SERA
United States
Environmental Protection
Agency
Work Breakdown Structure-Based Cost Model
for Cation Exchange Drinking Water Treatment
Office of Water (4607M)
EPA ***_*_*****
December, 2017
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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. General Overview of WBS Models 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. Cation Exchange Model 28
3.1 Overview of Cation Exchange Treatment Process 28
3.2 Input Sheet 30
3.3 Model Assumptions Sheet 37
3.4 Vessel Constraints Sheet 39
3.5 Regeneration and Backwash Sheet 40
3.6 Pumps, Pipe and Structure Sheet 40
3.7 Instrumentation and Control Sheet 41
3.8 Residuals Management Sheet 41
3.9 O&M and HVAC Sheets 42
3.10 Indirect Sheet 43
3.11 Output Sheet 43
3.12 Ancillary Model Components 43
3.13 List of Abbreviations and Symbols in this Chapter 44
3.14 References 44
Appendix A. Valves, Instrumentation and System Controls 46
Appendix B. Building Construction Costs 52
Appendix C. Residuals Management Costs 61
Appendix D. Indirect Capital Costs 70
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
Appendix E. General Assumptions for Operating and Maintenance Costs 93
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
1. Introduction
This report describes a cost model for one of several drinking water treatment technologies. 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
model described in this document differs from the drinking water cost models previously used by
the Agency in that the new model is 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 Model for Cation Exchange Drinking Water Treatment
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.
• Chapter 3 describes the individual model, design criteria and assumptions for the selected
treatment technology.
• 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 Model for Cation Exchange Drinking Water Treatment
2. General Overview of WBS Models
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 Model for Cation Exchange Drinking Water Treatment
Exhibit 2-1. Structure of the WBS Models
User Input Required
User Input Optional
Reference Sheets
(applicable only for some
models; includes guidance
on setting input
parameters and critical
design assumptions)
j k
WBS Engineering
Analysis
WBS System Cost
Analysis
(component functions)
Cost Equations
O&M and Indirect
Sheets
Annual O&M
requirements
Some indirect costs
WBS Component
List
(applicable components
such as tanks, vessels,
piping, instrumentation,
and building)
Input Sheet
(user-defined design
parameters such as flow
rates, raw water quality,
bed depth)
Critical Design
Assumptions Sheets
(includes key design criteria,
e.g., loading rate, bed
expansion; O&M and indirect
assumptions)
(documented cost and useful
life estimates by component
type and size; some
engineering reference data)
WBS Cost Database
Process Capital Costs
Useful Life Data
Indirect Costs
Add-on Costs
O&M Costs
Total Annualized Cost
Output Sheet
(design of applicable components
and systems, e.g., vessels, tanks,
membranes, backwash, pumps,
pipes, valves; structure design;
chemical and media requirements)
Engineering Design Sheets
4
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
Exhibit 2-2. Sample of Input Spreadsheet
MULTI-STAGE BUBBLE AERATION SYSTEM DESIGN AND COST INPUT
STEP 1
Select Contaminant
tI For VOCs, default design; available up to 1 MGD only, because information on using MSBA for these contaminants in larger systems is limited
Select one of the eiqht standard desiqns at riqht
OR
Select "CLEAR FOR MANUAL ENTRY"
STEP 3:
fQpthrtzl far sfMdwd distorts}
Enter or change values in the and : cells below,
under "Manual Inputs"
0.030 mgd standard design
<- Ufiag this dtsigi
0.124 mgd standard design
0.305 mgd standard design
0.740 mgd standard design
2.152 mgd standard design
7.365 mgd standard design
22.614 mgd standard design
75.072 mgd standard design
CLEAR FOR MANUAL ENTRY
See model documentation for more information on standard designs
l>p«t Coaplctt — Rtsilti Rtidf
STEP 4:
Results are ready I'no need to click button)
Generate Results
Results summaru fsee OUTPUT" sheet fo
details 1
Direct Capital Cost: $107,737
Total Capital Cost: J158.337
Annual 0&M Cost: $7,232
Annualized Cost: 123.623 f 16.3 years
at 7*1
MANUAL INPUTS
Ciffsix w-c- rtqwrid; ci-tts in i . wc
Desiqi Flow
Average Flow
I Select units
For iiforaatioi:
Treatment system design flow r
Bypass design flow r
0.030 MGD
0.007 MGD
0.030 f)GD
0.000 TlGD
Current bypass percentage is 05!. Go to Critical Design Assumptions to change this value.
Adjust bypass percentage
Optimise Number
of Basins
Dtsiq* Tfpe
pre-eaqi»eered packaqe
<--- pick an*
Vendor packages include aboveground stainless steel, plastic, or fiberglass basins and typically are used
by small systems
Niaber of operatikq basils
Air to water ratio
1
40
3
8
Guidance: For VOCs, typical air to water ratios are between 10:1 and 300:1
MaiiaiH water depth
feet
Guidance: VOCs require no more than 2 to 3 feet water depth, beyond this depth no significant gain is
realised (Lowry peer review comments)
Guidance: for VOCs, minimum of 6 stages, maximum of 12 stages, vendor uses 8 stages for most
applications (Lowry peer review comments)
Niabtr of staqes
Pilot rale coistut
0.17
Pilot air iiteisiti
2.54
Estimate only, based on pilot rate constant and air intensity. To increase, increase air to water ratio and/or
Theoretical Percent Removal
90.07%
number of stages
Number of Basins (including redundancy)
1
units
Basin
.ength (including quiescent chamber)
4
feet
Basin Width
2.5
feet
Basin Height (including freeboard)
5
feet
Adjust freeboard
Diffusers per stage
1
units
Total diffusers
8
units
Adjust basin length constraints
B»i» l»i>
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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 Model for Cation Exchange Drinking Water Treatment
Exhibit 2-3. Sample of Output Spreadsheet
OUTPUT SUMMARY
P«n»Hn
l«li* U.itx
Technoloqy
Contaminant Type
System Sixe Cateqory
Desiqn FIdu
Number of Barinr
Number of S ~ -3 ¦;c-s per Earir.
Barin Lenqth
Barin Width
Barin Heiqht
DiffurersperStaqe
Total diff users
Off-Gas Treatment
Direct O-ap-ih-al Cart
Add-on Cart
Tat<*. ,
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rtr trtejj
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It*.
D*rifii Q«»titj
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//>
fi
*3
Baffles
1.3.1
* »iti
12.5 ifflaffl*
12.5
ifflaffle
$
123
*
4*2
7
1
'1.4
1.4.1
Diffu*rx
* «>itr
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14
cf>
Ji
44
*
345
14
1
2-
13 ».
13
4.51t
4.432
17
ADDITIONAL WBS COMPONENTS NOT SHOWN
Afi.A
JAi-Otf-lHtof-
am
AM
AM
AM
AM
*.7
C»c..t. P .d
2 <7
2
CT
i-57
1.314
37
1
Direct cut c«ttf"J
T ¦ t«1 Gvi^Mc*
Process carts
$ 101,53$ Exclude* alternate cost line item? in italics, uithaut a
in the 'Use:'" column. In<
ludes
•rtallation, t
anspartat
on, and O&P
Buildinq casts
$ (.,25$ See indirect assumpt
anssheet to exclude buildinqs
Total direct capital cost
*107.797 Total of process and fc
uildinq casts
Hf/l+mrf
Add-.. Li.* lt»
T.t«l
G«id«c*
Permits
t 111
Pilot Study
t
No pilotstudy required for this technology
Land Cart
$ $2(.
For 0.04 acres
Total add-on costs
#1.038
Total of permitr, pilatinq, and land
Indirect Capital Cost Details /T-Vj".ir,ifov-ct arrimm>tjmarjAj^-i tz> i-:.- ciuo'i- ir^ifitvJuo!ir,Jin-rtitj-r?*r
I.direct Li.* It*. T¦ t a 1 P»rc*.t G«id«.c*
Architectural Fees for Treatment Building
H'S. Excluded ty default f or small jyxtemr
Site Work
$ 1,423
Yard Pipinq
* 1,107
Calculated bared onryxtem requiremer.tr.
Standby Pauer
Calculated bared onxyxtem requirements. Excluded by default forxmallxyxtemr.
Electrical (including yard uirinq)
$ 10,154
10y. Percentaqe ir applied only to process cast. Euildinq direct casts include electrical cam
ponents.
Procerx Engineering
* 21,554
20 X
Mircellaneour Allouance
A 10,740
10x
Sales Tax
0x
Financing durinq Conrtruction
OX
Conrtruction Management and GC Overhead
t 2,383
Includes bond and inrurance only far pre-enqineered packaqes
Total indirect capital cost
*50.162
Total of indirect line items
TOTAL CAPITAL COST DETAILS
City Index 1.r>l) City Mr, $ 158.997
Annual Operating and Maintenance Cost Details (its
o A.ir.. titrj- \irs-:'m/iyvjv
L.t.r
14
t 44.12
#lhr t 5(t
1
Ad.i.irtr«ti«*
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14
141
krxfTr
Irslrr
$ 27.43
f 2*.34
Ihr % 3*1
fkr % 3.444
1
1
1 Includes labor for reqular aper
r
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
component, because costs can differ substantially across materials. For example, most pipes can
be constructed of stainless steel, 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
Example Components
Vessels
Pressure vessels
Tanks/basins
Storage
Backwash
Mixing
Contact
Flocculation
Sedimentation
Filtration
Pipes
Process
Backwash
Chemical
Inlet/outlet
Bypass
Valves (see Appendix A for further details)
Check (one-way)
Motor- or air-operated
Manual
Pumps
Booster
Backwash
High-pressure (for membrane systems)
Chemical metering
Mixers
Rapid
Flocculation
Inline static
Instrumentation (see Appendix A for further details)
Pressure gauge
Level switch/alarm
Chlorine residual analyzer
Flow meter
pH meter
Air monitor/alarm
High/low pressure alarm
Gas flow meters—rotameters
Scales
System controls (see Appendix A for further details)
Programmable logic control units
Operator interface equipment
Controls software
Chemicals
Acids
Bases
Coagulants and coagulant aids
Antiscalants
Corrosion control
Oxidants and disinfectants
Treatment media
Activated alumina
Activated carbon
Membranes
Sand
Resins
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
Component Classes
Example Components
Building (see Appendix B for further details)
Structure
Heating and air conditioning systems
Concrete pad
Indirect Capital Components (see Appendix D for further
details)
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 Model for Cation Exchange Drinking Water Treatment
Exhibit 2-6. Standard Flow Rate Categories Used in WBS Standard Designs
Size Category
Population Served
Design Flow (MGD)
Average Flow (MGD)
1
25 to 100
0.030
0.007
2
101 to 500
0.124
0.035
3
501 to 1,000
0.305
0.094
4
1,001 to 3,300
0.740
0.251
5
3,301 to 10,000
2.152
0.819
6
10,001 to 50,000
7.365
3.200
7
50,001 to 100,000
22.614
11.087
8
Greater than 100,000
75.072
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
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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 Model for Cation Exchange Drinking Water Treatment
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). 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),
2
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 Model for Cation Exchange Drinking Water Treatment
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
System Size (Design Flow)
Less than 1 MGD
System Size (Design Flow)
1 MGD or greater
Low
Manual
Manual
Medium
Manual*
Automated
High
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:
"3
1. Open the Excel workbook named "WBS GAC.xlsm." 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
042514.xlsm" for April 25, 2014).
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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 MGD standard design for GAC treating TCE with a
pressure design uses a design flow of 2.152 MGD and an average flow of 0.819 MGD. 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
042514.xlsm" for April 25, 2014).
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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 Model for Cation Exchange Drinking Water Treatment
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.
Exhibit 2-8. General Design Assumptions Used in the WBS-based Models
Element
Assumption
Can be changed by:
Influent pumps
Include flooded suction
Replacing unit costs or cost coefficients
extracted from the WBS cost database
All pumps
Design flow incorporates a safety factor of
25 percent
Editing the critical design assumptions
sheet of each technology
Access space for pumps
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
Editing the critical design assumptions
sheet of each technology
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
Element
Assumption
Can be changed by:
Pipe size
Based on a maximum of 3 feet of head
loss per 100 feet of pipe
Editing the engineering lookup table
extracted from the WBS cost database
Process pipe size
Based on maximum flow to each unit (not
total system flow)
Cannot be changed
Tank and pressure vessel
capacity
Based on design capacity, freeboard and
standard manufactured sizes
Cannot be changed
Pressure vessel diameter
Based on user input, within limits specified
on a technology-specific basis
Changing user inputs (for diameter) and
editing the critical design assumptions
sheet of each technology (for constraints)
Storage tank diameter
Assumes a cylindrical design, with
diameter equal to one half of the height
Cannot be changed
Access space for tanks and
pressure vessels
Provide service space around each unit
equal to its diameter (half its diameter for
small systems), to a maximum of 6 feet
Editing the critical design assumptions
sheet of each technology (only maximum
can be changed)
Process vessels and basins, all
pumps and chemical feed
systems
Multiple units required to protect from
single point failure
Editing the critical design assumptions or
input sheet of each technology (depending
on the specific item)
Chemical storage
Storage requirement based on 30-day
delivery frequency
Editing the critical design assumptions
sheet of each technology
Concrete pad under heavy
equipment
1 foot thick for large systems, 6 inches
thick for small systems
Editing the critical design assumptions
sheet of each technology
Office space
100 square feet per employee for large
systems (excluded for small systems)
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
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-
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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 Model for Cation Exchange Drinking Water Treatment
Exhibit 2-9. Sample of Index Spreadsheet
INDEX
T ,iu. '-v-ctj p-.cih l'> :vj ?di.» j,i. "¦ .J "i!c ¦ .ni" *•: <.jo '!ax.k y if t"-.-: .V-i'-i:-: *'jno .sO.
User-adjustable Input or Assumption
Variable Name and Link
Access soace per oump'blower for custom designed systems
space pumps cust
Access space per j>umD,l'blo\ver for pre-erigineered packages
scace pumos >xe
Additional blower head above water depth
a d-d blow head
• Additional building after.-.
add 2nd buildino
Administrative LQE as a peicent of average technical labor
Clencal percent
Air conditioning EER
EER
Air to water ratio
air water ratio
Always include IJEPA compliance costs'?
include NEPA
: Annual cooling degree days
cool DD
•Annual heating degree days
heat DD
Average Flow
averaoe flow 1
Basin excavation depth above which deeper boreholes are needed
deep bore need
Bedding depth below pipe
bedding deoth
: Bedding depth surrounding the pipe
beddmo oct
: Blower efficiency
blower effcy
! Blower safety factor
dower safetv factor
Borehole depth (oackage systems)
Gore depth p
: Borehole depth for deep basins
bore depth max
Borehole depth for shallow basins
bore depth mm
Borehole needed every x square feet
hole per sf
¦ Boreholes per job
hole- per foo
Buffer space around other sides of buildings
non fire suffer
Builder's risk insurance percentage
br ins pet
: Building height
Buildino height
Coefficient of passive pressure
Coeff kp
Communications hardware
comm hardware
• Component level
comoonent level 1
Computer workstations per x operators
workstation ratio
•Concrete pad thickness
Dad thick
Concrete pad thickness for srrall systems
Dad thick small
:Concrete thickness
cone thick
: Contaminant-Specific Of-gas Assumptions
contaminant lookuo
•Cooling table for buildings 500 square teet or greater
cooling table
Cooling table for buildings less than 500 ft2
coolmo table shed
• Cooling ventilation/infiltration load
cool viload
Cost for parts & maintenance for pumps and bioweis
Dump maint rate
i Density of air
PA
Design Flow
design flow 1
: Design safety factor for standby power
std safetv factor
•Design Type
desion tyoe 1
Diffuser access space
diffuser access soace
Drive controllers per blower
S blower
Drive controllers oer booster pump
S booster oumo
: Drive controllers oer catalytic oxidizer
S CO
iDrive controllers oer thermal oxidizer
S TO
Efficiency of pumps
oumo effcv
•Electric resistance heating efficiency
resist eff
iElectncal percentage
elect pet
Engineering percentage for large systems
enq pet large
Engineering percentage for medium systems
ena oct medium
: Engineering percentage for small systems
ena pet small
•Ethernet modules
pic ethernet
Excess air required
CO ex air
Excess air required
TO ex air
: Externa! air piping
air oipe add
•Financing percentage
finance oct
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 Model for Cation Exchange Drinking Water Treatment
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 Model for Cation Exchange Drinking Water Treatment
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 Model for Cation Exchange Drinking Water Treatment
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:
23
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
• 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.
24
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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
ZC. c
Average Useful Life = — = —
Z4 A
n=l
where:
Cn denotes the cost of component n, n=l to N
C denotes total cost of all N components
An denotes the annual depreciation for component n, which equals Cn/Ln
A denotes total annual depreciation for the N components.
25
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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 over time (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).
26
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
2.5
EBCT
EPA
GAC
gpm
GREPs
MGD
O&M
P&ID
PPI
TCE
WBS
List of Abbreviations and Symbols in this Chapter
empty bed contact time
U.S. Environmental Protection Agency
granular activated carbon
gallons per minute
generally recommended engineering practices
million gallons per day
operating and maintenance
piping and instrumentation drawing
Producer Price Index
tri chl oroethyl ene
work breakdown structure
2.6 References
American Water Works Association (AWW A). 1990. Water Quality and Treatment: A
Handbook of Community Water Supplies. Fourth Edition. New York: McGraw Hill.
A WW AJ 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/homchl4.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 Model for Cation Exchange Drinking Water Treatment
3. Cation Exchange Model
Certain positively charged ions can be removed from a water source through the use of cation
exchange treatment systems. In this process, positively charged ions such as sodium or hydrogen
are displaced from their locations on insoluble, solid exchange resins by ions of the same charge
in solution. Through the selective use of particular resins, specific contaminant cations in the
feed water can be targeted for removal and replacement by more desirable ions. Typically,
contaminant cations such as barium, radium and strontium are removed from the feed water by
displacing like-charged ions, typically sodium, attached to sulfonates or carboxylates in a
polystyrene matrix. Cation exchange is generally used in what is called "water softening"
processes where hardness ions such as calcium and magnesium are removed from feed water and
replaced by sodium or potassium.
The work breakdown structure (WBS) model for cation exchange includes standard designs for
the removal of hardness. The standard designs also may be appropriate for removing radium. As
discussed in Clifford (1999), a system run to hardness breakthrough will also achieve a steady
state of radium removal after about five regeneration cycles. The model can be used to estimate
the cost of cation exchange for the removal of other co-occurring contaminants of interest as
well. Users wishing to simulate the use of cation exchange for treatment of other contaminants
will need to adjust default inputs (e.g., bed volumes before regeneration, 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 Cation Exchange Treatment Process
The cation exchange treatment process includes the following components:
• Booster pumps for influent water
• Pressure vessels that contain the cation resin bed
• Tanks and pumps for backwashing the pressure vessels
• Tanks, mixers and eductors for delivering the brine used in regenerating the resin
• Associated piping, valves and instrumentation.
The type of synthetic resin used in cation exchange will vary based on feed water quality.
Depending on pH, total dissolved solids (TDS) and concentration of the contaminant to be
treated, there are several resins to choose from. Cation exchange resins fall into two broad
categories; strong-acid cations (SAC) and weak acid cations (WAC). The capacity of SACs is
independent of pH, whereas WAC resins have exchange capacity only at alkaline pH. The
functional group of a SAC resin is typically sulfonate (S03-1). For WAC resins, the functional
group is typically caboxylate (COOH). The WBS model currently considers only SAC resins.
Resins also are available in different physical forms. Gel type resins have capacities higher than
macroporous resins and have a better operating efficiency. Macroporous resins have better
physical stability, better organic fouling and oxidation resistance than gel type resins
(AWWA/ASCE, 1998).
28
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
Each individual resin will have a specific selectivity index, which describes the order in which
ions are preferred by a particular resin. Although most commercially available resins will have
similar selectivity indexes (AWWA/ASCE, 1998), knowing the particular selectivity index of a
resin can be important designing an effective system, so that resins can be chosen that will
minimize the impact of non-targeted (or competing) ions in the feed water. The design of a
cation exchange system must take into account the competing ions in the feed water. These ions
can decrease the number of available bonding sites on the resin beads for the target contaminant.
Consequently, they reduce the efficiency of the resin beads and increase regeneration frequency.
The cation exchange treatment process consists of the following steps: service, backwash and
regeneration. In the service step, feed water flows through one or more resin beds, under pressure
and is collected and removed at the bottom. As the water makes its way through the beds, the
contaminant ion is attracted to the oppositely charged sites on the resin, thus displacing a weakly
bonded sodium ion from the resin. The target ion then bonds with the resin and slowly builds up
in the beds until the exchange capacity is reached. The target ion builds up on the resin and its
concentration wave front moves slowly through the column. When the target ion wave front
reaches the outlet of the column, contaminant "breakthrough" occurs. At this point, the resin
must be regenerated.
The backwashing step is performed before regeneration to remove debris from the resin. In the
backwashing step, water is passed upflow through the resin bed to remove debris (CH2MHill,
1999). Regeneration of the beds consists of three steps. First, applying a high concentration
sodium chloride solution reverses the cation exchange process, displacing the contaminant ion
and returning all the exchange sites in the sodium form. Second, the resin is "slow rinsed" by
passing treated water downflow through the bed to displace the regenerant from the bed. Some
designers prefer counter-flow designs in which the brine and slow rinse are passed upflow.
Finally, a fast rinse with water is necessary to remove the remaining traces of brine from the
resin bed before the unit is returned to service (CH2MHill, 1999; Clifford et al., 1997 and 1998).
The waste regenerant (brine) will have a high concentration of the contaminant ion and may need
to be disposed of and treated separately.5
Exhibit 3-1 provides a schematic drawing for cation exchange. The schematic shows a system
designed to allow operation with vessels in parallel, which is the default for hardness removal. A
system designed for operation with vessels in series would require additional piping between the
two cation exchange units. See below under "Number of Vessels in Series" for further discussion
of parallel and series operation. Cation exchange systems can be either custom-engineered
designs or 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 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.
5 Note that this paragraph describes regeneration of SAC resins. WAC resins use a different regeneration solution.
The model is not currently designed to estimate costs for WAC resins and their associated regeneration designs.
29
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
Exhibit 3-1. Typical Schematic Layout for Cation Exchange
Pun
Cet'-ir Exchange Unit
Cation Exchange Un
if ir h trni ]
¦ Ceswlfugal-
Pump
(UN
ilJ Flow Meter w! 1
Pressure Gauge
U 1 Head Loss \
Senior
'j Temperature
Wcter
> HlglvLow
Alarm
^ Turbidity
pH Meier
Conductivity
LINK
m fluent
Treated
Brine Bypass
~ - " "I
BdCkwasti
DO
l\)
Manual
Valve
Check
Valve
Control
Valve
Cation Exchange
Typical Schematic Layout
Cation Exchwt
3.2 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 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:
• Design and average flow (see Section 2.3)
• Influent hardness concentration
• Resin type
• Bed volumes treated before regeneration
• Number of vessels in series (i.e., parallel or series operation)
• Theoretical total empty bed contact time (EBCT)
• Bed depth and pressure vessel dimensions and geometry
• Brine delivery method
• Residuals management
• Number of booster pumps (optional)
• Number of redundant vessels (optional)
• Backwash pumping (optional)
30
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
• Backwash storage (optional)
• System automation (optional, see Section 2.3)
• Component level (optional, see Section 2.3).
Influent Hardness Concentration
The input sheet requires the user to input the influent hardness concentration (as calcium
carbonate in milligrams per liter or CaCC>3 in mg/L). The model uses this input to calculate
residuals characteristics. Also, if the user selects automated calculation of regeneration frequency
(see "Bed Volumes before Regeneration" below), the model uses the input, along with the resin's
useable exchange capacity, in determining the frequency with which regeneration is required.
The model standard designs assume an influent hardness of 200 mg/L, as CaCC>3, consistent with
very hard water.
Resin Type
As discussed above, the type of resin employed is a key factor in the design of a cation exchange
system. The input sheet requires the user to select the type of resin. The model standard designs
use a strong acid polystyrenic macroporous resin. If a different resin type is chosen, the user
should verify that the regenerant dose level and useable exchange capacity are appropriate for the
new resin type or manually enter the appropriate number of bed volumes before regeneration
(see below).
Bed Volumes Treated before Regeneration
Cation exchange beds can be run for 100 to 1,000 bed volumes before regeneration is necessary.
This value is commonly known as "run length." A number of variables, including feed water
quality, regenerant dose level, resin type and resin volume, will affect the run length. Competing
ion concentration in the feed water is of primary concern, because high levels of these ions will
increase hardness leakage levels and may take up active bonding sites on the resin, reducing the
number of bed volumes before breakthrough.
The input sheet offers two methods for the user to select the bed life of the cation exchange resin:
a calculation based on influent hardness concentration or manual entry of the number of bed
volumes. Under the first method, the user must enter the resin's useable exchange capacity in
kilograins (as CaCC^) per cubic foot of resin (kilograins CaCCVft3). Manufacturers provide
tables of resin operating capacity as a guide for process design. These values will usually vary
depending on the regenerant dose level and other conditions (such as TDS, pH and ion
"3
concentration) between 20 and 30 kilograins CaCCVft of resin (1 pound = 7 kilograins). Under
the second method, the user can input the number of bed volumes directly. This second method
is best used when factors other than influent hardness (e.g., competing ions such as sodium and
potassium) affect the run length or when a contaminant other than hardness is targeted. Under
either method, the user must enter the regenerant dose level (pounds of sodium chloride or NaCl
per cubic foot of resin). The regenerant level determines how much of the resin's exchange
capacity is restored and, therefore, the run length. The user should ensure that the value entered
for resin exchange capacity or bed volumes before regeneration is consistent with the regenerant
dose selected and the resin type used.
31
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
The model standard designs use the first method and assume a resin useable capacity of 27
kilograins CaCCVft3 at a regenerant dose of 15 pounds per cubic foot. The reference data sheet
in the model provides alternate values for the capacity restored at different regenerant dose
levels.
Number of Vessels in Series (parallel or series operation)
Cation exchange vessels can operate in series or in parallel. Therefore, the input sheet requires
the user to select the number of vessels in series. Entering one vessel in series results in a parallel
configuration, while entering two vessels in series results in a series configuration. If the user
selects a system with two vessels in series, the model automatically increases the number of
valves per vessel to allow for interconnecting piping. Systems set in parallel are generally used to
increase throughput. In a parallel configuration, one or more vessels are in use, while other
vessels are being regenerated or are on standby (Clifford, 1999). For contaminants that are
difficult to remove, a treatment train consisting of a number of vessels in series can improve
contaminant removal. In such designs, first vessel in each train is a roughing vessel and the
second is a polishing vessel. Series operation is rarely required for hardness removal. Therefore,
the model standard designs assume parallel operation (i.e., one vessel in series).
Theoretical Empty Bed Contact Time
EBCT is defined as the volume of resin, including voids, divided by the flow rate. Most
traditional cation exchange systems will have an EBCT of 1.5 to 7.5 minutes (AWWA/ASCE,
1998; Clifford, 1999). The EBCT used to design a system should be determined based on a pilot
study or previous experience with cation exchange systems for similar influent waters. The input
sheet requires the user to enter the appropriate EBCT in minutes. For systems in a series
configuration, this value is the total EBCT of each treatment train (i.e., with two vessels in
series, the EBCT of each vessel would be half the value entered). For information, the model
shows the EBCT per vessel to clarify this point. The model standard designs use an EBCT of 2.5
minutes.
Bed Depth and Pressure Vessel Dimensions and Geometry
The input sheet requires the user to enter the desired bed depth of the cation resin bed and the
geometry of the pressure vessel to be used. Geometry options are upright cylinders for small to
medium sized systems and horizontally laid long cylinders for very large systems. For either
configuration, the user needs to enter the straight height or length of the vessel and the diameter
of the vessel.
Bed depths for cation exchange typically range between 30 inches and 12 feet. Based on
generally recommended engineering practices (GREPs), however, the guidance in the model
recommends the use of a typical bed depth that ranges between 2.5 feet and 6 feet. For
preliminary design, sources of bed depth estimates include past engineering experience,
manufacturer recommendations and published treatment studies. The model also requires that the
bed depth is less than twice the vessel diameter. The model standard designs use bed depths that
meet this constraint and are within the recommended range.
For upright (i.e., vertical) vessels, commercial units typically are available from 5 to 10 feet in
height and from 3 to 12 feet in diameter. The input sheet will display warning signs if the
32
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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.
Autosize Routine
To aid users, the model includes a button labeled "Autosize." This button activates 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 annualized 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. For standard designs, the U.S. Environmental Protection
Agency (EPA) used the autosize routine to select dimensions that meet all required constraints.
Brine Delivery Method
The input sheet provides the user with two methods for delivering brine to the cation exchange
beds. The options are to use either brine mixing tanks or salt saturators. Salt saturators store large
quantities of salt in beds and use automated controls to pass water through the salt beds and
produce saturated brine. Mixing tanks add and mix salt to fixed quantities of water to create
brine. The model standard designs assume the use of brine mixing tanks.
Residuals Management
Ion exchange systems generate two primary residuals streams: spent regenerant brine (including
backwash water) and spent resin. In the cation exchange model, spent brine can be generated on
an intermittent or continuous basis. For the standard designs, very large systems generate spent
brine on a continuous basis because regeneration must occur continuously (i.e., at least one
vessel requires regeneration at any given time). Although it is regenerated, ion exchange resin
will eventually reach the end of its useful life. Therefore, spent resin is generated on an
intermittent basis.
The input sheet requires the user to choose from among several options for management of each
of the residuals streams. Exhibit 3-2 shows the management options available for spent brine.
33
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
Exhibit 3-2. Management Options for Spent Brine
Options for Stage 1 of Management
Options for Stage 2 of Management
Holding tank with or without coagulant addition (for flow
equalization and suspended solids removal)*
Direct discharge to surface water**
Discharge to POTW
Hazardous waste disposal
No holding tank
Direct discharge to surface water**
Discharge to POTW
Evaporation pond**
Septic system***
* May result in generation of secondary residuals (holding tank settled solids).
** Likely to be feasible only if an ocean outfall is available.
*** Results in generation of secondary residuals (evaporation pond solids).
**** Can result in generation of secondary residuals (septic tank solids).
The management options shown in Exhibit 3-2 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. For designs that result in intermittent regeneration, flow equalization can be
necessary, for example, to prevent instantaneous flow from overwhelming the capacity of a
publicly owned treatment works (POTW). For designs that result in continuous regeneration,
however, spent brine is generated continuously, with little variation in flow. A holding tank
likely would not serve a useful purpose for these designs. 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
regenerant 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 employed.
The user can change this option on the critical design assumptions sheet.
Exhibit 3-2 also includes the option for an evaporation pond. Given the potentially large
quantities of spent brine, this management method may be appropriate for facilities in 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 indirect assumptions sheets. Appendix
E and Appendix D contain information on these parameters. The use of an evaporation pond
results in a secondary residuals stream, in the form of evaporation pond solids.
A holding tank would not be necessary with an evaporation pond, even for designs with
intermittent brine generation, 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,
because the septic tank serves as a holding tank. The model always includes a holding tank when
hazardous waste disposal is required for spent brine, to store the waste for shipment.
Exhibit 3-2 does not include the option for recycling spent brine to the head of the treatment
plant (i.e., combining the spent brine with influent water to be treated). Because spent brine is
laden with contaminants removed from the ion exchange resin, this option is not likely to be
feasible for this residuals stream. Under certain circumstances, however, spent brine can be
recycled for reuse in more than one regeneration cycle (Clifford, 1999). Although this option is
34
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
not common in softening applications, the user can enable on the critical design assumptions
sheet (see Section 3.3).
Management options available for spent resin include the following:
1. Disposal as non-hazardous solid waste
2. Disposal as hazardous waste
3. Disposal as radioactive waste
4. Disposal as radioactive and hazardous waste.
The same options are available for secondary solid residuals (e.g., holding tank solids), when
generated. 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.
The solid residual 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.
For spent brine, the standard designs assume the use of a holding tank for all systems except
those generating brine continuously. The standard designs assume discharge to a POTW for the
second stage of spent brine management for all systems. For spent resin and holding tank solids,
the standard designs assume non-hazardous waste landfill disposal.
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 MGD 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 model standard designs leave this input
blank, excluding booster pumps for small systems (less than 1 MGD design flow) and accepting
the default calculations for larger systems.
Number of Redundant Vessels
This optional input controls the model's calculation for the number of redundant vessels. At a
minimum, based on the Technology Design Panel recommendations, there should be at least one
redundant vessel in a cation exchange system. An exception would be small systems designed
with multiple vessels required to treat the maximum design flow (either more than one parallel
treatment train or a single line with multiple vessels in series). In such systems, the average daily
flow is low enough, relative to the design flow, that the multiple vessel design provides sufficient
redundancy without additional vessels. The system can operate at reduced, but greater than
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
average, flow, even while one vessel is off-line for regeneration or resin replacement. Thus, the
number of redundant vessels can be zero for certain small systems having at least two vessels.
The model assumes that redundant vessels (and other redundant items of equipment) are used
during downtime periods for other vessels and swapped into operation intermittently, with other
vessels then becoming standby. For this reason, the model's operating and maintenance (O&M)
estimate includes labor for operating valves and reading instruments associated with redundant
vessels.
The input sheet allows the user to specify the number of redundant vessels. If the user leaves this
optional input blank for a large system (1 MGD or greater design flow), the model calculates the
number of redundant vessels based on a redundancy frequency specified on the critical design
assumptions sheet. If the user leaves this optional input blank for a small system (less than 1
MGD design flow), the model does not add redundant vessels, unless the design selected by the
user results in a single operational vessel. In this latter scenario, the model adds one redundant
vessel. The standard designs leave this input blank, resulting in the following redundancy results:
• No redundant vessels for small systems (less than 1 MGD design flow), except in cases
where the design results in only one operating vessel
• One vessel every four treatment trains for larger systems (1 MGD design flow or greater).
Backwash Pumping
The backwash process can require new pumps or use existing pumps (either influent supply
pumps or treated water pumps). 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
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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.
3.3 Model Assumptions Sheet
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 a pressure vessel diameter that
generates 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 vessel 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 assumptions, resin life, annual resin loss,
inclusion of a pilot study, 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
Loading rate is the velocity of flow through the resin measured in units of flow rate per unit area
(e.g., gallons per minute per square foot or gpm/ft2). The surface area of the treatment pressure
vessels must be selected to maintain loading rates within reasonable bounds. The model assumes
2 2
a minimum loading rate of 5 gpm/ft and a maximum loading rate of 15 gpm/ft .
Backwash Assumptions
Backwash of cation exchange beds typically is accomplished by passing water through the bed at
a rate of 4 to 6 gpm/ft2 for 5 to 15 minutes. The model assumes 6 gpm/ft2 for 15 minutes.
Regeneration Assumptions
Successful and efficient regeneration of the resins is a crucial part to any cation treatment
system. Manufacturers will suggest regenerant rates for each particular resin. In a "complete"
regeneration of an exhausted resin after breakthrough has occurred, the resin will be regenerated
to nearly 100 percent of its original operating capacity. "Complete" regenerations will typically
use at least 15 pounds NaCl per cubic foot resin using a 3 to 12 percent NaCl solution delivered
at a flow rate of 0.5 gallons per minute per cubic foot (gpm/ft3) of resin (AWWA/ASCE, 1998;
Clifford, 1999). Best results are achieved when the regenerant concentration is between 8 to 12
percent NaCl. Cation exchange softener systems can use "partial regeneration" techniques if
doing so is more cost effective. In partial regeneration, the bed is typically regenerated to 25 to
75 percent of its full operating capacity based on the regeneration level used. This can reduce the
total quantity of waste regenerant produced, lowering the costs associated with disposal of the
brine. The model standard designs assume a nearly complete regeneration (15 pounds cubic foot,
restoring the resin to 27 kilograins per cubic foot). Users can model partial regeneration by
adjusting the regeneration dose level and resin useable capacity inputs (e.g., using lower
regenerant dose to restore the resin to a lower, partial useable capacity). In other situations, reuse
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
of spent regenerant can also help reduce waste management costs. Clifford (1999) states that
spent regenerant use can be considered if:
• Significant excess regenerant is in the solution
• The regenerant is highly preferred to the contaminant at the ionic strength of the
regenerant
• Some leakage of the contaminant can be tolerated in the service cycle.
Regenerant reuse, however, is not typical in softening systems.
The model includes the following regeneration assumptions:
• Brine concentration of 0.9 pounds per gallon
"3
• Regenerant loading rate of 0.4 gpm/ft
• No regenerant reuse
• Slow rinse with 2 bed volumes of water
• Fast rinse with 10 bed volumes of water.
Resin Life and Annual Resin Loss
Although ion exchange resin is regenerated, the resin bed will eventually reach the end of its
useful life and require replacement. The model assumes a resin useful life of 7 years. Also,
during operation of a cation exchange system, some resin can be lost over time through natural
attrition. Therefore, the model assumes that systems balance the resin loss by adding new resin to
the bed. The model also assumes the lost resin ends up in the spent backwash residuals and
includes the resin loss in the calculation of suspended solids in the spent backwash. The model
assumes an annual resin loss rate of 4.5 percent.
Include Pilot Study Costs
As discussed above, the standard designs in the model assume the system is designed for
removal of hardness (i.e., softening). Because softening is an established technology that
typically does not require a site-specific pilot study, the model does not include the cost of a pilot
study. Including pilot study costs could be appropriate, however, when estimating costs for a
system designed to remove contaminants other than hardness. Users can include pilot study costs
by changing the value of the assumption titled "Include pilot study costs?" on the indirect
assumptions sheet from 0 to 1.
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.
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
Package Systems
The 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
sheets, while others are in the engineering design formulae. Exhibit 3-3 shows the design
modifications used in the model for small systems.
Exhibit 3-3. Variant Design Inputs and Assumptions for Small Systems
Small System Design
Modification
Explanation
Model Location
Reduced spacing
between vessels and
other equipment
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.
Design equations on
the pumps, pipes and
structure sheet
No redundant vessels
(but a minimum of two
operating vessels)
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).
Input sheet
Reduced instrumentation
requirements
Instrumentation required for small systems is limited to flow meters,
high/low alarms, pH controls, conductivity meters and sampling ports
Critical design
assumptions sheet
Simplified system
controls for automated
systems
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, PC workstations, printers, operator interface software
and plant intelligence software included for large, automated,
custom-engineered systems.
Component selection
logic in the output
sheet and WBS cost
database
No booster pumps
Small systems result in limited head loss and typically do not require
additional booster pumps.
Input sheet
No backwash pumps or
tanks
Small systems typically use existing pumps and water supplies and
do not require separate backwash pumps or backwash water
storage.
Input sheet
Reduced concrete pad
thickness
Small capacity systems require less structural support.
Critical design
assumptions sheet
Reduced indirect costs
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).
Indirect assumptions
sheet
3.4 Vessel Constraints Sheet
The vessel 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 vessels required and the
quantity of resin needed, given the input values selected by the user.
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
3.5 Regeneration and Backwash Sheet
As discussed above, cation exchange beds require both backwashing to remove debris and
regeneration to restore exchange capacity. The regeneration and backwash sheet calculates the
quantity of brine (sodium chloride) needed for regeneration, along with the water volume needed
for regular backwashing, plus the slow rinse and fast rinse steps of regeneration. Using these
values, the sheet calculates the backwash and brine storage tank volumes, pumping requirements
and backwash and regeneration downtime. It also calculates the number and size of mixers for
brine tanks and eductors for delivering the brine to the system.
If the user chooses the option to calculate the number of bed volumes before regeneration based
on influent hardness and the resin's useable capacity (rather than entering it manually), this sheet
uses the following equation:
Number of Bed Volumes ( AFVesseiCvessei ) / ( Hvessei * RVvessel )
Where:
AFvessel = average flow per vessel (gallons per day)
RVvessei = volume of resin per vessel (gallons)
Cvessei = useable capacity per vessel (kilograms)
= volume of resin per vessel (ft3) * capacity of resin in (kilograins/ft3)
15.432
Hvessei = hardness per vessel per day (kilograms)
= influent hardness (milligrams/liter) * AFvessei * 1,000,000 * 3.7845
For the input parameters assumed in the model standard designs, the calculation results in 309
bed volumes before regeneration.
3.6 Pumps, Pipe and Structure Sheet
Other elements of the technology for which the size and cost need to be determined include
pumps 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 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.
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
This sheet also performs calculations for the following pipes:
• Influent and effluent piping
• Process piping
• Backwash piping
• Brine/regeneration piping
• Bypass piping (if a bypass percentage is specified).
The size (diameter) of pipes is determined using a pipe flow look-up table that is part of the
WBS cost database. 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, 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 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 brine, 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 space criteria specified on the critical design assumption sheet.
The space requirements for vessels, 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 vessels, is based on the
footprint of the vessels 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 ion exchange vessels
and the other containing all other equipment. The number of buildings affects the total land
required and energy costs for heating, ventilating and cooling.
3.7 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 trains) and assumptions from the
critical design assumptions sheet (e.g., x number of valves per treatment train). The assumptions
correspond to the general schematic layout for this technology shown in Exhibit 3-1. 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.
3.8 Residuals Management Sheet
The residuals management sheet estimates the volume and mass of residuals, their characteristics
and the capital and O&M costs for residuals management, based on the management options
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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 can include:
• Holding tanks
• Pumps
• Evaporation ponds (including excavation and lining)
• Septic tanks and drain field components
• Coagulant feed and mixing equipment
• Valves, piping and instrumentation.
Specific O&M requirements associated with residuals can include:
• Residuals pump labor, materials and energy
• POTW discharge fees
• Coagulant usage
• Spent resin transportation and disposal costs
• Spent brine transportation and disposal costs (when hazardous waste disposal is required)
• Secondary residuals (holding tank solids, septic tank solids or evaporation pond solids)
transportation and disposal costs.
3.9 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 cation exchange 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:
• Sodium chloride usage (for brine)
• Replacement resin (both natural attrition replacement and periodic complete replacement;
note that spent resin disposal is calculated on the residuals management sheet)
• Operating energy for backwash pumps
• Operator labor and materials for backwash pump maintenance (if regeneration occurs
weekly or more frequently)
• Operator labor for resin changeouts
• Operator labor for regeneration.
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
The sheet determines annual sodium chloride use based on the regeneration requirements
calculated on the regeneration and backwash sheet. Because cation exchange systems are
regenerated frequently, the associated pumping facilities can entail significant energy
consumption and can require significant maintenance. Therefore, the model includes backwash
pump operating energy among its O&M costs. When regeneration occurs weekly or more
frequently, the model also explicitly includes labor and materials for maintaining the backwash
pumps.
For manual and semi-automated systems, regeneration requires constant operator attention.
Therefore, the model assumes labor equal to the actual time to accomplish regeneration for these
systems. For automated systems, the model assumes 10 minutes per regeneration event to verify
that the automated regeneration cycle is initiated and operating properly. The user can change
this latter assumption on the O&M assumptions sheet.
3.10 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
• Sitework
• 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.
3.11 Output Sheet
The output sheet contains the list of components identified for cation exchange 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). Sections 2.1 and 2.3 provide
further details about the output sheet. 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.
3.12 Ancillary Model Components
The model contains five ancillary sheets: index, standard inputs, autosize, cost equations 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
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
can adjust these standard inputs, if desired. The autosize component performs the iterative
calculations required when the user clicks the "Autosize" button on the input sheet. The cost
equations sheet uses the component-level cost curve equations from the WBS cost database to
generate unit costs on an item-by-item basis. The lookup tables sheet is for internal model use in
populating the drop-down boxes on the model input sheet.
The cation exchange model also includes a reference data sheet containing information on
influent hardness, regenerant dose level and resin useable capacity. As discussed in Section 3.2,
the user may refer to the information in this reference sheet in determining how to adjust inputs.
3.13 List of Abbreviations and Symbols in this Chapter
CaC03
calcium carbonate
EBCT
empty bed contact time
EPA
U.S. Environmental Protection Agency
ft3
cubic feet
gpm/ft2
gallons per minute per square foot
gpm/ft3
gallons per minute per cubic foot
GREPs
generally recommended engineering practices
HVAC
heating, ventilation and air conditioning
MGD
million gallons per day
mg/L
milligrams per liter
NaCl
sodium chloride
O&M
operating and maintenance
POTW
publicly owned treatment works
SAC
strong-acid cations
TDS
total dissolved solids
WAC
weak-acid cations
WBS
work breakdown structure
3.14
References
American Water Works Association and American Society of Civil Engineers (AWWA/ASCE).
1998. Water Treatment Plant Design. Third Edition. New York: McGraw-Hill.
CH2MHill. 1999. Arsenic Treatment Evaluation: Draft Report. Prepared for City of
Albuquerque, New Mexico Public Works Department.
Clifford, D.A. 1999. "Ion Exchange and Inorganic Adsorption." Water Quality and Treatment.
Chapter 9. New York: American Water Works Association-McGraw Hill.
Clifford, D.A., G. Ghurye, A.R. Tripp and J. Tong. 1997. Field Studies on Arsenic Removal in
Albuquerque, New Mexico using the University of Houston/EPA Mobile Drinking Water
Treatment Facility. Phases 1 and 2 Report to the City of Albuquerque. December.
Clifford, D.A., G. Ghurye, A.R. Tripp and J. Tong. 1998. Field Studies on Arsenic Removal in
Albuquerque, New Mexico using the University of Houston/EPA Mobile Drinking Water
Treatment Facility. Phase 3 Report to the City of Albuquerque. August.
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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 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
Assumption
Chlorine analyzers
For chlorine and hypochlorite disinfection, 1 per treatment train to monitor residual
Conductivity meters
Varies by technology
Dissolved oxygen analyzers
Varies by technology
Drive controllers
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
Electric enclosures
Only for technologies with significant electric-powered equipment outside a building
structure
Flow meters
1 for the influent or effluent line and 1 for backwash discharge. Some technologies
also include flow meters on process lines.
Head loss sensors
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.
High/low alarms
1 per backwash tank and 1 per chemical storage tank
Level switch/alarms
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.
ORP sensors
Varies by technology
Particle meters
Varies by technology
pH meters
1 each for the influent and effluent lines for systems with pH adjustment, plus others
on a technology-specific basis
Pressure transducers
Included in the cost of flow meter assemblies for venturi and orifice plate meters
Sampling ports
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.
Total dissolved solids monitors
Varies by technology
Temperature meters
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.
Total organic carbon analyzers
Varies by technology
Turbidity meters
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
47
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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 (AWW A, 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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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
Exhibit A-2. I/O Port Requirements for Instrumentation and Control
Instrument Type
Inputs to and Outputs from PLC System
Alarm (level switch/alarm, high/low alarm or low alarm)
1 input and 1 output—discrete
Chlorine analyzer
1 input—analog
Conductivity meter
1 input—analog
Dissolved oxygen analyzer
1 input—analog
Drive controller
3 inputs (1 for the auto switch position, 1 for the run status signal
and 1 for overload or fault signal) and 1 output—discrete
Flow meter
1 input—analog
Venturi and orifice plate meters also include inputs and outputs
for the associated pressure transducer (below)
Head loss sensor
1 input—discrete
Motor/air-operated valve
1 input and 1 output—analog
ORP sensor
1 input—analog
Particle meter
1 input—analog
pH meter
1 input—analog
Pressure transducer
1 input—analog
Sampling port
1 input—discrete
Total dissolved solids monitor
1 input—discrete
Temperature meter
1 input—analog
Total organic carbon analyzer
1 input—analog
Turbidity meter
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 Model for Cation Exchange Drinking Water Treatment
Exhibit A-3. General Design Assumptions for System Controls
Small
Medium
Large
Item of Control Equipment
System
(<1 MGD)
System
(1-10 MGD)
System
(>10 MGD)
WBS Assumption
PLC Equipment
PLC Rack/Power Supply
A,S
A,S
A,S
1 base and expansion bases
as needed for I/O (see text)
CPU
A,S
A,S
A,S
2 per system1
I/O Discrete Output Module
A
A
A
1 for every 32 outputs2
I/O Discrete Input Module
A,S
A,S
A,S
1 for every 32 inputs2
I/O Combination Analog Module
A,S
A,S
A,S
1 for every 12 inputs (for A
and S) and outputs (for A
only)3
Ethernet Module
A,S
A,S
A,S
2 per system1
Base Expansion Module
A,S
A,S
A,S
1 per expansion base
Base Expansion Controller Module
A,S
A,S
A,S
1 per expansion base
UPS
A,S
A,S
A,S
1 per system
Operator Equipment
Operator Interface Unit - limited
functionality
NA
A,S
A,S
2 per system1 (see text)
Operator Interface Unit - advanced,
fully functional
A,S
NA
NA
2 per system1 (see text)
Computer Workstations
NA
A,S
A,S
1 per operator
Laser Jet Printer
NA
A,S
A,S
1 per 4 workstations
Dot Matrix Printer
NA
A,S
A,S
1 per 4 workstations
Software
PLC Programming Software
NA
A,S
A,S
1 per workstation
Operator Interface Software
A,S
NA
NA
1 per system
PLC Data Collection Software
NA
A,S
A,S
1 per workstation
Plant Intelligence Software
NA
A,S
A,S
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.6 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.
6 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 Model for Cation Exchange Drinking Water Treatment
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 pic 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 pic 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) >17 AND < 25
THEN pic 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 pic 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 pic 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 (AWW A). 2001. Instrumentation and Control, Manual of
Water Supply Practices—M2. Third Edition. Denver, Colorado: AWWA.
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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 ft —
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 Model for Cation Exchange Drinking Water Treatment
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 ft
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 Model for Cation Exchange Drinking Water Treatment
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
Lower Quality Building
Medium Quality
Building
Higher Quality Building
Very Small Lower
Quality Building
Craftsman
NBCE
Foundation: reinforced
concrete pads under
pilasters.
Floor. 6" rock base, 4"
concrete with reinforcing
mesh.
Foundation: continuous
reinforced concrete.
Floor. 6" rock base, 5"
concrete with reinforcing
mesh or bars.
Foundation: continuous
reinforced concrete.
Floor. 6" rock base, 6"
concrete with reinforcing
mesh or bars.
Foundations as required
for normal soil conditions;
a 4" concrete floor with
reinforcing mesh and a 2"
sand fill.
RSMeans
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: 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: 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.
not applicable
Saylor
Foundation: concrete strip
and spread footings, 4'
foundation wall.
Slab on grade: reinforced
concrete, vapor barrier, 4"
thick, on 4' sand or gravel
base.
Foundation: concrete strip
and spread footings, 4'
foundation wall.
Slab on grade: reinforced
concrete, vapor barrier, 5"
thick, on 4' sand or gravel
base.
Foundation: concrete strip
and spread footings, 4'
foundation wall.
Slab on grade: reinforced
concrete, vapor barrier, 6"
thick, on 4' sand or gravel
base.
not applicable
' = feet;" = inches
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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 ft building (100 feet on a side) would
have one support column in the center, with a 50 foot roof span. A 30,000 ft2 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 ft ) 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
Lower Quality Building
Medium Quality
Building
Higher Quality Building
Very Small Lower
Quality Building
Craftsman
NBCE
Roof structure: glu-lams
wood or steel trusses on
steel intermediate
columns, short span.
Roof cover, panel ized
roof system, 1/4" 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.).
Roof structure: glu-lams
wood or steel trusses on
steel intermediate
columns, short span.
Roof cover, panel ized
roof system, 1/4" 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.).
Roof structure: glu-lams
wood or steel trusses on
steel intermediate
columns, span exceeds
70'.
Roof cover: panelized
roof system, 1/4" 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.).
Steel roof purlins 4/4 to
5!4 feet on centers, 26-
gauge galvanized steel
on roof
RSMeans
Roof. 1.5" galvanized metal deck, open web steel joists, joist girders, on columns
and walls; total load = 60-65 lbs/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.)
not applicable
Saylor
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.)
not applicable
' = 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 Model for Cation Exchange Drinking Water Treatment
1
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 ft ).
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
Lower Quality Building
Medium Quality
Building
Higher Quality Building
Very Small Lower
Quality Building
Craftsman
NBCE
8" reinforced concrete
block or brick, unpainted.
(Same for both lower and
medium quality.)
8" reinforced concrete
block or brick, unpainted.
(Same for both lower and
medium quality.)
8" reinforced concrete
block or brick with
pilasters 20' on centers,
painted sides and rear
exterior, front wall brick
veneer
Steel frames/bents set 20'
to 24' on centers, steel
wall girts 3/4' to 4/4' on
centers, post and beam
type end wall frames, 26-
gauge galvanized steel
on ends and sides
RSMeans
Concrete block,
reinforced, regular weight,
hollow, 4x8x16', 2,000 psi
Tilt-up concrete panels,
broom finish, 5/4" thick,
3,000 psi
Brick face composite wall-
double wythe: utility brick,
concrete block backup
masonry, 8" thick, perlite
core fill.
not applicable
Saylor
Concrete block, 4x8x16',
reinforced
Tilt-up concrete panel, 6"
thick, no pilasters.
Brick cavity wall,
reinforced, 10" thick.
not applicable
' = 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 ft ) buildings (other than those used to store chlorine gas).
Exhibit B-4 shows the interior finish options that EPA selected for each source.
7
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 Model for Cation Exchange Drinking Water Treatment
Exhibit B-4. Interior Finish Selections for NBCE, RSMeans and Saylor
Building
Variable
Lower Quality Building
Medium Quality
Building
Higher Quality Building
Very Small Lower
Quality Building
Craftsman
NBCE
Concrete floors. Rest
rooms: unfinished
wallboard partitions and 2
low cost fixtures.
Concrete floors. Rest
rooms: painted gypsum
wallboard partitions and 2
average fixtures.
Concrete floors. Rest
rooms: enameled gypsum
wallboard partitions, 3
good fixtures, vinyl
asbestos tile floors.
Minimal quality, minimal
duty, functional,
unattractive
RSMeans
One minimal quality 2-
fixture restroom per 5,000
ft2 building area.
Unpainted walls.
Concrete floors.
Fiberglass ceiling board
on exposed grid system
covering 10 percent of
building area.
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 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.
not applicable
Saylor
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.
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.
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.
not applicable
' = 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 Model for Cation Exchange Drinking Water Treatment
Exhibit B-5. Mechanical Services Selections NBCE, RSMeans and Saylor
Building
Variable
Lower Quality Building
Medium Quality
Building
Higher Quality Building
Very Small Lower
Quality Building
Craftsman
NBCE
No sprinklers. 1 small
rotary vent per 2,500 ft2 of
floor area.
Sprinklers. 1 medium
rotary vent per 2,500 ft2 of
floor area. (Same for both
medium and higher
quality.)
Sprinklers. 1 medium
rotary vent per 2,500 ft2 of
floor area. (Same for both
medium and higher
quality.)
Minimal quality, minimal
duty, functional, no
sprinklers
RSMeans
Gas-fired water heater.
No sprinklers.
Gas-fired water heater.
Wet pipe sprinkler
system. (Same for both
medium and higher
quality.)
Gas-fired water heater.
Wet pipe sprinkler
system. (Same for both
medium and higher
quality.)
not applicable
Saylor
Gas-fired water heater (1
per 5,000 ft2), 50 gallon,
100 GPH. No sprinklers.
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.)
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.)
not applicable
' = 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 ft ) 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 Model for Cation Exchange Drinking Water Treatment
Exhibit B-6. Electrical Services Selections for NBCE, RSMeans and Saylor
Building
Variable
Lower Quality Building
Medium Quality
Building
Higher Quality Building
Very Small Lower
Quality Building
Craftsman
NBCE
Lighting: low cost
incandescent fixtures,
20'x30' spacing
Lighting: low cost single
tube fluorescent fixtures
20'x20' spacing
Lighting: 4" single tube
fluorescent fixtures
10'x12' spacing
Minimal quality, minimal
duty, basic wiring and
minimal lighting fixtures
RSMeans
Lighting: Incandescent
fixtures recessmounted,
type A: 1 W/ft2, 8 FC. 6
lighting fixtures, 1 wall
switch and 2.5
receptacles per 1,000 ft2.
1 W miscellaneous
power.
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 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.
not applicable
Saylor
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.
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.
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.
not applicable
' = feet
" = inches
A = amp
EMT = electrical metallic tubing
FC = foot candles
PVC = polyvinyl chloride
RGS = rigid galvanized steel
W = watt
B.3 List of Abbreviations and Symbols in this Appendix
EPA U.S. Environmental Protection Agency
ft 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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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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: 19th Annual
Edition.
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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
Residuals Generated
Type of
residual
Generation
Frequency
Spent regenerant1
Liquid
Intermittent
Adsorptive Media
Spent backwash
Liquid
Intermittent
Spent media
Solid
Intermittent
Greensand, Granular Activated Carbon,
Spent backwash
Liquid
Intermittent
Biological Treatment
Spent media
Solid
Intermittent
Anion Exchange, Cation Exchange
Spent brine
Liquid
Intermittent/
continuous
Spent backwash
Liquid
Intermittent
Spent resin
Solid
Intermittent
Spent backwash/tank drain and crossflow
Liquid
Intermittent
Microfiltration, Ultrafiltration
Cleaning waste
Liquid
Intermittent
Spent membrane modules
Solid
Intermittent
Membrane concentrate
Liquid
Continuous
Reverse Osmosis, Nanofiltration
Cleaning waste
Liquid
Intermittent
Spent membrane elements
Solid
Intermittent
Used cartridge filters
Solid
Intermittent
Packed Tower Aeration, Multi-stage Bubble
Aeration
Off-gas
Gas
Continuous
Ultraviolet disinfection, Ultraviolet Advanced
Oxidation
Spent lamps, ballasts and intensity
sensors
Solid
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
events) x capacity factor. The variable, capacity factor, is present to account for less than
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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
factor is the same variable discussed in Section C.2 and is intended to account for less than
perfect staggering between generation events.
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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
o
the residuals is removed in a holding tank
• 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
• 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.
g
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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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
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.
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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.
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.
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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
• 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
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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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:
• 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,
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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 (AWW A). 2013. 2012 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.
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
model cost estimates (i.e., the potential redundancy would tend to make model cost results
higher).
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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
Architectural Feea
<$250,000
9.0%
$250,000 to $500,000
8.0%
$500,000 to $1,000,000
7.0%
$1,000,000 to $5,000,000
6.2%
$5,000,000 to $10,000,000
5.3%
$10,000,000 to $50,000,000
4.9%
>$50,000,000
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 R011110-10.
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
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
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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.
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
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• Small pumps / blowers -100 pounds
• Medium pumps / blowers -300 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)
• Profit for installing contractor (i.e., a 10 percent rate of profit charged on materials,
installation and overhead costs).
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Exhibit D-2. Transportation Cost Estimation Methods
Equipment Category
Transportation Costs
Vessels, Tanks, Towers - steel
$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.
Vessels, Tanks, Towers -
plastic/fiberglass
$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.
Pipes
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.
Valves-steel/iron
Weight Class 60
LTL rate = $101.45/100 lb
Small valves: $30.00 (1"—4" diameter)
Medium valves: $80.00 (5"—9" diameter)
Large valves: $400.00 (10"+ diameter)
Valves-plastic
Weight Class 70 - plastics
LTL rate = $115.41/100 lb
Small valves: $10.00 (1"—3" diameter)
Medium valves: $20.00 (4"—6" diameter)
Large valves: $80.00 (>6" diameter)
Pumps and blowers
Weight Class 85
LTL rate = $132.08/100 lb
Small units: $130.00 (0-50 gpm)
Medium units: $400.00 (51—300 gpm)
Large units: $790.00 (>300 gpm)
Mixers
Weight Class 85
LTL rate = $132.08/100 lb
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)
Miscellaneous Equipment
5% of equipment cost
System Controls
None
Chemicals, Resins and Filter Media
$0.22/lb for hazardous materials
$0. 27/lb for filter media and resins
$0.18/lb for 150 lb chlorine cylinders
$0.24/lb for 1 ton chlorine cylinders
$0.06/lb for all other chemicals
RO/NF and MF/UF Skids and
Equipment
5% of equipment cost
Instrumentation
Varies with cost of equipment. Range is $9.95 to $104.35 per unit of equipment.
lb = pound
gpm = gallons per minute
" = inch
RO/NF = reverse osmosis/nanofiltration
MF/UF = mi c rof i I trati on/u I traf i I trati o n
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
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,
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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
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-
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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 Vi 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
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
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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
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.
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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.
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
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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 ft . 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 ft 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.9
Also as a default, the models do not include standby power at all for small systems with a design
flow of less than 1 MGD. 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,
9
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, 2001a)
• St. Joseph, Missouri electrical costs as a percentage of non-electrical process costs = 8.7
percent (AWWC, 2001b).
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
Contingency as a Percent of Base Costs
Up to $100,000
10%
$100,000 to $500,000
8%
$500,000 to $1,500,000
6%
$1,500,000 to $3,000,000
4%
Over $3,000,000
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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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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
Total
Cost
Budget
Contingency
Budget
Estimate
Contingency
(% of
budget)
Final
Project
Cost
Contingency Costs
Incurred by Project Phase
(Design / Procurement /
Construction)
Contingency
Incurred /
Budgeted
<$15
8.09
0.46
6%
$7.76
0.34 (0.04/0.10/0.20)
74%
$15—$50
30.22
1.55
5%
$29.51
1.15(0.20/0.30/0.65)
74%
$50-$100
70.70
3.09
4%
$68.19
2.24 (0.25/0.83/ 1.16)
72%
>$100
214.02
15.56
7%
$206.50
13.63 (2.00/4.24/7.39)
87%
All costs are in millions of dollars. Incurred contingency costs exclude excludes three phases: Project Planning Phase,
Demolition, and Start Up.
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
Base Contingency Factor
<$500,000
6.7%
$500,000 to $3,000,000
5.8%
$3,000,000 to $15,000,000
4.9%*
$15,000,000 to $50,000,000
4.1%*
$50,000,000 to $100,000,000
3.2%*
>$100,000,000
5.8%*
* Percentages based on Cll-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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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
Exhibit D-7. WBS Default Complexity Factors by Technology
Technology
Risk Level Assigned to
Technology
Default Complexity
Factor
Acid Feed
Low
0.5
Cation Exchange
Low
0.5
Caustic Feed
Low
0.5
Nontreatment Options
Low
0.5
Potassium Permanganate Addition
Low
0.5
Granular Activated Carbon
Average
1
Chlorine Gas
Average
1
Packed Tower Aeration
Average
1
Adsorptive Media
High
1.5
Anion Exchange
High
1.5
Biological Treatment
High
1.5
Microfiltration and Ultrafiltration
High
1.5
Greensand Filtration
High
1.5
Hypochlorite Addition
High
1.5
Multi-stage Bubble Aeration
High
1.5
Reverse Osmosis and Nanofiltration
High
1.5
Ultraviolet Advanced Oxidation Processes
Very high
2
Ultraviolet Disinfection
Very high
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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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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 MGD, 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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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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
2.3
LO
CO
I
O
Other Public Sector
3.5
"st
I
LO
O
Private Sector
4.6
o
LO
I
CsJ
"st
Other
3.9
O
O
I
Private Systems
DWSRF
5.6
0.8-6.2
Other Public Sector
4.4
LO
LO
I
CO
Private Sector
6.5
4.3-7.7
Other
5.9
O
o
I
o
o
All Systems
DWSRF
2.6
CO
"st
I
o
Other Public Sector
3.8
1.9-4.5
Private Sector
5.2
LO
LO
I
CO
"st
Other
4.3
O
o
I
o
o
All Systems and Lenders
0.0-10.0
D.17 Construction Management and General Contractor Overhead
As discussed in Section D.4.2, 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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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
Exhibit D-9. Cost of Performance Bonds
Project Direct Cost Range
Performance Bond Cost
<$100,000
2.5%
$100,000 to $500,000
$2,500 plus 1.5% of the amount over $100,000
$500,000 to $2,500,000
$8,500 plus 1.0% of the amount over $500,000
$2,500,000 to $5,000,000
$28,500 plus 0.75% of the amount over $2,500,000
$5,000,000 to $7,500,000
$47,250 plus 0.70% of the amount over $5,000,000
>$7,500,000
$64,750 plus 0.60% of the amount over $7,500,000
Source: RSMeans (2006), reference table R013113-80.
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
Construction Management Fee
<$100,000
10%
$100,000 to $250,000
9%
$250,000 to $1,000,000
6%
$1,000,000 to $5,000,000
5%
$5,000,000 to $10,000,000
4%
>$10,000,000
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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WBS-Based Cost Model for Cation Exchange Drinking Water Treatment
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. 7 January.
AWWC. 2001a. Seymour, Indiana Process Cost Estimate.
AWWC. 2001b. 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. 67th Annual Edition. Kingston,
Massachusetts: RSMeans Company.
RSMeans. 2009c. Facilities Construction Cost Data. 24th Annual Edition. Kingston,
Massachusetts: RSMeans Company.
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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Exhibit E-1. Operator Labor Assumptions for Three Levels of Automation
Task
Manual
Semi-automated
Automated
Record system operating parameters from process
instruments (includes routine sampling)
5 minutes per day
per instrument
5 minutes per day
5 minutes per day
Preventative maintenance and calibration of process
instruments
10 minutes per
month per
instrument
10 minutes per
month per
instrument
10 minutes per month
per instrument
Verify and adjust pump operating parameters
5 minutes per day
per pump
5 minutes per day
per pump
None
Preventative maintenance of pumps
30.25 hours per
year per pump
30.25 hours per
year per pump
30.25 hours per year
per pump
Verify and adjust valve positions
5 minutes per
week per valve
5 minutes per
week per valve
None
Preventative maintenance and inspection of valves
5 minutes per year
per valve
5 minutes per year
per valve
5 minutes per year per
valve
Visual inspection of facility
1 minute per day
per 100 square
feet of facility
1 minute per day
per 100 square
feet of facility
1 minute per day per
100 square feet of
facility
Inspect and maintain chemical supplies
60 minutes per
month per
chemical supply
tank
60 minutes per
month per
chemical supply
tank
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,
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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
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
Task
Interval
Estimated
Minutes/Task
Estimated Hours/Year
Check bearing temperature
Monthly
5
1
Changing lubricant/ adjusting power level
Monthly
30
6
Disassemble for inspection, reassemble
Monthly
60
12
Check oil
Quarterly
10
0.67
Check lubricated bearings for saponification
Quarterly
10
0.67
Removal of bearings and replace, reassemble
Quarterly
60
4
Check packing and replace if necessary, reassemble
6 months
60
2
Vibration readings
6 months
10
0.33
Remove casing and inspect pump
Annual
120
2
If parts are worn, replace
Annual
varies
covered by pump materials
percentage and pump
useful life
Clean deposits and/ or scaling
Annual
60
1
Clean out stuffing box piping
Annual
30
0.5
Measure and record suction and discharge pipe head
Annual
5
0.08
Total Hours/Year:
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.
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Visual Inspection of Facility
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
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).
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.
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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.
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
• Repai r 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
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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.
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
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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
• 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/ft of building area
• Mid quality buildings, 2 watts/hour/ft of building area
• High quality buildings, 4 watts/hour/ft 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
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2
a weighted average of 1.0 watt per hour per ft, 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).
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
Value used
Ventilation air change rate for contactor areas
3 air changes/hour
Ventilation air change rate for pump areas
20 air changes/hour
Ventilation air change rate for chemical storage areas
2 air changes/hour
Ventilation air change rate for offices
2 air changes/hour
Pressure drop across ventilation fans
0.25 pounds/ft2
Number of days with mechanical ventilation for small systems (less than 1 MGD)
90 days/year
Number of days with mechanical ventilation for medium systems (1 to 10 MGD)
120 days/year
Number of days with mechanical ventilation for large systems (greater than 10 MGD)
185 days/year
Building height
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 Ac|iangcs / 33,000,000
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where:
DAYS = days per year with mechanical ventilation
Pdrop = pressure drop across ventilation fans (pounds/ft )
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.
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.
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Exhibit E-5. Assumptions for Calculating Heating and Cooling Requirements
Variable
Value used
R-value for walls
13 hour - ft2 - °F /BTU
R-value for ceilings
38 hour -ft?-°F /BTU
Annual heating degree days
4,923 degree days
Annual cooling degree days
1,697 degree days
Heating ventilation/infiltration load
168,679 BTU/cfm
Cooling ventilation/infiltration load
51,771 BTU/cfm
Electric resistance heating efficiency
98%
Heat pump heating coefficient of performance
3.2
Natural gas non-condensing furnace efficiency
80%
Natural gas condensing furnace efficiency
95%
Diesel non-condensing furnace efficiency
78%
Diesel condensing furnace efficiency
85%
Air conditioning energy efficiency ratio
11 Whr/BTU
Heat pump cooling energy efficiency ratio
10.1 Whr/BTU
Maximum capacity for heat pump heating
200 thousand BTU per hour
Maximum capacity for other heating options
6,148 thousand BTU per hour
Maximum capacity for heat pump cooling
50 tons
Maximum capacity for other cooling options
113.32 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
user should select values for the heating and cooling measures, respectively, that are consistent
with one another (i.e., reflective of a realistic climate).
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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 / Railing
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)
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.
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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:
Heating ventilation and infiltration heat loss = CFM x Hyiioad
Cooling ventilation and infiltration heat loss = CFM x Cviioad
where:
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
System Design Flow:
System Design Flow: 1
System Design Flow: 10
Selected
Less than 1 MGD
to 10 MGD
MGD or greater
Buildings 500 ft2 or greater
Low
Neither
Heating Only
Heating and Cooling
Medium
Heating Only
Heating and Cooling
Heating and Cooling
High
Heating and Cooling
Heating and Cooling
Heating and Cooling
Buildings less than 500 ft2
Low or Medium
Neither
Neither
Heating Only
High
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 Economy (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 White stone Facility Maintenance and Repair Cost Reference
2009-2010. Fourteenth Annual Edition. October.
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