NC0023973_Permit Modification App_20150316

Cape Fear
Public Utility Authority
Stewardship.Sustainability.Service.
March 6, 2015
Mr. Jeff Poupart
Wastewater Branch Supervisor
N.C. Department of Environment and Natural Resources RECEIVED/DENR/DWR
Division of Water Resources
1617 Mail Service Center MAR 1 6 2015
Raleigh,N.C. 27699-1617 Water Quality
Permitting Section
RE: Cape Fear Public Utility Authority
M'Kean Maffitt(Southside) Wastewater Treatment Plant
Pending 24 MGD NPDES Permit Modification Application—CFPUA SSWWTP NPDES
Permit NC0023973 —Additional Modification Request—Whole Effluent Toxicity(WET)
Testing
Dear Mr. Poupart:
The current CFPUA SSWWTP NPDES permit NC0023973 establishes an acute WET (AWET)
test requirement-pass/fail methodology for determining acute toxicity in a single effluent
concentration. It is performed quarterly as a Ceriodaphnia dubia 24 hour static test upon a
sample consisting of 90%plant effluent as a means of demonstrating no significant acute
mortality. The SSWWTP has experienced previous difficulty in consistently passing its AWET
test.
Beginning in September 2012 intermittent whole effluent toxicity to Ceriodaphnia dubia had
been observed. Because the SSWWTP had demonstrated a strong record of compliance with
NPDES permit WET requirements prior to that period, the CFPUA informally began Toxicity
Identification Evaluation(TIE) procedures by conducting preliminary testing in an effort to
identify the cause of toxicity. Prior to September 2012, SSWWTP WET testing performed by
ETS and Pace had not observed toxicity in the SSWWTP effluent in more than two years of
regular quarterly NPDES monitoring. Furthermore,the effluent was never reported to be toxic
over at least the previous seven years. Meritech began serving as the provider of WET testing
beginning in July 2012 with the September 2012 results being the first indicator of toxicity.
Meritech and ETS conducted preliminary TIE testing and split sample analysis. Tetra Tech
assisted CFPUA with a full Phase I TIE and Phase II testing in early 2013. As a result of these
investigations, several observations were identified: (a) ammonia levels seemed to influence
WET testing outcomes; minor process modifications were considered in an effort to reduce
effluent ammonia levels; (b)vessel headspace conditions seemed to influence WET testing
outcomes; test procedure manipulations were tried with open and closed test vessels; (c)
significant pH shifts were noted during the conduct of the tests which also seemed to influence
the WET testing outcomes.
235 Government Center Drive,Wilmington, N.C. 28403
Phone: [phone] Fax: [phone]
WASTEWATER TREATMENT: www.cfpua.org

Cape Fear
Public Utility Authority
Stewardship.Sustainability.Service.
Late 2012 through the middle of 2013 seemed to be characterized by mixed passing and failing
AWET test results. At about this time,CFPUA began considering use of the Chronic WET test
(CWET) in lieu of the AWET. In preparation for conducting CWET testing,the NCDENR
Division of Water Quality Surface Water Protection Section was consulted in an effort to
establish the IWC applicable to our conditions; in their 07.03.2013 email,a copy of which
accompanies,they established the IWC at 3.03%. Also about this time,the NCDENR Aquatic
Toxicology Unit offered to perform supplemental tests, particularly CWET, and to assist our
analysis and interpretation of the data. From about the middle of 2013 until the end of 2014, we
consistently passed both the quarterly AWET and CWET tests. In December 2014,we
unfortunately experienced another AWET failure,but passed the CWET. Follow-up testing
during January yielded passes for both AWET and CWET tests.
During the course of these deliberations,NCDENR had maintained that the preferred toxicity
testing assignment when the IWC is known is chronic testing(reference 11.04.2013 ATU
summary report and CFPUA 01.14.2014 correspondence; copy accompanies). Given the
previously documented uncertainties in SSWWTP WET testing compliance,we believe that the
best and most prudent course of action is to transition to use of the CWET test within our
NPDES permit as soon as practical. NCDENR is currently reviewing CFPUA's 24 MGD major
NPDES permit modification application which was submitted in late 2014. If DWR is receptive
to acceptance of the 3.03% IWC, CFPUA would request DWR consider incorporating the
CWET requirement into the NPDES for the existing 12 MGD secondary facility as well as all
future flows(16 MGD; 20 MGD; 24 MGD)under the currently applicable advanced level of
treatment prescribed for the Cape Fear River estuary.
Please let us know at your earliest convenience if this request can be accommodated, and let us
know if there are any questions or concerns we can address.
Sincerely,
Kenneth L. Vogt,Jr.,P.E. BCEE
Wastewater Treatment Superintendent
cc: Jim Flechtner
Frank Styers
Beth Eckert
Milton Vann
Craig Wilson
Bryan Blake(McKim& Creed)
Attachments
235 Government Center Drive,Wilmington, N.C. 28403
Phone: [phone] Fax: [phone]
WASTEWATER TREATMENT: www.cfpua.org

Ken Vogt
From: Pam Ellis
Sent Wednesday,July 03,2013 11:45
To: Ken Vogt
Subject FW:South Side Dilution Factor-from Jim McKay
Attachments: Dilutation factor for CFPUA Southside WWTP.xlsx
•
From: Mckay,James [mallto;james,mckay nadenr.aovl
Sent: Wednesday,July 03, 2013 10:55 AM
To: Pam Ellis
Cc: Gore, Deborah
Subject: South Side Dilution Factor
Please contact me if you have further questions.
Sincerely,
Jim McKay,Environmental Engineer
NC DENR/Division of Water Quality/Surface Water Protection Section
Point Source Branch
1617 Mail Service Center, Raleigh,NC 27699-1617
919/807-6404(work);919/807-6489(fax)
**Please note,my email address has changed to [e-mail]
E-mail correspondence to and from this address may be subject to the North Carolina Public Records law and may be
disclosed to third parties.

Calculation of Dilution Factor for CFPUA Southside WWTP.
Goal: To evaluate Tetra Tech's modeling work in 2001 report to determine dilution factors
to be used to perform headworks analysis for Wilimgton's Southside WWTP,and for
performing RPAs.
Basis:
From the internal document MIXING ZONES IN NORTH CAROLINA dated July 23,1999,
(1)Dilution is calculated as: D =(Om+CU/QW
where Q,is the maximum permitted wasteflow,and
Q„is the critical upstream streamflow,generally the summer 7Q10 flow.
From Tetra Tech's report dated May 2001,page 4-11,the minimum dilution for the
Southside WWTP is listed as 33 near the bottom.
The permitted flow for the Southside plant is 12.0 MGD x 1.55 CFS/MGD=18.6 CFS.
Entering these values into Equation(1)above gives:33=(18.6+Qu)/18.6.
Multiply both sides by 18.6 to get: 613.8=(18.6+Qu)
=613.8-18.6=595.2 CFS. This is the calculated"S7Q10".
(2)IWC=[Qw/(Qw +Qu)]X 100%=18.6/(18.6+595.2)X 100%=3.03%. Round to 3%for WET testing.
(2.a) IWC=1/Dilution X 100%=1/33 X 100%= 3.0% Check
Jim McKay
6 27 2012

Cape Fear
Public Utility Authority
Stewardship.Sustainability.Service.
January 14, 2014
Cindy Moore, Unit Supervisor
Aquatic Toxicology Unit/Environmental Sciences Section
North Carolina Division of Water Resources/DENR
1621 Mail Service Center
Raleigh, NC 27699-1621
Dear Ms. Moore:
Subject: Voluntary Toxicity Identification Evaluation for M'Kean Maffitt WWTP
Permit Number NC0023973
Enclosed for your review is a Toxicity Identification Evaluation(TIE)report completed by Tetra Tech, Inc.
for the M'Kean Maffitt WWTP, NC0023973. We began experiencing sporadic acute toxicity failures in
September 2012. Following exhaustive investigation by staff during the fall of 2012 and the winter of
2013 we decided that a more formal approach was needed and contracted with Tetra Tech in March
2013 to conduct an analysis of existing toxicity and plant operational data. We also asked they conduct
a TIE to aid with identifying the root cause of the toxicity. The July 15, 2013 TIE report summarizes their
findings and includes seven attachments: A through G. This report should not be considered conclusive,
adopting its findings as accepted for implementation,or representing the final position of the Authority.
We sincerely appreciate the investigative support provided by you and your staff in the DWR Aquatic
Toxicology lab. Your assistance with evaluating results from certified laboratories to determine accuracy
of reported results provided insight to the complexity of our toxicity problem. Split sample laboratory
results have often been vastly different between labs;frequently one lab has reported a "Pass"and the
other lab a"Fail. Your findings along with those of Tetra Tech, Inc.indicate that the acute toxicity
observed in M'Kean Maffitt effluent is being caused by extreme rise in pH during the toxicity testing
period which results in a rise in concentration of un-ionized ammonia. The amount of un-ionized
ammonia is affected by small differences in pH and may explain disparity between lab results. While
there is some evidence leading to this conclusion, I don't believe the Authority fully accepts this finding
as being conclusive and exclusive as unanswered/unaddressed questions remain.
Toxicity testing results using closed vessels versus open cups confirms that pH rise is correlated with
mortality of test organisms for those samples reported as"Fail." Not only has the cause of extreme rise
of pH In samples not yet been fully explained,it does not simulate actual field conditions. Rising pH
during toxicity testing was not reported for most samples taken prior to September 2012. Although the
evidence points towards pH and related un-ionized ammonia concentration as a possible cause,we
believe that the variability of testing results leaves open the possibility for some constituent other than
ammonia being the source of toxicity.
We appreciate your offer to perform chronic testing to assist us with determining the effect of our
effluent on mortality and reproduction. Three chronic testing events have been performed and all
results indicate no toxicity expressed at dilutions well above in-stream waste concentrations (IWCs)
235 Government Center Drive, Wilmington, NC 28403
t: 910-799-6064 f: 910.799-6066 www.cfpua.org

NM Cape Fear
Public Utility Authority
Stewardship.Sustainat ty.Service.
believed representative of the volumes,confluence location,and mixing characteristics of the M'Kean
Maffitt plant with the Cape Fear River, We are requesting your assistance with conducting one
additional chronic test in March 2014. This will provide us with four quarters of monitoring to cover all
seasons. We are hoping that chronic testing continues to have consistent results and does not
demonstrate extreme variability as we have observed with acute testing.
You indicated in the summary report sent to us November 4,2013 that"...the preferred toxicity testing
assignment when the IWC is known" is chronic testing. While all CWET efforts to date are very
promising,and although we are considering a request to change our toxicity test assignment, in the
meantime we recognize the need to continue to investigate the root cause of acute toxicity. We remain
curious about anomalies in AWET results, including varying results obtainable in static renewal,non-
renewal,flow through, open system and closed system options. In addition,and even though this plant
was not designed for ammonia conversion or nitrogen removal,we continue to investigate and
implement plant adjustments and changes intended to reduce or eliminate effluent toxicity. We are
evaluating these changes and adjustments specifically as they relate to their impact on toxicity testing
results. Split sample toxicity testing results for monitoring performed in December 2013 were reported
as a "Pass"from both labs with 0%mortality.
We plan to continue to be proactive with our investigation of intermittent toxicity. Thank you for the
collaborative support provided to aid with resolving our toxicity problem. If you have any questions
about the TIE report, please feel free to call me at 910.332.6586 or email me at [e-mail].
Sincerely,
Kenneth L.Vogt Jr., P,E., B.0 E.E.
Wastewater Treatment Superintendent
Copies: J. Flechtner,M. Richardson, B. Eckert,P. Ellis,T.Clements
235 Government Center Drive, Wilmington, NC 28403
t: 910-799-6064 f: 910-799-6066 www.cfpua.org

Division of Water Resources
November 4,2013
MEMORANDUM
To: Milton Vann
ORC, M'Kean Maffit Southside WWTP
Through: Cindy A. Moore
Supervisor,Aquatic Tox oology Branch
From: Carol Hollenkamp
Environmental Sen r pecialist,Aquatic Toxicology Branch
Subject: Summary of the Whole Effluent Toxicity Tests Performed by the Aquatic
Toxicology Branch Laboratory for M'Kean Maffit Southside WWTP between
June and September 2013.
PURPOSE
This report summarizes the Whole Effluent Toxicity(WET)tests conducted by the Aquatic Toxicology
Branch(ATB)laboratory for the Cape Fear Public Utility Authority's(CFPUA)M'Kean Maffitt Southside
WWTP(SSWWTP)between June and September 2013. The intent is to provide supplemental data to assist
with the current study being performed by CFPUA and its consultant,Tetratech,to identify and solve the
toxicity issues that SSWWTP has been experiencing. This report does not provide a detailed analysis of all
the tests and analyses that CFPUA has conducted,as that will be in CFPUA's final report. ATB will be
conducting at least one additional test in December 2013 and this information should further assist in
resolving the unusual and intermittent toxicity issues that SSWWTP has been experiencing.
BACKGROUND
SSWWTP(NC0023973)began experiencing intermittent toxicity failures on acute pass/fail Ceriodaphnia
dubia tests in September 2012. The failure that occurred in September 2012 was SSWWTP's first failure
that involved using a North Carolina(NC)certified laboratory on an acute daphnid test since 1999.
After the September 2012 failure,SSWWTP began proactively investigating the cause of the failure and
initial investigations indicated that ammonia may be the cause of toxicity. In January 2013,the facility
began splitting effluent samples between two NC-certified laboratories. The intermittent nature of the
failures has occurred both: 1)when splitting effluent samples among laboratories and 2)from quarter to
quarter at the same laboratory. Split tests have been performed using the following five laboratories:
Environmental Testing Solutions, Inc.(ETS); Meritech Inc.;Pace Analytical Raleigh;Tetratech; and the DWR
ATB Laboratory. ETS,Meritech,and Pace Analytical Raleigh are all certified to conduct acute Ceriodaphnia
tests for NPDES compliance in North Carolina.

Most of the failures have had a large increase in pH from the beginning of the test to the end of the test;
however,not all tests with large increases in pH have failed. The EPA"Acute Manual" notes in Section 9.5.9
that"pH drift during acute,static-renewal,or non-renewal toxicity tests may contribute to artifactual
toxicity when ammonia or other pH-dependent toxicants(such as metals)are present. This problem can be
minimized by conducting a test in a static-renewal mode rather than a non-renewal mode,or the problem
can be avoided by conducting the test in a flow-through mode,rather than a static-renewal or non-renewal
mode" (USEPA 2002). SSWWTP does have high ammonia levels(typically 20-30 mg/L)and therefore would
be susceptible to ammonia toxicity due to pH drift. However,conducting flow-through testing is not an
economically-feasible option anymore,and because the test is only 24 hours,renewals are also not a good
approach. Although the EPA"Chronic Manual"offers acceptable techniques for pH adjustments,these are
not included in the EPA"Acute Manual".
It should be also noted that prior to March 2011, Pace Analytical in Asheville had performed all toxicity
testing for SSWWTP. A review of the tests conducted by Pace Asheville between 2006 and 2010 shows a
much smaller variation in pH,with the pH rarely rising above 8.0. The pH on the December 2010 sample
did show a large drift and passed only due to a large variation in the test treatments,which skews the
statistics to be less sensitive to detecting higher rates of mortality as statistically significant. The pH drifted
from 7.45 to 8.12 and the percent mortality was 22.5%;this was not statistically significant on this
particular test. Pace Asheville closed in 2011.
Although Pace Asheville did not have large shifts in pH exceeding 8.0 between 2006 and 2010,ATB
conducted an acute Ceriodaphnia pass/fail test on August 17,2006 that failed due to 100%mortality in the
90%test treatment. However,the test conducted by ATB was not a permit compliance test or a split test,
but simply part of the routine bioassay compliance inspections performed by the Regional Offices.
Although ATB tests are not used to determine compliance with permit limits,it should be noted that the
ATB test that failed also exhibited a large upward pH shift similar to the large pH shift observed in recent
failures. The initial pH of the 90%treatment was 7.92 and the final pH was 8.45. ATB also conducted
another routine bioassay compliance inspection test on September 29,2010. This test was a split with Pace
Asheville and both tests passed with pHs that only drifted up to 7.9 and 8.1.
Between January and September 2013,there have been 6 sampling events in which samples split among
labs have resulted in one lab passing and the other lab failing the test. Often,the difference is extreme.
For instance,one lab may have little or no mortality and the other lab may have extremely high mortality.
One lab is not consistently failing and one lab is not consistently passing. This indicates the variable results
are not due to standard lab technique,but due to characteristics of the sample chemistry during testing and
sometimes statistical insensitivity caused by high control or test treatment variability. CFPUA's
investigation has also indicated that when headspace of the samples is eliminated,pH drift is minimized
and the test will pass at 24 hours. This finding is also indicative that the toxicity is due to a pH-dependent
toxicant.
ATB policy for disagreeing split tests is that all WET monitoring results must be submitted. Then,ATB
conducts a review to evaluate if all required quality assurance(QA)practices and quality control(QC)
criteria have been met for each of the tests. If all QA/QC criteria on each test are met and no difference
between can be found among them,the passing result is accepted as the final result. DWR received a letter
Page 2 of 10

dated August 28,2013 from CFPUA regarding the July 2013 disagreeing split samples indicating that a pass
and a fail received on a split sample is considered a pass. ATB would like to clarify that this is after ATB
reviews all tests performed on the split sample and determines that the all QA/QC criteria were met.
Although we do occasionally have disagreeing split test results,the frequency of the disagreement for the
SSWWTP split tests is unprecedented. Because an acute test failure triggers the immediate requirement for
a facility to continue testing until a passing result is received,ATB has advised CFPUA that when they
receive a pass and a fail,follow-up testing will not be required unless the review of the split tests indicates
that the passing test did not meet all QA/QC criteria. In other words,SSWWTP does not have to
immediately initiate follow-up testing if it performs a split test and receives a passing result and a failing
result. ATB will notify CFPUA if follow-up testing is required after the split tests are reviewed.
Due to the unprecedented rate of disagreeing split test results and the sudden appearance of intermittent
failures in SSWWTP's toxicity tests,ATB participated in split tests conducted on the sample collected in June
2013. The June sample was split between ETS, Meritech,Tetratech,and ATB. Meritech and ATB failed,
whereas ETS and Tetratech passed. After these results were reviewed,it was noted that ATB and Meritech
had the highest pH drift and that they both used soft surface water as opposed to the synthetic laboratory
water used by ETS and Tetratech. ATB then participated in another round of split tests in July to help
understand if the type of culture or dilution water was affecting the pH drift.
CULTURE/DILUTION WATER
Under EPA and DWR protocol,the water used as the culture and/or dilution water for freshwater toxicity
tests can be prepared either from high purity laboratory water or non-toxic surface water. The laboratory
prepared water is typically referred to as either soft synthetic water(hardness of 30-50 mg/L CaCO3)or
moderately hard synthetic water(hardness of 80-100 mg/L CaCO3). DWR requires that all water used for
dilution water on NPDES compliance tests have a hardness of 30-50 mg/L CaCO3 because this is most
reflective of receiving waters across North Carolina and hardness can play a critical role in the toxicity of
some substances,most notably metals.
Each of the labs that have performed testing for SSWWTP uses a different type of water. The types of
water used by each lab are summarized below in Table 1.
Table 1: Type of Water Used by Each Lab
Laboratory Culture Water Dilution Water
ETS Moderately Hard Synthetic Soft Synthetic
Meritech Soft Surface Soft Surface
Tetratech Moderately Hard Synthetic' Moderately Hard Synthetic'
Pace(Raleigh) Soft Surface Soft Surface
DWR ATB2 Soft Surface Soft Surface
'Based on preliminary reports,ATB believes Tetratech conducted the tests in moderately hard synthetic water,but
soft synthetic water may have been used on some of the tests they performed.
2ATB's primary laboratory water is soft surface water,but ATB also maintains cultures and reference toxicant tests for
moderately hard and soft synthetic water cultures.
Page 3 of 10

In order to look into the varying test results,the DWR ATB laboratory participated in the July 2013 sampling
event using various types of culture and dilution water on acute tests as well as conducting a chronic full-
range test. The objectives of the ATB tests in July were: 1)to assess whether and how the type of dilution
water affected tests results while removing the effect of variability among laboratories and 2)to evaluate if
a chronic test might be a more appropriate toxicity test assignment for SSWWTP. ATB performed four
acute Ceriodaphnia tests and one chronic full-range Ceriodaphnia test on the July sample. In September,
ATB performed another chronic full-range Ceriodaphnia test. These six tests are described in Table 2.
Table 2: Tests performed by ATB in July and September 2013 for CFPUA SSWWTP
Date Test Type Culture Water Dilution Water
(Test Water)
7/17/13 Acute#1 Soft Surface Soft Surface
7/17/13 Acute#2 Soft Synthetic Soft Synthetic
7/17/13 Acute#3 Moderately Hard Synthetic Soft Synthetic
7/17/13 Acute#4 Moderately Hard Synthetic Moderately Hard Synthetic
7/17/13 Chronic#1 Soft Surface Soft Surface
9/11/13 Chronic#2 Soft Synthetic Soft Synthetic
Acute test#4 was to evaluate if performing the test in hard water has any effect on the results. ATB
protocol requires that tests be performed in soft water(water with a hardness of 30-50 mg/L CaCO3),
unless it is determined that an alternate hardness range would be more appropriate for the testing
objectives. Therefore,acute test#4 is not a valid test option unless it was demonstrated that the receiving
waters consistently have a hardness value between 80-100 mg/L CaCO3.
Chronic test#1 was to evaluate if chronic testing would be more appropriate for SSWWTP. When toxicity
testing was first assigned to the facility,the Instream Waste Concentration(IWC)was unknown. Per DWR
policy,when the IWC is unable to be calculated,acute testing at 90%effluent at 24 hours is assigned.
Recently,the facility completed a study in which there may be sufficient information to evaluate the IWC.
Chronic testing at the facility's IWC is the required toxicity testing assignment when the IWC is known as
this is a more comprehensive evaluation of the effect on the receiving waters. It is estimated that the
facility's IWC may be as low as 3%;therefore,the chronic test was run at the following five concentrations
of effluent: 3,6,12,24,and 48%.
Chronic Test#2 was to evaluate if the chronic test results exhibited variability among months and water
type. ATB will conduct another chronic test in December 2013 to further explore the potential of variability
among seasonality and water type.
RESULTS&DISCUSSION
ACUTE TESTS
The results of the acute tests are presented in Table 3. In addition to the standard Information regarding
toxicity tests,ATB also analyzed the total ammonia concentrations of the effluent and the Initial and final
Page 4 of 10

ammonia concentrations in each of the test treatments. The total ammonia of the 100%effluent was 22
mg/L. The total ammonia concentrations of each of the treatments as well as the potential concentration
range of un-ionized ammonia (NH3)are shown in Table 3. Ammonia is relatively unique in its behavior as
pH and temperature changes. When ammonia dissolves in water,some of the molecules react to form the
ammonium ion NH4+,and the equilibrium between these species is affected by pH and temperature. The
toxicity of ammonia to some aquatic species appears to be primarily caused by the un-ionized form. The
equilibrium shifts to increase the un-ionized ammonia concentration with increasing pH and increasing
temperature(USEPA 1993).
Table 3: July 2013 ATB Acute Tests Results
Acute Test#1 Acute Test#2 _Acute Test#3 Acute Test#4
Culture Water Soft Surface Soft Synthetic Moderately Hard Moderately Hard
Test Water Soft Surface Soft Synthetic Soft Synthetic Moderately Hard
Effluent pH 7.51 7.51 7.51 7.51
Initial pH treatment 8.08 8.0 8.12 8.09
Final pH treatment 8.29 8.34 8.33 8.35
Initial total ammonia 20 20 20 20
(mg/L)
Initial un-ionized 1.25-1.8564 1.006-1.495 1.25-1.8564 1.25-1.8564
ammonia range'(mg/L)
Final total ammonia 14 17 18 16
(mg/L)
Final un-ionized 1.3384-1.526 1.7208-1.962 1.6252-1.853 1.872-2.128
ammonia range'(mg/L)
%Mortality 57.5% 30% 95% 82.5%
Pass/Fail Pass(Insensitive, Pass(Insensitive, Fail(Valid) Fail(Valid)
Invalid) Invalid)
'Calculated from Table 10,Percent Un-ionized Ammonia in Aqueous Ammonia Solutions,from EPA's"Acute Manual",
2002. The range was calculated by multiplying the%un-Ionized ammonia from the table by the total ammonia value
of the treatment,at 24'C for the low range and 26'C for the high range
The range of the toxic form of ammonia,un-ionized ammonia,which is predicted to be found in the
samples,is close to the predicted Median Lethal Concentrations(LC50s)calculated from an EPA study(see
Table 4). The LC50 is the concentration of a substance at which 50%of a population is killed during a
certain amount of time. In this case,the time period is 24 hours.
Page 5 of 10

Table 4: Calculated Un-ionized and Total Ammonia LCSos(mg/L)*
pH Percent Un-ionized Ammonia Total Ammonia Un-ionized Ammonia Total Ammonia
Unionized at Expected 24hr LC50 24hr LC50 Expected 24 hr LC50 48hr LC50
25°C
7.6 2.21 1.48 67 1.14 52
7.7 2.77 1.61 58 1.24 45
7.8 3.46 1.73 50 1.33 38
7.9 4.32 1.83 42 1.42 33 _
8.0 5.38 1.93 36 1.49 28
8.1 6.68 2.01 30 1.55 23
8.2 8.27 2.08 25 1.61 20
8.3 10.2 2.14 21 1.65 16
8.4 12.5 2.19 18 1.69 14
8.5 15.2 2.23 15 1.73 11
*Table Adapted from"Table 3-2,Calculated Un-Ionized Ammonia LCSOs(mg/L)based on 24-hr and 48-hr results of a
Cerlodaphnia dubla Toxicity Test Conducted at pH 8.0 and 25°C," USEPA 1993.
The intermittent nature of the toxicity may be occurring because the expected ranges of the toxic un-
ionized ammonia concentrations are so close to the LCSO values. Critical fluctuations in the amount of un-
ionized ammonia occur with minute shifts in pH and temperature values. Additionally,the rate at which pH
drifts upwards and ammonia dissipates out of the sample will be slightly different for each test. Small
differences can result in critical differences in the amount of un-ionized ammonia for each toxicity test. For
example,in a sample with 24 mg/L total ammonia at 25.0°C,5.38%of it would be in the toxic un-ionized
ammonia form at a pH of 8.0. With an increase of only 0.3 pH units,the percent of ammonia in the toxic
form almost doubles to 10.2%. These percentages correspond to 1.29 mg/L at pH 8.0,and 2.45 mg/L at 8.3.
The un-ionized ammonia expected 24 hr LC50s are 1.93mg/L at 8.0 and 2.14 mg/L at 8.3. With a shift of
just 0.3 pH units,the percentage of un-ionized ammonia in the sample has gone from being 67%of the
LCSO to 114%of the LC50. Micro-variations in temperature, pH,and the rate of change in ammonia in the
sample coupled with the rate of pH shift,can each cause critical changes in toxicity among replicates and
among laboratories.
CHRONIC TESTS
The results of the chronic tests are shown in Table 5. Both tests indicate that no acute or chronic toxic
effects would be expected at IWCs of 48%or less. On the July test,there was a statistically significant effect
at 48%. However, per DWR policy,a significant effect must show statistical significance coupled with a 20%
or greater decrease in reproduction. Therefore,the effect at 48%is not considered a significant toxic effect
because the reduction in reproduction was 17%. On the September test,there was an inversion in the
amount of reproduction at 3%,with the 3%treatment showing a 31.8%reduction in reproduction
compared to the control. However,this effect was not statistically significant. The 6, 12,24,and 48%
treatments all had higher reproduction than the 3%, indicating the reduction at 3%was an anomaly. The
reason there was a large reduction in reproduction but not a statistically significant effect at 3%was that 3
of the 10 replicates did not reproduce at all,while the other 7 replicates had very high rates of reproduction
causing them to rank very high in the Steele's Rank test.
Page 6 of 10

Table 5. July&September 2013 ATB Chronic Full-Range Test Results
Chronic Test#1 Chronic Test 42
Test Start Date 7/17/13 9/11/13
Water Type Soft Surface Water Soft Synthetic Water
Test Endpoints ChV1=>48% ChV1=>48%
NOEC2=48% NOEC2=48%
LOEC3=>48% LOEC3=>48%
Control Survival 100% 90%
Control Mean 32.5 31.7
Reproduction
Test Treatment Survival 100%at all concentrations 100%at all concentrations
Test Treatment Mean 29.4 at 3% 21.6 at 3%(this is a non-statistically
Reproduction 30.7 at 6% significant inversion)
32.1 at 12% 32.0 at 6%
31.1 at 24% 34.4 at 12%
27.0 at 48%(statistically significant, 33.3 at 24%
but<20%reduction so no effect) 29.8 at 48%
Initial Sample pH 7.55 for sample collected 7/16 7.46 for sample collected 9/10
7.51 for sample collected 9/12
Initial Treatment pH 7.84 at 3% 7.80 at 3%
8.16 at 48% 7.99 at 48%
Final Treatment pH 7.75 at 3% 7.73 at 3%
8.16 at 48% 8.19 at 48%
Initial Sample Total Not measured 100%effluent: 25
Ammonia(mg/L)
Final Sample Total Not measured Friday 3%: 0.81
Ammonia(mg/L) Friday 48%:8.4
Monday 3%: 0.9
Monday 48%: 8.4
Wednesday 3%:0.8
Wednesday 48%: 9.4
1ChV=Chronic Value. The Chronic Value is the geometric mean of the No Observed Effect Concentration and the
Lowest Observed Effect Concentration. For standard North Carolina multi-concentration chronic WET tests,a ChV
lower than the permit limit for the fadlity is considered a"Fail".
1NOEC=No Observed Effect Concentration. In this test,this is the highest effluent concentration tested at which
there is no significant reduction in reproduction from the control.
3LOEC=Lowest Observed Effect Concentration. In this test,this is the lowest effluent concentration tested that shows
a significant reduction In reproduction from the control.
ALGAL ANALYSIS
A phycologist with DWR Environmental Sciences Sectio's Ecosystems Branch evaluated aliquots of the July
samples received on 7/15/13 and 7/17/13. He reported that: "There were no known problematic forms of
algae. The algae present were sparse,mainly some greens,and epiphytic in nature. There were also some
stalked rotifers,ciliates,and sheathed bacteria"(Vander Borgh,7/22/2013 email communication).
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STATISTICS
The acute tests demonstrate that sometimes the statistics for acute pass/fail tests with 4 replicates at an
alpha level of 0.01 may not be powerful enough to detect differences between the control and tests
concentrations when there is high variability in either the control or the test cups. EPA guidance in the
document"Understanding and Accounting for Method Variability in WET Applications under the NPDES
Program"advises that tests lack sensitivity when the percent minimum significant difference(PMSD)
exceeds the 90th percentile from their data set of reference toxicant tests. For an acute Ceriodaphnia test
this upper boundary is 21%. In the event that the PMSD exceeds the upper bound and there is no
significant difference between the means for the control and the IWC treatment,then the test is
considered invalid. If the PMSD exceeds the upper bound and there is a significant difference,then the test
is considered valid(USEPA 2000). There was an unusually high variation in the test treatments on the ATB
tests. The high variation in the test cups on the surface water test and the soft synthetic water tests cause
the PMSD to be extremely high, resulting in the statistics being insensitive and unable to detect a statistical
difference even with extremely high mortality rates. For instance,the surface water test showed no
mortality in the control. However,the 4 treatment cups ranged from 0%mortality in one replicate; 70%
mortality in two replicates;and 100%mortality in the fourth replicate. Due to the high variability in
treatment response,the PMSD for the test would require 107%reduction in reproduction before a
statistical significant effect was noted.This percent reduction is not possible. Therefore,the statistics did
not find a 57.5%reduction in reproduction significant at a 0.01 alpha level. Per EPA guidance,this test
should be considered invalid. As with the unprecedented rate of disagreeing split test results,this extreme
variability in test replicates could potentially be linked to micro-variations in temperature, pH,and the rate
of pH change versus the rate of ammonia change in each of the test cups. ATB will use these results to
identify additional statistical considerations that may need to be incorporated into the ATB Acute Pass/Fail
Statistical Protocol. However,despite the weakness of statistics in some of the tests,the role this plays in
this particular situation is a minor one and does not change the unusually high number of fails and
disagreeing split test results with this particular effluent during the past year.
SUMMARY
ATB's acute tests did not clearly demonstrate whether or how the type of water used would affect the
result of the test. However,a few observations should be noted:
1. The initial amount of total ammonia was the same for all treatments,regardless of dilution water.
2. The final amount of total ammonia varied among the dilution water used in the treatments,with
the surface water showing the most reduction from the initial result to the final result. However,
this is a one-time,small dataset and replication would be needed to determine if this is repeatable
and statistically significant.
3. All water types showed a significant amount of mortality in the acute tests,but the statistical power
of the soft synthetic water and the soft surface water tests was insufficient to detect significant
differences due to the amount of variability in the treatment replicates.
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Technically,following ATB guidelines,the soft synthetic water test and the soft surface water test passed.
These tests showed a 30%and 57.5%mortality rate,respectively,which are rates that would rarely pass.
However,the statistics were too insensitive to detect these mortality rates as significant due to the
extreme variability in test treatment response. These passing results would be considered invalid by EPA
guidelines;therefore,for the purposes of this study,they should not be considered as useful or valid
passing results as they do not clearly demonstrate a lack of effect. The other acute tests failed statistically,
with 82.5%and 90%mortality. All controls had 100%survival,so the weakness in the statistics was due to
the high variability in the 90%treatments.
The two chronic tests conducted by ATB indicate that conducting chronic tests would be a good choice for
SSWWTP if it can demonstrate that its IWC is below 48%. Total ammonia values were relatively consistent
for the 3%effluent concentration and the 48%effluent concentration on the Friday,September 13 and
Monday,September 16 changeovers and the termination date on Wednesday,September 18. The
ammonia values and pH drift were more significant in the 48%than in the 3%effluent concentration.
However,ATB recommends conducting more chronic tests to ensure they don't exhibit the same type of
variability as the acute tests. ATB has arranged to conduct another multi-concentration chronic test at the
same effluent concentrations in December.
Chronic testing is always the preferred toxicity testing assignment when the IWC is known,as this is a more
comprehensive evaluation of the effect on the receiving waters. Acute testing is only assigned for major
dischargers when an IWC is unable to be estimated. Changing the toxicity test assignment to chronic
testing at the IWC is consistent with DWR's policy to protect surface waters for chronic toxicity. In fact,if
the SSWWTP does have an approved IWC,the required test assignment is the chronic test. This change in
testing would not be a strategy to avoid dealing with the disparity in acute toxicity results or in addressing
the high ammonia levels in the effluent,but rather to be consistent with rules for the protection from
chronic toxicity in all surface water streams. In the future,it is likely SSWWTP will need to address its
ammonia output in light of EPA's recently updated ammonia water quality standards,which can be found
at the following link:
http://water.ei a.eov/scitech/sweuidance/standards/criteria/aalife/ammonia/index.cfm.
EPA advocates for all states to adopt the new nutrient water quality criteria,and there is the potential in
the future that NC will be required to adopt the EPA ammonia water quality standards. Although it is not
clear if or how the application of these standards would affect dischargers,there is the potential that this
might affect the amount of ammonia that could be discharged by SSWWTP.
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REFERENCES
North Carolina Pass/Fail Methodology for Determining Acute Toxicity in a Single Effluent Concentration,
Version 3.0. Revised December 2010,or subsequent versions.
USEPA 1993. Methods for Aquatic Toxicity Identification Evaluations. Phase II Toxicity Identification
Procedures for Samples Exhibiting Acute and Chronic Toxicity. EPA/600/R-92/080.
USEPA 2000. Understanding and Accounting for Method Variability in WET Applications Under the National
Pollution Discharge Elimination System. EPA 833-R-00-003.
USEPA 2002. Short Term Methods for Estimating the Acute Toxicity of Effluents and Receiving Waters to
Freshwater Organisms. Fifth Edition. EPA821-R-02-012.
Vander Borgh, Mark. DWR/ESS/EB. Personal email communication,7/22/2013.
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