Status of WWTF Nitrogen Reduction Efforts May 3, 2012 Angelo Liberti, Chief Surface Water Protection Office of Water Resources ext 7225

Evaluation of Nitrogen Targets And WWTF Load Reductions DEM used MERL tank experiments to predict changes in water quality and WWTF nitrogen reduction necessary to meet water DO standards and reduce chlorophyll to acceptable levels.

Evaluation of WWTF Reduction Scenarios

WWTF Nitrogen Limits 5 mg/l –UBWPAD –Woonsocket (3 mg/l) –NBC-Fields Pt. –NBC Bucklin Pt. –East Greenwich –Warren –No. Attleborough –Attleboro –Grafton –Uxbridge –Northbridge –(max extent) Limits May – October, require operation of treatment to remove N to max extent possible November-April –East Providence – (5.9 mg/l) –Cranston –West Warwick –Warwick –Smithfield (10 mg/l) –Burrillville (max extent) 8 mg/l

Status of Compliance with Nitrogen Limits MA WWTFs Upper Blackstone (UBWPAD) 5 mg/l EPA issued 8/08. Appealed. 5/10 EAB Upheld limits. Under US First Circuit Court mediation. May – Oct 2011 Ave = 4.0 mg/l (1048 lb/d) Attleboro 8 mg/l EPA issued 6/08; Permit upheld on appeal 9/15/09. Administrative Order issued: interim limits 33 mg/l. Design full scale pilot 12/31/10. Construction by 10/31/11. Evaluation & schedule for additional mods 12/31/12. Report & Schedule 2/28/14 May – Oct 2011 Ave = 26.9 mg/l (782 lb/d) Dec 11- March 12 Ave = 15.3 mg/l (562 lb/d) North Attleborough 8 mg/lEPA issued 2/08; AO issued (complete construction late 2012) May – Oct 2011 Ave = 6.4 mg/l (217 lb/d) Grafton 8 mg/lNo action to date Uxbridge 8 mg/lNo action to date Northbridge NAEPA issued 9/06; reduce N to max extent

RI WWTF Nitrogen Reductions Nitrogen removal at 11 RI WWTFs - reduces their summer season nitrogen loading by 65%, dropping to 48% as WWTF flows reach approved design flows. EP FP, BP Warren Woonsocket

Above Seasonal Pycnocline - > 4.8 mg/l Below Seasonal Pycnocline All values >4.8 mg/l During Larval Recruitment Season, not: < 2.9 mg/l for 24 hours, < 1.4 mg/l for one hour more than twice, exceed cumulative exposure limits (RIDOCS) Oxygen Criteria - Stratified Waters (not to be exceed more than once in three years)

36.2% of assessed NB (38.7% including MA) is impaired for Dissolved Oxygen Providence/Seekonk River and Greenwich Bay experience hypoxic conditions about 25-30% of the time during the recruitment season (about 1-2 months) Upper Bay about 15-20% (about days) Upper West and East Passages about 7% (1-3 weeks) West Passage (area of concern) less than a week (2%) Mt Hope Bay is about 5% (10 days on average) NOTE: Inter-annual variability influenced by weather patterns. Estimates can also be lower because of data gaps. Dissolved Oxygen Indicator Map

Hypoxia was an above average year for BR, CP, NP, GB, SR, MV and MH Several rainfall events along with warmer temperatures contributed to several hypoxic events throughout the month of September in Greenwich Bay and the Providence River. (example: Bullock Reach) 19-32% of all events within the Providence River occur during September.

Translating the RIDOCS Results into Impairment Listings for Oxygen in Narragansett Bay Blanks indicate no data available for analysis Non-Bold indicates data missing during critical period Percentage of time station is exceeding criteria during recruitment season Station Name Upper Bay: Phillipsdale Bullock Reach Conimicut Pt North Prudence West Passage: Greenwich Bay Sally Rock Wickford Cove12.2 Mt. View Quonset Pt GSO Dock East Passage: Popposquash Pt Mt. Hope Bay T-Wharf

EcoGEM Preliminary Review Changes made to Input Files based on DEM’s Review –DIN concentration entered for individual component of the River Inputs. –Inputs with multiple River components are flow-weighted, not averaged. –East Providence WWTF based on actual data. (resulted in minor change from previous estimate)

EcoGEM Preliminary Review (Continued) Model skill will be presented by model element. Additional documentation of the data used for model calibration to be provided. Determine if 2006 and 2007 are representative of appropriate environmental conditions to base future management option upon. Review approach for establishing nitrogen loading to Mount Hope Bay segment. Determine the degree to which EcoGEM input parameters can be changed without impacting the exchange rates from ROMS?

Next Steps Complete WWTF upgrades and continue with enhanced storm water controls BMPs/LID. Continue fixed station monitoring network Continue coordination with researchers that received funding under the NOAA CHRP to develop observational and modeling tools. Apply appropriate tools to evaluate need for additional controls.