Using Watershed-Scale Nutrient. Evaluation of Wastewater Treatment Alternatives

Transcription

1 Using Watershed-Scale Nutrient Modeling Approaches for Integrated Evaluation of Wastewater Treatment Alternatives Bruce F. Douglas, Michael Winchell, Amy Macrellis, Brent Toth, Alan Benevides, Jon Schock WEFTEC 2009 October 13, 2009

2 Acknowledgements Project Funding by: 2

3 Acknowledgements Carol Baker, Town of South Kingstown Art Gold, University of Rhode Island Rob Adler, US EPA Rachel Gilbert, Woodard & Curran Jim Geremia, James J. Geremia & Assoc. Inc. Craig Swanson & Jen Cragan, ASA Brent Toth, Stone Environmental Liz Scott & Brian Zalewsky, RI DEM Jim Boyd, RI CRMC 3

4 Contents t 1 Introduction ti - Project Location and Background 2 Soil and Water Assessment Tool (SWAT) 3 Methodology 4 Results 5 Conclusions 4

5 Project Location South Kingstown and Charlestown, RI 5

6 Study Area Green Hill Pond Eastern area of Ninigret Pond At the boundary between Charlestown and South Kingstown in Rhode Island Green Hill Pond Eastern Ninigret Pond Satellite image of Green Hill Pond and eastern Ninigret Pond, ESRI Imagery

7 Project Background A study of wastewater management and nutrient control Project completed in anticipation of a Total Maximum Daily Load (TMDL) for Green Hill Pond and the eastern section of Ninigret Pond Original TMDL goal called for an 80% reduction in nitrogen loading to the ponds Further research by ASA revealed 48% nitrogen reduction would meet water quality objectives RIDEM agreed to a 61% nitrogen reduction goal SWAT model used to quantify nitrogen loading 7 Allowed for the transparent comparison of management alternatives

8 Contents t 1 Introduction ti - Project Location and Background 2 Soil and Water Assessment Tool (SWAT) 3 Methodology 4 Results 5 Conclusions 8

9 SWAT Model Hydrology Place image here. It should fit in this text box and should align on the left with the picture above. Delete text box if still visible after placing and sizing picture. Hydrologic Cycle Modeled at watershed scale Courtesy of Texas A & M University Subbasins and Hydrologic Response Units modeled for finer resolution 9

10 SWAT Model Nutrient t Cycling Place image here. It should fit in this text box and should align on the left with the picture above. Delete text box if still visible after placing and sizing picture. Nutrient Cycle Physically models environmental processes Fate and transport of nitrogen Courtesy of Texas A & M University 10

11 Contents t 1 Introduction ti - Project Location and Background 2 Soil and Water Assessment Tool (SWAT) 3 Methodology 4 Results 5 Conclusions 11

12 Watersheds and Groundwater Recharge Areas Model Area Delineation Watershed boundaries Groundwater recharge area boundaries Surface Water and Groundwater Each modeled in SWAT Hydrogeologic boundaries were previously not considered in pond nutrient input 12

13 Hydrologic Response Units HRUs Finest level of spatial resolution for modeling nitrogen input and output Inputs calculated and tracked at the HRU level Hot Spots The HRU structure allowed the identification of localized areas with relatively higher nitrogen loading 13

14 Model Inputs Agricultural fertilizer Onsite Wastewater Treatment Systems (OWTS) Pet waste Lawn fertilizer Atmospheric Nitrogen Deposition i Wildlife 14

15 Model Calibration Calibration period from Hydrologic calibration targets induced mean annual Evapotranspiration (ET) and percent of surface runoff vs. baseflow. Nitrogen calibration targets included mean annual leaching rates from agricultural fertilizer, lawn fertilizer, and wastewater systems. 15

16 Contents t 1 Introduction ti - Project Location and Background 2 Soil and Water Assessment Tool (SWAT) 3 Methodology 4 Results 5 Conclusions 16

17 Current Nitrogen Loading to Green Hill Pond Watershed Source N Input (kg/yr) N Load (kg/yr) N Load (%) Impervious Surface Accumulation N/A Residential Fertilizer 14, Pet Waste 1, Wastewater 22,494 18, Agricultural Fertilizer 8,792 1, Natural N/A 4, Waterfowl Deposition in Ponds Atmospheric Deposition on Watershed-Scale Nitrogen Loading to Green Hill Pond, Current Conditions (2007) Ponds 17 2,517 2,

18 Current Nitrogen Loading: Green Hill Pond Watershed 07% 0.7% 3.3% 8.7% 0.4% 3.1% Environmental sources comprise 24.4% of the total nitrogen input 15.3% Pond surface deposition (atmospheric) % 63.7% R es idential F ertiliz er Wastewater S ources Agric ultural F ertiliz er Natural Impervious S urface Accumulation Pet Waste Pond S urface Deposition Wildfowl Depos ition Wildfowl deposition Natural nitrogen in the watershed Wastewater represents the largest source of nitrogen input, 63.7%

19 Current Nitrogen Loading : Green Hill Pond Watershed Current conditions Total nitrogen loading by HRU Hot spots identified High density commercial and residential areas Areas with large agricultural fertilizer inputs 19

20 Predicted Nitrogen Loading at Buildout: Green Hill Pond Watershed Source N Input (kg/yr) N Load (kg/yr) N Load (%) Impervious Surface Accumulation N/A 1, Residential Fertilizer 15, Pet Waste 2, Wastewater 22,680 18, Agricultural Fertilizer 6, Natural N/A 4, Waterfowl Deposition in Ponds Atmospheric Deposition on Watershed-Scale Nitrogen Loading to Green Hill Pond, Baseline Buildout Conditions Ponds 20 2,517 2,

21 Predicted Nitrogen Loading at Buildout: Green Hill Pond Watershed 0.4% 0.8% 8.7% 4.3% 33% 3.3% Proportional wastewater input increased slightly in buildout 63.7% to 64.4% 15.0% % R es idential F ertiliz er Wastewater S ources Agricultural F ertiliz er Natural Impervious S urface Accumulation Pet Waste Pond Surface Deposition Wildfowl Depos ition 64.4% Actual nitrogen loading increased by only 73 kg/year Agricultural fertilizer proportion loading decreased Environmental nitrogen sources remained significant

22 Predicted Nitrogen Loading at Buildout: Green Hill Pond Watershed Nitrogen loading rates of baseline buildout conditions 100% buildout scenario Agricultural nitrogen replaced by residential and commercial nitrogen Existing Adaptive Management program in place 22

23 Results Green Hill Pond Watershed Buildout Nitrogen Load Current Adaptive Management plan Slight decrease in total nitrogen load for Green Hill Pond was expected due to proactive local OWTS management Buildout scenario assumed new and repaired OWTS to be denitrifying and meet state regulations Loss of agricultural land Agricultural land developed in buildout scenario resulted in reduced nitrogen fertilizer applications 23

24 Contents t 1 Introduction ti - Project Location and Background 2 Soil and Water Assessment Tool (SWAT) 3 Methodology 4 Results 5 Conclusions 24

25 Conclusions Comparing Alternatives 61% nitrogen reduction was required Wastewater t Management talternativesti 64% of nitrogen load was attributed to wastewater Only regional wastewater treatment met the 61% criteria by removing all wastewater nitrogen from the watershed Nitrogen management alternatives Construction of a breachway to increase tidal flushing could be designed d to meet the 61% nitrogen reduction goal The use of nitrogen treatment trenches filled with a carbon media to denitrify if groundwater on a large scale was considered d 25

26 Predicted Nitrogen Reductions for Green Hill Pond Watershed Wastewater Management Alternatives Nitrogen Reduction (%) Current Plan for Adaptive Management 0 Optimization by Upgrading all OWTS to Denitrifying Systems 27 Regional Wastewater Treatment and Collection 64 Decentralized Collection and Treatment of Hot Spot Areas 22 Nitrogen Management Alternatives Nitrogen Reduction (%) Breachway Allowing Additional Tidal Flushing of Salt Pond 80 Nitrogen Reduction Treatment Alternatives Trenches Analysis Results with Carbon for Buildout Media Conditions

27 Thank you Bruce F. Douglas, P.E.; env.com Water Resources Management Group Stone Environmental, Inc; 27