FROM: Jeff Coburn, RTI International 

TO: Brenda Shine, EPA/OAQPS 

FOR: EPA Docket No. EPA-HQ-OAR-2011-0002 

DATE: July 12, 2011 

SUBJECT: Technology Review for Heat Exchange Systems 

1. Purpose

This memorandum documents the technology review for heat exchange systems. It reviews 

control alternatives and estimates the costs and environmental impacts for the alternatives 

identified. 

2. Legislative Background

The Clean Air Act (CAA) requires EPA to review promulgated standards periodically to ensure 

new source performance standards (NSPS) and national emissions standards for hazardous air 

pollutants (NESHAP) reflect advances in emissions reduction technology. Specifically, Section 

112(d)(6) of the Clean Air Act (CAA) states that “[t]he Administrator shall review, and revise as 

necessary (taking into account developments in practices, processes, and control technologies), 

emission standards promulgated under this section no less often than every 8 years.” Similarly, 

Section 111(b)(1)(B) requires EPA to review NSPS for a given source category every 8 years, 

and, if appropriate, revise such standards. To facilitate these required reviews, EPA is evaluating 

key emission sources that exist across several source categories to provide a consistent 

framework when evaluating the emissions from these key sources for a particular source 

category. This memorandum documents one such technology review for heat exchange systems. 

3. Introduction

Heat exchangers are devices or collections of devices used to transfer heat from process fluids to 

another fluid (typically air or water) without intentional direct contact of the process fluid with 

the cooling fluid (i.e., non-contact heat exchanger). The focus of this technology memorandum 

is on water-cooled heat exchangers. The term “heat exchange system” is used in this 

memorandum to refer collectively to water-cooled heat exchangers and the associated cooling 

water handling system. There are two types of heat exchange systems: closed-loop recirculation 

systems and once-through systems. Closed-loop recirculation systems are marked by the use of 

a cooling tower to cool the heated water leaving the heat exchanger and then return the newly 

cooled water to the heat exchanger for reuse. For closed-loop recirculation systems, the heat 

exchange system consists of a cooling tower, all heat exchangers that are serviced by that cooling 

tower, and all water lines to and from the heat exchanger(s). Once-through systems typically use 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

2 

river or pond water as the influent cooling fluid to the heat exchangers, and the heated water 

leaving the heat exchangers is then discharged from the facility. For once-through systems, the 

heat exchange system consists of one or more heat exchangers servicing an individual process 

unit and all water lines to and from the heat exchanger(s). 

At times, the heat exchanger’s internal tubing material can corrode or crack, allowing some 

process fluids to mix or become entrained with the cooling water. Pollutants in the process 

fluids may subsequently be released from the cooling water into the atmosphere when the water 

is exposed to air (e.g., in a cooling tower for closed-loop systems or trenches/ponds in a oncethrough system). This technology memorandum specifically considers methods to reduce 

emissions from cooling water that has unintentionally contacted a process fluid within in a heat 

exchanger. Note that intentional direct contact of water with process fluids results in the 

formation of a wastewater, which is not covered in this technology memorandum. 

4. Description of Emission Releases

Once-through heat exchange systems generally transport the cooling water leaving the heat 

exchangers in open sewer lines or trenches to a holding pond to allow the water to cool prior to 

discharge. Fugitive air emissions of pollutants from the water may occur along the transport 

lines and from the surface of the holding pond or receiving water body. Some facilities may use 

a spray in the holding pond to help cool the water, but this also increases water contact with the 

air and therefore the potential for air emissions. Emissions from once-through heat exchange 

systems are similar to releases from wastewater treatment units and are fugitive in nature. The 

emissions occur via volatilization at the air-liquid interface within the transport lines or in the 

surface impoundments. Not all pollutants will be emitted from the cooling water to the same 

extent. Highly volatile compounds (i.e., those with high Henry’s Law constants) are expected to 

be nearly completely released from the cooling water while only a small fraction of the less 

volatile compounds are emitted; the remainder of the less volatile compounds would remain in 

the water through the collection and holding units. 

It is costly to completely cover these once-through cooling water sources to prevent air releases. 

Furthermore, covering these units would only serve to suppress the volatile emissions that would 

be released later from the receiving water body. It would be very costly to build a treatment 

system for the cooling water which would not actually need treatment except for the small period 

of time a leak at the heat exchanger might exist. That is, it is not generally feasible to prescribe 

or enforce a standard of performance because the pollutant or pollutants are not emitted through 

a conveyance designed and constructed to emit or capture such pollutant(s) and that the 

application of a measurement methodology, which would require such a conveyance to be 

installed, is not generally feasible in light of the technological and economic limitations. 

Closed-loop heat exchange systems typically use closed piping to transport the water to and from 

the cooling tower. Emissions from closed-loop heat exchange systems occur primarily at the 

cooling tower, as this is generally the only point for exposure of the cooling water with the 

atmosphere. Cooling towers may be designed as either natural draft or mechanical draft. 

Natural draft cooling towers are large hyperbolic structures (often associated with nuclear power 

plants) that use natural convection of warmed air to create air flow across the water, thereby 

cooling the water. Mechanical draft cooling towers use large fans to force air through or across 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

3 

the cooling water to cool the water. Figure 1 shows a typical mechanical, induced-draft 

industrial cooling tower. The cooling towers are designed to have a high surface area for airwater contact for the purposes of cooling the water. Most industrial cooling towers have 

multiple exhaust fans that are used to draw ambient air through water that is cascading down the 

outer-portion of the tower; the air is then exhausted from very short, wide fan openings at 

multiple locations across the top of the cooling tower. Emissions can also occur across the 

openings at the sides of cooling towers as wind blows across the unit. Emissions occur primarily 

due to volatilization of light organics from the water. A small fraction of the recirculating water 

may become entrained in the exhausted air and leave the cooling tower as a water mist. This 

water mist is commonly referred to as “drift” or “drift losses.” All pollutants contained in the 

water mist, including low volatility compounds, can be released to the atmosphere via the 

cooling tower drift. 

Figure 1. An induced-draft industrial cooling tower. 

Although emissions from closed-loop systems are expected to be released primarily in the 

exhaust air from the cooling towers, it is not generally feasible to prescribe or enforce a standard 

of performance because the pollutant or pollutants are not emitted through a conveyance 

designed and constructed to emit or capture such pollutant(s) and that the application of a 

measurement methodology, which would require such a conveyance to be installed, is not 

feasible due to technological and economic limitations. First, not all of the emissions occur from 

the exhaust gas fans at the top of the cooling tower; fugitive releases can also occur through 

openings along the side or bottom of the cooling tower. To capture all of the emissions would 

require that the whole cooling tower be enclosed. This is not practical or technically feasible 

considering the size of the cooling towers and the volume of gas that would be required to be 

handled within the enclosure system and considering the heat transfer requirements of the 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

4 

cooling tower. While it may be technically feasible to install ducts on each exhaust fan to 

capture and route the primary exhaust gas to a single stack for potential treatment and/or release, 

such an installation still suffers from technical and economic limitations. Such a proposed 

capture and exhaust stack would still have to be very large due to the size of the physical 

dimensions of the cooling towers, the volume of air exhausted, and the need to transport the 

exhaust air away from the cooling tower (otherwise, the stack itself will reduce the cooling 

efficiency of the cooling tower, leading to process operation issues for the heat exchanger served 

by the cooling tower). Given the large exhaust volumes and the high moisture content of the 

exhaust, routine measurements that provide the necessary detection limits needed to identify 

typical heat exchanger leaks are not available. Furthermore, such a capture system would not 

capture all of the emissions from the cooling tower. 

Based on the nature of the emission releases from heat exchange systems (both once-through and 

closed-loop systems as described above), it is generally not feasible to prescribe or enforce a 

standard of performance for heat exchange systems. Specifically, the application of a 

measurement methodology, which would require a conveyance designed and constructed to emit 

or capture the emissions from the heat exchange system to be installed, is not feasible in light of 

the technological and economic limitations associated with atmospheric releases from heat 

exchange systems. 

Differences in emissions from once-through heat exchange systems and closed-loop heat 

exchange systems were evaluated using emission models. This evaluation was completed 

because direct emission measurements are not available for these sources (due to the 

measurement method limitations just discussed). Wastewater emission models (e.g., using mass 

transfer correlations) can be used to predict the releases from the open cooling water sources 

used in a once-through heat exchange system. Although the emissions will vary based on the 

design and operation of the cooling water collection and holding units in once-through systems, 

highly volatile compounds are projected to be nearly 100 percent emitted from the cooling water 

while only a small fraction of low volatility compounds will be released. These results are 

similar to modeling results for the releases projected for cooling towers used in closed-loop heat 

exchange systems. Again, emissions from the cooling tower can vary based on the air-liquid 

flow ratio and mass transfer efficiency. Given the uncertainty and variability of emissions from 

these sources, the emissions potential for both once-through and closed-loop heat exchange 

systems are expected to be essentially equivalent. 

5. Identification of Control Alternatives

Since it is not feasible to prescribe or enforce a standard of performance for heat exchange 

systems, design, equipment, work practice, and operational standards for reducing emissions 

from heat exchange systems were identified and evaluated. 

Potential Equipment Design and Operational Standards 

As the heat exchange systems evaluated in this memorandum are designed as non-contact 

systems, any contact that does occur happens as a result of an unintentional equipment failure 

that results in a leak of the process fluid into the cooling water. No construction material was 

identified that, in all cases, could not unintentionally leak. Certain design or operational 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

5 

conditions were identified that would effectively reduce or eliminate the leak from the heat 

exchanger from contaminating the cooling water and subsequently be emitted. A brief 

description of these design and operational conditions follows: 

• Heat exchangers where the cooling water pressure significantly exceeds the process fluid 

pressure. For these heat exchangers, if a crack in the heat exchanger occurs, water will 

leak into the process fluid rather than the process fluid leaking into the cooling water. 

Note that there will be a pressure drop across the heat exchanger for both the water and 

process fluid, and most heat exchangers operate with countercurrent flow. The process 

fluid inlet side of the heat exchanger, which will be the location of the maximum process 

fluid pressure within the heat exchanger, will also be the water outlet side of the heat 

exchanger (location of minimum water pressure within the heat exchanger). It is 

conceivable that a leak into the cooling water can still occur even though the inlet water 

pressure exceeds the inlet fluid pressure. Therefore, it is necessary to specify that the 

minimum cooling water pressure at any point within the heat exchanger exceeds the 

maximum process fluid pressure within the heat exchanger. Typical language used in 

previous rules for heat exchangers describe these heat exchangers as those that “operate 

with the minimum pressure on the cooling water side at least 35 kilopascals [i.e., 

5.0 pounds per square inch absolute (psia)] greater than the maximum pressure on the 

process side.” 

• Heat exchangers that employ an inert (not volatile) intervening cooling fluid between the 

process and the cooling water and isolates the cooling water from the process fluid. The 

intervening fluid must remain enclosed and cannot be sent through a cooling tower or 

otherwise allowed routine contact with the atmosphere; otherwise, emissions would 

simply be transferred from the cooling water release points to the intervening fluid 

release points. Provisions would be needed for draining the intervening fluid for 

maintenance purposes. One could conceive of a situation in which a leak develops 

between the process fluid and a second leak develops between the intervening fluid and 

the cooling water. If this occurs, and the process fluid pressure exceeds the water 

pressure, the intervening process fluid chamber would become filled with process fluid 

and the process fluid would leak into the cooling water. Thus, while a heat exchanger 

designed to use an intervening fluid is much less likely to leak (because two leaks would 

have to occur) than a heat exchanger that does not employ an intervening fluid, this type 

of design does not necessarily guarantee that process fluid leaks that contaminate the 

cooling liquid will never occur. 

The question arises: should these design and operational alternatives be required for all new or 

modified sources? As process fluid pressures are dictated by process operational conditions, and 

many chemical processes operate at elevated pressure, it is impractical to require the cooling 

water supply to operate at a pressure exceeding the process fluid pressures in all cases. Typical 

industrial water supply systems operate at a of 30 to 100 psi gauge pressure (psig). If the process 

fluid is at a high pressure, commonly available water supply systems could not supply cooling 

water at these same high pressures. Additionally, the heat exchanger housing would have to be 

designed to handle these high pressures. It would be cost-prohibitive and energy intensive to 

require heat exchanger water pressures to exceed process fluid pressures in all applications. 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

6 

The use of an intervening process fluid requires a specially designed process heater. It would 

generally be impossible to retrofit a process heater to use an intervening fluid without completely 

replacing the heat exchanger. This would be a cost-prohibitive requirement for existing heat 

exchange systems. New installations could be designed to use an intervening fluid; however, the 

use of an intervening fluid generally reduces the heat transfer efficiency of the heat exchanger, so 

there are additional costs associated with using an intervening fluid because the heat exchangers 

would be larger when using an intervening fluid. It is beyond the scope of this evaluation to 

determine the precise costs associated with requiring the use of an intervening fluid, as this can 

vary significantly by size and operational needs of a specific heat exchanger. Also, it is difficult 

to quantify the emission reductions achieved by such an application because there are no data to 

determine how often these systems do eventually leak. However, the fact that such systems 

could eventually develop leaks into the cooling water would suggest that monitoring to identify 

incidence of leaks may still be needed. Therefore, a facility would have to undergo significant 

costs to design and install a heat exchanger with an intervening fluid, and still incur ongoing 

costs to monitor for leaks. As described presently, a monitoring and repair program to identify 

leaks is effective at reducing emissions from heat exchange systems. While it is not possible to 

develop a quantitative cost-effectiveness value for a requirement to use an intervening fluid in 

new heat exchanger installations, the additional costs associated with such a requirement do not 

appear to be reasonable considering the limited emission reductions that would be achieved 

beyond the implementation of a monitoring and repair program to identify leaks. In fact, in most 

cases, it would be extremely expensive to implement with little to no emission reductions. While 

the use of an intervening fluid may be evaluated in more detail for specific source categories, 

particularly for heat exchangers handling process fluids that are highly toxic or corrosive (e.g., 

hydrogen fluoride), it appears that, for typical heat exchanger systems, the use of an intervening 

fluid in new or existing heat exchangers is not practical, taking into consideration the cost of 

achieving limited emission reductions (beyond those achieved through a monitoring and repair 

program) and considering the environmental and energy impacts of such a requirement. 

Potential Monitoring Alternatives 

A variety of different work practices were identified as potential emission reduction measures for 

heat exchange systems. These work practices can be loosely grouped as visual inspections, 

surrogate monitoring, water sampling and analysis, and stripping column air analysis. 

Visual inspections have been used by several facilities. For heat exchangers servicing a gaseous 

process fluid, gas entering the cooling water will collect in these high points in the line. If these 

locations have a site glass, visual inspections can be used to identify these leaks. For oncethrough cooling systems, the owner or operator can visually inspect the holding pond for a 

visible organic sheen. The presence of an organic sheen indicates that a heat exchanger is likely 

to be leaking. Visual inspections are expected to be able to identify very large leaks, but they 

will not be able to identify leaks that do not exceed solubility limits of the cooling water. 

Surrogate monitoring methods include monitoring of chemical usage rates (e.g., chlorine, 

hypochlorite, or bromine usage rates), monitoring of free chlorine in the cooling water, and 

monitoring of the oxidation/reduction potential of the cooling water. When a leak of a 

degradable organic pollutant occurs, the added organic matter in the cooling water causes 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

7 

increased microbial growth. The oxidation/reduction potential or free chlorine concentration 

may be used to monitor for microbial growth (Suslow, 2004). When microbial growth is found, 

disinfectant chemical use rates are increased to control the biological growth. Microbial growth 

in the heat exchanger will reduce the heat transfer efficiency and may cause plugging of the 

water tubes. Consequently, essentially every closed-loop heat exchange system is monitored for 

microbial growth. Several consecutive days of increased biological growth or increased 

disinfectant chemical use rates would indicate a leak has occurred. Since surrogate monitoring is 

commonly performed on a daily or per shift frequency, these methods should be able to detect 

leaks fairly quickly. However, there may be lag period between the initiation of the leak and 

significant microbial growth, so there may be some delay between the first occurrence of the leak 

and a change in the surrogate monitoring level. For this same reason, surrogate monitoring may 

not be able to identify leaks in once-through systems even if monitoring is used to control 

microbial growth from the source water used in the system. Surrogate monitoring methods can 

detect leaks that do not exceed water solubility limits, so these methods should be more sensitive 

than visual inspections. However, as there is commonly some background level of microbial 

growth and disinfectant use, surrogate monitoring methods generally are not sensitive enough to 

identify smaller heat exchanger leaks. Based on the available data, monitoring of surrogate 

parameters will only detect relatively large leaks and could miss leaks that would generate 

significant organic emissions (Corsi et al., 2004). 

Water sampling methods include total hydrocarbon (THC), total organic carbon (TOC), or 

speciated chemical analysis. Common industrial water supply can have TOC concentrations of 

1 to 5 parts per million by weight (ppmw). Consequently, THC or TOC monitoring may be able 

to identify an increase in THC or TOC of 1 ppmw by monitoring before and after the heat 

exchanger, but are generally not sensitive enough to identify smaller leaks. Using knowledge of 

the process fluid, analysis of specific pollutants can be used to identify a leak. For example, for 

an ethylene unit, monitoring for ethylene in the cooling water leaving the heat exchanger can be 

used to identify a leak. By targeting a specific chemical or limited set of chemicals, very low 

water detection limits can be achieved; common detection limits are approximately 10 to 20 parts 

per billion by weight (ppbw). For very volatile compounds, the direct water concentration and 

flow rate can be used to estimate the emissions from the heat exchange system by assuming 

100 percent of the pollutant will be emitted. For less volatile compounds in closed-loop heat 

exchange systems, the concentration of semi-volatile compounds can slowly build-up within the 

recirculated cooling water, because not all of the compound will be emitted from the cooling 

tower. For these compounds, direct water sampling of the cooling water leaving the heat 

exchanger may be able to identify very small leaks, but this concentration may not correlate with 

the actual emissions from the system (when assuming 100 percent emissions). Sampling can be 

performed before and after the cooling tower (which is the same as monitoring before and after a 

heat exchanger or set of heat exchangers) to get a better estimate of the actual emissions or leak 

rate, but this tends to reduce the sensitivity of the method. For example, if the concentration of a 

cresol builds up to 200 ppbw, it may be difficult to detect a change in concentration across the 

heat exchanger of 20 ppbw even though the detection limit for cresol may be less than 20 ppbw. 

Nevertheless, the elevated concentrations of cresol provide reasonable evidence that a leak 

exists. It may be reasonable to compare the concentrations in the cooling water leaving the heat 

exchanger with the source water used in a once-through system or the water used as make-up in 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

8 

a closed-loop system to ensure that any elevated concentrations are due to a leak in the heat 

exchanger rather than background water contamination. 

The modified El Paso method (TCEQ, 2003) uses a dynamic or flow-through system for air 

stripping a sample of the water and analyzing the resultant off-gases for volatile organic 

compounds (VOC) using a common flame ionization detector (FID) analyzer. This method was 

originally developed for use by El Paso Products Company in the early 1970s for cooling tower 

water characterization, and it has been the popular monitoring choice in Texas for many years. 

The modified El Paso method helps to overcome potential losses of highly volatile components 

during water sampling. Also, based on the liquid and air flow rates used in the modified El Paso 

method, the air concentration detection limit of approximately 1 ppm by volume (ppmv) (as 

methane) corresponds to a water concentration of approximately 15 ppbw. Therefore, the 

modified El Paso method provides similar detection limits as speciated water analysis. It also 

simulates, to some extent, the losses that might occur from the cooling water, so leaks of semivolatile compounds that are not easily stripped from the cooling water in the cooling tower are 

also not fully stripped in the stripping column. While the stripping column may not exactly 

simulate the stripping efficiency of the specific cooling tower being monitored within the heat 

exchange system, the stripping column provides a reasonable proxy of the air emissions from the 

heat exchange system. 

Leak Repair Considerations 

Regardless of the monitoring method used, once a leak is identified, it must be repaired or 

isolated to prevent the process fluid from contaminating the cooling water. Many industrial heat 

exchangers use a shell and tube design, where the process fluid is in the tubes with the cooling 

water flow in the shell. If the specific tube that is leaking can be identified, that tube can be 

plugged, thereby preventing the process fluid from flowing through that tube and isolating the 

leaking section of the heat exchanger. This procedure diminishes the effective area for heat 

exchange, thereby reducing the overall efficiency of the heat exchanger bundle. Depending on 

the age of the heat exchanger and the number of tubes that have been blocked already, the heat 

exchanger bundle may need to be replaced. In some installations, the leaking heat exchanger 

bundle can be isolated, removed from service, and replaced without interruption of the process 

served by the heat exchanger. However, there can be installations where a heat exchange system 

may not have excess capacity to allow one bundle to be removed without shutting down the 

process unit. 

It takes time to identify the precise location of a leak and affect its repair. Some heat exchange 

systems may include multiple heat exchanger bundles from different processes. Speciated 

chemical analysis is typically used as a fingerprint to identify which process fluid is leaking, 

thereby identifying the likely process unit associated with the leak. However, it takes additional 

monitoring to identify which heat exchanger bundle is leaking, and additional time to identify the 

specific tube that has the leak. Plugging a tube can be done fairly quickly, but it may take 

additional time to obtain parts needed if the heat exchanger bundle must be replaced. The repair 

should be accomplished as soon as practical, and in most cases, this will take no longer than 45 

days. For specially sized or designed heat exchangers, there may be instances where the 

necessary equipment may take several months to obtain. Under this circumstance, it may be 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

9 

reasonable to allow the repair to be delayed until the part can be obtained. Most special order 

parts can be obtained within 90 days of an order, so a total repair time of 120 days should be 

sufficient to locate the leak, order the parts, and complete the repair. Delay of repairs may also 

be reasonable for small leaks that can only be repaired if the process unit is shut down. 

Requiring the unit to shut down specifically for the repair may generate more emissions than 

would occur by delaying repair. Also, requiring the unit to shut down could result in significant 

lost revenue, which could (potentially) make the requirement for immediate repair very costly. 

6. Costs of Monitoring Alternatives

This section describes the costs associated with various work practice monitoring alternatives. 

Costs were not developed for specific equipment design or operational alternatives because these 

costs can vary widely by application and are expected to be very high in most applications. 

While these equipment design or operational alternatives can be very expensive, there may be 

instances where they can be considered. For example, if a certain source category has units that 

only operate at low pressures, it may be reasonable, at least for new sources, to require that the 

water-side pressure exceed the process fluid pressure at all points in the heat exchanger. The 

equipment or design alternatives identified in Section 5 should be evaluated for a specific source 

category to determine if, based on the operational characteristics of the processes and the hazards 

associated with the pollutants contained in the process fluids, these alternatives are economically 

viable or needed to reduce risks associated with potential pollutant releases. 

General manufacturing industry sector labor rates (May 2009 dollars) were used to develop the 

costs for labor-related requirements for the different work practice monitoring alternatives 

described in Section 5. These costs were based on mean hourly labor rates and were developed 

for different labor classes (technical, managerial, administrative, maintenance, and operating 

labor classes). The hourly labor rates were burdened with fringe benefits and overhead to 

calculate the loaded hourly labor rate for each labor class. The labor classes used in the analysis 

and the loaded hourly labor rate calculated for each labor class are summarized in Table 1. 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

10 

Table 1. Summary of 2009 Hourly Labor Rates 

Labor Class 

(A) 

Mean 

hourly 

labor rate1

($/hr) 

(B) 

Fringe 

benefit 

loading 

rate 

I 

Overhead 

and profit 

rate 

(D = A x B x C)

Loaded wage 

rate 

($/hr) 

1. Professional specialty and Technical 

(SOC Code: 17-2081) 39.53 1.5 1.4 83.01 

2. Executive, administrative and managerial

(SOC Code: 11-9041) 57.80 1.5 1.4 121.38 

3. Administrative support, including clerical 

(SOC Code: 43-0000) 17.31 1.5 1.4 36.35 

4. Installation, Maintenance, and Repair 

(SOC Code: 49-0000) 22.08 1.5 1.4 46.37 

5. Plant and System Operators, All 

(SOC Code: 51-8099) 22.72 1.5 1.4 47.71 

1

 Labor rates as reported by U.S. Department of Labor, Bureau of Labor Statistics (U.S. DOL, 2010). Labor rates for 

May 2009 for general manufacturing industry sector: 2-digit NAICS code 31 through 33 

(http://stats.bls.gov/oes/oes_dl.htm accessed in December 2010). 

Visual Inspections and Surrogate Monitoring Costs 

For the most part, visual inspections and/or surrogate monitoring is already widely used in nearly 

all industrial cooling water applications. As such, there are limited costs associated with a 

requirement to perform visual inspections and/or surrogate monitoring. The primary additional 

cost associated with such a regulatory program would be the development of a quality assurance 

(QA) plan to document the inspections/monitoring procedures, the baseline monitoring value or 

acceptable range, and the parameter values that would trigger corrective action (i.e., indicate a 

leak that must be repaired). Thus, no additional equipment is assumed to be needed to 

implement visual inspections or surrogate monitoring, and only minimal labor costs would be 

incurred for QA plan development, recordkeeping, and reporting. 

Table 2 summarizes the costs associated with a visual inspections and surrogate monitoring 

program. The cost of developing a QA plan is expected to be a one-year cost per facility; if there 

are multiple heat exchange systems at the facility, the cost per heat exchange system would be 

the total QA plan cost divided by the number of heat exchange systems affected by the rule. It is 

assumed that the QA plan has a useful life of 5 years when annualizing these costs. The 6 hours 

for recordkeeping are based on an additional minute per day to record the results of the visual 

inspections and surrogate monitoring (beyond those routinely required by the facility). 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

11 

Table 2. Summary of Costs Associated with Surrogate Monitoring 

Activity/Requirement 

Number of labor hours by labor class 

per year for activity/requirement 

Total Cost 

Technical 

Managerial 

($) 

Administrative 

Operators 

QA plan (1st year cost only) 10 1 2 0 1,024 

Recordkeeping 0 0 0 6 286 

Reporting (assumes semi-annual reporting) 4 0.4 0.8 0 410 

Water Sampling Monitoring Costs 

Water sampling costs are dependent on the particular analytical method used and, for speciated 

organic analysis, the number of compounds that must be analytically determined. TOC analysis 

costs range from $50-75 per sample, and speciated chemical analysis via EPA Method 601/602 

costs approximately $250/sample (based on on-line price lists: Analytical Laboratories, Inc., 

http://analyticallaboratories.com/page.cfm?pageid=90; Analytical Resources, Inc., 

http://arilabs.com/portal/downloads/ARI_price_list.pdf; Environmental Testing Inc., 

http://www.eti-lab.com/files/Price.pdf). Since most cooling water can have fairly significant and 

potentially variable TOC concentrations, both inlet and outlet samples from the heat exchanger 

may be needed to identify a leak. Traditionally, this “delta” concentration is determined using 

triplicate analysis at each sampling location, requiring six samples total. Therefore, costs of 

typical TOC sampling can range from $300 to $450 per event. As such, TOC water sampling 

costs approximately the same or even more than speciated water sampling using only one sample 

of the cooling water after the heat exchanger. Of course, if a delta concentration were needed 

from the speciated organic monitoring, speciated organic monitoring would cost more than TOC 

monitoring, but if the speciated organic analysis can be correctly targeted, a single concentration 

analysis should be adequate. 

Like the surrogate monitoring approach, a QA plan will need to be developed for water sampling 

monitoring. Because these types of water samples must be collected in specific ways and may 

require different sampling locations than those used for routine sampling used to control 

disinfectant addition. Therefore, additional hours are projected for this task compared to the 

surrogate monitoring QA plan. The cost of developing a QA plan is expected to be a one-year 

cost per facility; if there are multiple heat exchange systems at the facility, the cost per heat 

exchange system would be the total QA plan cost divided by the number of heat exchange 

systems affected by the rule. It is assumed that the QA plan has a useful life of 5 years when 

annualizing these costs. Labor time is also required to collect the samples for each sampling 

event and for recordkeeping and reporting. Table 3 provides the labor estimates for a water 

sampling monitoring program. As the annual cost of a water sampling program is dependent on 

the number of sampling events, the costs in Table 3 are provided per sample or sampling event 

(except for the QA plan as discussed previously and reporting costs, which are per periodic 

reporting event) so that the costs can be scaled for different monitoring frequencies. 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

12 

Table 3. Summary Costs Associated with Water Sampling Monitoring 

Activity/Requirement 

Number of labor hours by labor class 

per year for activity/requirement 

Total Cost 

Technical 

Managerial 

Adminis-

($) 

trative 

Operators 

QA plan (1st year cost only) 32 2 4 0 3,045 

TOC analysis costs/sample 60 

Method 301/302 analysis costs/sample 250 

Sample express shipping cost/event 30 

Sample shipping & results review labor/event 0.5 0 0.5 0 60 

Single sample collection labor/event 0 0 0 1 48 

Triplicate in-out sample collection labor/event 0 0 0 1.5 72 

Recordkeeping labor/event 0 0 0 0.25 12 

Reporting labor/reporting event 2 0.2 0.4 0 205 

Example costs for quarterly Method 301/302 sampling with semiannual reporting for single heat 

exchange system 

First year costs [QA plan + 4×(sampling+shipping+analysis+recording)+2×reporting] 5,055 

Subsequent year costs [4×(sampling+shipping+analysis+recording)+2×reporting] 2,010 

Average annualized costs [CRF1×QA plan + subsequent year costs] 2,750 

1

 CRF = capital recovery factor = 0.2439 based on 5 year life and 7 percent annual interest. 

Modified El Paso Monitoring Costs 

Stripping columns can be purchased for use by the facility personnel or the facility can hire a 

contractor to come to the facility and perform the stripping column (modified El Paso) 

monitoring without the facility purchasing the equipment. The decision to purchase the 

equipment will depend on the number of sampling events required to be performed each year. 

Stripping column equipment costs and testing fees were obtained from a testing contractor 

(Boudreaux, 2010). These costs as well as other costs associated with a periodic modified El 

Paso monitoring program are summarized in Table 4. As with a water sampling program, the 

annual costs for a modified El Paso monitoring program are dependent on the number of 

sampling events per year (which is dependent on both the number of heat exchange systems that 

must be monitored and the monitoring frequency). As such, many of the costs in Table 4 are 

provided per monitoring event so that the costs can be scaled for different monitoring 

frequencies. 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

13 

Table 4. Summary Costs Associated with Modified El Paso Monitoring 

Activity/Requirement 

Number of labor hours by labor 

class per year for 

activity/requirement 

Total Cost 

Technical 

Managerial 

Adminis-

($) 

trative 

Operators 

QA plan (1st year cost only) 32 2 4 0 3,045 

Stripping column 3,850 

FID analyzer 10,000 

Contracted analysis, first or single event 680 

Contracted analysis, 2nd or 3rd locations/event1 195 

In-house sampling/monitoring event 0 0 0 3 143 

Recordkeeping/monitoring event 0 0 0 0.25 12 

Technical review of results/monitoring event 0.5 0 0 0 42 

Training/training event (annual) 2 0 0 6 450 

Reporting/reporting event 2 0.2 0.4 0 205 

Example costs for quarterly in-house El Paso monitoring with semiannual reporting for single 

heat exchange system 

First year costs [QA plan + stripping column+ FID analyzer + 4×(in-house 

sampling+recording+tech review)+ 2×reporting + training] 18,545 

Subsequent year costs [4×(sampling+recording+review)+2×reporting+training] 1,650 

Average annualized costs [CRF2×(QA plan+column+analyzer) + subsequent year costs] 5,770 

1

 Sampling of 4 or more heat exchange systems is not expected to be completed within 1 day, so additional lodging 

expenses would be incurred, which are not included in the model. Purchasing an in-house system is comparable 

to contract sampling and is the assumed option when 4 locations or more are required to be monitored. 2

 CRF = capital recovery factor = 0.2439 based on 5 year life and 7 percent annual interest. 

Like the surrogate and water sampling monitoring approach, a QA plan will need to be 

developed for modified El Paso monitoring. The costs of developing the QA plan for using the 

modified El Paso method are expected to be similar to the costs of developing a QA plan for 

water sampling; the costs are “one-time” per facility, but are expected have a useful life of 

5 years when annualizing these costs. Similarly, if a stripping column is purchased, it is assumed 

that one system will be purchased for the facility and the equipment is expected to have a useful 

life of 5 years. While costs are provided separately for the FID analyzer (because some facilities 

have available FID analyzers), all stripping columns are assumed to be purchased with a new 

FID analyzer. It is estimated to take 3 hours per sampling event to set-up, run, then clean the 

stripping column to prepare it for re-use. Additionally, annual training is assumed to be needed 

to properly implement this monitoring method in-house; these costs are per facility rather than 

per heat exchange system. 

The modified El Paso method can be set up to run continuously for continuous monitoring of the 

heat exchange system. For this option, the equipment costs for the stripping column and FID 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

14 

analyzer would be incurred per heat exchange system rather than per facility. A shelter would be 

needed to house the stripping column system for a continuous application; the costs of such a 

shelter were estimated to be $10,000 per heat exchange system. Daily checks of the continuous 

monitoring system would also be needed to ensure the system is operating correctly; 0.5 operator 

hours per day were estimated for these daily checks. 

Annualized Costs of Alternative Monitoring Programs 

The total annualized costs of water sampling and modified El Paso monitoring programs at 

different monitoring frequencies were estimated based on the costs presented in Tables 3 and 4. 

As the cost to perform triplicate inlet-outlet TOC sampling is essentially identical to the cost of 

performing a single speciated organic analysis, only the cost for a water sampling program using 

a single sample for speciated organic analysis per sampling event are presented here. These 

same costs apply for the TOC sampling approach. For modified El Paso monitoring, it is 

assumed the facility would elect to purchase a stripping column and FID analyzer and perform 

in-house monitoring when the total annualized costs for in-house monitoring was less than the 

costs for contracted services. For the annual monitoring frequency option, annual reporting was 

assumed. For all other monitoring frequencies, semi-annual reporting was assumed to be 

required. Table 5 presents the costs of key options assuming there is only one heat exchange 

system present at the facility. Table 6 presents similar costs per monitored heat exchange 

system when 2 monitored heat exchangers are present at the facility. 

Table 5. Summary of Monitoring Costs as a Function of Monitoring Frequencies with One 

Monitored Heat Exchange System at the Facility 

Monitoring Method 

Capital 

and 1x 

Costs 

Annualized 

Capital 

Cost 

Annual 

Operating 

Costs 

Total 

Annualized 

Costs 

Sample 

Events 

per 

Year 

 Water sampling $ 3,045 $ 743 $ 604 $ 1,347 1 

 El Paso - contracted out $ 3,045 $ 743 $ 947 $ 1,690 1 

 El Paso - buying system $ 16,895 $ 4,120 $ 854 $ 4,974 1 

 Water sampling $ 3,045 $ 743 $ 2,007 $ 2,750 4 

 El Paso - contracted out $ 3,045 $ 743 $ 3,316 $ 4,059 4 

 El Paso - buying system $ 16,895 $ 4,120 $ 1,648 $ 5,769 4 

 Water sampling $ 3,045 $ 743 $ 5,202 $ 5,944 12 

 El Paso - contracted out $ 3,045 $ 743 $ 9,089 $ 9,831 12 

 El Paso - buying system $ 16,895 $ 4,120 $ 3,221 $ 7,341 12 

 Water sampling $ 3,045 $ 743 $ 21,174 $ 21,917 52 

 El Paso - contracted out $ 3,045 $ 743 $ 37,949 $ 38,691 52 

 El Paso - buying system $ 16,895 $ 4,120 $ 11,084 $ 15,204 52 

 El Paso - continuous $ 26,895 $ 6,559 $ 9,569 $ 16,129 8760 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

15 

Table 6. Summary of Monitoring Costs per Heat Exchange System as a Function of 

Monitoring Frequencies when Two Monitored Heat Exchange System are Present at the 

Facility 

Monitoring Method 

Capital and 

1x Costs 

Annualized 

Capital 

Cost 

Annual 

Operating 

Costs 

Total 

Annualized 

Costs 

Sample 

Events 

per 

Year 

 Water sampling $ 1,522 $ 371 $ 604 $ 975 1 

 El Paso - contracted out $ 1,522 $ 371 $ 705 $ 1,076 1 

 El Paso - buying system $ 8,447 $ 2,060 $ 628 $ 2,688 1 

 Water sampling $ 1,522 $ 371 $ 2,007 $ 2,378 4 

 El Paso - contracted out $ 1,522 $ 371 $ 2,346 $ 2,718 4 

 El Paso - buying system $ 8,447 $ 2,060 $ 1,422 $ 3,482 4 

 Water sampling $ 1,522 $ 371 $ 5,202 $ 5,573 12 

 El Paso - contracted out $ 1,522 $ 371 $ 6,179 $ 6,550 12 

 El Paso - buying system $ 8,447 $ 2,060 $ 2,995 $ 5,055 12 

 Water sampling $ 1,522 $ 371 $ 21,174 $ 21,546 52 

 El Paso - contracted out $ 1,522 $ 371 $ 25,339 $ 25,710 52 

 El Paso - buying system $ 8,447 $ 2,060 $ 10,857 $ 12,918 52 

 El Paso - continuous $ 25,372 $ 6,188 $ 9,343 $ 15,531 8760 

Similar cost tables to Tables 5 and 6 can be developed for facilities with three or more monitored 

heat exchange systems. Note that the monitoring cost per monitored heat exchange system 

decreases as the number of monitored heat exchange systems at the facility increases. Also note 

that in-house modified El Paso monitoring becomes the most economical alternative as the 

monitoring frequency increases to monthly. When there are three or more monitored heat 

exchange systems present at the facility, the cost of quarterly in-house modified El Paso 

monitoring is comparable to the cost of quarterly water sampling or contracted El Paso 

monitoring services. 

7. Costs of Implementing Repairs

The cost of implementing repairs includes the cost of pinpointing the precise heat exchanger that 

is leaking and repairing or isolating the leak. A detailed chemical analysis of the cooling water 

(or the purge gas when using the modified El Paso method) can be used to pinpoint the leak 

when different processes may be serviced by the same heat exchange system. Although this may 

not always be needed (e.g., if only one process is serviced by the heat exchange system), a flat 

analytical cost of $400 was assumed to be incurred each time a leak was detected. 

Most of the repairs are expected to be performed by plugging a specific heat exchanger tube. No 

attempt was made to develop costs of replacing the heat exchanger. It is assumed that a heat 

exchanger that is leaking to the extent that it needs to be replaced is effectively at the end of its 

useful life, so the cost of replacing the heat exchanger is an operational cost that would be 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

16 

incurred by the facility as a result of routine maintenance and equipment replacement and it is 

not attributable to the work practice standard. However, all other corrective actions taken by the 

facility to repair or isolate the leak are included in the costs of implementing repairs. Table 7

presents the costs estimated for the average leak requiring repair. 

Table 7. Summary Costs Associated with Leak Repair 

Activity/Requirement 

Number of labor hours by labor class 

per year for activity/requirement Total Cost 

Operator Maintenance ($) 

Labor for finding and repairing leak 20 40 2,809 

“Fingerprint” speciated sample analysis 400 

Material costs for repair 

(assumed to equal costs for labor) 2,809 

Total Repair Costs (per event) 6,018 

8. Impact Estimates for Heat Exchange Systems

Impact Model for Heat Exchange Systems 

The emission reductions achieved by a monitoring and repair program will depend on the 

monitoring frequency (how quickly a leak is identified), the size threshold of the leaks that must 

be repaired, and the water usage rate (for once-through systems) or recirculation rate (for closedloop systems). To evaluate different monitoring and repair program requirements, a spreadsheet 

impact model was developed to estimate the cost and emission reductions achieved from the 

implementation of a monitoring and repair program. The impact model assesses the cost and 

emission reductions for four different sizes of heat exchange systems based on the water use or 

recirculation rates as follows: 5,000 gallons per minute (gpm); 15,000 gpm; 40,000 gpm; and 

110,000 gpm. 

An important, but uncertain, factor that affects the baseline emission estimates (and therefore the 

potential emission reductions that can be achieved) is the distribution of heat exchange system 

leaks prior to the implementation of the monitoring and repair program. For each model heat 

exchanger, six different model leak concentrations were used to assess the impacts of a given 

monitoring and repair program as presented in Table 8. Except for the lowest model leak, each 

model leak interval was designed to cover a factor of 5 difference in concentration ranges. Each 

of these leak concentration was assigned an initial leak frequency, which is also provided in 

Table 8. From these initial assumptions, the baseline emissions for each model heat exchanger 

can be calculated. 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

17 

Table 8. Model Leak Concentration Values and Initial Leak Distribution 

Description of Representative Leak Interval 

Model Leak 

Concentration in 

Cooling Water (ppbw) 

Initial Leak 

Frequency 

Distribution 

No detectable leaks (0 to 5 ppbw) 1 0.45 

 Leaks from >5 to 25 ppbw 10 0.25 

 Leaks from >25 to 125 ppbw 50 0.15 

 Leaks from >125 to 600 ppbw 250 0.10 

 Leaks from >625 to 3,000 ppbw 1,200 0.04 

 Leaks greater than 3,000 ppbw 6,000 0.01 

Implementation of a leak monitoring and repair program is expected to alter the distribution of 

leaks in subsequent years. This pattern has been observed in the implementation of leak 

detection and repair (LDAR) programs for equipment leaks (Parrish et al., 2007). The leak 

frequency after implementation of the monitoring and repair program was estimated from the 

initial leak frequency distribution, the leak threshold for the monitoring program, and a “leak 

reduction factor.” The original frequency of leaks larger than the leak repair threshold is 

multiplied by this leak reduction factor to calculate the subsequent leak frequency in Year 2 and 

later years. For example, using a leak reduction factor of 0.10 and an initial leak frequency of 

0.04 (i.e., for 1,200 ppbw model leak concentration), the subsequent leak frequency would be 

0.004 (0.1×0.04). If a leak reduction factor of 0.3 is used, then the subsequent leak frequency 

would be 0.012 (0.3×0.04). The cumulative leak frequency distribution must add up to 1, so the 

leak frequency of leaks less than the leak repair threshold must be increased when the frequency 

of leaks greater than the leak repair threshold is reduced. It was assumed that the relative 

distribution of leaks less than the leak repair threshold remained the same as in the initial leak 

frequency distribution, but the magnitude of each leak frequency less than the repair threshold 

was scaled-up so that the sum of all leak frequencies (including those above the repair threshold) 

equals 1. Note that the subsequent leak frequency is applied per annual period and not per 

monitoring period. For example, a subsequent leak frequency of 0.012 for a model leak 

concentration would imply that 1.2 percent of heat exchange systems would develop a leak 

represented by that model leak concentration at some point during the year. Thus, the 

subsequent year (annual) leak frequency distribution is independent of the monitoring frequency, 

and only varies based on the leak threshold. 

The sensitivity of the impact estimates on the leak reduction factor selected was evaluated using 

leak reduction factors of 0.10 and 0.30 (see Annex A – Sensitivity Analysis). The lower (0.10) 

leak reduction factor resulted in only a 5 percent increase in the projected emissions reductions; 

however, the lower (0.10) leak reduction factor also resulted in lower implementation costs 

(because fewer repairs are required in subsequent years and more recovery credits are earned). 

Therefore, while the emission reductions estimated by the impacts model do not appear to be 

highly sensitive to this parameter, this parameter can be significant when evaluating the overall 

cost-effectiveness of a given monitoring option. A leak reduction factor of 0.3 is recommended 

for most analyses, and should provide a relatively conservative estimate of the emission 

reductions and costs associated with a monitoring and repair option. 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

18 

Although each model concentration was envisioned to represent a range of concentrations, the 

model logic only evaluates the actual value of the model leak concentration with the repair 

threshold of the monitoring program. Therefore, the 50 ppbw model leak concentration may 

include a 100 ppbw leak concentration based on the representative concentration range (from 25 

ppbw to 125 ppbw as shown in Table 8), but since 50 ppbw is less than the 100 ppbw leak repair 

threshold, the 50 ppbw model leak would not trigger a required repair based on the logic used in 

the impact model. A repair of the model leak occurs when that model leak concentration equals 

or exceeds the repair threshold. 

Although the monitoring frequency does not impact the annual leak frequency distribution, it 

does determine how quickly a leak will be discovered. After the implementation of the 

monitoring and repair program, a new leak is assumed to exist for half the monitoring frequency 

plus the time it takes to effect repair. For most leaks, repairs are completed 45 days after the leak 

monitoring event that identified the leak (the maximum time period allowed for leak repair when 

criteria for delay of repair are not met). For repairs that can be delayed, repairs are assumed to 

be completed 120 days after the leak monitoring event that identified the leak. While some 

repairs may be delayed for more than 120 days, this value represents the maximum delay period 

for repairs delayed due constraints on the availability of parts, equipment, or personnel. The 

exact proportion of repairs that will be delayed is difficult to assess. Model analyses were 

performed at delay of repair factors of 20 and 50 percent (i.e., 20 percent or 50 percent of all 

leaks below the delay of repair threshold were delayed; see Annex A – Sensitivity Analysis). 

Since all leaks are eventually repaired, the repair costs are not affected by the number of leaks 

for which repair is delayed. The emissions reductions dropped by only 1 percent when using a 

50 percent delay of repair factor. While this also causes a 1 percent change in the recovery 

credits, the overall model is not very sensitive to this parameter. A delay of repair factor of 0.5 

(50 percent) is recommended for most heat exchange system model analyses. 

The monitoring costs as presented in Section 6 apply to each heat exchange system regardless of 

the model leak concentration or assumed leak frequency. As noted in Section 6, the monitoring 

cost per heat exchange system of implementing a monitoring program becomes less when more 

than one heat exchange system is present at the facility. Most of the costs presented in this 

section are based on the costs determined for a single heat exchange system at the facility; costs 

per heat exchanger would be lower if multiple heat exchange systems are present at a typical 

facility. For heat exchangers with model leak concentrations exceeding the repair threshold, the 

repair costs (presented previously in Table 7) are also added to the monitoring costs to get a total 

program cost for that model heat exchange system/leak concentration combination. The impacts 

of all model leak concentrations for a given model heat exchange system are weighted by their 

distribution frequency to determine an average cost per model heat exchange system for the 

monitoring and repair program. 

Process fluid that leaks into the cooling water is product lost from the industrial process. 

Repairing the leak results in a net product recovery credit because product not lost as a result of a 

repaired leak can be sold; therefore, the monitoring costs are offset, to some extent, by the 

increased product sales. The product recovery credit is a function of the value of the process 

fluid. For this analysis, a product recovery credit of $500 per ton of organic pollutant emissions 

reduced was used to account for the recovery of lost product fluid when the repair is fixed. For 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

19 

most chemical applications, it is expected that the recovery credit will be approximately in this 

range. For example, organics recovered in a petroleum refinery are expected to be 

approximately $1.75/gallon, based on average crude and gasoline spot prices (based on 

September 7, 2007 OGJ crack spread spot prices of $74.96/bbl ($1.78/gal) for brent crude and 

$87.04/bbl ($2.08/gal) for product value per barrel; reported in Oil and Gas Journal, September 

17, 2007, p. 90). Assuming an average petroleum refinery process stream specific gravity of 

0.75, the recovery credit is $560 per ton organic emissions reduced. 

Impact Model Results for Alternative Monitoring and Repair Programs 

It is anticipated that the primary variables of a monitoring and repair program would be the 

monitoring frequency and the leak repair threshold. While some monitoring methods may not be 

capable of identifying leaks at a certain leak threshold, any monitoring method can be used in the 

program if the method can reliably identify leaks at the repair threshold. As the cost of water 

sampling is similar to the cost of modified El Paso monitoring (using the lower of contracted or 

in-house monitoring), the model evaluations developed for this section assumed that modified El 

Paso monitoring would be used. This assumption is not intended to suggest that modified El 

Paso monitoring is preferred over water sampling; this assumption is used to provide a common 

data set with which to evaluate the affects of monitoring frequency and repair thresholds. For 

each model heat exchanger, program costs were developed for an array of monitoring 

frequencies ranging from annual to continuous for four different leak thresholds. Table 9 

summarizes the parameters used in the analysis. 

Table 9. Model Input Parameters used to Assess Relative Importance of Leak Threshold 

Concentrations and Monitoring Frequency 

Model Input Parameter Value and Units 

Number of heat exchange systems at the facility 1 

Monitoring frequency Varies, options are: annually; quarterly; monthly; 

weekly; and continuously (hourly) 

Leak repair threshold /delay of repair threshold Varies, option combinations are: 1,000/5,000 ppbw; 

80/800 ppbw; 40/800 ppbw; and 10/800 ppbw 

Leak reduction factor 0.3 

Repair time for normal leak events 45 days 

Repair time for delayed repairs 120 days 

Fraction of detected leaks less than the delay of 

repair threshold that are delayed 

0.50 

Organic recovery credit $500/ton 

Figures 2, 3, 4, and 5 provide the results of the model impacts for 5,000 gallon per minute 

(gpm), 15,000 gpm, 40,000 gpm, and 110,000 gpm model heat exchange systems, respectively. 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

20 

$‐

$2,000

$4,000

$6,000

$8,000

$10,000

$12,000

$14,000

$16,000

$18,000

‐ 0.50 1.00 1.50 2.00

Emission Reductions (tpy per model HE system)

5,000 GPM HE System

Annual

Quarterly

Monthly

Weekly

Continuous

Figure 2. Impact results for 5,000 gpm model heat exchange (HE) system using the model 

parameters in Table 9. 

$‐

$2,000

$4,000

$6,000

$8,000

$10,000

$12,000

$14,000

$16,000

$18,000

‐ 1.00 2.00 3.00 4.00 5.00

Emission Reductions (tpy per model HE system)

15,000 GPM HE System

Annual

Quarterly

Monthly

Weekly

Continuous

Figure 3. Impact results for 15,000 gpm model heat exchange (HE) system using the model 

parameters in Table 9. 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

21 

$(4,000)

$(2,000)

$‐

$2,000

$4,000

$6,000

$8,000

$10,000

$12,000

$14,000

‐ 2.00 4.00 6.00 8.00 10.00 12.00 14.00

Emission Reductions (tpy per model HE system)

40,000 GPM HE System

Annual

Quarterly

Monthly

Weekly

Continuous

Figure 4. Impact results for 40,000 gpm model heat exchange (HE) system using the model 

parameters in Table 9. 

$(12,000)

$(10,000)

$(8,000)

$(6,000)

$(4,000)

$(2,000)

$‐

$2,000

$4,000

$6,000

‐ 5.00 10.00 15.00 20.00 25.00 30.00 35.00

Emission Reductions (tpy per model HE system)

110,000 GPM HE System

Annual

Quarterly

Monthly

Weekly

Continuous

Figure 5. Impact results for 110,000 gpm model heat exchange (HE) system using the 

model parameters in Table 9. 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

22 

The most cost-effective monitoring programs are represented by those at the bottom and right 

side of the graphs in Figures 1 through 4. Options in the middle of the graphs are inefficient 

because they have higher costs but achieve less emission reductions than other monitoring 

programs. It is evident from the graphs presented in Figures 1 through 4 that lowering the leak 

definition (moving to the right for programs marked by the same-colored symbol) is generally 

more cost-efficient than increasing the monitoring frequency (shifts across different-colored 

symbols). Based on the model inputs in Table 9, quarterly sampling with a leak definition of 

40 ppbw in the water (or 3.1 ppmv in the El Paso stripping column air steam) provides 

essentially identical emission reductions (within the uncertainty of the model) at lower cost than 

monthly sampling with a leak definition of 80 ppbw in the water (or 6.2 ppmv in stripping air). 

Although even lower leak definition repair thresholds may prove cost-effective for certain 

applications, it is important that the leak threshold be a factor of 2 or 3 times greater than the 

analytical detection limit. Otherwise, it could be difficult or impossible to conclude that a leak 

does not exist because the repair threshold is at or below the analytical detection limit. For 

typical FID gas analyzers, detection limits of 1 ppmv in the air are typical. As such, a stripping 

air concentration of 3.1 ppmv organics (as methane), which corresponds with 40 ppbw organics 

as methane in the cooling water, would be considered the lowest repair threshold level that can 

be routinely assessed using the modified El Paso method. The 40 ppbw also appears to be a 

reasonable minimum leak definition repair threshold based on typical speciated organic 

analytical test methods. For select process streams or pollutants, it may be possible to achieve 

lower detection limits on a routine basis. In this case, a 10 ppbw or lower repair threshold should 

be considered (in addition to a 40 ppbw repair threshold) as one of the control options. 

It is also clear from Figures 1 through 4 that a given monitoring and repair program option is 

more cost-effective for larger heat exchange systems. For example, the 40,000 gpm model heat 

exchanger shows a net savings for annual monitoring options and a small savings or break even 

costs for the quarterly monitoring options, while the 110,000 gpm model heat exchanger shows a 

net savings for annual, quarterly, and monthly monitoring options. Therefore, it may be 

appropriate to have different monitoring frequencies for different-sized heat exchange systems. 

The size-range selected for the different thresholds will depend predominately on the typical 

number of heat exchange systems present at a facility within a given source category and the 

recovery credit (value of the product stream). 

Based on Figures 1 through 4, and assuming 40 ppbw is the minimal quantifiable leak 

concentration, “optimal” monitoring options appear to include: annual at 80/800 ppbw; annual 

at 40/800 ppbw; quarterly at 40/800 ppbw; and monthly at 40/800 ppbw. The weekly or 

continuous monitoring frequency options greatly increase the cost of the monitoring program 

without significantly reducing the emissions compared to monthly monitoring for the model heat 

exchange systems evaluated in this analysis. For the single heat exchange system scenario 

(upper-end cost scenario), Table 10 provides detailed cost information for these “optimal” 

monitoring options. 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

23 

Table 10. Detailed Results from Option Cost-Effectiveness Evaluation1

Leak 

Repair 

/Delay 

Threshold 

(ppbw) 

Monitoring 

Frequency 

Model HE 

System 

Size 

(gpm) 

Capital 

and 1x 

Costs 

($) 

Annualized 

Cost w/o 

Recovery 

Credits 

($/yr) 

Annualized 

Cost w/ 

recovery 

credits 

($/yr) 

VOC 

Emission 

Reduction 

(tons/yr) 

CostEffect 

($/tons) 

Incremental 

Cost-Effect 

($/tons) 

5,000 gpm model heat exchange (HE) system 

80/800 annual 5,000 $3,045 $2,087 $1,569 1.03 $1,517 

40/800 annual 5,000 $3,045 $2,484 $1,937 1.09 $1,770 $6,172 

40/800 quarterly 5,000 $3,045 $4,853 $4,179 1.35 $3,099 $8,820 

40/800 monthly 5,000 $16,895 $8,136 $7,433 1.41 $5,290 $57,599 

15,000 gpm model heat exchange (HE) system 

80/800 annual 15,000 $3,045 $2,087 $535 3.10 $172 

40/800 annual 15,000 $3,045 $2,484 $843 3.28 $257 $1,724 

40/800 quarterly 15,000 $3,045 $4,853 $2,831 4.05 $700 $2,607 

40/800 monthly 15,000 $16,895 $8,136 $6,028 4.22 $1,430 $18,866 

 40,000 gpm model heat exchange (HE) system 

80/800 annual 40,000 $3,045 $2,087 $(2,052) 8.28 $(248) 

40/800 annual 40,000 $3,045 $2,484 $(1,893) 8.75 $(216) $334 

40/800 quarterly 40,000 $3,045 $4,853 $(541) 10.79 $(50) $665 

40/800 monthly 40,000 $16,895 $8,136 $2,515 11.24 $224 $6,762 

110,000 gpm model heat exchange (HE) system 

80/800 annual 110,000 $3,045 $2,087 $ (9,296) 22.77 $(408) 

40/800 annual 110,000 $3,045 $2,484 $ (9,554) 24.08 $(397) $ (197) 

40/800 quarterly 110,000 $3,045 $4,853 $ (9,981) 29.67 $(336) $(76) 

40/800 monthly 110,000 $16,895 $8,136 $ (7,320) 30.91 $(237) $2,146 

1

 Impacts based on single heat exchange system and model input parameters summarized in Table 9. 

Considerations of Very Small Heat Exchange Systems (“Sample Coolers”) 

As seen in Figures 1 through 4 and Table 10, the larger the heat exchange system, the more costeffective it is to monitor and repair leaks. Conversely, as the cooling water flow rates become 

smaller, it becomes less cost-effective to monitor and repair leaks. Logic dictates that, at some 

flow level, the potential emission reductions achieved do not justify the costs of the monitoring 

program. While this lower flow limit is unlikely to apply to conventional industrial heat 

exchange systems, small water cooling systems used to collect process samples or used in 

conjunction with monitoring equipment (“sample coolers”) are expected to meet the definition of 

a once-through heat exchange system, and these may have very low flow rates. The impacts 

model was used to evaluate a potential applicability flow limit for a given heat exchange system 

monitoring program. Model heat exchange system flow rates of 1, 10, 100, and 1,000 gpm were 

assessed in this analysis. The monitoring costs developed for the impacts model are directly 

applicable to any heat exchange system; the repair costs developed for the impacts model are 

potentially different. For these sample coolers, direct replacement of the leaking cooler is the 

expected repair scenario. It was assumed that the repair costs for a leaking heat exchanger 

provided a reasonable estimate of the sample cooler replacement cost. As new equipment is 

expected to have a lower likelihood of leaking, a leak reduction factor of 0.1 was used for this 

analysis. The baseline leak distribution was also adjusted upward because these “sample 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

24 

coolers” are not expected to be monitored for biologicals (or other potential leak indicators) as 

regularly as conventional industrial heat exchange systems are monitored. The high model leak 

concentrations (model leaks of 1.2 and 6 ppmw) were each assumed to represent 10 percent of 

the sample coolers. The moderate model leak concentrations (model leaks of 250 and 50 ppbw) 

were each assumed to represent 15 percent of the sample coolers. Even with a relatively high 

frequency of leaks, the cost-effectiveness of annual or quarterly monitoring generally exceeded 

$10,000 per ton VOC reduced for heat exchange systems with cooling water flow rates at or 

under 100 gpm. While there are uncertainties associated with applying the heat exchange 

impacts model for “sample coolers,” this analysis suggests that routine heat exchange monitoring 

programs should not apply to very small heat exchange systems or “sample coolers.” 

Furthermore, the analysis suggests that a reasonable flow rate threshold for excluding “sample 

coolers” would be a heat exchange system with cooling water flow rate of 100 gpm or less. 

9. Application of Impact Model for a Specific Source Category 

This section provides an example of how to use the heat exchange system impacts model to 

determine impacts for a specific source category. The heat exchange system impacts model is 

provided in a Microsoft ExcelTM workbook. This section contains numerous references to 

specific sheets or cells within the workbook; it may be useful to have the workbook (or “impacts 

model”) open for easy reference as you read this section. 

Step 1. Revise the labor rates for the specific industry, if desired. The heat exchange system 

impacts model includes labor rates (in May 2009 dollars) for general manufacturing industry 

sector (2-digit NAICS code 31 to 33) in the “labor rates” sheet within the impacts model. 

Industry-specific labor rates are available from the Bureau of Labor Statistics (BLS) (U.S. DOL, 

2010) for specific NAICS codes. For the NAICS code associated with the specific source 

category, the mean hourly labor rates for the specified SOC Code Numbers specified in the 

model can be found and entered into the spreadsheet. The new values should be entered in 

shaded cells (Cells I3 to I7 of sheet “labor rates”). If desired, the fringe benefits loading factor 

and overhead and profit rate can be adjusted in the corresponding cells in columns C and D. 

Step 2. Determine the number of heat exchange systems per facility for which to estimate 

facility costs (per heat exchange system). The monitoring costs are calculated in the “Cost by 

monitoring method” sheet. As discussed previously, the cost per heat exchange system is a 

function of the number of heat exchange systems that will need to be monitored at a specific 

facility. The number of heat exchange systems should be entered in the yellow-highlighted 

Cell I9 in the “Cost by monitoring method” sheet. There are five monitoring frequencies 

evaluated in the macro: four periodic frequencies specified in the green highlighted cells (Cells 

R9 to R12) in the “Cost by monitoring method” sheet and a continuous monitoring option. If 

desired, the periodic monitoring frequencies in Cells R9 to R12 can be adjusted to evaluate 

different monitoring frequencies than those pre-loaded in the spreadsheet. In general, no other 

edits should be made to this sheet.1 Run the macro provided by pushing the “Generate 

Control_Options Costs” button to automatically calculate an array of costs for different 

monitoring frequencies and store the results for further use in the “Control_Options” sheet. 

 

1 If additional edits to the costing assumptions are deemed necessary (i.e., hours required for training, reporting, or 

other elements), these should be made prior to running the “Generate Control_Option Costs” macro. 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

25 

Step 3 (Optional). Review the table starting at Cell B9 in the “Control_Options” sheet. After 

running the “Generate Control_Options Costs” macro, costs for the various control options 

(monitoring frequencies) will be generated and stored in this table. The “Control_Options” sheet 

also houses the repair cost estimates. The top 30 rows of the “Control_Options” sheet are used 

in the “Cost by HEsize” sheet for projecting the impacts per model heat exchange system. If you 

choose to do so, you can use subsequent rows in the “Control_Options” sheet to store costs for 

previously evaluated sets of runs. One advantage of using the general manufacturing labor rates 

is that several cost tables are already developed and stored in this sheet; however, with the 

macro, these costs can be easily and quickly updated, so most users will find this step 

unnecessary. 

Step 4. The next step in the process is to evaluate the specific options in the “Cost by HEsize” 

sheet. There is a drop down selection for the monitoring method and frequency in Row 10, and 

yellow-highlighted input selections for the leak definition (in terms of water concentration), 

delay of leak threshold concentration, leak reduction factor (“Reduct_Factor”), fraction of leaks 

that below the delay-of-repair threshold that are delayed (“Fr_Delayed”), and the VOC credit. 

The results of the model analysis are summarized on a per heat exchange system level for four 

different model heat exchange system water circulation sizes: 5,000 gpm; 15,000 gpm; 40,000 

gpm; and 110,000 gpm. The macro “Generate Impact Results Summary” allows the evaluation 

of using modified El Paso monitoring at all frequencies included in the current 

“Control_Options” table. These results will be in the placed in the “Results_temp” sheet. The 

macro will automatically highlight the results range which can then be copied into one of the 

three “Results_#” sheets (where # = 1, 2, or 3). The “Results_#” sheets are used to save the 

specific model run results for further analysis. The selected range from the “Results_temp” sheet 

would be copied to Cell B1, I1, P1, or W1 in one of the “Results_#” sheets as appropriate. 

Step 5. Repeat Step 4 as needed for different model run evaluations for a given model plant (i.e., 

a given number of heat exchange systems at a facility). Each “Results_#” sheet is designed to 

hold results for 4 different model runs. The model runs in a given sheet can be used to evaluate 

the effect of different leak definitions or the impact of different model assumptions (e.g., 

different leak reduction factors or differences in fraction of leaks for which delay of repair is 

used). Graphs are provided to illustrate the results of the different model runs for each of the 

four model heat exchange systems (see Rows 77-98). It is anticipated that the results for any 

given sheet will only alter the yellow highlighted in Cells D11:G13 of the “Cost by HEsize” 

sheet. The results output by the macro will include these inputs (along with the number of heat 

exchange systems per facility) for documentation of the run results. The results summary does 

not store the initial leak distribution (i.e., the yellow highlighted in Cells M11:M16 of the “Cost 

by HEsize” sheet). If the initial leak distribution is varied across these runs, the leak distribution 

should also be saved to document these inputs as well. 

Step 6. Repeat Steps 2 through 5 as needed for different model plants (i.e., to develop impacts 

for different numbers of heat exchange systems per facility). It is likely that the impacts for a 

specific industry may entail developing costs for a variety of model plant sizes or complexities, 

which may require costs to be evaluated for several different numbers of heat exchange systems. 

For example, evaluation of three different model facilities may be desired for different facility 

complexities: a simple model facility with one heat exchange system to be monitored; a 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

26 

moderately complex facility with two heat exchange systems to be monitored; a complex facility 

with four heat exchange systems to be monitored. Steps 2 through 5 would have to be repeated 

of each of these model plants. The three “Results_#” sheets were originally designed to house 

impact results for three different model plants, with each sheet representing the results for a 

given model plant. However, you could alternatively use one results sheet to house the results 

for a specific set of model inputs (leak definition and repair threshold), and use the four columns 

to house the results for different model plants. If this second option is used, the graphs included 

in the “Results_#” sheets at Row 80 will be meaningless, but it may be easier to quickly copy the 

selected results to the “NW_Impacts” sheet for calculation of nationwide impacts. 

Step 7. Assign a nationwide number of heat exchange systems that can be represented by each 

model heat exchange system / model plant combination. The costs and emission reductions 

presented are per heat exchange system. By multiplying the costs and emission reductions by the 

number of heat exchange systems, nationwide impacts are developed for the source category. 

The “NW_Impacts” sheet provides a means to calculate the number of heat exchange systems 

represented by each model heat exchange system / model plant combination for up to four model 

plants. The inputs needed for these calculations are the total number of heat exchange systems in 

the source category and the relative distribution of heat exchange systems by size and model 

plant. Note: the number of the number of heat exchange systems used for each model plant 

combination is rounded to whole numbers for the impact calculations, so there may be a slight 

difference in the number of heat exchangers calculated in Cell F32 and the total number of heat 

exchange system input in Cell G5 due to rounding. 

Step 8. Identify the specific control options for evaluation to calculate the nationwide impacts 

and enter those results in the “NW_Impacts” sheet (see Cell J32). As noted previously, if a 

single sheet contains output for the different model plants, it may expedite the manual process of 

transferring selected results to the “NW_Impacts” sheet (but the graphs in the “Results_#” sheets 

will be of little value). Once the impacts for the selected control options are entered (or copied) 

into the “NW_Impacts” sheet, the sheet will automatically calculate the nationwide impacts in 

the final results table. 

10. References

Boudreaux, W. 2010. E-mail with attachment from Wayne Boudreaux, EnRUD Resources, Inc., 

to Cindy Wang Hancy, RTI International. “CWT Estimate.” November 2, 2010. 

Corsi, R, et.al. 2004. Assessment of Selected Leak Detection, Sampling, Testing, Measurement 

and Monitoring Methods for Estimating Emissions of Highly Reactive Volatile Organic 

Compounds from Industrial Cooling Waters. University of Texas at Austin for TCEQ. 

September 2004. Docket Item No. EPA-HQ-OAR-2003-0146-0004. 

Lucas, B. 2008. Memorandum from B. Lucas, EPA/SPPD, to Project Docket File (EPA Docket 

No. EPA-HQ-OAR-2003-0146). Cooling Towers: Control Alternatives and Impact 

Estimates. October 30, 2008. 

Parrish, K., D. Randall, and J. Coburn. 2007. Memorandum from Kristin Parrish, David 

Randall, and Jeff Coburn, RTI International, to Karen Rackley, EPA/SPPD. Final Impacts 
Technical Memorandum – Technology Review for Heat Exchange Systems 

July 12, 2011 

27 

Analysis for Regulatory Options for Equipment Leaks of VOC in Petroleum Refineries. 

October 30, 2007. Docket Item No. EPA-HQ-OAR-2006-0699-0089. 

Texas Commission on Environmental Quality (TCEQ). 2003. Sampling Procedures Manual, 

Appendix P: Air Stripping Method (Modified El Paso Method) for Determination of Volatile 

Organic Compound Emissions from Water Sources. 

Suslow, Trevor V. 2004. Oxidation-Reduction Potential (ORP) for Water Disinfection 

Monitoring, Control, and Documentation. University of California, Davis; Division of 

Agriculture and Natural Resources; Publication 8149. ISBN 978-1-60107-319-8. 

U.S. Department of Labor (DOL), Bureau of Labor Statistics. 2010. Occupational Employment 

Statistics: May 2009 Employment and Wage Estimates. 

http://stats.bls.gov/oes/current/oessrci.htm; Last accessed in December 2010. 
Technology Review for Heat Exchange Systems 

Annex A – Sensitivity Analysis 

An impacts model was developed to estimate the emission reductions achieved and the costs 

incurred for different monitoring options for heat exchange system. The output of the model 

depends, to some extent, on some of the assumptions used in the model. This Annex presents the 

results of various impact model runs for a heat exchange system with a cooling water flow rate 

of 40,000 gallon per minute (gpm) for four different monitoring options: 

1. Quarterly monitoring with a leak definition of 80 parts per billion by weight (ppbw) 

strippable organics in the cooling water. 

2. Quarterly monitoring with a leak definition of 40 ppbw strippable organics. 

3. Monthly monitoring with a leak definition of 80 ppbw strippable organics. 

4. Monthly monitoring with a leak definition of 40 ppbw strippable organics. 

The model itself helps to account for different sized heat exchange systems, different number of 

heat exchange systems at a given facility that require monitoring, and different monitoring 

frequencies and different action thresholds. There are other underlying assumptions within the 

model that are generally fixed, and the purpose of this analysis is to assess the sensitivity of the 

model to these fixed assumptions. Table A-1 summarizes some of the basic default parameters 

for the impacts model. 

The time allowed for repair or for delayed repair is generally specified as part of the monitoring 

requirements, and these are, for the most part, limited by the time required to identify the specific 

tube or heat exchanger bundle that is leaking, order necessary parts (if needed), and isolate and 

repair the leak. Similarly, the organic recovery credit can generally be determined for a given 

source category based on the product value of the process fluid lost as a result of the leak. 

Consequently, this sensitivity analysis focuses on the “leak reduction factor” and on the fraction 

of leaks for which repair can be delayed. 

Table A-1. Heat Exchange System Impact Model Input Parameters 

Model Input Parameter Value and Units 

Leak reduction factor 0.3 

Repair time for normal leak events 45 days 

Repair time for delayed repairs 120 days 

Fraction of detected leaks less than the delay of repair 

threshold that are delayed 0.50 

Organic recovery credit $500/ton 
Technology Review for Heat Exchange Systems: Annex A – Sensitivity Analysis 

A-2 

Typically, when a facility implements a leak detection and repair program (e.g., for equipment 

leaks), the number of leaks above the repair threshold is reduced in subsequent monitoring 

events, which causes a shift in the leak distribution for subsequent monitoring events. A “leak 

reduction factor” is applied to the portion of the initial leak distribution for leaks above the repair 

threshold to account for this phenomenon. A leak reduction factor of 0.3 is suggested for use in 

the heat exchange impacts model based on engineering judgment; this would reduce the 

probability of a leak at levels above the leak repair threshold in subsequent years to 30 percent of 

the leaks in the baseline year. For the sensitivity analysis, the results of using this default leak 

reduction factor are compared to alternative leak reduction factors of 0.1 and 0.5 for the model 

heat exchange system and for different monitoring options. Table A-2 summarizes the results of 

this analysis in terms of emissions reductions and costs. 

The fraction of leaks for which delay can be repaired is another uncertain input parameter. For 

units that operate continuously with minimal downtime, the fraction of leaks that may be delayed 

may be higher than for batch systems or processes that run continuously but for shorter 

durations. The fraction of leaks that may be delayed may be dependent on the age of the process 

equipment as well. Older equipment may be more likely to need significant repair or 

replacement, whereas newer equipment may only need to plug a single tube in the heat 

exchanger. The suggested default value for the fraction of leaks that can be delayed is 0.5; for 

this sensitivity analysis, delay fractions of 0.2 and 0.8 were also investigated. Table A-3

summarizes the results of these impact model runs. 

Table A-2. Sensitivity Analysis for Leak Reduction Factor1

Leak 

Reduction 

Factor 

Capital and 

1x Costs ($) 

Annualized 

Cost w/o 

Recovery 

Credits ($/yr) 

Annualized 

Cost w/ 

recovery 

credits ($/yr) 

VOC 

Emission 

Reduction 

(tons/yr) 

CostEffectiveness 

($/ton) 

Quarterly Monitoring with a Leak Action Level of 80 ppbw 

0.1 $3,045 $4,312 $(1,027) 10.68 $(96)

0.3 $3,045 $4,456 $ (646) 10.20 $(63)

0.5 $3,045 $4,601 $(264) 9.73 $(27)

Quarterly Monitoring with a Leak Action Level of 40 ppbw 

0.1 $3,045 $4,565 $(1,089) 11.31 $(96)

0.3 $3,045 $4,853 $ (541) 10.79 $(50)

0.5 $3,045 $5,142 $7 10.27 $1 

Monthly Monitoring with a Leak Action Level of 80 ppbw 

0.1 $16,895 $7,594 $2,119 10.95 $194 

0.3 $16,895 $7,738 $2,423 10.63 $228 

0.5 $16,895 $7,883 $2,726 10.31 $264 

Monthly Monitoring with a Leak Action Level of 40 ppbw 

0.1 $16,895 $7,847 $2,049 11.59 $177 

0.3 $16,895 $8,136 $2,515 11.24 $224 

0.5 $16,895 $8,424 $2,981 10.89 $274 

1

 Impacts based on single 40,000 gpm heat exchange system with a delay of repair threshold of 800 ppbw. 
Technology Review for Heat Exchange Systems: Annex A – Sensitivity Analysis 

A-3 

Table A-3. Sensitivity Analysis for Fraction of Leak for Which Repair is Delayed1

Fraction 

Delayed 

Repair 

Capital and 

1x Costs ($) 

Annualized 

Cost w/o 

Recovery 

Credits ($/yr) 

Annualized 

Cost w/ 

recovery 

credits ($/yr) 

VOC 

Emission 

Reduction 

(tons/yr) 

CostEffectiveness 

($/ton) 

Quarterly Monitoring with a Leak Action Level of 80 ppbw 

0.2 $3,045 $4,456 $ (675) 10.26 $ (66)

0.5 $3,045 $4,456 $ (646) 10.20 $ (63)

0.8 $3,045 $4,456 $ (616) 10.14 $ (61)

Quarterly Monitoring with a Leak Action Level of 40 ppbw 

0.2 $3,045 $4,853 $ (580) 10.87 $ (53)

0.5 $3,045 $4,853 $ (541) 10.79 $ (50)

0.8 $3,045 $4,853 $ (502) 10.71 $ (47)

Monthly Monitoring with a Leak Action Level of 80 ppbw 

0.2 $ 16,895 $7,738 $2,393 10.69 $ 224 

0.5 $ 16,895 $7,738 $2,423 10.63 $ 228 

0.8 $ 16,895 $7,738 $2,452 10.57 $ 232 

Monthly Monitoring with a Leak Action Level of 40 ppbw 

0.2 $ 16,895 $8,136 $2,477 11.32 $ 219 

0.5 $ 16,895 $8,136 $2,515 11.24 $ 224 

0.8 $ 16,895 $8,136 $2,554 11.16 $ 229 

1

 Impacts based on single 40,000 gpm heat exchange system with a delay of repair threshold of 800 ppbw. 

Reviewing the results presented in Tables A-2 and A-3, a few factors are noteworthy. First, it is 

clear that the model is not very sensitive to the assumed fraction of leaks for which delay of 

repair is allowed. Using 0.5 as the base case for the “fraction of delayed repair,” altering the 

fraction of delayed repair causes less than a 0.1 percent change in the emission results. For 

example, for quarterly sampling at a leak action level of 40 ppbw, the change in emissions is 

0.08 tons/yr, or 0.08/10.79 = 0.7 percent. The lack of sensitivity to the fraction of delayed repair 

is due, in part, to the assumption in the impacts model that the delay will be for 120 days. This 

time period is based on a delay associated with ordering necessary equipment or scheduling 

specialists. Longer delays may be allowed for repairs that require a process shutdown, but these 

should be a limited number of cases, and they will also be limited to leaks that do not get 

significantly larger over time. Long delay of repairs are not likely because a leak is likely to get 

worse with time and trigger the delay of repair threshold, so that the repair can no longer be 

delayed. 

The model is more sensitive to the “leak reduction factor.” Using 0.3 as the base case for the 

leak reduction factor, altering the leak reduction factor causes a 3 to 5 percent change in the 

emission results, with the 5 percent change associated with the quarterly monitoring alternatives 

and the 3 percent change associated with the monthly monitoring alternatives. It is also 

interesting to note that these different degrees of sensitivity could impact what monitoring 

provisions achieve the greatest emission reduction. For most options considered, quarterly 

monitoring at a leak action level of 40 ppbw provides more emission reduction than monthly 
Technology Review for Heat Exchange Systems: Annex A – Sensitivity Analysis 

A-4 

monitoring at a leak action level of 80 ppbw; however, at a leak reduction factor of 0.5, monthly 

monitoring at a leak action level of 80 ppbw is projected to achieve slightly greater emissions 

reductions than quarterly monitoring at a leak action level of 40 ppbw. These results suggest that 

these two monitoring options achieve essentially equivalent emission reductions within the 

uncertainty of the analysis. The leak reduction factor also impacts the costs of the monitoring 

program (more than just the magnitude of the recovery credit), with higher costs (associated with 

more repairs) at higher leak reduction factors, so the cost-effectiveness of an overall monitoring 

option is much more significantly impacted by the selected leak reduction factor than the fraction 

of delayed repair. 

The total emission reductions achieved by a monitoring program will be very sensitive to the 

leak initial leak distribution, particularly the proportion of larger leaks. However, most decisions 

are made based on incremental differences between monitoring options rather than total 

reductions achieved by any given option. For the incremental costs between control options, the 

initial distribution is less important than how that distribution is affected by the monitoring 

program itself. Thus, it is anticipated that the leak reduction factor will be as important as (or 

more important than) the initial distribution when evaluating the incremental cost-effectiveness 

of an option, and it is this incremental assessment that is most important when selecting a 

monitoring option. 

Table A-4 provides some of the same data as Table A-2, but shows the incremental costeffectiveness for two similar options (in this case, quarterly monitoring at leak action levels of 

40 and 80 ppbw). The incremental emission reductions varied from 0.54 to 0.63 tons per year 

(tons/yr) and exhibited an uncertainty of approximately ± 8 percent. Altering the leak reduction 

factor also altered the incremental cost-effectiveness of these options by approximately 

± $300/ton. 

Table A-4. Effect of Leak Reduction Factor on Incremental Impacts1

Monitoring 

Frequency and 

Leak Action Level 

Capital and 

1x Costs ($) 

Annualized 

Cost w/o 

Recovery 

Credits ($/yr) 

Annualized 

Cost w/ 

recovery 

credits ($/yr) 

VOC 

Emission 

Reduction 

(tons/yr) 

CostEffectiveness 

($/ton) 

Leak Reduction Factor of 0.1 

Quarterly, 80 ppbw $3,045 $4,312 $(1,027) 10.68 $(96)

Quarterly, 40 ppbw $3,045 $4,565 $(1,089) 11.31 $(96)

Difference $0 $253 $(62) 0.63 $(98)

Leak Reduction Factor of 0.3 

Quarterly, 80 ppbw $3,045 $4,456 $ (646) 10.20 $(63)

Quarterly, 40 ppbw $3,045 $4,853 $ (541) 10.79 $(50)

Difference $0 $397 $105 0.59 $178 

Leak Reduction Factor of 0.5 

Quarterly, 80 ppbw $3,045 $4,601 $(264) 9.73 $(27)

Quarterly, 40 ppbw $3,045 $5,142 $7 10.27 $1 

Difference $0 $541 $271 0.54 $502 

1

 Impacts based on single 40,000 gpm heat exchange system with a delay of repair threshold of 800 ppbw.