WQ0001740_Appx-D-2 DWR Additional Information Request_20140612

Pat McCrory
Governor
4*-
'♦ R
NorthCarolina Department of Environment• Natural Rr
June 12, 2014
Tim Woody, Wastewater and Reuse Superintendent
City of Raleigh
P.O. Box 590
Raleigh, NC 27602
Dear Mr. Woody:
John E. Skvarla, III
Secretary
Subject: 5 -Year Evaluation of Remedial Strategy
Additional Information Request
City of Raleigh Residuals Program (D)
Wake County
The Division has reviewed the 5 -Year Evaluation of Remediation Strategy, Biosolids Fields at the Neuse
River Wastewater Treatment Plant, Wake County, NC under Permit#WQ0001730, received on April 7,
2014. It is the Division's intent to use this report to provide a summary of the remedial actions to the
Environmental Management Commission (EMC), and to make recommendations for the continued
implementation of the approved variance. In preparation of this, the Division would like a few
clarifications to the information in the report and additional information that will be helpful to update the
EMC.
Please address the items on the following pages by July 11, 2014. If the City needs additional time to
prepare a response, please contact me prior to July 3rd, so an appropriate timeframe can be established.
Beginning on page 8, items listed do not need a response prior to the Division updating the EMC. The
City may wish to provide addition clarification if deemed necessary, or use the comments to improve
future reports.
All revised and/or additional documentation shall be signed, sealed and dated, with three copies submitted
to my attention at the address below. If the entire report is updated, the Division would appreciate an
electronic copy for review.
If you have any questions regarding this request, please do not hesitate to contact me at [phone], or
jon.ris ag [e-mail]. Thank you for your cooperation.
Sincerely,
l
Jonisgaard
Supervisor, Non -Discharge Permitting Unit
cc: Raleigh Regional Office, Water Quality Regional Operations Section
Eric Lappala, P.E. — Eagle Resources (PO Box 11189, Southport, NC 28461-1189)
Permit Application File WQ0001730
1636 Mail Service Center, Raleigh, North Carolina 27699-1636
Phone: [phone] Internet: htto://Portal.ncdenr.org/web/wq
An Equal Opportunity 1 Affirmative Action Employer — Made in part with recycled paper

General Comments:
The purpose of the submitted report is to meet the requirements of Order 4 (f) of the Approved 2010
Petition for Variance from Ground Water Regulations 15A NCAC 2L .0107(K)(3)(A) and 15A NCAC 2L
.0106Q) by the City of Raleigh. This condition states that:
"Beginning in January 2014 and every five years thereafter, Raleigh shall evaluate the
effectiveness of the overall remediation strategy required herein to determine if new or
additional treatment technologies exist that could be implemented cost-effectively while
maintaining safety of human health and the environment. These evaluations and reports
shall also include review of modeling results against observed data. Collection of
additional data and information to improve model calibration or to better evaluate
potential treatment technologies may be requested by the DWQ. "
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.
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.
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 of the 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.
Throughout the reports, there are conclusions made that the model "reasonably" represents NO3
concentration. Please provide more detail on the criteria used to determine if a "reasonable" fit is shown.
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 helpful to include
a table showing the NPDES debits included in the approved variance for each year, as well as the
predicated values in the updated model.
City of Raleigh - 5 -Year Evaluation of Remediation Strategy Page 2 of 10
WQ0001730

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.
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.
Comments on specific sections:
Figure 1 (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.
City of Raleigh - 5 -Year Evaluation of Remediation Strategy Page 3 of 10
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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
hermit debit". Please provide more detail about why those two sets of curves annear so different.
160,000 -
140,000
120,000 -
N
d
100,000 -
C
80,000
d
N
60.000
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Q
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tic
40,000 '
m
O
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20,000 -
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4...Replica
of SSA Model
-Replica ofSSA Model - Difference between
SSA Model and 10 mg/loading used for Debit
--Updated Model Baseline, no Additional
Loading
-Updated Model- Difference Between No
Additional Loading and 10 m&A loading
0 Mbit Values from Permit
_.._,..__
.........
0
1.4
Jan -80
Dec -89 Jan -00 Dec -09 Jan -20 Dec -29 Jan -40 Dec -49 Jan -60
F•igurr 7. ••d miparismi NO3 dschat7.;c to the Ncu>c W%cr and its tributaries that drain the CORITO fields ander historic Inn
further luadingl and additiomil constant lauding of 5U IlWachratarting in 2013 Oa the aciccted 385 acres and heading front the
SSA nwdctc.
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 IOmg/1 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.
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Also in Figure 7 it seems reasonable that the models that take into account the l Omg/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 from year to year. This assumption appears to be supported by the results shown
for the updated model (there is an approximately 44,000 lbs/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 lOmg/l
curve.
Section 1.3.1 describes a comprehensive 2011 field sampling program including field 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 modelcalibration 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.
Section 1.3.7 Candidate Area for the Resumption of Biosolids Application: The Evaluation states that
fields that 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 observations 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.
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 50 lb/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 estuary from all sources?
This additional contribution needs to be added to their permitted TN load.
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 of nitrate nitrogen which are not being considered by the model.
City of Raleigh - 5 -Year Evaluation of Remediation Strategy Page 5 of 10
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Section 2 Groundwater Containment Systems: Table 1 (Page 20) does not identify over what time
period the averages were calculated. In paragraph 3 it is stated that the majority of flow 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 gaud 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.
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.
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 mg/l and then in the last
sentence it is stated that the concentration was 33.6 mg/l. Please explain this discrepancy.
In the first paragraph on page 23, it is stated that the flow to the NRWWTP has increased by
approximately 6,740gallons 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.
In the third paragraph on page 23, the contribution of flow 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 1 on
page 20. Specifically, Table 1 indicates that the majority of the flow is from Fields 500. Please clarify.
Section 3 Evaluation of Monitored Natural Attenuation: Table 3 is very difficult to interpret. It is
unclear if the specified rate of Nitrate 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 clarify. It is not clear what data is
associated with the term"Trend". It-assurried that -the data-iridicate(I-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 clarify.
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.
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.
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.
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.
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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
modeITplease-clarify-the-eity's-recommendations-for-future-implementation-ofthe-variance.
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.
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.
Section 6.3 Monitored Natural Attenuation Conclusions:. The P 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.
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 mg/1". 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.
City of Raleigh - 5 -Year Evaluation of Remediation Strategy Page 7 of 10
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Additional items (response to these items is optional)
Figure 2 (Page 5) Is the modeled NO3 Concentration represented by the green line?
Figure 3. (Page 6) The two fitted lines are not identified clearly. It is unknown what the "VS2DT Agr ate
1401b/ac/yr 2011" line represents and the dashed red line is not identified at all.
25
1.0 10.0 100.0
1N031 in Soil Moisture or Groundwater, mg/1)
NVre 3.: - NImNured :md Modeled NO3 profile for 1,16136
City of Raleigh - 5 -Year Evaluation of Remediation Strategy Page 8 of 10
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Figure 4. (Page 7) the dashed black line is not identified.
��!l r '; � � � ��� i�' i - � � _�T
100
0-
12/31170 12/31/90 12/31/10 12/31/30 12/31/50
4— Ifercula I hin of It aic I- aria NO3 h L I if it the Iron I torn, used U, input I it the tmhrc vnnc r"Ifinut n I If ilel anti Cn Iti I tutc, I
ronccnirAtion in rcclnfvj;c fit the grocind".1ter ., .111pul from tl,v column In"dol for Field 36.
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.
140
130
120
110
100
90
80
70
60
50
0
z 40
T
Z 30
20
10
0
0 10 20 30 40 50 60 70 80 90 100 110 120 330 140 150
Observed NO3 Concentration as of 12131/2.013, mg1l
I i,-" 21 1 "03 ( .1 '1" -d J ,1 1% ON —.1 S-1— t,
City of Raleigh - 5 -Year Evaluation of Remediation Strategy Page 9 of 10
WQ0001730
Lid—
1+
1.65
8/
H,
X;
1.2,
82X
Compliance Wells
13 Su dace Water Stations
L'i
—Unear(Compliance Wells)
Linear (Surface Water
'Stations) I I 1 1 1
7-
13
T_
0 10 20 30 40 50 60 70 80 90 100 110 120 330 140 150
Observed NO3 Concentration as of 12131/2.013, mg1l
I i,-" 21 1 "03 ( .1 '1" -d J ,1 1% ON —.1 S-1— t,
City of Raleigh - 5 -Year Evaluation of Remediation Strategy Page 9 of 10
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The x-axis label on Figures 23, 25, 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.
400
350
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2
v 250
c
m
M 200
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To
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a 100
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0 10 20 $04.....- 60 70
Months since 1/1/2008
I'i urc 2 is Niolld} no%, of yroundtcttld macs of W dcliccrcd Io iltc NIONANI i' from the tedial coniaintucnl ti stents.
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 NO3
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 likely future NO3
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.
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.
City of Raleigh - 5 -Year Evaluation of Remediation Strategy Page 10 of 10
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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-tc-Fields-500-and-50—Itis-assumed-that-the wells referenced are mw -1-T7 and mw -2-0-3; bu
it is not specified. Please clarify if necessary.
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.
Wetland A
4.50
3.50
A
A
3.00
0 2.50
2.00
z
o 1.50
A
a 1.00
0.50
0.00
12/18 1/17 2/16 3/18 4/18 5/18 6/17 7/17 8/17 9/16 10/16 11/15 12/16 1/15 2/14 3/16 4/16
Fi,u:i 31i,—('eulpari>(u) or\03 111:1, i1= infiml and uolHuly fur WHImIcl ;1.
City of Raleigh - 5 -Year Evaluation of Remediation Strategy Page 11 of 10
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4
*Mass in ib/day
E3 Mass Out Ib/day
1
i
I i
' 1
a
i
13
i
{
0.00
12/18 1/17 2/16 3/18 4/18 5/18 6/17 7/17 8/17 9/16 10/16 11/15 12/16 1/15 2/14 3/16 4/16
Fi,u:i 31i,—('eulpari>(u) or\03 111:1, i1= infiml and uolHuly fur WHImIcl ;1.
City of Raleigh - 5 -Year Evaluation of Remediation Strategy Page 11 of 10
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