NC0026051_Denial_19880607

K
State of North Carolina
Department of Natural Resources and Community Development
Division of Environmental Management
512 North Salisbury Street • Raleigh, North Carolina 27611
James G. Martin, Governor June 71 1988 R. Paul Wilms
S. Thomas Rhodes, Secretary Director
Mr. Douglas G. Cullinane
Durham County Engineer
120 E. Parrish Street, Law Building
Suite 100
Durham, NC 27701
SUBJECT: Request for Modification or
Waiver of Monitoring Requirements
FiPDES Permit No. NC0026051
Durham Country WWTP
Durham Countv
Dear Mr. C:311inane:
In ar.cordance with your request £0r. permit modiftc:ration received February
11, 1988, the Division has reviewed the subject Permit. You requested changing
BODS limits to CBODS limits for the subject Permit. The County can receive
limits for CBODS. However, those limits would not be the same as your current
BOD5 limits. Our current allocation methodology relates model predications of
allowable ultimate CBOD to BODS through the use of or. empirically derived CROD
to BODS ratio. Therefore, there is no double -counting and BODS is simply used
as a surrogate to CBOD-ult for ease of compliance monitoring. The same approach
can be used for CBODS. However, the County of Durham will bave to submit data
that will allow a CBOD-ult to CBODS ratio to be empirically determined. If the
County changes to CBODS, your limits will probably become more restrictive. As
another point to consider, you should .realize that APHA is developing a standard
method for long-term BOD measurement and the draft versions of that protocol
discourage the use of nitrogen inhibitors. The three problems associated with
the use of nitrogen 'i.nhfbitors are:
They can also inhibit: CBOT) decay:
2. The effect of the inhibitor diminishes unpredicttibty with time; and
3. The inhibitor can become a substrate and artificially increase
estimates of CBOD. Although this is for long-term BOD tests, it also
has implications in determining appropriate CBOD-utt to CB005 ratios.
Pollution Prevention Pain
P.O. Box 27687, Raleigh, North Carolina 27611-7697 Telephone [phone]
An Equal Oppornmiry AHirrnatiw Action Employer

I
Page 2
In response to your concerns on the toxicity limit, the use of effluent
bioassay as a limit in an NPDES permit is considered to be equivalent to other
limited parameters with respect to responsibilities of the discharger. The
holder of the permit is responsible for meeting all limits even when the
constituent is discharge to a municipality by an indirect source. You commented
that "toxicity when present is unexpected and not predictable and not created by
the POTW" with further implication that the Permittee should not be held
accountable. If this logic is accepted then most other permit parameters would
also not be limited.
You also contend that the State should identify a specific toxic component
and establish a limit for the specific compound. It is obvious the State does
not have the resources to perform these consultant services for all
dischargers. An additional comment by the County suggests that the primary
purpose of the Toxicity Limitation is for control of chlorine. This is
incorrect. The limit is utilized for control of all toxic constituents.
Another comment regards susceptibility of the Ceriodaphnia to minor
effluent effects such as hardness, alkalinity, salinity, and ionic strength for
unacclimated test organisms. First, our laboratory has performed these tests in
surface waters from across the State and found them quite tolerant of normal
variability. With regard to acclimation, historically the viewpoint of
toxicologists has been that ncclilnation is not provided for in -stream, and
therefore not accommodated in the testing. Because the issue of acclimation is
quite complex, we will base our position on the fact that both effluent
fluctuations and natural movement of biological organisms do not allow
acclimation and our testing should not either. It is important to remember that
whole effluent toxicity is not any different than other numerical limits
regarding acclimation. If we allow some sort of accommodation for acclimation
in whole effluent testing then all our numerical standards will also have to
reflect acclimation. Our standards do not, nor do EPA's Criteria Documents
reflect any sort of acclimation other than that received during the testing
period. In other words, the use of whole effluent toxicity tests are treated in
the same manner as our other standards for toxic substances.
You have suggested that the Fathead Minnow be utilized as a test organism
in place of the Ceriodaphnia. A Fathead Minnow chronic test will cost
approximately $2,000.00 compared to the $350.00 Ceriodaphnia test. This may
not be acceptable to the County of Durham. If however, the County would like to
pursue the use of this test, we suggest that you perform several side by side
comparisons of the two protocols to judge relative sensitivities. If the
Fathead test is reasonably close to the Ceriodaphnia then the Division might
consider the alternate test protocol. This decision should be considered with
caution since our laboratory does not routinely perform this type of testing.
We do not currently have the staffing to maintain a quality assurance program to
monitor outside laboratories performing this type of test. We are offering this
as an option for use in negotiations, although we feel that we should remain
with the Ceriodaphnia Test Protocol.
If this decision is unacceptable to you, you have the right to an
adjudicatory hearing upon written request within thirty (30) days following
receipt of this letter. This request must be in the form of a written petition,
conforming to Chapter 150E of the North Carolina General Statutes, and filed
with the Office of Administrative Hearings, Post Office Drawer 1.1666, Raleigh,
North Carolina, 27604. Unless such a demand is made, this decision shall be
final and binding.

Page 3
If you have any questions concerning this permit, please contact Mr. Arthur
Mouberry at 919/733-5083. A
AM/Is
nc el
R. Paul Wilms
cc: Permits and Engineering
Raleigh Regional Office
Technical Services Branch
I

DIVISION OF ENVIRONMENTAL MANAGEMENT
February 25, 1988
MEMORANDUM
TO: Arthur Mouber
THROUGH: Steve Tedder V
FROM: Trevor Clements*( —
SUBJECT: Comments regarding City of Durham's permit modification requests:
Durham County WWTP (NC0026051)
I have reviewed the letters from the City of Durham regarding various permit
modifications and I offer the following comments:
1) Changing BODS limits to CBODS limits:
Durham has made this request for three of their other facilities as well
(Lick Creek, Eno river, Farrington Road). As I stated in my previous memo back
in October of 1987, the City can receive limits for CBODS, however those limits
will probably not be the same as their current BODS limits. Our current alloca-
tion methodology relates model predictions of allowable ultimate CBOD to BODS
through the use of an empirically derived CBOD to BODS ratio-. -Therefore,-there
is no double -counting and BODS is simply used as a surrogate to CBOD-ult for
ease of compliance monitoring. The same approach can be used for CBODS, however
Durham will have to submit data that will allow a CBOD-ult to CBODS ratio to be
empirically determined or DEM can perform this as I proposed earlier this month
(see attached memo 2/22/88).
EPA has done some research regarding differences between the two -_ratios__. In_
a study of 10 facilities in 1981, EPA found the CBOD-ult/CBODS ratio to exceed
the CBOD-ult/SODS ratio by as much as 79 percent and the average difference to
be 21 percent. Of these 10 facilities, 5 utilized activated sludge treatment
technologies. The CBOD-ult/CBODS ratio averaged 2.15 for these 5 facilities,
which represents a 43 percent increase over DEM's routine assumption (1.5) for
- the CBOD-ult/BODS ratio. If this result were applied to a facility -with--a PODS
_ limit of 5 mg/l, the corresponding CBODS limit would be 3.5 mg/l.- My point in
providing this information is that Durham should recognize that, if they switch
to CBODS, their limits will most likely become more restrictive.
As another point to consider, Durham should realize that APHA is developing
a standard method for long-term BOD measurement and the draft versions of that
protocol discourage the use of nitrogen inhibitors. Three problemsareasso-
-- -: - ciatied with the--use-of nitrogen -inhibitors: 1)-they can -also ---inhibit CBOD - 1 - -- - --
decay, 2)_the-effect of the inhibitor diminishes unpredictably with. -time, -and
3) the inhibitor can become a substrate and artificially increase estimates of
CBOD. Granted, this is for long-term BOD tests, but it also has implications in
determining appropriate CBOD-ult to CBODS ratios.

-2-
2) Toxicity limits:
The Division has developed the toxicity testing program in accordance with
the General Statutes and Administrative Codes of North Carolina. The Environ-
mental Management Commission has approved of our program and, therefore, any
philosophical arguments such as those presented in Durham's letter should be
addressed to the Commission. For your reference, I have attached another copy
of the memo prepared by Ken Eagleson with regard to Durham's last request along
these lines.
Please let me know if I can be of further assistance in this matter.
Attachments
JTC
CC: Ken Eagleson
Central Files

T.cWelos
FEB l s isea
i
ON
C[J I
COUNTY OF DURHAM
ENGINEERING OFFICE
February 11, 1988
FEB 17 lei-
16 �t.A DW. of Envirortmew ;-z,,
Mr. R. Paul Wilms, Director !�-A / Ralelgh, N. C.
Division of Environmental Management r✓�',",,,✓
N.C. Department of Natural Resources
and Community Development v
Post Office Box 27687
Raleigh, North Carolina 27611
Re: NPDES Permit #NC0026051
Treatment Plant (WWTP), Durham County
Dear Mr. Wilms:
Pursuant to your letter dated January 11, 1988, (signed by
Arthur Mouberry) and received in this office on January 19, 1988,
the County of Durham hereby requests a waiver or modification under
Regulation 15 NCAC 2B. 0508(b) of permit requirements for Biological
Oxygen Demand-5 day (BOD5), Toxicity. These requirements and the
reasons for our request are discussed below.
With regard to BOD5, we request that the permit be modified to
require Carbonaceous Oxygen Demand (CBOD5) instead of BOD5. Recent
laboratory results indicate that there is significant difference
between BOD5 and CBOD5 in the range of the BOD limits of this
permit. It would seem reasonable to use CBOD5 since the stream model
used by your staff to determine the waste load allocation includes
parameters for both carbonacuous biochemical oxygen demand and
nitrogenous oxygen demand. Without this change in our permit, we
could be penalized for the Ammonia (NH3) remaining in our effluent,
in both the limit for BOD5 and NH3. The requirements of 15 NCAC 2B.
0500 appear to be out of date on this issue. These regulations do
not refer to the most recent addition of "STANDARD METHODS' or 40
CFR Part 136 which deal with this issue effectively. The 16th
edition of "STANDARD METHODS", dated 1985, Page 526, includes the
following statement:
"Measurements of BOD that include both carbonaceous
oxygen demand and nigrogenous oxygen demand generally
are not useful; therefore, where appropriate, an
120 E. Parrish Street, Law Bldg., Suite 100, Durham, N.C. 27701 [phone]
Equal Employment/Affirmative Action Employer

inhibiting chemical may be used to prevent ammonia
oxidation. With this technique, carbonaceous and
nitrogenous demands can be measured separately. The
inclusion of ammonia in the dilution water demonstrates
that there is no intent to include the oxygen demand of
reduced nitrogen forms in the BOD test. ---Currently,
many biological treatment plant effluents contain sig-
nificant numbers of nitrifying organisms. Because
oxidation of nitrogenous compounds can occur in such
samples, inhibition of nitrification is recommended
for samples of secondary effluent, for samples seeded
with secondary effluent, and for samples of polluted
waters."
It is interesting to note that the above quote is from Section
507 Oxygen Demand (Biochemical) of the 16th edition of 'STANDARD
METHODS' which is the environmental Protection Agency's (EPA's)
approved method for (BODS) as shown in Table IB of 40 CFR Part 136
as contained in the Federal Register, Vol. 51, No. 125, dated June
30, 1986.
With regard to toxicity, the permit appears to require toxicity
testing and compliance at a 99 percent level. We would like to
refer you to a recent article in the August, 1987, JOURNAL of the
Water Pollution Control Federation by Max M. Grimes titled, "The
Impact of EPA's BioMonitoring Policy of POTW's". (Article was
provided previously to you in a City of Durham letter dated
September 17, 1987, concerning Northside WWTP). This article points
out many problems with applying toxicity testing limits to POTW's.
We do not object to toxicity testing as a monitoring requirement.
However, to subject the County to potential enforcement action due
to inability to achieve a specified toxicity limit when the County
has little control over the problem, does not seem appropriate.
Enforcement should be limited to failure to monitor, failure to
pursue a toxicity reduction evaluation and meet milestone dates, or
for deficient operations of an approved pretreatment program. The
permit should recognize that toxicity when present is unexpected and
not predictable and not created by the POWT. In our opinion, 15
NCAC 2B. 0208 requires the State to set a concentration limit on the
"toxic substance" once identified by the State. The emphasis should
be on identifying the toxic substance with the County and State
working together rather than through enforcement action. The plant
is not specifically designed to remove toxicity and failure of a
toxicity test does not reflect poor design, poor operation,
reluctance to build new facilities or a willful act by the County.
If this limit on toxicity is intended to address chlorine
toxicity, then we feel that it would be better addressed through a
numeric standard and permit limit since chlorine analysis is less
expensive, easier, and can be performed at much greater frequency
than biomonitoring.

We also have concerns about the test procedure being required.
The Ceriodaphnia bioassay can be susceptible to many minor effects
of otherwise harmless constituents such as hardness, alkalinity,
salinity and ionic strength changes for test organisms that have not
been acclimated. For example, we have observed daphnia in the final
clarifier at the same time that the plant effluent failed the
toxicity test. We would like to have the option of using either
Ceriodaphnia or the Fathead minnow in carrying out this monitoring
as a possible way of avoiding some of the problems inherent in the
test organisms.
Your consideration of these possible modifications of the
proposed permit would be appreciated. Also, although your letter
cited Regulation 15 NCAC 2B 0508(b) as being available to us to
pursue these modification requests, we have some concern that that
regulation may not be so broad as to cover waiver modification in
all of these areas discussed above. We defer to the Division of
Environmental Management's interpretation of its own regulations and
therefore are utilizing the suggested procedure. However, if this
procedure is not available, we ask that these requests for
modifications also be considered requests for an adjudicatory
hearing in order to preserve our rights on all of these issues.
sincerely,
Douglas G. Cullinane, P.E.
County Engineer
DGC/kn
CC: Mr. Robert Van Tilburg, Division of Environmental Management
North Carolina Department of Natural Resources and
Community Development, Post Office Box 27687, Raleigh,
North Carolina 27611
Mr. William Telford, Jr., Superintendent of Plants, Department
of Water Resources, 101 City Hall Plaza, Durham, North
Carolina 27701
Mr. John P. Bond, III, County Manager, 102 E. Main Street,
Durham, North Carolina 27701
Mr. T. Russell Odom, County Attorney, 102 E. Main Street,
Durham, North Carolina 27701

October 22,1987
To: Trevor Clemmens
From: Ken Eagleson
Subject: Comments Regarding Whole Effluent Toxicity Testing in the
Durham Eno, Lick Creek and Farrington Road Permits
The use of effluent bioassay as a limit in an NPDES permit is considered to
be equivalent to other limited parameters with respect to responsibilities of the
discharger. The holder of the permit is responsible for meeting all limits even
when the constituent is discharged to a municipality by an indirect source. The
comment from the City of Durham states that "toxicity when present is
unexpected and not predictable and not created by the POTW" with further
implication that they should not be held accountable. If this logic is accepted then
most other permit parameters should also not be limited. It is important that
whole effluent toxicity testing remain as a limited parameter.
The City of Durham also contends that the State should identify a specific
toxic component and establish a limit for the specific compound. It is obvious the
State does not have the resources to perform these consultant services for all
dischargers. An additional comment by the City suggests that the primary
purpose of the Toxicity Limitation is for control of chlorine. This is incorrect.
The limit is utilized for control of all toxic constituents.
Another comment regards susceptibility of the Ceriodaphnia to minor
effluent effects such as hardness, alkalinity, salinity and ionic strength for
unacclimated test organisms. First, our laboratory has performed these tests in
— - - - — -surface waters f om acrosMe state and found them quite tolerant of normaT -
variability. With regard to acclimation, historically the viewpoint of toxicologists
has been that acclimation is not provided for in -stream and therefore not
accommodated in the testing. I suggest that the issue of acclimation is quite
complex and we should base our position on the fact that both effluent
fluctuations and natural movement of biological organisms do not allow
acclimation and our testing should not either. It is important to remember that
whole effluent toxicity is not any different than other numerical limits regarding
acclimation.. If we allow some sort of accommodation for acclimation in whole
- effluent testing then all our numerical standards will also -have -to reflect -
acclimation. Our standards do not, nor do EPA's Criteria Documents reflect any
_ sort of acclimation other than that received during the testing period. In other

words, the use of whole effluent toxicity tests are treated in the same manner as
our other standards for toxic substances.
The City has suggested that the Fathead Minnow be utilized as a test
organism in place of the Ceriodaphnia. I would like to point out that a Fathead
Minnow Chronic test will cost approximately $2000.00 compared to the $350.00
Ceriodaphnia test. This may not be acceptable to the City of Durham. If however
the City would like to pursue the use of this test I would suggest that they perform
several side by side comparisons of the two protocols to judge relative
sensitivities. If the Fathead test is reasonably close to the Ceriodaphnia then the
Division might consider the alternate test protocol. This decision should be
considered with caution since our laboratory does not routinely perform this type
of testing. We do not currently have the st2ffmg to maintain a quality assurance
program to monitor outside laboratories performing this type of test. I am
offering this as an option for use in negotiations although I feel that we should
remain with the Ceriodaphnia Test Protocol.
The City cites the regulation 15 NCAC 02B.0208 as requiring the State to
establish specific limits for specific compounds and restrict these numerically in
the permit. While I do not disagree with this approach I feel that another section
of our regulations 15 NCAC 0213.0211 L requires the use of whole effluent
toxicity testing using chronic techniques. 15 NCAC 02B.0206 3 specifies that the
toxicity limits be allocated at 7Q10. Attached are additional citations regarding
regulatory authority and toxicity testing for your review.
cc: Steve Tedder

DIVISION OF ENVIRONMENTAL MANAGEMENT
January 22, 1987
MEMORANDUM
TO: Steve Tedder
Alan Klimek
Dennis Ramsey
Regional water Quality Supervisors
Regional Supervisors
FROM: George T. Everett 4-;r_ :��
SUBJECT: Water Quality Toxics Program
Over the past few years the aquatic toxicology program has proven
extremely valuable in our efforts to ensure protection of the surface
waters of North Carolina. The staff of both headquarters and the
regional offices have performed extremely well in the implementation of
this very important aspect of our program.
As each of you are aware, our approach, to date, has been to
address whole effluent toxics evaluations prior to chlorination. This
strategy was implemented with the uAderstanding that chlorine (which -
has toxic properties) would be addressed by a national policy and
possible water quality standards.
The divisional staff as well as EPA regional and headquarters
staffs have been evaluating whole effluent toxics strategies, as well
as the chlorine issue for several years. The national policy for tox-
ics control and the increased emphasis on toxics control during third
_ _____round��rmittingxequires a modi€icaticnto--our-activities within the -
Water Quality Program relating to toxics control.
Therefore, effective immediately, the staff of the water Quality
Program is directed to initiate the incorporation of whole effluent
toxic limitations into NPDES issued permits by the following crite-
rion:
A. All major industrial and major municipal permits issued will
contain appropriate whole effluent toxic limits and monitoring
requirements;.
B. All facilities which have complex wastewaters-; whether classi-
fied major or minor are to have whole effluent toxic limits,
incorporated into permit limits and monitoring requirements at
reissuance. Complex wastewaters include any waste other than
domestic waste and chlorine;

C. Domestic wastewaters (100%) with only chlorine as an additive
and not classified a major discharger will not, at this time,
receive whole effluent toxic limitations.
In addition to these directives, all limitations, monitoring,
etc., whether required by permit, administrative letter, or compliance
activities, will he applied to end -of -pipe treatment (post -chlorination).
All previously affected facilities that are currently conducting
self -monitoring for toxics will be notified that the sample collection
point is to be changed to post -chlorination. This notification will he
handled by the Technical Services Branch and regional staff will be
advised by copy. All consultants wiLl be notified by the Technical
Services Branch as to these directives by letter.
All permits which have been issued with whole effluent toxic lim-
itations will be modified to reflect the changes individually.
_ Most of you are aware that the staff has been developing an
abbreviated mini -chronic bioassay test. This work has been completed
and the method approved by EPA as acceptable in NPDES permits. This
approval is very significant economically. The previously approved
full range chronic tests ranged in cost from $1000-$2000/per test. The
North Carolina abbreviated test is now being conducted by consultants
for costs as low as $250/test. All limits (chronic) to be incorporated
into permits will specify the abbreviated test procedure. -
- We view this as a major positive step in conducting our activities
to meet both state and federal laws and regulations. I urge each of
You to discuss this issue with your respective staffs to allow imple-
mentation by an informed staff. -
Attached to this memorandum is a brief summary which discusses
national policy, third round permitting strategy and the statutes and
regulations which necessitate the actions detailed in this correspon-
dence.
If there are questions, please contact myself or Steve Tedder at
733-5083.
cc: R. Paul Wilms
L. P. Benton, Jr. -
Arthur .Mouberry -
Ken Eagleson
Bob DeWeese
Larry Ausley

RE: Biomonitoring Requirements and Limitations
On March 9, 1984, EPA issued a national policy statement recom-
mending that state and federal regulatory agencies use biological
techniques as a complement to chemical -specific analysis when assessing
effluent discharges toxicity and use effluent toxicity as a control
parameter in writing permit limits. This statement•of national policy
was published in the Federal Register/volume 49, No. 48/Friday, March
9, 1984/Notices.
Section 101(a)(3) of the national Clean Water Act states "it is
the national policy that the discharge of toxic pollutants in toxic
amounts be prohibited;"
The national policy statement, which is entitled, "Policy for the
Development of water Quality -Based Permit Limitations for Toxic Pollu-
tants" further states "to control pollutants beyond Best Available
Technology (BAT) Economically Achievable, secondary treatment, and
other Clean water Act technology -based requirements in order to meet
water quality standards, the EPA will use an integrated strategy con-
sisting of both biological and chemical methods to address toxic and
nonconventional pollutants from industrial and municipal sources. EPA
and the States will use biological techniques and available data on
a ..<>. chemical effects to assess toxicity impacts and human health hazards
based on the general standard of no toxic materials in toxic amounts.
Under section 308 and section 402 of the Clean Water Act, EPA or the
State may require NPDES permit applicants to provide chemical, toxic-
ity, and instream biological data necessary to assure compliance with
standards. Where violations of water quality standards are identified
or projected, the State will be expected to develop water quality -based
effluent limits for inclusion in any issued permit. where there is a
significant likelihood of toxic effects to bi_gta_ia the -receiving
vaTer, EPA and the States may impose permit limits or effluent toxicity
and may require an NPDES permittee to conduct a toxicity reduction
evaluation."
The Environmental Protection Agency has also issued the Third
Round Permits Issuance Strategy. This strategy for the next generation
Of NPDES permits, From FY87-FY91, is directed toward implementation of
the national policy. The principal goal of the Third Round Permit
Issuance Strategy is to eliminate toxicity in receiving waters that
results from point source discharges. Water quality -based controls for
toxics and toxicity will be routinely incorporated into third round
- -permits. Third round permits for all major industrial and _municipal
dischargers should contain whole effluent toxicity testing requirements
and limitations. Toxicity testing requirements and limitations should
also be required for all minor permittees suspected of contributing to
receiving water problems. -

To put the national policy in perspective to State laws, regula-
tions and statutes, one should refer to General Statute (G.S.) 143-211,
Chapter 143, Article 21 of the North Carolina Environmental Management
Laws. G.S. 143-211 is the declaration of public policy and states "It
is hereby declared to be the public policy of this State to provide for
the conservation of its water and air resources. Furthermore, it is
the intent of the General Assembly, within the context of this Article,
to achieve and to maintain for the citizens of the State a total envi-
ronment of superior quality." This same statute further states "Stan-
dards of water and air purity shall be designed to protect human
health, to prevent injury to plant and animal life, to prevent damage
to public and private property, to insure the continued enjoyment of
the natural attractions of the State."
General Statute 143-215(a) states "The Environmental Management
Commission is authorized and directed to develop, adopt, modify and
revoke effluent standards and limitations and waste treatment manage-
ment practices as it determines necessary to prohibit, abate, or
control water pollution. The effluent standards or limitations or
_management practices may provide, without limitation, standards or
limitations or management practices for any point source or sources;
standards, limitations, management practices, or prohibitions for toxic
wastes or combinations of toxic wastes discharged from any point source
or sources; and pretreatment standards for wastes discharged to any
disposal system subject to effluent standards or limitations or manage-
ment practices."
To further correlate these statutes with the national policy, G.S.
143-215(c) further states "In adopting effluent standards and limita-
tions and management practices the EMC shall be guidedbythe same
considerations and criteria set forth in federal law for the guidance
of federal agencies administering the Federal Water Pollution Control
Program."
Monitoring requirements for discharges are also incorporated into
G.S. 143-215.66, which states "All persons subject to the provisions of
G.S. 143-215.1 who cause such discharges or emissions shall establish
and maintain adequate water and air monitoring systems and -report the ---
data obtained there from the EMC."
The North Carolina Administrative Code (NCAC) Title 15 Subchapter
2B, also provides guidance to the Division relating to toxics control.
Within. this document a toxic substance is defined as "Any substance
or combination of substances including disease -causing agents, which
after discharge and upon exposure, ingestion, inhalation, or assimila-
tion into any organism, either directly from the environment or indi-
rectly by ingestion through food chains, will cause death, disease,
behavioral abnormalities, cancer, genetic mutations, physiological
malfunctions (including malfunctions in reproduction) or physical
deformities -in such organisms or their offspring."

NCAC 2B.0206 also establishes the flow design criteria for toxic
limitations as: "The governing flow criterion for water quality stan-
dards, including toxic substances, generally shall be the minimum
average flow for a period of seven consecutive days that has an average
recurrence of once in 10 years (7Q10)."
NCAC 2B.0208 also addresses toxic substances as well as NCAC
2B.0211(L) which states: "Toxic substances - only such amounts, whether
alone or in combination with other substances or wastes (whole efflu-
ent) will not render the waters injurious to public health, secondary
recreation, or to aquatic life and wildlife (either through chronic or
acute exposure or through bioacummulation), or impair the waters for
any designated uses, .... acceptable levels of chronic exposure may be
determined by test procedures deemed appropriate by the director;
Additional reference materials relating to methods and procedures
involving whole effluent toxicity testing include the following:
Methods for
to
asuring the Acute Toxicity of Effluents
and Marine Oroanisms. EPA Document
March, 1985
Short -Term Methods for Estimating the Chronic
Toxicity of Effluents and Receiving Waters to
Freshwater -Organisms. EPA Document 600/4-85/014
December 1985
North Carolina Ceriodaphnia Chronic Effluent
Bioassay Procedure (Revised December 1986)
Technical Support Document for Water Quality -
based Toxics Control. USEPA, September, 1985.

DIVISION OF ENVIRONMENTAL MANAGEMENT
February 22, 1988
MEMORANDUM
TO: Steve Tedder, Acting Chief
Water Quality Section V�!
FROM: Trevor Clements, Supervisor\``
Technical Support Unit (�
SUBJECT: Technical considerations of using CBODS versus BOD5 as
measurements of compliance
Background
The issue of using CBOD5 measurements rather than BODS measurements for
compliance purposes has been raised by several municipalities (e.g. Winston-
Salem, Lexington, Durham, etc.). In most cases, the permittee has pointed to
two reasons for changing to CBOD5: 1) APRA Standard Methods (16th Edition)
encourage the use of nitrogen inhibitors in measuring BOD5, which effectively
provides a CBODS measurement, and 2) The presence of both NH3-N and nitrifying
bacteria in the effluent can increase the BOD within the first 5 days such that,
even if the facility is meeting 2 mg/l NH3-N (DEM's typical lower limit on ammo-
nia nitrogen) and a low CHOU, they may not be able to comply with their BOD5
requirement. There are both pros and cons associated with the use of CBODS and
the following is intended for your guidance in making decisions_ regarding
requests by permittees to switch to CBOD5.
CBOD5 refers to the amount of carbonaceaous biochemical oxygen demand that
is exerted within a given volume of water over a period of 5 days._ As opposed
to total BOD5, an effort must be made to remove the influence of any nitrogenous
component of the demand. Prior to advances in wastewater treatment with regard
to nitrification, this was not thought to be necessary since most nitrogen
demand was not exerted until 12-20 days into the sample measurement --the period
necessary to build up an adequate population of nitrifying bacteria necessary to
oxidize the ammonia nitrogen present in the wastewater. However, with many
advanced treatment plants routinely employing nitrification, nitrifying bacteria
are often present in the effluent and, subsequently, the nitrogen may begin oxi-
dizing within the first 5 days of the HOD test. It is thought that this process
can be prevented through the use of nitrogen inhibitors.
Some facilities have stated that DEM is unfairly double -counting the effect
of nitrogen by limiting both BOD5 and NH3-N, since BOD5 measured without inhi-
bition may be influenced by. NH3-N. However, this notion is not correct. It is
important to remember that BODS and NH3-N are simplified measurements employed
for ease of facility compliance monitoring. In actuality, a facility's limits
are based upon the predicted impacts of carbonaceous and nitrogenous biochemical
oxygen demand (CBOD and NBOD, respectively) instream. These parameters, in
turn, are related to the compliance parameters of BOD5 and NH3-N for implemen-
tation to an NPDES permit. BODS must be empirically related -to BOD5 through the
use of long-term HOD tests, whereas NH3-N is stoichiometrically related to NBOD.
Therefore, as long as the CBOD:BOD5 ratio employed is representative of a
discharge, no double -counting has occurred. Nonetheless, this does not address

the difficulties associated with BOD5 measurement as stated above.
Although there has been some skepticism over use of nitrogen inhibitors for
long term BOD measurements, their use in measuring BOD5 appears to be accepted
as is demonstrated by their inclusion in the Standard Methods (APHA, 1986). The
type of problems that occur with the long term tests (i.e. weakening effect of
inhibitors over time, the development of a BOD substrate with constant addition
of inhibitor over time, and the suppression of CBOD with the addition of too
much inhibitor over time) do not appear to be of consequence with regard to
short term, 5 day tests. Therefore, DEM should consider allowing the use of
inhibited samples (CBOD5) for compliance purposes. However, several steps must
be taken prior to simply changing a permit monitoring requirement.
Since all permit limits for BOD are based upon CBOD.BOD5 relationships, new
CBOD:CBOD5 relationships and, subsequently,. effluent CBOD5 limits_.for a given
effluent will have to be established prior to a change in the monitoring. A one
to one correspondance between BOD5 and CBODS appears to be unlikely. A study of
ten facilities by EPA (1981) found the CBOD:CBOD5 ratio to exceed the CBOD:BOD5
ratio by as much as 79 percent, and the average difference to be 21 percent.
Five of these facilities utilized activated sludge technologies and the
CBOD:CBODS ratio for these plants averaged 2.15, which is a 43 percent increase
over DEM's routine assumption (1.5) for the CBOD.BOD5 ratio. In review of this
study, variation appeared to depend on the level of NH3-N and NO2+NO3 present in
the effluent, which supports the concern stated above.
Recommendations
It is recommended that at least 3 long term tests with concurrent CBOD5 and
BOD5 measurements be performed on any facility prior to changing their NPDES
permit to reflect compliance for CBOD5. Samples for the 3 tests should be taken
on separate days to reflect differences in facility operation in order to obtain
a clearer picture of the true range of operation. These tests will he used to
determine an appropriate CBOD:CBOD5 ratio as a basis for a revised permit limit.
Until a standard method for long term HOD tests is promulgated (still in draft),
DEM should perform the long term tests upon a letter of request by the facility.
Apparently, some facilities may already be submitting CBOD5 measurements for
compliance rather than BODS as is currently required in all permits. It would
be prudent to send a letter out to all permittees (and certified labs) with BOD
monitoring requirements stating that total BOD5 measurements (with no inhibition
of nitrogen demand) must be submitted unless permission has been granted by DF,M
(and EPA?) to submit CBOD5 measurements. The letter could outline the steps
required for permit modification and warn the permittee that a change to CBOD5
will likely result in a CBOD5 effluent limit that is lower than their current
BOD5 limit.
i do not know what kind of response such a letter will solicit. However,
this point (regarding no use of nitrification inhibitors unless permission is
given) must be made in order to provide for consistency throughout the state.
It is not fair to those permittees that accurately report effluent concentra-
tions in BODS, for the state to ignore those who submit data that does not
reflect true compliance with their permit requirements. At the same time, DEM
must address the fact that Standard Methods recommends the use-oof-ifiRlb tors in
measuring "BOD5." Such a letter would clarify DEM's position and, at the same
time, offer an alternative to those facilities that felt squeezed by the

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limitations of the total BOD5 test.
In the mean time, it might be wise for DEM to pick a few candidates and
begin collecting additional long term and CBOD5 data. This will help iron out
problems before the procedure is actually applied. In addition, it will allow a
data base to begin compiling. I suggest that facilities with various levels of
nitrification be chosen for this pilot study, since this appears to be a key
element.
Please let me know if further assistance in this matter is needed.
CC: Dennis Ramsey
Bob DeWeese -
Arthur Mouberry -
Jay Sauber -