WQ0001740_Appx-D-3 City's Response to Info. Request_20140829

if�aley.A
,
August 28, 2014
Division of Water Resources
Non -Discharge Permitting Unit
Division of Water Resources
1628 Mail Service Center
Raleigh, NC 27699-1628
Attention: Jon Risgaard
Subject:
Dear Mr. Risgaard
RE'EVVEDI1)EVR/D11VR
v 241y
N'y r Quality
P�'tR ing Section
Permit No. WQ0001730
June 12, 2014 Additional
Information Request
Five Year Evaluation
Response Letter
Please find attached the additional information you requested in your letter dated June 12, 2014 for our
Five Year Evaluation of Remediation Strategy report. Thank you again for the information submittal
extension from July 11, 2014 to September 1, 2014, as described in the attached e-mail. We have also
included a CD of a short Power Point covering the information in our report for your use. Please fill free
to contact me or Jesse Luper at our main number 919-996-3700 if you have any questions.
Sincerely,
Tim Wo d� y
Resource Recovery Superintendent
City of Raleigh
cc: John Carman -Public Utilities Director
TJ Lynch- Assistant Public Utilities Director
Jesse Luper—Assistant W&S Superintendent
COR WWTP Central Files
OFFICES • 222 WEST HARGETT STREET • POST OFFICE BOX 590 • RALEIGH. NORTH CAROLINA 27602
RECYCLED PAPER

Luper, Jesse
From: Risgaard, Jon <[e-mail]>
Sent: Wednesday, July 02, 2014 9:52 AM
To: Luper, Jesse
Cc: Woody, Tim; Bolich, Rick; Mcdaniel, Chonticha
Subject: RE: Revised Additional Response Time Needed
Jesse,
Sorry that we missed each other on the phone, and thank you for sending the extension request via email. I am comfortable extending the deadline to
September 1, 2014 for the City's response to our request for additional information on the 5 -Year Evaluation of Remedial Strategy. Please keep a copy of this
email with your records and attach a copy of it with the additional information requested.
Pror,
Jon Risgaard - Supervisor, Non -Discharge Permitting Unit
Water Quality Permitting Section
1636 Mail Service Center
Raleigh, NC 27699-1636
919-807-6958
http://portal.ncdenr.org/web/wq/aps/lau
From: Luper, Jesse fmailto:Jesse.Luoer(a)raleighnc.00v]
Sent: Tuesday, July 01, 2014 2:38 PM
To: Risgaard, Jon
Cc: Woody, Tim
Subject: Revised Additional Response Time Needed
Please see my revised request below.
In the 5 -Year Evaluation of Remedial Strategy Additional Information Request letter, dated June 12, 2014, you requested that all items be addressed by July 11,
2014. We are requesting that the response time be extended to September 1, 2014. Please let me know if this extension can be granted. Please feel free to
contact me if you have any questions. Thanks
a7eb.4%4 oet
Assistant W&S Superintendent
Public Utilities/ Reuse Division

Phone [phone]
Fax [phone]
NBP
CERTIFIED
EMS
From: Luper, Jesse
Sent: Monday, June 30, 2014 5:33 PM
To: '[e-mail]'
Cc: Woody, Tim
Subject: Additional Response Time Needed
In the 5 -Year Evaluation of Remedial Strategy Additional Information Request letter, dated June 12, 2014, you requested that all items be addressed by July 11,
2014. We are requesting that the response time be extended to July 31, 2014. Please let me know if this extension can be granted. Please feel free to contact me
if you have any questions. Thanks
09e55%15& et
Assistant W&S Superintendent
Public Utilities/ Reuse Division
Phone [phone]
Fax [phone]
NBP
CERTIFIED
EMS

i
Mr. Jon Risgaard
Supervisor
Non -Discharge Permitting Unit
Division of Water Resources
NCDENR
1636 Mail Service Center
Raleigh, NC
27699-1636
August 28, 2014
Subject: Response to June 12, 2014 Additional Information Request, City of Raleigh Residuals Program
Dear Jon:
This letter provides our response to your request for additional information regarding our report entitled
Five -Year Evaluation of Remediation Strategy, Biosolids Fields at the Neuse River Wastewater Treatment
Plant, Wake County, North Carolina under Permit #W00001730 (5-Year—Report) dated April 7, 2014.
We appreciate your review of the report and understand that the report serves to provide information content
and format to assist you in updating the Environmental Management Commission (EMC) on the continued
implementation of the variance from the Commission's 2L rules granted to the City of Raleigh Public
Utilities Department (CORPUD) in 2009 (Variance).
The 5 -Year Report provides a summary of environmental monitoring and analyses that have been conducted
by CORPUD from the time the Variance was granted through the present. A significant portion of the report
summarizes the additional field investigations and modeling used to support the Division's 2013 approval of
the resumption of Biosolids application to areas recommended in our 2012 report Method and Results
Demonstrating the Acceptability of Resuming Biosolids Application to Selected Areas of the City of Raleigh
Neuse River Waste Water Treatment Plant Fields (2012 Report). That report documented and provided
results from the updated groundwater flow and transport models (Updated Model) that used new information
to improve upon the models developed for the Supplemental Site Assessment (SSA) that were used to
support the Variance (Variance Model).
The 2012 report documented the additional site monitoring data and tests collected since the Variance
approval, and the use of that data to provide a more correct and complete description of the source of NO3 in
recharge to the groundwater system than that used in the Variance Model by documenting the presence and
transport of residual NO3 below the root zone of the CORPUD fields. These high residual concentrations
that were documented by the field investigations described in the 2012 Report are the result of the slow rate
of movement of water through the vadose zone caused by the low permeability of the soil and saprolite
materials below the fields.
The slower travel through the vadose zone resulted in smoothing out concentration variations and increasing
the durations of excess Plant Available Nitrogen (PAN) applied to the soil traveling to the watertable. This
updated and more correct source term for NO3 in modeled recharge as illustrated by the example for Field 36
in Figure 4 of the 5 -Year Report is the most significant finding of any studies since the approval of the
Variance.
Eagle Resources, P.A.
P.O. Box 11189 Southport NC 28461
QMUKAMR uiww can/orecnurrce rnm

ease &3=2r s
We hope our responses to your comments provide you with the information necessary to prepare your
presentation to the EMC. We are available to help you prepare/review that presentation. We also have
attached a PowerPoint Slides of the illustrations and tables from the 5 -Year Review Report as updated
by the comments contained herein for your use in that presentation.
Sincerely yours,
Eric G. Lappala, P.E., P.H.
Enclosures:
o Response to Comments
0 36" x 48" .pdf Copy of the Site Map (Figure 1)
o Updated Figure 22 from 5 -Year Report
o PowerPoint Slides of Tables and Figures from the 5 -Year Review Report
ir]

General Comment 1
The report has limited evaluation of new or additional treatment technologies that could be cost-
effectively implemented. Evaluation of treatment technologies is specifically required in
the approved Variance (page 15), and is intended to help the Commission evaluate if the
approved variance is still appropriate. For example, the use of Permeable Reactive Barriers
(PRBs) was not evaluated. PRBs have been successive in other applications to provide long-
term, passive treatment and may be suitable for treatment of hot spots. Please provide
additional discussion of new and additional treatment technologies that were considered, or an
explanation of why additional technologies were not considered.
Response
Since the Variance was necessary only to allow Monitored Natural Attenuation (MNA) as the
corrective action strategy for the majority of the Neuse River Wastewater Treatment Plant site (Site),
we assume that General Comment 1 refers to additional groundwater treatment technologies.
The three alternative technologies discussed in Section 3.1 of the report were considered to be inclusive
of technologies that are currently being used elsewhere. Permeable Reactive Barriers (PRBs) were
considered a subset of the Enhanced in-situ Biodenitrification (EISBD) alternatives discussed in section
3.1.1. Based upon the 15A NCAC 2L .0106(d)(2) Corrective Action Requirements and the need for
CORPUD to actively farm the fields, we concluded in preparing the report that EISBD (including
PRBs) would necessarily have to be implemented between the review boundary and the compliance
boundary.
Alternative 1 (the Full Containment Alternative) proposed by ENSR in 20051 comprised approximately
340 wells drilled to approximately 70 feet spaced at approximately 100 foot intervals along those
portions of the compliance boundary where data and modeling showed that the 2L NO3 standard of 10
mg/I had been or would likely be exceeded in the future as shown in Figure 1. The discounted cost for
this alternative was $22,524,850 using a 5.125% discount factor. This alternative was rejected because
a) the cost was judged to impose an economic hardship on the City, and b) virtually all of groundwater
containing NO3 in excess of the 2L standard at or beyond the compliance boundary discharges to the
Neuse River or its tributaries.
With the exception of those portions of the compliance boundary downgradient of fields 50 and 500,
the recommended remedial action alternative was NINA in concert with the inclusion of a nitrogen
debit in CORPUD's NPDES permit to account for nitrogen discharged via groundwater to the Neuse
River and its tributaries in excess of the discharge that would occur if the Site were in compliance with
the 2L standards.
As a supplement to the reasoning in the last paragraph in Section 3. 1.1 regarding the potential
effectiveness of PRBs as a subset of EISBD, the estimated cost to install PRBs up -gradient along the
74,318 feet (15.08 miles) of the compliance boundary that has been or would likely be impacted in the
future is $140,168,929 using a discount factor of 3% (Table 1). Clearly this exceeds the $22,524,850
that was determined by the EMC to impose undue economic hardship on the City.
' ENSR, 2005, City of Raleigh Neuse River Wastewater Treatment Plant Corrective Action Plan.
2 Eagle Resources, 2012, Method and Results Demonstrating the Acceptability of Resuming Biosolids
Application to Selected Areas of the City of Raleigh Neuse River Waste Water Treatment Plant Fields. 3

The comment suggests that PRBs could be used to reduce NO3 `hotspots'. It is not clear how the
Division would define such areas. Further, for the reasons stated in the last paragraph of Section 3.1.1,
and as documented in the 2012 report (p. 18) that was used by DWR to approve re-application of
biosolids to a portion of the NRW WTP fields 2, most of the existing high concentrations of NO3 are in
the vadose zone, and one or more of the alternative EISBD technologies discussed in the report would
have to be used to reduce these levels. PRBs cannot be effective in remediating the vadose zone.
Item
Units
Unit Cost
Total Cost
Trenching
74,318
ft
$200
$/ft
$14,863,501
Mob/Demob
1
ea
$50,000
$
$50,000
Biowall Materials
(Straw)
165,150
yd"3
$15
$/yd
$2,413,922
Straw Delivery (from 50
miles)
4,129
tons
1 $8
$/ton
$33,030
Subtotal
$17,360,453
Engineering @ 6%
1
ea
$1,041,627
ea
$1,041,627
Project Management @
5%
1
ea
$868,023
ea
$868,023
Total Capital Cost Estimate
$19,270,103
O&M for 30 years
Replacement Interval5
yrs
Number of
replacements
6
ea
Replacement
Installation
445,905
ft
$50
$/ft
$22,295,251
Replacement Biowall
mtis
990,900
yd^3
$15
$14,863,501
Replacement Delivery
6
ea
$33,030
$
$198,180
Subtotal
$37,356,932
Engineering @ 2%
1
ea
$747,139
ea
$747,139
Management @ %
1
ea
$373,569
ea
$373,569
Total 30 -year 0&M
$38,477,640
Total Capital & O&M Cost
$57,747,743
Discounted Cost @ 3%
for 30 yrs
$140,168,929
I'able L-- Estimated Cost for Permeable Reactive Barriers (PRBs).
z Eagle Resources, 2012, Method and Results Demonstrating the Acceptability of Resuming Biosolids
Application to Selected Areas of the City of Raleigh Neuse River Waste Water Treatment Plant Fields.

ra�e,('e WC45
General Comment 2
The report contains little discussion on the collection of additional data and information to
further improve model calibration. We believe that the Commission will want to see more
details on this item. Please provide more information supporting the need, or lack of need, for
additional data and information to improve the model.
Response
Because variability in subsurface materials at scales that are necessarily smaller than the scale of
discretization of the model (50 ft x 50 ft horizontally and approximately 15 feet vertically), field
tests cannot generally provide values of the hydraulic and transport parameters in the model
equations (hydraulic conductivity, effective porosity, and dispersivity) that are representative of the
necessary spatial averaging in the model and these averaged model parameters need to be obtained
by model calibration. Based upon our professional experience, additional field tests to provide
additional estimates of these parameters would not materially improve model calibration.
As documented in the 2012 report (p. 18), the Updated Model was successfully recalibrated to
average water levels computed from 437 water levels measured in 110 observation wells from 2000
through 2011. This additional data was not available for the Variance Model. The Normalized
Root Mean Square (NRMS) value of 5.9% for this fit is better than the industry standard and
NCDENR guidance level of 10% and the 6.7% achieved with the Variance Model.
Computed concentrations at any point in time and space are directly proportional to the source tenn
(e.g., all other hydraulic and transport parameters being equal, doubling the source concentration
will double the concentration at any down -gradient location). Consequently, the most important
and effective data to improve model calibration is definition of the source term for NO3. The report
summarized the extensive additional data collection documented in the 2012 report2 that showed
that the past and future flushing of residual NO3 from the vadose zone comprises the source of NO3
to groundwater. The variance model assumed that all residual NO3 was flushed from the vadose
zone immediately upon ceasing the application of biosolids in 2002. Field data collected and
documented in the 2012 report clearly showed that this was not the case.
If additional historic (1979-2013) NO3 concentrations in groundwater at additional locations were
available, they might have helped to improve model calibration. However, such data are not
available and clearly cannot be obtained after the fact. Installing additional monitoring wells and
surface water stations would not provide sufficient additional NO3 data for several years that might
help model calibration but there is no assurance that this would be the case.
We conclude that continued collection NO3 concentrations and water levels in existing monitoring
wells and NO3 concentrations from surface waters stations will provide the best information for
additional checking of the model.
General Comment 3
For the figures in the report that show modeled results vs. observed data of NO3, it is not
clear if the modeled results shown are.for the model approved as part of the variance or the
newly updated/calibrated model. It is important that the original model results are shown to
document accuracy ofthe model. The updated model should also be shown to support its
viability if it is intended to be used to predict conditions at the NRWWTF going forward.
Please clarify.

,We h'esar -5
Response
The figures in the report show modeled results vs. observed data for NO3 for the Updated Model
(based on the more accurate source terms emanating from the vadose zone as documented in the
2012 report (p. 33). We do not agree that it is necessary or important to evaluate the accuracy of
the Variance Model as that model, with DWR approval, has been supplanted by the Updated
Model. Model representativeness and accuracy can only be assessed by comparing modeled
results from any given model against measured values.
General Comment 4
Throughoutthe reports, there are conclusions made that the model "reasonably"
represents NO3 concentration. Please provide more detail on the criteria used to determine if
"reasonable" ft is shown.
Response
The reasonableness of the fit between modeled and observed values is based upon both quantitative
and qualitative metrics. Quantitative measures include the statistics shown in the review report for
the flow model.
As documented in the 2012 Report (p. 18) The Updated Model (groundwater flow) was
successfully recalibrated to average water levels computed from 437 water levels measured
in 110 observation wells from 2000 through 2011. The Normalized RMS value of 5.9% for
this fit is better than the industry standard and NCDENR guidance level of 10% and the
6.7% achieved with the Variance Model.
As documented in the 2012 Report (p. 19), sensitivity analyses performed on the Updated
Model (transport) confirmed, as expected from both theoretical and practical experience,
that the NO3 source term for each field defined as output from the vadose zone computed
with the VS2DT models was more important than variations in hydraulic conductivity for
the flow model and variations in effective porosity and dispersivity for the transport model.
Therefore, the only parameter varied for calibration of the transport model was the
multiplier on the VS2DT source term for those fields that were up gradient of one or more
monitoring wells for which NO3 data was available.
The Division previously accepted the reasonableness of the Updated Model (both flow and
transport). The 2012 report that documented the Updated Model and its degree of fit was used to
support approval of the resumption of biosolids application on the areas that were recommended in
that report. We do not believe that additional clarification of criteria to define reasonableness is
necessary.

We,('esUrM5
General Comment Number 5
A critical part of the variance is the estimate of the, flux of groundwater nitrogen from the impacted
fields that is moving into the Neuse River, and the accounting for that contribution as part of the
overall nitrogen flux coming into the River as part of the NPDES permit . It may be helpful to the
EMC members to see a figure showing the total amount of nitrogen discharged to the Neuse River
from the NRWWTF, the amount debited as part of the Variance agreement, the total accounted for
in the NPDES permit and the Permit limit on a yearly basis. It would be helpful if'the table also
includes projections of nitrogen loading from the various sources.for the next 2 or three permit
cycles. It would also be helpfid to include a table showing the NPDES debits included in the
approved variance for each year, as well as the predicted values in the updated model.
Response
As an initial matter, please recall that the methodology for calculating the NPDES permit nitrogen
debit (Debit), as established by DWR and the EMC, is not based on the total flux of nitrogen to the
Neuse River via groundwater at the Site, but the flux resulting from groundwater concentration at
the Site in excess of 10 mg/L. (As with any site, there would still be nitrogen flux to surface water
via groundwater at the Site if it fully met 2L standards; such groundwater flux is not regulated
under the Commission's rules or Neuse River Nutrient Management Strategy.)
As a second clarifying point, please note that the original Variance Model was used as the basis for
the Debit in CORPUD's NPDES permit. It was necessary to construct a replica of the Variance
Model for the 2012 report because of updated modeling software, but that replica model used the
same geometry, boundary conditions, recharge rates, values of hydraulic and transport parameters,
and N loading rates. The differences in computed N load between the Variance Model and the
replicated model were all less than 3%. All discussion of the Variance Model in this document and
in the 5 -year Report refers to the replica of the Variance Model prepared in connection with the
2012 report.
An update to Figure 7 is shown below followed by an explanation for all the curves shown.

160,000
100,000
> 120,000
1
a
d
w 100,000
H
M 80,000
s
m
d'+ 60,DOQ
2
20,000
/ I —
• -.- • Vnriauce Model Canst t N al 10 mgp in RctlurBe
Madel Total N lead Minus Load al
— Vpdncd Model Tatal n Wad
••'-• Updated Mcde1 VS267 Som. Mux 10 mg/I In
Recharge
�• apdatea M.&I na!al h Wed Min. twd al Yi
Oeb:l Values from permit
I/1(t1U 12(33/69 1/Ii 00 32f31/LNJ ifl/2U 32j31(29 lfl/d0 12(ilf4§
Figure 7 (Ree ised).—Comparison of the modeled discharge of BII NO, to the Neuse River and tributaries and that
discharged under the conditions where NO3 in recharge to groundwater did not exceed the NC21. Groundwater Standard of
III mg/1. Also shown is the NO3 values of the Debit that are in the Variance and the Permit.
Explanation for each of the curves in the updated Figure 7:
1) Variance Model Total N Load
Annual total N load to Neuse River and tributaries using the Variance Model resulting from
applying N in recharge under each field using excess PAN from Table 0-3 in the SSA, and
assuming no time delay of the excess by transit time in the vadose zone. That is, all excess PAN
was applied directly to the water table at the rates in SSA Table G-3. Following the cessation of
biosolids in 2003, all NO3 values in recharge were set to 0.00 mg/l. (As a reminder, the Variance
Model (replica) produces slightly different results than those obtained from the original version of
the model used to support the Variance.)
2) Variance Model Constant N at 10 mg/l in Recharge
Annual total N load to Neuse River and tributaries using the Variance Model resulting from
applying N in recharge at 10 mg/l for the duration that biosolids were applied to each field. This is
not a constant value because the number of active fields changed over the 1979 to 2003 period.
Following the cessation of biosolids in 2003, all NO3 values in recharge were set to 10.0 mg/I. The
maximum quasi -steady state loading for this curve was approximately 30,000 lb/yr.
3) Variance Model Total N Load minus Loading at 10 mg/l
R

Difference between Curves 1 and 2. The basis for the Debit in the NPDES permit was this
difference as computed with the original Variance Model.
4) Updated Model Total N Load
Annual total N load to Neuse River and tributaries using the Updated Model resulting from
applying N in recharge under each field using excess PAN from Table G-3 in the SSA as input to
flow and transport models of the vadose zone using the USGS VS2DT model for each field. The
red curve in Figure 4 of the report shows an example of the NO3 values applied at the top of the
vadose zone for Field 36 that was computed with equation 3 of the 2012 report. The black dashed
curve in Figure 4 shows the percolation below the root zone that was applied to the top of the
VS2DT model for Field 36.
5) Updated Model VS2DT Source Max 10 mg/l in Recharge
Annual total N load to Neuse River and tributaries using the Updated Model documented in the
2012 report to simulate the 71 year period from 1979 to 2050 with the NO3 concentrations in
recharge from each field that was used for the updated model but with a maximum concentration at
anytime of 10 mg/l.
The difference between Curve 2 above and Curve 5 is due to the difference in the methods used in
the two models to simulate NO3 in recharge reaching the watertable. Curve 2 was developed by
applying NO3 in recharge at a constant value of 10 mg/l for the period(s) that excess PAN as
documented in Table G-3 of the SSA was applied to each of the fields. Curve 5 as computed with
the Updated Model was developed by applying NO3 in recharge computed with the vadose zone
(VS2DT) model for each field with the constraint that the maximum concentration was 10 mg/l.
Therefore Curve 5 computed with the Updated Model more correctly included the effects of the
storage and transport of NO3 in and through the vadose zone.
6) Updated Model Total N Load Minus Load at 10 mg/l
Difference between Curves 4 and 5.
As requested, the following table and chart are also provided that show annual values from 2008 to
2050 used to prepare the revised Figure 7 plus historic N load from the NRW WTF from 2008 to 2013
and projected values from 2014 to 2050 provided by CORPUD. The projected N loading from the
NRWWTF is based upon the following assumptions:
a) Flow to the NRW WTP will increase at a rate of 2.6% annually. This is based upon new data
from the CORPUD collection System Capacity Study which utilizes Traffic Analysis Zones
population projections for the CORPUD service areas.
b) 2.25 mg/l of TN was assumed for as the future performance of the plant based on the
average discharge concentration since 2008.

tweK'esarw-5
10
Variance Model
Total N
Load to
Tributaries
& Neuse N Load in Excess
River of 10 m 4
Debit in
NPDES
Permit
U dated Model
Total N
Load to
Tributaries N Load in
& Neuse Excess of 10
River m /l
NRWWTP Plus
Updated Model
Discharge Load to Tributaries
from & Neuse in Excess
NRWWTP of 10 m /I
Year
lb/yr
lb/yr
%of
Neuse
Rule
Limit
lb/yr
lb/yr
lb/yr
%of
Neuse
Rule
Limit
lb/yr
Ib/r
%of
Neuse
Rule
Limit
2008
139,928
115,402
17%
120,058
107,967
75,576
11%
296,544
372,120
55%
2009
136,46
111,74
16%
117,18
109,883
76,958
11%
277,581
354,53
52%
2010
133,82
107,719
16%
114,246
111,125
77,791
11%
329,876
407,667
60%
2011
129,912
103,487
15%
110.370
111,369
77,671
11%
265 019
342,690
50%
2012
125,26
99,146
15%
106,196
111,650
77,602
11%
260,181
337,783
49%
2013
120,76
94,804
14%
102,022
111,163
76,878
11%
257,536
334 414
49%
2014
116,93
90,462
13%
97,549
109,869
75,172
11%
304,722
379,89
56%
2015
112,430
86,186
13%
93,276
108.772
73,8071
11%
311 092
384,899
56%
2016
107,759
82,020
12%
89,002
107,050
71,956
11%
319 180
391,136
57%
2017
104,029
77,965
11%
84,828
105,096
69,744
10%
327,479
397,22
58%
2018
100,521
73,954
11%
NA
102,949
67,490
10%
335,993
403,484
59%
2019
96,795
70,119
10%
NA
100,377
64,856
10%
344,729
409,585
60%
2020
92,557
66,350
10%
NA
98,274
62,734
9%
353,692
416,426
61%
2021
88,718
62,691
9%
NA
95,883
60,459
9%
362,888
423,34
62%
2022
86,03
59,165
9%
NA
93,275
57,804
8%
372,323
430,127
63%
2023
83,088
55,749
8%
NA
91,202
55,800
8%
382 004
437,803
64%
2024
80,222
52,443
8%
NA
88,849
53,643
8%
391,936
445,5791
65%
2025
77,439
49,247
7%
NA
86,521
51,343
8%
402,126
453,469
66%
2026
74,60
46,139
7%
NA
83,087
48,040
7%
412,581
460,621
67%
2027
71735
43,186
6%1
NA
80,030
45,145
7%
423,308
468454
697/.
2028
68,851
40,321
6%1
NA
78,007
43,30
6%
434,314
477,619
70%
2029
66,192
37,566
6%
NA
75,846
41,431
6%
445,607
487,037
71%
2030
64,07
34,899
5%
NA
74,163
39,859
6%
457,192
497,051
73%
2031
61,761
32,386
5%
NA
72,340
38,24
6%
469,079,
507,328
74%
2032
59,090
29,940
4%
NA
70,611
36,837
5%
481,2751
518,112
76%
2033
56,65
27,604
4%
NA
68,982
35,3275%
493,789
529,116
78%
2034
54,689
25,356
4%
NA
67,237
33,78
5%
506,62
540,416
79%
2035
52,610
23,240
3%
NA
65,942
32,687
5%
519,799
552 487
81%
2036
50,69
21,190
3%
NA
64,51
31,445
5%
533,314
564,759
83%
2037
48,483
19,228
3%
NA
62,974
30,164
4%
547,180
577,344
85%
2038
46,781
17,355
3%
NA
61,817
29,080
49-
561,407
590,487
87%
2039
45,002
15,592
2%
NA
60,531
27,944
451.
576,004
603,947
88%
2040
43,20
13,851
2%
NA
59,283
26,927
4%
590,980
617,90
91%
2041
41,769
12,176
2%1
NA
58,084
25778
4%
606,345
632123
93%
2042
39,871
10,589
2%
NA
56,768
24,580
4%
622,110
646,690
95%
2043
38,65
9,09
1%
NA
55,794
23,731
3%
638,285
662,016
97%
2044
37,43
7,239
1%
NA
54,701
22,744
3%
654,880
677,625
99%
2045
35,84
6,225
1%
NA
53,487.
21,724
3%
671,907
693,631
102%
2046
34,58
4,92
1%
NA
52.592
20,841
3%
689,377
710,218
104%
2047
33,218
3,624
1%
NA
51,568
19,90
3%
707 301
7247:2,05
107%
2048
31,919
2,434
0%
NA
50,576
19,092
3%
725,691
74782
109%
2049
30,965
1,266
0%
NA
49,602
18,113
3%
744,559
762,672
112%
2050
29,641
0%
NA
48,520
17,119
3%
763,917
781,036
114%
10

1 900,000
800.000
700,000
800;000
i.
m 500,000
I
400.000
r
300,000
200,000
100.000
0
2008 2028 2029 2038 2098
I�aie Pk--arces
Permitted TN Allocation vs. Discharge + Debit
The following Figure shows the N load subject to the 10 mg/I maximum as computed by both the Variance
Model and the Updated Model and the percentage (%) these loads are of the Neuse Limit for the NRWWTF.
The Debit values in the Variance are also shown on this figure.
11

is 0,000
140,000 -
130,000 -
120,000
110,000
100,000
m 90,000
3
80,000
d.°
70,000
N
" 60,000
,Q
lQ
-� 50.000
z
40,000
30,000
20,000
10,000
We&arces
Dec -08 Dec -13 Dec -18 Dec -23 Dec -28 Dec -33 Dec -38 Dec -43 Dec -48
5%
0%
3
General Comment Number 6
The monitoring data for the concentrations of nitrate nitrogen appear to have enough variability where
trends over time appear to be either non-existent or difficult to ascertain. The correlation between the
monitoring data and the model predictions are promising, however more time is needed to see if'the
consultant's model can predict the concentrations of nitrate nitrogen with a reasonable degree of accuracy.
Response
We agree that variability in the observed concentrations of NO3 in some of the wells is significant. For
groundwater observations these are caused by a combination of spatial and temporal variations in cropping
patterns and uptake of Plant Available Nitrogen (PAN); variations in percolation below the root zone that
leaches the residual NO3 in the vadose zone that are attributable to soil, topographic, and crop and native
vegetation patterns; and local scale variations in hydraulic conductivity, effective porosity, and depth to
Partially Weathered Rock (PWR). For surface water variations, this variability is caused by the previously
mentioned groundwater parameters as they affect rates and concentrations of NO3 in groundwater discharge
to surface drainage features above the sampling stations; and variability in processes that control surface
water runoff from the drainages above the stations, including storm intensity and duration, slope, drainage
area, vegetation and surface conditions that affect infiltration and runoff excess. Because the groundwater
flow and transport models do not model surface runoff, the surface water runoff contribution to NO3 loading
is not modeled. That contribution may either increase observed NO3 concentrations if the runoff contains
high concentrations of NO3 or reduce observed concentrations by dilution in those cases where the surface
water NO3 concentrations are low.
Because of this variability we used standard statistical trend analyses on the observed NO3 data for each
monitoring station to identify the trends shown in Table 3.
17.
i
I}—
Variance Model N Load in excess of 10 mg/1, Lb/Yr
Updated Model N Load In Excess of 10 mg/l, Lb/YT
Debit in Variance
• • Variance Model Total N in Excess of 10 mg/l, % of Limit
Updated Model Total N in Excess of 10 mg/l, % of Limit
1
I
Dec -08 Dec -13 Dec -18 Dec -23 Dec -28 Dec -33 Dec -38 Dec -43 Dec -48
5%
0%
3
General Comment Number 6
The monitoring data for the concentrations of nitrate nitrogen appear to have enough variability where
trends over time appear to be either non-existent or difficult to ascertain. The correlation between the
monitoring data and the model predictions are promising, however more time is needed to see if'the
consultant's model can predict the concentrations of nitrate nitrogen with a reasonable degree of accuracy.
Response
We agree that variability in the observed concentrations of NO3 in some of the wells is significant. For
groundwater observations these are caused by a combination of spatial and temporal variations in cropping
patterns and uptake of Plant Available Nitrogen (PAN); variations in percolation below the root zone that
leaches the residual NO3 in the vadose zone that are attributable to soil, topographic, and crop and native
vegetation patterns; and local scale variations in hydraulic conductivity, effective porosity, and depth to
Partially Weathered Rock (PWR). For surface water variations, this variability is caused by the previously
mentioned groundwater parameters as they affect rates and concentrations of NO3 in groundwater discharge
to surface drainage features above the sampling stations; and variability in processes that control surface
water runoff from the drainages above the stations, including storm intensity and duration, slope, drainage
area, vegetation and surface conditions that affect infiltration and runoff excess. Because the groundwater
flow and transport models do not model surface runoff, the surface water runoff contribution to NO3 loading
is not modeled. That contribution may either increase observed NO3 concentrations if the runoff contains
high concentrations of NO3 or reduce observed concentrations by dilution in those cases where the surface
water NO3 concentrations are low.
Because of this variability we used standard statistical trend analyses on the observed NO3 data for each
monitoring station to identify the trends shown in Table 3.
17.

eaje,('esarces
General Comment Number 7
Many of the statements in this document imply a level of certainty that is not supported by the duration of the
monitoring program, the results of the modeling, or the field data. Many factors can influence the accuracy
of analytical data, as well as the ability of capture wells to remove ground water from a specific area, and
none of these factors are mentioned in this document.
Response
The methods and data used to prepare all the models of flow and NO3 movement, including those used to
design the capture system, were consistent with industry practice and standards, as well as Division policy
documents. All the previous reports (CSA, SSA, CAP, Phase IIII Irrigation, and the 2012 report) from
which information was summarized in the 5 -year Report were approved by the Division by its acceptance of
those reports in connection with various CORPUD's various regulatory and compliance actions.
Specific Comment Number 1
Figure I (page 3) shows then entire site and location of wells, monitoring stations and remediation
strategies. This figure does a good job showing the general layout of the site, and locations of key elements,
but the font size is much too small to reasonably find and read the station id's or see .symbols on the map. In
addition the,figure does not seem to include surface water station locations for (SW -5, SW -8 & SW -25), nor
could all of the constructed wetlands be found on the map. A similar map would be very helpful in explaining
the site to the EMC. Please update the map and provide an electronic copy that can be included in a
PowerPoint presentation.
Response
Figure 1 was to have been presented as a 24" x 36" map at a scale of 1" = 500 feet to show all the monitoring
stations and site features. The constructed wetlands are included on this map. Surface water Stations SW -5
and SW -8 are west of the area shown on the map as provided, and SW -25 was inadvertently omitted. We
have included with this response a corrected map that includes these features. We apologize for not providing
the full size map with the report. We have increased the symbol size and changed the constructed wetland
symbol to a color that shows up better. For presentation in a PowerPoint presentation, the attached pdf
version of the corrected map should work if it is projected on a large screen (10 ft x 10 ft for example).
Specific Comment Number 2
Figure 7 (page 10) shows results of models that predict annual NO3 loading estimates. The figure shows the
expected difference in loading between the "updated model baseline" and the "updated model difference with
10 mg/L of loading". This difference seems to be much greater than the differences shown between the "SSA
model replica" and the "SSA model replica with 10 mg/L loading used,for permit debit". Please provide
more detail about why those two sets of curves appear so d f'erent.
The area under each curve in figure 7 represents the total mass of nitrate modeled to be discharged to the
Neuse River using the assumptions of the four different models. It is our understanding that all four models
have the .same initial amounts of nitrogen, and therefore the area under the "Replica SSA Model" and the
"Updated Model Baseline, No Additional Loading models" should be the same. Visual observation supports
this, but a summary table of annual loadings would help verify this. Also, extension of the figure to .show
where the x axis reaches ':steady state" would also be helpful. The area under the predicted curve for the two
models that deduct a possible 10 mg1l of loading from the groundwater discharge should also be the same.
Visual observation suggests that this is not the case. Please provide similar summary table, or other
additional information to clarify this.
Response
See response to General Comment 5. Also please note the following:
• The requested table is provided in the response to General Comment 5;
13

• The explanation of the 10 mg/I loading curves is provided in the explanation of curve 5 in the
response to General Comment 5; and
• Computation of the time it will take to reach the `steady state' referred to in the comment would entail
the time and expense of running the model until such time as that condition was achieved. Because
this time is of interest to both CORPUD and the Division we have fitted a second -order decay curve to
the modeled data from 2035 to 2053 shows that the debit will reach 0 lb/yr in approximately 2082.
Specific Comment Number 3
Also in Figure 7 it seems reasonable that the models that take into account the 10 mg/1 nitrate groundwater
standard should result in a step decrease in loading to the Neuse River for any given year compared to the models
that do not account for the loading up to the groundwater standard, assuming that flows are not changing
significantly./rom year to year. This assumption appears to be supported by the results shown for the updated
model (there is an approximately 44, 0001bs/year reduction in the loading at any time); however, the change for
the replica models seems to increase over time. Please explain the differences between the models and why the
decrease in the difference in loading occurs over time for the 10 mg1I curve.
Response
See response to General Comment 5 and Specific Comment 2.
Specific Comment Number 4
Section 1.3.1 describes a comprehensive 2011 field samplingprogram includingfield measurement s of in-situ
hydraulic conductivity at 14 boring locations at two depths. The hydraulic conductivity data, including a
comparison of the field -observed hydraulic conductivity and the adjusted value, should be provided. This
information is important because Section 1. 3.4 states that model calibration was achieved by manual and
automated fitting and adjusting the isotropic hydraulic conductivity of the Saprolite and PWR layers in the model.
The Division's GW Modeling Policy, issued May 31, 2007, states that "groundwater models should not be used as
a substitute for site-specific measurements of field data. Rather, the site specific measurements should be used to
constrain the modeling by providing data for model calibration ... " (Page 7). This information and many of the
model's other inputs are unknown to us and should be provided.
In addition, only data for Field 36 was provided (Figure 2). Data for the addition 29 fields did not seem to be
included in the attachments. Please submit the data for review, or explain why it is not necessary.
Response
Ksats measure vertical permeability in the soil and vadose zones, not hydraulic conductivity of the saturated zone.
However, these values were used as a general constraint on hydraulic conductivity during checks on the calibration
of the Updated Model, in accordance with Division modeling policy. The basis for the calibration of the Updated
Model in the 2012 report was accepted by the Division as demonstrated by your approval of that report as the basis
for approving the resumption of biosolids on the areas shown in Figure 1.
Field 36 is included in the 5 -year Report as an example only. The entire data and field and laboratory backup is in
the 2012 report. The 2012 report included these plots for all of the fields.
Specific Comment Number 5
Section 1. 3.7 Candidate Area for the Resumption of Biosolids Application: The Evaluation states that fields that
14

had no groundwater flow paths crossing the compliance boundary were identified as likely candidates for the
resumption of biosolids. A model was then run on these fields assuming application of biosolids at rates that
exceed the agronomic rates. The evaluation appears to conclude that this application will not cause exceedances
of the 2L standards at the compliance boundary after 50 years of application. This observation seems self-evident
in that fields were selected that do not have flow paths that intersect the compliance boundary. The study does not
report the potential changes in nitrate concentrations to the Neuse River resulting from over application. Please
provide comments on the accuracy of our understanding of the model and provide clarification on the potential for
surface water impacts where surface waters are identified as a groundwater receiver.
Response
You are correct that there was really no reason for the 2012 report to have evaluated the effect of over application
of nitrate on groundwater concentrations at the compliance boundary since the groundwater under all the fields
considered for resumed application of biosolids flows away from the compliance boundary. At the same time,
there is also no reason to assume that such over application will occur or to evaluate the effect of such hypothetical
over application on surface water. The conservative application rates that are being used and the rigorous best
management practices required by CORPUD's certified biosolids environmental management system will assure
that excess loading will not occur. Even if some small amount of overloading were to occur, as illustrated by
Figure 7, for at least the next permit cycle, the Debit remains conservative.
Specific Comment Number 6
Section 1.3.8: The graphs in this section show no change to the groundwater concentrations at the compliance
boundary due to the application of plus 5016/ac/yr load. "This is because no groundwater emanating from
beneath any of the identified candidate areas move across the compliance boundary before discharging to
surface drains. "I would like to see data/model of what will happen to the surface water concentrations/loads that
will then flow through their property and discharge the added nitrogen directly to the Neuse River, adding the
additional load in this manner as apposed through the groundwater. This load must be accounted for? It would be
if it were flowing out of their discharge pipe . How is this a possible loop hole when we have to meet the TMDL
load to the estuaryfrom all sources? This additional contribution needs to be added to their permitted TN load.
Response
See response to Specific Comment 5. As noted, the incremental load to surface water via groundwater due to
exceedances of the 2L standard is adequately accounted for by the Debit. There is no reason to assume that
additional loading will occur.
Specific Comment Number 7
Section 1.3.10.4.• The correlation coefficient for the data graphed on Figure 21 was not provided. Based on the
scatter of the data, it does not appear to be very high. The scatter suggests that there may be other factors
influencing the concentration ofnitrate nitrogen which are not being considered by the model.
Response
Figure 21 was not intended to demonstrate the correlation fit of observed to modeled data. Rather, it was intended
to
1) supplement the plots of measured and modeled NO3 concentrations shown by the examples in Figures 8
through 20 of the report and all of the Figures in Attachment 8 of the 2012 report for all monitoring
stations (the degree of fit over time at each station is best evaluated by these time plots); and
2) demonstrate that modeled concentrations at the end of 2013 were greater than observed concentrations at
the compliance boundary and in surface waters draining the fields, and thus, that the model is conservative.
Specific Comment Number 8
Section 2 Groundwater Containment Systems: Table I (Page 20) does not identify over what time period the
15

averages were calculated. In paragraph 3 it is stated that the majority offlow from the containment system comes
from the 7 wells of the Field 50 system. Based on the Actual Flow values provided in Table 1, Field 50 accounts
for 9,595 gal/d and Field 500 accounts for 24,388 gal/day, and therefore accounts for approximately 28% of the
total flow. It is also unclear of what significance is this data, and what conclusions are being made from the data.
Please provide further explanation.
Response
The average values shown in Table 1 on page 20 are the averages for the January 2008 through February 2014
period. These are the data reported to the Division on a monthly basis by CORPUD. The majority of the flow
comes from the 22 wells in Field 500. The report had a typographical error in this section regarding this. Here is
the corrected paragraph:
"Table 1 shows the design and measured average flow rates from each of the extraction wells for the period from
January 2008 through February 2014.. It is apparent from this table that the majority of the flow from the
containment system comes from the 22 wells of the Field 500 system. The actual average flow rate was 106% of
the design rate for Field 500, 121% of the design rate for Field 50, and 110% of the design rate for the total
system."
This information was provided as a part of the summary of the monthly reports on the operation of the
containment system which have been provided to the Division. It was included for completeness of the analysis
this data and no conclusions are or have been drawn from it.
Specific Comment Number 9
Table 2: Please include the average concentration of nitrogen for each year. This would make how the mass
loading was calculated easier to understand, and provide visual evidence of the consistency of the nitrate values.
The data for 2014 is incomplete and should be noted accordingly.
Response
Here is the updated Table 2. Mass was computed by the standard fonnula
LbNO3 = mg/I1,103 * MgalFi. , * 8.34.
Year
Flow to
NRWWTP
Average NO3 in
Flow to
NRWWTP
NO3 to
NRWWTP
Mgal
mg/I
Ib
2008
6.73
31
1756
2009
11.71
26
2558
2010
13.63
29
3245
2011
1 12.89
29
3168
2012
13.34
1 29 1
3172
2013
15.53
27
3467
2014
1.31
28
305
Total
75.15
17670
Table 2 (revised).— Summary of nater and NO3 removed from Field 50 and 500 groundwater containment systems. Note that the data for 2014
includes only the month of.lanuary.
Specific Comment Number 10
In the second paragraph on page 22, the average nitrate concentration delivered to the NRWWTP is discussed. At
one point it is stated that the concentration has averaged 30.4 mg11 and then in the last sentence it is stated that the
16

,�aie Ak5arces
concentration was 33.6 mg/l. Please explain this discrepancy.
Response
Please see the following corrected paragraph
"Monthly concentration data for inflow to the plant from CORPUD are available for the period January 2010
through January 2014. The average inflow to the plant concentration from these data is 29.2 mg/l. The monthly
average concentrations from sampling of all the extraction wells is available for the period from January 2008
through January 2014 and averaged 30.4 mg/1. The yearly volumes of groundwater and mass of NO3 delivered to
the NRWWTP from January 2009 through January 2013 are shown in Figure 23."
Specific Comment Number 11
In the first paragraph on page 23, it is stated that the flow to the NRWWTP has increased by approximately 6,740
gallons per month or 0.081 million gallons per year. This conclusion does not match with the data presented in
Table 2, which shows a more significant flow increase over time. Please explain this discrepancy.
Response
See the following revised chart and discussion using yearly data for clarity:
35
ca
25
OW
15
10
T
♦ Flow to Plant, Mgal/Yr
■ NO3, 1000 Ib/Yr
Average [NO3], mg/l
—Linear (Flow to Plant, Mgal/Yr) y = 0-1745x
—Linear (NO3, 1000 lb/Yr) y=1.4398(-
—Linear (Average [N031, mg/1) Y 0.
- 347.88
2983.8
2008 2009 2010 2011 2012 2013 2014
Figure 23 (Revised): - Annual flow of groundwater and mass of NO3 delivered to the NRWWTP from the remedial containment systems from
Table 2.
As shown on Figure 23, the 99% statistically significant rate of increase in flow is 0.175 million gallons / year, and
the rate of increase in mass of NO3 delivered is approximately 1;400 ]b/year. The slight decrease in the rate of
NO3 delivered to the plant may be the result of increases in flow caused by further development of the wells as the
17

iWepesarne5
result of pumping
Specific Comment Number 12
In the thirdparagraph on page 23, the contribution offlow and nitrate from the two extraction fields is discussed.
The % of flows contributed from the well fields does not match the data shown in Table I on page 20. Specifically,
Table I indicates that the majority of the flow is from Fields 500. Please clary.
Response
The third sentence of the paragraph in question is incorrect. It should read as follows:
"Approximately 72% of the groundwater captured is derived from the wells in Field 500."
Specific Comment Number 13
Section 3 Evaluation of Monitored Natural Attenuation: Table 3 is very difficult to interpret. It is unclear if the
specified rate offitrate Concentration Change is increasing or decreasing based on the levels provided. It is
assumed that <0.0 would be a negative slope or decrease in concentration, and that
>0.0 would be a positive slope or increase in concentration . Please clary. It is not clear what data is associated
with the term "Trend". It assumed that the data indicated as "Trend" is observed data. Please clarify. The table
identifies a category of wells as "Other Monitoring Wells ". It is assumed that this data if for the interior
monitoring wells. Please clam.
Response
The assumptions are correct: < 0.0 is a statistically significant linear decrease in concentration; > 0.0 is a
statistically significant increase in concentration; trend refers to observed concentrations; model refers to modeled
concentrations; and `Other Monitoring Wells' refers to wells in the on-going monitoring program that are interior
to the Site and not Compliance Monitoring Wells.
Specific Comment Number 14
In the second paragraph on page 29, it states the rate of decrease is approximately twice as large as the
magnitude of the increasing trends for the interior wells. Assuming the data is summarized as "Other monitoring
wells "the average "Trends"for the data is -3.39 and +3.19. This does not seem to indicate that the rate of
decrease is twice as great as the rate of increase. Please clarify.
Response
We have revised the first two paragraphs on page 29 and Table 3 as follows:
"NO3 time vs. concentration plots for all the compliance wells are included in Attachment 3. As shown in Table
3, approximately the same numbers of compliance wells show increasing and decreasing trends based on observed
values and the magnitude of the rate of decrease (3.38 mg/l/yr) is approximately twice as large as the magnitude of
the rate of increase (1.83 mg/l/yr).
Although the monitoring wells interior to the Site are not used to assess 2L compliance, they are included in this
analysis as a general indicator of the effectiveness of MNA following the cessation of biosolids application in
2003. As shown in Table 3, approximately the same numbers of these interior monitoring wells show increasing
and decreasing trends based on observed values. The magnitude of the rate of decrease (3.39 ung/I/yr) is
approximately the same as the magnitude of the increasing trends (3.19 mg/I/yr). The plots for all the interior
wells are included in Attachment 4 to this report."
1R

i 4e &Sauces
Compliance Monitoring Wells
Other Monitoring Wells
Statistically Significant Rate of
[NO3] Change, mg/I/year
% of
Total
Statistically Significant Rate of
[N031 Change, mg/I/year
% of
Total
<
0.0
No of
Stations
Data 9
53%
<
0.0
No of
Stations
Data 19
44%
Model 2
12%
Model 13
30%
Rate of
Change
Data -3.38
Rate of
Change
Data -3.39
Model -1.3
Model -2.09
0
No of
Stations
Data 1
6%
0
No of
Stations
Data 8
19%
Model 1
6%
Model 1
2%
0.0
No of
Stations
Data 7
41%
>
0.0
No of
Stations
Data 16
37%
Model 14
82%
Model 29
67%
Rate of
Change
Data 1.83
Rate of
Change
Data 3.19
Model 1.86
Model 1.64
Total Stations 1 17
Total Stations 43
Surface Water Stations
All MNA Stations
Statistically Significant Rate of
[N031 Change, mg/I/year
% of
Total
Statistically Significant Rate of
[NO3] Change, mg/I/year
% of
Total
<
0.0
No of
Stations
Data 9
75%
<
0.0
No of
Stations
Data 37
51%
Model 4
33%
Model 19
26%
Rate of
Change
Data -2.26
Rate of
Change
Data
Model -1.56
Model -0.91
0
No of
Stations
Data 2
17%
0
No of
Stations
Data 11
15%
Model 1
8%
Model 3
4%
0.0
No of
Stations
Data 1
8%
>
0.0
No of
Stations
Data 24
33%
Model 7
58%
Model 50
69%
Rate of
Change
Data 0.42
Rate of
Change
Data 2.43
Model 0.51
Model 1.64
Total Stations 12
Total Stations 72
Table 2(Rerised): - Comparison of trend in observed and modeled N*03 at NO IA titrations.
Specific Comment Number 15
Section 4.2 Evaluation of Removal Efficiencies of Wetlands: For Table 5, please explain the significance of the
"Probability of Significant Mass Removal" and how it is calculated. This only seems to add confusion and
complexity to the results.
Response
The purpose of including the analyses in Table 5 was to determine if a statistically significant reduction in NO3
had occurred between the sampling stations upstream and downstream of each constructed wetland using the data
from the time of construction (February 2013) to March 2014 and from the time the wetlands became fully
functional as the result of improvements in outlet structures (July 20] 3) to March 2014. The statistical test used
(one-way Analysis of Variance) tests to see if the population represented by the downstream samples is different
than the upstream samples by testing both the mean and variance of each of these populations. The probability of
mass removal in the table is the probability that there is a significant difference between the upstream and down
stream populations for each of the periods used for analysis.
19

The last column in Table 5 was included to account for the probability that mass is actually being removed and as
shown in the table is the product of the probability that mass is actually being removed and the average reduction
between the upstream and down stream stations.
To the extent that the statistical analysis is confusing it can just be disregarded. The overall conclusion is that the
wetlands are functioning as designed (though there is no regulatory requirement for them to remove a minimum
mass of NO3).
Specific Comment Number 16
Section 6 Conclusions: The conclusions do not make recommendations on whether the updated modeling results
should be used to calculate the NPDES nitrogen debit, and does not comment on the City's intent to update the
model and debit results in the future.
Response
There is no intent to use the Updated Model to recalculate the Debit at this time. As shown in the response to
General Comment 5, the current debit is conservative in that it overstates the discharge of NO3 to the Neuse River
and tributaries.
Specific Comment Number 17
Modeling shows that debit is significantly higher than it should be based on new modeling. This should be
reviewed in the next permit cycle table in the current permit is through 2017.
Response
See the response to General Comment 5 and Specific Comment 16.
Specific Comment Number 18
The conclusions do not make recommendation on if the groundwater containment system and the subsurface
wetlands systems should be continued to be operated, or if their area of coverage should be increased or
decreased.
Response
Although a case could certainly be made for discontinuing operation of the groundwater containment system and
the subsurface wetland systems, CORPUD intends to continue operating those systems as they currently operate at
least until the next 5 -year report required by the Variance. However based upon this review it is recommended that
the 29 extraction wells be reduced from triennial sampling to annual sampling. This sampling event would occur
concurrently with one of the existing sampling events (March, July, or November).
Specific Comment Number 19
Since no recommendations have been made it is assumed that the City support continuation of the current
variance agreement. Based on the effectiveness of the on-going remediation, and current predictive model,
please clary the City's recommendations for future implementation of the variance.
Response
The City does not propose any changes in the current implementation of the Variance. As discussed in the
response to Specific Comment 18, it does propose a modification to the approved Corrective Action Plan to reduce
the frequency of monitoring the 29 extraction wells.
20

Specific Comment Number 20
Section 6.1 Groundwater Modeling Conclusions: The first statement indicates that an additional nitrate source
was added to the hydrogeological model. Section 1.3.3 did not describe this addition and the impacts it had on the
results of the model. It seems reasonable that an additional source of nitrate the resulted in a "significant'
modification to the model would have an impact to the results, and likely cause increased predicted concentrations
of nitrate in the groundwater.
Response
No additional nitrate sources were added. The 2012 report describes the modifications to the source term used in
the Updated Model as output from models of the vadose zone under each field so as to account for the delay
caused by transport through this zone. The input to each of these models was the same as used as recharge to the
water table in the Variance Model. The conclusion statement refers to the delay through the vadose zone that was
not included in the Variance Model.
Specific Comment Number 21
Section 6.2 Groundwater Containment System Conclusions: The report states that "The containment system for
Field 500 is capturing essentially 100% of up -gradient groundwater and preventing the further down -gradient
migration of NO3. " and that, "The containment system for Field 50 is capturing approximately 50% of up -
gradient groundwater containing and reducing the down -gradient migration; " These statements are questionable,
as we do not appear to know enough about the volume and pathways of groundwater flow in these areas.
Response
The particle tracking method that was used in the Variance Model to design the spacing and approximate pumping
rates for the recovery wells is the same method used in the Updated Model. The analyses with the Updated Model
reported in the 5 -year Report however, used actual average pumping rates over the period the system has been
operating. Both the Variance Model and the Updated Model included the same hydrostratigraphic units (Saprolite,
Partially Weathered/Fractured Rock) and Fractured Bedrock, as well as zones on either side of intrusive dikes that
were assumed to be more permeable than any of the units and which cross -cut all units. Based upon field
investigations documented in the CSA, SSA, and the 2012 Report, there is no evidence that any of these later
permeable units occur within the modeled capture zones for fields 50 and 500. The Division has previously
accepted this conceptualization of the hydrogeologic units at the site and the Variance and Updated Models upon
which they were built as evidenced by its approval of the SSA and Corrective Action Plan, and by its modification
of the Permit to allow the resumption of biosolids application on the fields. It is not clear to us why the Division
now questions the understanding of the hydrogeology of the Site.
Specific Comment Number 22
Section 6.3 Monitored Natural Attenuation Conclusions: The 3rd conclusion states that since more observed than
modeled trends show decreasing nitrate concentrations over time, the model predicts longer times to achieve
compliance than is indicated by the observed data. The presence of a decreasing nitrate concentration does to
necessarily mean that the rate of decrease in the observed values is, or will continue to be, as great as in the
model. Therefore, it may not be reasonable to conclude that the model predicts a longer time to achieve
compliance than the observed data without presenting more data on the rate of change.
Response
The Variance does not specify a time frame to achieve compliance with 2L standards at the compliance boundary.
The conclusions of this review and the 2012 report that data and modeling show that concentrations at the
compliance boundary will be variable in the future and that it may take as much as an additional 30 to 40 years for
all NO3 concentrations to reach the 2L standard everywhere along the compliance boundary. This is the direct
result of the time it will take for NO3 in recharge to groundwater to be reduced in the vadose zone beneath the
21

e44e K'eMM-5
fields from which groundwater moves to the compliance boundary as well as the time it takes the compliant
concentrations from these fields to reach the compliance boundary.
Specific Comment Number 23
Section 6.4 Surface Wetlands Conclusions: The first paragraph supports the statement that the wetlands are
effective at removing nitrate by stating that the overall mass removal is only a small fraction of the mass entering
all the drainage areas. This is further qualified with the statement "if all loading to the fields is at the 2L standard
of 10 mg1I ". Please explain the significant of the qualifier concerning the 2L
standard. It seems that the conclusion statement is true independent of the loading to the fields.
Response
We have removed the qualifier from the conclusion and the revised conclusion is as follows:
"The fully functioning wetlands are effective at removing NO3 from the surface water. The loading to the Neuse
from continued discharge of groundwater surface water containing NO3 at concentrations greater than the NC 2L
standard of 10 mg/l has not resulted and will not result in exceeding the NC 2B standard for NO3. The N loading
to the Neuse from this source is accounted for by the Debit."
Additional Comment Number 1
Figure 2 (Page 5) Is the modeled NO3 Concentration represented by the green line?
Response
The green line represents the measured concentrations in Soil Boring SB -36-2. Please refer to the 2012 report for
the explanation of the vadose zone sampling and analyses from which this figure was taken.
Additional Comment Number 2
Figure 3. (Page 6) The two fitted lines are not identified clearly. It is unknown what the "VS2DTAgrate 140
lb/ac/yr 2011 " line represents and the dashed red line is not identified at all.
Response
The `VS2DT Agrate' refers to NO3 concentrations vs depth computed at the end of 2011 with the VS2DT model
for Field 36 using an agronomic uptake rate of 140 lb/ac/year to compute the concentrations of NO3 over the time
biosolids were applied to the field at the rates documented in the SSA Appendix G, as explained in the 2012
report. The red dashed line is the same using an agronomic uptake rate of 200 lb/ac. Both curves are shown to
show the sensitivity of the computed NO3 profiles with depth to the assumed agronomic uptake rate compared to
the measured NO3 values. The legend on Figure 3 inadvertently was not enlarged to include the definition of all
the curves.
We have included below a revision of Figure 3 that corrects the line style for the modeled curve in the legend and
which only includes the modeled curve for an agronomic uptake rate of 140 lb/ac/yr"
22

�a�'e �f'esairces
Field 36
0 — --- —
5 --O-58-36-1
�I � ! L I
♦ SFS -36-1 CORPUD Lab
i
--A—SB-36-2w 10 ♦ SB -36-2 CORPUD Lab --
5 1 Piezometer 36-1
CL
—Groundwater Level (PZ -36-1) I
0 15 —VS2DTAgrate1401b/ac/yr2011 i
20 -- -- — - - --- ---i---
25
1.0 10.0 100.0
[N031 in Soil Moisture or Groundwater, mg/1)
Figure 3(Recised)..- Measured and Modeled NO3 profile for Field 36
Additional Comment Number 3
Figure 4. (Page 7) the dashed black line is not identified
Response
The dashed black line is the percolation tate of water below the root zone used for the VS2DT simulation for the
example of Field 36. These are the same values as the recharge rates shown in Table G-3 of the SSA.
The legend on Figure 4 inadvertently was not enlarged to include the definition of all the curves. Please see below
the revised Figure 4 that identifies all the curves.
600 1 Field 36 NO3 Concentration in Recharge to Watertable 6
500
400
300
m
Z 200
100
d
4 y
1
0 4 ..�,-.a.i - .. 0
12/31/70 12/31/90 12/31/10 12/31/30 12/31/50
Figure 4(Revised).-. Percolation of water and NO3 below the root zone used as input to the radose zone column model and computed
concentration in recharge to the groundwater as output from the column model for Field 36.
93

Oa je &izrce5
Additional Comment Number 4
1.3.10.4 Effectiveness of Modeling at Compliance Wells and Surface Water Stations: Figure 21 shows what
appears to be a high level of variation between the fitted line and the data for the compliance wells. It may be
helpful to show how the level of variation has changed over time. Demonstration that the observed data is more
closely matching the predicted values would provide additional support of the proposed models. This is also an
example of where it is unclear which model is used to show closeness of the observed data.
Response.
See response to Specific Comment 7.
Additional Comment Number 5
The x-axis label on Figures 23, 23, and 27 are difficult to interpret; it would be helpful if dates were used
instead of time from a specified starting point, and if the same scale was used for figures showing data
over similar time spans. The secondary Y axis (Flow to Plant, Mga/month) in Figure 23 is also difficult to
use as it is difficult to compare the data in Figure 23 with data presented in Table 2.
Response
Please see the revised Figure 23. With this revision, we believe that the captions on Figures 25 and 27 are clear
and that these figures as intended show the variation in NO3 in all of the recovery wells and the trend in the
average concentration since the system has been in operation.
350 -
E
en 300
O
V 250
m
z
E 200
i
a+'
m 150
a
0
O 100
Z
N
H
50
0 1
J-08
J-09 J-10 J-11 J-12 J-13 J-14
1.60
1.40
1.20 L
0
1.00
m
0
0.80
c
a
0.60 °
3
0
LL
0.40
0.20
1M
Figure 23 (Revised).—Monthly now of groundwater and mass of NO3 delivered to the NRWWI'P frnm the remedial containment systems.
24
♦ A
■
, A
A E
■
■�AA
A
AAA AQ1
♦
■ ■
Y� A
•
■
■
A
♦ (N031
■ Lb NO3
■ ■
■
A Flow, mgal/mo
♦
—Linear ([NO3])
—Linear (Lb NO3)
-Linear Flow, m al mo
10
0 1
J-08
J-09 J-10 J-11 J-12 J-13 J-14
1.60
1.40
1.20 L
0
1.00
m
0
0.80
c
a
0.60 °
3
0
LL
0.40
0.20
1M
Figure 23 (Revised).—Monthly now of groundwater and mass of NO3 delivered to the NRWWI'P frnm the remedial containment systems.
24

,raj'e,f'esarces
Additional Comment Number 6
Section 1.3.10.1, 20.2, and 10.3 the report makes the following conclusions:
"We conclude from this evaluation that the model reasonably represents N0, concentrations in the
remedial wells and that it can be used as a reasonable tool to assess the effectiveness of the
hydraulic capture of groundwater from Fields 50 and 500. "
"We conclude from comparing the plots of observed and modeled concentrations in the compliance
wells that the model provides a reasonable tool to assess the likely future reductions in NO3 at the
compliance boundary as the result of natural attenuation. "
"We conclude from the comparison of modeled and observed concentrations in surface water drains
that the model is a reliable tool to assess present and likelyfuture N0, loading to surface water. "
The Division does not feel that there is sufficient data to support the conclusions; however it does seem
reasonable based on available data to continue the current remediation strategy and to continue to monitor
its effectiveness.
Response
Based upon the Division's acceptance of the 2012 report that was used to support the approved request for the
resumption of the application of biosolids on selected field areas, we do not understand why the Division now does
not feel the conclusions in the 5 -year Report, which are taken from the 2012 report, are not supported. CORPUD
and Eagle Resources would appreciate being advised of hydrogeologie models that have been developed by other
consultants and regulated parties that the Division considers more reasonable and reliable tools than the model
here. In addition, we would like to know if models used by the Division for its own regulatory purposes (e.g.,
Falls Lake nutrient management strategy) models are supported by as much monitoring data and are better
correlated to observed data than the model here. In any case, Additional Comment 6 does not seem to have any
practical significance. As stated elsewhere in this response, the City will continue the operation of the active
remediation system, the constructed wetlands and the monitoring program. However, please note as stated in the
response to Specific Comment 18, it is recommended that sampling and analyses of the remedial wells be reduced
to annual.
Additional Comment Number 7
Section 2.1 Effectiveness of Groundwater Capture by the Active Containment System. The report states that,
"Based upon where these (capture) zones cross the down -gradient (northern and eastern) boundaries of Field 500,
essentially 100% of the groundwater emanating from Field 500 is captured and the system has been 100%
effective in meeting the objectives of the containment system for that field. "
This statement is questionable, as we do not know how much of the ground water is escaping capture by traveling
beneath the well screens of the capture wells, or escaping through fractures in the bedrock beneath.
Response
See the response to Specific Comment 21.
25

ea*&Urrce5
Additional Comment Number 8
The text references Figure 22, however there is no Figure 22 in the report. It is assumed that the figure on
page 21 is Figure 22, but it is not labeled as such. The discussion references down -gradient monitoring
wells adjacent to Fields 500 and 50. It is assumed that the wells referenced are mw -117 and mw -203, but it
is not specified. Please clary ifnecessary.
Response
Figure 22 is included on page 22 but the drawing file had it labeled as Figure 2. Please see the attached Figure 22
11 x 17 version of this Figure with the correct number.
Please see the revised paragraph from page 25 that discusses the wells down -gradient from Fields 50 and 500:
The updated model was also used to generate likely NO3 future concentrations at locations of monitoring wells
that are down- gradient from the compliance boundaries of Fields 500 (well MW -203) and 50 (well MW -117) with
the remedial system in continuous operation if the system had not been turned on.
Additional Comment Number 8
Section 4.2 Evaluation of Removal Efficiencies of Wetlands. The lack of the year on the X-axis scale makes this
figure difficult to evaluate.
Response
See the revised title for Figures 30, 31, and 32
Figumro 30(Revised) .—Comparison of NO3 mass in inflow and outflow for Wetland A covering the period from the start of operation of the
wetland in February 2013 through April 2014.
Figure 31(Revised).— Comparison of NO3 mass in inflow and outflow for Wetland C covering the period from the start of operation of the
wetland in February 2013 through April 2014.
Figure 32(Revised) : - Comparison of NO3 mass in inflow and outflow for Wetland E covering the period from the start of operation of the
wetland in February 2013 through April 2014.
P

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EXPLANATION
Capture Zones
Envelope of Capture Zones
B
Locations for Comparison of Pumping Effectiveness
Steady State Watertehle while Pumping
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s
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Compliance Well
O
Monitoring Well
..
Recovery Well
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