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Home My WebLink AboutWQ0001740_Presentation 6_19_15_20150708Summa Of Ci of Ralei 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 Background • City of Raleigh's Neuse River WWTP o Located at 8500 Battle Bridge Rd., Raleigh, NC o Maximum capacity of 60 mgd o has an NPIDES discharge permit, non - discharge permit (residuals and spray irrigation of reclaimed water. Neuse River Wastewater Treatment Plant Site Map Background • 1980 - City began residuals application. oCurrently 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 • NCACO2L.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. o Deduct estimated excess groundwater nitrate concentration from NPDES permit allocation. o Evaluate the effectiveness of overall remediation strategy every 5 years 5- Year Variance Report • Elements of A - roved Groundwater Remediation Strateuyv: 1. Groundwater Containment System; 2. Monitored Natural Attenuation with Nitrate Debit to NPDES Outfall Permit; 3. Constructed Subsurface Flow Treatment Wetlands; and 4. 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. 6.73 31 ' 11.71 26 2,558 13.63 29 3,245 12.89 29 3,168 13.34 29 3,172 � 15.53 27 3,467 1 1.31 28 Provided by City of Raleigh 305 75.15 17,670 0 Constructed Subsurface Flow Wetlands • 3 wetland cells • Approved variance predicted removal of 28,5 to 42,800 pounds of nitro annually • The three wetlands remo, approximately 1,000 lbs (total) of nitrogen since constructed. • Nitrogen concentrations i the stream have declined faster than had been expected. 5- Year Report Off-site Riparian Suffer Restoration • Restoration of Butlers Branch site in Craven Coun 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 nitro per dear. 0 en offset 0 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/1) Debit in NPDES Year Permit (lb/yr) JL 115,402 75,576 120,058 111,748 �� 117,183 107,719 77,791 114,246 103,487 77,671 110,370 99,146 77,602 106,196 94,804 76,878 102,022= 90,462 75,172 97,549 86,186 13,807 93,276 82,020 71,956 89,002 965 OW 69,744 84,828 73,954 67,490 80,754 70,119 64,856 76,679 66,350 62,734 72,803 62,691 60,459 69,026 59,165 57,804 65,250 • Predicted N Load to Neuse River (in Excess of 10 mg/1) Debit in Year i NPDES Permit (lb/yr) 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 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 160,000I I -LII — — Variance Model Total N Load ....... Variance Model Constant N at 10 mg/I in Recharge 140,000 Variance Model Total N Load Minus Load at 10 mg/1 , — — Updated Model total N Load I • • • • • • Updated Model VS21)T Source Max 10 mg/I in 120,000 Recharge } 'k Updated Modal Total N Load Minus Load at 10 mg/1 7 Debit Valuesfram Permit vi G] m `W 100,000 0 •L ► - � 1 80,000 00 007 O] � 1 1 m O 50,000 c � �a o ► 40,000 c 1 Q 2 0, 000 or 0 1/1/1980 12/31/1989 1/1/2wo 12/31/2009 1/1/2020 12/31/2029 1/1/2040 12/3112049 Provided by City Of Raleigh 5- Year Report Monitored Natural Attenuation Provided by City Of Raleigh 160,000I I -LII — — Variance Model Total N Load ....... Variance Model Constant N at 10 mg/I in Recharge 140,000 Variance Model Total N Load Minus Load at 10 mg/1 , — — Updated Model total N Load I • • • • • • Updated Model VS21)T Source Max 10 mg/I in 120,000 Recharge } 'k Updated Modal Total N Load Minus Load at 10 mg/1 7 Debit Valuesfram Permit vi G] m `W 100,000 0 •L ► - � 1 80,000 00 007 O] � 1 1 m O 50,000 c � �a o ► 40,000 c 1 Q 2 0, 000 or 0 1/1/1980 12/31/1989 1/1/2wo 12/31/2009 1/1/2020 12/31/2029 1/1/2040 12/3112049 Provided by City Of Raleigh Permitted Total N Allocation to Neuse vs. Discharge and Debit in Permit Permitted Thl Allocation vs. Discharge + Debit 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.