MEMORANDUM

Tetra Tech, Inc.

10306 Eaton Place, Suite 340

Fairfax, VA 22030

phone 703-385-6000

fax 703-385-6007

TO: Paul Shriner and Lisa Biddle, EPA

FROM: John Sunda 

DATE: August 23, 2012

SUBJECT: IM Technology Cost Drivers

This memo discusses the assumptions used in developing the IM compliance costs for the 

purposes of identifying which assumptions are potentially cost drivers that can lead to 

(significant) over/under-estimation of costs. In general, a capital costs difference of 10% results 

in a total rule cost change of less than 1% (because a 7% interest rate amortized for 20 years has 

a .093 annualized factor.) Therefore, both prevalence and costs differential are considered. The 

results of this review are provided in the table below.
IM Technology Assumption Cost Drivers

Assumption Sensitivity1Prevalence2 Notes

Generator 

Intakes

Manufacturer 

Intakes

Reported through-screen of ≤0.5 fps 

in a facility survey is assumed IM 

compliant.

High 16% 18% 20% of generator intakes are ≥0.3 and ≤0.7 (±40%). 

For those that reported such data, 43% of intakes 

reported velocity at critical low flow and 57% 

reported velocity at mean flow.

Depth of water at the withdrawal 

point is an approximation of the 

wetted depth of intake screens at the 

reported through-screen velocity.

High High High Costs for New intake (Module 3 and 10.2) and 

Ristroph Traveling Screens (Module 1 and 10.3) are 

indirectly proportional to the assumed water

depth.

Use the default (median) intake water 

depth where data was not reported.

High 39% 25% Estimated screen width may be unrepresentative 

of actual intake screen width. Counts are for 

intakes with values equal to default and may 

include some actual values.

Facilities that did not report screen 

velocity data had values equal to the 

default median.

High 14% 50% Estimated screen width may be unrepresentative 

of actual intake screen width. Some unreported 

velocities may be <0.5 fps.

Facilities with intakes without 

traveling screens and velocities >0.6 

will comply by building larger intakes 

with ≤0.5 fps traveling screens or by 

installing wedgewire screens.

High 11% 38% Other less costly technology options may be 

available on a site-specific basis.

Facilities with intakes with traveling 

screens with a screen velocity >2.5 fps 

will comply by building larger intakes 

with ≤0.5 fps traveling screens or by 

installing wedgewire screens.

High 9% 4% Note that 2.5 fps is based on BPJ. The value is more 

related to issues regarding debris especially with 

respect to fine mesh. 5% of generator intakes and 

2% of manufacturer intakes are in the >2.5 to 3.0 

fps range.

That non-IM compliant intakes 

without traveling screens or velocities 

>2.5 fps will not use a technology 

option with lower cost than a 0.5 fps

larger intake or wedgewire screens.

High 13% 26% Technology options are very site-specific and there 

are no lower cost modules that apply to nontraveling screen intakes.
Assumption Sensitivity1

Prevalence2 Notes

Generator 

Intakes

Manufacturer 

Intakes

Facilities will schedule construction 

activities to coincide with routine 

maintenance downtime, and that the 

estimated technology construction 

downtime is based on the median 

downtime value that may be incurred.

High Low Moderate Most power generators have scheduled downtime 

to coincide with construction especially for 

traveling screens. Some manufacturing intakes 

must operate continuously and low downtime 

estimates for manufacturers (even for traveling 

screens) have been questioned in public 

comments.

That traveling screens without the full 

complement of modified Ristroph 

features must replace and upgrading

screen to achieve compliance.

Moderate 59% 32% Prevalence values include non-compliant intakes 

with traveling screens and velocity >0.6 fps. Many 

existing screens with partial Ristroph features may 

require replacement because they are not 

designed for continuous operation.

That intakes without the full 

complement of modified Ristroph 

features will require a new separate 

fish return.

Moderate 27% 9% Prevalence values include all intakes that reported 

a fish conveyance system (not just those with 

traveling screens). Only 3-4% reported separate 

fish and debris returns. Could eliminate added 

costs for fish return for intakes with existing fish 

return or conveyance system.

That the technology mix reported in 

2000 technical survey is 

representative of current conditions.

Moderate Moderate Moderate The general trend is for facilities to install more 

protective technology over time. Improvements 

made in last 12 years are not reflected in costs.

That nuclear facilities will incur capital 

and O&M costs that are 1.8 and 1.33-

1.44 times those costs for non-nuclear 

facilities, respectively.

Moderate 8% 0%

That the maximum reported intake 

flow for the years 1996, 1997, 1998, is 

representative of the design flow for 

technologies that do not involve 

replacement of existing traveling 

screens (e.g., new larger intake and 

wedgewire screens).

Moderate 34% 35% Difference in total flow for all intakes was 7% for 

generator intakes and 26% for manufacturing 

intakes. Prevalence values are intakes where 

maximum reported flow was < DIF.
Assumption Sensitivity1

Prevalence2 Notes

Generator 

Intakes

Manufacturer 

Intakes

That fish barrier nets are needed at all 

intakes on ocean and estuarine 

waterbodies in addition to 

replacement traveling screens or new 

larger intakes with traveling screens.

Low 13% 6% Costs for barrier nets are relatively low. Inclusion of 

barrier nets at estuarine facilities did not 

significantly affect total rule costs.

That intakes with inlets submerged 

>500 ft offshore or has canal length 

>5,000 ft are representative of intakes 

that will have difficulty installing fish 

returns

Low 3% 4% Prevalence values are for intakes assigned added 

costs.

1

The degree to which changes in the assumed value will affect changes in individual intake costs

2

Intake percentages are unweighted approximations for all intakes - not just those assigned technology costs
Some additional assumptions that may affect compliance costs include:

IM Compliance Assumptions

 That intakes that meet the following are baseline IM compliant:

o Are located in NY or coastal CA.

o Reported that associated cooling systems at the facility were closed-cycle cooling 

using cooling towers.

 That de minimis frequency is unknown, location is unknown, and at most roughly 5% of 

facilities. Technology costs will be overstated for those facilities. These facilities have 

such low impingement rates that the estimated benefits for these facilities are likely

small, and thus national level benefit estimates would not change as a result of these 

facilities being determine to be de minimis.

Technology Assignment Assumptions

 That existing intakes with reported intake velocities <0.6 and >0.5 can comply using 

variable speed pumps alone.

 That the cost of the single technology options selected will be equal to or greater than the 

cost of multiple partially effective technologies (e.g., fish avoidance technologies, flow 

reduction, etc).

1

Facilities will opt for such approaches where it is more cost effective to 

do so. 

 That fish returns at intakes where fish returns are difficult to install can do so, but at 

additional costs. (Costs of fish returns increased in final analysis.)

 That facilities with intakes described above that have design intake flow <10 MGD or 

water Depth at Intake >20 ft will select wedgewire screens instead of larger intakes,

except for intakes on oceans or lakes.

Assumptions Related to Technology Module Costs

Some cost module components may be important drivers for total costs. A detailed evaluation of 

individual cost module development assumptions is not presented here. Below are some of the 

more general cost module assumptions and those related to missing design and input data from 

the technical survey. 

 That the module capital and O&M costs estimates for each module are representative of 

the median national costs for that technology.

 That the assumed service life for each technology module is representative of the median 

national value.

 

1

Since site-specific conditions and technology availability and efficacy are unknown, EPA assigned a limited suite 

of single technologies with more predictable performance. As a result, costs are likely overestimated in some 

instances. 
 That the reported design intake flow is a good approximation of the required combined 

cooling and process water flow requirement.

 That the use of estimated median national costs will produce a reasonable estimate of 

national costs since actual costs that are higher and lower than the median will tend to be 

offset.

 That traveling screen total intake well depths have an average freeboard of 30 ft for 

freshwater rivers, 20 ft for lakes, and 15 ft for all others. (Affects cost of traveling 

screens.)