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

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.

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

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.

Background NCAC 02L .0106 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

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.

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.

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

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

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.

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.

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

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

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.

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

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

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

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

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

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.