WQ0001740_Report Summary for EMC 150612_20150708

AFF
�FLA.
NCDENR
North Carolina Department of Environment and Natural Resources
Pat McCrory Donald R. van der Vaart
Governor Secretary
Summary of City of Raleigh's 2014 Five -Year Variance Report
History
In 2009, the EMC approved a variance request from the City of Raleigh that affected the City's Corrective Action Plan
(CAP) to address elevated nitrate concentrations in the groundwater which resulted from the over application of
biosolids at the Neuse River Wastewater Treatment Plant (NRWWTP) in Raleigh, NC. The variance request was for relief
from the requirement of 15A NCAC 02L .0106(k) so that Raleigh would not be required to remediate groundwater to the
level of the standards beyond their compliance boundary at the NRWWTP land application site. Conditions of the
approved variance included (a) accounting for nitrogen contributions to the Neuse River from the groundwater as part
of the City's NPDES discharge allocation for nitrogen, (b) continued monitoring of the natural attenuation of
contaminated groundwater instead of actively remediating the entire groundwater contaminant plume, and (c) active
remediation of a portion of the contaminant plume that was migrating in the direction of former water supply wells.
Historical documentation of the variance decision is attached as an appendix of this document and includes the
following:
• Appendix A: EMC Final Decision Granting Variance
• Appendix B: Division's Corrective Action Plan (CAP) Final Approval and a Revised Attachment 2 clarifying
monitoring requirements
• Appendix C: EMC Meeting Minutes, November 19, 2009, Item 09-57 Request for Approval of Hearing Officer
Recommendations on the City of Raleigh Public Utilities Department Groundwater Variance Request
• Appendix D: Five -Year Evaluation of Remedial Strategy, Biosolids Fields at the Neuse River Wastewater
Treatment Plant, Wake County, North Carolina under Permit #WQ0001730, DWR additional information
request, City of Raleigh Response.
Currently, in addition to the debit to its NPDES nitrogen allocation discussed below, the City is implementing an
approved groundwater CAP, which includes the following remediation activities:
• Groundwater Containment System;
• Monitored Natural Attenuation;
• Constructed Subsurface Flow Treatment Wetlands; and
• Off-site Riparian Buffer Restoration.
Variance Condition
The approved variance (2009) requires the City to evaluate the effectiveness of the overall remediation strategy and to
determine if new or additional treatment technologies exist that could be implemented cost-effectively, including the
review of modeling results against observed data. The report is required for every 5 years, beginning in 2014. The
Non -Discharge Permitting Unit
1617 Mail Service Center, Raleigh, North Carolina 27699-1617
Phone: [phone] Internet: http://Dortal.ncdenr.org/web/wq
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Commission, at request of the Division or upon its own initiative, may reopen this variance to address potential changes
to its terms or conditions in light of new information or changed circumstances.
Report Findings
General
The City submitted the "Five -Year Evaluation of Remediation Strategy, Biosolids Fields at the Neuse River Wastewater
Treatment Plant, Wake County, North Carolina under Permit #WQ0001730" to NCDENR on April 7, 2014, and additional
information at NCDENR's request was submitted on August 29, 2014. The Five -Year Variance Report shows results of an
updated model which uses additional field investigations and data (i.e. updated groundwater flow and transport model).
The City indicates that the updated model provides a more accurate and complete description of the source of nitrate in
recharge to the groundwater system by documenting the presence and transport of residual nitrate below the root zone
in the land application fields; these high residual concentrations 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 these fields. In
addition, the slower travel through the vadose zone resulted in smoothing out concentration variations and increasing
the duration of excess Plant Available Nitrogen (PAN) in the soil traveling to the water table. The figure below shows the
predicted annual Nitrogen loading to the Neuse River from both the original variance model (red line and red dashed
line) and updated model (green line and green dashed line).
140,000
120,000
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d
100,000
v
c
A
80,000
z
w
N
3
N
Z 60,000
0
Ym
i
a
J
� 40,000
3
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C
Q
20,000
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1/1/1980 12/31/1989 1/1/2000 12/31/2009 1/1/2020 12/31/2029 1/1/2040 12/31/2049
Figure 1— Models of N Loading to Tributaries and Neuse River
It is important to note that both models show Nitrogen loading to be less than the specified debits from Raleigh's NPDES
permit (2008 - 2022). The debits of N loading to the Neuse River from Raleigh's NPDES permit beyond year 2022 have
not yet been determined.
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July 8, 2015

Computation of the time it will take the debit to reach 0 (zero) Ib/yr using the variance model shows that it will be
approximately in 2050, however, using the updated model, this time is extended to 2082.
Historic and projected annual values of N loading to the Neuse River are shown in table 1. (Full N loading data including
discharge from NRWWTP are on page 10 of the City's Response received August 29, 2014)
Table 1- Historic and projected annual N loading and Debit values in NPDES Permit
Year
Predicted N Load to Neuse River (in Excess of 10 mg/I)
Debit in NPDES
Permit (Ib/yr)
Variance Model (Ib/yr)
Updated Model (Ib/yr)
2008
115,402
75,576
120,058
2009
111,748
76,958
117,183
2010
107,719
77,791
114,246
2011
103,487
77,671
110,370
2012
99,146
77,602
106,196
2013
94,804
76,878
102,022
2014
90,462
75,172
97,549
2015
86,186
73,807
93,276
2016
82,020
71,956
89,002
2017
77,965
69,744
84,828
2018
73,954
67,490
80,754
2019
70,119
64,856
76,679
2020
66,350
62,734
72,803
2021
62,691
60,459
69,026
2022
59,165
57,804
65,250
Note - According to figure 1, the updated model predicts higher N load to Neuse River
than the variance model starting in year 2024 and beyond.
Although the updated model suggests that the debit could be reduced, the Division and the City recommend keeping
the current debit amounts in place through 2022 to provide an added measure of conservatism and to allow for further
calibration of the model based on field data. The EMC's decision to grant the variance was based partially on the results
of the original model. The Division had requested that the original model results also be compared with the
groundwater data obtained during the past five years in order to evaluate the effectiveness of the original model
(variance model) that was used for decision making on the variance in 2009. The City as part of the August 29, 2014
response indicated that, "the City disagrees that it is necessary or important to evaluate the accuracy of the variance
model" and did not provide the requested information. The five-year report indicates that the updated model provides a
more accurate expectation of the remedial activities, better matches the condition measured in the monitoring wells,
and meets the condition of the five-year evaluation requirement in the variance. The Division supports the continued
use of the original model for establishing the NPDES debits for an additional permit cycle due to the evidence that the
original model is more conservative in estimates of nitrogen flow to the Neuse River through approximately 2024, and
the EMC had based approval of the variance on the results of the original model. Additional monitoring data will likely
allow for further improvements to the model as part of the 2019 five-year evaluation.
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July 8, 2015

Groundwater Containment System
Active groundwater remediation at the site includes a groundwater capture and containment system for fields 50 and
500. This system is comprised of extraction wells to capture groundwater containing NO3 beneath up -gradient
fields/areas to prevent the migration of such groundwater into areas down gradient of the site where decommissioned
private water supply wells are located. The report concludes that the groundwater containment system captured 100%
of the groundwater emanating from field 500 and 50% for field 50. It's important to note that these percentages for the
effectiveness of the groundwater containment systems are calculated based on many assumptions about the volume
and pathways of groundwater flow in these areas. While the report suggests that the containment system capture can
be improved for field 50 by installation and operation of additional wells or by increasing the pumping rates of wells on
either side of the areas of non -capture, (a) such additional measures are not necessary to ensure the protection of
public health, and (b) any nitrogen loading to surface water from Field 50 is more than offset by the debit discussed
above.
Table 2 — Amount of Nitrate (NO3) Delivered to NRWWTP from Active Remediation System
Year
Flow to
NRWWTP
(Million Gallon)
Average NO3 in
Flow to
NRWWTP
(mg/0
NO3 to
NRWWTP
(Ib)
2008
6.73
31
1,756
2009
11.71
26
2,558
2010
13.63
29
3,245
2011
12.89
29
3,168
2012
13.34
29
3,172
2013
15.53
27
3,467
2014
1.31
28
305
Total
75.15
17,670
Monitored Natural Attenuation (MNA)
MNA is the remediation activity for the remainder of the site that is not affected by the groundwater containment
systems and includes triennial sampling of 73 monitoring stations. The evaluation was performed by assessing
statistically significant linear trends over time since 2003 when biosolids application ceased. Trend directions and
magnitudes for all monitoring stations are shown in the 5 -year report (page 28). The report concludes that MNA is
reducing concentrations at the compliance boundary and at approximately one half of the interior monitoring locations.
The report also evaluates three additional remedial alternatives to MNA including Enhanced in-situ Biodenitrification
(EISBD), Enhanced Flushing, and Phytoremediation methods. The report shows that these treatment technologies are
either not feasible for the site or are cost -prohibitive.
Constructed Subsurface Flow Treatment Wetlands
According to the approved variance (Final Decision Granting Variance - page 8, item#21), "the subsurface treatment
wetlands on streams at three locations on the site were predicted to remove approximately 28,500 to 42,800 pounds of
nitrogen annually (assuming removal efficiencies of 50% to 75%)". The 5 -year variance report shows that the wetlands
removed approximately 1,000 lbs (total) of nitrogen since constructed. This result indicates that the nitrogen
concentrations in the stream have declined faster than had been expected. However, the nitrogen loading to the Neuse
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July 8, 2015

River from this source (i.e. mass entering all drainages from the fields) is already accounted for in the City's NPDES
permit.
Off-site Riparian Buffer Restoration
Restoration of Butlers Branch site in Craven County, NC was completed in 2010. Restoration resulted in an estimated
4,191 pounds of nitrogen offset per year and included the following activities:
• Removal of nonpoint sources of pollution associated with agricultural practices
• Reduction of sediment and siltation within on-site and downstream receiving wasters
• Promotion of floodwater attenuation, and
• Providing terrestrial wildlife habitat
Division's Comments
• The Division supports continued monitoring and evaluation of the current corrective action plan and variance
using the current monitoring wells and surface water sampling locations. We are still at an early stage of the
monitored natural attenuation strategy, and more field data is needed to better evaluate the performance of
the corrective action plan and variance.
• The Division supports continued monitoring and evaluation the pumping rates and well integrity for wells in the
groundwater containment system. Field inspections are recommended and additional actions should be taken
based on the results of those inspections.
• The Division supports continued use the original debits from the September 2010 approved Corrective Action
Plan groundwater model for the next NPDES permit cycle (to be issued from 2015 to 2020)
• The Division recommends using the 2019 Five -Year Evaluation to further verify the accuracy of groundwater
models and to establish nitrogen debits for future NPDES permits beyond 2022.
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July 8, 2015

Appendix A
Final Decision Granting Variance
January 14, 2010

Appendix B
Corrective Action Plan (CAP) Final Approved
(and Revised Attachment 2)
September 2, 2010

Appendix C
Meeting Minutes, North Carolina Environmental Management Commission
Item 09-57 Request for Approval of Hearing Officer Recommendations on the
City of Raleigh Public Utilities Department Groundwater Variance Request
(page 18 — 42)
November 19, 2009

Appendix D
1. Five -Year Evaluation of Remedial Strategy, Biosolids Fields at the Neuse
River Wastewater Treatment Plant, Wake County, North Carolina under
Permit #WQ0001730
April 7, 2014
2. Division of Water Resources Additional Information Request
June 12, 2014
3. City of Raleigh Information Request Five Year Evaluation Response Letter
August 28, 2014