Tetra Tech, Inc.

10306 Eaton Place, Suite 340

Fairfax, VA 22030

phone 703-385-6000

fax 703-385-6007

TO: Paul Shriner, EPA

FROM: Kelly Meadows

DATE: July 30, 2010

SUBJECT: Estimating the number

noise or plume abatement and 

EPA requested that Tetra Tech develop

that may need to be considered for increased 

facility rule due to noise or plume abatement

for installing cooling towers as a 

analysis and rationale for the estimated universe of affected facilities. 

concluded that about one in four

addressed by the proposed 316(b) 

these technical factors; EPA has 

account for additional technologies or other mitigation activities at these facilities

Approach

To comply with a potential requirement for flow reduction, s

choose to install cooling towers to

conditions or at certain locations, the installation of cooling towers can lead to non

aquatic impacts such as plumes or noise. Facilities located in densely populated areas or 

on small sites may also have di

towers. In the majority of cases, these technical issues do not ultimately affect the 

feasibility of constructing the cooling tower, but they do affect the cost. The analysis 

below reflects EPA’s assumptions in estimating the number of facilities that may

 

1

See chapter 8 of the Technical Development Document. Instead of estimating which model facilities 

would require increased costs, EPA applied a cost increase to all exiting facilities.

2

In fact, EPA’s costs reflect the assumption that all facilities subj

will install cooling towers.

MEMORANDUM

10306 Eaton Place, Suite 340

, EPA

Kelly Meadows and Christine Wong

g the number of potential facilities with increased costs due to 

noise or plume abatement and space constraints

Tetra Tech develop an analysis to estimate the universe of facilities 

need to be considered for increased costs of compliance with the 316(b)

noise or plume abatement requirements, as well as space constraints

cooling towers as a compliance response. This memo documents 

analysis and rationale for the estimated universe of affected facilities. Tetra Tech has 

concluded that about one in four (25 percent) of the overall universe of facilities 

roposed 316(b) existing facility rule may be affected by one or more of 

these technical factors; EPA has increased its estimate of compliance costs accordingly to 

account for additional technologies or other mitigation activities at these facilities

To comply with a potential requirement for flow reduction, some facilities are likely to 

choose to install cooling towers to comply with this requirement.2 Under certain 

conditions or at certain locations, the installation of cooling towers can lead to non

aquatic impacts such as plumes or noise. Facilities located in densely populated areas or 

on small sites may also have difficulty identifying sufficient space to construct the 

towers. In the majority of cases, these technical issues do not ultimately affect the 

feasibility of constructing the cooling tower, but they do affect the cost. The analysis 

umptions in estimating the number of facilities that may

 

See chapter 8 of the Technical Development Document. Instead of estimating which model facilities 

would require increased costs, EPA applied a cost increase to all exiting facilities.

In fact, EPA’s costs reflect the assumption that all facilities subject to the flow reduction requirements 

1

with increased costs due to 

estimate the universe of facilities 

316(b) existing 

requirements, as well as space constraints,

This memo documents the 

Tetra Tech has 

of the overall universe of facilities 

one or more of 

accordingly to 

account for additional technologies or other mitigation activities at these facilities.

1

ome facilities are likely to 

Under certain 

conditions or at certain locations, the installation of cooling towers can lead to nonaquatic impacts such as plumes or noise. Facilities located in densely populated areas or 

sufficient space to construct the 

towers. In the majority of cases, these technical issues do not ultimately affect the 

feasibility of constructing the cooling tower, but they do affect the cost. The analysis 

umptions in estimating the number of facilities that may

See chapter 8 of the Technical Development Document. Instead of estimating which model facilities 

ect to the flow reduction requirements 
2

encounter these difficulties and establishes an approach for increasing the cost estimates 

accordingly.

Natural draft or mechanical draft cooling towers can produce a plume. Plumes

(comprised largely of water vapor) can create problems with fogging and icing, which 

have been recorded to create dangerous conditions for local roads and for air and water 

navigation, as well as cause aesthetic impacts. To estimate the number of facilities that 

would likely be subject to plume abatement requirements, Tetra Tech used two indicators 

as a proxy for potential impacts: proximity to airports and proximity to major roads. 

Tetra Tech selected a 2-mile radius from airports and a 0.5-mile radius from major roads 

as the distance thresholds for facilities likely to require plume abatement. EPA had 

previously mapped the prevalence of cooling towers and their proximity to highways, 

navigable rivers and lakes, and railways, and defined those facilities that were within 

several hundred meters from those types of areas as being in “close proximity.”3 Tetra 

Tech selected a 2-mile radius from airports as a proximity threshold to include this earlier 

definition of “close proximity,” plus a generous safety margin for aviation safety. Tetra 

Tech selected the 0.5-mile radius from major roads as a proximity threshold to account 

for the distance required to disperse fog or ice-forming plumes, plus a generous safety 

margin.4

Noise from mechanical draft cooling towers is generated by falling water inside the 

towers, plus fan or motor noise. Noise from power plant sites generally do not result in 

off-site levels more than 10 decibels (dB) above background levels.5 Facilities that make 

use of cooling towers, however, might expect the typical noise level to be approximately

70 dB within 50 feet of the tower.

6

 Because sound levels diminish approximately 5 dB 

per doubling of distance, and 55 dB falls between the sound level of rainfall and normal 

conversation

7

(and therefore would not be considered noise pollution), a buffer of 400 

feet would suffice for noise abatement at most sites.8In addition, EPA’s “Protective 

Noise Levels” guidance found that ambient noise levels of 55 dB was sufficient to protect 

public health and welfare and, in most cases, did not create an annoyance.9 As for noise 

pollution at the site itself, the New York State Department of Environmental 

 

3 Technical Development Document for the Proposed Section 316(b) Phase II Existing Facilities Rule, 

Chapter 6, Non-Water Quality Impacts, p. 6-7. 

4 The documentation from the NPDES permit renewal for Brayton Point was also considered (see 

http://www.epa.gov/ne/braytonpoint/index.html). In this case, the facility cited a proximity to highways 

and bridges as potential challenges to retrofitting to closed-cycle cooling. Using online aerial photos, the 

distance to the nearest major road is approximately 0.5 mile and the bridge is approximately 1.0 mile away. 

Dominion Energy ultimately concluded that a natural draft cooling tower was the best choice for its closedcycle cooling system; while Dominion has not publicly stated its rationale, it can be assumed that 

abatement of the cooling tower plume was at least one factor.

5 US EPA. 2002. Technical Development Document for the Proposed Section 316(b) Phase II Existing 

Facilities Rule, Chapter 6, Non-Water Quality Impacts, p. 6-9.

6

SPX. 2009. Cooling Tower Fundamentals, p 75.

7 American Speech-Language-Hearing Association. Noise and Hearing Loss. Accessed at 

http://www.asha.org/public/hearing/disorders/noise.htm on August 1, 2010.

8 Noise levels would be as follows: 70 dB at 50 feet, 65 dB at 100 feet, 60 dB at 200 feet, and 55 dB at 400 

feet.

9 EPA 550/9-79-100, November 1978.
3

Conservation’s “Assessing and Mitigating Noise Impacts” policy states that 60-70 dB is 

the beginning of the threshold for annoyance in non-industrial sites and that noise can 

exceed 65 dB (and up to 79 dB) in commercial or industrial sites. A common goal is to 

keep new noise sources from increasing the overall noise levels by 5-10 dB. Given that 

noise is measured on a logarithmic scale, adding a cooling tower that operates with a 

sound level of approximately 70 dB will be unlikely to add a significant level of noise to 

an already noisy industrial site.10 Given that noise appears to dissipate relatively quickly 

(and the fact that many industrial sites are large and a 400 foot buffer would not be a 

significant limitation), effects from noise are not expected to be significant at most sites. 

There will certainly be some sites that require noise mitigation, but the number of sites is 

likely to already be represented by the analyses for plume and population density.

Tetra Tech decided to use population density as a proxy indicator of facilities that might 

be subject to land or space constraints for installing cooling towers. Tetra Tech 

conducted a geographic information systems (GIS) analysis of various U.S. Census (2007 

figures) data to determine the point at which population blocks (blockgroups) indicate the 

transition from more densely developed urbanized areas to areas with ample space for 

development.11 After comparing several urban areas as examples, a threshold of 1000 

persons per square mile was selected as the approximate transition point. The figures 

below show areas color-coded and labeled according to Census population density (2007 

figures). For this analysis, a facility was considered to be development restricted if the 

facility was located within a blockgroup where population density was greater than or 

equal to 1000 persons per square mile.

Washington DC and Buffalo, New York were examined to estimate the selected 

threshold and the graphics are presented below. Topeka, Kansas and Salinas, California 

were also examined but are not presented below.

 

10 NYDEC. 2000. Assessing and Mitigating Noise Impacts, p. 14.

11 Tetra Tech also considered an analysis using the Census Urban Areas layer, but chose to use blockgroups 

instead because they allowed for the identification of low-density blockgroups within the urban area 

boundary. 
4

Population Density for Washington, DC
5

Population Density for Buffalo, NY
6

For the purpose of this analysis, facilities located within a blockgroup with a density

greater than 1000 persons per square mile are considered to be potentially subject to 

space constraints for installing cooling towers. 

Because proximity to airports, major roads, and densely populated areas may be 

correlated with the need for facilities to install technologies to mitigate those effects, the 

proximity analyses for all these of these factors are expected to complement one another. 

In other words, each of these technical challenges relate to a proximity to other uses of 

surrounding areas (e.g., roads, residential, etc.); as a result, it is reasonable to expect that 

separate analyses for each challenge would identify some of the same facilities.

Analysis

Tetra Tech plotted the longitudinal and latitudinal coordinate locations of the model 

power plant facilities used to develop compliance costs. Tetra Tech then plotted GIS 

layers to determine if facilities 1) fall within a 2-mile radius from all airports; 2) intersect 

the 0.5-mile radius from all major roadways (defined as a limited access road or 

highway); and 3) are located within a blockgroup with 2007 population density per sq 

mile ≥1,000 (FacilPopDens1000). The results are shown in the map below.
7
8

Results

Tetra Tech further refined the analysis with four additional steps. First, the universe 

(initially comprised of 891 facilities, including all power plants and manufacturers that 

completed a technical questionnaire) was limited to facilities with a design intake flow 

(DIF) of greater than 125 million gallons per day (MGD).12 Second, facilities that did not 

complete a detailed questionnaire were removed, as costs for these facilities will not be 

developed in the proposed rule.13 Third, manufacturers were removed from the analysis, 

as these sites are already assigned “difficult” level costs in the EPRI cost methodology. 

Fourth, statistical survey weights were added to properly adjust the representativeness of 

each facility.

Out of the 224 detailed questionnaire facilities (250 weighted) with a DIF greater than

125 MGD, the analyses showed that:

1) 50 (56 weighted) of these 224 are within 0.5 miles of a major road.

o 1 of these was within 2 miles of airports. 

o 12 of these are in high population density areas as defined by 

FacilPopDens1000.

 Of these 12, none are within 2 miles of airports.

2) 4 (4 weighted) of these 224 are within 2 miles of an airport.

o 1 of these was within 0.5 miles of a major road.

o None of these are within high population density areas.

3) 25 (28 weighted) of these 224 are within a high population density area.

o None of these are within 2 miles of an airport.

o 12 of these are within 0.5 miles of a major road.

As such, a total of 66 (29.4%) facilities (74 weighted or 29.6%) of the universe of 

facilities with a DIF >125 MGD facilities are subject to at least one constraint. Given the 

conservative nature of this analysis,14 rounding the percentage of facilities that may

require additional costs for abatement technologies or face challenges due to space 

constraints to 25% was deemed appropriate.

By comparison, Electric Power Research Institute (EPRI) conducted a survey of its 

members and found that approximately 23 percent of respondents answered that they

 

12 Lower flow facilities will require smaller cooling towers and be less likely to encounter issues with noise, 

plume, or space. Additionally, many low DIF facilities already employ closed-cycle cooling

13 In other words, only model facilities for which costs are generated for the proposed rule were included.

14 For example, the analysis did not account for prevailing wind direction, which may eliminate some 

facilities from the likely area of effect. In another example, noise abatement costs are relatively low; 

assigning a “difficult” level cost to a facility that is only required to mitigate noise impacts would likely be 

an overestimate of the compliance costs.
9

would be concerned space constraints, should they be required to retrofit with cooling 

towers.15,16 While this seems to be consistent with Tetra Tech’s analyses, over half of the 

facilities surveyed by EPRI had not yet studied the impacts of installing closed-cycled 

recirculating systems. In addition, EPA personnel have observed, during the course of 

site visits, situations in which space constrained facilities were able to creatively resolve 

technical issues.

17

 Additionally, based on EPA personnel best professional judgment, 

many facilities are conservative when estimating their required responses to potential 

regulations regarding cooling water intake structures. Furthermore, facilities that have 

not yet studied their site-specific impacts from installing closed-cycle cooling may not 

take into account the innovative or creative solutions that can be developed, even for 

space-constrained areas. As a result, the assumptions underlying EPA’s analysis are 

likely to be conservative and may overstate compliance costs. 

Given the results of the GIS analyses and the best professional judgment of EPA 

personnel, as well as the safety margins incorporated in the GIS analyses, Tetra Tech’s 

analysis supports a threshold of 25 percent of facilities that may be constrained by

cooling tower plume, noise, or space restrictions and should therefore be assigned an 

increased compliance cost.

 

15 Net Environmental and Social Effects of Retrofitting Power Plants with Once-Through Cooling to 

Closed-Cycle Cooling. EPRI, Palo Alto, CA: 2008. p4-59.

16 Forty six percent responded that there were local noise ordinances; there was no indication of whether 

these ordinances would be restrictive to installing cooling towers. There were no questions regarding 

impacts due to a cooling tower plume.

17 See, for example, the site visit report for McDonough Station.