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DO standard of 6.0
milligrams per liter.
Nitrogen is the pri-
mary pollutant causing
the low DO condi-
tions, with the most
significant loadings
from sewage treat-
ment plants. The Long
Island Sound TMDL for
nitrogen, developed by
both Connecticut and
New York, calls for an
overall reduction of 58.5 percent in total nitrogen from point
and nonpoint sources in both states by the year 2014. Of
that overall reduction, the TMDL process assigned reduc-
tion goals for point and nonpoint sources in Connecticut. On
the basis of this process, Connecticut's POTWs received a
64 percent reduction goal. To help implement the TMDL,
the Connecticut General Assembly passed Public Act No.
01-180 in June 2001. The legislation establishes the
framework for the Nitrogen Credit Exchange Program and
directs the Nitrogen Credit Advisory Board to administer this
program. A key component of the Nitrogen Credit Exchange
Program is the General Permit for Nitrogen Discharges,
which limits mass loadings of total nitrogen and includes
monitoring and reporting requirements for 79 POTWs in
Connecticut.
Permit Strategy
The CTDEP originally issued the General Permit for Nitrogen
Discharges on January 2, 2002, with an expiration date of
December 31, 2006, and reissued the General Permit on
December 1, 2005. The permit addresses only total nitrogen
discharges from the 79 POTWs. The facilities are subject
to the requirements of their individual National Pollutant
Discharge Elimination System (NPDES) permits for other
pollutants. Appendix 1 of the General Permit contains the
annual discharge limits, expressed in pounds per day, for
each applicable POTW. These limits represent the allocated
end-of-pipe loading for each facility.
The General Permit and the Nitrogen Credit Exchange Pro-
gram work in tandem to provide POTWs with alternatives for
achieving permit compliance. The General Permit requires
applicable POTWs to meet their specified annual discharge
limits. If the facilities cannot meet their specified limits,
they must purchase equivalent nitrogen credits. Facilities
with treatment that enables them to produce less than their
specified annual discharge load generate credits.
Connecticut's Clean Water Fund is a key component to
the success of the General Permit and the Nitrogen Credit
Exchange Program by making funds available to applicable
POTWs for nitrogen removal projects. The Nitrogen Credit
Advisory Board considers project costs when calculating
the cost per equivalent nitrogen credit. The availability of
funds affects the planning, design, and construction sched-
ule for nitrogen removal projects, which ultimately affects
the amount of total nitrogen that the POTWs can annually
remove from the sound. The Nitrogen Credit Advisory Board
uses the POTWs' actual removal loads to determine the
number of equivalent nitrogen credits available through the
Nitrogen Credit Exchange Program. Therefore, if resources in
the Clean Water Fund are limited, the POTWs might not be
able to complete their nitrogen removal projects and could
face challenges in meeting their annual discharge limits. As
a result, CTDEP might need to occasionally adjust the TMDL
schedule, which calls for POTWs to meet their respective
WLAs by 2014. In fact, according to the 2005 Annual Re-
port, when the CTDEP reissued the General Permit in 2005,
it increased the POTWs' 2006 annual discharge limits to
reflect the implementation pace of nitrogen removal projects
that could be maintained with available funds.
Connecticut's Clean Water Fund
Connecticut's Clean Water Fund provides financial assis-
tance to municipalities for planning, design, and construc-
tion of wastewater collection and treatment projects. Funds
available through the Clean Water Fund originate from five
accounts comprised of federal and state monies. The Clean
Water Fund provides a combination of grants (20 percent
of total project costs) and loans (80 percent of total project
costs) to municipalities that implement projects at the
direction of CTDEP. More information on Connecticut's Clean
Water Fund is at www.ct.gov/dep/cwp/view.asp?a=2719&q
=325578&depNav_GID = 1654
Permit Highlights
As noted previously, Connecticut designed the General
Permit and the Nitrogen Credit Exchange Program to work
in tandem to reduce POTW nitrogen loadings to Long Island
Sound. Without the Nitrogen Credit Exchange Program, the
79 POTWs covered under the General Permit would likely
face challenges in complying with their annual discharge
limits. The following subsections summarize the technical
aspects and functions of the Nitrogen Credit Exchange Pro-
gram and describe how the program relates to the General
Permit.
Nitrogen Removal Projects
The annual discharge limits contained in Appendix 1 of the
General Permit decrease each year from the assumption
that the aggregate amount of nitrogen discharged by the
79 POTWs will decrease as nitrogen removal projects are
completed. Facilities that perform better than their annual
discharge limit contained in the General Permit because of
Connecticut's General Permit
for Nitrogen Discharges
defines Total Nitrogen as the
total of the concentrations of
ammonia nitrogen, organic
nitrogen, nitrite nitrogen, and
nitrate nitrogen expressed as
milligrams of nitrogen per liter.
Permit limits are expressed in
terms of annual mass loading.
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What is a Nitrogen
Removal Project?
CTDEP has defined a nitro-
gen removal project as any
alteration of the physical
structure of a wastewater
treatment facility specifically
to remove nitrogen and that
is financed by the Clean
Water Fund (CTDEP 2006).
their nitrogen removal
project are eligible to
sell equalized nitrogen
credits through the
Nitrogen Credit Exchange
Program. Facilities that
cannot meet their annual
discharge limits (e.g.,
choose to defer nitrogen
removal project con-
struction) can purchase
equalized nitrogen credits
through the Nitrogen
Credit Exchange Program.
Equivalency Factors and Equivalent Nitrogen Credits
Credits bought and sold through the Nitrogen Credit Ex-
change are based on a facility's annual discharge limit; how-
ever, the annual discharge limit is an end-of-pipe limit and
does not account for attenuation of total nitrogen in Long
Island Sound. To ensure that all POTWs exchange equivalent
credits (i.e., credits that account for attenuation) through the
Nitrogen Credit Exchange Program, the CTDEP developed
equivalency factors for each POTW. The General Permit
provides each facility's equivalency factor in addition to its
annual discharge limits. The equivalency factor is essentially
a delivery factor that relates a facility's geographic location
to its relative effect on oxygen levels in western Long Island
Sound—the area that exhibits the greatest effects of exces-
sive nitrogen loading.
Annually, the CTDEP calculates the number of equivalent
nitrogen credits that a POTW has available to sell or that it
must purchase. The state makes this calculation by compar-
ing a POTW's annual mass loading of total nitrogen to its
Calculating Equivalency Factors
Accounting for attenuation of total nitrogen in Long Island
Sound is essential for exchanging equivalent nitrogen
credits. CTDEP and NYSDEC used modeling and monitoring
information to understand attenuation factors in Long Island
Sound and during riverine transport. CTDEP used these
factors to quantify relationships between discharge points
and the actual delivery of nitrogen to Long Island Sound.
Combined, these factors account for the relative impact
of nitrogen on DO depletion in Long Island Sound from
geographically distributed sources. To calculate the overall
equivalency factors, CTDEP multiplied the river delivery
factor for a specific tier within one of Connecticut's six Long
Island Sound management zones by the Long Island Sound
transport efficiency from a zone once the nitrogen reached
the edge of the Sound. CTDEP expresses the factors as the
decimal fraction of the nitrogen load delivered (CTDEP and
NYSDEC 2000).
annual discharge limit and then multiplies the difference
by the facility's equivalency factor. The result is the number
of equivalent nitrogen credits the POTW must purchase to
remain in compliance or that it has available to sell.
CTDEP works with the Nitrogen Credit Advisory Board to
set prices and administer the Nitrogen Credit Exchange
each year. The board sets prices on the basis of the cost of
the nitrogen removal projects implemented, the number of
pounds of nitrogen removed, and the cost of operating and
maintaining the facilities where projects have been imple-
mented. CTDEP and the Nitrogen Credit Advisory Board also
work cooperatively to ensure that reporting and accounting
under the exchange are accurate and that bills and credits
are disbursed according to the schedule set forth in the
underlying state law.
Permit Components
Discharge limits
The annual discharge limits applicable to each POTW are
specified in Appendix 1 to the General Permit. The Appendix
is incorporated in its entirety into the General Permit at sec-
tion 4(a). Appendix 1 presents a comprehensive list of each
POTW by management zone. For each POTW, the Appendix
lists the applicable equivalency factor and annual discharge
limit in pounds per day for the years 2006 through 2010.
Appendix 1 also presents each POTW's 2014 annual dis-
charge limit to meet the nitrogen WLA.
To provide a more realistic projection of expected perfor-
mance, CTDEP adjusted the annual discharge limits upward
in the current General Permit (see Permit Effectiveness).
The fact sheet for the General Permit states that CTDEP will
revise the annual discharge limits during the term of the
permit as new information becomes available regarding the
progress of achieving the final WLA.
All POTWs remain subject to effluent limitations for all other
parameters in their existing individual permits.
Monitoring and reporting requirements
Section 4(d) of the General Permit specifies the frequency
for total nitrogen monitoring for POTWs on the basis of the
design flow rate specified in each facility's individual per-
mit. Under the General Permit, POTWs with a design flow
rate of less than 10 million gallons per day must monitor
total nitrogen weekly. POTWs with a design flow rate equal
to or greater than 10 million gallons per day must monitor
total nitrogen twice per week. In addition, final effluent and
monitoring locations that are used to determine compliance
for the individual permit are also used to determine compli-
ance with the General Permit. The General Permit not only
requires facilities to monitor total nitrogen, but also the
average daily volume of effluent flow that corresponds to the
daily composite samples of total nitrogen.
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The General Permit provides reporting requirements in Sec-
tion 4(e). Facilities must submit three types of reports to
CTDER Facilities must provide information on total nitrogen
sampling and effluent flow volume on Monthly Operating
Reports and Nitrogen Analysis Reports-, these two reports
are fundamental to the Nitrogen Credit Exchange Program.
In addition, facilities must also provide monthly mass load-
ing of total nitrogen on Discharge Monitoring Reports, the
standard type of report required from all NPDES permittees.
Permit Compliance
Compliance conditions are presented in Section 4, Condi-
tions of this General Permit. The General Permit provides
two options for achieving compliance. Under the first option,
each permittee must have an annual mass loading of total
nitrogen that is less than or equal to its respective annual
discharge limits. Under the second option, permittees that
exceed their respective annual discharge limits can achieve
compliance by purchasing equivalent nitrogen credits
through the Nitrogen Credit Exchange Program. The number
of equivalent nitrogen credits must offset the amount of the
exceedance to achieve compliance. Permittees that exceed
their respective annual discharge limits and do not purchase
the necessary amount of equivalent nitrogen credits are out
of compliance and subject to enforcement.
Permit Effectiveness
Each year the Nitrogen Credit Advisory Board prepares an
annual report on the Nitrogen Credit Exchange Program for
the Joint Standing Environmental Committee of the Connect-
icut General Assembly. Monitoring data contained in these
reports indicate that Connecticut's POTWs have performed
below the aggregate permit limits during the period 2002-
2004. During 2005, however, the POTWs exceeded the ag-
gregate permit limit by 1,496 equalized pounds per day. The
POTWs exceeded the aggregate limit again in 2006. Table 1
below presents a summary of POTW performance in meeting
the aggregate nitrogen limit from 2002 to 2006.
Figure 1, from the 2005 Annual Report, shows the overall
equalized nitrogen discharged during 2002-2005, future
permit limits through 2010, and the 64 percent nitrogen
reduction goal to be met in 2014.
Figure 1. Annual Progress (2002-2005) and Future
Limits Necessary to Meet the TMDL for Long Island
Sound
20,000
2002 2003 2004 2005 2006 2007 2008 2009 2010
(CTDEP) 2007
The effectiveness of the General Permit in achieving annual
total nitrogen discharge limits and the final WLA is partially
dependent on weather conditions that affect nitrogen removal
Table 1. Summary of Nitrogen Credit Exchange Program Performance
Year
(Price per
credit)
Facilities
selling
credits
Number of equalized
nitrogen credits sold
(total value)
Facilities
buying
credits
Number of equalized nitrogen
credits purchased
(total cost)
Remaining credits
purchased by
CTDEP
2002
($1.65)
38
1,671,105
($2,757,323)
38
798,317
($1,317,223)
872,788
($1,440,100)
2003
($2.14)
37
1,134,876
($2,428,636)
40
989,194
($2,116,875)
145,682
($311,761)
2004
($1.90)
35
1,399,896
($2,659,804)
44
940,387
($1,786,736)
459,509
($873,068)
2005
($2.11)
28
623,408
($1,315,392)
50
1,169,553
($2,467,757)
2006
(Jan-Sept)
($3.40)
33
702,209
($2,387,510)
46
1,129,157
($3,839,134)
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performance. Unanticipated, adverse weather conditions,
characterized by wetter and colder winter and spring condi-
tions, hampered the performance of nitrogen removal treat-
ment during 2003 and 2005. (Although POTWs met the
aggregate permit limit for 2003, the actual load was very
close to the permit limit. There was only a difference of 401
equalized pounds per day between the actual load and the
permit limit.) In 2003 annual rainfall was 25 percent higher
than average and occurred during the winter and spring.
Similar conditions (i.e., it was wetter and colder than aver-
age) occurred during the first half of 2005. According to the
2005 Annual Report, the cold weather affected the perfor-
mance of POTWs using biological nitrogen removal technol-
ogy, and excessive rainfall resulted in high infiltration rates
that further affect performance. It is possible for nitrogen
removal treatment to improve over the course of the remain-
ing months in such years with warmer and dryer conditions.
This was the case in 2003; the POTWs were able to stay
just below the aggregate permit limit for that year. It was not
the case in 2005, however. While rainfall and temperatures
did improve in the second half of 2005, weather condi-
tions were adverse in October and likely contributed to the
POTWs' exceedance of the 2005 aggregate permit limit.
CTDEP purports in its 2005 Annual Report that as ad-
ditional facilities install nitrogen removal technology, the
potential to remove greater amounts of nitrogen in all
weather conditions will be achieved. Therefore, CTDEP
expects to witness a long-term downward trend in loading to
Long Island Sound. The Nitrogen Credit Advisory Board in its
2006 Annual Report recommended a training and technical
assistance program for POTW operators to improve nitrogen
removal efficiency in adverse weather conditions.
Although weather plays an important role, CTDEP also main-
tains that adequate funding for POTWs through the Clean
Water Fund is critical for enabling the POTWs to implement
nitrogen removal technologies and meet their respective an-
nual discharge limits. CTDEP has reported that as of Janu-
ary 2007, five denitrification projects are ready to enter the
construction phase; however, there is no Clean Water Fund
financing available for these projects. CTDEP's 2006 Annual
Report emphasizes the need for nitrogen removal projects to
continually move into the construction phase to ensure that
the state's 79 POTWs achieve the interim nitrogen compli-
ance reduction for 2009 and the final TMDL WLAs in 2014.
Lessons Learned
Paul Stacey of the Long Island Sound Program and other
CTDEP permits staff were asked a number of questions
regarding lessons learned from the state's general permit
and nutrient trading efforts. The questions asked and the
responses to them are summarized below.
4 What has been the most challenging part of the
project?
CTDEP's Municipal Facilities Program staff experi-
enced a few challenges associated with developing
and implementing the General Permit to achieve the
TMDL 2014 WLAs. During the development process
of the initial General Permit, conducting the neces-
sary outreach to garner support from the munici-
palities was a necessary, but challenging, aspect
of the project. CTDEP conducted a series of public
workshops around the state and put out an offer to
communities to hold one-on-one informational meet-
ings. During the reissuance process for the General
Permit, the stakeholder involvement process was not
as intensive. It consisted of a public notice, mailing,
and a formal hearing. The reissuance process did not
reveal any objectors to the General Permit. Limited
funding for denitrification projects is also a signifi-
cant challenge, particularly because of the large
demand for financing through the Clean Water Fund.
4 What could have been done differently to resolve the
challenges more easily?
Given the importance of adequate funding, there is
a need to continually educate and communicate with
the state legislature on the progress of the Nitrogen
Credit Exchange Program and the importance of
sustainable funding for denitrification projects. The
Nitrogen Credit Advisory Board could take time to
work with state legislators to ensure that they are
reading the annual reports and understanding the
effect funding has on meeting permit limits and
achieving the TMDL nitrogen reduction goals.
4 Would this approach be applicable to other water-
sheds? What characteristics would define other candi-
date watersheds?
Several watershed-based permitting and water quality
trading programs have analyzed the Long Island Sound
Nitrogen Credit Exchange Program. In fact, Virginia
largely modeled the state's newly developed water-
shed-based permitting legislation for watersheds in the
Chesapeake Bay on the approach taken in the Long
Island Sound.
4 If the approach were to be applied in another area,
what changes should be made?
Ownership of the program by its participants is essen-
tial. The state cannot provide 100 percent of the funds
necessary for POTWs to implement denitrification
projects. The state needs to get out early and educate
stakeholders on the costs and benefits of the program.
When state legislatures are involved in funding a
program, water program officials need to continually
educate legislators on the program's progress and fund-
ing needs.
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Resources
CTDEP and NYSDEC (Connecticut Department of Environmental Protection and New York State Department of Environmental
Conservation). 2000. A Total Maximum Daily Load Analysis to Achieve Water Quality Standards for Dissolved Oxygen in the
Long Island Sound, .
CTDEP (Connecticut Department of Environmental Protection). 2006. Report of the Nitrogen Credit Advisory Board for the
Calendar Year 2005 to the Joint Standing Environmental Committee of the General Assembly. May 19, 2006.
< www.ct.gov/dep/lib/dep/water/lis_water_quality/nitrogen_control_progra m/2005annrpt.pdf>.
Connecticut Department of Environmental Protection (CTDEP). 2007. 2006 Report of the Nitrogen Credit Advisory Board to
the Joint Standing Environmental Committee of the General Assembly. January 3, 2007.
.
Connecticut Clean Water Fund. No date. .
Note: All Web references current as of July 6, 2007.
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