A Review of Nitrogen Loading and A Review of Nitrogen Loading and Treatment Performance Treatment Performance Recommendations for OWTS in the Recommendations for OWTS in the Wekiva Study Area Study Area Wekiva FDOH Technical Review & Advisory Panel Meeting FDOH Technical Review & Advisory Panel Meeting February 15, 2006 February 15, 2006 Damann L. Anderson, P.E. Damann L. Anderson, P.E.
Purpose and Scope Purpose and Scope � Retained by stakeholders through FHBA Retained by stakeholders through FHBA � � Purpose: Purpose: To gain understanding of the To gain understanding of the � significance of N loading from OWTS significance of N loading from OWTS � Scope: Scope: Review data, make assessment of Review data, make assessment of � OWTS impacts relative to other sources OWTS impacts relative to other sources and FDOH recommended OWTS actions and FDOH recommended OWTS actions
Hydrogeology of the Wekiva Area
Potentiometric Surface of the Upper Floridan Aquifer, September 2001
Generalized Thickness of the ICU
Thickness of the ICU
Thickness of surficial sediments overlying the ICU
Assessment (WAVA) Wekiva Aquifer Vulnerability
Nitrogen Cycle Nitrogen Cycle
Nitrogen Removal/Reduction? Nitrogen Removal/Reduction? � Nitrogen is an element, can Nitrogen is an element, can’ ’t be reduced t be reduced � � Law of Conservation of Matter: Law of Conservation of Matter: � � "Matter can neither be created nor destroyed "Matter can neither be created nor destroyed“ “ � � However, we are releasing N that was not However, we are releasing N that was not � recently in the biosphere: recently in the biosphere: � Fertilizer Fertilizer � � Fossil Fuels Fossil Fuels � � We are not creating more N, just concentrating it We are not creating more N, just concentrating it � in certain areas in certain areas
SOURCES AND PATHWAYS OF WASTEWATER NITROGEN SOURCES AND PATHWAYS OF WASTEWATER NITROGEN IN THE SUBSURFACE ENVIRONMENT (Freeze & Cherry, 1979) IN THE SUBSURFACE ENVIRONMENT (Freeze & Cherry, 1979) Precipitation Sewage, Residuals, Livestock Fertilizer, Fossil Fuels, Industry NH 3 Organic-N NO 3 NH 3 N 2 O, N 2 NH 3, NO 3 Org. N Decomposition + NH 4 Ammonification N 2 O, N 2 Nitrification + NH 4 Unsaturated Denitrification soil Adsorption NO 3 Leaching Groundwater Denitrification in (aq) N 2 N 2 O NO 3 reducing zones
Man’ ’s Activities Disrupt the s Activities Disrupt the Man Natural N Cycle Natural N Cycle
Typical Onsite Wastewater Typical Onsite Wastewater Treatment System (OWTS) Treatment System (OWTS)
Estimated N Loading to OWTS Estimated N Loading to OWTS � N discharged to OWTS in WSA: N discharged to OWTS in WSA: � � 11.2 grams N per person per day 11.2 grams N per person per day � � 23.4 lbs N per home per year 23.4 lbs N per home per year � � 55,416 homes in WSA 55,416 homes in WSA � � 1.3 Million lbs N discharged 1.3 Million lbs N discharged to to OWTS OWTS � per year per year
Cross Section Cross Section Typical Septic Tank Typical Septic Tank
Subsurface Wastewater Subsurface Wastewater Infiltration System, trench type Infiltration System, trench type Biomat
Soil Infiltration System Soil Infiltration System Performance Performance
USF In situ Lysimeter Lysimeter USF In- -situ Facility Facility
Potential N Loading From OWTS Potential N Loading From OWTS � 23.4 lbs N per home discharged 23.4 lbs N per home discharged to to OWTS per year OWTS per year � � 21.1 lbs N from septic tank to SWIS (10% reduction) 21.1 lbs N from septic tank to SWIS (10% reduction) � � 15.8 lbs N from SWIS to GW (25% reduction) 15.8 lbs N from SWIS to GW (25% reduction) � � High High- -end estimate of OWTS N load to GW in WSA: end estimate of OWTS N load to GW in WSA: � 876,000 lbs/year 876,000 lbs/year � Further reduced by natural denitrification in GW zone Further reduced by natural denitrification in GW zone �
Denitrification by Heterotrophic Denitrification by Heterotrophic Bacteria Bacteria Simplified denitrification reaction is: Simplified denitrification reaction is: NO 3 NO 2 NO N 2 O N 2 NO NO NO N 2 O N 3 2 2 � Process performed by heterotrophic, facultative Process performed by heterotrophic, facultative � bacteria bacteria � Utilize nitrate instead of oxygen as electron acceptor Utilize nitrate instead of oxygen as electron acceptor � � Generally considered anoxic process, but recent Generally considered anoxic process, but recent � research indicates aerobic denitrification does occur. research indicates aerobic denitrification does occur. � Controlling factors in natural environment are DO, Controlling factors in natural environment are DO, � organic carbon, pH, temp., and nutrient availability organic carbon, pH, temp., and nutrient availability
Previous Studies of Natural Denitrification in Previous Studies of Natural Denitrification in Surficial GW GW Surficial Reference Soil Organic Dissolv. O NO 3 -N Denit. Rate 2 Content Conc. Conc. (ug NO 3 -N/g-d) (% wt.) (mg/L) (mg/L) Slater & Capone (1987) 0.5 <0.10 3.8 0.24 (sandy glacial outwash) Smith & Duff (1988) NR 0 - 5 0 - 25 0.009 - 0.24 (sand & gravel aquifer) Ward (1985) NR NR NR 52.4 - 64.5 (soil cores near OWTS drainfield) Trudell et al. (1986) 0.08 - 0.16 NR 8 - 15 0.086 - 1.32 (shallow sand aquifer) Bengtsson & Annadotter (1989) 0.2 9.9 - 1.3 3.8 0.20 (sandy aquifer matl.) Bradley et al. (1992) 0.07 - 2.22 <0.4 2.8 - 120 0.013 - 1.04 (fine sand water table)
Conditions Necessary for Denitrification Conditions Necessary for Denitrification � Oxidation of NH4-N to NO3-N (nitrification) � Oxidation of NH4-N to NO3-N (nitrification) � Presence of a subsequent anoxic � Presence of a subsequent anoxic environment (NO3-N acts as alternative environment (NO3-N acts as alternative electron acceptor in low O2 environments) electron acceptor in low O2 environments) � Sufficient residence time in the anoxic � Sufficient residence time in the anoxic environment for denitrification to occur environment for denitrification to occur � Adequate carbon source for denitrifying � Adequate carbon source for denitrifying bacteria in the anoxic environment bacteria in the anoxic environment
Correlation of Denitrification Rate vs Soil Organic Content from Previous Studies 1.2 Denitrification Rate, (ug NO 3 -N/g/d) 1 0.8 0.6 0.4 y = 0.442x + 0.0194 r 2 = 0.8286 0.2 0 0 0.5 1 1.5 2 2.5 Soil Organic Content, (% wt.)
Relationship between denitrification capacity and Relationship between denitrification capacity and mineralizable carbon (17 soils) (Burford & Bremner, 1975) mineralizable carbon (17 soils) (Burford & Bremner, 1975) 400 (ug of N evolved as N 2 or N 2 O/g of soil Y = 0.856x-23.1 r = 0.99 Denitrification capacity 300 200 100 0 100 200 300 400 500 Mineralizable C (ug/g of soil)
Florida OSDS Research Project: Florida OSDS Research Project: Early Modeling Results Early Modeling Results
Field Assessment of existing onsite wastewater treatment systems (OWTS)
Indian River Lagoon OWTS Study Indian River Lagoon OWTS Study
Tracer study to determine GW flow Tracer study to determine GW flow velocity, direction, dilution velocity, direction, dilution
Mass balance model to estimate Mass balance model to estimate N reduction in GW zone N reduction in GW zone
LEGEND MINIATURE WELL POINT LOCATIONS MONITORING WELLS DW-6 NESTED PIEZOMETERS P3 PIEZOMETERS SW-7 14.34 GW ELEVATION CONTOUR NOTE: ALL ELEVATIONS ARE IN METERS BASED E C N ON A TBM ELEVATION SET AT 15.24. E F GROUND WATER 1 4 . FLOW 3 6 1 4 . 3 4 SEPTIC TANK DRAINFIELD 1 TRENCHES 4 P1 . 3 3 TRENCH 3 TW-17 TW-16 1 4 . TW-18 TRENCH 2 3 TW-22 TW-19 1 TW-20 W5 TW-2 TW-21 TW-1 TW-3 TW-23 TW-6 TW-10 TW-4 TW-5 TRENCH 1 HOUSE TW-24 TW-8 P2 TW-7 TW-11 TW-9 TW-12 GROUND WATER 1 4 . TW-25 2 FLOW 9 TW-13 TW-14 TW-15 TBM SW-11 DW-8 DW-10 SW-9 TW-26 TW-27 TW-28 W4
LEGEND NO3-N (1.8 M BGS) 1993 1995 DRAINFIELD TRENCHES SEPTIC TANK TRENCH 3 50 TRENCH 2 HOUSE 40 10 30 TRENCH 1 2 0 10 GROUND WATER FLOW
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