indirect Capital Components (see Appendix D for further
details)
Example Components
Concrete pad
Geotechnical investigations
Standby power generators
The level of component detail (and by implication, design detail) in Exhibit 2-5 indicates that
the WBS-based approach is more sophisticated, and potentially more time consuming, than the
factored or parametric cost estimating methods used in earlier efforts. Nevertheless, the
Technology Design Panel considered it the right approach to developing unit costs for policy
analysis. Furthermore, EPA believes that developing unit cost models that are more
comprehensive, flexible and transparent will facilitate the policy analysis process by addressing a
frequent topic of dispute over regulatory cost estimates. Finally, the WBS-based models are
driven by technical scope and selection of suitable equipment and material to achieve a defined
treatment objective. This approach is superior to cost estimating methods that are not defined by
a desired treatment level or that cannot be changed easily to reflect raw water quality.
2.3 Model Use
This section provides basic guidance on operating the WBS technology models. As discussed
above, each model is an Excel workbook comprising a series of spreadsheets. In general, users
need only be concerned with the input sheet and output sheet, although advanced users might
also wish to examine the critical design assumptions spreadsheets.
2.3.1 Input Sheet Structure and Use
The input sheet in each of the technology models is similar to that pictured in Exhibit 2-2. A
step-by-step input process allows the user to quickly generate costs for standard designs built
into the model, modify those designs or construct an alternative design.
Overview of the Input Process
Many models require basic information from the user before choosing an appropriate standard
design. For example, contaminant selection is the first choice that must be made in several of the
models. Such choices are made using a drop-down list at the top of the input sheet.
After making any basic, top-level choices, the user can click on one of the eight standard design
buttons. Each button corresponds to a system size category in the flow characterization paradigm
described below in Exhibit 2-6. The model will populate all inputs with values appropriate for
the selected design, then compute all costs. The direct capital cost, total capital cost and annual
O&M cost are displayed on the input sheet; details are available on the output sheet (see Section
2.3.4). More information on the standard designs is provided below.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
Exhibit 2-6. Standard Flow Rate Categories Used in WBS Standard Designs
Size Category
1
2
3
4
5
6
7
8
Population Served
25 to 100
101 to 500
501 to 1,000
1,001 to 3,300
3,301 to 10,000
10,001 to 50,000
50,001 to 100,000
Greater than 100,000
Design Flow (MGD)
0.030
0.124
0.305
0.740
2.152
7.365
22.614
75.072
Average Flow (MGD)
0.007
0.035
0.094
0.251
0.819
3.200
11.087
37.536
The user can modify the standard designs by entering values in the gold and blue input cells,
under the "Manual Inputs" heading on the input sheet. (Alternately, the user can click the button
marked "CLEAR FOR MANUAL ENTRY" and enter all of the input values by hand.) In any
case, the manual inputs section contains several types of cells:
• Required user inputs, highlighted in gold
• Optional user inputs, highlighted in blue
• Greyed-out inputs, which are not required for a given design
• Information and guidance, with text in green.
Some inputs, such as system flows, must contain a numeric value. Others have a drop-down
arrow that appears when the cursor is positioned in the input cell. These cells must contain one of
the drop-down values. Required inputs must be populated; optional inputs can be left blank to
accept model defaults or changed by the user to examine the effect of different assumptions. The
Autosize button, described below, is available in some models to facilitate design.
The input sheet in each model verifies user inputs against certain design constraints that reflect
GREPs. If user inputs result in designs that violate these constraints, a warning message appears
on the input sheet, explaining which input value needs to be corrected. In addition, the message
"Input Incomplete—Check for Error Messages Below" appears at the top of the input sheet.
Once all inputs are complete and the model has verified that they meet design constraints, the
message at the top of the input sheet changes to "Input Complete—Press 'Generate Results'."
The user must click the "Generate Results" button to tell the model to generate costs. Once the
user has clicked the button, the message at the top of the model changes to "Input Complete—
Results Ready," and total costs are displayed on the input sheet. The output sheet provides more
details for the total costs.
Standard Designs
The input sheet in each of the technology models contains up to eight buttons, which correspond
to the eight standard flow sizes in the flow characterization paradigm for public water systems
(see Exhibit 2-6). These buttons populate all of the input fields with appropriate values for the
selected design flow. The values in each standard design meet all relevant design constraints.
Each model includes a separate sheet, entitled "standard inputs," that documents the specific
input values included in each standard design. Advanced users can adjust the standard designs by
changing the values on the standard input sheet. For example, a user could change all the
11
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WBS-Based Cost Models for Drinking Water Treatment Technologies
standard designs to use high cost components, rather than the default of low cost components
(see Section 2.3.2 under "Component Level"), by changing values in the appropriate column on
the standard input sheet. The standard input sheet highlights values that have been changed by
the user and includes a button ("Reset to Defaults") that resets the standard designs back to their
original settings. Users that make significant adjustments to the standard designs should take care
to verify that their new designs still meet design constraints by checking for warning messages
on the input sheet after each new design is run.
The Autosize Routine
The models also can be used to estimate costs for systems with design flows other than the eight
standard sizes. To aid in developing designs for other flows, some models include a button
labeled "Autosize." This button activates a computer-aided design routine that attempts to find a
design meeting all relevant design constraints for a given design and average flow. For example,
the user could change design flow to 3 million gallons per day (MGD) and average flow to 1
MGD, then click the autosize button. This would populate some input fields with values that are
both appropriate for a 3 MGD system and that meet all design constraints. More information on
the autosize routines, including details on which inputs are and are not populated, is available in
the technology-specific chapters of this document.
In the rare case that the autosize routine cannot find a design meeting all constraints, it will
display a pop-up warning message. This does not mean that it is impossible to design a system
for the selected size. The user might still be able to develop a design by manually adjusting the
input values, paying careful attention to the warning messages on the input sheet. It might be
necessary to relax some of the design constraints by adjusting values on the critical design
assumptions sheet.
Manual Input and "Generate Results"
All of the models allow the user to enter input values by typing them directly into the appropriate
fields on the input sheet. Users can develop complete designs from scratch, populating all the
input fields manually. Users also can adjust designs generated by the standard design or autosize
buttons, by adjusting one or more input fields manually after clicking one of these buttons. In
either case, after completing the manual changes, users should do two things:
• Verify that no warning messages appear to ensure that the design meets all relevant
constraints
• Click the button labeled "Generate Results."
The second step is necessary to tell the models that the design process is complete and to select
the appropriate items of equipment for inclusion in total costs on the output sheet. This step is
particularly important if the system automation or component level inputs are adjusted manually,
because these inputs have a significant impact on the selection of equipment. To ensure correct
calculation of costs, however, users should click the "Generate Results" button after completing
manual changes to any of the inputs. It is not necessary to click this button when the input sheet
message reads "Input Complete—Results Ready." This message will appear, for example, when
the standard designs or autosize routine are used without subsequent manual changes to input
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WBS-Based Cost Models for Drinking Water Treatment Technologies
values. The standard design buttons and the autosize button automatically incorporate the
"Generate Results" step, telling the models to select the appropriate items of equipment.
2.3.2 Common Inputs
The user inputs in each model are largely technology-specific and are described in detail in the
technology chapters of this document. There are certain inputs, however, that are common to all
of the technology models. These common inputs are described below.
Design and Average Flow
Each model needs the design and average flow to determine the size and number of treatment
components needed. Design flow is the peak instantaneous flow of product water from a
treatment system, while average flow is the annual average flow, taking into account daily and
seasonal variations in demand.
Design flow can be entered in MGD or in gallons per minute (gpm). In either case, the design
flow is meant to represent a maximum instantaneous flow. Average flow can be entered in
MGD, in gpm or as a percentage of design flow.
The standard design functions included in each model (see above) can populate design and
average flow with values based on the flow characterization paradigm for public water systems.
The flow paradigm includes eight model size categories, as shown in Exhibit 2-6. These size
categories represent populations ranging from 25 persons to greater than 100,000 persons. Based
on the values in Exhibit 2-6, the ratio of average flow to design flow ranges from 25 percent for
very small systems to 50 percent for large systems.
Component Level
Each model includes an optional input that determines whether the cost estimate generated is a
low, medium or high cost estimate. This input, labeled "component level" or "cost level," drives
the selection of materials for items of equipment that can be constructed of different materials.
For example, a low cost system might include fiberglass pressure vessels and PVC piping. A
high cost system might include stainless steel pressure vessels and stainless steel piping. The
component level input also drives other model assumptions that can affect the total cost of the
system, including assumptions about system automation (see "System Automation" below),
building quality and heating and cooling (see Appendix B).2 If the component level input is left
blank, the models will generate a low cost estimate. The user can change this input to select a
medium or high cost estimate.
System Automation
As described in Appendix A, control of drinking water treatment systems can be manual,
automated or semi-automated. The method of control can have a significant impact on both
capital and O&M costs. Each model includes an optional input that allows the user to select from
among the three control options. If the system automation input is left blank, the control option
selected is determined by the system size and the component level input selected (see above),
In some cases (e.g., the membrane models, which are under development), this input also determines the source
water quality that the model treats. In these models the input is called the "cost level."
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WBS-Based Cost Models for Drinking Water Treatment Technologies
using the logic shown in Exhibit 2-7. The user can change the system control input to force the
design of a system with manual, automated or semi-automated control.
Exhibit 2-7. Default Assumptions for System Control
Component Cost Level Selected
Low
Medium
High
System Size (Design Flow)
Less than 1 MGD
Manual
Manual*
Automated
1 MGD or greater
Manual
Automated
Automated
* Automated for multi-stage bubble aeration and several other forthcoming technology models (e.g., anion exchange, cation
exchange and ultraviolet disinfection).
2.3.3 Input Sheet Examples
Several examples are presented here to clarify the use of the WBS model input sheet. The
examples refer to particular technology models. Detailed information about the inputs for these
models can be found in the appropriate technology-specific chapters.
Standard Design
The simplest way to generate a design is by use of the standard design buttons. Suppose that a
user wishes to estimate costs for a system designed to treat trichloroethylene (TCE) using
granular activated carbon (GAC), serving a population of approximately 8,000 people. The
following are step-by-step instructions for using the adsorptive media model to generate such a
cost estimate:
1. Open the Excel workbook named "WBS GAC.xlsm."3 Depending on your settings and
version of Excel, a message might appear regarding "active content" in the workbook.
For the models to function properly, macros must be enabled. Take the appropriate steps
to enable macros (for example, clicking "Options" and selecting "Enable this content,"
depending on your version of Excel).
2. Navigate to the input sheet by clicking on the tab labeled "INPUT" at the bottom of the
Excel window. (It is also possible to page through the sheets by pressing Ctrl-Page Up
and Ctrl-Page Down.) Scroll to the top of the input sheet.
3. The GAC model requires that the user first choose the contaminant. Select "TCE" from
the "Select Contaminant" dropdown list.
4. The GAC model also requires that the user choose between pressure and gravity designs
(see the appropriate technology chapter for discussion of the difference between design
types). Select "Pressure" from the "Select Design Type" dropdown list.
5. The user wishes to use a standard design appropriate for a population of 8,000 people.
Exhibit 2-6 indicates that size category 5, with a design flow of 2.152 MGD, is
appropriate for such a system. Therefore, click on the design button labeled "2.152 MGD
3 Note that your model file name might vary. It likely will include a date following the model title (e.g., "WBS GAC
O42514.xlsm" for April 25, 2014).
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WBS-Based Cost Models for Drinking Water Treatment Technologies
standard design." After a few seconds, the model will display the message "Using this
design" next to the design button and "Input Complete—Results Ready" underneath the
buttons. It displays the direct capital cost, total capital cost and annual O&M cost on the
input sheet.
6. If desired, scroll down on the input sheet to see what inputs are used for the standard
design. For instance, the 2.152 MOD standard design for GAC treating TCE with a
pressure design uses a design flow of 2.152 MOD and an average flow of 0.819 MOD. It
assumes a carbon life of 66,600 bed volumes and a total theoretical empty bed contact
time (EBCT) of 7.5 minutes.
Modified Standard Design
Suppose that the user wishes to design a GAC system treating TCE for a population of 1,000,
using source water that entails a different carbon life and EBCT than that assumed in the
standard designs (e.g., because the source water contains a higher initial concentration of TCE).
The user determines that the source water characteristics entail a carbon life of 40,000 bed
volumes and an EBCT of 10 minutes. The following are step-by-step instructions for using the
GAC model to generate such a cost estimate:
1. Open the Excel workbook named "WBS GAC.xlsm"4 and take the appropriate steps to
enable macros (see Step 1 described in the "Standard Design" section above). Navigate to
the input sheet, scroll to the top of that sheet and select "TCE" and "Pressure" from the
appropriate dropdowns (see Steps 2, 3 and 4 described in the "Standard Design" section
above).
2. The user wishes to design a system for a population of 1,000 people. Exhibit 2-6
indicates that size category 3, with design flow 0.305 MGD, is appropriate for this
population, so start by clicking the "0.305 MGD standard design" button.
3. The user wishes to design a system with a carbon life of 40,000 bed volumes. Scrolling
down the input sheet, note that the standard design uses an input carbon life of 66,600
bed volumes. Type the number 40,000 in the gold input cell to change the carbon. Note
that the green informational text below the input cell changes to show the number of
months between regenerations. Note also that the message above the manual inputs
changes to "Input Complete—Press 'Generate Results'" to indicate that costs have not
been updated for your new input.
4. The user wishes to design a system with an EBCT of 10 minutes. Scroll down to the cell
labeled "Theoretical Empty Bed Contact Time" and enter the number 10.
5. Changing the EBCT will change the optimal vessel geometry. To quickly estimate costs
for this new EBCT, click the "Autosize" button next to the inputs for vessel geometry.
The input values will flicker briefly while the model tries several different values and
then settles on a new value. Because the Autosize button was clicked, it is not necessary
4 Again, your model file name might vary. It likely will include a date following the model title (e.g., "WBS GAC
O42514.xlsm" for April 25, 2014).
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WBS-Based Cost Models for Drinking Water Treatment Technologies
to click the "Generate Results" button; the message above the manual inputs reads "Input
Complete—Results Ready," and the total costs are displayed on the input sheet.
Suppose that the user also wishes to estimate a high-end cost for this system. In this case, take
the following additional steps:
6. Scroll down and place the cursor in the input cell labeled "Component Level." A
dropdown arrow appears to the right of the cell. Click on the arrow and choose "high
cost."
7. Scroll back to the top of the sheet. Note that the sheet indicates that the user must click
"Generate Results." Click that button. The model displays costs for the high-end system.
To see what components are included, switch to the Output sheet and examine the details.
2.3.4 Output Sheet Structure and Use
The output sheet in each of the technology models is similar to that pictured in Exhibit 2-3. In
addition to the details described in Section 2.1, the output sheet includes several important totals:
• Process cost, which is the sum of the installed capital cost of all equipment required for
the treatment process
• Building cost, which is the sum of the installed capital cost of all buildings and the
concrete pad
• Direct capital cost, which is the sum of the process and building costs
• Total capital cost, which is the total of the direct capital cost, the indirect capital costs and
add-on costs (see Sections 2.4.3 and 2.4.4)
• Annual O&M cost (see Section 2.4.5)
• Total annualized cost (see Section 2.4.6).
The capital equipment section of the output sheet includes a column labeled "Use?" This column
tells the model which line items to include in the direct capital cost. Specifically, items with a
value of 1 in the "Use?" column are included in the total; items with a value of 0 or a blank are
not included in the total. Advanced users can manually adjust this column to include or exclude
certain items of equipment. For example, a user could examine process costs without booster
pumps by changing the "Use?" value to 0 for those pumps. The "Generate Results" button,
which is present on both the input and output sheets, will reset the "Use?" values back to pre-
programmed default values, as driven by system size and input values.
The output sheet also includes a button labeled "Record Output in a New Workbook." This
button generates a complete copy of the output sheet that will not change. Using this button
allows users to record the detailed design output for comparison purposes. For example, a user
could record the output from the standard design for 0.03 MGD, then select the 0.124 MGD
standard design and compare the output results for the two designs.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
2.3.5 Critical Design Assumptions Sheet Structure and Use
Each of the technology models includes at least three critical design assumptions sheets:
• One for process and building design assumptions
• One for assumptions used in calculating annual O&M costs
• One for assumptions used in calculating certain indirect capital costs
Some models include additional critical design assumptions sheets (e.g., in the aeration models,
for assumptions associated with off-gas treatment).
These sheets contain design constraints and structural and chemical engineering assumptions
based on GREPs. Users can review these sheets for details on significant assumptions used in the
models. Advanced users might want to modify certain assumptions, particularly if adapting a
model for use with a source water quality different than assumed in the standard designs or to
reflect site-specific conditions. Most of the assumptions include a comment column explaining
the use of the assumption and/or providing guidance on appropriate values.
Most of the significant design assumptions are technology-specific and discussed in detail in the
technology chapters of this report. However, there are certain assumptions that are common to
many of the models. Exhibit 2-8 summarizes the general design assumptions that are common
across most of the models. As Exhibit 2-8 indicates, these assumptions are based on a
combination of sources, including standard design handbooks, engineering textbooks and
comments of external reviewers. Note that some of the general design assumptions (and some
technology-specific assumptions, as discussed in the relevant technology chapters) differ for
small versus large systems. In general, these differences are because small systems can often be
built as packaged, pre-engineered or skid-mounted systems. In most cases, the different design
and cost assumptions for small systems are based on comparison of model outputs with as-built
designs and costs for actual small treatment systems.
The user can change some of the assumptions shown in Exhibit 2-8 by editing the critical design
assumptions sheet; others would require changes to the WBS cost database used by all the
models. The final column of Exhibit 2-8 provides guidance on how to change each assumption.
For example, the design of pumps for any treatment system is based on the peak flow
requirements of the system, including a safety factor. As specified in Exhibit 2-8, the critical
design assumptions sheet assumes a safety factor of 25 percent. A user could change this factor
based on an actual pump performance curve.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
Exhibit 2-8. General Design Assumptions Used in the WBS-based Models
Element
Influent pumps
All pumps
Access space for pumps
Pipe size
Process pipe size
Tank and pressure vessel
capacity
Pressure vessel diameter
Storage tank diameter
Access space for tanks and
pressure vessels
Process vessels and basins, all
pumps and chemical feed
systems
Chemical storage
Concrete pad under heavy
equipment
Office space
Assumption
Include flooded suction
Design flow incorporates a safety factor of
25 percent
Provide a minimum of 4 feet of service
space around three sides of each unit,
assuming the fourth side can share access
space with relevant tanks or vessels
Based on a maximum of 3 feet of head
loss per 100 feet of pipe
Based on maximum flow to each unit (not
total system flow)
Based on design capacity, freeboard and
standard manufactured sizes
Based on user input, within limits specified
on a technology-specific basis
Assumes a cylindrical design, with
diameter equal to one half of the height
Provide service space around each unit
equal to its diameter (half its diameter for
small systems), to a maximum of 6 feet
Multiple units required to protect from
single point failure
Storage requirement based on 30-day
delivery frequency
1 foot thick for large systems, 6 inches
thick for small systems
100 square feet per employee for large
systems (excluded for small systems)
Can be changed by:
Replacing unit costs or cost coefficients
extracted from the WBS cost database
Editing the critical design assumptions
sheet of each technology
Editing the critical design assumptions
sheet of each technology
Editing the engineering lookup table
extracted from the WBS cost database
Cannot be changed
Cannot be changed
Changing user inputs (for diameter) and
editing the critical design assumptions
sheet of each technology (for constraints)
Cannot be changed
Editing the critical design assumptions
sheet of each technology (only maximum
can be changed)
Editing the critical design assumptions or
input sheet of each technology (depending
on the specific item)
Editing the critical design assumptions
sheet of each technology
Editing the critical design assumptions
sheet of each technology
Editing the critical design assumptions
sheet of each technology
Sources: U.S. EPA (1997); AWWA (1990); AWWA/ASCE (1998); Viessman and Hammer (1993); GREPs; and information
from manufacturers and technology experts who reviewed model critical design assumptions.
Cost Estimation Method
Equipment unit costs can be derived in one of two ways. The first (and recommended) method
uses component-specific cost equations developed from unit costs collected from equipment
vendors. The component cost equations are best-fit equations (developed using statistical
regression analysis across the sizes available for each item) that estimate the unit cost of an item
of equipment as a function of its size. Under the cost equation option, the models will generate
unit costs for each item of equipment by applying the appropriate cost equation to the exact size
determined by the design calculations.
The second method uses unit cost lookup tables extracted from the WBS cost database. These
lookup tables are based on quotes from equipment manufacturers for discrete equipment sizes.
To maintain vendor confidentiality, the tables do not identify the individual vendors associated
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WBS-Based Cost Models for Drinking Water Treatment Technologies
with the quotes and the unit costs typically are averages across multiple vendors. Under the
lookup table option, for each item of equipment, the models will search the appropriate lookup
table to locate a unit cost that best meets the design requirements for the component. In general,
this means that the models will select the discrete equipment size for each item of equipment that
is equal to or greater than the size determined by design calculations.
By default, the assumption is set to 1, to use the component-specific cost equations. The user can
set the assumption to a blank value to select the lookup table method. EPA believes the cost
equations method is most appropriate for generating national cost estimates and for most user-
specified designs. Using the equations, instead of the price quotes, allows the models to generate
unit costs for equipment of the exact size determined by the design calculations. For example, a
WBS model design might require a 250 gallon steel tank, but the available price quotes might be
limited to 100 gallon, 500 gallon and various larger sizes. The cost equation for steel tanks will
allow the WBS model to generate a unit cost for the intermediate sized 250 gallon tank. The
lookup table method would use the cost for the 500 gallon tank. The models retain the lookup
table method for users who wish to examine the specific cost data points on which the
component-specific cost equations are based.
2.3.6 Index Sheet Structure and Use
Each technology model includes an index of all inputs and critical design assumptions, including
hyperlinks to their locations. Exhibit 2-9 shows an example of the index sheet. The sheet
provides an alphabetized list of all inputs and assumptions. Due to the great number of inputs
and assumptions in the WBS models, the Find feature in Excel can be useful in locating a
specific input or assumption.
Next to the description of each input or assumption is a blue, underlined hyperlink. It shows the
internal name of the input or assumption used in the engineering formulas throughout the WBS
model. Clicking on the hyperlink takes the user to the cell where the assumption can be viewed
or adjusted.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
Exhibit 2-9. Sample of Index Spreadsheet
I INDEX
This page provides an index to all user-adjustable inputs and assumptions, Ciick on a variable name to go directly to the adjustable cells.
User-adjustable Input or Assumption
Access space per pump/blower for custom designed systems
Access space per pump/blower for pre-engineered packages
Additional blower head above water depth
Additional building after...
Administrative LOE as a percent of average technical labor
Air conditioning HER
Air to water ratio
Always include NEPA compliance costs?
Annual cooling degree days
Annual heating degree days
Average F!ow
Basin excavation depth above which deeper boreholes are needed
Bedding depth below pipe
Bedding depth surrounding the pipe
Blower efficiency
Blower safety factor
Borehole depth (package systems}
Borehole depth for deep basins
Borehole depth for shallow basins
Borehole needed every x square feet
Boreholes per job
Buffer space around other sides of buildings
Builder's risk insurance percentage
Building height
Coefficient of passive pressure
Communications hardware
Component level
Computer workstations perx operators
Concrete pad thickness
Concrete pad thickness for small systems
Concrete thickness
Contaminant-Specific Off-gas Assumptions
Cooling table for buildings 500 square feet or greater
Cooling table for buildings less than 500 ft2
Cooling ventilation/infiltration load
Cost for parts & maintenance for pumps and blowers
Density of air
Design Flow
Design safety factor for standby power
Design Type
Diffuser access space
Drive controllers per blower
Drive controllers per booster pump
Drive controllers per catalytic oxidizer
Drive controllers per thermal oxidizer
Efficiency of pumps
Electric resistance heating efficiency
Electrical percentage
Engineering percentage for large systems
Engineering percentage for medium systems
Engineering percentage for small systems
Ethernet modules
Excess air required
Excess air required
External air piping
Financing percentage
Variable Name and Link
space_pum ps_c u st
space pumps ore
add_biow_head
add_2nd_building
Cieric3l_oercent
EER
air_water_ratio
include NEPA
copJ^DD
heat_DD
averag.e_flQw_i
deep_bore_need
faedding_depth
bl owe rs af ety_fa ct o r
bore_depth_min
hole_j>erjpb
non_fire_buffef
br_ins_pct
Bui Idingji eight
Coeff_Kp
comm_hardware
componentjevelj
wgrkst3tign_ratio
pad_thick
pad_thick_srnall
concjhic^k
contaminantJoQkup
coolirig_table
c,oo.ii,nQ ta,bj,,i sbld..
purnp^maintj'ate
PA
std_safety_factor
design JypeJ
diffuseF_access__spsce
S_blower
S_booster_pump
S_CO
S TO
elect_pct
eng_pctjarg6
eng_pct_medium
engpctsmail
2.4 General Cost Assumptions
An important feature of the WBS models is that they build up cost estimates from component-
level data. Each model shows the user the cost build-up, which makes the cost estimates more
transparent, giving the user an opportunity to evaluate the impact of design and unit cost
assumptions on treatment costs. There are several types of costs that need to be aggregated into a
total cost estimate: equipment costs, building cost, residuals discharge cost, indirect capital costs,
add-on costs and annual O&M costs. The sections below describe how each type of cost enters
the WBS models.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
The build-up process for equipment costs is straightforward. The design sheets in the model
generate the required dimensions and quantities for each item in the WBS list of equipment
components and materials. Then, the model obtains unit costs to match the component size and
material (e.g., a 10-inch diameter PVC pipe or a 4,000-gallon steel backwash tank). The model
multiplies unit costs by the quantity estimate (e.g., 30 feet of pipe or 2 tanks) to obtain total
component costs. Direct capital cost equals the sum of these costs across the selected
components, including costs for treatment equipment and buildings.
The models enable equipment unit costs to be derived in one of two ways (using lookup tables or
cost equations, as described in Section 2.3.5 under "Cost Estimation Method"). Regardless of the
method used, the estimates are intended to provide enough information to establish a budgetary
or preliminary cost estimate. EPA's goal is for the resulting costs to be within +30 percent to -15
percent of actual cost.
Consistent with this goal, WBS models contain several cost-related assumptions that allow the
models to produce costs for some components without having detailed site-specific information
(e.g., pipe fitting sizes). Exhibit 2-10 summarizes these assumptions.
Exhibit 2-10. General Equipment Cost Assumptions
1. Costs are preliminary estimates based on major components as shown on piping and instrumentation diagrams or typical
layout drawings. Costs include consideration of package plants where relevant (see model-specific chapters for more
details).
2. All equipment costs include costs of transportation and installation.
3. All equipment costs are based on cost quotes from manufacturers or RSMeans database.
4. Long-term storage of chemicals (greater than 30 days) is not taken into account unless specifically mentioned.
5. Cost of waste disposal (residuals) is accounted for using the methods outlined in Section 2.4.2 and Appendix C.
6. Building layout is for the process itself, with room for operation, maintenance and replacing equipment, if needed.
7. Building costs are estimated using unit costs per square foot (see Section 2.4.1 and Appendix B for more details).
8. Costs for a reinforced-concrete pad floor to handle equipment loads are added to building costs. Costs associated with
special unit or site-specific foundation requirements are not included and should be evaluated on a case-by-case basis.
9. To account for the cost of fittings, pipe lengths are determined by applying a multiplier to the overall system building layout
length. The resulting lengths are considered conservative (i.e., erring on the high side), so that the resulting cost covers the
installed cost of the pipe and fittings. The specific multipliers are as follows:
Combined influent and effluent pipe length is 2 times the length of the overall system building layout length.
Process pipe length is 2 times the length of the overall system building layout length.
Backwash pipe length is 2.5 times the overall system layout length.
Chemical piping length is 1 times the overall system layout length.
2.4.1 Building Costs
The WBS model building costs use three sources: RSMeans 2009 Square Foot Costs (RSMeans,
2008), Saylor 2009 Commercial Square Foot Building Costs (Saylor, 2009) and the Craftsman
2009 National Building Cost Estimator software model (described in Craftsman, 2008).
Appendix B provides a detailed description of these sources and the approach to developing
building costs. It also provides the unit costs included in the WBS cost database.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
In each WBS technology model, there are four possible design configurations for buildings: three
construction design and quality categories (low, medium and high) and small, very low cost,
prefabricated ("shed-type"). The WBS models select from among these configurations based on
system size, structure size and user input for component level (see Section 2.3.2), as shown in
Appendix B. Unit costs (in dollars per square foot) for each configuration vary by structure size.
When appropriate, the WBS models add costs for building heating and cooling systems as line
items separate from the base building costs. Whether the WBS models include these systems also
depends on system size, structure type and user input for component level, as shown in Appendix
B.
The indirect assumptions sheet in each model includes a flag that determines whether to include
building costs in the total capital cost. Users can include or exclude building costs by setting this
flag to one or zero, respectively. Users can also change the assumptions about the inclusion of
heating and cooling systems on the indirect assumptions sheet.
2.4.2 Residuals Management Costs
Many of the treatment technologies covered by the WBS-based models generate liquid, semi-
solid (sludge) and/or solid residuals. For these technologies, the models each include a sheet that
estimates the cost of various options for managing these residuals. The residuals management
options available for a given technology vary depending on the types of residuals generated, their
quantity, the frequency of generation (e.g., intermittent versus continuous) and their
characteristics. Examples of residuals management options include (but are not limited to): direct
discharge to surface water, discharge to a publicly owned treatment works, land disposal of
solids and storage and/or treatment of sludge or liquid waste prior to disposal or discharge. The
individual technology chapters of this document describe the specific residuals management
options available for each technology. Appendix C provides detailed information about the data
and assumptions used to estimate costs for the various residuals handling and disposal options.
2.4.3 Indirect Capital Costs
Indirect capital costs are costs that are not directly related to the treatment technology used or the
amount or quality of the treated water produced, but are associated with the construction and
installation of a treatment process and appurtenant water intake structures. Indirect costs can be
considerable and must be added to cost estimates if they are not included as a line item
component or a factor in the major (cost driver) elements of a technology. They include indirect
material costs (such as yard piping and wiring), indirect labor costs (such as process engineering)
and indirect burden expenses (such as administrative costs).
The WBS models compute the costs of site work, geotechnical investigation, yard piping and
standby power based on the system requirements, as determined during the direct capital cost
buildup. Other indirect costs are computed as a percentage of the installed process cost, building
cost or direct capital cost estimate. The indirect assumptions sheet in each WBS model (see
Section 2.3.5) contains guidance regarding a typical range of percentages for each item and
indicates the base cost to which the percentage will be applied. The guidance also describes
conditions that might require an assumption outside the range of typical values. Finally, guidance
on the output sheet notes that items such as installation costs and contractor overhead and profits
are already included in the direct capital cost estimate, but entries can be made to increase these
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WBS-Based Cost Models for Drinking Water Treatment Technologies
cost items should circumstances merit higher costs. Any of these costs can also be excluded by
modifying assumptions on the indirect assumptions sheet. Costs that are computed as a
percentage can be excluded simply by setting the percentage to zero. Those that are computed
based on system requirements can be included or excluded by setting the appropriate flag to one
or zero on the indirect assumptions sheet.
The WBS models report the total capital cost directly below this section of the output sheet so
the user can determine the impact of altering the indirect cost assumptions on total capital costs.
Appendix D provides descriptions of the default assumptions for the following indirect costs:
• Mobilization and demobilization
• Architectural fees for treatment building
• Equipment transportation, installation and contractor overhead and profit
• Construction management and general contractor overhead
• Process engineering
• Site work
• Yard piping
• Geotechnical
• Standby power
• Yard wiring
• Instrumentation and control
• Contingency
• Financing during construction
• Legal, fiscal and administrative
• Sales tax
• City index
• Miscellaneous allowance.
2.4.4 Add-on Costs
Add-on costs are costs that may be attributed to one or more aspects of the treatment technology.
These add-on costs include permit costs (e.g., for construction and discharge permits), pilot and
bench testing costs and land use costs. Users can include or exclude these costs by setting
appropriate flags on the indirect assumptions sheet (see Section 2.3.5).
Permits
Systems installing new treatment technologies to comply with revised drinking water standards
will often need to build a new structure to house the new treatment train and might need to build
auxiliary structures to store chemicals (e.g., chlorine, which must be stored in a separate
building). In all jurisdictions, such construction activities require a building permit and
inspections to ensure that the structure meets local building codes. New treatment trains can also
create a new waste stream or supplement an existing one. New waste streams such as new point
source discharges to surface water generally require a state or federal permit; additions to
existing flows often require revisions to existing permits. The WBS models include costs for the
following permits:
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WBS-Based Cost Models for Drinking Water Treatment Technologies
• Building permits
• Permits under the National Pollutant Discharge Elimination System (when residuals
discharge to surface water is present)
• Storm water permits (for systems requiring one acre of land or greater)
• Risk management plans (when certain chemicals are present in large quantities)
• Compliance with the National Environmental Protection Act (included by default only at
the high cost component level - see Section 2.3.2).
Pilot Study
Site-specific pilot tests are often required by regulatory agencies to better define design
conditions and to ensure that the proposed technology will protect public health. In addition,
pilot tests and bench-scale tests can be run for non-regulatory reasons, e.g., to determine
appropriate loading and chemical feed rates, waste handling requirements or other process
parameters. Options for pre-design and pre-construction testing can include full- or small-scale
pilot studies, bench tests and desktop feasibility studies. Costs for pilot testing vary accordingly.
Pilot studies range from inexpensive small-scale efforts to full-scale tests that might be
warranted by site-specific conditions. Three variables affecting the costs of a pilot study are:
technology requirements, testing protocols and state requirements. Some states determine test
requirements on a case-by-case basis, particularly where drinking water standards or regulations
such as noise, air emissions, plume abatement or surface water discharges (e.g., the National
Pollutant Discharge Elimination System) are relatively stringent. The diversity of state
requirements, along with the many options for pre-design testing, means that requirements for
pilot- or bench-scale studies are difficult to define. Nevertheless, the WBS models include
default pilot study costs based on vendor quotes and estimated analysis costs. The user can alter
these costs by adjusting the permit cost data extracted from the central WBS cost database if site-
specific conditions warrant.
Land Cost
Regardless of whether a system needs to purchase additional land on which to build the new
treatment train, there is an opportunity cost associated with using land for water treatment rather
than an alternative use. The WBS models capture this cost in a land cost estimate that is based on
the calculated land requirement (in acres) and a unit cost per acre. Each model estimates land
required for additional structures (buildings and external equipment), plus a 40-foot buffer on
one side for emergency vehicle access and 10 feet on the other three sides as a buffer between
buildings or as a minimum open space. The user can change the assumptions about buffer
spacing using the critical design assumptions sheet for each technology.
The WBS models incorporate land costs based on unit land costs that vary by system size and
land requirements that vary by technology and system size. Average land costs per acre are
estimated as probability-weighted averages using data from the Safe Drinking Water Information
System on system size and location, data for rural land costs for 50 states and data on urban land
costs for approximately 125 cities and metropolitan areas.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
2.4.5 Annual O&M Costs
The O&M costs in each WBS model include annual expenses for:
• Labor to operate and maintain the new treatment equipment and buildings
• Chemicals and other expendable items (e.g., replacement media) required by the
treatment technology
• Materials needed to carry out maintenance on equipment and buildings
• Energy to operate all equipment and provide building heating, cooling, lighting and
ventilation
• Residuals discharge fees.
The individual technology chapters of this document describe additional, technology-specific
O&M costs.
O&M costs calculated in the models do not include annual costs for commercial liability
insurance, inspection fees, domestic waste disposal, property insurance and other miscellaneous
expenditures that are not directly related to the operation of the technology. These costs are
highly site-specific. Users wishing to include them should add the appropriate site-specific
estimates to the model results.
The WBS models calculate annual O&M costs based on the inputs provided by the user in the
input and O&M assumptions sheet. These inputs include system size, raw and finished water
quality parameters and other factors that affect operation requirements. Appendix E contains the
design assumptions used to develop default costs for the O&M sheet.
2.4.6 Total Annualized Cost
The output sheet in each model includes an estimated useful life, in years, for each WBS
component. The models take these component useful lives from the WBS cost database. The
useful lives vary by component type (e.g., buildings generally last longer than mechanical
equipment) and by material (e.g., steel tanks generally last longer than plastic tanks). The models
use the component useful lives to calculate an average useful life for the entire system. The
calculation uses a reciprocal weighted average approach, which is based on the relationship
between a component's cost (C), its useful life (L) and its annual depreciation rate (A) under a
straight-line depreciation method. The formula below shows the reciprocal weighted average
calculation:
n s^
Average Useful Life = -^ = —
x-i > A
n=l
where:
Cn denotes the cost of component n, n=l to N
C denotes total cost of all N components
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WBS-Based Cost Models for Drinking Water Treatment Technologies
An denotes the annual depreciation for component n, which equals Cn/Ln
A denotes total annual depreciation for the N components.
The models use this average useful life for the system, along with a discount rate, to annualize
total capital cost, resulting in capital cost expressed in dollars per year. The models use a default
discount rate of 7 percent, which users can adjust directly on the output sheet. The models add
annual O&M cost to the annualized capital cost to arrive at a total annual cost in dollars per year.
2.4.7 Updating and Adjusting Costs
There are many factors that contribute to the variation in capital and O&M costs for the same
treatment technology. One variable is location, which is captured by the city index indirect cost.
Another is time—over time, the nominal price of materials, labor and land can change due to
inflation. If relative prices do not change overtime (i.e., if innovative materials or production
technologies do not affect production cost relative to the price of other goods), then nominal
component prices can be adjusted using standard cost indices. The WBS cost database
incorporates the following indices to adjust prices to values in a common year:
• The Producer Price Index (PPI) consists of a family of indices that measure the average
trends in prices received by producers for their output (BLS, 2010). Within the PPI is the
family of commodity-based indices. The commodity classification structure of the PPI
organizes products by similarity of end use or material composition. Fifteen major
commodity groupings (at the two-digit level) make up the all-commodities index. Each
major commodity grouping includes (in descending order of aggregation) subgroups
(three-digit level), product classes (four-digit level), subproduct classes (six-digit level)
and individual items (eight-digit level). The WBS cost database assigns components to
the most closely related PPI commodity index. The selected price index for a component
is generally the index with the smallest product space. For example, prices for stainless
steel pressure vessels are escalated using a four-digit level index called BLS 1072 Metal
Tanks.
• Building and construction costs are escalated using either the Engineering News-Record
Construction Cost Index or the Building Cost Index (ENR, 2013).
• Labor costs are escalated using the Employment Cost Index for "not seasonally adjusted,
total compensation, private industry and public utilities" (BLS, 2000; SIC series: 252).
The Bureau of Labor Statistics releases this index quarterly. The WBS cost database
utilizes an annual average.
• The Consumer Price Index is used to adjust land costs and components that have not been
assigned a specific PPI (BLS, 2007).
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WBS-Based Cost Models for Drinking Water Treatment Technologies
2.5 List of Abbreviations and Symbols in this Chapter
EBCT empty bed contact time
EPA U.S. Environmental Protection Agency
GAC granular activated carbon
gpm gallons per minute
GREPs generally recommended engineering practices
MGD million gallons per day
O&M operating and maintenance
P&ID piping and instrumentation drawing
PPI Producer Price Index
TCE trichloroethylene
WBS work breakdown structure
2.6 References
American Water Works Association (AWWA). 1990. Water Quality and Treatment: A
Handbook of Community Water Supplies. Fourth Edition. New York: McGraw Hill.
AWWA/American Society of Civil Engineers (ASCE). 1998. Water Treatment Plant Design.
Third Edition. New York: McGraw-Hill.
Bureau of Labor Statistics (BLS). 2007. BLS Handbook of Methods: The Consumer Price Index.
Updated June 2007. Online at http://www.bls.gov/opub/hom/pdf/homchl7.pdf
BLS. 2010. BLS Handbook of Methods: The Producer Price Index. Last updated 10 July. Online
at http://www.bls.gov/opub/hom/pdf/homch 14.pdf
BLS. 2000. Employment Cost Indices, 1976-1999. September. Online at
http://www.bls.gov/ncs/ect/sp/ecbl0014.pdf
Craftsman Book Company. 2008. 2009 National Building Cost Manual. 33rd Edition. October.
Engineering News-Record (ENR). 2013. Building and Construction Cost Indexes. Online at
http://enr.construction.com/economics/
RSMeans. 2008. 2009 Square Foot Costs. 30th Annual Edition. Kingston, Massachusetts:
RSMeans Company.
Saylor Publications, Inc. 2009. 2009 Commercial Square Foot Building Costs: 19th Annual
Edition.
U.S. Environmental Protection Agency (U.S. EPA). 1997. Discussion Summary: EPA
Technology Design Workshop. Washington, D.C.: U.S. EPA, Office of Groundwater and
Drinking Water.
Viessman, W.J. and M.J. Hammer. 1993. Water Supply and Pollution Control. 5th Edition.
Harper Collins College Publishers, New York, NY.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
3. Granular Activated Carbon Model
Granular activated carbon (GAC) is a porous adsorptive media with extremely high internal
surface area. GACs are manufactured from a variety of raw materials with porous structures,
including bituminous coal, lignite coal, peat, wood, coconut shells and others. Physical and/or
chemical manufacturing processes are applied to these raw materials to create and/or enlarge
pores, resulting in a porous structure with a large surface area per unit mass. GAC use in
drinking water treatment has been steadily increasing since the 1980s (AWWA, 2011).
GAC is useful for the removal of taste and odor compounds, natural organic matter, volatile
organic compounds (VOCs), synthetic organic compounds, disinfection byproduct precursors
and radon. Organic compounds with high molecular weights are readily adsorbable. However,
low molecular weight compounds, such as aliphatics, ketones, acids, aldehydes, colloidal
organics and alcohols, are not readily adsorbed. Treatment capacities for different contaminants
vary depending on the properties of the different GACs, which in turn vary widely depending on
the raw materials and manufacturing processes used.
The work breakdown structure (WBS) model can estimate costs for two types of GAC systems:
• Systems where the GAC bed is contained in pressure vessels in a treatment configuration
similar to that used for other adsorptive media (e.g., activated alumina), referred to herein
as "pressure GAC"
• Systems where the GAC bed is contained in open concrete basins in a treatment
configuration similar to that used in the filtration step of conventional or direct filtration,
referred to herein as "gravity GAC."
The WBS model for GAC includes standard designs for the treatment of a number of different
contaminants, including atrazine, radon and various VOCs. However, the model can be used to
estimate the cost of GAC treatment for the removal of other contaminants as well. Users wishing
to simulate the use of GAC for treatment of other contaminants will need to adjust default inputs
(e.g., bed volumes before breakthrough, bed depth) and critical design assumptions (e.g.,
minimum and maximum loading rates). This chapter includes discussion of inputs and
assumptions that might require adjustment and these values are highlighted in gold in the model.
3.1 Overview of the Treatment Process
The GAC treatment process includes the following components:
• Booster pumps for influent water
• Contactors (either pressure vessels or concrete basins) that contain the GAC bed
• Tanks and pumps for backwashing the contactors
• GAC transfer and storage equipment
• Spent GAC reactivation/regeneration facilities (optional)
• Associated piping, valves and instrumentation.
When water is treated with GAC, it passes through the treatment columns or beds containing
GAC. The contaminants are adsorbed by the GAC until the carbon is no longer able to adsorb
28
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WBS-Based Cost Models for Drinking Water Treatment Technologies
new molecules. At this point, the result is reduced removal of the contaminant. Once the
contaminant concentration in the treated water reaches an unacceptable level, the carbon is
considered "spent" and must be replaced by virgin or reactivated GAC. GAC beds also require
periodic backwash to prevent head loss or biomass accumulation. Backwash should be
minimized so the spent carbon at the top of the column does not mix with the unspent carbon at
the bottom, creating a mixed bed and the possibility of "leakage" of the target contaminant.
The specific design of a GAC treatment facility depends on the type of contactor and the system
configuration used. GAC can have one or more vessels in each treatment train. In the model, a
parallel configuration has one vessel per train and the series configuration has two or more
vessels per train. In drinking water treatment, GAC configuration generally is a downflow fixed
(packed) bed parallel system. The system can have single or multiple adsorbers operated under
pressure (i.e., in a pressure GAC system) or fed by gravity (i.e., in a gravity GAC system).
Pressure contactors are more cost effective for small systems because they can be purchased off
the shelf as prefabricated, packaged units (see below). Pressure GAC systems can be operated at
higher suspended solids concentrations with less frequent backwashing and over a wide range of
flow rates due to the allowable pressure variances. Pressure GAC systems are also enclosed, so
there is no visual observation of the system. A gravity contactor design is better for systems that
do not have large variances in flow, pressure or turbidity (AWWA/ASCE, 1998). They are also
generally used in larger installations because they can be made larger than off-the-shelf pressure
vessels and because common wall design can minimize space requirements. Exhibit 3-1 and
Exhibit 3-2 provide schematic drawings for a pressure GAC facility and a gravity GAC facility,
respectively.
Pressure GAC systems can be either custom-engineered designs or pre-engineered package
plants. Package plants typically include all primary process components mounted on a skid that
is pre-assembled in a factory and transported to the site. A default assumption in the model is
that pressure GAC systems with design flow less than 1 million gallons per day (MGD) use
package plants. Section 3.3 provides a description of cost adjustments for small package systems.
The model does not include package plants for gravity GAC designs, because these designs are
commonly used by larger treatment systems.
As discussed above, the GAC model includes standard designs for a number of contaminants.
The standard designs for atrazine assume treatment of unfiltered surface water. The standard
designs for radon and the various VOCs assume treatment of groundwater. Users wishing to
simulate the cost impact of water quality different from that assumed in the standard designs
should adjust the appropriate inputs (e.g., bed volumes before breakthrough, backwash interval).
See Chapter 2 for further discussion of standard designs in general.
29
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WBS-Based Cost Models for Drinking Water Treatment Technologies
Exhibit 3-1. Typical Schematic Layout for Pressure GAC Treatment
s—**-
—>-!\HX]—(-» j
Influent J^-—"C
Treated Water
INSTRUMENTATION
Q pH Meter © Turbidity Q High/Low
Meier Alarm
©H«dLo» ©Temperature©
-INES
Influent
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IX
Manual
Vatve
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Valv*
Control
Valve
Pressure GAC System
Typical Schematic Layout
Pressure GAC System 11-25-2013.vsd
30
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WBS-Based Cost Models for Drinking Water Treatment Technologies
Exhibit 3-2. Typical Schematic Layout for Gravity GAC Treatment
ex
Optional equipment not shown:
- GAC transfer
- Bypass piping
Water
to Disinfection
INSTRUMENTATION
(™}Temperature
Meter
Flo» Meter wl
Pressure Gauge
Turbi
""tor
idity (T)Hlgh/Low
tor W Alarm
LINES
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0
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S«nsor
tx
4»
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Gravity GAC System
Typical Schematic Layout
Gravity GAC System 11-25-2013.vsd
3.2 Input Sheet
This sheet accepts the user-defined design parameters that determine fundamental process
requirements. The user can indicate system size and select basic equipment characteristics such
as bed depth and vessel geometry. Key design considerations that the user identifies on this sheet
are described in greater detail below and include the following:
• Contaminant (e.g., trichloroethylene, atrazine, radon)
• Design type (pressure or gravity)
• Design and average flow (see Section 2.3)
• Carbon life
• Contaminant removal requirements
• Number of contactors in series (i.e., parallel or series operation) (pressure GAC designs
only)
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WBS-Based Cost Models for Drinking Water Treatment Technologies
• Bed depth and contactor dimensions
• Interval between backwashes, GAC transfer method and residuals management
• Number of booster pumps (optional)
• Number of redundant vessels (optional)
• Backwash pumping (optional)
• Backwash storage (optional)
• System automation (optional, see Section 2.3)
• Cost estimation method (optional, see Section 2.3)
• Add-on (i.e., pre- or post-treatment) (optional)
• Retrofit (i.e., operational modification) (optional).
Contaminant and Design Type
The WBS model for GAC includes two "drop-down" list boxes that allow the user to select
among standard designs for (1) removal of different contaminants (e.g., tricholoroethylene,
atrazine, radon5) and (2) pressure or gravity designs. These boxes are located at the top of the
input sheet, above the standard design buttons. The user should verify that the selections shown
in these boxes are correct before populating the other design input values. The user can change
the contaminant and/or design type modeled by picking different selections from the two lists.
After doing so, the user should then repopulate the input sheet with values appropriate for the
new contaminant and/or design type by clicking one of the standard design buttons or manually
adjusting inputs and clicking the "Generate Results" button (see Section 2.3 for further
discussion of each of these methods).
Carbon Life
When the contaminant concentration in water treated by GAC reaches an unacceptable level, the
carbon is considered "spent" and must be replaced by virgin or reactivated GAC. This
concentration is known as the contaminant breakthrough concentration. The service life of a
GAC bed is the length of time until this breakthrough concentration is reached. Carbon life
varies depending on site-specific conditions and the quality of the carbon. Factors affecting the
adsorption properties of GAC include: type of carbon, surface area, pore size distribution and
surface chemistry. The maximum amount of adsorption possible is proportional to the surface
area of the pores. The size and type of the particles affect the pressure drop through the bed, the
requirements for the backwash rate and the rate at which equilibrium is achieved.
Because of the number of factors affecting carbon life, this parameter is best determined using
pilot studies or Rapid Small Scale Column Tests (RSSCTs). RSSCTs are laboratory tests
designed and operated under hydraulic and influent water conditions that are calibrated to
simulate those in full-scale adsorbers. The simulation considers fluid dynamic parameters such
5 The current model also has an option to use GAC for post-treatment to quench hydrogen peroxide for an ultraviolet
advanced oxidation process (UVAOP). This option should only be used in conjunction with the UVAOP model,
which is under development.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
as flow rate, GAC particle size, Reynolds number and diffusivity among others (Crittenden et al.,
1991).
The input sheet allows the user to select a method for determining carbon life from among three
options:
• Specifying carbon life directly in months
• Specifying carbon life directly in bed volumes
• Calculating carbon life using the Freundlich isotherm method.
The Freundlich isotherm method (described in Exhibit 3-3) relies on theoretical calculations that
predict the adsorptive capacity of GAC for a given contaminant. It does not account for factors
such as fouling, the presence of other organics and carbon losses. Therefore, it may result in high
estimates of bed life. Also, the availability of data for making this theoretical calculation does
not negate nor replace the need for a pilot study. A pilot study must be conducted to test the
efficacy of GAC treatment onsite prior to investing in full-scale GAC treatment units. Therefore,
users should make use of the theoretical method only in the absence of site-specific pilot or
RSSCT data for initial assessment of carbon life and suitability of GAC for treatment. When the
user elects to use the Freundlich isotherm method, the input sheet displays the calculated bed life
for reference.
Exhibit 3-3. Freundlich Isotherm Method for Carbon Life Estimation
Carbon life can be estimated theoretically using a Freundlich isotherm, which is an empirical relationship used to predict the
adsorptive capacity of GAC for a given contaminant at a given treated effluent contaminant concentration. The Freundlich
isotherm is expressed using the following equation:
X/M = KfCe1'"
where:
X = mass of contaminant absorbed
M = mass of GAC
Ce = effluent concentration
Kf and 1/n are the isotherm constants
In a Freundlich isotherm curve, the log x/M is plotted against the log Ce. The isotherm curve can provide a design estimate for
the adsorptive life of the GAC. Each type of GAC has its own isotherm curve and breakpoint characteristics for identical
contaminants. The isotherm can predict the maximum possible carbon capacity and best attainable water quality for a given
water and a particular carbon. Therefore, in theory, the isotherm constants may be used to help predict the service life of the
GAC bed and to aid in the design of a GAC filtration system. However, the equation provides at best, a very rough estimate of
carbon life when applied to columnar operation. Increasing bed depth, empty bed contact time and/or running contactors in a
series operation mode can improve effluent water quality and carbon efficiency.
There are a number of limitations to the Freundlich isotherm model. First, the model is only applicable to batch adsorber
systems where sufficient time is provided to allow the system to reach equilibrium. Therefore, estimates of carbon life using
the Freundlich isotherm constants should be used for continuous treatment processes only when no better estimate is
available. Second, isotherm data are based on bench-scale tests. Traditionally, it has been very difficult to accurately predict
adsorption capacities for full-scale, dynamic, multi-component column applications using bench-scale equilibrium (isotherm)
tests for single components. There are issues in accurately measuring isotherms at drinking water concentrations (1
microgram per liter and below). Third, measuring isotherms assumes that the disappearance of the contaminant is due only to
adsorption. Controls are needed to be sure other mechanisms (volatilization, adsorption on the container surface,
biodegradation) are not responsible for decreases in concentration. Finally, single constituent isotherms have not been
effective in predicting the effect of interaction between multiple constituents.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
Carbon life for atrazine removal calculated using the Freundlich isotherm method is on the order
of a few hundred months. Actual carbon life has proven to be much shorter in pilot- and full-
scale implementation. Therefore, the model standard designs assume a carbon life of 12 months
for atrazine removal to be conservative and account for the factors noted above. Standard designs
for radon assume a carbon life of 24 months (2 years), given that a GAC bed used for radon
removal can last for many years, assuming no limiting water quality conditions exist. Standard
design assumptions for VOCs are under development; values used in the model are based on
preliminary results from EPA pilot tests.
Contaminant Removal Requirements
For a given set of site-specific conditions, there is a minimum empty-bed contact time (EBCT)
required to produce water of acceptable quality. EBCT is defined by the following equation:
EBCT = Bed Volume/Volumetric Flow Rate
Because the minimum EBCT required varies depending on the specific contaminant treated, the
required contaminant removal percentage, the type of GAC used and other influent water
characteristics (e.g., the presence of competing chemical species), EBCT is best determined
using pilot studies or previous experience with GAC systems for similar influent waters.
For radon, however, EBCT can be determined theoretically. This is because, in theory, a steady
state condition develops in the bed in which the rate of radon adsorption equals the radioactive
decay of adsorbed radon. Thus, adsorption of radon can be modeled using the equation shown in
Exhibit 3-4
Exhibit 3-4. Modeling Radon Adsorption
Adsorption of radon can be modeled using the equation:
Ce/Co = e-Kss*EBCT
where:
Ce = effluent concentration
Co = influent concentration
Kss = steady state rate coefficient (in hours-1)
EBCT = empty bed contact time (in hours)
Thus, if Ce, Co and Kss are known, the required EBCT can be calculated as:
EBCT = Ln[ (Co/Ce) * Kss ]
The input sheet requires the user to select a method for determining EBCT either by specifying
EBCT directly (the preferred method) or calculating it by entering contaminant concentrations
(or percent removal) and Kss. This latter method should be used only for radon. Reported values
for Kss for radon range from 1.3 to 5.7 hours"1 (Drago, 2000). For reference, when the user elects
to use a KSS to calculate EBCT for radon, the input sheet displays the resulting EBCT. Typical
EBCT values are between 5 and 25 minutes for organic chemicals (AWWA/ASCE, 1998), while
34
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WBS-Based Cost Models for Drinking Water Treatment Technologies
typical EBCTs for radon are much higher. The model standard designs for atrazine use an EBCT
of 15 minutes, based on the recommendations of peer reviewers. The standard designs for radon
use an EBCT of 30 minutes, consistent with 75 percent removal and a Kss of 3 hours"1.
Number of Contactors in Series (Parallel or Series Operation)
For pressure GAC trains with high EBCT values (e.g., greater than 10 minutes), a treatment train
consisting of a number of vessels in series can be effective. The use of multiple vessels in a
series (or lead/lag) can extend overall bed life compared to a single vessel with a similar total
bed volume. Initial vessels in the series serve as roughing vessels and subsequent vessels are
polishing vessels. When GAC in the roughing vessel is spent, this media is replaced and the
polishing vessel moves to the start of the series, becoming the roughing vessel. The use of
vessels in series also can allow the carbon in the lead vessel to reach saturation and can increase
total capacity by about 10 to 30 percent (Calgon, 1999). Because of the high EBCT required for
atrazine and radon (15 to 30 minutes), the model standard designs assume three vessels in series
when pressure GAC designs are selected for these contaminants. Gravity GAC systems typically
are operated with contactors in parallel, rather than series. Therefore, when gravity designs are
selected, the GAC model designs systems with contactors in parallel and disables this input.
Bed Depth and Contactor Dimensions
For both design types (pressure and gravity), the input sheet requires the user to input the desired
depth of the GAC bed. For gravity contactors, typical bed depths are between 3 and 10 feet. For
pressure contactors, typical bed depths are between 2 and 8.5 feet. For preliminary design, other
sources of a reasonable bed depth include the designer's past experience, manufacturer
recommended bed depth and published literature. The model standard designs use bed depths
meeting these constraints. The specific input fields for contactor dimensions other than bed depth
differ between the two design types, as described below. For both design types, the model
includes a computer-aided design routine, also described below, to assist users in selecting
dimensions.
Pressure Vessel Dimensions and Geometry
For pressure GAC designs, the input sheet requires the user to select vessel geometry. Options
are vertical vessels for small to medium sized systems and horizontally laid long vessels for large
systems. For either configuration, the user needs to input the straight height or length of the
vessel and the diameter of the vessel. Pressure vessels used in this application typically are
upright cylinders, with a diameter ranging from 1.5 to 14 feet and up to 14 feet in height. Very
large systems (e.g., with design flows greater than 2,000 gallons per minute [gpm]) can use
horizontally laid vessels 20 to 40 feet long and up to 14 feet in diameter.
The input sheet will display warning signs if the dimensions of the selected vessel are outside the
boundaries specified on the critical design assumptions sheet. These boundaries include loading
rates, which are discussed in more detail in Section 3.3, and transportation limitations. For large
treatment plants, on-site assembly of tanks might be an option to overcome transportation
limitations. To allow this option, the user should increase the maximum dimensions permitted on
the critical design assumptions sheet.
Gravity Contact Basin Dimensions
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WBS-Based Cost Models for Drinking Water Treatment Technologies
For gravity GAC designs, the input sheet requires the user to input the desired width and length
of the GAC contact basins. GAC contact basins typically are square. The input sheet will display
warning signs if the dimensions of the selected basin are outside the boundaries specified on the
critical design assumptions sheet. These include loading rates, which are discussed in more detail
in Section 3.3, and reasonable size limitations based on generally recommended engineering
practices (GREPs). The size limitations (which can be modified by the user on the critical design
assumptions sheet) are:
• GAC bed depth of 3 to 10 feet
• Width and length of 6 to 30 feet.
Autosize Routine
To aid users, the model includes buttons labeled "Autosize" for each design type (pressure or
gravity). These buttons activate a computer-aided design routine that attempts to find a design
that meets all relevant design constraints for a given design and average flow and minimizes
capital cost. Using the autosize routine, the model will automatically select bed depth, geometry
and dimensions that meet all constraints, thus reducing trial and error by users, particularly for
systems with design flows other than the eight standard sizes provided on the input sheet. Note
that all other inputs must be complete before using the autosize routine.
Interval between Backwashes
Like conventional filters, GAC contactors must be backwashed periodically to remove solids,
maintain the desired hydraulic properties of the bed and possibly to control biological growth.
The physical properties of GAC particles affect filtration and backwash properties. These
physical properties include particle hardness, size and bed uniformity. Generally, a large
uniformity coefficient is recommended to maintain hydraulic and contaminant removal
uniformity. Particle density and size also affect backwashing. Generally, the harder the particle,
the less attrition of GAC during backwashing. The interval between backwash occurrences is a
function of the turbidity in the water and is typically 24 to 72 hours, although the interval can be
even longer for post-filter applications of GAC. For example, based on peer reviewer comments,
unfiltered surface water will require backwash every 24 to 48 hours while filtered surface water
will require backwash every 14 to 30 days. The typical backwash interval for groundwater can be
7 days or more. The input sheet requires the user to enter the interval (in hours) between
backwash events. The model standard designs use 48 hours between backwashes for atrazine,
consistent with unfiltered surface water and 168 hours (7 days) for radon and various VOCs,
consistent with groundwater. Users wishing to model treatment of these contaminants in
different quality water (e.g., atrazine in groundwater or filtered surface water) should adjust the
backwash interval.
GAC Transfer Method
Transfer equipment is needed to remove spent GAC from the contactors and fill the contactors
with regenerated or replacement GAC. The transfer of the media to and from the contactors can
be accomplished manually or mechanically using eductors. The GAC model does not consider
the use of slurry pumps because this method could result in excessive attrition of the media. The
input sheet requires the user to select the transfer method. The model standard designs select
manual transfer for systems for which this option resulted in relatively low labor requirements
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WBS-Based Cost Models for Drinking Water Treatment Technologies
(i.e., those requiring infrequent removal of small quantities of media). The standard designs use
eductors for all other systems.
Residuals Management
GAC systems generate two residuals streams on an intermittent basis: spent backwash and spent
media. The input sheet requires the user to choose from among several options for management
of each of these residuals streams. Exhibit 3-5 shows the management options available for
spent backwash.
Exhibit 3-5. Management Options for Spent Backwash
Options for Stage 1 of Management
Holding tank with or without coagulant addition (for flow
equalization and suspended solids removal)*
No holding tank
Options for Stage 2 of Management
Direct discharge to surface water
Discharge to POTW
Recycle to head of treatment train
Direct discharge to surface water
Discharge to POTW
Septic system*
Evaporation pond*
* Results in generation of secondary residuals (holding tank settled solids, septic tank solids or evaporation pond solids).
The management options shown in Exhibit 3-5 include the option for a holding tank. The
purpose of the holding tank is to equalize the rate of flow at which residuals are released or
discharged. When averaged over the time between generation events, backwash flow is relatively
low. However, instantaneous flow during a generation event is much higher. If spent backwash is
recycled to the head of a treatment plant, recommended engineering practice is that the recycle
stream should be no more than 5 to 10 percent of total system flow (U.S. EPA, 2002; U.S. EPA,
1996). Given the instantaneous backwash flow rates, if recycling is chosen for stage 2 of
management, a holding tank would always be necessary to prevent recycle flow from exceeding
this recommendation. It also may be reasonable to include a holding tank for the other stage 2
options (e.g., to prevent instantaneous flow from overwhelming the capacity of a publicly owned
treatment works [POTW]).
The use of a holding tank can result in the generation of a secondary residuals stream, in the
form of solids that settle from the spent backwash during the holding period. When a holding
tank is used, the model includes the option to add a coagulant to promote the settling of these
solids and reduce suspended solids levels in the holding tank effluent. As a default, the model
assumes coagulant addition is not utilized. The user can change this option on the critical design
assumptions sheet.
Exhibit 3-5 also includes the option for an evaporation pond. Given the quantities of spent
backwash generated, use of this management method is unlikely, but might be considered for
facilities in very dry climates. The required area for an evaporation pond depends on local
climate. After selecting an evaporation pond, the user should carefully review the climatic
parameters on the critical design assumptions sheet. For more information, see Appendix C.
Furthermore, to ensure that heating, cooling and standby power costs are computed consistently,
the user should review the climatic parameters in the operating and maintenance (O&M) and
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indirect assumptions sheets. Appendix E and Appendix D contain information on these
parameters. The use of an evaporation pond results in the generation of a secondary residuals
stream, in the form of evaporation pond solids.
A holding tank would not be required with an evaporation pond, because the design of the pond
would provide sufficient capacity to handle instantaneous flow. A holding tank also would not be
required with a septic system, since the septic tank itself serves as a holding tank.
Carbon regeneration or replacement is necessary when the adsorption capacity is used up and
contaminant breakthrough has occurred. The regeneration process has four basic steps: drying,
vaporization, pyrolysis and oxidation of the pyrolized residue (char). Common methods include
multiple hearth, rotary kiln, fluidized bed furnace and infrared furnace. Some systems have the
ability to regenerate GAC onsite, but most small systems haul away the spent GAC for off-site
regeneration (U.S. EPA, 1993) or disposal in a non-hazardous solid waste landfill. The input
sheet, therefore, requires the user to select from among the following seven options for handling
spent GAC:
1. On-site regeneration
2. Off-site regeneration
3. Off-site regeneration when spent GAC would be classified as hazardous waste
4. Disposal as non-hazardous solid waste
5. Disposal as hazardous waste
6. Disposal as radioactive waste
7. Disposal as radioactive and hazardous waste.
Management options available for secondary residuals (e.g., holding tank solids) include the four
disposal methods (i.e., options 4 through 7 above).6
The model does not include on-site regeneration of spent media that would be classified as
hazardous, because this option would likely entail excessive costs associated with permitting the
treatment unit. When on-site regeneration is selected (option 1 above), the system will include
on-site regeneration capacity using a multiple hearth furnace and on-site facilities (tanks or
basins) for GAC storage before and after regeneration. The disposal options (options 4 through 7
above) for spent GAC are present for situations where the media is used on a throwaway basis
without regeneration. For both secondary residuals and spent GAC, the disposal options (options
4 through 7 above) assume disposal in an off-site facility.7
For spent backwash, the model standard designs assume the use of a holding tank for systems
generating residual flow rates greater than 100 gpm during backwash. The standard designs
assume discharge to a POTW for the second stage of spent backwash management. For spent
GAC for atrazine, the standard designs assume off-site regeneration for all but the smallest
6 Users can also select land application, instead of landfilling, for non-hazardous secondary residuals by changing an
option on the critical design assumptions sheet. Appendix C discusses this option in more detail.
7 The management options do not include disposal in an on-site facility. This option would be economically viable
only for facilities with an existing on-site landfill—a factor that is highly site-specific. For these facilities, the cost of
this option would be less than that for off-site disposal, because it would involve much lower transportation costs.
Therefore, the off-site disposal options included provide a conservative cost estimate for these facilities.
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system size. For the smallest system size for atrazine, the standard designs assume throwaway
operation using an off-site non-hazardous waste landfill. For radon, the standard designs assume
throwaway operation using an off-site radioactive waste facility for all system sizes, because of
concerns about the feasibility of regenerating carbon used for radionuclides removal. For
systems that generate holding tank solids, the standard designs assume non-hazardous waste
landfill disposal for this residuals stream.
Number of Booster Pumps
Review of actual as-built designs for small systems using various technologies (U.S. EPA, 2004)
shows that these systems often can operate without additional booster pumps using existing
supply pump pressure. Therefore, the model assumes zero booster pumps for small systems (less
than 1 MOD design flow). For larger systems, the model calculates the number of pumps using a
method that attempts to minimize the number of pumps, while still accommodating variations in
flow and providing redundancy to account for possible equipment failure. The model includes an
optional input that allows the user to change these default calculations by specifying the number
of pumps required to operate the treatment system. If the user enters zero, the model excludes
booster pumps from the design and cost estimate. The standard designs for atrazine leave this
input blank, excluding booster pumps for small systems and accepting the default calculations
for larger systems. The standard designs for radon exclude booster pumps for all sizes of
pressure GAC systems, because the designs assume the treatment of groundwater with sufficient
existing supply pump pressure. They leave the input blank for gravity GAC systems, thereby
including booster pumps for large systems (1 MGD or greater design flow).
Number of Redundant Contactors
This optional input controls the model's calculation for the number of redundant contactors. At a
minimum, based on the Technology Design Panel recommendations, there should be at least one
redundant contactor in a GAC treatment system. An exception would be small pressure systems
designed with multiple contactors required to treat the maximum design flow (either more than
one parallel treatment train or a single line with multiple contactors in series). In such systems,
the average daily flow is low enough, relative to the design flow, that the multiple contactor
design provides sufficient redundancy without additional vessels. The system can operate at
reduced, but greater than average, flow, even while one contactor is off-line for backwashing or
GAC replacement. Thus, the number of redundant contactors can be zero for certain small
systems having at least two vessels.
The model assumes that redundant contactors (and other redundant items of equipment) are used
during downtime periods for other contactors and swapped into operation intermittently, with
other contactors then becoming standby. For this reason, the O&M estimate in the model
includes labor for operating valves and reading instruments associated with redundant contactors.
The input sheet allows the user to specify the number of redundant contactors. If the user leaves
this optional input blank for a large pressure GAC system (1 MGD or greater design flow) or any
gravity GAC system, the model calculates the number of redundant contactors based on a
redundancy frequency specified on the critical design assumptions sheet. If the user leaves this
optional input blank for a small pressure GAC system (less than 1 MGD design flow), the model
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does not add redundant contactors, unless the design selected by the user results in a single
operational contactor. In this latter scenario, the model adds one redundant contactor.
The standard designs leave this input blank, resulting in the following redundancy results:
• No redundant contactors for small systems (less than 1 MGD design flow), except in
cases where the design results in only one operating filter
• One redundant contactor every four treatment trains for larger pressure systems (1 MGD
or greater design flow)
• One redundant contactor total for medium gravity systems (1 MGD to less than 10 MGD
design flow) gravity systems
• Two redundant contactors total for larger gravity systems (10 MGD or greater design
flow).
Backwash Pumping
The backwash process can require new pumps or use existing pumps (either influent supply
pumps or treated water pumps, assuming these pumps can deliver unchlorinated treated water).
The practicality of using existing pumps can vary on a site-specific basis, depending on the
performance characteristics of the existing pumps and the differences in head required between
normal operation and during backwash. By default, the model assumes existing pumps are
sufficient for backwash for small systems (less than 1 MGD design flow), but includes the costs
of new backwash pumps for larger systems. The model includes an optional input that allows the
user to change these default assumptions by explicitly selecting "existing pumps" or "new
pumps." If the "existing pumps" option is selected, the costs of backwash pumps will be
excluded from the output sheet. If "new pumps" is selected, these costs will be included. The
standard designs leave this input blank, thereby assuming the use of existing pumps for small
systems (less than 1 MGD design flow), but including the costs of backwash pumps for larger
systems.
Backwash Storage
Backwash tanks may not be required on most installations, particularly for large systems that
have treated water storage capacity. The model assumes that systems with design flow less than
1 MGD do not require backwash tanks because the quantity of backwash water required is low.
The model also assumes that systems of 10 MGD and larger design flow do not require
backwash tanks because existing storage capacity is sufficient. The model includes backwash
tanks for intermediate-sized systems. The model includes an optional input that allows the user
to change these default assumptions by explicitly selecting "existing storage" or "new storage."
If the "existing storage" option is selected, the costs of backwash tanks will be excluded from the
output sheet. If "new storage" is selected, these costs will be included. The standard designs
leave this input blank, thereby including the costs of backwash tanks for intermediate-sized
systems (1 MGD to less than 10 MGD design flow) only.
Add-On (Pre- or Post-Treatment)
The WBS model for GAC includes an optional input that allows the user to specify that the GAC
treatment system is an addition to an existing treatment plant, intended as pre- or post-treatment
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WBS-Based Cost Models for Drinking Water Treatment Technologies
for another primary treatment process. When the user selects "add-on" for this input, the model
changes certain assumptions and calculations to reflect this scenario. Specifically, the model
excludes (or reduces the quantity or size of) certain capital components that would already be
present at the existing treatment plant. For example, the model includes only the incremental
system control components that would be required to integrate with the existing treatment
process control system. It includes O&M cost items, but calculates many of them on an
incremental basis (e.g., the labor hours cover only the additional hours required to operate the
new GAC process).
In the "add-on" scenario, the model also excludes certain indirect costs that would be required in
constructing a full new treatment plant. Specifically, the model does not include yard piping,
because installing the add-on process should not require additional exterior pipelines. It also does
not include standby power costs, because the additional electrical demand from the add-on
process should not require significant additional standby capacity. Add-on systems using
pressure GAC exclude geotechnical costs, because the pre-existing geotechnical survey for the
treatment plant should be sufficient to cover the construction associated with the add-on process.
However, add-on systems using gravity GAC include geotechnical costs because additional
surveying may be needed for excavation of the contact basins.
Finally, although the GAC process is assumed to be an addition to an existing treatment plant in
the add-on scenario, the model does include the full cost of buildings and land for the
incremental footprint of the process. While some treatment plants might be able to accommodate
the new process within existing space, others will require expansion to house the process.
Therefore, the inclusion of buildings and land is conservative (i.e., errs on the side of higher
costs) in terms of the actual cost of installing the process. Furthermore, even where existing
buildings and land are sufficient, the use of this existing space represents an economic
opportunity cost that is appropriate to include in regulatory cost estimates.
Retrofit (Operational Modification)
When faced with changing regulatory requirements (e.g., lower concentration limits) or new
contaminants in the water supply, existing GAC treatment plants can sometimes achieve
additional removal by increasing carbon regeneration or replacement frequency so that the
removal capacity of the media is restored before breakthrough at a new, lower target
concentration (or breakthrough of the new contaminant). In other words, the GAC treatment
system achieves the additional removal by modifying operations to reflect a new, shorter carbon
life.
The WBS model for GAC includes an optional input that directs the model to estimate costs for
this type of operational modification. When the user selects "retrofit" for this input, the model
also requires the user to provide input for the new, shorter carbon life. The input options for the
post-modification carbon life are identical to those for the original carbon life described above.
After the user enters the new carbon life, the model estimates the incremental costs associated
8 The current model includes a set of standard designs that use the add-on optional input to model the use of GAC
for post-treatment to quench hydrogen peroxide for UV-AOP. These standard designs should only be used in
conjunction with the UVAOP model, which is under development. Standard designs for other contaminants leave
the add-on optional input blank.
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with the operational modification. Except when on-site regeneration is selected, these costs are
limited to incremental O&M costs (e.g., GAC media costs and incremental labor costs associated
with more frequent regeneration or replacement). When on-site regeneration is selected, the
model also includes capital costs associated with expanding the multiple hearth furnace to
provide additional regeneration capacity. The model standard designs do not consider operational
modifications and leave this input blank.
3.3 Model Assumptions Sheets
There are three sheets that contain assumptions needed to facilitate process design: the critical
design assumptions sheet, the O&M assumptions sheet and the indirect assumptions sheet. These
sheets contain a variety of structural and chemical engineering parameters used in the
engineering design sheets. They also interact with the input sheet to determine if the user inputs
violate good engineering practices. For example, if a user selects contactor dimensions that
generate a surface loading rate that is too high or low, a warning message will appear on the
input sheet. The warning message will advise the user to adjust contactor dimensions or bed
depth to achieve a surface loading rate within GREPs.
There are more than 100 critical design assumptions in the model that cover process, O&M and
indirect cost parameters. Key critical design assumptions include surface loading rate, bed
expansion, backwash assumptions, regeneration and transfer assumptions, bypass percentage and
assumptions applicable to package plants. The following sections provide descriptions and
default values for these assumptions. Any assumption value can be modified, as needed.
Surface Loading Rate
A loading rate is the velocity of flow through the media measured in units of flow rate per unit
area (e.g., gallons per minute per square foot [gpm/ft2]). The surface area of the contactors must
be selected to maintain loading rates within reasonable bounds because water can channel
through the carbon bed if the loading rate is too low and pressure requirements may be excessive
if the loading rate is too high. For GAC treatment systems, loading rates usually are between 2
gpm/ft2 and 10 gpm/ft2. Higher loading rates may be used in site-specific situations where
hydraulics and tests allow. The model assumes a maximum loading rate of 10 gpm/ft2 and a
minimum loading rate of 0.5 gpm/ft2.
Bed Expansion
Vessel height (in pressure GAC designs) or contact basin depth (in gravity GAC designs) must
account for bed expansion during backwash. Gravity contactors also must provide freeboard to
prevent media washout. Bed expansion values should be taken from media vendor catalogues
and verified in pilot studies. Typical bed expansion generally is at least 50 percent
(AWWA/ASCE, 1998). The model assumes bed expansion of 50 percent and gravity designs add
2 feet of freeboard above bed expansion.
Backwash Assumptions
Backwash rates appropriate for specific GACs are provided by the manufacturer. Backwash rates
should be sufficient to fluidize the bed and should allow for the expansion of the GAC media
during backwash (AWWA/ASCE, 1998). The model assumes a backwash rate of 12 gpm/ft2 and
a backwash duration of 10 minutes.
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Regeneration and Transfer Assumptions
When the user selects regeneration (either on-site or off-site), a key assumption relates to GAC
losses during regeneration and transfer. The model expresses this assumption as the GAC
makeup rate, because it is used to calculate the quantity of virgin GAC required per year to
replace these losses. For on-site regeneration, the model assumes a GAC makeup rate of 10
percent per year. Makeup carbon needs are higher for off-site transportation and regeneration, so
the model assumes a makeup rate of 30 percent per year.
For on-site regeneration, a number of additional key assumptions are needed to size the
regeneration and storage facilities. These assumptions are regeneration facility run time,
regeneration facility redundancy and GAC storage facility capacity. Section 3.5 below,
describing the backwash and regeneration sheet, discusses the use of these assumptions.
Bypass Percentage
Systems may choose to treat only a portion of their production flow, using a smaller treatment
system and blending treated water with raw water while still achieving treatment targets. The
bypass percentage is that portion of production flow that goes untreated. If bypass is used, the
model designs the treatment system to treat a flow equal to (100 minus bypass percentage)
multiplied by design flow and adds bypass piping and associated valves to the components
included on the output sheet. The model assumes no bypass, but the user can incorporate bypass
by entering a percentage of bypass flow on the critical design assumptions sheet.
Package Systems
The GAC model handles package systems by costing all individual equipment line items (e.g.,
vessels, interconnecting piping and valves, instrumentation and system controls) in the same
manner as custom-engineered systems. This approach is based on vendor practices of partially
engineering these types of package plants for specific systems (e.g., selecting vessel size to meet
flow and treatment criteria). For small systems (less than 1 MGD design flow), the model applies
a variant set of design inputs and assumptions that are intended to simulate the use of a package
plant. Also included are assumptions that reflect the smaller capacity and reduced complexity of
the treatment systems. These design modifications typically reduce the size and cost of the
treatment system. Some are adjustable on the input sheet or the critical design assumptions sheet,
while others are in the engineering design formulae. Exhibit 3-6 shows the design modifications
used in the GAC model for small systems.
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Exhibit 3-6. Variant Design Inputs and Assumptions for Small Systems
Small System Design
Modification
Reduced spacing
between vessels and
other equipment
No redundant vessels
(but a minimum of two
operating vessels)
Reduced instrumentation
requirements
Simplified system
controls for automated
systems
No booster pumps
No backwash pumps or
tanks
Reduced concrete pad
thickness
Reduced indirect costs
Explanation
This assumption simulates skid placement of treatment vessels (and
of pumps, if included in the design), resulting in reduced system
footprint and, therefore, reduced costs for interconnecting piping,
building structures, certain indirect costs and O&M.
Small systems typically do not include redundant treatment vessels
because they are designed to operate at reduced capacity during
the brief periods when one vessel is not operating (e.g., during
backwash).
Instrumentation required for small systems is limited to flow meters,
high/low alarms, turbidity meters (in gravity systems) and sampling
ports.
Package plants, when automated, typically are controlled by a
single, pre-programmed operator interface unit mounted on the skid.
Therefore, for small systems, the model uses this type of operator
interface only and excludes the multiple programmable logic
controllers, computer workstations, printers, operator interface
software and plant intelligence software included for large,
automated, custom-engineered systems.
Small GAC systems result in limited head loss and typically do not
require additional booster pumps.
Small systems typically use existing pumps and water supplies and
do not require separate backwash pumps or backwash water
storage.
Small capacity systems require less structural support.
Package plants require less effort to design and install. Therefore,
the model reduces or eliminates certain indirect costs (e.g.,
mobilization/demobilization, construction management) for small
package plants (see Appendix D for complete details).
Model Location
Design equations on
the pumps, pipes and
structure sheet
Input sheet
Critical design
assumptions sheet
Component selection
logic in the output
sheet and WBS cost
database
Input sheet
Input sheet
Critical design
assumptions sheet
Indirect assumptions
sheet
3.4 Contactor Constraints Sheet
The contactor constraints sheet contains calculations that utilize the user-defined parameters
from the input sheet and the boundary values from the critical design assumption sheet to
determine the validity of the input values. This sheet also determines the number of contactors
required and the quantity of GAC needed, given the input values selected by the user. For gravity
GAC designs, this sheet also calculates the total volume of concrete required and, because
contact basins are constructed below grade, determines excavation and backfill requirements.
3.5 Backwash and Regeneration Sheet
The backwash and regeneration sheet calculates the total backwash volume required to backwash
one contactor, based on the contactor surface area, backwash loading rate and backwash time.
The sheet uses this value to calculate backwash storage requirements. Water for backwash can be
stored in steel, fiberglass or plastic backwash tanks. This sheet calculates the total volume of
each tank. Because it is appropriate for larger systems, this sheet also considers the use of
concrete basins for backwash storage. For concrete basins, the model assumes one basin and
calculates length, width and depth based on standard dimensional ratio assumptions. The user
can change these assumptions on the critical design assumptions sheet. Based on these
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dimensions, the model then calculates the total volume of concrete required, along with
excavation and backfill requirements.
This sheet also calculates the GAC bed life using the method specified on the input sheet
(directly specified in months or bed volumes or calculated using the Freundlich Isotherm
method). Based on this bed life and the quantity of GAC calculated on the contactor design
sheet, this sheet then calculates the annual GAC regeneration or replacement needs.
For systems using on-site regeneration, the sheet calculates the design capacity of the
regeneration facility (multiple hearth furnace) and the GAC storage requirements. To determine
regeneration facility capacity, the sheet first calculates average daily regeneration required in
pounds of GAC per day, based on the total quantity of GAC for all contactors and the bed life.
The sheet then calculates design regeneration capacity using the following equation:
D = (A / Run time) x Redundancy
where:
D is design regeneration facility capacity in pounds per day
A is average daily regeneration rate in pounds per day
Run time is the regeneration facility run time as a percentage of full time operation as
specified on the critical design assumptions sheet (the default assumption is 85 percent to
account for routine maintenance)
Redundancy is an additional safety factor expressed as a percentage greater than or equal
to 100 percent and specified on the critical design assumptions sheet (the default
assumption is 100 percent, providing no additional capacity beyond that needed to
account for downtime during maintenance).
The sheet calculates GAC storage requirements for spent GAC (i.e., awaiting regeneration),
regenerated GAC (i.e., awaiting use) and virgin GAC (i.e., makeup GAC to replace losses). The
quantity of each type of GAC stored is equal to the GAC capacity of a single contactor
multiplied by a factor specified on the critical design assumptions sheet. The default capacity
factor for each of spent, regenerated and virgin GAC is 1.33. GAC storage for each can be steel
tanks or concrete basins and the sheet calculates the size of these storage facilities using the same
approach as for backwash tanks and basins.
3.6 Retrofit Sheet
When the "Retrofit (operational modification)" input is set to "retrofit" on the input sheet, the
retrofit sheet performs the calculations required to estimate the cost associated with operational
modifications to use a new, shorter carbon life. This sheet duplicates the bed life and
regeneration calculations on the backwash and regeneration sheet using the new carbon life in
place of the original carbon life. It then compares the results to those on the backwash and
regeneration sheet to calculate the incremental GAC usage associated with the operational
modification. This sheet also calculates the other incremental requirements associated with the
operational modification, such as operator labor, energy use and regeneration furnace capacity (if
required).
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3.7 Pumps, Pipe and Structure Sheet
Other elements of the technology for which the size and cost need to be determined include
pumps, piping and GAC transfer equipment (eductors). The pumps, pipe and structure sheet
performs the required calculations to determine the number and size (in terms of flow capacity)
of the following pumps:
• Booster pumps
• Backwash pumps (if required).
This sheet uses the input values for flow and water quality parameters, as well as the pertinent
parameters detailed on the critical design assumption sheet, to determine the number of pumps
needed, including redundant units. Pump sizing depends on the maximum corresponding flow
rate. For example, booster pumps are sized based on the system design flow and backwash
pumps are sized based on the total backwash flow. As discussed in Section 2.3, the sizing of all
pumps incorporates a safety factor, which is specified on the critical design assumptions sheet.
This sheet also performs calculations for the following pipes:
• Influent and effluent piping
• Process piping
• Backwash piping
• Bypass piping (if a bypass percentage is specified).
The size (diameter) of pipes is determined using a pipe flow lookup table. The pipe diameter
selection method incorporates a reasonable head loss and flow velocity, as documented in
Exhibit 2-8. These design assumptions may result in some over sizing of pipes and, therefore,
the resulting cost estimates may be conservative (i.e., err on the high side).
The flow used to determine influent and effluent pipe size is the design peak flow. The diameter
of interconnecting process piping uses the same pipe flow chart, after splitting the inflow by the
number of parallel treatment trains. A similar approach is used in determining the size and
capacity of backwash and bypass piping. The length of these pipes is determined using the
assumptions documented in Exhibit 2-10, which are designed to account for the cost of fittings.
This sheet also calculates the housing area for this technology based on the footprint of the
technology components and the spacing criteria specified on the critical design assumption sheet.
The space requirements for contactors, pumps, tanks and service space are based on
manufacturer specification, "to scale" drawings and the experience of engineers. The amount of
additional concrete needed to support heavy equipment, such as pumps and pressure contactors,
is based on the footprint of the contactors and pumps.
For smaller space requirements (less than a square footage specified on the critical design
assumptions sheet), the model assumes a single building containing all process equipment. For
larger requirements, the model assumes two buildings, one containing the GAC contactors and
the other containing all other equipment. The number of buildings affects the total land required
and energy costs for heating, ventilating and cooling.
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3.8 Instrumentation and Control Sheet
The instrumentation and control sheet calculates requirements for valves, instrumentation (e.g.,
flow meters) and automated system controls. The number of valves and instruments is based on
the number of process components (e.g., number of treatment lines) and assumptions from the
critical design assumptions sheet (e.g., x number of valves per treatment line). The assumptions
correspond to the general schematic layout for this technology shown in Exhibit 3-1 and Exhibit
3-2. Sizing of valves corresponds to the size of the appropriate pipe determined on the pumps,
pipes and structure sheet. Appendix A describes the method used in the WBS models to estimate
the number and type of system control components.
3.9 Residuals Management Sheet
The residuals management sheet estimates the volume and mass of residuals, their characteristics
and the capital and O&M requirements for residuals management, based on the management
options selected on the input sheet and the approach outlined in Appendix C. Depending on the
management options chosen, specific items of capital equipment for residuals may include:
• Holding tanks
• Pumps
• Septic tanks and drain field components
• Coagulant feed and mixing equipment
• Valves, piping and instrumentation.
Specific O&M requirements associated with residuals may include:
• Residuals pump labor, materials and energy
• POTW discharge fees
• Coagulant usage
• Spent GAC transportation and disposal costs
• Secondary residuals (holding tank or septic tank solids) transportation and disposal costs.
3.10 O&M and HVAC Sheets
The O&M and heating, ventilating and air conditioning (HVAC) calculations cover two sheets:
the O&M sheet (annual labor, materials and energy usage) and the HVAC sheet (HVAC capacity
requirements). The O&M sheet derives annual O&M requirements for GAC treatment based on
the engineering design, O&M critical design assumptions and input values. It determines the
following O&M requirements based on the approach outlined in Section 2.4 and Appendix E:
• Operator labor for system operation and maintenance
• Managerial and clerical labor
• Booster pump maintenance materials and operating energy
• Facility maintenance materials
• Energy for building lighting and HVAC.
In addition, the O&M sheet adds the following technology-specific O&M requirements:
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• Operating energy for backwash pumps
• Operator labor and materials for backwash pump maintenance (if backwash occurs
weekly or more frequently)
• Operator labor for managing backwash events
• Operator labor for media transfer
• Operator labor for contactor maintenance (for gravity GAC designs)
• Materials for contactor maintenance (accounts for vessel relining in pressure designs,
because GAC can be corrosive and for concrete and underdrain maintenance in gravity
designs)
• Labor, materials, energy and natural gas usage for on-site GAC regeneration (if this
option is chosen by the user).
Because GAC systems are backwashed frequently, backwash pumping facilities consume more
energy than in other technologies and can require significant maintenance. Therefore, the model
includes backwash pump operating energy among its O&M costs. When backwash occurs
weekly or more frequently, the model also explicitly includes labor and materials for maintaining
backwash equipment. The sheet determines materials for backwash pumps using the same
approach outlined in Appendix E for booster or influent pumps. Backwash pump labor uses the
equation described in Appendix E for booster or influent pumps, except that the maximum total
backwash flow is substituted for system design flow. Backwash pump energy consumption also
follows the approach in Appendix E, except that, rather than assuming continuous operation, the
calculation uses the number of hours per year during which backwash pumps operate.
For manual and semi-automated systems, backwashing requires constant operator attention.
Therefore, the model assumes labor equal to twice the actual time to accomplish backwash for
these systems. For automated systems, the model assumes 1 minute per backwash event to verify
that the automated backwash cycle is initiated and operating properly. The user can change this
latter assumption on the O&M assumptions sheet.
The model also assumes the annual cost of materials for contactors is equal to 1 percent of their
pre-installation capital cost. For gravity GAC designs, the O&M sheet determines labor for basin
maintenance assuming 1 hour per week for each contact basin. The user can change these
assumptions on the O&M assumptions sheet.
The O&M sheet determines labor, materials and energy requirements for on-site regeneration
using equations derived in U.S. EPA (2000) and presented in Exhibit 3-7.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
Exhibit 3-7. O&M Equations for On-Site Regeneration of GAC
O&M Requirement
Labor (in hours/year)
Materials cost ($/year)
Energy (in kilowatt-hours/year)
Natural gas (in therms/year)
Equation
2.2515 * (regeneration system capacity in pounds per day)07554
8,451 .4 * (regeneration system capacity in pounds per day)0 2017
9.1217 * (regeneration system capacity in pounds per day)1 °475
28.161 * (regeneration system capacity in pounds per day)
3.11 Indirect Sheet
As stated in Section 2.4, indirect capital costs are costs that are not directly related to the
treatment technology used or the amount or quality of the finished water, but that are associated
with the construction and installation of a treatment technology and water intake structures. The
indirect sheet derives capital costs for the following components of indirect costs:
• Construction management and general contractor overhead
• Standby power
• Geotechnical
• Site work
• Yard piping.
Appendix D contains detailed information on the derivation of these and other indirect costs. The
sheet also contains calculations to estimate permit costs.
3.12 Output Sheet
The output sheet contains the list of components identified for GAC based on the WBS
approach. For each component, the output sheet provides information on size (e.g., tank capacity
or pipe diameter) and quantity, as well as estimated capital cost and estimated useful life. The
output sheet also contains cost estimates for indirect capital costs (e.g., mobilization and
demobilization, site work and yard piping), add-on capital costs (for permitting, pilot testing and
land) and annual O&M costs. These estimates are described generally in Section 2.4 and in more
detail in Appendix D (indirect costs) and Appendix E (O&M costs). Finally, the output sheet
combines the total capital cost, system useful life and annual O&M cost to estimate total
annualized cost, as discussed in Section 2.4. Sections 2.1 and 2.3 provide further details about
the output sheet.
3.13 Ancillary and Reference Model Components
The model contains several ancillary sheets: index, standard inputs, autosize, cost equations, cost
coefficients, cost data, engineering data and lookup tables. The index is a hyperlinked list of
user-adjustable inputs and assumptions that can assist the user in finding these inputs and
assumptions, should they wish to change them. The standard inputs worksheet documents the
inputs used in the standard designs. Advanced users can adjust these standard inputs, if desired.
The model uses the autosize sheet when performing the iterative calculations required when the
user clicks the "Autosize" button on the input sheet. The cost equations and cost coefficients
sheets use the component-level cost curve equations to generate unit costs on an item-by-item
basis. The cost data and engineering data sheets contain component cost and engineering
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WBS-Based Cost Models for Drinking Water Treatment Technologies
reference data extracted from the central cost database. The lookup tables sheet is for internal
model use in populating the drop-down boxes on the model input sheet.
The GAC model also includes a reference sheet containing information on Freundlich isotherms.
As discussed in Section 3.2, the user may refer to the information in this reference sheet in
determining how to adjust inputs.
3.14 List of Abbreviations and Symbols in this Chapter
EBCT empty bed contact time
EPA U.S. Environmental Protection Agency
GAC granular activated carbon
gpm gallons per minute
gpm/ft2 gallons per minute per square foot
GREPs generally recommended engineering practices
HVAC heating, ventilating and air conditioning
MGD million gallons per day
O&M operating and maintenance
POTW publicly owned treatment works
RSSCT Rapid Small Scale Column Test
UVAOP ultraviolet advanced oxidation process
VOC volatile organic compound
WBS work breakdown structure
3.15 References
American Water Works Association (AWWA). 2011. Water Quality & Treatment: A Handbook
on Drinking Water Quality. Sixth Edition. J.K. Edzwald, Ed. New York: McGraw-Hill.
American Water Works Association and American Society of Civil Engineers (AWWA/ASCE).
1998. Water Treatment Plant Design. Third Edition. New York: McGraw-Hill.
Calgon. 1999. Application Bulletin: Use of Carbon Adsorption in Processes in Groundwater
Treatment. Company Brochure. Reprinted from Environmental Progress, November 1989.
Crittenden, J. C., P.S. Reddy, H. Arora, J. Trynoski, D.W. Hand, D.L. Perram and R.S.
Summers. 1991. "Predicting GAC performance with Rapid Small-Scale Column Tests." Journal
AWWA 83, no. 1 (January).
Drago, J. 2000. Radon Removal Technologies for Small Communities. San Francisco:
Kennedy/Jenks Consultants.
U.S. Environmental Protection Agency (U.S. EPA). 1993. Very Small Systems Best Available
Technology Cost Document. Prepared by Malcolm Pirnie. September.
U.S. EPA. 1996. Technology Transfer Handbook: Management of Water Treatment Plant
Residuals. United States Environmental Protection Agency, Office of Research and
Development. EPA 625-R-95-008. April 1996.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
U.S. EPA. 2000. Design and Cost Estimates for Advanced Water Treatment Technologies. Final
Draft—Volume I. Office of Research and Development, National Risk Management Research
Laboratory. Cincinnati.
U.S. EPA. 2002. Filter Backwash Recycling Rule: Technical guidance manual. United States
Environmental Protection Agency, Office of Groundwater and Drinking Water. EPA 816-R-02-
014. December 2002.
U.S. EPA. 2004. Capital Costs of Arsenic Removal Technologies, U.S. EPA Arsenic Removal
Demonstration Project, Round 1. EPA-600-R-04-201. Cincinnati, OH: U.S. EPA, National Risk
Management Research Laboratory.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
4. Packed Tower Aeration Model
Aeration processes, in general, rely on the diffusion of contaminants from treated water to non-
contaminated air. Packed tower aeration (PTA) employs towers filled with a packing media that
is designed to mechanically increase the area of water exposed to the non-contaminated air. PTA
can be used to reduce the concentration of volatile contaminants including: volatile organic
compounds (VOCs), disinfection byproducts, radon gas, hydrogen sulfide, carbon dioxide and
other taste- and odor-producing compounds. PTA has been identified by EPA as a best available
technology for removal of a number of common VOCs such as benzene, trichloroethylene and
xylene(40CFR141.61).
The work breakdown structure (WBS) model for PTA includes standard designs for the
treatment of a number of different contaminants, including methyl tertiary-butyl ether (MTBE),
radon and various VOCs. However, the model can be used to estimate the cost of PTA treatment
for the removal of other contaminants as well. Users wishing to simulate the use of PTA for
treatment of other contaminants will need to adjust default inputs (e.g., Henry's coefficient,
molecular weight) and, potentially, critical design assumptions (e.g., minimum and maximum
packing height). This chapter includes discussion of inputs and assumptions that might require
adjustment and these values are highlighted in gold in the model.
4.1 Overview of the PTA Treatment Process
The PTA treatment process includes the following components:
• Towers with internal parts for water distribution and packing support
• Packing material, usually pieces of plastic in shapes designed to maximize the surface
area of water in contact with air
• Blowers for forcing air into the towers
• Booster pumps for pumping water into the towers
• A clearwell to collect treated water after aeration.
In addition, the process requires storage and delivery systems for chemicals used to clean the
system and to prevent buildup of scale within the system. Depending on the contaminant being
removed and local requirements, PTA can also require off-gas treatment systems. Finally, like
other technologies, PTA requires accessory equipment such as pipes, valves, control systems and
a building to house the equipment. Exhibit 4-1 provides a schematic drawing for PTA.
When water is treated with PTA, the contaminated water is pumped to the top of the tower
(typically cylindrical), where it is introduced through a spray header as a fine mist. As the water
falls through the packing media, it is exposed to counter-current airflow, meaning that the drops
of water fall down through the tower while the blower sends air up through the tower. This
counter-current design increases the effective "windspeed" to which the drops of water in the
tower are exposed. The packing material increases the surface area of the water droplets to
provide maximum air-to-water contact. This increased surface area assists volatile contaminants
in passing from the liquid to the gaseous phase. When compared to other aeration and air
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WBS-Based Cost Models for Drinking Water Treatment Technologies
stripping treatment technologies, liquid to gas transfer has been found to be especially high in
packed tower aerators (Millet, 1993). The contaminants leave the top of the tower, entering the
atmosphere or off-gas treatment, while the treated water collects below the tower in a clearwell.
Exhibit 4-1. Typical Schematic Layout for PTA
-.
Cenfrrfugal
Pump
-0
.Kj
Metering
Pump
Control
Chemical Tank
Optional equipment not shown:
• Day tanks for acid, caustic, and
corrosion control chemicals
- Off-gas treatment
- Bypass piping
Metering
Pump
C7
....f^j...!....,
Caustic Tank
z
Meteriog
Z
Treated Water to
Disinfection
INSTRUMENTATION
fQ) AirFiow (Q Temperature (7s High/Low
v- Meter ^ Meter ^-^ A'a"^
^IKES
Influent
N4
Packed Tower Aeration
Typical Schematic Layout
PTA 12-1 0-201 3- vsd
4.2 Input Sheet
The input sheet accepts the user-defined design parameters that determine fundamental process
requirements. The user can indicate system size, select contaminant characteristics, set treatment
goals and select basic equipment characteristics. Key design considerations that the user
identifies on this sheet are described in greater detail below and include the following:
• Contaminant
• Design and average flow (see Section 2.3)
• Contaminant removal (percent or target concentration)
• Safety factors
• Contaminant characteristics (e.g., Henry's coefficient, molecular weight)
• Operating temperature and characteristics of air (density and viscosity)
• Packing characteristics (size, surface area, critical surface tension, friction factor)
• Clearwell detention time
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WBS-Based Cost Models for Drinking Water Treatment Technologies
• Off-gas treatment
• Number of booster pumps and blowers (optional)
• Number of redundant towers (optional)
• Component level (optional, see Section 2.3)
• System automation (optional, see Section 2.3)
• Retrofit (optional).
Note that the PTA model uses an automated, iterative process to calculate equipment
requirements and operating parameters that achieve the treatment goals selected by the user and
meet design constraints consistent with generally recommended engineering practices (GREPs).
Section 4.4 describes this design process in more detail. This design process runs whenever the
user clicks the "Generate Results" button on the input sheet. Note that all inputs must be
complete before generating results. The input sheet includes a summary of relevant design results
(costs and tower design parameters) so that users can quickly review the results, adjust inputs as
required and run the design routine again. The input sheet will warn users when input values
have changed from the last time they ran the design routine, prompting them to re-run the
routine. This warning, however, will not detect changes to the model's critical design
assumptions (see Section 4.3) since the last design run, so expert users should remember to re-
run the design routine before evaluating changes to those values.
Contaminant
The WBS model for PTA includes a "drop-down" list box that allows the user to select the
contaminant being treated. This drop-down box is located at the top of the input sheet, above the
standard design buttons. The user should verify that the selection shown in this box is correct
before populating the other design input values. The user can change the contaminant modeled
by picking a different selection from the list. After doing so, the user should then repopulate the
input sheet with values appropriate for the new contaminant by clicking one of the standard
design buttons or manually adjusting inputs and clicking the "Generate Results" button (see
Section 2.3 for further discussion of each of these methods).
Currently, the model includes standard designs for the treatment of MTBE, radon and various
VOCs. The model, however, can be used to design PTA systems for the removal of other
contaminants by selecting the "other" option from the contaminant drop-down menu. To use the
model for other contaminants, the user would manually enter the removal percentage and
contaminant characteristics in the input sheet, to reflect what is applicable for the targeted
contaminant.
Contaminant Removal
The model requires that the user specify the initial contaminant concentration, then select
whether to design based upon percent removal or target effluent concentration. The model will
size equipment and set operating conditions to meet or exceed the target removal efficiency,
taking into account the safety factors (see below). If percent removal is chosen, the value should
be entered as a decimal (i.e., 0.5 for 50 percent removal). If a target effluent concentration is
chosen, the value should be entered in picocuries per liter (pCi/L) for radon or micrograms per
liter (|ig/L) for other contaminants. The model standard designs use an influent concentration of
200 |ig/L for MTBE and 300 pCi/L for radon. They use target effluent concentrations of 20 |ig/L
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WBS-Based Cost Models for Drinking Water Treatment Technologies
for MTBE and 30 pCi/L for radon. Standard design assumptions for VOCs are under
development.
Safety Factors
Safety factors are placed on two key constants used in the design calculations to account for
variations in influent characteristics and operating conditions and to account for uncertainty in
estimating these constants. The safety factors are applied in calculating the overall transfer rate
constant (Kia) and in using Henry's coefficient, respectively. The safety factors should be
entered as values greater than 1. Guidance provided in the model indicates that each of these
safety factors should be between 1.2 and 1.4 (i.e., providing a 20 to 40 percent margin of safety).
The model's standard designs use the highest safety margin in this range: 1.4. The values
selected for these inputs can have a significant effect on design and cost output. Therefore, users
should vary these values within limits appropriate for their application to examine the sensitivity
of the output.
Contaminant Characteristics
The chemical characteristics of the contaminant to be removed are of utmost importance in the
design of a PTA system. Key among these is the Henry's coefficient (also known as Henry's
Law constant), which is a partition coefficient describing the tendency of a contaminant to
separate between the gas and liquid phases at equilibrium. The smaller the Henry's coefficient,
the more difficult it is to remove the contaminant from the influent water. Henry's coefficient
takes into account the solubility, molecular weight and vapor pressure of the contaminant. The
constant may be estimated using these parameters, but is more commonly estimated
experimentally. The user input for Henry's coefficient must be in the units: atmospheres * cubic
meters [of water] / cubic meters [of air] (atm * m3/m3). The Henry's reference sheet in the WBS
model provides information on Henry's coefficients provided in the literature, estimating the
constant using other contaminant characteristics and converting the constant from other
commonly used units.
Values for Henry's coefficient reported in the literature can vary among sources. When faced
with conflicting data for Henry's coefficient, users should carefully evaluate the results to
determine their sensitivity to the range of Henry's coefficient reported. This sensitivity analysis
can be accomplished by selecting various values for the Henry's coefficient input and/or various
values for the Safety factor (Henry's) input.
The model standard designs for MTBE use a Henry's coefficient of 0.0117 atm * m3/m3, a value
measured in Fischer et al. (2004) at 10 degrees Centigrade (C) (the operating temperature used in
the standard designs). The model standard designs for radon take the average of Henry's
coefficient values reported in Sander (1999) and Hess et al. (1983), after conversion of the
reported values to the appropriate units. Because the values reported in the literature were for 25
degrees C, the standard designs adjust the resulting value to 10 degrees C using a temperature
dependence constant from Sander (1999) (see discussion below under "Operating
Temperature"). The resulting value, after adjustment, is 1.85 atm * m3/m3.
The other contaminant characteristics required by the model are molecular weight, molar
volume, boiling point and melting point. Melting point is required only if data for the
contaminant's boiling point are not available. These characteristics typically can be obtained
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WBS-Based Cost Models for Drinking Water Treatment Technologies
from common chemical reference materials. The model standard designs use the inputs shown in
Exhibit 4-2
Exhibit 4-2. Default Contaminant Characteristics Inputs
Input
Henry's coefficient
Molecular weight (kg/kmole)
Molar volume (rrWkmole)
Boiling point (degrees K)
Melting point (degrees K)
MTBE
0.0117
88.1492
0.126
328.2
Not required
Radon
1.85
222
0.0505
211
Not required
kg/kmole = kilograms per kilomole
rrWkmole = cubic meters per kilomole
Operating Temperature and Characteristics of Air
Although air and water entering the PTA tower typically will be at different temperatures, the air
temperature does not significantly affect the water temperature and the air quickly takes on the
water temperature. Therefore, the PTA model uses a single equilibrium operating temperature,
which is primarily controlled by water temperature. Although operating temperature can vary
seasonally, the use of safety factors in the model should accommodate these variations. This
input should be entered in degrees Kelvin (K) (i.e., degrees C + 273). The model standard
designs use 283 degrees K (10 degrees C), typical of groundwater temperatures in the United
States.
Users should be aware that operating temperature can have a significant effect on Henry's
coefficient and use care to select a Henry's coefficient consistent with the input operating
temperature. Unfortunately, most values for Henry's coefficient found in the literature are for 20
to 25 degrees C, not for typical groundwater temperatures. In the absence of Henry's coefficient
data for appropriate operating temperatures, users can adjust the available values to an
appropriate temperature using a temperature dependence constant and the temperature
adjustment calculator provided on the Henry's reference sheet. Like Henry's coefficient itself,
temperature dependence constants reported in the literature can vary among sources. When
adjusting for temperature and faced with conflicting values for this constant, users should
carefully evaluate the results to determine their sensitivity to the range of Henry's coefficient
resulting from different values for the temperature dependence constant.
The other operating parameter inputs required by the model are the density and viscosity of air,
which should be selected consistent with the equilibrium operating temperature, although they
can also vary depending on other factors (e.g., altitude). The air and packing reference sheet
provides typical values for these inputs at various operating temperatures. For standard designs,
EPA used an air density of 1.247 kilograms per cubic meter and an air viscosity of 1.79x10"
kilograms per meter * seconds, consistent with the default operating temperature of 10 degrees
C.
Packing Characteristics
Packing usually consists of small (1 to 2 inch diameter) pieces of plastic that are shaped to
maximize the surface area of each piece. Shapes can include "snowflake" or "saddle" designs.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
The model requires the user to input the packing size, surface area of the packing, the critical
surface tension of the packing and a friction factor. In general, these characteristics should be
obtained from vendor information. The air and packing reference sheet, however, contains
packing characteristics for various types of commercially available packing.
The model standard designs use 2 inch plastic saddles as the packing material. They use values
for surface area, critical surface tension and friction factor consistent with this type of packing.
The WBS cost database includes unit costs specifically for 2 inch plastic saddles. It also
currently includes unit costs for 3.5 inch packing. For users that desire other packing types, the
model includes an optional input to specify an alternative unit cost (in dollars per cubic meter)
that will override the model's calculated unit cost. In addition to adjusting the physical packing
characteristic inputs, users with a different packing type (particularly of a different material, such
as ceramic) should also enter a unit cost for this optional input.
Clean/veil Detention Time
The input sheet requires the user to choose a detention time for the clearwell that receives the
treated water. The model includes clearwells because it is anticipated that the addition of PTA
treatment will trigger the requirement for a clearwell to accommodate disinfection contact time.
Based on GREPs, the guidance in the model recommends a detention time of 5 to 10 minutes.
Users that do not desire to include clearwells (e.g., if a clearwell already exists) can enter zero
for detention time to exclude the cost of this item. The model standard designs use 5 minutes for
detention time.
Off-Gas Treatment
For contaminants other than radon, the input sheet requires the user to specify a level of VOC
releases (in pounds per day [Ibs/day]) at which an air pollution control system might be needed
and warns the user when an air pollution system might be required. This level is likely to vary
based on local air pollution control requirements, but, as a default, the model standard designs
use 1 Ibs/day for this limit. The limit used is the maximum emission level for all VOCs for
California's South Coast Air Quality Management District. For radon, the off-gas control
technology options available in the model are not appropriate (would not be effective); therefore,
the off-gas control system inputs are disabled for radon.
If off-gas treatment is needed, the model provides three treatment options for the design of the
air pollution control system: granular activated carbon (GAC), thermal oxidation and catalytic
oxidation. If the GAC option is chosen, the model requires the user to specify whether the GAC
will be regenerated or used on a throwaway basis and also gives the user the option of entering
the expected bed-life of the media. For thermal and catalytic oxidation, the model requires the
user to choose if heat recovery will be utilized (either recuperative or regenerative). The model
standard designs for MTBE select off-gas control options that minimize the cost of off-gas
control for all designs where estimated off-gas levels exceeded the lib/day limit.
Number of Booster Pumps and Blowers
The model calculates the number of pumps and blowers using a method that attempts to
minimize the number of pumps and blowers, while still accommodating variations in flow and
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WBS-Based Cost Models for Drinking Water Treatment Technologies
providing redundancy to account for possible equipment failure. The model includes two
optional inputs that allow the user to change these default calculations by specifying the number
of pumps and/or blowers required to operate the treatment system. If the user enters zero for the
number of pumps, the model excludes pumps from the design and cost estimate. Entering zero
can be used, for example, to simulate a situation where existing pumps are sufficient to operate
the PTA system. Blowers cannot be excluded from the model designs. The model standard
designs leave these inputs blank, accepting the default calculations.
Number of Redundant Towers
The input sheet allows the user to specify the number of redundant towers. If the user leaves this
optional input blank, the model calculates the number of redundant towers based on redundancy
assumptions specified on the critical design assumptions sheet (see Section 4.3). The model
standard designs leave this input blank, accepting the default calculations.
Retrofit
When faced with changing regulatory requirements (e.g., lower concentration limits) or new
contaminants in the water supply, existing PTA treatment facilities can sometimes achieve
additional removal by increasing the air-to-water ratio (e.g., by replacing existing blowers with
more powerful units) and/or increasing the height of existing towers (e.g., by adding new
sections to the existing tower shell, along with additional packing).
The WBS model for PTA includes an optional input that directs the model to estimate costs for
either of these types of modifications to an existing system. The retrofit optional input allows the
user to choose a modification to achieve: additional removal of the contaminant already specified
above on the input sheet or removal of a new contaminant other than the one the system was
originally designed to remove. In the first scenario, the model requires only the new target
concentration or percent removal. In the second scenario, the model also requires the
contaminant characteristics for the new contaminant. The input options for the new removal
requirement and contaminant characteristics are identical to those for the corresponding original
inputs described above. In either scenario, an optional input allows the user to specify whether to
install additional tower height as part of the retrofit design, as opposed to modifying air-to-water
ratio only.
After the user enters the required data and runs the model design process by pressing "Generate
Results," the model estimates the incremental costs associated with the retrofit modification to
the existing plant. These incremental costs include the following items of capital equipment:
• Replacement blowers
• Additional aeration tower shell sections, liquid redistributors and packing (if additional
tower height is installed)
• Additional process piping to reach the top of the new tower height (if additional tower
height is installed).
They also include the following operating and maintenance (O&M) items:
• Incremental labor, materials and energy for the new blowers
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WBS-Based Cost Models for Drinking Water Treatment Technologies
• Incremental materials for tower maintenance (if additional tower height is installed)
• Incremental energy for pumps to move water to the top of the new tower height (if
additional tower height is installed)
• Incremental building lighting because of the increase in operator labor hours.
The retrofit scenarios also exclude building costs (because all new equipment is assumed to be
outside), land costs (because minimal additional footprint would be required) and certain indirect
costs (site work, yard piping and geotechnical).
4.3 Model Assumptions Sheets
There are four sheets that contain assumptions needed to facilitate process design: the critical
design assumptions sheet, the O&M assumptions sheet, the indirect assumptions sheet and the
off-gas assumptions sheet. These sheets contain a variety of structural and chemical engineering
parameters used in the engineering design sheets. The automated design process also uses
information from these sheets to select designs that are consistent with good engineering
practices. For example, the design process will not select very small tower diameters that result
in a tower area smaller than the minimum specified on the critical design assumptions sheet.
There are more than 100 critical design assumptions in the model that cover process, O&M and
indirect cost parameters. Key critical design assumptions include tower design constraints,
minimum number of towers and other tower redundancy assumptions, air pipe length per tower,
chemical usage rates and bypass percentage. The following sections provide descriptions and
default values for these assumptions. Any assumption value can be modified, as needed.
Users should be aware that any change to critical design assumptions (particularly tower design
constraints) could cause changes in the model results that will not be reflected in the model
output until the iterative design program is run again. The input sheet warning will detect
changes to inputs, but not to critical design assumptions, since the last design run. Therefore,
users who wish to change critical design assumptions should click "Generate Results" on the
input sheet after completing their changes, but before reviewing model output.
Tower Design Constraints
The model's automated design process (see Section 4.4) will only select designs that meet
certain GREPs with respect to the dimensions of the aeration vessels. These GREPs are specified
on the critical design assumptions sheet and constrain the maximum packing height, the
minimum and maximum tower diameter and the ratio of the tower dimensions (height to
diameter). For these constraints, the model assumes the following:
• Tower diameter must be greater than or equal to 0.5 feet
• Tower diameter must be less than or equal to 10 feet
• Packing height must be greater than or equal to 1.5 times the tower diameter
• Packing height must be less than or equal to 10 times the tower diameter
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WBS-Based Cost Models for Drinking Water Treatment Technologies
• Packing height must be less than or equal to 6.1 meters (approximately 20 feet).9
These constraints are based on generally accepted engineering practice for PTA towers and were
suggested by the technology experts who reviewed the critical design assumptions. For example,
tower heights usually vary between 10 and 30 feet tall, but some may be even taller (depending,
for example, on contaminant and packing characteristics). Packed tower aerators with 10 to 12
feet of packing have been found to be effective at removing 95 percent of VOCs and 99 percent
removal efficiency can be expected in standard towers with 20 feet of packing (Millet, 1993).
Also, in practice, towers are taller than they are wide. The minimum constraint on the ratio of
height to diameter used in the model (1.5:1) is relatively low for standard towers, which usually
are several times taller than their diameter. The model, however, uses this low ratio to maintain a
practical geometry for radon removal, which, in theory, could be achieved with a low packing
height. The maximum constraint on the ratio of height to diameter (10:1) is required to maintain
the structural stability of the towers.
Minimum Number of Towers and Redundancy Assumptions
The model includes a critical design assumption for the minimum number of towers. The model
assumes a minimum of two towers, which causes the automated design process (see Section 4.4)
to design the PTA towers using the principle of operational redundancy. This means that it
always includes a minimum of two towers, each sized to handle 50 percent of system design
flow. This approach allows the system to still operate at 50 percent flow (which is greater than
average flow for typical systems) even with one of the pair of towers out of service, either for
scheduled maintenance or because of failure.
Operational redundancy is more cost effective than true 100 percent redundancy, which would
provide a minimum of two towers, each sized to handle the full design flow. With 100 percent
redundancy, one tower would be an emergency backup that is only used during maintenance or
failures. Although 100 percent redundancy provides a slightly greater margin of safety,
protecting against the rare instance where peak demand coincides with a failure, it is also more
expensive, since the system must purchase two full-sized components, one of which might never
be needed at full capacity.
Although PTA towers do not typically "fail" like mechanical components can, they can require
periodic maintenance (e.g., for packing cleaning, rehabilitation or replacement). Thus,
operational redundancy is appropriate for towers, allowing the system to continue to operate
during maintenance periods. For PTA towers, 100 percent redundancy would be extreme, given
that unscheduled failure is unlikely.
The model also includes critical design assumptions to specify the number of redundant towers
for small systems (less than 1 million gallons per day design flow) and a redundancy frequency
(redundant towers per operating towers) for larger systems. Because PTA towers are out of
service only infrequently and the model default calculations provide operational redundancy, the
model assumes zero redundant towers for all system sizes.
9 The model uses a separate constraint for MTBE, allowing taller towers because of the difficulty in removing this
contaminant. The model assumes a maximum packing height of 13 meters (approximately 40 feet) for MTBE.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
Users desiring 100 percent redundancy can change the minimum number of towers to one and
increase the redundancy assumptions (or enter the number of redundant towers on the input
sheet) to provide the appropriate number of full-sized redundant units.
Air Pipe Length per Tower
The PTA model assumes 100 feet of air piping per tower to account for piping from the blowers
to the base of the towers. Like the pipe length assumptions documented in Exhibit 2-10, this
assumption is meant to incorporate additional length to account for the cost of fittings.
Chemical Usage Rates
The PTA process can require the use of chemicals to clean the system, prevent buildup of scale
within the system and/or prevent corrosion. The need for this depends on the quality of influent
water. As a default, the model assumes addition of sodium hexametaphosphate to the influent
water. Users can change the type of phosphate chemical used to tetrasodium polyphosphate or
remove the addition of phosphate chemicals on the critical design assumptions sheet. Acid
addition (sulfuric or hydrochloric acid) to influent water, with sodium hydroxide addition to
treated water to readjust pH, can also be used to prevent scaling, although natural carbon dioxide
removal by the PTA process might render this unnecessary. By default, the model does not
consider acid addition, although users can change this assumption on the critical design
assumptions sheet.
By default, the model assumes continuous chemical addition (or acid addition, if selected) by
specifying that chemicals are added 365 days per year. Intermittent, periodic addition might lead
to adding a high dosage at one time, which could have an adverse effect on the treatment system.
Users, however, can simulate intermittent chemical addition or cleaning by reducing the number
of days per year during which chemicals are added (and, likely, increasing the dosage rates).
The critical design assumptions sheet contains the following dosage rates and solution strengths
for phosphate chemicals: 5 milligrams/liter of 10 percent sodium hexametaphosphate or 4
percent tetrasodium polyphosphate. If acid and caustic addition are selected, the model calculates
acid addition to reduce pH from 7.5 to 5.5. Users can change these values on the critical design
assumptions sheet.
Bypass Percentage
Because PTA treatment can remove contaminants to very low levels, systems may choose to
treat only a portion of their production flow, using a smaller treatment system and blending
treated water with raw water while still achieving treatment targets. The bypass percentage is
that portion of production flow that goes untreated. If bypass is used, the model designs the
treatment system to treat a flow equal to (100 minus bypass percentage) multiplied by design
flow and adds bypass piping and associated valves to the components included on the output
sheet. The model assumes no bypass, but the user can incorporate bypass by entering a
percentage of bypass flow on the critical design assumptions sheet.
4.4 Tower Design Sheets
The WBS model for PTA adapts the engineering design approach developed in an earlier EPA
model for PTA, then applies the WBS-based unit cost methodology to the designs generated
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through this approach. The engineering design approach applied in the model uses an automated,
iterative process to calculate equipment requirements and operating parameters that achieve the
treatment goals selected by the user and meet design constraints consistent with GREPs. This
design process runs whenever the user clicks the "Generate Results" button on the input sheet.
Note that all other inputs must be complete before generating results. In order to maintain the
functionality of the automated design process, the tower design calculations span multiple sheets
(specifically, the Onda, tower design and design macros sheets).
The automated design process uses the user-defined parameters from the input sheet and the
boundary values from the critical design assumption sheet to select operating parameters and
determine the number and size of towers needed. The design of ancillary components (e.g.,
pipes, pumps, blowers, chemical storage, structures) is then calculated based on these operating
parameters and tower design.
Tower Design
The automated, iterative design process starts with two key assumptions: the minimum air-to-
water ratio possible for the contaminant (i.e., the air-to-water ratio below which removal percent
drops to zero) and a liquid loading rate of 25 gallons per minute per square foot. As necessary,
the iterative process then adjusts these two key parameters to meet the tower diameter and
packing height constraints specified on the critical design assumptions sheet. In addition, the
design process requires the following:
• Air-to-water ratio must be less than 350:1
• Air pressure gradient must be such that flooding conditions are avoided.
These two constraints are not adjustable by the user. The starting point and constraints on air-to-
water ratio are based on GREPs. Typical air-to-water ratios for counter-current airflow PTA
designs are in the 30:1 to 100:1 range (AWWA/ASCE, 1998). However, for contaminants such
as radon that are more volatile (i.e., have a large Henry's coefficient) lower air-to-water ratios
will be sufficient (e.g., 3:1 to 30:1 for radon). Conversely, contaminants that are less volatile
(i.e., with a smaller Henry's coefficient) will require higher air-to-water ratios, particularly to
obtain high removal efficiencies. The constraint on air pressure gradient is required for the PTA
system to operate. Air pressure gradient is calculated based on air-to-water ratio and liquid
loading.
In those rare cases where input parameters are such that the design process cannot find a design
meeting all the constraints, the model places a red warning notice at the top of the output sheet.
There are two possible warning notices:
• "Cannotfind design meeting constraints, please adjust input values " - this message
indicates that the design selected by the automated process does not meet all of the
constraints above. The user should change values in the Input sheet or relax the packing
height and tower diameter constraints on the Critical Design Assumptions sheet.
• "Realistic design constraints require overdesign. System as costed outperforms requested
percent removal - When this message is displayed, the design selected by the automated
process meets all of the constraints above. The user, however, should be aware that the
system as designed will achieve a greater removal efficiency than was requested on the
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Input sheet. The actual percent removal achieved by the system as designed is shown on
the output sheet.
If the design process is able to find a design that meets all the constraints, a dialog box will
appear indicating that the simulation (i.e., the iterated design process) ran successfully.
At completion, the automated design process selects the number of towers required and their
dimensions. Based on this design, the tower design sheet determines the quantity and/or size of
the following components:
• Tower shells
• Tower internals, including support plates, liquid distributors and liquid redistribution
rings
• Packing material.
The automated design process also determines values for the following key operating
parameters:
• Liquid loading and flow per tower
• Air loading, pressure gradient and flow
• Air-to-water ratio.
These operating parameters are used, along with the tower design, in the design of ancillary
equipment and the calculation of O&M costs.
Clean/veil Design
The tower design sheet also designs the clearwell used to collect treated water after aeration. The
length and width of the clearwell are selected based on the size of the PTA towers (i.e., clearwell
dimensions are such that it spans the base of all of the towers). Then, the tower design sheet
calculates the depth of the clearwell so that its volume is sufficient to provide the detention time
specified in the input sheet, plus freeboard. The sheet also calculates the total volume of concrete
required, along with excavation and backfill requirements.
4.5 Retrofit Sheet
When the user specifies a retrofit scenario on the input sheet and runs the model design process
by pressing "Generate Results," the retrofit sheet performs the calculations required to estimate
the cost associated with the system modifications needed to increase removal or remove a new
contaminant. This sheet interacts with the automated design routine to duplicate the tower design
calculations using the new removal requirements or contaminant characteristics, given the
physical constraints of the existing system (e.g., the retrofit design cannot modify the existing
tower diameter). This sheet then calculates the incremental requirements for the additional
capital and O&M cost items associated with the retrofit (as listed in Section 4.2).
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4.6 Chemical Use Sheet
As discussed in Section 4.3, the PTA model can design for the continuous or intermittent
addition of chemicals to clean the system, prevent buildup of scale within the system and/or
prevent corrosion. The chemical use sheet calculates the amounts of these chemicals needed per
day based on the dosage assumptions on the critical design assumptions sheet. This sheet also
calculates the number and size of storage tanks needed for these chemicals. The model assumes
separate day tanks, in addition to the primary bulk storage tanks, are required if daily usage of a
given chemical at design flow exceeds a number of gallons specified on the critical design
assumptions sheet. The model includes mixers for both the bulk storage and day tanks (if
included) to maintain the uniformity of each chemical solution. This sheet calculates the number
and size of these mixers. The chemical use sheet also calculates the number and size (in terms of
flow capacity) of the chemical metering pumps. As discussed in Section 2.3, the sizing of all
pumps incorporates a safety factor, which is specified on the critical design assumptions sheet.
4.7 Off-Gas Sheet
Based upon the user inputs, the PTA model determines the type of off-gas treatment, if any, to
include in the system design and cost. The off-gas sheet uses the design flow, influent
concentration and removal requirements to determine the amount of contaminant released in the
air stream each day. The sheet uses this contaminant treatment requirement along with the rate of
air flow from the towers to determine the design requirements for off-gas treatment. For
treatment using GAC, this sheet calculates the bed-size and number of gas-phase GAC adsorbers
and determines the media requirements (including replacement media and spent media
transportation and disposal) to operate the adsorbers. For thermal and catalytic oxidizers, it
calculates the number of units needed and the natural gas and energy required to operate them.
4.8 Pumps, Pipe and Structure Sheet
Other elements of the technology for which the size and cost need to be determined include
pumps, blowers and piping. The pumps, pipe and structure sheet performs the required
calculations to determine the number and size (in terms of flow capacity) of the booster pumps,
based on the system design flow. It determines the number and size of the blowers based on the
design air flow calculated on the tower design sheet. As discussed in Section 2.3, the sizing of all
pumps incorporates a safety factor, which is specified on the critical design assumptions sheet.
This sheet also performs calculations for the following pipes:
• Influent and effluent piping
• Process piping
• Air piping
• Bypass piping (if a bypass percentage is specified)
• Acid piping and sodium hydroxide piping (if acid addition is selected)
• Sodium hexametaphosphate or tetrasodium polyphosphate piping.
The size (diameter) of the water and chemical pipes is determined using a lookup pipe flow chart
that is one of the ancillary model components. The pipe diameter selected in the WBS model
assumes a reasonable head loss and flow velocity, as documented in Exhibit 2-8. These design
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assumptions may result in some over sizing of pipes, which means the costs for pipes may be
conservative (i.e., err on the high side).
The flow used to determine influent and effluent pipe size is the design peak flow. The diameter
of interconnecting process pipes uses the same pipe flow chart, after splitting the inflow by the
number of towers. The diameter of the various chemical distribution pipes is determined
following the same approach. Air pipe size is assumed equal to the process pipe size. With two
exceptions, the length of these pipes is determined using the assumptions documented in Exhibit
2-10, which are designed to account for the cost of fittings. The first exception is that process
piping incorporates additional length beyond that specified in Exhibit 2-10 to account for the
height of the towers. The second exception is that air pipe length is calculated directly from the
number of towers and a default assumption contained on the critical design assumptions sheet
(see Section 4.3).
This sheet also calculates the housing area for this technology based on the footprint of the
technology components and the spacing criteria specified on the critical design assumptions
sheet. The space requirements for pumps, blowers, tanks and service space are based on
manufacturer specification, "to scale" drawings and the experience of engineers. The amount of
additional concrete needed to support heavy equipment, such as pumps and blowers, is
calculated using the footprint of the equipment. The model assumes a single building containing
pumps, chemical storage and office space. Towers and blowers are located outside the building.
4.9 Instrumentation and Control Sheet
The instrumentation and control sheet calculates requirements for valves, instrumentation (e.g.,
flow meters) and automated system controls. The number of valves and instruments is based on
the number of process components (e.g., number of treatment lines) and assumptions from the
critical design assumptions sheet (e.g., number of valves per treatment line). The assumptions
correspond to the general schematic layout for this technology shown in Exhibit 4-1. Sizing of
valves corresponds to the size of the appropriate pipe determined on the pumps, pipe and
structure sheet. Appendix A describes the method used in the WBS models to estimate the
number and type of system control components.
4.10 O&M and HVAC Sheets
The model's O&M and heating, ventilating and air conditioning (HVAC) calculations cover two
sheets: the O&M sheet (annual labor, materials and energy usage) and the HVAC sheet (HVAC
capacity requirements). The O&M sheet derives O&M requirements based on the engineering
design, O&M critical design assumptions and input values. The HVAC sheet determines the
capacity of the heating and/or cooling systems to be included on the output sheet. Together, the
two sheets determine the following O&M requirements based on the approach outlined in
Section 2.4 and Appendix E:
• Operator labor for system operation and maintenance
• Managerial and clerical labor
• Booster pump maintenance materials and operating energy
• Facility maintenance materials
• Energy for building lighting and HVAC.
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In addition, the O&M sheet adds the following technology-specific O&M requirements10:
• Operator labor and materials for blower maintenance
• Operating energy for blowers
• Materials for clearwell maintenance
• Materials for tower maintenance.
The model calculates labor and materials for blowers using an approach identical to that for
pumps described in Appendix E. Blower energy is calculated based on average daily operating
air flow. Materials for clearwell maintenance use the same assumptions specified for pumps.
Materials for tower maintenance assume an annual cost equal to 4 percent of the pre-installation
capital cost of the towers, including internals and packing. Users can change these percentage
assumptions on the critical design assumptions sheet.
4.11 Indirect Sheet
As stated in Section 2.4, indirect capital costs are costs that are not directly related to the
treatment technology used or the amount or quality of the finished water, but that are associated
with the construction and installation of a treatment technology and water intake structures. The
indirect sheet derives capital costs for the following components of indirect costs:
• Construction management and general contractor overhead
• Standby power
• Geotechnical
• Site work
• Yard piping.
Appendix D contains detailed information on the derivation of these and other indirect costs.
This sheet also contains calculations to estimate permit costs.
4.12 Output Sheet
The output sheet contains the list of components identified for PTA based on the WBS approach.
For each component, the output sheet provides information on size (e.g., tank capacity or pipe
diameter) and quantity, as well as estimated capital cost and estimated useful life. The output
sheet also contains cost estimates for indirect costs (e.g., mobilization and demobilization, site
work and yard piping), add-on costs (for permitting, pilot testing and land) and O&M costs.
These estimates are described generally in Section 2.4 and in more detail in Appendix D (indirect
costs) and Appendix E (O&M costs). Finally, the output sheet combines the total capital cost,
system useful life and annual O&M cost to estimate total annualized cost, as discussed in Section
2.4. Sections 2.1 and 2.3 provide further details about the output sheet.
4.13 Ancillary and Reference Model Components
The model contains several ancillary sheets: index, standard inputs, cost equations, cost
coefficients, cost data, engineering data and lookup tables. The index is a hyperlinked list of
10 Note that the chemical use sheet calculates annual chemical usage and the off-gas sheet calculates O&M
requirements associated with off-gas control technologies.
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user-adjustable inputs and assumptions that can assist the user in finding these inputs and
assumptions, should they wish to change them. The standard inputs worksheet documents the
inputs used by EPA in its standard designs. Advanced users can adjust these standard inputs, if
desired. The cost equations and cost coefficients sheets use the component-level cost curve
equations to generate unit costs on an item-by-item basis. The cost data and engineering data
sheets contain component cost and engineering reference data extracted from the central cost
database. The lookup tables sheet is for internal model use in populating the drop-down boxes on
the model input sheet.
The PTA model also includes two reference sheets: Henry's reference and air and packing
reference. As discussed in Section 4.2, the user may refer to the information in these reference
sheets in determining how to adjust inputs.
4.14 List of Abbreviations and Symbols in this Chapter
atm*m3/m3 atmospheres * cubic meters (of water) per cubic meters (of air)
C Centigrade
EPA U.S. Environmental Protection Agency
GAC granular activated carbon
GREPs generally recommended engineering practices
HVAC heating, ventilation and air conditioning
K Kelvin
Ibs/day pounds per day
MTBE methyl tertiary-butyl ether
O&M operating and maintenance
pCi/L picocuries per liter
PTA packed tower aeration
|ig/L micrograms per liter
VOC volatile organic compound
WBS work breakdown structure
4.15 References
American Water Works Association and American Society of Civil Engineers (AWWA/ASCE).
1998. Water Treatment Plant Design. Third Edition. New York: McGraw-Hill.
Fischer, A., M. Miiller and J. Klasmeier. 2004. "Determination of Henry's law constant for
methyl tert-butyl ether (MTBE) at groundwater temperatures." Chemosphere, Vol. 54, No. 6,
pages 689-694.
Hess, A.F., I.E. Dyksen and HJ. Dunn. 1983. "Control Strategy - Aeration Treatment
Technique." Occurrence and Removal of Volatile Organic Chemicals From Drinking Water.
American Water Works Association Research Foundation, Denver, Colorado.
Millet, Paul C. 1993. Design Considerations for VOC Removal. Cambridge: SEA Consultants,
Inc.
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Sander, R. 1999. Compilation of Henry's Law Constants for Inorganic and Organic Species of
Potential Importance in Environmental Chemistry (Version 3). Germany: Max-Planck Institute
of Chemistry.
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5. Multi-Stage Bubble Aeration Model
Multi-stage bubble aeration (MSBA) is usually employed in drinking water treatment systems to
remove volatile organic compounds (VOCs) or radon gas from source water and to improve the
taste and odor of the water. This technology is more often used to treat groundwater sources, as
VOCs in surface water systems can diffuse naturally into the air in the course of treatment,
storage and delivery without further treatment. In MSBA, volatile compounds are stripped from
water by injecting bubbles of air into a volume of contaminated water. This, in effect, increases
the surface area of water exposed to air and allows for the diffusion of VOCs out of the water.
The work breakdown structure (WBS) model for MSBA model includes standard designs for the
treatment of a number of contaminants, including radon and various VOCs. However, the model
can be used to estimate the cost of MSBA treatment for the removal of other volatile
contaminants as well. Users wishing to simulate the use of MSBA for treatment of other
contaminants will need to adjust default inputs (e.g., air-to-water ratio, number of stages) and,
potentially, critical design assumptions (e.g., maximum air surface intensity). This chapter
includes discussion of inputs and assumptions that might require adjustment and these values are
highlighted in gold in the model.
5.1 Overview of the MSBA Treatment Process
The MSBA treatment process includes the following components:
• Aeration basins that contain baffles and diffusers for injecting the air bubbles
• Blowers for delivering the air to the diffusers
• Booster pumps for pumping treated water out of the aeration basin (or subsequent
clearwell)
• Associated piping, valves and instrumentation.
In MSBA, contaminated water is pumped from the water source (a well) to shallow basins for
aeration. The basins are typically constructed of concrete (AWWA/ASCE, 1998), although
vendors supply basins constructed of other materials such as stainless steel and plastic (Lowry
Systems, 2013; Aeromix, 1999). To increase gas exchange, the basins are shallower than in
typical single-tank diffusion aerators and are subdivided into smaller compartments, or "stages,"
using baffles. Inside each stage, perforated pipes or porous plates known as diffusers release
small bubbles that rise through the water column, causing turbulence and allowing for the
exchange of volatile compounds. As the bubbles pass through the water, volatile contaminants
pass from the liquid to gaseous phase, leaving the water "stripped" of VOCs. Once stripped from
the water, contaminants pass freely into the atmosphere. A blower located outside of the storage
tank provides air to the system.
Many MSBA systems include a clearwell to collect treated water after aeration; other systems
(particularly pre-engineered packages) pump directly from the aeration basins into distribution or
subsequent treatment. To account for the cost of a clearwell, EPA has developed a separate WBS
model that generates costs for this component. In generating national costs, EPA would add costs
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from the separate clearwell model to costs from the MSBA model for scenarios that incorporate
clearwells.
Aeration technologies, including MSBA, will remove other volatile compounds in addition to the
target contaminant. Design of these systems, particularly selection of air-to-water ratio (see
below), should consider the removal of these other volatiles and of co-occurring target
contaminants. Typically, the compound that is most difficult to remove will control selection of
design parameters. For example, systems with co-occurring trichloroethylene (TCE) and
tetrachloroethylene (PCE) should be designed based on removal of TCE. Also, all aeration
systems remove carbon dioxide along with the target contaminants. This can reduce the
corrosivity of the treated water, with useful side benefits (e.g., compliance with the lead and
copper rule). Although the standard designs in the MSBA model do not explicitly consider
carbon dioxide removal, users should be aware that consideration of this impact on treated water
pH can reduce or eliminate the need for post-treatment corrosion control.
Exhibit 5-1 provides a schematic drawing for MSBA.
Exhibit 5-1. Typical Schematic Layout for MSBA
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WBS-Based Cost Models for Drinking Water Treatment Technologies
5.2 Input Sheet
The input sheet accepts the user-defined design parameters that determine fundamental process
requirements. The user can indicate system size and select basic equipment characteristics such
as air-to-water ratio and number of stages. Key design considerations that the user identifies on
this sheet are described in greater detail below and include the following:
• Contaminant
• Design and average flow (see Section 2.3 and below)
• Design type (pre-engineered package or custom design)
• Number of operating basins
• Air-to-water ratio
• Maximum water depth
• Number of stages
• Pilot rate constant and air intensity (optional)
• Off-gas treatment
• Number of booster pumps (optional)
• Number of blowers (optional)
• Number of redundant basins (optional)
• Component level (optional, see Section 2.3)
• System automation (optional, see Section 2.3).
Contaminant
The WBS model for MSBS includes a "drop-down" list box that allows the user to select the
contaminant being treated. This drop-down box is located at the top of the input sheet, above the
standard design buttons. The user should verify that the selection shown in this box is correct
before populating the other design input values. The user can change the contaminant modeled
by picking a different selection from the list. After doing so, the user should then repopulate the
input sheet with values appropriate for the new contaminant by clicking one of the standard
design buttons or manually adjusting inputs and clicking the "Generate Results" button (see
Section 2.3 for further discussion of each of these methods).
Currently, the model includes standard designs for the treatment of radon and various VOCs. The
model, however, can be used to design MSB A systems for the removal of other contaminants,
such as other VOCs or carbon dioxide, by selecting the "other" option from the contaminant
drop-down menu. To use the model for other contaminants, the user would manually enter the
removal-related inputs (e.g., air-to water ratio, number of stages) to reflect what is applicable for
the targeted contaminant.
Design and Average Flow
MSBA technology is known to be available from vendors in pre-engineered package units in
sizes as large as 2,000 gallons per minute, which is approximately 1.44 million gallons per day
(MGD) (Lowry Systems, 2013). According to peer review comments, these modular pre-
manufactured systems are treating up to 5 MGD in carbon dioxide applications by using multiple
modular basins in parallel. Designs for radon are likely to go much larger in size due to the ease
of stripping of this contaminant. Therefore, for radon, the MSBA model includes designs for all
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eight standard flow sizes shown in Exhibit 2-6. For VOCs, the model only includes standard
designs up to 1 MOD because many of these contaminants are more difficult to strip than radon
and information on the use of this technology for these contaminants in larger systems is limited.
Design Type
As discussed above, MSBA systems are available as pre-engineered vendor packages or as
custom designed systems. The input sheet includes a drop-down menu to choose between these
two design approaches. Pre-engineered packages use aboveground stainless steel, fiberglass or
plastic aeration basins. The model assumes that custom design systems will use in-ground
concrete basins. Larger systems applying this technology likely would use custom-designed
MSBA systems for their applications, rather than package units, although the point at which
custom-designed concrete basins become more cost-effective depends on site-specific removal
requirements (e.g., air-to-water ratio). For example, according to peer review comments, package
systems could be used for radon up to 8 to 10 MGD, if removal requirements are low (air-to-
water ratio of 3 to 5).
The model costs package systems by costing all individual equipment line items (e.g., basins,
blowers, instrumentation and system controls) in the same manner as custom-engineered
systems. This approach is based on vendor practices of partially engineering these types of
package plants for specific systems (e.g., selecting basin and blower size to meet flow and
treatment criteria). The model standard designs assume the use of pre-engineered packages up to
1MGD.
Number of Operating Basins
As discussed in Section 5.3, MSBA basins are limited in length by practical constraints to 12 feet
for package basins or 60 feet for in-ground concrete basins. Beyond this length, systems will use
multiple basins in parallel. The input sheet requires that the user enter the number of operating
basins and will provide warnings if the calculated basin length exceeds the practical constraints.
If the calculated basin length exceeds the applicable constraint, the user can increase the number
of basins, decrease air-to-water ratio, decrease number of stages or increase water depth.
However, adjustments to inputs other than to the number of basins can change removal
efficiency.
Optimize Number of Basins
To aid users, the model includes a button labeled "Optimize Number of Basins." This button
activates a computer-aided design routine that automatically selects the minimum number of
basins needed to satisfy the maximum length constraints, while maintaining the current values
for all other inputs. Using this design routine can reduce trial and error by users, particularly for
systems with design flows other than the standard sizes provided on the input sheet. Note that all
other inputs should be complete before using the basin optimization routine. For standard
designs, EPA used the basin optimization routine to select the minimum number of basins
required to remain within the length constraints.
Air-to-Water Ratio
The air-to-water ratio of the aerator is a measure of the volume of air passing through the system
per volume of water. In general, higher air-to-water ratios increase contaminant removal
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efficiency. Other factors that substantially affect contaminant removal efficiency include depth
of bubble rise (water depth, discussed below), number of stages (discussed below), bubble size
and water temperature. Air-to-water ratios between 11:1 and 30:1 can achieve 99 percent
removal efficiencies for radon gas (Drago, 2000). Peer reviewers recommended the following
ranges of air-to-water ratio for several contaminants, depending on removal required:
• For radon, 3:1 to 30:1 to cover removal rates from 70 to 99.9 percent
• For TCE, 20:1 (90 percent) to 80:1 (99.9 percent)
• For PCE, 15:1 (90 percent) to 60:1 (99.9 percent).
The standard designs in the WBS model assume air-to-water ratios consistent with very high
required removal rates. For example, they assume 20:1 for radon. Standard design assumptions
for VOCs are under development; values used in the model are based on preliminary results from
EPA pilot studies.
Maximum Water Depth
Maximum water depth is the depth of water in the basin when the system is operating at design
flow. It is a critical input for determining the size of the aeration basin; the WBS model uses this
value, along with freeboard (discussed in Section 5.3), to determine the overall height of the
basin. Depth also is a determining factor in the ultimate removal rate achieved and is critical in
determining blower energy requirements. According to peer reviewers, it is good practice to keep
depth to the minimum required for removal. Increasing depth beyond this minimum does almost
nothing for removal (bubbles are nearly saturated as they rise to the surface) and will
dramatically increase the power required by the blower. Based on reviewer recommendations,
the model standard designs assume 3 feet of water depth for all contaminants.
Number of Stages
Aeration basins for MSB A contain baffles that break the basin into a series of stages. The
number of stages affects design calculations for the number and size of the baffles. The number
of stages also works with the air-to-water ratio to determine contaminant removal efficiency.
While increasing the number of stages can increase the removal efficiency, a basin cannot
accommodate an unlimited number of stages. Each individual stage must be large enough to
accommodate the diffusers and piping necessary for providing air into the stage. Furthermore,
according to peer reviewers, there is little increase in removal beyond a certain number of stages
(eight for radon, twelve for VOCs). Based on peer review comments, the model standard designs
use six stages for radon and eight for VOCs.
Pilot Rate Constant and Air Intensity
The following theoretical relationship describes contaminant removal by MSBA:
Ce/Co = (1 + k * t)"1
where:
Ce = contaminant concentration in treated water
Co = contaminant concentration in influent water
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t = contact time of a single stage (in minutes)
n = number of stages
k = rate constant (in 1/minutes)
Furthermore, the rate constant (k) is, theoretically, directly proportional to air intensity
(measured in cubic feet of air per minute per cubic foot of water). When pilot studies are used to
determine the rate constant, the resulting data can be converted to a rate constant for full-scale
systems using the following relationship11:
kfcll-scale = ( (|>fiill-scale / ^pilot ) * kpiiot
where:
(() = air intensity in cubic feet of air per minute per cubic foot of water.
The WBS model provides optional inputs for pilot study results for rate constant and air
intensity. When the user provides these inputs, the model uses the theoretical relationships
discussed above to generate an estimate of removal efficiency for the current design. Users can
then vary their inputs (e.g., for air-to-water ratio) to see the theoretical impact on removal
efficiency. Users should be aware that the removal efficiency shown in the model is only an
estimate. Actual removal can vary, for example, if conditions (e.g., temperature) or design
factors (e.g., bubble size) differ from those used in the pilot study.
Off-Gas Treatment
For contaminants other than radon, the input sheet requires the user to specify influent water
concentration and estimated percent removal.12 These two inputs are used only to determine
whether off-gas treatment might be required; the model does not use them in system design. The
input sheet also requires the level of VOC releases (in pounds per day [Ibs/day]) at which an air
pollution control system might be needed. Based on these three input values, the input sheet
warns the user when an air pollution system might be required. The level at which off-gas
treatment is needed is likely to vary based on local air pollution control requirements, but, as a
default, the model standard designs use 1 Ib/day for this limit. The limit used is the maximum
emission level for all VOCs for California's South Coast Air Quality Management District. For
radon, the off-gas control technology options available in the model are not appropriate (would
not be effective). Therefore, the off-gas control system inputs are disabled for radon.
If off-gas treatment is needed, the model provides three treatment options for the design of the
air pollution control system: granular activated carbon (GAC), thermal oxidation and catalytic
oxidation. If the GAC option is chosen, the model requires the user to specify whether the GAC
will be regenerated or used on a throwaway basis and also gives the user the option of entering
the expected bed-life of the media. For thermal and catalytic oxidation, the model requires the
11 Based on data from batch and pilot studies, Drago (2000) provides the following alternate relationship for
determining the rate constant specifically for radon: k = 36.9 * c|>080. When radon is the target contaminant, the
model uses this formula in place of the user input for pilot rate constant and air intensity to generate the estimated
removal percentage.
12 If the user provides pilot study data for rate constant and air intensity, the model uses the resulting theoretical
percent removal estimate; separate user input for percent removal is not required in the off-gas section of the input
sheet.
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user to choose if heat recovery will be utilized (either recuperative or regenerative). The model
standard designs for VOCs do not include off-gas treatment because none of the designs generate
estimated off-gas levels that exceed the 1 Ib/day limit.
Number of Booster Pumps and Blowers
These two optional inputs allow the user to enter the number of pumps and blowers required to
operate the treatment system. If the user leaves these optional inputs blank, the model calculates
the number of pumps and blowers using default methods. The default method for pumps
attempts to minimize the number of pumps, while still accommodating variations in flow and
providing redundancy to account for possible equipment failure. The default for blowers assumes
a minimum of one blower per basin plus one redundant blower, consistent with vendor designs.
The model will include multiple blowers per basin if required to provide sufficient air-to-water
ratio. If the user enters zero for the number of booster pumps, the model excludes booster pumps
from the design and cost estimate. Entering zero can be used, for example, to simulate a situation
where existing pumps are sufficient to operate the MSBA system. Blowers cannot be excluded
from the model designs. The model standard designs leave these inputs blank, accepting the
default calculations.
Number of Redundant Basins
The input sheet allows the user to specify the number of redundant basins. If the user leaves this
optional input blank, the model adds the number of redundant basins specified on the critical
design assumptions sheet. According to EPA's Technology Design Panel, basins are not
considered for redundancy and peer reviewers commented that redundant basins are very rarely
used with this technology, when employed for drinking water treatment. Therefore, the default
critical design assumption is zero redundant basins. The model standard designs leave this input
blank, accepting the default of zero redundant basins.
5.3 Model Assumptions Sheets
There are four sheets that contain assumptions needed to facilitate process design: the critical
design assumptions sheet, the O&M assumptions sheet, the indirect assumptions sheet and the
off-gas assumptions sheet. These sheets contain a variety of structural and chemical engineering
parameters used in the engineering design sheets.
There are more than 100 critical design assumptions in the model that cover process, O&M and
indirect cost parameters. Key critical design assumptions include freeboard, maximum basin
length, maximum air surface loading intensity, minimum basin length-to-width ratio, quiescent
chamber length, access space for diffusers, pump and blower head (operating pressure) and
bypass percentage. The following sections provide descriptions and default values for these
assumptions. Any assumption value can be modified, as needed.
Freeboard
The WBS model adds freeboard to the user input for maximum water depth in determining the
overall depth of the basin. Freeboard typically should be 1 to 3 feet (AWWA/ASCE, 1998). The
model assumes a freeboard of 2 feet.
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Maximum Basin Length
In theory, basin length is not an important parameter in MSBA basin design. Basin length can be
selected based on space available at the site, as long as the length is sufficient to accommodate
the required number of stages with diffusers and piping and the basin provides sufficient surface
area (see maximum air surface loading intensity, below). From a practical standpoint, there are
constraints on basin length. Pre-engineered plastic, fiberglass or stainless steel basins are
available in specific lengths, with the largest being 12 feet long. Vendors have designed in-
ground concrete basins up to 60 feet in length. Therefore, the WBS model assumes the maximum
reasonable length of MSBA basins is 12 feet for package systems and 60 feet for custom-
designed systems.
Maximum Air Surface Intensity
Air surface intensity is the flow of air into the basin in cubic feet per minute per square foot
(cfm/ft2) of basin surface area. Air surface intensity determines the amount of swell that occurs
within the confined area of the basin. Although swell is also a function of bubble size, vendors
generally apply a limit on air surface intensity that can be a key factor in determining the
required surface area of the basin and, therefore, determines the number of basins needed. The
WBS model uses this maximum air surface intensity, along with length-to-width ratio and
diffuser space requirements (see below), to size the MSBA basins. Based on peer reviewer
recommendations, the model assumes a maximum air surface intensity of 16.5 cfm/ft .
Minimum Length-to-Width Ratio
MSBA basins are longer than they are wide. Therefore, in sizing basins, the model assumes a
minimum length-to-width ratio of 1.5:1.
Quiescent Chamber Length
MSBA vendors include an extra stage, called a quiescent chamber, at the end of each basin that
does not receive air. The WBS model calculates the length of the quiescent chamber by assuming
its length is a proportion of the length of an individual stage. Based on review of vendor
schematics, this chamber typically is approximately one half the length of an individual stage.
Therefore, this assumption is set to 0.5.
Access Space for Diffusers
As discussed above, the contact basins and individual stages in an MSBA system must be large
enough to accommodate the diffusers and piping necessary for providing air into the system. The
model calculates the space required based on the actual size (diameter and length) of the
diffusers selected by the model. The model assumes additional spacing of 1 inch is required in
each dimension for access and water flow.
Pump Head
The MSBA model includes booster pumps for pumping treated water out of the aeration basins
(or a subsequent clearwell). The head (or operating pressure) of these pumps, along with flow,
determines the energy requirements for operating the pumps. Because the MSBA basins break
the pressure head created by source water pumps, high-lift pumps often are required to
repressurize the treated water for distribution. Therefore, the MSBA model uses higher pressure
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booster pumps than the WBS models for many other (pressurized) technologies. The model
assumes a booster pump head of 75 pounds per square inch (psi), consistent with a typical
distribution system requirement of 60 to 90 psi. Although users can adjust this assumption,
thereby changing energy requirements, they should be aware that the pump capital costs in the
MSBA model are for these high-lift pumps, not the lower pressure booster pumps used in some
other models. Decreasing the pump head assumption will not change these capital costs.
Additional Blower Head above Water Depth
The head (or operating pressure) of the blowers used to introduce air into the MSBA basins (in
conjunction with flow) determines the energy requirements for operating the blowers. The model
assumes the blower head required is equal to the water depth, plus a design assumption to
account for blower, filter and piping losses. The default value is 10 inches.
Bypass Percentage
Systems may choose to treat only a portion of their production flow, using a smaller treatment
system and blending treated water with raw water to achieve treatment targets. The bypass
percentage is that portion of production flow that goes untreated. If bypass is used, the treatment
system is designed to treat a flow equal to (100 minus bypass percentage) multiplied by design
flow and adds bypass piping and associated valves to the components included on the output
sheet. The model assumes no bypass, but the user can incorporate bypass by entering a
percentage of bypass flow on the critical design assumptions sheet.
5.4 Basin Constraints Sheet
The basin constraints sheet contains calculations that draw upon the user-defined parameters
from the input sheet and the boundary values from the critical design assumption sheet to
determine the dimensions of the aeration basins, the size and number of baffles within the basins
and the number and size of diffusers. The sheet determines basin dimensions (length and width)
based on the space required for diffusers, the minimum surface area required (based on
maximum air surface intensity) and the minimum length-to-width ratio. For in-ground concrete
basins used in custom designed systems, this sheet also calculates the total volume of concrete
required and, because the basins are constructed below grade, determines excavation and backfill
requirements.
5.5 Off-Gas Sheet
Based upon the user inputs, the MSBA model determines the type of off-gas treatment, if any, to
include in the system design and cost. The off-gas treatment sheet uses the design flow, influent
concentration and removal requirements to determine the amount of contaminant released in the
air stream each day. The sheet uses this contaminant treatment requirement along with the rate of
air flow from the columns to determine the design requirements for off-gas treatment. For
treatment using GAC, this sheet calculates the bed-size and number of gas-phase GAC adsorbers
and determines the media requirements (including replacement media and spent media
transportation and disposal) to operate the adsorbers. For thermal and catalytic oxidizers, this
sheet calculates the number of units needed and the natural gas and energy required to operate
them.
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5.6 Pumps, Pipe and Structure Sheet
Other elements of this technology for which the size and cost need to be determined include
pumps, blowers and piping. The pumps, pipe and structure sheet performs the required
calculations to determine the number and size (in terms of flow capacity) of the booster pumps
based on the system design flow. It determines the number and size of the blowers based on the
design air flow, which is determined by multiplying system design flow by the air-to-water ratio
and converting to cubic feet per minute. As discussed in Section 2.3, the sizing of all pumps
incorporates a safety factor, which is specified on the critical design assumptions sheet. Blower
design also incorporates a safety factor of 25 percent, which is specified on the critical design
assumptions sheet.
This sheet also performs calculations for the following pipes:
• Influent and effluent piping
• Process piping
• Air piping
• Bypass piping (if a bypass percentage is specified).
The size (diameter) of the water and chemical pipes is determined using a lookup pipe flow chart
that is part of the WBS cost database. The pipe diameter selection method assumes a reasonable
head loss and flow velocity, as documented in Exhibit 2-8. These design assumptions may result
in some over sizing of pipes, which means the costs for pipes may be conservative (i.e., err on
the high side).
The flow used to determine influent and effluent pipe size is the design or peak flow. The
diameter of interconnecting process pipes uses the same pipe flow chart, after splitting the inflow
by the number of columns. Air pipe size is assumed equal to the process pipe size. With one
exception (air piping), the length of these pipes is determined using the assumptions documented
in Exhibit 2-10, which are designed to account for the cost of fittings. The length of external air
piping between the blowers and the basins is calculated as one times the overall system layout
length (a value that can be changed on the critical design assumptions sheet). Like the pipe
length assumptions documented in Exhibit 2-10, this assumption is meant to incorporate
additional length to account for the cost of fittings. To this external piping, the model adds air
piping internal to the basins, based on the basin dimensions and the number of diffusers.
This sheet also calculates the housing area for this technology based on the footprint of the
technology components and the spacing criteria specified on the critical design assumptions
sheet. The space requirements for basins, pumps and tanks and service space are based on
manufacturer specification, "to scale" drawings and the experience of engineers. The amount of
additional concrete needed to support heavy equipment, such as pumps and blowers, is
calculated using the footprint of the equipment.
For smaller space requirements (less than the square footage specified on the critical design
assumptions sheet), the model assumes a single building containing all process equipment. For
larger requirements, the model assumes two buildings: first one contains an aeration basins and
the second one contains pumps and blowers. The number of buildings affects the total land
required and energy costs for heating, ventilating and cooling.
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5.7 Instrumentation and Control Sheet
The instrumentation and control sheet calculates requirements for valves, instrumentation (e.g.,
flow meters) and automated system controls. The number of valves and instruments is based on
the number of process components (e.g., number of treatment lines) and assumptions from the
critical design assumptions sheet (e.g., number of valves per treatment line). The assumptions
correspond to the general schematic layout for this technology, shown in Exhibit 5-1. Sizing of
valves corresponds to the size of the appropriate pipe determined on the pumps, pipe and
structure sheet. Appendix A describes the method used in the WBS models to estimate the
number and type of system control components.
5.8 O&M and HVAC Sheets
The model's O&M and heating, ventilating and air conditioning (HVAC) calculations cover two
sheets: the O&M sheet (annual labor, materials and energy usage) and the HVAC sheet (HVAC
capacity requirements). The O&M sheet derives O&M requirements for MSBA treatment based
on the engineering design, O&M critical design assumptions and input values. The HVAC sheet
determines the capacity of the heating and/or cooling systems to be included on the output sheet.
Together, the two sheets determine the following O&M requirements based on the approach
outlined in Section 2.4 and Appendix E:
• Operator labor for system operation and maintenance
• Managerial and clerical labor
• Booster pump maintenance materials and operating energy
• Facility maintenance materials
• Energy for building lighting and HVAC.
In addition, the O&M sheet adds the following technology-specific O&M requirements13:
• Operator labor and materials for blower maintenance
• Operating energy for blowers.
The model calculates labor and materials for blowers using an approach identical to that for
pumps described in Appendix E. Blower energy is calculated based on average daily operating
air flow.
5.9 Indirect Sheet
As stated in Section 2.4, indirect capital costs are costs that are not directly related to the
treatment technology used or the amount or quality of the finished water, but are associated with
the construction and installation of a treatment technology and water intake structures. The
indirect sheet derives capital costs for the following components of indirect costs:
• Construction management and general contractor overhead
• Standby power
• Geotechnical
13 Note that the off-gas sheet calculates O&M requirements associated with off-gas control technologies.
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• Site work
• Yard piping.
Appendix D contains detailed information on the derivation of these and other indirect costs.
This sheet also contains calculations to estimate permit costs.
5.10 Output Sheet
The output sheet contains the list of components identified for MSBA based on the WBS
approach. For each component, the output sheet provides information on size (e.g., tank capacity
or pipe diameter) and quantity, as well as estimated capital cost and estimated useful life. The
output sheet also contains cost estimates for indirect costs (e.g., mobilization and demobilization,
site work and yard piping), add-on costs (for permitting, pilot testing and land) and O&M costs.
These estimates are described generally in Section 2.4 and in more detail in Appendix D (indirect
costs) and Appendix E (O&M costs). Finally, the output sheet combines the total capital cost,
system useful life and annual O&M cost to estimate total annualized cost, as discussed in Section
2.4. Sections 2.1 and 2.3 provide further details about the output sheet.
5.11 Ancillary Model Components
The model contains several ancillary sheets: index, standard inputs, cost equations, cost
coefficients, cost data, engineering data and lookup tables. The index is a hyperlinked list of
user-adjustable inputs and assumptions that can assist the user in finding these inputs and
assumptions, should they wish to change them. The standard inputs worksheet documents the
inputs used by EPA in its standard designs. Advanced users can adjust these standard inputs, if
desired. The cost equations and cost coefficients sheets use the component-level cost curve
equations to generate unit costs on an item-by-item basis. The cost data and engineering data
sheets contain component cost and engineering reference data extracted from the central cost
database. The lookup tables sheet is for internal model use in populating the drop-down boxes on
the model input sheet.
5.12 List of Abbreviations and Symbols in this Chapter
r\
cfm/ft cubic feet per minute per square foot
EPA U.S. Environmental Protection Agency
GAC granular activated carbon
HVAC heating, ventilating and air conditioning
Ibs/day pounds per day
MGD million gallons per day
MSBA multi-stage bubble aeration
O&M operating and maintenance
PCE tetrachloroethylene
psi pounds per square inch
TCE trichloroethylene
VOC volatile organic compound
WBS work breakdown structure
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5.13 References
Aeromix. 1999. BREEZE™Low Profile Mass Transfer System. Company Brochure.
American Water Works Association and American Society of Civil Engineers (AWWA/ASCE).
1998. Water Treatment Plant Design. Third Edition. New York: McGraw-Hill.
Drago, Joseph A. 2000. Radon Removal Technologies for Small Communities. San Francisco:
Kennedy/Jenks Consultants.
Lowry Systems. 2013. Air Strippers. Online at http://www.lowryh2o.com/AirStrippers.html
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Appendix A. Valves, Instrumentation and System Controls
A.1 Valves in the WBS Models
There are many types of valves used to control water and chemical flow rates, pressure and
direction in a water treatment plant. Valves can be distinguished by function, mode of operation,
materials of construction, size (i.e., diameter), design or shape and connection method. For
purposes of estimating valve costs, the most important of these distinctions are function, mode of
operation, size and materials of construction. Therefore, the work breakdown structure (WBS)
models group valves according to these four distinctions. The WBS models identify valve size
explicitly, using the same methodology used to size pipes. The WBS models also explicitly
identify materials of construction. The output sheet of each model includes line item costs for
valves of each material (plastic, stainless steel and cast iron), so that the user can observe
variations in cost among materials.
To distinguish by function and mode of operation, the WBS models use a generic nomenclature.
The WBS models identify valves as one of the following:
• Check valves
• Manual valves
• Motor/air-operated valves.
Check valves are those that serve the function of backflow prevention. They generally do not
vary significantly in mode of operation or design/shape.
The other two categories of valves serve the function of flow control and are distinguished by
their mode of operation (i.e., whether they are manual or automated). An example of a valve that
must be a manual valve is an emergency shut-off valve that, in an extreme event such as
complete power failure, can be shut off by an operator. Manual valves can vary in design
according to their specific opening/closing method (e.g., hand wheel or chain). Automated valves
(identified in the WBS models as motor/air operated) can be motor-operated valves, air-operated
valves or solenoid valves. Solenoid valves are electrically operated on/off control valves. Motor-
operated valves open and close more slowly than solenoid valves. This action reduces likelihood
of a water hammer. While the different opening/closing methods for manual and automated
valves have various advantages and disadvantages, cost differences among designs are relatively
small and the WBS unit costs do not distinguish between them at this level of detail. The key
cost difference is whether the valves are automated or manual, because of the cost of the motor,
air actuator or solenoid.
A.2 Instrumentation for Process Measurements
Each of the models includes the cost of various instruments that perform process measurements.
Most of these measurement devices are categorized into the following groups:
• Hydraulic measurement instruments and control devices. Hydraulic measurement
instruments include: flow meters, pressure gauges, head loss sensors and water level
meters/alarms. Hydraulic control devices include: pump control, motor control and valve
control.
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• Water quality measurement and control devices. These include water quality parameter
measurement devices, such as pH meters, oxidation-reduction potential (ORP) sensors,
temperature meters, turbidity meters and sampling devices and ports.
The WBS models determine instrumentation requirements for each technology based on review
of the schematic flow diagram for the appropriate technology, along with certain general
assumptions that are applied to all of the technologies. Exhibit A-l documents the general
assumptions about instrumentation that are applied in the WBS models. Slightly different
assumptions hold when a model is intended as an add-on to an existing process (e.g., acid feed)
rather than a complete process (e.g., anion exchange).
Exhibit A-1. General Design Assumptions for Instrumentation
Instrument Type
Chlorine analyzers
Conductivity meters
Dissolved oxygen analyzers
Drive controllers
Electric enclosures
Flow meters
Head loss sensors
High/low alarms
Level switch/alarms
ORP sensors
Particle meters
pH meters
Pressure transducers
Sampling ports
Total dissolved solids monitors
Temperature meters
Total organic carbon analyzers
Turbidity meters
Assumption
For chlorine and hypochlorite disinfection, 1 per treatment train to monitor residual
Varies by technology
Varies by technology
1 per each pump (including booster, backwash and chemical metering pumps) or
other motorized item of equipment (e.g., mixers, blowers) in fully automated systems
Only for technologies with significant electric-powered equipment outside a building
structure
1 for the influent or effluent line and 1 for backwash discharge. Some technologies
also include flow meters on process lines.
Continuous level sensors. 1 per process vessel for technologies with pressure
vessels. Some technologies omit head loss sensors for systems with design flows
less than 1 million gallons per day.
1 per backwash tank and 1 per chemical storage tank
1 per process basin; 2 per contact tank for chemical disinfection technologies.
Technologies with chemical cleaning use 1 per chemical tank in the cleaning system.
Varies by technology
Varies by technology
1 each for the influent and effluent lines for systems with pH adjustment, plus others
on a technology-specific basis
Included in the cost of flow meter assemblies for venturi and orifice plate meters
1 per process vessel, plus 1 each for the influent line, effluent line and discharge side
of the backwash line for complete process models. Others are included on a
technology-specific basis.
Varies by technology
Varies by technology; often 1 for the influent and/or effluent lines, except for add-on
models. Some technologies omit temperature meters for systems with design flows
less than 1 million gallons per day.
Varies by technology
Varies by technology
Several types of flow meters can appear in the model output: propeller, venturi, orifice plate and
magnetic flow meters. In general, the choice of meter depends on the cost level and design flow
of the system, although some technologies require particular types of flow meters for specific
purposes. For smaller and/or low-cost systems, the preference order in the models will have
propeller flow meters as a first choice; for intermediate systems, venturi flow meters top the
preference order; and for larger and/or high-cost systems, the top preference is magnetic flow
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meters. In all cases, the component buildup will display the price for all available types of flow
meters at a given size, so that a user can assess the cost impact of different types.
The critical design assumptions sheet of each model incorporates these general assumptions.
Therefore, the user can adjust instrumentation assumptions on a technology-specific basis.
Individual technologies—in particular, aeration technologies and chlorine and hypochlorite
disinfection—have additional or differing instrumentation requirements.
A.3 Control Systems
Automated control systems comprise the hardware and software used to monitor and control a
treatment process. There are two general types of systems: programmable logic controls (PLCs)
and/or remote telemetry units (RTUs). PLCs are stand-alone microprocessor-based control
systems that can be programmed to monitor and control process equipment. RTUs were
originally developed to communicate with systems from remote, outdoor locations. Newer RTU
models can provide full equipment control through remote operator interface (AWWA, 2001).
Because the WBS cost models (except for the nontreatment model) pertain to centralized
treatment facilities, the assumptions reflect the control of all system components using a PLC
system; RTUs are generally more appropriate for remote communications.
PLC hardware consists of a rack-mounted system with plug-in slots for the input and output
(I/O) modules, which provide connections for the instruments and equipment, and one or more
central processing unit (CPU) modules, which process the monitoring data inputs and control
command outputs. The PLC equipment requires a power supply unit to operate the PLC data and
command processing functions. In addition, an uninterruptible power supply (UPS) will protect
the PLC system from undesired features such as outages and surges that can adversely affect the
performance of the PLC unit. A system operator can monitor and operate with the PLC using
either a computer or an operator interface unit, which is a panel mounted on the PLC enclosure.
These units can be as simple as 2-line light-emitting diode text panels or as advanced as full
color touch panels. The WBS models have default assumptions that PLC systems for smaller
drinking water systems will be operated using an advanced, fully-functional operator interface
unit after the control system installer has programmed the PLC. Larger systems will include an
operator interface unit with more limited functionality and use at least one computer workstation
with PLC programming software and printers to accomplish more advanced control functions
from a central location. Large systems also include plant intelligence software to assist operation
of the extensive control system.
The PLC system design in the WBS models depends on the design of the treatment system,
which dictates the total number and type of I/O connections. The PLC system receives input
signals from and transmits output signals to ports on instruments and equipment controllers. The
I/O signals may be discrete or analog, depending on the type of equipment generating or
receiving the signals. Discrete signals indicate which of two conditions apply such as whether a
switch is on or off. Analog signals indicate a value along a predefined range such as temperature
or rate of flow. Exhibit A-2 identifies the assumptions used in the WBS models to determine the
total number of I/O connections required for the PLC system.
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Exhibit A-2. I/O Port Requirements for Instrumentation and Control
Instrument Type
Alarm (level switch/alarm, high/low alarm or low alarm)
Chlorine analyzer
Conductivity meter
Dissolved oxygen analyzer
Drive controller
Flow meter
Head loss sensor
Motor/air-operated valve
ORP sensor
Particle meter
pH meter
Pressure transducer
Sampling port
Total dissolved solids monitor
Temperature meter
Total organic carbon analyzer
Turbidity meter
Inputs to and Outputs from PLC System
1 input and 1 output— discrete
1 input— analog
1 input— analog
1 input— analog
3 inputs (1 for the auto switch position, 1 for the run status
and 1 for overload or fault signal) and 1 output— discrete
signal
1 input— analog
Venturi and orifice plate meters also include inputs and outputs
for the associated pressure transducer (below)
1 input— discrete
1 input and 1 output— analog
1 input— analog
1 input— analog
1 input— analog
1 input— analog
1 input— discrete
1 input— discrete
1 input— analog
1 input— analog
1 input— analog
The degree of automated control at a treatment facility can range from none to a fully automated
control system that can monitor and control the hydraulic regime at the plant, the chemicals
addition system, the power system and the communication system. To reflect potential ranges in
treatment costs, the WBS models can provide equipment and operator labor cost outputs for
three degrees of control:
• Fully automated control with safety overrides
• Semi-automated control where instruments provide data and information to the control
station, but operators manually activate valves and mechanical equipment (e.g., this
option removes outputs from the PLC system and removes automated drive controllers
from mechanical equipment)
• Fully manual control where operators collect data directly from the instruments and
manually activate valves and mechanical equipment.
Users can select among these three control schemes using the system automation input in each
WBS model (see Section 2.3). Exhibit A-3 shows the general design assumptions about control
equipment used for each control scheme in the WBS models. The paragraphs below provide
additional information regarding the equipment components and calculations.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
Exhibit A-3. General Design Assumptions for System Controls
Item of Control Equipment
Small
System
(<1 MGD)
Medium
System
(1-10 MGD)
Large
System
(>10 MGD)
WBS Assumption
PLC Equipment
PLC Rack/Power Supply
CPU
I/O Discrete Output Module
I/O Discrete Input Module
I/O Combination Analog Module
Ethernet Module
Base Expansion Module
Base Expansion Controller Module
UPS
A,S
A,S
A
A,S
A,S
A,S
A,S
A,S
A,S
A,S
A,S
A
A,S
A,S
A,S
A,S
A,S
A,S
A,S
A,S
A
A,S
A,S
A,S
A,S
A,S
A,S
1 base and expansion bases
as needed for I/O (see text)
2 per system1
1 for every 32 outputs2
1 for every 32 inputs2
1 for every 12 inputs (for A
and S) and outputs (for A
only)3
2 per system1
1 per expansion base
1 per expansion base
1 per system
Operator Equipment
Operator Interface Unit- limited
functionality
Operator Interface Unit - advanced,
fully functional
Computer Workstations
Laser Jet Printer
Dot Matrix Printer
NA
A,S
NA
NA
NA
A,S
NA
A,S
A,S
A,S
A,S
NA
A,S
A,S
A,S
2 per system1 (see text)
2 per system1 (see text)
1 per operator
1 per 4 workstations
1 per 4 workstations
Software
PLC Programming Software
Operator Interface Software
PLC Data Collection Software
Plant Intelligence Software
NA
A,S
NA
NA
A,S
NA
A,S
A,S
A,S
NA
A,S
A,S
1 per workstation
1 per system
1 per workstation
1 per workstation
A— included in a fully automated system
S— included in a semi-automated system
NA— not applicable for this design size
Note: Fully manual systems do not include system controls
1 . Includes one to provide redundancy
2. Discrete input and output modules can have fewer I/O connections, but price differences are small. To keep the
equipment requirement calculation tractable, the WBS models use a 32-connection module, which will slightly overstate
cost when fewer connection points are needed on the last module.
3. A combination module accommodates 8 inputs and 4 outputs. This 2-to-1 ratio is generally consistent with the ratio of
analog inputs- to-outputs in the WBS models for a fully automated system.
The primary PLC system is a rack and power supply (i.e., a "base") with nine slots for control
modules.14 The CPU module requires one slot. An ethernet module necessary for PLC
programming requires a second slot, leaving seven for I/O modules. If additional I/O slots are
needed to accommodate instruments and equipment, then up to four additional expansion bases
can be added, giving the single CPU the capacity to run up to 8,192 I/O connections. Each
expansion base has nine module slots and is linked to the CPU module on the primary base.
14 Bases with fewer slots are also available, but cost differences across base sizes are small. To keep the equipment
requirement calculation tractable, the WBS models use a 9-slot base, which will slightly overstate cost when fewer
slots are needed.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
The total number of PLC racks and power supplies include the primary rack and any expansion
racks. The calculation for the total number of racks must take into account the module slots that
will be occupied by all types of modules including the CPU module, the ethernet module and
expansion base controller modules. Each expansion rack requires a base expansion controller
module, which occupies one of the module slots on the expansion rack, leaving eight slots for
I/O modules. Each expansion rack also requires a base expansion module, which is attached to
the outside of the rack and, therefore, does not require a module slot. The following calculations
illustrate how the WBS models calculate total PLC racks:
IF (pic cpu + pic ethernet + pic discrete input + pic discrete output +
pic combination analog) < 9
THEN/7/c rack = 1, pic base expansion = 0, pic base expansion controller = 0
IF (pic cpu + pic ethernet + pic discrete input + pic discrete output +
pic combination analog) > 9 AND < 17
THEN/7/c rack = 2, pic base expansion = 1, pic base expansion controller = 1
IF (pic cpu + pic ethernet + pic discrete input + pic discrete output +
pic combination analog) > 77 AND < 25
THEN/>/c rack = 3, pic base expansion = 2, pic base expansion controller = 2
IF (pic cpu + pic ethernet + pic discrete input + pic discrete output +
pic combination analog) > 25 AND < 33
THEN/7/c rack = 4, pic base expansion = 3, pic base expansion controller = 3
IF (pic cpu + pic ethernet + pic discrete input + pic discrete output +
pic combination analog) > 36 AND < 41
THEN/>/c rack = 5, pic base expansion = 4, pic base expansion controller = 4
A.4 List of Abbreviations and Symbols in this Appendix
CPU central processing unit
I/O input and output
ORP oxidation-reduction potential
PLCs programmable logic controls
RTUs remote telemetry units
UPS uninterruptible power supply
WBS work breakdown structure
A.5 References
American Water Works Association (AWWA). 2001. Instrumentation and Control, Manual of
Water Supply Practices—M2. Third Edition. Denver, Colorado: AWWA.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
Appendix B. Building Construction Costs
B.1 Introduction
The work breakdown structure (WBS) cost database incorporates building costs from three
sources: RSMeans 2009 Square Foot Costs (RSMeans, 2008), Saylor 2009 Commercial Square
Foot Building Costs (Saylor, 2009) and the Craftsman 2009 National Building Cost Estimator
(NCBE) software model (described in Craftsman, 2008). Each of these sources enables a user to
create a cost estimate by combining costs for different elements of a building—for example, the
foundation, exterior walls or light fixtures.
For each source, the WBS cost database includes three sets of options to represent low, medium
and high building design and material qualities. Section B.2 provides descriptions of the relevant
options for each source within these categories, as well as the options selected for each of the
three building types used in the WBS models. The WBS models cost heating and cooling
systems as individual capital cost line items separate from the building construction costs.
Therefore, the building costs discussed here exclude heating and cooling systems.
For each of the three types of building, EPA developed cost buildups for 24 building sizes
ranging from 500 to 200,000 square feet and tabulated costs for each of the models. The resulting
costs from each model are included in the WBS cost database. The database escalates these costs
from 2008 dollars using the Engineering News-Record Building Cost Index (ENR, 2013) and
averages them following the same procedure as for other components, as described in Chapter 2.
The WBS models use these costs to estimate costs per square foot for buildings larger than 500
square feet (ft2).
EPA also developed a fourth building type that applies only to structures smaller than 500 ft2—
essentially a shed with steel walls and a roof. This additional building type allows the WBS
models to use, for very small systems, building costs that reflect very inexpensive building
construction methods and materials. For this type of building, EPA used the Craftsman NCBE
model to estimate costs for a low-profile steel building. However, the WBS models do not use
this building type for chlorine storage buildings because chlorine gas use necessitates a non-
corrodible building material and special ventilation requirements. Thus, for chlorine storage
buildings smaller than 500 ft2, the WBS models use the same unit costs as for larger buildings.
B.2 Buildup Options and Building Quality Selections
EPA developed building cost estimates using comparable assumptions across data sources: the
Craftsman NBCE model, building costs from RSMeans 2009 Square Foot Costs and Saylor 2009
Commercial Square Foot Building Costs. Each source provides unit costs for different building
types and construction qualities.
The Craftsman NBCE model is a software model that generates building cost estimates based on
user input (i.e., building size and quality of building features and fixtures). Given the variation in
unit costs for components by size, it appears to function as a parametric model. The costs in the
NBCE model are based on data obtained from U.S. government building cost surveys.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
The RSMeans and Saylor manuals contain unit costs, usually in dollars per square foot, for
various building components (e.g., exterior walls, floor structure or roof structure). The costs are
based on data obtained from the construction industry and independent research of construction
costs. By combining unit costs across components, one can build up a total building unit cost.
The approach is essentially a WBS cost approach where most components are priced on the basis
of building area, with little or no variation in the cost per unit area as building size increases. For
example, the RSMeans unit cost for a foundation slab varies with the thickness of the slab (EPA
chose thicker slabs for higher quality buildings), but not with the building size. Notable
exceptions are the cost of exterior walls and roof structures. Exterior wall cost in dollars per ft2
declines as building size increases because the ratio of exterior wall linear footage to square
footage declines. For roof structures, EPA chose roof spans based on the length of a side of the
building (assumed square). For building side lengths greater than 70 feet, EPA included support
columns to give a maximum roof span of 70 feet. Larger buildings, therefore, may have
somewhat more expensive superstructures on a per-square-foot basis, since they may have a
wider roof span or support columns.
EPA chose inputs to the NBCE model and chose components from the RSMeans and Saylor
manuals to reflect the different levels of building quality used in the WBS models (high,
medium, low and very small low quality).
Based on the NBCE industrial building quality classifications, EPA determined that the NBCE
Class 1&2 (best/good quality), Class 3 (average quality) and Class 4 (low quality) reflected WBS
high, medium and low quality buildings, respectively. EPA used the NBCE low-profile steel
building for very small low quality buildings.
The RSMeans and Saylor manuals do not contain building types that are closely comparable to
the very small low quality building. Therefore, there are no RSMeans or Saylor costs for this
type of structure. RSMeans and Saylor building cost estimates were "built" by selecting specific
building elements of differing quality for each type of building from the assemblies sections of
their respective manuals.
For each source, EPA obtained cost estimates for the following building areas in square feet:
500; 1,000; 2,000; 3,000; 4,000; 5,000; 7,500; 8,000; 10,000; 12,000; 15,000; 18,000; 20,000;
24,000; 25,000; 30,000; 36,000; 42,000; 48,000; 50,000; 54,000; 60,000; 100,000 and 200,000.
The resulting costs do not include costs for site improvements (e.g., land, landscaping, parking
and utilities), permits, furnishings and production equipment, homeland security responses or
contingency allowance.
The RSMeans and Saylor costs include installation costs as well as overhead and profit for the
contractors installing the building components, but do not include architectural fees or general
contractor markup for general conditions, overhead and profit (RSMeans, 2008; Saylor, 2009).
According to Craftsman (Ogershok, 2009), the NBCE model's costs do not include installing
contractor markup directly, but do include a markup of 30 percent for the general contractor,
which they assume to also cover the installing contractor's markup. Since the Craftsman costs
were generally lower than those from Means or Saylor and since the installing contractor's
markup in Means and Saylor is usually 30 percent or more, EPA assumed that the 30 percent
markup in the Craftsman costs was passed along directly to the installing contractor and further
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WBS-Based Cost Models for Drinking Water Treatment Technologies
markup would be required for the general contractor. Architectural fees and the general
contractor's markup are included in the WBS model indirect cost output, as described in
Appendix D.
Each source has a different set of options. They can be grouped into six categories:
• Substructure
• Superstructure
• Exterior closure
• Interior finish
• Mechanical services, excluding heating and cooling
• Electrical services.
B.2.1 Substructure
Building substructure was selected using application scenarios for each of the three quality
options. For low quality buildings, EPA assumed an average industrial use scenario. For medium
quality buildings, EPA assumed a heavy industrial use scenario. For higher quality buildings,
EPA assumed a heavy industrial with live loads use scenario. EPA assumed light foot traffic for
the very small (less than 500 ft2) buildings (other than those used to store chlorine gas).
Exhibit B-l shows the detailed choices that EPA made for each of the three sources.
Exhibit B-1. Substructure Selections for NBCE, RSMeans and Saylor
Building
Variable
Craftsman
NBCE
RSMeans
Saylor
Lower Quality
Building
Foundation: reinforced
concrete pads under
pilasters.
Floor. 6" rock base, 4"
concrete with reinforcing
mesh.
Foundation: poured
concrete; strip and spread
footings.
Slab: 4" reinforced,
industrial concrete with
vapor barrier and granular
base. Site preparation for
slab and trench for
foundation wall and
footing. 4' foundation wall.
Foundation: concrete strip
and spread footings, 4'
foundation wall.
Slab on grade: reinforced
concrete, vapor barrier, 4"
thick, on 4' sand or gravel
base.
Medium Quality
Building
Foundation: continuous
reinforced concrete.
Floor. 6 " rock base, 5"
concrete with reinforcing
mesh or bars.
Foundation: poured
concrete; strip and spread
footings.
Slab: 5" reinforced, heavy
industrial concrete with
vapor barrier and granular
base. Site preparation for
slab and trench for
foundation wall and
footing. 4' foundation wall.
Foundation: concrete strip
and spread footings, 4'
foundation wall.
Slab on grade: reinforced
concrete, vapor barrier, 5"
thick, on 4' sand or gravel
base.
Higher Quality
Building
Foundation: continuous
reinforced concrete.
Floor. 6" rock base, 6"
concrete with reinforcing
mesh or bars.
Foundation: poured
concrete; strip and spread
footings.
Slab: 6" reinforced, heavy
industrial concrete with
vapor barrier and granular
base. Site preparation for
slab and trench for
foundation wall and
footing. 4' foundation wall.
Foundation: concrete strip
and spread footings, 4'
foundation wall.
Slab on grade: reinforced
concrete, vapor barrier, 6"
thick, on 4' sand or gravel
base.
Very Small Lower
Quality Building
Foundations as required
for normal soil conditions;
a 4" concrete floor with
reinforcing mesh and a 2"
sand fill.
-
-
' = feet " = inches
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WBS-Based Cost Models for Drinking Water Treatment Technologies
B.2.2 Superstructure
EPA assumed the same quality of superstructure for each of the three quality options—metal
deck and open web steel joists, supported by columns and exterior walls. However, the
superstructure support column spans range up to 70 feet, depending upon building size. To
establish the column span, EPA computed the length of a building side, assuming the building to
be square. For buildings with side lengths larger than 70 feet, EPA included support columns in a
square grid to provide a roof span of 70 feet or less, assuming that the roof would also be
supported on the exterior walls. For instance, a 10,000 ft2 building (100 feet on a side) would
have one support column in the center, with a 50 foot roof span. A 30,000 ft building (173 feet
on a side) would have four support columns at 58 foot intervals. Since the sources included roof
spans in increments of 10 feet, EPA rounded up to a 60 foot roof span for this building.
EPA used a steel building quality superstructure for the very small (less than 500 ft2) buildings
(other than those used to store chlorine gas).
Exhibit B-2 displays the superstructure options that EPA selected for each source.
Exhibit B-2. Superstructure Selections for NBCE, RSMeans and Saylor
Building
Variable
Craftsman
NBCE
RSMeans
Saylor
Lower Quality
Building
Roof structure: glu-lams
wood or steel trusses on
steel intermediate
columns, short span.
Roof cover, panel ized
roof system, Vi" plywood
sheathing, 4-ply built-up
roof. 10 ft2 of skylight per
2,500 ft2 of floor area (1-
2'x 4'skylight 40' to 50'
O.C.).
Medium Quality
Building
Roof structure, glu-lams
wood or steel trusses on
steel intermediate
columns, short span.
Roof cover, panel ized
roof system, 1/2" plywood
sheathing, 4-ply built-up
roof. 24 ft2 of skylight per
2,500 ft2 of floor area (1-
4'x 6' skylight 40' to 50'
O.C.).
Higher Quality
Building
Roof structure, glu-lams
wood or steel trusses on
steel intermediate
columns, span exceeds
70'.
Roof cover, panelized
roof system, 1/2" plywood
sheathing, 4-ply built-up
roof. 32 ft2 of skylight per
2,500 ft2 of floor area (1-
4'x 8' skylight 40' to 50'
O.C.).
Roof. 1 .5" galvanized metal deck, open web steel joists, joist girders, on columns
and walls; total load = 60-65 Ibs/ft2. Column spacing chosen to give a maximum
span of 70', with the building assumed square. Steel columns.
Roof cover. Built-up tar and gravel roof covering with flashing, perlite/EPS
composite insulation. Roof hatches with curb. (Same for all quality levels.)
Roof, metal deck, open web steel joists, on columns and walls. Wide flange steel
columns, steel beams and girders. Column spacing chosen to give a maximum span
of 70', with the building assumed square.
Roof cover, built-up tar and gravel. (Same for all quality levels.)
Very Small Lower
Quality Building
Steel roof purlins 41/2 to
51/2 feet on centers, 26-
gauge galvanized steel
on roof
-
-
' = feet
" = inches
EPS = expanded polystyrene
o.c. = on center
B.2.3 Exterior Closure
EPA used different building exterior qualities to estimate unit costs that vary by exterior
material. EPA selected reinforced concrete block exteriors for the lower quality buildings,
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WBS-Based Cost Models for Drinking Water Treatment Technologies
15
reinforced tilt-up concrete panel exteriors for the medium quality buildings and brick-faced,
reinforced cavity/composition wall exteriors for the higher quality buildings. EPA used
corrugated metal exteriors for the very small lower quality structures (smaller than 500 ft2).
A cavity wall (e.g., masonry) is a wall in which the inner and outer wythes are separated by an
air space, but tied together with wires or metal stays. A composition wall is a wall combining
different materials to work as a single unit. A tilt-up wall is a method of concrete construction in
which wall sections are cast horizontally at a location adjacent to their eventual position and
tilted into place after removal of forms.
Exhibit B-3 shows the exterior closure options that EPA selected for each model.
Exhibit B-3. Exterior Closure Selections for NBCE, RSMeans and Saylor
Building
Variable
Craftsman
NBCE
RSMeans
Saylor
Lower Quality
Building
Medium Quality
Building
8" reinforced concrete block or brick, unpainted. (Same
for both lower and medium quality.)
Concrete block,
reinforced, regular weight,
hollow, 4x8x16', 2,000 psi
Concrete block, 4x8x16',
reinforced
Tilt-up concrete panels,
broom finish, 51/2" thick,
3,000 psi
Tilt-up concrete panel, 6"
thick, no pilasters.
Higher Quality
Building
8" reinforced concrete
block or brick with
pilasters 20' on centers,
painted sides and rear
exterior, front wall brick
veneer
Brick face composite wall-
double wythe: utility brick,
concrete block backup
masonry, 8" thick, perlite
core fill.
Brick cavity wall,
reinforced, 10" thick.
Very Small Lower
Quality Building
Steel frames/bents set 20'
to 24' on centers, steel
wall girts 31/2' to 41/2' on
centers, post and beam
type end wall frames, 26-
gauge galvanized steel
on ends and sides
-
-
' = feet
" = inches
psi = pounds per square inch
B.2.4 Interior Finish
Choices of interior finish reflect the quality and duty of the interior construction materials such
as floor coverings, wall coverings and ceilings. EPA selected functional, minimally attractive
interior finishes for the lower quality buildings and more functional and attractive interiors for
medium and higher quality buildings. EPA also selected functional, unattractive interior finishes
for the very small (less than 500 ft2) buildings (other than those used to store chlorine gas).
Exhibit B-4 shows the interior finish options that EPA selected for each source.
15 Tilt-up concrete panel exteriors were selected in the RSMeans and Saylor cost estimation buildups. Tilt-up
concrete panels were not an exterior option in the Craftsman NBCE cost estimation model; therefore, reinforced
concrete block exterior was selected in the Craftsman NBCE cost estimation model for medium quality buildings.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
Exhibit B-4. Interior Finish Selections for NBCE, RSMeans and Saylor
Building
Variable
Craftsman
NBCE
RSMeans
Saylor
Lower Quality
Building
Concrete floors. Rest
rooms: unfinished
wallboard partitions and 2
low cost fixtures.
One minimal quality 2-
fixture restroom per 5,000
Unpainted walls.
Concrete floors
Fiberglass ceiling board
on exposed grid system
covering 10 percent of
building area.
One restroom per 5,000
ft2 building area, with 2
economy fixtures, baked
enamel partitions
Unpainted walls.
Concrete floors. Ceiling:
5/8" gypsum board on
metal frame, covering 10
percent of building area.
Medium Quality
Building
Concrete floors. Rest
rooms: painted gypsum
wallboard partitions and 2
average fixtures.
One minimal quality 2-
fixture restroom per 5,000
ft2 building area. Painted
walls. Vinyl composition
tile floors covering 10
percent of building area.
Fiberglass ceiling board
on exposed grid system
covering 10 percent of
building area.
One restroom per 5,000
ft2 building area, with 2
standard fixtures, baked
enamel partitions. Painted
walls. Vinyl composition
floor covering 10 percent
of building area. Ceiling:
5/8" gypsum board on
metal frame, covering 10
percent of building area.
Higher Quality
Building
Cnnrrptp floors Rp^t
rooms: enameled gypsum
wallboard partitions, 3
good fixtures, vinyl
asbestos tile floors.
One high quality 3-fixture
restroom per 5,000 ft2
building area. Acrylic
glazed walls. Vinyl
composition tile floors
covering 10 percent of
building area. Fiberglass
ceiling board on exposed
grid system covering 10
percent of building area.
One restroom per 5,000
ft2 building area, with 3
standard fixtures, baked
enamel partitions. Painted
walls. Vinyl composition
floor covering 10 percent
of building area. Ceiling:
5/8" gypsum board on
metal frame, covering 10
percent of building area.
Very Small Lower
Quality Building
Minimal quality, minimal
duty, functional,
unattractive
__
' = feet
" = inches
B.2.5 Mechanical Services
Mechanical services include fire protection, plumbing, heating, ventilation and cooling. The
WBS models cost heating and cooling systems as individual capital cost line items separate from
the building construction costs, so the mechanical services included in the building costs are
limited to fire protection, plumbing and ventilation. EPA assumed no sprinkler systems for the
lower quality buildings and normal hazard wet sprinkler systems for medium and higher quality
buildings. EPA also assumed no sprinkler systems for the very small (less than 500 ft2) buildings
(other than those used to store chlorine gas).
Exhibit B-5 shows the mechanical services options that EPA selected for each source.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
Exhibit B-5. Mechanical Services Selections NBCE, RSMeans and Saylor
Building
Variable
Craftsman
NBCE
RSMeans
Saylor
Lower Quality
Building
No sprinklers. 1 small
rotary vent per 2,500 ft2 of
floor area.
Gas-fired water heater.
No sprinklers.
Gas-fired water heater (1
per 5,000 ft2), 50 gallon,
100 GPH. No sprinklers.
Medium Quality
Building
Higher Quality
Building
Sprinklers. 1 medium rotary vent per 2,500 ft2 of floor
area. (Same for both medium and higher quality.)
Gas-fired water heater. Wet pipe sprinkler system.
(Same for both medium and higher quality.)
Gas-fired water heater (1 per 5,000 ft2), 50 gallon, 100
GPH. Exposed wet sprinkler system, normal hazard.
(Same for both medium and higher quality.)
Very Small Lower
Quality Building
Minimal quality, minimal
duty, functional, no
sprinklers
-
-
' = feet
" = inches
GPH = gallons per hour
B.2.6 Electrical Services
EPA included the cost of light fixtures and convenience power, along with associated wiring and
conduits. EPA selected inexpensive lighting fixtures that provide minimal lighting and a minimal
number of wall switches and receptacles for the lower quality buildings and selected increasingly
expensive lighting fixtures that provide bright lighting and an increased number of wall switches
and receptacles for the medium and higher quality buildings. EPA also selected minimal lighting
fixtures for the very small (less than 500 ft2) buildings (other than those used to store chlorine
gas).
EPA did not include electrical feed, switchgear, motor control centers, etc. in building costs.
These costs are likely to vary significantly by technology for buildings of the same size and
quality; for example, a mid-sized reverse osmosis system and a small packaged conventional
filtration system might occupy roughly the same footprint in similar buildings, but the reverse
osmosis system will likely have much greater power requirements. It is therefore not appropriate
to base these costs on the building's area or quality. These costs are included in the indirect cost
buildup based on a percentage of process cost, as described in Appendix D.
Exhibit B-6 shows the electrical services options that EPA selected for each source.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
Exhibit B-6. Electrical Services Selections for NBCE, RSMeans and Saylor
Building
Variable
Craftsman
NBCE
RSMeans
Saylor
Lower Quality
Building
Lighting: low cost
incandescent fixtures,
20'x30' spacing
Lighting: Incandescent
fixtures recessmounted,
typeA:1W/ft2,8FC.6
lighting fixtures, 1 wall
switch and 2.5
receptacles per 1,000 ft2.
1 W miscellaneous
power.
Lighting: Incandescent
fixtures, surface mounted,
100 W, commercial
grade, 10 per 1,000 ft2 for
1 W/ft2 total. 1
commercial grade single-
pole switch and 2.5
commercial-grade duplex
receptacles per 1,000 ft2.
In slab/PVC conduit and
wire for 60 A current,
length assumed equal to
building perimeter for a
square building.
Medium Quality
Building
Lighting: low cost single
tube fluorescent fixtures
20'x20' spacing
Lighting: Fluorescent
fixtures recess mounted
in ceiling: T-12, 40 W
lamps, 2 W/ft2, 40 FC. 10
lighting fixtures, 2.5 wall
switches and 5
receptacles per 1,000 ft2.
1.5 W miscellaneous
power.
Lighting: Fluorescent
fixtures, recessed, 2 13 W
bulbs each, 16 per 1,000
ft2 for 2 W/ft2 total. 2.5
commercial grade single-
pole switches and 5
commercial-grade duplex
receptacles per 1,000 ft2.
EMT conduit and wire for
60 A current, length
assumed equal to
building perimeter for a
square building.
Higher Quality
Building
Lighting: 4" single tube
fluorescent fixtures
10'x1 2' spacing
Lighting: Fluorescent
fixtures recess mounted
in ceiling: T-12, 40 W
lamps, 4 W/ft2, 80 FC. 20
lighting fixtures, 5 wall
switches and 10
receptacles per 1 ,000 ft2.
3 W miscellaneous
power.
Lighting: Fluorescent
fixtures, recessed, 2 13 W
bulbs each, 31 per 1,000
ft2 for 4 W/ft2 total. 5
commercial grade single-
pole switches and 10
commercial-grade duplex
receptacles per 1 ,000 ft2.
RGS conduit and wire for
60 A current, length
assumed equal to
building perimeter for a
square building.
Very Small Lower
Quality Building
Minimal quality, minimal
duty, basic wiring and
minimal lighting fixtures
-
-
' = feet
" = inches
A = amp
EMT = electrical metallic tubing
FC = foot candles
PVC = polyvinyl chloride
RGS = rigid galvanized steel
W = watt
B.3
EPA
1.2
List of Abbreviations and Symbols in this Appendix
U.S. Environmental Protection Agency
ftz square feet
NBCE National Building Cost Estimator
WBS work breakdown structure
B.4 References
Craftsman Book Company. 2008. 2009 National Building Cost Manual: 33rd Edition. October.
Engineering News-Record (ENR). 2013. Building and Construction Cost Indexes. Online at
http://enr.construction.com/economics/
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Ogershok, Dave, Craftsman Book Company. 2009. Personal communication with Danielle Glitz,
SAIC. 6 March.
RSMeans. 2008. 2009 Square Foot Costs. 30th Annual Edition. Kingston, Massachusetts:
RSMeans Company.
Saylor Publications, Inc. 2009. 2009 Commercial Square Foot Building Costs: 191 Annual
Edition.
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Appendix C. Residuals Management Costs
C.1 Introduction
The purpose of this appendix is to outline the approach used to estimate costs for managing the
residuals generated by different drinking water treatment technologies. The work breakdown
structure (WBS) model for each treatment technology includes its own residuals cost estimate.
Each model allows the user to choose from different residual management options that reflect the
methods most likely to be used for the drinking water treatment technology being modeled.
Based on the residuals management option selected, each model identifies the specific
component equipment and operating and maintenance (O&M) requirements and generates costs
using the WBS approach based on engineering design. Costs for residuals management
equipment appear as line items in the model output, as is the case for other WBS elements. The
residuals management design also affects indirect costs, land costs and building costs.
The residuals management options available in each model are specific to the technology being
modeled, driven by the types of residuals generated, their quantity, the frequency of generation
(e.g., intermittent versus continuous) and their characteristics. There are, however, similarities
among groups of technologies that generate similar residuals. Exhibit C-l, below, lists the
technology groups, the residuals generated and the frequency of generation.
The technology-specific chapters of this report identify the residuals management options
available in each model. Because many of the options are similar within (or even across)
technology groups, this appendix describes the methodology and assumptions used for each
option in a single location, rather than repeating the information in each technology chapter. The
residuals management options that may be included in a given model include the following:
• Holding tanks (with or without coagulant addition)
• Direct discharge to surface water
• Discharge to a publicly owned treatment works (POTW)
• Recycle to treatment plant headworks
• Evaporation ponds
• Septic system
• Off-site disposal (non-hazardous, hazardous, radioactive or hazardous and radioactive)
• Land application
• Liquid hazardous waste disposal
• Deep well injection
• Off-gas treatment.
Section C.2, below, describes general design methods and assumptions common across residuals
management options. With two exceptions, subsequent sections describe each of the above
options. Deep well injection is included as an option only in the reverse osmosis/nanofiltration
model and, therefore, is discussed in detail in the chapter relating to that model. Off-gas
treatment is relevant only to aeration technologies and, therefore, is discussed in detail in
chapters relating to aeration models (e.g., packed tower aeration, multi-stage bubble aeration).
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Exhibit C-1. Technologies and Residuals Generated
Specific Technology Models
Adsorptive Media
Greensand, Granular Activated Carbon,
Biological Treatment
Anion Exchange, Cation Exchange
Microfiltration, Ultrafiltration
Reverse Osmosis, Nanofiltration
Packed Tower Aeration, Multi-stage Bubble
Aeration
Ultraviolet disinfection, Ultraviolet Advanced
Oxidation
Residuals Generated
Spent regenerant1
Spent backwash
Spent media
Spent backwash
Spent media
Spent brine
Spent backwash
Spent resin
Spent backwash/tank drain and crossflow
Cleaning waste
Spent membrane modules
Membrane concentrate
Cleaning waste
Spent membrane elements
Used cartridge filters
Off-gas
Spent lamps, ballasts and intensity
sensors
Type of
residual
Liquid
Liquid
Solid
Liquid
Solid
Liquid
Liquid
Solid
Liquid
Liquid
Solid
Liquid
Liquid
Solid
Solid
Gas
Solid
Generation
Frequency
Intermittent
Intermittent
Intermittent
Intermittent
Intermittent
Intermittent/
continuous
Intermittent
Intermittent
Intermittent
Intermittent
Intermittent
Continuous
Intermittent
Intermittent
Intermittent
Continuous
Intermittent
Notes:
1 . Generated when the technology is used with media regeneration, rather than on a throw away basis.
The chlorine gas, hypochlorite, nontreatment, potassium permanganate feed, caustic feed and acid feed models are not
shown because no process residuals are generated.
C.2 General Assumptions
Some of the general assumptions used in developing the costs for management of residuals are
listed below:
• For intermittently generated liquid residuals (e.g., filter backwash), the models calculate
residuals quantities based on the volume of a single generation event (e.g., backwashing
one vessel) and assuming a staggered schedule between generation events (e.g., if vessels
must be backwashed every 48 hours and there are two vessels in operation, the facility
will backwash vessel one at 0 and 48 hours and backwash vessel two at 24 and 72 hours).
• For intermittently generated liquid residuals, flow rates depend on whether flow
equalization is used (e.g., through the use of holding tanks, as described in Section C.3).
• Without flow equalization, the maximum residuals flow rate for intermittently generated
liquid residuals is single generation event volume/event duration.
• With flow equalization, the models assume residuals are released continuously during the
time between generation events. Therefore, the maximum residuals flow rate for
intermittently generated liquid residuals is (single generation event volume/time between
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events) x capacity factor. The variable, capacity factor', is present to account for less than
perfect staggering between generation events. The models assume capacity factor equals
2, but the user can change this assumption on the critical design assumptions sheet of
each model.
• The models size residuals piping, valves and other downstream equipment based on the
maximum flow rates calculated as described above for intermittently generated liquid
residuals and on the maximum continuous flow rate determined by the engineering
models for continuously generated liquid residuals.
• The models assume the length of interconnecting piping between treatment process
equipment and residuals management equipment is equal to 1 times the overall system
building layout length. Like the pipe length assumptions documented in Exhibit 2-10,
this assumption is designed to account for the cost of fittings.
• With a few exceptions (noted in the individual model chapters), the models assume an
additional 40 feet of piping is required for liquid residuals to reach their ultimate
destination (e.g., the discharge point, head of the treatment plant or evaporation pond).
Except when this piping is used to recycle the residual, the models assume this piping is
buried and, therefore, include the cost of excavation, bedding, thrust blocks, backfill and
compaction for the additional pipe length. The user can change the assumption about the
length of the additional residuals piping on critical design assumptions sheet of each
model.
• The models generally assume that total suspended solids (TSS) in the influent water are
completely removed during treatment and accumulate in the residuals generated. This
assumption provides a conservative (high) estimate of the TSS concentration in the
residuals. Assumptions about the concentration of TSS in the influent water vary on a
technology-by-technology basis, but the user can change the assumption on the critical
design assumptions sheet of each model.
C.3 Holding Tanks
The purpose of a holding tank is to equalize the rate of flow at which residuals are released or
discharged. A holding tank may be desirable for intermittently generated liquid residuals that
ultimately are recycled to the treatment plant headworks or discharged to a POTW. The
instantaneous flow of intermittently generated liquid residuals (e.g., filter backwash) during a
generation event can be quite high. The use of a holding tank allows the discharge of these
residuals over the time between generation events, so that the ultimate flow is lower, but more
continuous. When residuals such as filter backwash are recycled to the head of a treatment plant,
recommended engineering practice is that the recycle stream should be no more than 5 percent to
10 percent of total system flow (U.S. EPA, 2002; U.S. EPA, 1996). Flow equalization through
the use of a holding tank may be necessary to meet this generally recommended engineering
practice. It also may be reasonable to include a holding tank for other discharge options (e.g., to
prevent instantaneous flow from overwhelming the capacity of a POTW).
When holding tanks are used for intermittently generated liquid residuals, the models determine
the capacity required as follows: single generation event volume x capacity factor. This capacity
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factor is the same variable discussed in Section C.2 and is intended to account for less than
perfect staggering between generation events.
Holding tanks can also be desirable for certain continuously generated liquid residuals (e.g.,
membrane reject) to accommodate variations in flow that occur as influent flow varies. In this
case, the models determine the capacity required based on a desired detention time. The user can
change this detention time on the critical design assumptions sheet of the appropriate models.
When holding tanks are included, residuals pumps are required to move residuals from the
holding tank to their ultimate destination. The models size these pumps based on maximum
residuals flow rate, as discussed in Section C.2. The models also include maintenance labor,
materials and energy for these pumps in the O&M calculations using the same approach
described for booster pumps in Appendix E.
When holding tanks are used, they can result in the generation of secondary residuals in the form
of solids that settle in the holding tank. The models also allow for the addition of coagulant to the
holding tank to increase the percentage of TSS removed. Users can model this option by
changing the appropriate triggering variable on the critical design assumptions sheet of each
model. When the coagulant addition option is chosen, users also can choose the coagulant used.
Options available (specified on the critical design assumptions sheet) are polymers, ferric
chloride or both ferric chloride and polymers.
By default, holding tanks can be constructed of plastic, fiberglass or steel or they can be open
concrete basins. When the coagulant addition option is chosen, however, the models
automatically assume the tanks will be open concrete basins, to allow for easier solids cleanout.
The models also size the tanks so that a minimum settling time is achieved. When coagulant
addition is chosen, the models also add other required equipment, specifically mixers and dry
feeders or metering pumps.
The following are the model assumptions relevant to solids generation and coagulant addition:
• Without coagulant addition, most models assume that 25 percent of the TSS present in
the residuals is removed in a holding tank16
• With coagulant addition, this assumption increases to 50 percent
• With coagulant addition, the holding tanks must provide a minimum settling time of 90
minutes
• Coagulant dose is 10 milligrams per liter
• Coagulant sludge production factor is 1 pounds of sludge per pound of polymers added
and 0.99 pounds of sludge per pound of ferric chloride added
• Holding tank solid density is 25 pounds per cubic foot
16 Exceptions are models, such as anion exchange, that assume low influent solids or include pretreatment filtration
to remove influent solids. These models assume no settling in the holding tank without coagulant addition, because
of the low solids content present (or remaining) in the water being treated.
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• Holding tank solids are removed when the solids accumulation reaches 10 percent of tank
capacity.
The user can change each of these assumptions on the critical design assumptions sheet of the
individual models.
C.4 Direct Discharge to Surface Water
Some liquid residuals may be amenable to direct discharge to surface water. Such discharges
require a National Pollutant Discharge Elimination System permit, the costs of which are
included in the add-on costs line item for permits. The only items of capital equipment required
for direct discharges are piping and valves, although the models will include pumps if holding
tanks are used in conjunction with direct discharge (see Section C.3, above).
C.5 Discharge to POTW
Discharge to a POTW is another possible management option for liquid residuals. The discharge
should meet certain pretreatment requirements and must not overwhelm the capacity of the
POTW. The only items of capital equipment required for POTW discharges are piping and
valves, although the models will include pumps if holding tanks are used in conjunction with
POTW discharge (see Section C.3, above).
Discharge to a POTW, however, entails certain charges that are included in the O&M costs of
each model when this discharge option is included. POTW rate structures vary nationwide, but
the most common types of charges are the following:
• Flat fees (e.g., dollars per month).
• Volume-based fees (e.g., dollars per 1,000 gallons discharged).
• TSS-based fees (e.g., dollars per pound of TSS in the discharge if over a certain TSS
concentration). For this fee type, the models assume that the POTW TSS discharge limit
over which a fee is imposed to be 250 parts per million (which is the most common limit
for cities with a limit on TSS).
Individual POTW rate structures can reflect a combination of one or more of these fee types. To
model POTW charges in a way that is nationally representative, the models include all three fee
types and calculate them based on unit charges that represent the average for each fee type based
on data from AWWA (2013). The user can change these average unit charges in the central WBS
cost database. Alternatively, the user can model a specific type of POTW rate structure by
selecting the appropriate option on the critical design assumptions sheet of each model. The user
can indicate which fee types to include (e.g., flat fee only). The model will then use "typical"
unit charges for the selected fee type(s). These "typical" unit charges, which can be changed in
WBS cost database, reflect the average including only cities that use that specific fee type (i.e.,
the average not counting zeros).
C.6 Recycle to Treatment Plant Headworks
Certain liquid residuals can be recycled to the treatment plant headworks provided the system
complies with the backwash recycling rule and the practice does not negatively impact finished
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water quality. The recommended engineering practice is that the recycle stream should be no
more than 5 to 10 percent of total system flow (U.S. EPA, 2002; U.S. EPA, 1996). The only
items of capital equipment required for recycling are piping and valves, although a holding tank
(and, therefore, pumps) also would be necessary in most cases to meet the recommendation.
C.7 Evaporation Ponds
When large quantities of liquid residuals are generated (e.g., spent brine from ion exchange), an
evaporation pond can be an appropriate management method, particularly for facilities in dry
climates. Holding tanks are never necessary with an evaporation pond, even for designs with
intermittent generation frequency, because the design of the pond would provide sufficient
capacity to handle instantaneous flow. A minimum of two cells is recommended to ensure
availability of storage space during cleaning, maintenance or emergency conditions (U.S. EPA,
1987).
When evaporation ponds are selected, the models include the following evaporation pond capital
expenses: excavation, backfill, lining and dike construction. Also, when evaporation ponds are
selected, the models always include the cost of a geotechnical investigation (see Appendix D).
These items are in addition to the pipes and valves required to deliver residuals to the pond. The
models make the following assumptions to design evaporation ponds:
• Arid climate with annual average precipitation of 70 centimeters per year (cm/yr)
• Average annual pan evaporation rate is 180 cm/yr
• Evaporation ratio (which takes into account conversion of pan to lake evaporation rate
and the effect of salinity) of 0.7
• 180 days of storage with no net evaporation
• Evaporation pond safety factor (which accounts for years with below average
evaporation) of 1.1
• Maximum evaporation pond cell area of 5 acres.
The user can change each of these assumptions on the critical design assumptions sheet in each
model that includes the evaporation pond option. If evaporation ponds are selected, the user
should also review the other climate-based assumptions included in the model (e.g., the heating
and cooling requirements on the O&M assumptions sheet) to determine that they are sufficiently
consistent with the assumption of an arid climate that is implicit in the selection of evaporation
ponds as a residuals management method.
The use of an evaporation pond results in the generation of a secondary residual stream in the
form of evaporation pond solids. The models calculate the accumulation of evaporation pond
solids by including all suspended and dissolved solids present in the residuals. The models
assume evaporation pond solids removal frequency of once per year. Users can change this latter
assumption on the critical design assumption sheet of the appropriate models.
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C.8 Septic System
Based on comments from peer reviewers, discharge to an in-ground septic tank and drain field (a
septic system) might be an option for some liquid residuals with intermittent generation in small
systems using certain technologies (e.g., adsorptive media, anion exchange). Users selecting this
option should evaluate whether the characteristics of the residuals are appropriate for this type of
discharge. Holding tanks are never necessary with septic systems because the design of the septic
tank would provide sufficient capacity to handle instantaneous flow.
When a septic system is selected, the models include the following capital expenses:
• Septic tanks
• Excavation for septic tanks
• Distribution boxes
• Distribution pipe (perforated polyvinyl chloride)
• Drain field trench excavation
• Drain field gravel.
These items are in addition to the pipes and valves required to deliver residuals to the septic tank.
Also, when a septic system is selected, the models always include the cost of a geotechnical
investigation (see Appendix D). The models make the following assumptions to design septic
systems:
• Minimum septic tank discharge time of 2 days
• Minimum septic tank volume of 1,000 gallons
• Maximum septic tank volume of 100,000 gallons
• Septic tank volume safety factor of 150 percent
• Long-term acceptance rate (a value, based on soil type, used by states/localities to
determine the minimum drain field infiltration area) of 0.5 gallons per day per square foot
• Septic drain field trench width of 4 feet
• Septic drain field trench depth of 4 feet
• Septic drain field trench gravel depth below distribution pipe of 1 foot
• A minimum of two septic drain field trenches
• A maximum septic drain field trench length of 100 feet
• 8 feet between drain field trenches
• Septic drain field trench total gravel depth of 28 inches, based on 1 foot below and 1 foot
above the distribution pipe and a 4 inch pipe diameter
• Septic drain field buffer distance of 10 feet
• Septic tank over excavation depth of 1 foot above and to each side of the tank
• A maximum of 7 distribution pipe connections per distribution box
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• Septic system distribution pipe diameter of 4 inches.
These assumptions are based on values typically found in state and local regulations for septic
systems. The user can change each of these assumptions on the critical design assumptions sheet
of each model that includes the septic system option. The use of a septic system results in the
generation of a secondary residual stream in the form of septic tank solids. The models calculate
the accumulation and disposal cost for these solids using the same assumptions used for holding
tank solids (except that addition of coagulant is not included for septic systems).
C.9 Off-Site Disposal
For solid residuals, including secondary residuals like holding tank solids or evaporation pond
solids, most of the models offer two options: disposal in a hazardous or non-hazardous off-site
landfill. The models do not include disposal in an on-site landfill as an option. This option would
be economically viable only for facilities with an existing on-site landfill—a factor that is highly
site-specific. For these facilities, the cost of this option would be less than that for off-site
disposal, because it would involve much lower transportation costs. Therefore, the off-site
disposal options available in the models provide a conservative cost estimate for these facilities.
For certain solid residuals, many of the models also offer two additional options: off-site disposal
as a radioactive waste or off-site disposal as a hazardous and radioactive waste. The radioactive
waste disposal options assume that the residuals are classified as low-level radioactive wastes
(LLRW), instead of technologically-enhanced, naturally-occurring radioactive materials
(TENORM). In some cases, TENORM is accepted at traditional non-hazardous or hazardous
waste disposal facility. In such cases, disposal costs would be lower than those at specialized
radioactive waste disposal sites. Therefore, the LLRW disposal costs assumed in the models
provide a conservative cost estimate for cases where residuals might be classified instead as
TENORM.
The models calculate annual disposal costs for non-hazardous solid residuals as follows:
Annual disposal costs = Disposal costs + Transportation costs
where:
Disposal costs = quantity of solids per disposal event (in tons per event) x disposal
frequency (in events per year) x unit cost for non-hazardous waste disposal (in dollars
per ton)
Transportation costs = quantity of solids per disposal event (in tons per event) x disposal
frequency (in events per year) x distance to disposal site (in miles) x unit cost for non-
hazardous waste transportation (in dollars per ton per mile).
The disposal costs for hazardous, radioactive and hazardous radioactive solid residuals are
calculated in a similar fashion. For transportation costs, however, there is a minimum charge per
shipment applied. If transportation costs calculated based on dollars per ton per mile are less than
this minimum, the models calculate transportation costs based on this minimum.
The following are the model assumptions relevant to off-site landfill disposal:
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• 10 miles to the nearest non-hazardous waste disposal site
• 200 miles to the nearest hazardous waste disposal site
• 700 miles to the nearest radioactive or hazardous radioactive waste disposal site
• Maximum waste shipment size of 18 tons.
The user can change each of these assumptions on the critical design assumptions sheet of each
model.
C.10 Land Application
When secondary solids (e.g., holding tank solids, evaporation pond solids) are non-hazardous,
most models provide the option of assuming land application instead of landfill disposal. Users
can select this option on the critical design assumptions sheet. When land application is chosen,
the models assume that transportation and disposal costs for the secondary solids are zero,
although they still include the operator labor costs associated with managing the secondary
solids.
C.11 Liquid Hazardous Waste Disposal
In some site-specific cases, the only viable option for certain liquid residuals (e.g., anion
exchange brine) might be off-site disposal as a hazardous waste. When this option is chosen, the
models automatically include a holding tank, which is required to store the residuals for
shipment. Any solids that settle in the holding tank also are assumed to require hazardous waste
disposal.
The models calculate costs for the liquid hazardous waste disposal option similarly to the off-site
hazardous waste landfill option (e.g., disposal cost + transportation cost, with a minimum charge
per shipment), except that unit costs are different. These unit costs are specific to off-site liquid
hazardous waste disposal, instead of off-site hazardous waste solids landfilling, and expressed in
dollars per gallon or dollars per gallon per mile. The models assume the maximum liquid
hazardous waste shipment size is 6,000 gallons.
C.12 List of Abbreviations and Symbols in this Appendix
cm/yr centimeters per year
LLRW low-level radioactive waste
O&M operating and maintenance
POTW publicly owned treatment works
TENORM technologically-enhanced, naturally-occurring radioactive materials
TSS total suspended solids
WBS work breakdown structure
C.13 References
American Water Works Association (AWWA). 2013. 2072 Water and Wastewater Rate Survey.
Denver, Colorado: AWWA. February.
U.S. Environmental Protection Agency (U.S. EPA). 1987. DewateringMunicipal Wastewater
Sludge. EPA Design Manual. EPA/625/1-87/014. September.
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U.S. EPA. 1996. Technology Transfer Handbook: Management of Water Treatment Plant
Residuals. United States Environmental Protection Agency, Office of Research and
Development. EPA 625-R-95-008. April.
U.S. EPA. 2002. Filter Backwash Recycling Rule: Technical Guidance Manual. United States
Environmental Protection Agency, Office of Groundwater and Drinking Water. EPA 816-R-02-
014. December.
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Appendix D. Indirect Capital Costs
D.1 Introduction
Indirect capital costs are costs that are not directly related to the treatment technology used or the
amount or quality of the treated water produced, but are associated with the construction and
installation of a treatment technology and appurtenant water intake structures. These costs
represent some of the expenditures required in order to get a technology or the treated water
production process up and running. They include indirect material costs (such as yard piping and
wiring), indirect labor costs (such as process engineering) and indirect burden expenses (such as
administrative costs).
Indirect capital costs included in the work breakdown structure (WBS) models include the
following:
• Mobilization and demobilization
• Architectural fees for treatment building
• Equipment delivery, equipment installation and contractor overhead and profit
• Site work
• Yard piping
• Geotechnical
• Standby power
• Electrical infrastructure
• Instrumentation and control
• Process engineering
• Contingency
• Miscellaneous allowance
• Legal, fiscal and administrative
• Sales tax
• Financing during construction
• Construction management and general contractor overhead
• City index.
The following sections describe each of these indirect cost elements in more detail, address their
effect on capital costs and explain the reasoning behind including them as an additional indirect
capital cost allowance or contingency.
D.2 Mobilization and Demobilization
Mobilization and demobilization costs are costs incurred by the contractor to assemble crews and
equipment onsite and to dismantle semi-permanent and temporary construction facilities once the
job is completed. The types of equipment that may be needed include: backhoes, bulldozers,
front-end loaders, self-propelled scrapers, pavers, pavement rollers, sheeps-foot rollers, rubber
tire rollers, cranes, temporary generators, trucks (e.g., water and fuel trucks) and trailers. In some
construction contracts, mobilization costs also include performance bonds and insurance.
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To estimate mobilization and demobilization costs in the absence of site-specific data, the WBS
models use a multiplication factor of 2 to 5 percent. The models apply this multiplication factor
to direct process costs, building costs and the physical portions of indirect capital costs (site
work, yard piping, geotechnical, standby power, electrical, instrumentation and control and
miscellaneous). Examples of mobilization and demobilization percentages include:
• Buckeye, Arizona Water System Infrastructure Improvements (multiple projects)
Mobilization/Demobilization/Bonds/Insurance = 5 percent (Scoutten, Inc., 2009)
• City of New Port Richey Maytum Water Treatment Plant Modifications,
Mobilization/Demobilization (limit included in bid instructions) = 4 percent (Tampa Bay
Water, 2006)
• Alton Water Works Mobilization = 1 percent (AWWC, 1999)
• Fairfax Water Authority New Intake, Mobilization = 4.6 percent, Demobilization =1.8
percent, Total = 6.4 percent (FWA, 2003)
• Fairfax Water Authority Trunk Sewer Project Mobilization = 5 percent (FWA, 2003)
• Forest Park Water Treatment Plant, Chalfont, PA = 0.26 percent (Allis, 2005).
The last example, for the Forest Park treatment plant, applied to a retrofit of an existing
conventional filtration facility with a membrane system. The project involved modifications to
existing buildings and treatment basins and the construction of one new building. Since the
project involved less new construction than a greenfield project, the mobilization cost may be
lower than it otherwise would be.
Mobilization/demobilization costs tend to be proportionately higher for smaller projects because
of fixed costs that are the same regardless of project size. For example, if construction requires
use of a large crane, then the mobilization/demobilization cost will be the same regardless of
whether it is onsite for a long time to complete a large construction project or a short time to
complete a small project. Therefore, small projects will most likely have
mobilization/demobilization percentages in the higher end of the range and larger projects will
tend to have values in the lower end of the range. The default values in the WBS models reflect
this type of variation. For small systems with a design flow less than 1 million gallons per day
(MGD), the default mobilization/demobilization factor is 5 percent. For medium systems (design
flows between 1 MGD and 10 MGD), the default factor is 4 percent and for large systems
(design flows above 10 MGD), the default factor is 2 percent. The models make an exception in
the case of small systems that use pre-engineered package treatment plants. Because these
package plants typically are skid-mounted, they require only a short time to install onsite and
should use a minimum of heavy equipment in the process. Therefore, the models assume a
mobilization/demobilization factor of 0 percent for small, pre-engineered package systems. The
user can change this assumption on the indirect assumptions sheet of each model.
Because the installation costs in the models include rental of equipment for installation (see
Section D.4.2), there may be some redundancy between the default mobilization and
demobilization costs and the installation costs (which are included in the model unit costs). The
extent of this redundancy is difficult to determine, but is a potential source of conservatism in
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model cost estimates (i.e., the potential redundancy would tend to make model cost results
higher).
D.3 Architectural Fees for Treatment Building
The architectural fees for the treatment building include the costs of designing the structure and
preparing technical drawings. By convention, the architectural fee also includes the fees for
structural, electrical and mechanical engineering associated with the treatment building
(RSMeans, 2013). Furthermore, the architectural fees include the costs of preparing final
drawings and the tender document package. The building costs in the WBS cost database (see
Appendix B) do not include architectural fees, so the fees are added as an indirect cost. The
models apply the architectural percentage only to treatment building costs, not to other process
costs.
The WBS models use architectural fees from RSMeans (2013), based upon the direct cost of the
building, as shown in Exhibit D-l. The models make an exception in the case of small systems
with a design flow of less than 1 MGD. Because they are typically housed in small, prefabricated
buildings that require a minimum of design and engineering, the models assume no architectural
fee for these small systems. The user can change this assumption on the indirect assumptions
sheet of each model.
Exhibit D-1. Architectural Fees
Building Direct Cost Range
<$250,000
$250,000 to $500,000
$500,000 to $1,000,000
$1,000,000 to $5,000,000
$5,000,000 to $10,000,000
$10,000,000 to $50,000,000
>$50,000,000
Architectural Fee3
9.0%
8.0%
7.0%
6.2%
5.3%
4.9%
4.5%
a. The architectural fee is a percentage of the direct cost for buildings. It includes a structural engineering fee, as well as
mechanical and electrical engineering fees that are associated with the building.
Source: RSMeans (2013), reference table R01 1 110-10.
D.4 Equipment Delivery, Equipment Installation and Contractor
Overhead and Profit
The equipment unit cost estimates in the WBS database include the cost of equipment delivery,
equipment installation and contractor overhead and profit (O&P). Because these costs are
included in the direct or process costs, the default value of this multiplier in the WBS models is 0
percent. If the user has site-specific or technology-specific data that show delivery, installation or
O&P costs outside of typical ranges, the user can change this factor on the indirect assumptions
sheet of each model to better account for actual installation costs.
The sources of unit cost quotes include manufacturers, vendors, published construction cost data
reference books and peer-reviewed literature. Price quotes for an item vary across sources
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because of inherent price variability or product quality differences that are not relevant to overall
performance. The U.S. Environmental Protection Agency (EPA) addressed this source of price
variability by including quotes from multiple vendors in the WBS cost database; the unit costs
used in the WBS models are simple averages across vendor quotes. Differences also arise
because vendors include different information in price quotes. For example, prices obtained from
RSMeans (2013) include all components needed for installed process costs (i.e., delivered
equipment, installation and O&P costs). Quotes from other sources may not include installation
costs, contractor O&P or transportation costs. Thus, before EPA calculated average costs, all
prices needed to be adjusted to the same installed cost basis. EPA converted costs to this basis by
adding transportation, installation and O&P costs where they were missing from the original unit
price estimates.
D.4.1 Equipment Delivery
Incorporating delivery costs in unit costs that will be used for a national cost analysis is
challenging because of variability in the methods used to assess transportation costs. For
example, transportation costs can be based on a cost per mile, a cost per unit of weight, a cost per
unit of volume, a cost per region or within a radius or a proportion of sales price. EPA developed
standardized transportation cost multipliers that vary by equipment type and size. The type of
multiplier selected for each equipment category is based on a likely method of transportation.
For tanks, vessels and towers, EPA applied a transportation cost based on equipment volume
units (e.g., gallons). For iron and steel tanks, the cost is based on a vendor quote of shipping
costs of $1,000 per 10,000 gallons of tank volume. For fiberglass tanks, the cost is based on a
vendor quote of shipping costs of $600 per 10,000 gallons of tank volume. EPA included
minimum and maximum transportation costs for tanks, vessels and towers. For steel equipment,
the minimum transportation cost is $500, which applies to all items with volumes below 5,000
gallons, and the maximum transportation cost is $5,000, which applies to all items with volumes
over 50,000 gallons. For plastic/fiberglass equipment, the minimum transportation cost is $500,
which applies to all items with volumes less than 10,000 gallons, and the maximum
transportation cost is $3,000, which applies to all items with volumes over 50,000 gallons. For
very small plastic/fiberglass equipment, EPA used an alternative minimum shipping charge of
$100, which applies to all items with volumes less than 100 gallons.
To estimate transportation costs for pipe, EPA calculated delivery costs per linear foot of pipe
using vendor delivery cost estimates and linear feet/truck load estimates. EPA averaged two
vendor delivery estimates for 30-inch and 48-inch American Water Works Association C200
steel pipe to obtain an estimate of $197.75 for a truckload of pipe. Information obtained from
vendors was used to estimate the number of linear feet of each size pipe that could fit in a
truckload.
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For valves, pumps, blowers and mixers, EPA developed transportation cost estimates based on
equipment weight and costs for "less than a load" (LTL) shipments obtained from vendors. The
estimates assume an average delivery distance of 100 miles. For shipping cost estimation
purposes, average weights were assumed for the small, medium and large sizes of valves, pumps,
blowers and mixers. The assigned weights (which are based on the actual weights of valves,
pumps, blowers and mixers for which EPA received vendor quotes) are as follows:
• Small steel valves -30 pounds
• Medium steel valves ~ 80 pounds
• Large steel valves ~ 400 pounds
• Small pumps / blowers -100 pounds
• Medium pumps/blowers-3 00 pounds
• Large pumps / blowers - 600 pounds
• Small mixers - 50 pounds
• Medium mixers - 100 pounds
• Large mixers - 400 pounds.
Since the density of 304 stainless steel is approximately 5.6 times greater than the density of
polyvinyl chloride, the following weights were assigned to plastic valves:
• Small plastic valve - 5 pounds
• Medium plastic valves - 15 pounds
• Large plastic valves - 70 pounds.
EPA rounded shipping costs to the closest $10 increment. Exhibit D-2 provides the weight
categories and LTL costs for valves, pumps, blowers and mixers, along with a complete
summary of transportation cost methods for all categories of equipment.
EPA assumed a 5 percent markup on miscellaneous equipment and filter components for
membrane systems. For system control components, EPA assumed no transportation costs,
because the vendors contacted did not charge for shipping on large orders (i.e., greater than
$300). Transportation costs for chemicals, resins and filter media are averages of delivery costs
obtained from vendors. EPA used shipping rates for standard service from a vendor for
instrumentation transportation costs; the vendor uses fixed shipping rates that vary according to
the equipment price.
D.4.2 Installation, Overhead and Profit
EPA incorporated installation and O&P costs using multipliers derived from RSMeans (2013)
cost data. RSMeans provides complete installed cost estimates for the unit costs in its database.
The following cost components are reported for each unit cost:
• Bare material costs, including delivery
• Installation labor, materials and any rental cost for installation equipment
• Overhead for installing contractor (i.e., labor and business overhead costs)
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Profit for installing contractor (i.e., a 10 percent rate of profit charged on materials,
installation and overhead costs).
Exhibit D-2. Transportation Cost Estimation Methods
Equipment Category
Vessels, Tanks, Towers - steel
Vessels, Tanks, Towers -
plastic/fiberglass
Pipes
Valves-steel/iron
Weight Class 60
LTL rate = $101. 45/1 00 Ib
Valves-plastic
Weight Class 70 - plastics
LTL rate = $115.417 100 Ib
Pumps and blowers
Weight Class 85
LTL rate = $132.08/100 Ib
Mixers
Weight Class 85
LTL rate = $132.08/100 Ib
Miscellaneous Equipment
System Controls
Chemicals, Resins and Filter Media
RO/NF and MF/UF Skids and
Equipment
Instrumentation
Transportation Costs
$1 ,000 per 10,000 gallons of volume for each tank. There is a minimum shipping
charge of $500 and a maximum of $5,000.
$600 per 10,000 gallons of volume for each tank. There is a minimum shipping charge
of $500 and a maximum of $3,000. Very small tanks (less than 100 gallons) have an
alternate minimum shipping charge of $100.
Varies by pipe diameter and material of construction.
Plastic pipes: range is $0.07-$41.20 per 100 linear feet.
Iron and steel pipes: range is $6.46-$494 per 100 linear feet.
Small valves: $30.00 (1"-4" diameter)
Medium valves: $80.00 (5"-9" diameter)
Large valves: $400.00 (10"+ diameter)
Small valves: $10.00 (1"-3" diameter)
Medium valves: $20.00 (4"-6" diameter)
Large valves: $80.00 (>6" diameter)
Small units: $130.00 (0-50 gpm)
Medium units: $400.00 (51-300 gpm)
Large units: $790.00 (>300 gpm)
Small mixers: $70.00 (includes mounted and portable mixers)
Medium mixers: $130.00 (includes inline and static mixers)
Large mixers: $400.00 (includes turbine, rapid, flocculant, impeller mixers)
5% of equipment cost
None
$0.22/lb for hazardous materials
$0. 27/lb for filter media and resins
$0.18/lb for 150 Ib chlorine cylinders
$0.24/lb for 1 ton chlorine cylinders
$0.06/lb for all other chemicals
5% of equipment cost
Varies with cost of equipment. Range is $9.95 to $104.35 per unit of equipment.
Ib = pound
gpm = gallons per minute
" = inch
RO/NF = reverse osmosis/nanofiltration
MF/UF = microfiltration/ultrafiltration
These component cost data provide enough information to calculate adjustment factors that can
be applied to price quotes that exclude installation and O&P costs. By dividing total unit cost,
which includes all components, by bare material cost including delivery, EPA obtained
adjustment factors for several types of equipment in the WBS cost database. For example, if the
bare material cost, including delivery, for an item of equipment is $1.00 and the total unit cost is
$1.78, then the adjustment factor is 1.78. When unit costs obtained for the database did not
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include installation, overhead and profit (as is typical when obtaining costs from manufacturers),
EPA applied these adjustment factors to escalate the unit costs so that they represented the full
installed cost. For example, if a manufacturer's price for a 20,000 gallon steel tank was $25,000,
EPA would first add delivery cost ($1,000 per 10,000 gallons capacity, as described in Section
D.4.1), resulting in a cost with delivery of $27,000. EPA would then multiply that cost by the
appropriate adjustment factor (for instance, 1.17) to obtain a complete unit cost—that is, the total
unit cost in this example would be ($25,000 + $2,000) x 1.17 = $31,500.
Most of the installation and O&P multipliers in the WBS cost database fall between 1.03 and
1.73, with an average around 1.36.
D.5 Site Work
Every construction site requires a certain amount of site preparation and finish work. Site work
costs include site preparation, excavation and backfilling, temporary and permanent road
construction, retaining wall construction, final grading, landscaping, parking lots, fencing, storm
water control structures, yard structures, site cleanup, waste disposal and utilities.
Estimating the site work cost based on a factor applied to the direct capital cost is an approach
commonly used when detailed information about the site plan is not known. Under this approach,
site work costs are typically estimated between 5 and 15 percent of the direct capital costs,
depending on project size and scope.
Site work costs vary directly with the land area requirement. The WBS models generate land
area estimates, which allows the models to use an alternative cost estimation approach based on
total project land area instead of total project costs. RSMeans (2013) provides an analysis of
actual reported project and component costs for different types of construction. Of the many
building categories reported in the summary database, the "factory" category best fits the scope
of construction associated with drinking water treatment plants. Therefore, the models use the
national average median project cost for site work at factories from RSMeans (2013). The WBS
cost database automatically updates this unit cost to current year dollars using the Engineering
News-Record (ENR) Building Cost Index (see Chapter 2). The models compute a site work cost
based on this unit cost and the total project land area, excluding land used for residuals holding
lagoons and evaporation ponds. Since the models include the cost of excavation and backfill for
these facilities, there is no need to include them in the site work calculations.
EPA believes that using an approach based on land area instead of direct process costs provides a
better estimate of site work costs because the unit costs from RSMeans (2013) are primarily
based on quantities of area and earthwork volume. Furthermore, this approach is less sensitive to
cost fluctuations caused by high cost equipment—the site work cost for a 0.5-acre project site
will be the same regardless of whether the treatment building houses chemical addition or a
membrane filtration process. This is particularly important because expensive, advanced
treatment technologies often have smaller footprints than lower-cost, conventional technologies
such as conventional filtration. Basing site work costs on process costs will tend to overstate site
work costs for such advanced technologies.
Although the default site work cost in the WBS models reflects a median value, the user can
enter a different rate in the WBS cost database based on site-specific conditions. A higher cost
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factor should be entered for projects where the site conditions may require higher-than-average
site work costs (e.g., a site with steep terrain that may require retaining walls). Conversely, a
lower rate should be entered for projects where the site conditions may require lower-than-
average site work costs (e.g., a site where little grading is needed and where requirements for
infrastructure and other site improvement are minimal or where portions are already in-place).
D.6 Yard Piping
Yard piping costs reflect the costs to install piping for untreated, partially treated and treated
water to and from the site, between new treatment plant buildings or between existing and new
treatment units. It does not include piping of treatment residuals to a residuals treatment system,
to disposal in a sewer or to a direct discharge connection; those costs are included as explicit
capital cost line items in the relevant WBS technology models, as discussed in Appendix C.
Yard piping costs include the following components:
• Trench excavation, backfill and pipe bedding
• Piping from the boundary of the building buffer zone to and from the building inlet and
building outlet and in between buildings that house water treatment components
• Optionally, piping from the water source to the property boundary and piping from the
property boundary to the distribution system connection
• Thrust blocks.
The sections below describe each of these components.
D.6.1 Trench Excavation, Backfill and Pipe Bedding
Costs of pipe contained in the WBS cost database are installed costs for aboveground pipes
within the treatment facility. Yard piping generally is installed below ground. Therefore, yard
piping entails additional costs. These costs include trench excavation costs, bedding costs,
backfill costs and thrust block costs (discussed in Section D.6.3).
Technology land area requirements are calculated on a basis of starting with a square building
with the required footprint and adding a non-fire buffer (10 feet) on three sides of each building
and a fire buffer (40 feet) on the fourth side. The general configuration assumption is that the fire
buffer will be located along the front side and the distance between buildings will be two times
the non-fire buffer distance (20 feet) and, therefore, yard piping will not cross the fire buffer
area. Thus, the minimum initial trench length is 20 feet (10 feet at inlet and 10 feet at outlet) for a
system with one building or 30 feet (20 feet inlet and outlet and 10 feet between buildings) for a
system with two buildings. Since the inlet and outlet piping may not always line up and may
extend inside the building perimeter, an offset distance is added to the 10 foot buffer distance
based on the building size. The offset distance is assumed to be 1A the length of one side of the
building footprint (based on square root of total building footprint).
The models assume yard piping will be buried with the top of the pipe set at or below the local
frost depth. Where frost depth is less than 30 inches, a minimum depth of 30 inches is assumed
to provide a protective cover. The default frost depth is 38 inches and corresponds to the frost
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depth in St. Louis. Users can change the frost depth on the indirect assumptions sheet of each
model based, for example, on the climate data for a selected city in the climate database
(AFCCC, 2000). Trench depth also incorporates the pipe diameter and the bedding depth, which
the models assume to be 6 inches below the bottom of the pipe. This default value is sufficient to
approximate bedding requirements for large size pipes laid in soils where bedding is necessary.
The user has the option of changing the default value on the indirect assumptions sheet of each
model.
Trench width is equal to the pipe diameter plus 1 foot on either side. Trench volume is based on
the calculated trench length times the trench cross-sectional area, which incorporates trench
width and depth and assumes sloped trench sides, with an angle of 45 degrees (expressed in
radians on the indirect assumptions sheet). Excavation and backfill costs are based on total
trench volume plus thrust block volume and the unit cost for excavation and backfill. Although
backfill quantities are generally smaller than excavation quantities, they are assumed to be the
same in the WBS models. This approach is assumed to cover to the cost of backfill and the cost
of spreading or hauling excess soil off site. Pipe bedding volume accounts for the bedding depth,
incorporating additional volume to account for the sloped sides of the trench and the assumption
that the bedding covers 25 percent of the pipe diameter. The user can change this latter
assumption on the indirect assumptions sheet of each model.
D.6.2 Piping
The basic assumptions for yard piping from the boundary of building buffer zone to and from the
building inlet and building outlet and in between buildings are:
• Pipe length will be equal to trench length plus two times the trench depth.
• Pipe costs will be based on an equivalent pipe length, which will include an additional
length to account for cost of fittings (e.g., elbows). The equivalent length will be equal to
two times the pipe length, using the same factor used for process piping within the
buildings (see Section 2.4).
• Yard piping costs do not include valves.
• Piping materials, diameter and unit cost are the same as those selected in the treatment
model for inlet and outlet piping within the building.
In addition, the indirect assumptions sheet in each model contains an optional assumption for the
length of yard piping from the water source and another optional assumption for the desired
length of yard piping to the distribution system. Therefore, if the technology is not the initial step
in the treatment train, the default value length of pipe from the water source should be 0 feet,
because there is already a pipe from the water source to the existing facility. Similarly, if the
technology is not the last technology in the treatment train, then the default value should be 0
feet. As a default, these assumptions are set to zero.
D.6.3 Thrust Blocks
Yard piping costs include concrete thrust blocks to hold small pipe elbows and other fittings in
place. The basis of the thrust block volume calculation is thrust force in pounds. The models
derive thrust force using a lookup table based on pipe diameter. Users can modify this lookup
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table on the engineering lookup sheet of the WBS cost database. The values in the lookup table
assume a pipe test pressure of 150 pounds per square inch and a pipe elbow angle of 90 degrees
and account for block weight. Although both vertical and horizontal elbows are expected in
every pipe-laying job, the thrust block calculations assume horizontal thrust blocks.
Using the data from the thrust force lookup table, the models calculate bearing surface area based
on a conservative approach found in U.S. Army Corps of Engineers guidance (U.S. ACOE,
1992). The calculation is:
Area = 1.5*T/(Soil Density*Kp*Depth*R)
where:
1.5 is a safety factor, which is typical for thrust block design
T is the thrust force required, derived as discussed above
Soil Density is the minimum soil bulk density, which the models assume is 1.55 grams
per cubic centimeter (97 pounds per cubic foot) consistent with loamy sand, which is also
on the lower end of the range for sandy soils (1.5-1.8) and the upper end of the range for
silty clay (1.4-1.5) (MNNRSC, 2003)
Kp is the coefficient of passive pressure, which the models assume to be 3, based on an
internal angle of friction of the soil (phi) of 30 degrees
Depth is the depth to bottom of the block, which the models calculate based on trench
depth and pipe diameter
R is a reduction factor of 0.467, based on phi of 30 degrees and a vertical bearing surface
(CADOT, 2001, Figure 8).
Users can adjust soil density, Kp and R on the indirect assumption sheet of each model. Note that
this approach is conservative in that it considers only the bearing force of the vertical surface,
which is perpendicular to the thrust force, and ignores the frictional force exerted on the bottom
surface of the block. Use of deeper trench depths will result in lower thrust block costs.
D.7 Geotechnical Investigation
Construction cost estimates generally include a geotechnical allowance to provide for
investigation of subsurface conditions. Subsurface conditions can affect the foundation design
and construction technique. For example, a high groundwater table or soft substrate may require
special construction techniques such as piles and dewatering. Thus, the actual costs of addressing
subsurface conditions are site specific and can vary considerably. In addition, where a system is
adding treatment technology to a site with existing structures and, therefore, the site already has
an existing geotechnical investigation, additional geotechnical investigation may not be required.
To account for these variations, the models include assumptions that allow the user to select
whether geotechnical investigation costs should be included for low, medium and high cost
estimates. The default values for these assumptions include geotechnical costs only for high-cost
systems. However, the models always include geotechnical costs (regardless of the value
selected for these assumptions) when certain components are included in the technology design,
such as septic systems, evaporation ponds or below-grade structures like basins.
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Geotechnical investigations can be as simple as digging trenches or test pits to determine the soil
conditions underlying small, lightweight structures. For larger, heavier structures, site
investigations generally involve drilling boreholes to extract samples of rock or soil for further
study. Cost estimates in the WBS models reflect either test pit costs or borehole costs, depending
on the building footprint size. For footprints of 2,000 ft2 or smaller, the WBS models have costs
based on hand digging test pits. All larger structures have costs based on the costs of drilling
boreholes. The following sections describe the method for estimating costs for each approach.
D.7.1 Borehole Cost Analysis
The cost analysis for drilling boreholes includes preparation activities (e.g., staking the field) and
actual drilling. Thus, a key cost driver is the number of boreholes needed. An additional factor is
the required drilling depth.
For a large industrial building, a borehole should be drilled at the expected location for each
column foundation and at locations where concentrated loads are expected to occur such as under
tanks and heavy equipment. The models assume four boreholes is reasonable for structures in the
range of 2,000 to 4,000 ft2. For larger structures, the models assume an additional borehole for
every 1,000 ft2 in additional space. Thus, the requirement for structures in the range of 4,001 to
5,000 ft is five boreholes. This approach is based on the assumption that column footings are
spaced approximately 32 feet apart.
Drilling depth depends on a structure's weight and existing knowledge of subsurface conditions.
Nevertheless, a rough criterion used to develop WBS cost estimates is that boreholes should
penetrate at least 1.5 times the width of the footings below the lowest portion of the footing
(Krynine and Judd, 1957). The lowest portion of the footing must be below the frost line, which
ranges from almost 0 feet to more than 5 feet in the continental United States. The WBS models
assume a frost line depth of 38 inches, an additional safety depth of 22 inches and a footing
width of 3 feet to obtain a minimum borehole depth of approximately 10 feet (5 feet + 1.5x3
feet).
EPA selected three different boring depths to represent a range of geologic conditions and
building bearing loads. A boring depth of 10 feet applies to relatively light structures in areas
where the soil conditions are predictable without any expectation of deeper strata that exhibit
poor shear strength. A boring depth of 25 feet applies to moderately heavy structures in areas
where subsurface conditions are less well defined, but no severe conditions are expected and
where underground structures, such as basins, as deep as 20 feet need to be constructed.
Similarly, a boring depth of 50 feet deep applies to heavy structures in areas where extreme or
unknown subsurface conditions (such as strata with poor shear strength) may exist.
EPA developed cost estimates based on cost data for drilling activities that use a truck-mounted,
2.5-inch auger with casing and sampling from RSMeans (2013). Exhibit D-3 identifies the cost
elements included in borehole drilling. The WBS cost database automatically updates the unit
costs for these elements to current year dollars using the ENR Construction Cost Index (see
Chapter 2). Costs are applied based on the selected borehole depth and total structure area
rounded up to the nearest thousand ft2.
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Exhibit D-3. Cost Elements Included in Borehole Drilling
Item
• Borings, initial field stake out and determination of elevations
• Borings, drawings showing boring details
• Borings, report and recommendations from professional engineer
• Borings, mobilization and demobilization, minimum
• Borings, drill rig and crew with truck mounted auger (output 55 feet/day)
• Borings, cased borings in earth, with samples, 2.5-inch diameter.
Source: RSMeans, 2013, 02 32 13.10-0200.
D.7.2 Test Pit Cost Analysis
For smaller, less expensive buildings, boreholes are less cost effective compared to test pits or
trenches that can be dug by hand or by using earth moving equipment if it is already available at
the site. Because geotechnical investigations may precede site work, excavating equipment may
be available to dig test pits. Therefore, for small buildings, the models use hand-dug test pits as
the basis for costs. The models assume one pit for buildings up to 1,000 ft2 and two pits for
buildings of 1,001 to 2,000 ft2.
Pit widths range from 4 feet by 4 feet to 6 feet by 8 feet (Krynine and Judd, 1957). Because this
test method is limited to small buildings, the models assume pits that are 4 feet by 4 feet wide.
Pit depth of 7 feet is based on a footing width of 2 feet and a frost depth of 5 feet (5 feet + 1.5x2
feet). The unit excavation and backfill costs are based on data from RSMeans (2013) for hand
dug pits in heavy soil. The cost of surveying and the soil sample evaluation report and
recommendation from a Professional Engineer are assumed to be the same as for borings.
D.8 Standby Power
A new treatment facility sometimes requires a standby power source that can produce enough
energy to operate the facility in the event of an electricity outage. Thus, the power rating or
capacity of the standby generator should be sufficient to power critical operating components at
the rated maximum flow capacity of the equipment (i.e., the design flow). Critical components in
a treatment plant include pumps, lighting and ventilation. In addition, standby power can be
required to provide space heating (if an electrical resistance heater or heat pump is used) and/or
cooling in the event of a power outage. As a default, the WBS models do not include heating or
cooling in their estimate of standby power requirements. The user can change the assumptions
about inclusion of heating and/or cooling in standby power on the indirect assumptions sheet of
each model.
17
Also as a default, the models do not include standby power at all for small systems with a design
flow of less than 1 MOD. These small systems typically operate for only a few hours each day,
placing water in storage for use during the rest of the day. This operating procedure means small
systems can handle short term power outages simply by postponing their operating hours,
17 Note that if the assumption about including heating in standby power is changed, heating requirements will only
be included in standby power if an electrical resistance heater or heat pump is used, because the other heating
options (e.g., natural gas heat) do not use electricity.
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without the need for standby power systems. The user can change the assumption about
including standby power for small systems on the indirect assumptions sheet of each model.
The generation capacity requirement for critical systems is based on the maximum daily load,
which is the potential energy demand to meet production at the design flow rate. Since the
energy requirements calculated in the models are based on continuous operation (24 hours/day
and 365 days/year), the maximum power requirement in kilowatts (KW) can be estimated using
the following equation:
power requirement for critical operating components (KW) =
[annual power use by critical operating components (MWh/yr) / 365 (day/yr) / 24 (hr/day)] *
1,000 (KW/MW)
where:
hr = hours
MW = megawatt
MWh/yr = megawatt hours per year
yr = years
Standby power costs primarily comprise equipment purchase (e.g., a generator) and installation.
Additional costs include fuel purchase and storage. Annual fuel costs for standby power
generation are hard to estimate or predict, given the unpredictable nature of using the standby
power generator. Typical standby generators consist of diesel engine powered generators
(NREL, 2003). Installation costs include provisions for a foundation, fuel storage and louvered
housings for larger systems. For the diesel generators typically used for standby power, EPA
used installed unit costs from RSMeans (2009a). The WBS cost database automatically updates
these unit costs to current year dollars using the Producer Price Index from the Bureau of Labor
Statistics for motors, generators and motor generator sets (see Chapter 2). The models multiply
the appropriate unit cost, which users can change in the WBS cost database, by the calculated
standby power requirement in KW, after applying a minimum requirement of 1.5 KW (based on
the smallest available standby power generator).
D.9 Electrical
The electrical cost allowance in a construction cost estimate will primarily account for electric
wiring inside structures, such as wiring for motors, duct banks, motor control centers, relays and
lighting. The unit costs for buildings in the WBS models (see Appendix B) already incorporate
general building electrical, such as building wiring and lighting fixtures and electrical
engineering associated with those components. In addition, certain electrical costs (motor/drive
controllers, variable frequency drives and switches) are included in direct costs for system
controls and pumps. Technologies with significant process equipment located outside include an
electrical enclosure as an explicit line item. Thus, the indirect cost electrical allowance only
accounts for additional electrical equipment associated with the treatment facility, including
outdoor lighting, yard wiring, switchgear, transformers and miscellaneous wiring. Yard wiring
consists primarily of the infrastructure that connects a new treatment facility to the power grid
and, if necessary, converts voltage.
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Typical electrical percentages include:
• Building electrical as a percentage of building cost = 7.7 to 13.0 percent, depending on
building size and quality (Association for the Advancement of Cost Engineering
International [AACEI] building cost model results)
• Seymour, Indiana electrical costs as a percentage of non-electrical process costs = 12.1
percent (AWWC, 200la)
• St. Joseph, Missouri electrical costs as a percentage of non-electrical process costs = 8.7
percent (AWWC, 200Ib).
Based on these data, the electrical percentage in the WBS models is 10 percent as a default.
Users can change this assumption on the indirect assumptions sheet of each model.
D.10 Instrumentation and Control
Instrumentation and control (I&C) costs include a facility control system and software to operate
the system. The WBS models include detailed process cost estimates for instrumentation and
control, as described in Appendix A. Therefore, the default value for I&C on the indirect
assumptions sheet is 0 percent. This line item remains among the indirect costs on the output
sheet of each model, however, to allow the user to incorporate any site-specific or technology-
specific data that cannot be accommodated by altering the I&C design assumptions in the WBS
models.
D.11 Process Engineering
Process engineering costs include treatment process engineering, unit operation construction
supervision, travel, system start-up engineering, operating and maintenance manual development
and production of record drawings. Process engineering as a percent of installed process capital
cost ranges from 5 to 20 percent. For example, Brayton Point Power Plant Water Works process
engineering costs were estimated at 8 percent of installed capital costs (Stone and Webster,
2001).
The ratio of process engineering to installed process capital cost varies based on system size and
the complexity of the treatment process. In particular, engineering cost as a percentage of process
cost tends to decrease as the size of the treatment plant increases. The default values in the WBS
models reflect this pattern: 8, 12 and 20 percent for large, medium and small systems,
respectively. The WBS models apply these percentages to installed process costs, but not
building costs, because structural, mechanical and electrical engineering fees are included in the
architectural fee (Section D.3).
The process engineering percentages at 13 EPA demonstration sites for low-flow packaged
systems ranged from 20 to 80 percent, with a mean of 36 percent (U.S. EPA, 2004). These
percentages, however, also include permitting and administrative costs. Because these costs are
separate line items in the WBS models, these percentages overstate stand-alone process
engineering costs. Furthermore, engineering costs can be higher for technologies in the
demonstration phase than for those in wide use. Therefore, EPA retained its assumption of 20
percent process engineering cost for small systems.
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D.12 Contingency Cost
Contingency cost reflects the degree of risk that management assigns to a project. This cost
should reflect the statistical probability of additional project costs because of uncertainties and
unlikely or unforeseen events (AACEI, 1996). These unforeseeable additional costs to the project
occur because of changes in design, materials, construction methods and/or project schedule.
Contingency reflects a judgment by project management or bidders to account for unforeseeable
costs, thereby avoiding cost overruns. Contingency costs are included as part of a construction
contract allowing the contractor to be paid extra upon authorization of design and construction
changes by the project engineer (AACEI, 1996).
The risk of additional unforeseen costs associated with construction projects tends to vary with
project size and complexity. Therefore, EPA developed contingency factors using both project
size (i.e., total direct cost) and complexity (i.e., the technology being modeled) as input
variables. Ideally, a contingency cost estimate is based on statistical data or experience from
similar projects. By their nature, however, contingency costs are site specific and difficult to
predict; two estimators may recommend different contingency budgets for the same project
(Burger, 2003). EPA examined recommended contingency values, tabulated by project size,
from an economic analysis of water services (GeoEconomics Associates Inc., 2002). The
recommendations are presented in Exhibit D-4. These contingency rates, which range from 2 to
10 percent, are applied to the base costs (i.e., direct costs) to derive contingency cost. These rates
apply to projects of low to average complexity. Water treatment construction projects typically
fall into this category, depending on the technology being installed.
Exhibit D-4. Recommended Contingency Rates from an Economic Analysis of
Water Services
Project Base (Direct) Cost
Up to $100,000
$100,000 to $500,000
$500,000 to $1,500,000
$1,500,000 to $3,000,000
Over $3,000,000
Contingency as a Percent
of Base Costs
10%
8%
6%
4%
2%
Source: GeoEconomics Associates Inc. (2002)
The WBS models would ideally include only the part of a contingency budget that is actually
spent, rather than the total amount budgeted. EPA therefore considered a Construction Industry
Institute (2001) study, which included both budget estimates and actual spending for contingency
in a series of heavy construction projects. Exhibit D-5 presents the relevant results. The factors
are expressed as a percentage of the total budget, rather than direct costs. These projects are not
limited to water treatment systems and include a variety of heavy construction projects. The data
in Exhibit D-5 show that, with the exception of very large projects (those with total project costs
of over $100 million), the contingency cost tends to decrease as project size increased. The
average contingency factor decreases from 6 to 4 percent before increasing to 7 percent for very
large projects. Such very large projects are generally beyond the size of projects that can be
modeled using the WBS models. Exhibit D-5 also shows that unforeseen problems during
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construction tend to account for a higher share of contingency cost than design or procurement
problems.
Exhibit D-5. Average Contingency Costs in Budgets for Heavy Industrial Projects
Project
Size
<$15
$15-$50
$50-$ 100
>$100
Budgeted Costs
Total
Budget
8.09
30.22
70.70
214.02
Contingency
Estimate
0.46
1.55
3.09
15.56
Contingency
(% of budget)
6%
5%
4%
7%
Final
Project
Cost
$7.76
$29.51
$68.19
$206.50
Project Phase Contingency Costs
Incurred (Excluding Project
Planning Phase, Demolition and
Start Up)
Design
0.04
0.20
0.25
2.00
Procurement
0.10
0.30
0.83
4.24
Construction
0.20
0.65
1.16
7.39
Contingency
Incurred /
Budgeted
74%
74%
72%
87%
All costs are in millions of dollars.
Source: Cll (2001)
The contingency factors in Exhibit D-5 are higher than the recommended values in Exhibit D-4.
Because Exhibit D-5 data is empirical and the basis for the estimates in Exhibit D-4 is not clear,
EPA based its contingency factors in the WBS models primarily on the values in Exhibit D-5,
but incorporated additional price categories below $15 million with contingency factors above 6
percent. To create the contingency factors, EPA first converted the figures in Exhibit D-5, which
are expressed as percentages of a total budget, to markups. For instance, if the contingency
budget is 7 percent of a total budget, it represents a markup of 7 / (100 - 7) percent = 7.5 percent.
EPA modified the markups by a factor of 0.77, which is the average ratio of incurred to budgeted
contingency costs in Exhibit D-5. Exhibit D-6 presents the resulting base contingency factors.
These represent the contingency or risk prior to consideration of technology complexity.
Exhibit D-6. WBS Model Contingency Factors Prior to Consideration of
Technology Complexity
Project Direct Cost Range
<$500,000
$500,000 to $3,000,000
$3,000,000 to $15,000,000
$15,000,000 to $50,000,000
$50,000,000 to $100,000,000
>$100,000,000
Base Contingency Factor
6.7%
5.8%
4.9%*
4.1%*
3.2%*
5.8%*
* Percentages based on CII-Benchmarking & Metrics Analysis Results (Cll, 2001).
While there are techniques and computer programs designed to estimate contingency factors for
large projects based on construction activity risk simulation, the engineering costing literature
and the example projects EPA reviewed do not provide specific quantitative guidance regarding
the effect of project complexity on contingency costs. Nevertheless, the anecdotal evidence
suggests that risks (and, therefore, contingency costs) increase when project complexity
increases.
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Among the WBS technologies, project complexity depends on the type of technology employed
and the general degree of experience with the technology as it will be applied. Well-established
technologies, which have a depth of construction and technology installation and operational
history under a variety of conditions, are expected to have low risk with respect to unforeseen
problems during construction and installation. Recently developed technologies or ones that have
had limited application to a variety of water quality conditions and project sizes (or to the
conditions at the project in question) are expected to have a higher degree of risk.
To account for differences in contingency values associated with technology type and project
complexity, EPA identified four categories of project complexity and assigned multipliers that
the models use to adjust the contingency factors (up or down) from Exhibit D-6:
• Low complexity = base contingency factor x 0.5
• Average complexity = base contingency factor x 1.0
• High complexity = base contingency factor x 1.5
• Very high complexity = base contingency factor x 2.0.
Thus, for each technology, the applied contingency factor combines the effects of project size
and technology complexity to obtain the project specific contingency factor. EPA assigned a
project complexity category to each WBS technology based on general knowledge and the
application history of the technology to drinking water treatment. Exhibit D-7 shows this default
complexity category assignment. The user can change these values on the indirect assumptions
sheet of each model if specific knowledge of the technology and its expected performance under
the site-specific conditions warrant such a change.
The WBS models assume that contingency costs are incurred only in high cost scenarios (see
Section 2.3). For low and medium cost estimates, the models assume construction is completed
with a minimum of unforeseen site-specific costs and, therefore, that none of the contingency
budget is incurred. Users can change this assumption on the indirect assumptions sheet of each
model.
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Exhibit D-7. WBS Default Complexity Factors by Technology
Technology
Acid Feed
Cation Exchange
Caustic Feed
Nontreatment Options
Potassium Permanganate Addition
Granular Activated Carbon
Chlorine Gas
Packed Tower Aeration
Adsorptive Media
Anion Exchange
Biological Treatment
Microfiltration and Ultrafiltration
Greensand Filtration
Hypochlorite Addition
Multi-stage Bubble Aeration
Reverse Osmosis and Nanofiltration
Ultraviolet Advanced Oxidation Processes
Ultraviolet Disinfection
Risk Level Assigned to
Technology
Low
Low
Low
Low
Low
Average
Average
Average
High
High
High
High
High
High
High
High
Very high
Very high
Default Complexity
Factor
0.5
0.5
0.5
0.5
0.5
1
1
1
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
2
2
D.13 Miscellaneous Allowance
In a cost estimate for a construction project, an allowance may be included for conditions or
events that the estimator can anticipate, but whose cost is not known with any degree of
certainty. If, for example, the site is expected to have contaminated soil that may require
remediation, the allowance will incorporate the resulting costs. An allowance differs from a
contingency cost, which provides contract coverage for unpredictable conditions. The allowance
funds account for anticipated additional costs that should become apparent at a later stage of the
project (for example, upon completion of the site investigation activities and the detailed
engineering design). Much of this cost is associated with knowledge of site-related conditions.
In a national average cost estimate such as the one that the WBS models generate, it is not
possible to allow for the specific conditions associated with any given site. However, the models
include an allowance line item to simulate an average effect due to such conditions. The line also
accounts for the level of detail in the WBS design, since the models do not include all minor
process components.
The WBS models assume a miscellaneous allowance of 10 percent as a default. Since the
allowance addresses a modeling uncertainty, there is little guidance available from the cost
estimation literature. Instead, the assumption must be validated by comparing WBS output to
actual water treatment facility construction costs. Users can change the miscellaneous allowance
on the indirect assumptions sheet of each model.
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D.14 Legal, Fiscal and Administrative
This category includes project management, accounting and administrative activities related to
the project, excluding permitting. The cost can range from 2 to 5 percent of the process cost. In
the WBS models, this category is considered to account for administrative costs that the
purchaser incurs in the course of procurement. These costs are distinct from the construction
management fee, which is included as a separate indirect cost (Section D. 17). The WBS models
use a default value of 2 percent. Users can change this assumption on the indirect assumptions
sheet of each model.
D.15 Sales Tax
Water treatment plant projects may be exempt from the sales tax, particularly those constructed
with public funds. The default value in the WBS models is 0 percent, which reflects the status of
taxes in social cost analysis. Taxes are considered a transfer payment and not an actual social
cost, which is based on the concept of opportunity cost. Transfer payments are not included in
social cost analysis, so a default value of 0 percent is appropriate for social cost analysis. The
WBS models include a sales tax line item among indirect costs because the models can also be
used for private cost analysis (e.g., for a specific utility), which includes transfer payments.
Users can enter a sales tax percentage on the indirect assumptions sheet of each model in cases
where consideration of transfer payments is appropriate.
D.16 Financing During Construction
Engineering cost estimates include interest for financing of the project. Drinking water systems
can obtain financing through various sources including Drinking Water State Revolving Funds
(DWSRF), public-sector financing, private-sector borrowing or equity instruments. Exhibit D-8
shows interest rates for drinking water treatment projects derived from the EPA 2006
Community Water Systems Survey. The default value in the WBS models is 5 percent, which is
toward the higher end of the range of financing costs for public and private systems, and
implicitly assumes 1 year of financing during construction. For small systems with design flow
less than 1 MOD, the models assume 0 percent financing during construction, implicitly
accounting for the very short construction time required for these systems. Users can change the
assumptions for both large and small systems on the indirect assumptions sheet of each model.
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Exhibit D-8. Average Interest Rates for Capital Funds
System Ownership Type and
Lender
Average Interest Rate
(All System Sizes)
Range of Average Interest Rates
Public Systems
DWSRF
Other Public Sector
Private Sector
Other
2.3
3.5
4.6
3.9
1.0-3.5
0.5-4.4
4.2-5.0
0.0-4.9
Private Systems
DWSRF
Other Public Sector
Private Sector
Other
5.6
4.4
6.5
5.9
0.8-6.2
3.1-5.5
4.3-7.7
0.0-10.0
All Systems
DWSRF
Other Public Sector
Private Sector
Other
2.6
3.8
5.2
4.3
All Systems and Lenders
1.0-4.3
1.9-4.5
4.3-5.5
0.0-10.0
0.0-10.0
D.17 Construction Management and General Contractor Overhead
As discussed in Section DA.2, the component costs in the WBS cost database include the cost of
installation, including O&P for the installing contractor. However, the installation cost does not
cover the cost of insurance, performance bonds, job supervision or other costs associated with
the general contractor. The WBS models account for these costs by combining costs and fees for
the following items:
• Builder's risk insurance
• Performance bonds
• Construction management.
Builder's risk insurance is casualty insurance for the project during construction and may cover
various risks, such as vandalism, fire, theft or natural disasters. According to RSMeans (2009c),
a national average rate is 0.34 percent of the project cost. EPA adopted this assumption for the
WBS models. Users can adjust this rate on the indirect assumptions sheet of each model.
Performance bonds compensate the owner for losses due to contractor failure to complete work
according to specifications. RSMeans (2006) estimates the costs based on the total direct cost of
the project, as described in Exhibit D-9.
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Exhibit D-9. Cost of Performance Bonds
Project Direct Cost Range
<$100,000
$100,000 to $500,000
$500,000 to $2,500,000
$2,500,000 to $5,000,000
$5,000,000 to $7,500,000
>$7,500,000
Performance Bond Cost
2.5%
$2,500 plus 1 .5% of the amount over $100,000
$8,500 plus 1 .0% of the amount over $500,000
$28,500 plus 0.75% of the amount over $2,500,000
$47,250 plus 0.70% of the amount over $5,000,000
$64,750 plus 0.60% of the amount over $7,500,000
Source: RSMeans (2006), reference table R0131 13-80.
The construction management fee is paid to the general contractor and covers the cost of job
supervision, an on-site office, main office overhead and profit. Various sources provide
individual estimates for these items, but the WBS models roll them into a construction
management fee to reflect a cost structure that the owner might see. RSMeans (2009c) provides a
table of typical construction management rates for jobs of various sizes. EPA adapted those rates
to develop those shown in Exhibit D-10.
Exhibit D-10. Construction Management Fees
Project Direct Cost Range
<$100,000
$100,000 to $250,000
$250,000 to $1,000,000
$1,000,000 to $5,000,000
$5,000,000 to $10,000,000
>$10,000,000
Construction Management Fee
10%
9%
6%
5%
4%
3.2%a
a. The reference quotes a fee range of 2.5% to 4% for a $50 million project. The WBS models assume an intermediate rate for
projects over $10 million.
Source: RSMeans (2009c), division 01 11 31.20.
The indirect line item for construction management and general contractor overhead sums all of
these costs. The costs can be omitted individually on the indirect assumptions sheet of each
model, either by an assumption that directly controls inclusion or exclusion or by setting the
appropriate percentage to zero. For example, in the case of small systems that use pre-engineered
package treatment plants, the models exclude the construction management fee portion by
default and include only the performance bond and builder's risk insurance. Because package
plants typically are skid-mounted and assembled offsite, they typically do not require a general
contractor to supervise their installation. Instead, their installation is managed by a single entity,
often the vendor that supplied the package.
D.18 City Index
This indirect cost accounts for city-specific and regional variability in materials and construction
costs. The city index factor included in the WBS models is expressed as a decimal number,
assuming a national average of 1.0. The default value in the WBS models is set to the national
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average of 1.0, which is appropriate for estimating national compliance costs. Users wishing to
adjust estimated costs to be more reflective of potential costs in specific geographic locations can
change the city index value on the output sheet. For example, to estimate costs for a city where
construction costs are 90 percent of the national average, the user would change the city index to
0.9. One source for region- or location-specific adjustment factors is RSMeans (2013), which
publishes average construction cost indices for various three-digit zip code locations.
D.19 List of Abbreviations and Symbols in this Appendix
DWSRF Drinking Water State Revolving Funds
EPA U.S. Environmental Protection Agency
ENR Engineering News-Record
ft2 square feet
I&C instrumentation and control
KW kilowatt
LTL less than a load
MGD million gallons per day
O&P overhead and profit
WBS work breakdown structure
D.20 References
Association for the Advancement of Cost Engineering International (AACEI). 1996.
Certification Study Guide. Morgantown, West Virginia.
Allis, William A. 2005. Personal communication with L. Petruzzi, SAIC. April.
Air Force Combat Climatology Center (AFCCC). 2000. Engineering Weather Data: 2000
International Edition. Published by the National Climatic Data Center.
American Water Works Corporation (AWWC). 1999. Preliminary Cost Estimate Summary:
Alton Water Treatment Plant, H&Sno. 1862. 1 January.
AWWC. 200la. Seymour, Indiana Process Cost Estimate.
AWWC. 200Ib. St. Joseph, Missouri Cost Estimate.
Burger, Riaan. 2003. "Contingency, Quantifying the Uncertainty." Cost Engineering 45, no. 8. 8
August.
California Department of Transportation (CADOT). 2001. Earth Pressure Theory and
Application.
Construction Industry Institute (CII). 2001. Benchmarking & Metrics Analysis Results. Austin,
Texas. May.
Fairfax Water Authority (FWA). 2003. New Construction Works Brochures. Virginia.
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GeoEconomics Associates Incorporated. 2002. An Economic Analysis of Water Services. Chapter
5.
Krynine, D.P. and W.R. Judd. 1957. Principles of Engineering Geology and Geotechnics.
McGraw-Hill. New York.
Minnesota Natural Resources Conservation Services (MNNRSC). 2003. General Guide for
Estimating Moist Soil Density. 10 May.
National Renewable Energy Laboratory (NREL). 2003. Gas-Fired Distributed Energy Resource
Technology Characterizations. U.S. Department of Energy.
RSMeans. 2006. Facilities Construction Cost Data. 21st Annual Edition. Kingston,
Massachusetts: RSMeans Company.
RSMeans. 2009a. Assemblies Cost Data. 34th Annual Edition. Kingston, Massachusetts:
RSMeans Company.
RSMeans. 2009b. Building Construction Cost Data. 67* Annual Edition. Kingston,
Massachusetts: RSMeans Company.
RSMeans. 2009c. Facilities Constru
Massachusetts: RSMeans Company.
RSMeans. 2009c. Facilities Construction Cost Data. 24th Annual Edition. Kingston,
RSMeans. 2013. Facilities Construction Cost Data 2014. 29th Annual Edition. Norwell,
Massachusetts: Reed Construction Data LLC.
Scoutten, Inc. 2009. Opinion of Probable Cost for Town Of Buckeye Water And Wastewater
Infrastructure and Water Resources Improvements Associated with 2009 Development Fees.
Revised 11 May. Online at http://www.buckeyeaz.gov/DocumentView.aspx?DID=640
Stone and Webster. 2001. Brayton Point Station Permit Renewal Application. Five Volumes.
Tampa Bay Water. 2006. West Pasco Infrastructure Project, Maytum WTP Modifications,
Project No. 05903. Memorandum from Kenneth R. Herd, Director of Operations and Facilities,
to Jerry L. Maxwell, General Manager. 1 December.
United States Army Corp of Engineers (U.S. ACOE). 1992. Revision of Thrust Block Criteria in
TM5-813-5/AFM88-10 VOL. 5 Appendix C. Publication Number: ETL 1110-3-446. 20 August.
U.S. Environmental Protection Agency (U.S. EPA). 2004. Capital Costs of Arsenic Removal
Technologies, U.S. EPA Arsenic Removal Demonstration Project, Round 1. EPA-600-R-04-201.
Cincinnati, OH: U.S. EPA, National Risk Management Research Laboratory.
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Appendix E. General Assumptions for Operating and
Maintenance Costs
E.1 Introduction
The work breakdown structure (WBS) models calculate operating and maintenance (O&M) costs
independently for each treatment technology. Nevertheless, there are several general assumptions
and estimation functions that are common to the O&M estimates across the treatment models.
This appendix describes those assumptions and functions. Any O&M cost element that is
technology-specific is included in the chapter describing that technology in the main document.
The O&M costs estimated in the WBS models primarily include annual expenses for:
• Labor to operate and maintain the new treatment equipment
• Chemicals required by the treatment
• Materials needed to carry out maintenance (including small tools)
• Energy.
Costs for commercial liability insurance, inspection fees, domestic waste disposal, property
insurance and other miscellaneous expenditures that are not directly related to the operation of
the technology are included in the WBS models by applying a miscellaneous allowance to the
total annual O&M costs. This calculation uses the same miscellaneous allowance percentage that
is applied to capital costs as an indirect line item (see Appendix D). Users can change this
percentage on the indirect assumptions sheet of each model.
The WBS models calculate O&M costs based on the inputs provided by the user on the input
sheet and values specified on the O&M assumptions sheet. These inputs include system size, raw
and finished water quality parameters and other factors that affect operation requirements such as
an option in the activated alumina model to regenerate media or operate on a throw away basis.
The design equations and assumptions incorporated in the O&M sheets are described below.
Despite provisions for user inputs, there are several factors that can affect site-specific O&M
costs in ways that are not readily reflected in the WBS outputs. These include:
• Operator expertise
• Equipment quality, design, installation and degree of automation
• Environmental conditions (e.g., changes in raw water quality over time).
Some O&M costs components, such as energy for pumping water or chemicals for treatment, are
well defined and readily estimated using an engineering cost approach. Other O&M cost drivers,
however, depend on multiple factors that are difficult to quantify and, therefore, represent a
challenge for estimating costs. For example, the required level of effort to operate or maintain a
technology depends on the level of complexity and sophistication of the installed technology, the
size of the treatment system, the professional level or education and training of the operator and
state and local regulations for process staffing.
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To complicate matters further, there are trade-offs between system capital costs and O&M costs.
Higher cost equipment may require less intensive maintenance or less hands-on operation. For
example, using mixers and tanks to prepare brine solution for regenerating an anion exchanger
might reduce equipment costs compared to using salt saturators. However, salt saturators require
less labor to use and potentially reduce the need for a salt storage facility. Also high quality,
highly automated systems can significantly reduce labor requirements, but increase capital costs.
The U.S. Environmental Protection Agency (EPA) included some adjustments to O&M costs in
the WBS models to account for some types of savings, which are described below.
E.2 Labor Costs
The WBS models calculate the annual hours of O&M labor in the following categories:
• Operator labor for operation and maintenance of process equipment
• Operator labor for building maintenance
• Managerial and clerical labor.
The WBS model labor hour estimates are intended to be incremental. That is, they only include
labor associated with the new treatment system components.
E.2.1 Operator Labor for Operation and Maintenance of Process Equipment
System operation includes the following primary tasks:
• Collecting data from process instruments and recording system operating parameters
• Preventative maintenance and calibration of process instruments
• Verifying the proper operation of pumps, valves and other equipment and controlling the
treatment process by adjusting this equipment
• Preventative maintenance of pumps, valves and other equipment
• Inspection and maintenance of chemical supplies
• Visual inspection of the treatment facility and system components
• Other, technology-specific tasks (e.g., managing regeneration, backwash or media
replacement).
Labor required for these tasks is sensitive to the level of system automation. As discussed in
Section 2.3 and Appendix A, the user has the option to choose from three levels of automation:
manual, semi-automated and fully automated. The assumptions about labor required for each
task vary depending on the level of automation selected, as shown in Exhibit E-l and discussed
below. Users can change these assumptions, if desired, on the O&M assumptions sheet of each
model.
EPA compared model results using these assumptions with annual labor hours reported for 12
different water treatment facilities. Most of the resulting model estimates were within +50
percent to -30 percent of the annual labor hours reported for the sample facilities.
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WBS-Based Cost Models for Drinking Water Treatment Technologies
Exhibit E-1. Operator Labor Assumptions
Task
Record system operating parameters from process
instruments (includes routine sampling)
Preventative maintenance and calibration of process
instruments
Verify and adjust pump operating parameters
Preventative maintenance of pumps
Verify and adjust valve positions
Preventative maintenance and inspection of valves
Visual inspection of facility
Inspect and maintain chemical supplies
Level of Automation
Manual
5 minutes per day
per instrument
Semi-automated
Automated
5 minutes per day
10 minutes per month per instrument
5 minutes per day per pump
None
30.25 hours per year per pump
5 minutes per week per valve
None
5 minutes per year per valve
1 minute per day per 100 square feet of facility
60 minutes per month per chemical supply tank
Collecting Data from Process Instruments and Recording System Operating
Parameters
For manual systems, the models assume 5 minutes per day per instrument associated with day-
to-day operation of the treatment process (e.g., flow meter, head loss sensor). Instruments
associated with intermittent processes (e.g., backwash flow meters) are not included in this
estimate, because observation of these instruments is included the operator labor associated with
managing the intermittent process. In semi-automated and automated systems, the control system
handles the task of collecting information from the various process instruments, so operator labor
is reduced to 5 minutes per day to keep a record of operating parameters.
Preventative Maintenance and Calibration of Process Instruments
Regardless of the level of automation, the models assume 5 minutes per month for each
instrument, including those associated with intermittent processes. While some instruments (e.g.,
chlorine residual analyzers) may require calibration more frequently than monthly, others (e.g.,
head loss sensors) will require limited, less frequent maintenance. Therefore, the models use 10
minutes per month as an average across the various types of instruments.
Verify and Adjust Pump Operating Parameters
For manual and semi-automated systems, the models assume 5 minutes per day per pump,
including metering pumps associated with continuous chemical feed processes. Pumps
associated with intermittent processes (e.g., backwash pumps) are not included in this estimate,
because operation of these pumps is included the operator labor associated with managing the
intermittent process. In automated systems, the control system handles this task, so no additional
operator labor is required.
Preventative Maintenance of Pumps
Regardless of level of automation, the models assume 30.25 hours per year for large, frequently
operated pumps (e.g., booster pumps). This estimate does not include small chemical metering
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pumps, but does include backwash pumps when these are operated more frequently than weekly.
The estimate of 30.25 hours per year is based on a list of recommended pump maintenance
activities from a vendor and the assumptions for each activity shown in Exhibit E-2.
Exhibit E-2. Pump Maintenance Activities
Interval
Monthly
Quarterly
6 months
Annual
Task
Check bearing temperature
Changing lubricant/ adjusting power level
Disassemble for inspection, reassemble
Check oil
Check lubricated bearings for saponification
Removal of bearings and replace, reassemble
Check packing and replace if necessary, reassemble
Vibration readings
Remove casing and inspect pump
If parts are worn, replace
Clean deposits and/ or scaling
Clean out stuffing box piping
Measure and record suction and discharge pipe head
Estimated Minutes/Task
5
30
60
10
10
60
60
10
120
varies
60
30
5
Total:
Estimated
Hours/Year
1
6
12
0.67
0.67
4
2
0.33
2
covered by pump
materials percentage
and pump useful life
1
0.5
0.08
30.25
Verify and Adjust Valve Positions
For manual and semi-automated systems, the models assume 5 minutes per week per valve on
the main process line. In automated systems, the control system handles this task, so no
additional operator labor is required.
Preventative Maintenance and Inspection of Valves
Regardless of level of automation, the models assume 5 minutes per year per valve on the main
process line.
Visual Inspection of Facility
r\
Regardless of level of automation, the models assume 1 minute per week per 100 square feet (ft)
of treatment system floor plan to conduct visual inspection of the overall process. This daily
inspection is in addition to inspection conducted as part of routine operation and maintenance of
major operational components (instruments, pumps and valves), as discussed above.
Inspect and Maintain Chemical Supplies
The models assume that chemical supplies, whether they are associated with continuous addition
or intermittent use, require additional attention beyond that included in daily visual inspection. In
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particular, they also require labor associated with receiving chemical shipments. Regardless of
level of automation, the models assume 60 minutes per month for each chemical storage tank.
Although counted on the basis of the number of tanks, this estimate is intended to cover all
components associated with the chemical supply system (e.g., checking pipes and valves for
leaks and inspecting and maintaining small metering pumps).
Technology-Specific Tasks
Many of the technologies include activities in addition to day-to-day operation that may require
operator attention, depending on the level of automation (e.g., intermittent regeneration,
backwash or media replacement). Where this is the case, the technology chapters in the main
document describe the specific assumptions required to calculate operator labor.
E.2.2 Labor for Building Maintenance
The WBS models include a building maintenance cost based on the building area (i.e., using a
unit cost in dollars per square foot per year). EPA developed this cost based on two sources:
Whitestone Research (2009) and RSMeans (2013). Specifically, EPA selected a list of
appropriate building maintenance repair and repair tasks from those listed in the two sources.
The selected tasks include those associated with preventative maintenance, small repairs and
major repairs. EPA estimated a frequency for each task by averaging the frequency
recommended in each of the two sources. Exhibit E-3 identifies the tasks included in the
maintenance and repair buildup. The models include maintenance and repair tasks for heating
and cooling systems only for buildings with the relevant systems. To avoid double-counting, the
task list does include tasks in the following categories:
• Maintenance of treatment system components that are already explicitly considered in the
models' maintenance labor and materials costs (e.g., pumps, valves, instruments)
• Full replacement of items that are explicitly given a useful life in the models (e.g., piping,
heating and cooling systems)
• Repair tasks with a lower frequency than the useful life assumed in the models for the
related WBS line item (e.g., skylight replacement has a recommended frequency of 40
years, whereas the models assume a useful life for the entire building of 37 to 40 years).
9
For the buildup, EPA assumed a baseline building area of 4,000 ft and building components
corresponding to a medium-quality building (see the assumptions in Appendix B). EPA
estimated costs for each task using data from RSMeans (2013) and assuming that preventative
maintenance and minor repairs would be conducted using in-house labor, while major repairs
would be conducted using outside contractors. These costs include both labor and materials.
Because repair needs do not follow a strict schedule, EPA annualized costs with no discount
rate—that is, a $100 task with a typical frequency of 5 years is assigned an annual cost of $20.
Labor accounts for most of the cost for the maintenance and repair tasks. Further, the Building
Cost Index and Construction Cost Index, the only two cost indices in the WBS cost database that
combine labor and material costs, do not include the costs of materials that are likely to be used
in building maintenance. The WBS cost database therefore uses the Employment Cost Index to
escalate the building maintenance costs to current year dollars.
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Exhibit E-3. Building Maintenance and Repair Tasks
• Minor repairs and refinishing for concrete floors
• Repairs and waterproofing for exterior concrete block walls
• Repairs and refinishing for doors
• Roofing debris removal and inspections
• Minor repairs and replacement for roofing membranes and flashing
• Repairs to skylights
• Repairs and refinishing for interior concrete block walls
• Repairs and refinishing for drywall
• Office painting
• Vinyl tile flooring replacement
• Repairs, refinishing and replacement for acoustic tile ceilings
• Preventive maintenance, repairs and replacement for lavatories and lavatory fixtures
• Water heater preventive maintenance, cleaning and servicing, overhauls and replacement
• Repairs to pipe joints and fittings
• Cleaning of drains
• Maintenance, repair and replacement of gutters
• Repair and replacement of fans
• Inspection and replacement of sprinkler systems
• Maintenance, inspection, repair and replacement of electrical systems including switchgear, receptacles, wiring devices,
voice/data outlets and structure ground
• Replacement of lamps, ballasts and lighting fixtures
• Standby generator maintenance and inspection
• Preventive maintenance of computers
E.2.3 Managerial and Administrative Labor
The models contain an assumption that managerial and administrative support levels for a new
treatment plant are equal to 10 percent of the total operator hours for system operation and
maintenance. This estimate is not intended to represent total administrative and managerial time
at a drinking water system, because total time includes many tasks unrelated to operating a new
treatment train. It only represents incremental time needed to provide administrative support for
the new treatment plant, e.g., processing supply orders. It also does not include labor time
associated with recordkeeping and reporting burden estimates that EPA must estimate and report
independently to comply with Paperwork Reduction Act requirements. Users can change the 10
percent assumption for either or both of managerial and administrative labor on the O&M
assumptions sheet of each model.
E.2.4 Labor Unit Costs
To estimate the cost of the labor calculated in each of the categories above, the models multiply
labor hours by unit costs from the WBS cost database. These unit costs reflect average loaded
wage rates for applicable labor categories (i.e. technical, managerial and administrative) and vary
across system size. The WBS cost database uses the Employment Cost Index to escalate the rates
to current year dollars. Users can change the wage rates, if desired, in the WBS cost database.
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E.3 Chemicals
Each of the WBS models calculates annual chemical usage (in pounds or gallons per year) on a
technology-specific basis. The technology chapters in the main document describe these
calculations. In some models, these calculations also reflect the selected option for regeneration
or disposal of spent chemicals. Annual chemical costs equal the product of the annual chemical
requirements and the unit chemical costs in the WBS cost database.
E.4 Materials
The WBS models calculate the annual cost of materials in the following categories:
• Materials for maintenance of booster or influent pumps
• Materials for maintenance and operation of other, technology-specific equipment
• Replacement of technology-specific equipment that occurs on an annual basis
• Materials for building maintenance.
Pumps are operated continuously (or nearly continuously) and require preventive and routine
maintenance. Pumps are common to all the technologies. Each of the models assumes the annual
cost of materials for pumps is equal to 1 percent of their pre-installation capital cost to account
for consumable supplies and small parts requiring frequent replacement. This assumption is
based on input from the technology experts who reviewed the WBS models and commented that
the initial assumption of 5 percent was too high. Users can change this assumption on the O&M
assumptions sheet of each model. Although accidents or improper operation can result in a need
for major repairs that increase maintenance materials costs beyond 1 percent, the models do not
include these types of costs.
Some of the technologies include other equipment that may require significant maintenance (e.g.,
the blowers in the packed tower aeration and multi-stage bubble aeration technologies). The
models for these technologies include annual costs for maintenance materials. The technology
chapters in this document describe the specific calculations. In general, these calculations are
based a percentage of the pre-installation capital cost of the equipment.
Some of the technologies also include equipment components (e.g., membrane filter cartridges)
that require frequent replacement. Rather than treat these components as frequently replaced
capital items, the models handle the replacement costs in the O&M sheet. The replacement cost
calculations are based on assumptions about replacement frequency and unit costs from the WBS
component cost database. The specific calculations are in the technology sections of the main
document.
The WBS models compute a cost for building maintenance that combines labor and materials.
The cost is discussed in Section E.2.2.
E.5 Energy
All of the WBS models calculate the annual cost of energy in the following categories:
• Energy for operation of booster or influent pumps
• Energy for operation of other, technology-specific items of equipment
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Energy for lighting
Energy for ventilation
Energy for cooling
Energy for heating.
E.5.1 Energy for Pumps and Other Equipment
Booster or influent pumps are equipment common to all the technologies. Because these pumps
are operated continuously (or nearly continuously), they can represent significant energy
consumption. Therefore, each of the WBS models calculates pump operating horsepower based
on average flow, pump head and pump efficiency. The models then convert this operating
horsepower to megawatt-hours/year assuming continuous operation. To calculate annual cost, the
models then multiply the annual power requirement by the unit cost for electricity contained in
the WBS component cost database.
Some of the technologies include other equipment that consumes significant quantities of energy
(e.g., blowers, backwash pumps, mixers). For those technologies, the model also calculates the
energy for such equipment explicitly. The technology chapters in the main document describe
the specific energy calculations. In general, those calculations are similar to the energy
calculation for pumps.
E.5.2 Energy for Lighting
The models calculate annual lighting requirements based on the building square footage estimate
and the quality level of the building (see Appendix B). The building capital costs in the WBS
cost database include the cost of light fixtures for the following light requirements:
• Sheds and low quality buildings, 1 watt/hour/ft2 of building area
r\
• Mid quality buildings, 2 watts/hour/ft of building area
• High quality buildings, 4 watts/hour/ft2 of building area.
Multiplying the appropriate light requirement by 8.8 results in an energy usage rate in kilowatt
hours per ft per year. This conversion is based on operation of the lights 24 hours per day, 365
days per year. EPA evaluated these assumptions by calculating the granular activated carbon
contactor, pipe gallery and furnace area lighting requirements at the Richard Miller Water
Treatment Plant in Cincinnati, Ohio. For this facility, the lighting requirements are 1.5, 1.0 and
0.8 watts per hour per ft for the contactor, pipe gallery and regeneration areas, respectively, with
a weighted average of 1.0 watt per hour per ft2, which is at the low end of the range that EPA
uses in the models. Technologies with different types of process equipment that require more
frequent access may require more lighting. Users can change the lighting requirement for each
level of building quality on the O&M assumptions sheet of each model.
Because many systems are not lit during times an operator is not present, the models reduce
lighting energy requirements when a full-time operator presence is not required (possible for
small systems for many technologies) using the following factor (with a maximum of 1 to
account for large systems that might require more than one full-time operator):
Operator hours per year/ (24*365).
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E.5.3 Energy for Ventilation
The models calculate ventilation requirements based on the assumptions shown in Exhibit E-4.
The technology experts who reviewed the assumptions for the WBS models confirmed the
reasonableness of these assumptions, although one expert commented that the air change rate for
pumps could be lower for systems in a northern climate. The WBS models continue to use the
value shown, however, because it is believed to be more reasonable for a national average
estimate and results in a more conservative (i.e., higher) estimate of ventilation energy
consumption. All of the models use these same assumptions with the exception of chlorination,
which has special ventilation requirements as described in that technology section. Users can
change the ventilation assumptions, if desired, on the O&M assumptions sheet of each WBS
technology model.
Exhibit E-4. Assumptions for Calculating Ventilation Requirements
Variable
Ventilation air change rate for contactor areas
Ventilation air change rate for pump areas
Ventilation air change rate for chemical storage areas
Ventilation air change rate for offices
Pressure drop across ventilation fans
Number of days with mechanical ventilation for small systems (less than 1 MGD)
Number of days with mechanical ventilation for medium systems (1 to 10 MGD)
Number of days with mechanical ventilation for large systems (greater than 10 MGD)
Building height
Value used
3 air changes/hour
20 air changes/hour
2 air changes/hour
2 air changes/hour
0.25 pounds/ ft2
90 days/year
120 days/year
185 days/year
20 feet
MGD = million gallons per day
The models first use the air change rate assumptions to calculate an overall weighted average air
change rate for each building based on the equipment present in that building. The models then
use this weighted average air change rate for each building in the following formula:
Ventilation energy (MWh/yr) = DAYS x 24 x 0.746 x Pdrop x FP x H x Achanges / 33,000,000
where:
DAYS = days per year with mechanical ventilation
Pdrop = pressure drop across ventilation fans (pounds/ft2)
FP = building footprint (ft2)
H = building height (feet)
Achanges= weighted average air change rate for the building (air changes/hour)
E.5.4 Energy for Heating and Cooling
The models calculate heating and cooling requirements based on the assumptions shown in
Exhibit E-5. Users can change these assumptions, if desired, on the O&M assumptions sheet of
each WBS technology model. These assumptions are described in greater detail below.
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R-values are a measure of the effective resistance to heat flow of an insulating barrier such as a
building envelope. The R-values assumed in the models (13 for walls, 38 for ceilings) are based
on the use of standard building materials. The user can change these values to reflect higher
efficiency construction materials. In doing so, however, the user should also examine the unit
building costs in the WBS cost database (see Appendix B) to determine if they are consistent
with the use of such construction materials.
Exhibit E-5. Assumptions for Calculating Heating and Cooling Requirements
Variable
R-value for walls
R-value for ceilings
Annual heating degree days
Annual cooling degree days
Heating ventilation/infiltration load
Cooling ventilation/infiltration load
Electric resistance heating efficiency
Heat pump heating coefficient of performance
Natural gas non-condensing furnace efficiency
Natural gas condensing furnace efficiency
Diesel non-condensing furnace efficiency
Diesel condensing furnace efficiency
Air conditioning energy efficiency ratio
Heat pump cooling energy efficiency ratio
Maximum capacity for heat pump heating
Maximum capacity for other heating options
Maximum capacity for heat pump cooling
Maximum capacity for other cooling options
Value used
13hour-ft2-°F/BTU
38 hour- ft2 -°F /BTU
4,923 degree days
1 ,697 degree days
168,679 BTU/cfm
51,771 BTU/cfm
98%
3.2
80%
95%
78%
85%
11 Whr/BTU
10.1 Whr/BTU
200 thousand BTU per hour
6, 148 thousand BTU per hour
50 tons
11 3.32 tons
BTU = British thermal unit
cfm = cubic feet per minute
Whr = watt hour
The next four values in the exhibit (annual heating and cooling degree days and heating and
cooling ventilation/infiltration loads) are climate-related. EPA derived these values from data in
the Air Force Combat Climatology Center Engineering Weather Data Version 1.0 (U.S. Air
Force, 2000). Specifically, EPA selected climate data for 21 cities distributed geographically
throughout the United States and calculated total annual heating and cooling losses. The values
used in the WBS models are those for the city (St. Louis) that represents the median total annual
heating and cooling loss from among the 21 cities. Therefore, the values used are intended to
represent a climate that produces a national median total heating and cooling requirement. The
user can change these values to represent a specific different climate. In doing so, however, the
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user should select values for the heating and cooling measures, respectively, that are consistent
with one another (i.e., reflective of a realistic climate).
The remaining values in the exhibit are related to the efficiency and performance of heating and
air conditioning equipment. These values are based on data from the following sources:
• 10 CFR 430.32
• Canadian Office of Energy Efficiency (2009)
• ACEEE(2012).
The user can modify these values, as desired, to reflect the use of more or less efficient
equipment.
The WBS models use the assumptions in Exhibit E-5, along with estimated building
dimensions, to calculate total annual heating and cooling losses. The models consider both
conductance losses and ventilation/infiltration losses. The models calculate conductance losses
for each building using the following formulae:
Conductance heating loss = 4 x S x H x HDD x 24 / Rwaii + FP x HDD x 24 / Rceiiing
Conductance cooling loss = 4 x S x H x CDD x 24 / Rwan + FP x CDD x 24 / Rceiiing
where:
S = length of building side in feet (assumed to equal the square root of the building
footprint)
H = building height (feet)
HDD = annual heating degree-days
CDD = annual cooling degree-days
FP = building footprint (ft2)
Rwaii = R-value for walls
Rceiiing = R-value for ceiling.
The equations above represent the total heat transfer in British thermal units (BTU)/year through
all four walls and the ceiling of each building. The models assume heat transfer through the
building floor is negligible.
To calculate ventilation and infiltration losses, the models first calculate the air exchange rate in
cubic feet per minute (cfm) for each building using the following formula:
Air exchange rate (cfm) = FP x H x Achanges / 60
where:
H = building height (feet)
FP = building footprint (ft2)
Achanges = weighted average air change rate for the building (air changes/hour, as
described above in the section on ventilation)
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Note that, unlike the calculation for ventilation energy use, this calculation does not incorporate
assumptions about the frequency of mechanical ventilation. This is because heating and cooling
losses occur regardless of whether ventilation is achieved by mechanical or natural means.
The models then apply the air exchange rate calculated above to determine ventilation and
infiltration losses (in BTU/year) for each building using the following formulae:
where:
Heating ventilation and infiltration heat loss = CFM x HVn0ad
Cooling ventilation and infiltration heat loss = CFM x Cyiioad
CFM = air exchange rate (cfm, as calculated above)
Hyiioad = heating ventilation/infiltration load (in BTU/cfm)
Cviioad = cooling ventilation/infiltration load (in BTU/cfm)
The models then sum conductance losses and ventilation/infiltration losses to determine total
annual heating and cooling requirements for each building. For cooling, the models add cooling
required to compensate for the waste heat generated by pumps (and other technology-specific
mechanical equipment).
The models then calculate heating and cooling energy consumption for each of several options
using these requirements, BTU values for the appropriate fuel (i.e., electricity, natural gas or oil)
and the efficiency factors shown in Exhibit E-5. For heating, the options are electric resistance
heating, electric heat pump, natural gas condensing or non-condensing furnace and diesel
condensing or non-condensing furnace. For cooling, the options are conventional air
conditioning and electric heat pump. As indicated by the final two assumptions in Exhibit E-5,
some of these options are not applicable for systems requiring large heating or cooling capacity
(i.e., large systems with large buildings). Specifically, electric resistance heating and heat pumps
are not useable for heating beyond a maximum capacity of 240,000 BTU/hour and heat pumps
are not useable for cooling beyond this same maximum capacity. When total annual heating or
cooling losses are greater than these maximum capacities, the models do not include these
options among those displayed on the output sheet.
The models determine whether to include heating and cooling costs (both capital and O&M)
based on building size, system design flow and user input for component level (see Section 2.3),
as shown in Exhibit E-6. Users can change these assumptions on the indirect assumptions sheet
of each model. When heating and/or cooling are included, the models choose among the heating
and cooling system options based on the total annualized cost of each option (annual energy cost,
plus capital cost of the system annualized as discussed in Section 2.4). The models select the
option with the lowest annualized cost for inclusion in the system capital costs and add the
corresponding annual energy cost to O&M costs.
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Exhibit E-6. WBS Model Assumptions Regarding Inclusion of Heating and Cooling
Component Cost Level
Selected
System Size (Design Flow
Less than 1 MGD
1 to 10 MGD
10 MGD or greater
Buildings 500 ft2 or greater
Low
Medium
High
Neither
Heating Only
Heating and Cooling
Heating Only
Heating and Cooling
Heating and Cooling
Heating and Cooling
Heating and Cooling
Heating and Cooling
Buildings less than 500 ft2
Low or Medium
High
Neither
Heating Only
Neither
Heating Only
Heating Only
Heating Only
E.5.5 Energy Unit Costs
To estimate the cost of the energy consumption calculated in each of the categories above, the
models use unit costs from the WBS component cost database. These unit costs represent
national averages for each fuel (electricity, natural gas and diesel) obtained from the U.S.
Department of Energy's Energy Information Administration. Because energy costs are highly
variable, users can change these energy unit costs, if desired, in the WBS cost database.
E.6 List of Abbreviations and Symbols in this Appendix
BTU British thermal unit
cfm cubic feet per minute
EPA U.S. Environmental Protection Agency
ft2 square feet
O&M operating and maintenance
WBS work breakdown structure
E.7 References
American Council for an Energy Efficient Enconomy (ACEEE). 2012. Heating. Last updated
December. Online at http://www.aceee.org/consumerguide/heating.htm.
Canadian Office of Energy Efficiency. 2009. Heating with Gas - Comparing Annual Heating
Costs.
RSMeans. 2013. Facilities Maintenance and Repair Cost Data 2014. 21st Annual Edition.
Norwell, Massachusetts: Reed Construction Data.
U.S. Air Force. 2000. Air Force Combat Climatology Center Engineering Weather Data.
Version 1.0.
Whitestone Research. 2009. The Whitestone Facility Maintenance and Repair Cost Reference
2009-2010. Fourteenth Annual Edition. October.
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