1. Jon Risgaard, Wastewater Branch Rick Bolich, Raleigh Regional Office
Summary of City of Raleigh, Neuse River WWTF Five-Year Evaluation of Variance From Groundwater Regulations Groundwater and Wastewater Committee Informational Item July 8, 2015
Jon Risgaard, Wastewater Branch
Rick Bolich, Raleigh Regional Office

2. City of Raleigh’s Neuse River WWTP
Background
City of Raleigh’s Neuse River WWTP
Located at 8500 Battle Bridge Rd., Raleigh, NC
Maximum capacity of 60 mgd
has an NPDES discharge permit, non-discharge permit (residuals and spray irrigation of reclaimed water.

3. Neuse River Wastewater Treatment Plant Site Map
NPDES Outfall
Brownfield Road
Mial Plantation Road
The Neuse River Wastewater Treatment Plant is located in southeastern Wake County. The property is bounded by the Neuse River to the north and east and by Old Baucom Road, Mial Plantation Road, Shotwell Road, and Battlebridge Road
Old Baucom Road
2005

4. 1980 – City began residuals application.
Background
1980 – City began residuals application.
Currently have 1,439 acres permitted for land application
Groundwater monitoring revealed nitrate concentrations above 02L standard beyond the compliance boundary in several wells.
Raleigh paid $73,936 fine in 2002 for over-application of residuals leading to groundwater quality violations beyond compliance boundary & suspended residuals application.

5. Background
NCAC 02L Requires “active treatment” of groundwater contamination beyond compliance boundary
The EMC approved Raleigh’s variance request in 2009, allowing monitored natural attenuation for groundwater.
Deduct estimated excess groundwater nitrate concentration from NPDES permit allocation.
Evaluate the effectiveness of overall remediation strategy every 5 years

6. 5- Year Variance Report
Elements of Approved Groundwater Remediation Strategy:
Groundwater Containment System;
Monitored Natural Attenuation with Nitrate Debit to NPDES Outfall Permit;
Constructed Subsurface Flow Treatment Wetlands; and
Off-site Riparian Buffer Restoration.

7. 5- Year Report Monitored Natural Attenuation Alternatives
Variance requires evaluation of treatment strategy to determine if additional treatment technologies are feasible.
The report evaluated three additional remedial alternatives to MNA including:
Enhanced in-situ Biodenitrification
Enhanced Flushing
Phytoremediation methods.
The report shows that these treatment technologies are either not feasible for the site or are cost-prohibitive.

8. 5- Year Report Groundwater Containment System
Groundwater capture and containment system for fields 50 and 500.
Prevent the migration of groundwater to decommissioned private water supply wells.
Groundwater containment system captured estimated 100% of the groundwater emanating from field 500 and 50% for field 50.
Year
Flow to NRWWTP
(Million Gallon)
Average NO3 in Flow to NRWWTP
(mg/l)
NO3 to NRWWTP
(lb)
2008
6.73 31
1,756
2009
11.71 26
2,558
2010
13.63 29
3,245
2011
12.89
3,168
2012
13.34
3,172
2013
15.53 27
3,467
2014
1.31 28
305
Total
75.15
17,670
Provided by City of Raleigh

9. Constructed Subsurface Flow Wetlands
3 wetland cells
Approved variance predicted removal of 28,500 to 42,800 pounds of nitrogen annually
The three wetlands removed approximately 1,000 lbs (total) of nitrogen since constructed.
Nitrogen concentrations in the stream have declined faster than had been expected.
Provided by City Of Raleigh

10. 5- Year Report Off-site Riparian Buffer Restoration
Restoration of Butlers Branch site in Craven County, NC (Completed in 2010)
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
Estimated 4,191 pounds of nitrogen offset per year.

11. 5- Year Report Monitored Natural Attenuation
Monitored Natural Attenuation (MNA) is the remediation activity for the remainder of the site
Includes triennial sampling of 73 monitoring stations.
Trend directions and magnitudes for all monitoring stations are shown in the 5-year report (page 28).
Monitoring results used to evaluate predictive model of groundwater flows to Neuse River, and Nitrogen debits in NPDES permit.

12. 5- Year Report Monitored Natural Attenuation
Monitored Natural Attenuation (MNA)
Updated Model to improve accuracy based on:
Refining the model grid from 60x60 feet to 20x20 feet.
Additional Nitrate sampling results at various depths
Water percolation from the soil zone
Nitrate fate and transport in the vadose zone
The report concludes that MNA shows reducing nitrogen concentrations at and within the compliance boundary

13. 5- Year Report Monitored Natural Attenuation
Predicted N Load to Neuse River (in Excess of 10 mg/l )
Debit in NPDES Permit (lb/yr)
Variance Model (lb/yr)
Updated Model (lb/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

14. 5- Year Report Monitored Natural Attenuation
Predicted N Load to Neuse River (in Excess of 10 mg/l )
Debit in NPDES Permit (lb/yr)
Variance Model (lb/yr)
Updated Model (lb/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 - The updated model predicts higher N load to Neuse River than the variance model starting in year 2024 and beyond.

15. 5- Year Report Monitored Natural Attenuation
Provided by City Of Raleigh

16. 5- Year Report Monitored Natural Attenuation -- Variance Model
Provided by City Of Raleigh

17. 5- Year Report Monitored Natural Attenuation – Updated Model
Provided by City Of Raleigh

18. 5- Year Report Monitored Natural Attenuation
Provided by City Of Raleigh

19. Permitted Total N Allocation to Neuse vs. Discharge and Debit in Permit
Provided by City Of Raleigh

20. Staff Assessment
Remediation activities appear to be working as intended based on 5 yrs worth of data.
Support continued monitoring and evaluating the current corrective action plan and variance using current monitoring wells and surface water sampling locations.
Support continued monitoring and evaluating the groundwater containment system.
Support continued use of the original debit schedule from the September 2010 approved Corrective Action Plan for the next NPDES permit cycle (to be issued from 2015 to 2020)
Use the 2019 Five-Year Evaluation to further verify the groundwater model and establish debits schedule for NPDES permits beyond 2022.