United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-95/135 September 1995
vvEPA Project Summary
Pollution Prevention Opportunity
Assessment United States Naval
Base Norfolk Naval Air Station
Dan Bowman and Jan DeWaters
This report summarizes work con-
ducted at the U.S. Navy's Naval Base
Norfolk, Naval Air Station (NAS) located
at Sewells Point in Norfolk, VA under
the U.S. Environmental Protection
Agency's (EPA's) Waste Reduction
Evaluations at Federal Sites (WREAFS)
Program, with support provided under
the Strategic Environmental Research
and Development (SERDP) Program.
SERDP is a cooperative effort between
DoD, DOE and EPA to develop environ-
mental solutions that enhance mission
readiness in Defense operations.
Under the Chesapeake Bay Agree-
ment, Naval Base Norfolk is a member
of the Tidewater Interagency Pollution
Prevention Program. At NAS Norfolk,
the Navy and EPA have evaluated tech-
niques and technologies to reduce
waste generation from cooling tower
operations, cooperating on the Pollu-
tion Prevention Opportunity Assess-
ment which identified areas for waste
reduction during operation and mainte-
nance of the NAS cooling towers. The
study followed procedures outlined in
EPA's Facility Pollution Prevention
Guide. Opportunities were identified for
reducing the generation of waste from
cooling tower water treatment opera-
tions. The options for changes in op-
erational and treatment processes and
procedures were evaluated for their
potential to achieve pollution preven-
tion objectives, as well as for technical
and economic feasibility.
This Project Summary was developed
by EPA's National Risk Management
Research Laboratory, Cincinnati, OH,
to announce key findings of the re-
search project that is fully documented
in a separate report of the same title
(see Project Report ordering informa-
tion at back).
Introduction
The purposes of the WREAFS Program
are to identify new technologies and tech-
niques for reducing wastes from process
operations and other activities at Federal
sites, and to enhance the implementation
of pollution prevention/waste minimization
through technology transfer. New tech-
niques and technologies for reducing waste
generation are identified through waste
minimization opportunity assessments and
may be further evaluated through joint re-
search, development, and demonstration
projects.
A cooling tower is an enclosed device
designed for the evaporative cooling of
water by direct contact with air. Cooling
towers are used in conjunction with air
conditioning and industrial process equip-
ment, acting as the heat sink for these
systems by providing a continuous source
of cool water for process operations. Open-
system recirculating cooling towers are
typically chosen for operation with air con-
ditioning and refrigeration equipment be-
cause they are relatively inexpensive and
minimize heat rejection costs while con-
serving water.
All of the cooling towers at the Norfolk
Naval Air Station identified in this PPOA
are of the recirculating, open-system type.
The Navy and EPA are currently evaluat-
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ing techniques and technologies to re-
duce wastes generated from cooling tower
operations within the Norfolk MAS. Ap-
proximately 28 open-system recirculating
cooling towers are currently operated at
18 buildings within the MAS. These units
range in size from 5 to 300 tons, and are
all associated with comfort cooling sys-
tems that operate on a seasonal basis
(approximately 6 mo/yr).
General Process Description
Approximately 598 buildings or struc-
tures are located at the Norfolk MAS. Of
these, 18 buildings are equipped with air
conditioning systems that operate in con-
junction with evaporative recirculating cool-
ing towers for a continuous supply of
process water. The air conditioning sys-
tems provide comfort cooling during warm
spring and summer months, largely be-
tween April and October. The MAS cool-
ing towers do not operate during the cool
season. Table 1 is a master equipment
list of the 28 cooling towers providing pro-
cess water for the air conditioners which
service these 18 buildings. As described
in Table 1, these cooling towers are lo-
cated on building roofs, adjacent to an
exterior wall, or in a courtyard outside of
the building and range in capacity from 5
to 300 tons. One cooling tower ton is
equivalent to the removal of 15,000 BTU/
hr.
Table 1 indicates that only 10 of the 28
towers are currently receiving chemical
treatment for control of scale, corrosion,
and biological fouling. The remaining
18 towers are primarily small units and do
not receive chemical treatment during the
operating season.
The last column in Table 1 lists the
system water volume in gallons for the 10
towers receiving treatment. The volumes
are used to derive some of the alternative
treatment costs. These system volumes,
estimated by Base personnel, depend to
a large extent on unit size, but are also
Table 1. Master Equipment List - Cooling Towers at Norfolk Naval Air Station
Equipment #
Building
Location
Size (Tons)
Volume (Gallons)
Cooling Towers Receiving Chemical Treatment*
081275
028197
028198
021087
024341
081218
093171
093172
SP367
SP254*
SP256*
V53
V53
SP29**
U16**
SP45
SP91
SP91
East outside
Roof
Roof
Roof
Roof
West courtyard
East side
South side
Behind building
Behind building
75
200
200
150
175
300
300
125
100
40
127
600
1,000
1,200
1,400
3,500
2,500
1,250
1,000
400
Cooling Towers Not Receiving Treatment*
022189
080394
086933
080385
080386
080387
080388
022188
080389
052754
086998
093369
097454
021751
085676
085677
050597
083286
LP13
LP13
LP13
LP2
LP2
LP3
LP3
LP4
LP4
S33
S33
SP238
SP64
T26
T26
T26
U48
V82
Roof east side
Roof west side
Roof west side
Roof west side
Roof east side
Roof west side
Roof east side
Roof east side
Roof west side
Roof
West side
South end
Outside building
Roof east side
Roof west side
Roof
West side
Roof
25
25
25
25
25
25
25
25
25
20
5
20
20
20
60
60
7.5
45
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
* Refers to status of treatment at the time of report preparation, August 1994.
"Chemical treatment has been instituted at these new units since the site visit in June 1994.
***The cooling towers currently not receiving treatment are designed for chemical treatment.
—These two new units have not yet been issued equipment identification numbers.
influenced by the cooling tower locations
and piping systems.
Cooling Tower Discharge
Practices
All cooling towers at the MAS receive
makeup water from the City of Norfolk
public water supply. Each of the cooling
towers is equipped with a discharge valve
which directed the tower blowdown into
floor drains located in the vicinity of the
heat exchanger and condensed water
pump.
Cooling Tower Maintenance
Activities
Maintenance and operation of the cool-
ing towers and air conditioning units are
performed by the Public Works Command
(PWC), under contract to the MAS. PWC
personnel do not currently have a system-
atic method for managing the MAS cool-
ing towers. Ten of the 28 MAS cooling
towers are serviced under a chemical treat-
ment contract to PWC by one of two wa-
ter treatment specialists. Each of these 10
units is maintained by a treatment repre-
sentative, whose primary responsibility in-
cludes cooling tower water testing and
treatment.
The remaining towers, which are not
serviced by a chemical contractor, are the
responsibility of the PWC mechanics.
These units receive no chemical treat-
ment during the operating season aside
from the occasional addition of biocide to
control excessive fouling. General main-
tenance activities for the cooling towers
not serviced by a water treatment special-
ist include an annual overhaul of each
unit, which is performed during the winter
months while the unit is not operating.
Following the annual overhaul, PWC
maintenance personnel apply an algicide
to each of the cooling tower units not
serviced by a chemical contractor. A 1-gal
container of algicide is fed by continuous
drip to each unit to control biological growth
in the system. Some of the towers may
occasionally receive additional biocide dur-
ing the operating season to control exces-
sive biological fouling, although application
rates and schedules vary.
Chemical Addition Program
At the Norfolk MAS, PWC personnel
purchase the chemicals, and a water treat-
ment contractor tests the tower water, ad-
justs control parameters such as bleed
and makeup water flowrates, and admin-
isters chemicals as needed.
Of the 28 towers in operation, 10 are
currently receiving chemical treatment, and
are serviced under contract by one of two
cooling tower water treatment specialists
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who also service other units on base. Four
of these units are equipped with chemical
pumps and metering systems but were
not included in a chemical treatment con-
tract at the time of the site visit in June
1994. Chemical treatment programs have
recently been implemented at these four
units. In the future, all towers at the MAS
would be included in a chemical addition
program.
General Procedure for
Chemical Procurement
The procedure for procurement and ad-
ministration of water treatment chemicals
involves a cooperative effort between ap-
propriate PWC personnel and the water
treatment or chemical contractor respon-
sible for the unit. Each of the cooling tow-
ers under contract to a water treatment
specialist is inspected sporadically to en-
sure that the tower is operating properly
and is receiving adequate chemical treat-
ment. Operating malfunctions are adjusted
and corrected by the contractor. If the
contractor determines that additional
chemicals must be purchased, PWC is
notified. PWC personnel order the appro-
priate materials for delivery to the specific
building at the specific zone on base. Once
the chemicals arrive on site, the contrac-
tor returns to administer treatment.
PWC personnel who were interviewed
during the site visit stated that under no
circumstances do PWC maintenance per-
sonnel administer chemicals to the MAS
cooling towers, regardless of whether or
not the towers are maintained under con-
tract by a water treatment specialist. How-
ever, at the time of the site visit, two
towers were observed that were not cur-
rently under contract by a water treatment
specialist, but that were connected to a
chemical holding tank and an engaged
metering pump. Thus, the actual chemical
administration procedures as practiced re-
main somewhat uncertain.
A chemical exchange program exists
within each zone on base. Most chemi-
cals are stored in the mechanical room of
the building in which they are used. As
more chemicals are needed by a particu-
lar building, PWC will first check to see
that excess chemicals do not exist in stor-
age at another building before ordering a
new supply. This procedure avoids stock-
piling of surplus chemicals.
Chemical Descriptions and
Usage Data
The chemicals used for cooling tower
water treatment at the Naval Air Station
are presented in Table 2 along with their
primary ingredients, type of control, appli-
cation rate, and frequency of use. Typical
application rates for each chemical, shown
in Table 2, have been combined with cost
information to estimate annual usage rates
and associated costs. Usage rates are
based on a 6-mo operating season, and
assume that all towers operate with 4
cycles of concentration at 100% capacity
for 12 hr/day. As described above, the
chemicals applied to each of the MAS
cooling towers, which total approximately
814 gal, are ultimately discharged to the
environment through tower bleed. The to-
tal annual chemical costs for the MAS
cooling towers currently receiving chemi-
cal treatment are estimated at $13,900.
For water usage, Table 3 provides bleed
rates and make up requirements with
monthly costs.
Description of Available
Options
Non-treatment
Although non-treatment alternatives may
eliminate the application and subsequent
discharge of cooling tower water treat-
ment chemicals, these may entail excess
water usage rates to control the accumu-
lation of suspended solids in the system.
In addition, improper treatment and man-
agement of cooling tower water may re-
sult in excessive buildup of scale deposits
and biological fouling, ultimately resulting
in system failure.
Option 1. No Treatment
Eighteen of the MAS cooling towers cur-
rently have no formal chemical treatment
program. One option for pollution preven-
tion is to extend this practice to all 28
MAS cooling towers. Under this scenario,
the towers would receive annual mainte-
nance. During the off-season, the units
would be externally cleaned with wire or
nylon brushes, the heat exchanger end
plates would be removed, and the tubes
reddened with a round wire brush to re-
move scale deposits as needed. Approxi-
mately one gal of algicide would be added
to each unit by means of a drip feed.
Refraining from chemical treatment
would result in the annual consumption of
approximately 28 gal of algicide at a cost
of approximately $15 each, for a total of
$420.00/yr. This represents a savings of
approximately $13,300 annually in chemi-
cal costs, and a substantial reduction in
the discharge of cooling tower water treat-
ment chemicals to the environment. How-
ever, failure to properly maintain the towers
during the operating season results in the
buildup of scale deposits and significant
algal growth, often leading to operational
down-time for necessary repair work and
mid-season cleaning. This is costly in
terms of employee man-hours. In addi-
tion, the operational lifetime of a unit, typi-
cally in the range of 15 to 20 yr, is
significantly reduced by improper mainte-
nance and also by failure to provide ad-
equate corrosion protection. Systems
clogged by excessive scale deposits often
require acid dosing to clear blocked pas-
sageways; this is an aggressive treatment
procedure and can be harmful to the ma-
terials of construction, especially where
corrosion has already exposed oxidized
portions of the metallic surface. Thus, while
a no-treatment option appears to be cost
effective in terms of operating expenses,
ultimately, the expense of new equipment
purchases due to system failure makes
this option less attractive.
Option 2. Continuous Bleed-off or
Blowdown
The purpose in using recirculating cool-
ing systems is to conserve makeup water.
Systems using higher cycles of concen-
tration use less water. Achievable cycles
of concentration depend on the concen-
tration of ions such as calcium and silica
in the makeup water, since these accu-
mulate throughout evaporative losses
which take place in the cooling tower. The
risk of severe scale or corrosion problems
increases dramatically with higher cycles
of concentration. Solids and impurities will
continue to accumulate until the system
water is removed through bleed-off or
blowdown. Dissolved oxygen increases in
a recirculating system because the water
is reaerated during each passage through
the cooling tower. In normal practice, a
portion of the recirculating water will be
removed through system blowdown in or-
der to maintain the concentration of dis-
solved solids and gases at a required
level, thereby preventing scale deposits
and corrosion.
Maximum concentration factors are rec-
ommended for open cooling water sys-
tems according to the hardness of the
water and the type of treatment applied.
Systems receiving makeup water of rela-
tively low hardness or those which re-
ceive effective scale-inhibiting treatment
may operate at high concentration fac-
tors, maximizing the portion of recirculat-
ing water and minimizing the makeup water
requirements. Without treatment, concen-
tration values of about 3 to 7 are enough
to cause some salts to precipitate out as
scale. Various water treatment approaches
and devices have historically avoided scale
formation by increasing the bleed and
makeup water rates rather than control-
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Table 2. Treatment Chemicals Currently Used in Norfolk NAS Cooling Towers
Trade Name
Principal Ingredients
Type of Control
Application Rate
Usage Rate
Chemicals Used in Cooling Towers for Buildings SP367. SP254. and SP256
Formula 1100* Poly [oxyethylene- (dimethyliminio) ethylene-
(dimethyliminio) ethylene dichloride]
Formula 1109* Disodium ethylene bisdithiocarbamate
sodium dimethyldithiocarbamate
ethylene thiourea
Formula 2055 Sodium hydroxide
methylene phosphonic acid
Formula 7200 Potassium hydroxide
1-hydroxyethylidene-1, 1-disphosphonic acid
Biocide
Biocide
Scale/corrosion
inhibitor
Dispersant/
antifoulant
Chemicals Used in Cooling Towers for Buildings SP45. SP91. V53. SP29and U16
Dicaton Sodium hydroxide Non-Acid descaler
GAX-16* Poly ethylene- ethylene dichloride
GAX-20* 2,2-dibromo-3 nitrilopropionamide
GAX-26 5-chlor-2 methyl-4-isothiazolin-3-one
2-methyl-4-isothiazolin-3-one
GCO-10-LM Sodium molybdate
polyethylene- ethylene dichloride
GCO-10 Poly ethylene- ethylene dichloride
Penetrex Not Available""
Biocide
Biocide
Biocide
Scale/corrosion
inhibitor
w/biocide
Scale/corrosion
inhibitor
w/biocide
Dispersant/ antifoulant
2 qt/wk/300 ton
1/2 qt/wk/100 ton
2 qt/wk/300 ton
1/2 qt/wk/100 ton
1 qt/100 ton/day
approximately
30 gal/yr
2.5 gal/1,000 gal system
water
1/4 to 1/2pt/1,000gal
makeup water"
1/4 to 1/2pt/1,000gal
makeup water**
1/2 gal/1,000 gal system
water
1/2 to 1 pt/1,000gal
makeup water"
1/2 to 1 pt/1,000gal
makeup water"
1/2 pt/'1,000 gal
system water
1/wk
1/wk
1/wk
1/wk
Continuous
At start-up and
shutdown
At start-up or
cleanup
1/every other wk
1/every other wk
At start-up and
shutdown
Continuous
Continuous
At start-up and
shutdown
* Biocides are generally alternated on a weekly basis, to increase the effectiveness of treatment.
** Dosage varies depending on system load.
*** Principal ingredients are listed as proprietary information and are not available.
ling calcium carbonate or silicate forma-
tion by chemical or mechanical means.
Minimum dissolved solids and mineral
concentrations could be maintained by
operating the cooling tower with a con-
tinuous supply of fresh water and a maxi-
mum flow of tower bleed. A once-through
system would avoid the buildup of solids,
gases and impurities in the process wa-
ter, thereby limiting the potential for scale
deposits and corrosion, and would elimi-
nate the need for administration and dis-
charge of chemicals to the environment
through cooling tower blowdown. However,
the high operating costs of large amounts
of makeup water make this a fairly unat-
tractive option. Makeup water requirements
and associated costs are reduced drasti-
cally by operating at higher cycles of con-
centration.
Although a continuous bleed will avoid
the buildup of dissolved solids and gases,
the potential still exists for algal and bac-
terial growth. Thus, the system may still
malfunction during the operating season if
the biofouling is allowed to progress. Each
cooling tower unit should still receive an
annual overhaul and application of a 1-gal
biocide drip, which will increase annual
operating costs accordingly.
Additional Options and
Recommendations
In addition to the two pollution preven-
tion options identified above, the PPOA
team noted 6 alternative treatment options
available. Table 4 provides an overview of
all the options. A detailed discussion of
the treatment options is provided in the
full report. Three technologies described,
including the DIAS-AID Tower Treatment
XP-300, the KDF process, and the mag-
netic treatment application combined with
integrated technologies, are attractive eco-
nomically as well as for pollution preven-
tion. Recommendations for further research
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Table 3. Bleed and Makeup Water Requirements and Monthly Costs at Different Cycles of Concentration*
Cycles of Concentration
10
16
Evaporation (gpm)
Total bleed rate (gpm)
Makeup water (gpm)
Water cost ($/mo)**
3
3
6
$443.09
3
1.5
4.5
$335.07
3
1
4
$297.84
3
0.75
3.75
$279.22
3
0.4
3.4
$253.16
3
0.33
3.33
$247.95
3
0.2
3.2
$238.27
'Assumes a 100-ton open-system recirculating cooling tower operating at full capacity for 12 hr/day, with a 10°F temperature drop across the tower.
Pump circulation rate is 300 gal/min.
"Costs are based on a combined water and sewer cost of $3.40/1000 gal. Norfolk City water prices are currently $1.34/1000 gal, and sewer prices are
$2.06/1000 gal. Since cooling towers at the Norfolk NAS are generally not provided separate metering systems for drainage, combined rates are
charged for makeup water. It is obvious from the above table that as the operating cycles of concentration increase, the volume of bleed discharged to
the drain is substantially reduced. Separate metering systems would allow calculation of a credit for makeup water which is not discharged to the drain
(e.g., evaporative losses), and would result in substantial savings.
Table 4. Summary of Treatment Options: Advantages and Disadvantages
Treatment Option
Advantages
Disadvantages
1. No Treatment
2. Continuous bleed
3. Conventional
chemical addition
4. DIAS-aid tower
treatment XP-300
5. pH adjustment
6. Base exchange and
ion exchange
processes
7. KDF process
8. Magnetic applications
•Minimal chemical costs
•Minimal discharge of chemicals to environment
•Minimal chemical costs
•Minimal discharge of chemicals to environment
•Fairly reliable method
•Several chemical options available for customized
treatment
•Recently developed product which has demonstrated
effective treatment
•Operates with little or no system bleed
•Cost effective, in terms of chemical and water use
•Minimal chemical costs; sulfuric acid an economical choice
•Minimal discharge of chemical to environment
•Minimal chemical costs
•Minimal discharge of chemical to environment
•Produces soft, non-scaling water
•Minimal chemical costs
•Minimal discharge of chemical to environment
•Waste product consists of recyclable metallic alloy
•System is self-regulating by responding to changes in pH
•Minimal chemical costs
•Minimal discharge of chemical to environment
•Lifetime warranty
•Minimizes maintenance demands
•Effective against scale and corrosion
•High maintenance demands
•Poor system operation
•Reduced operating lifetime of equipment
•Excessive water consumption and associated
costs
•Treatment can be costly in terms of chemicals
purchased, required testing and maintenance
•Chemicals may be limited in discharges
•Limited operating experience on which to base a
level of confidence
•Additional intermittent treatment may be needed for
control of biological growth
•Difficult to maintain adequate control
•Undesirable dissolved solids may still accumulate in
system
•Softened water may be corrosive
•Generally quite expensive
•Provide scale control only
•Limited operating experience on which to base a
level of confidence
•Additional filter unit necessary for solids removal
•May cost slightly more than conventional chemical
treatment
•Operating experience shows inadequate control
over microbial growth; dosing with biocide or acid
may be necessary to maintain a clean system
•Limited operating experience on which to base a
level of confidence
•Additional sidestream treatment usually necessary
for solids removal
•Additional control may be required for microbial
growth
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Table 4. (continued)
Treatment Option
Advantages
Disadvantages
9. Ozonation, U. V. light
treatment
10. Sidestream treatment
•Minimal chemical costs
•Minimal discharge of chemical to environment
•Effective Sterilization Techniques
•Effective treatment for solids removal and control of
fouling
•Minimal chemical costs
•Minimal discharge of chemical to environment
•Several options are available
•Generally quite expensive
•U. V. limited to small size; ozone limited to larger size
units
•Not effective against scale or corrosion
•Generally used in conjunction with another treatment
method to reduce solids and the potential for
microbial growth; not an effective stand-alone
treatment methodology
include site visits to facilities which em-
ploy each of these three types of treat-
ment technologies, in order to gather
operating data and to observe the sys-
tems in operation. Additional information
gained through site visits would be used
to select an appropriate technology option
to be used in a demonstration project de-
signed to evaluate the potential for effec-
tively treating the MAS cooling tower water.
The full report was submitted in fulfill-
ment of Contract No. 68-D2-0181, Work
Assignment No. 1-011 by TRC Environ-
mental Corp. under the sponsorship of
the U.S. Environmental Protection Agency.
-------
Dan Bowman and Jan DeWaters are with TRC Environmental Corp., Chapel
Hill, NC 27514.
Kenneth R. Stone is the EPA Project Officer (see below).
The complete report, entitled "Pollution Prevention Opportunity Assessment
United States Naval Base Norfolk Naval Air Station," (Order No. PB95-
264040; Cost: $27.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
National Risk Management Research Laboratory
U. S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection Agency
National Risk Management Research Laboratory
Cincinnati, OH 45268
Official Business
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