reducing nutrient loading from onsite wastewater...
TRANSCRIPT
Reducing Nutrient Loading from Onsite Wastewater Systems
Chesapeake Bay Watershed and
North Carolina Piedmont Project Experiences
Victor A. D’Amato, PE
Presentation outline
Introduction - Nutrient removal in decentralized systems
Chesapeake Bay TMDL Implementation
• TN Removal BMP Panel
• Nutrient Attenuation Panel
NC Piedmont Nutrient Load Reducing Measures
• Malfunctioning onsite systems
• Discharging onsite systems
• What does the data say?
Conclusions and recommendations
• Additional examples
Nutrient Removal in Onsite Systems
“Attenuation”
Exsitu treatment
Insitu treatment
Nutrient Remvoal in Onsite Systems
Nitrogen • Several insitu processes remove nitrogen
• Main process is sequential nitrification-denitrification insitu or exsitu
• Drainfields are designed to nitrify
• Denitrification requires anoxic conditions and labile carbon
• Summary: removal highly variable depending on conditions between
system and receiving water
Phosphorus • Immobilized by forming insoluble complexes with minerals in soil
• Best removals in unsaturated, finely textured soils
• Some vegetative uptake
• Summary: nearly complete removal is commonly observed in non-
coastal areas; little indication that sorptive capacity is an issue
Chesapeake Bay Watershed TMDL Implementation
US EPA Bay Program Office (Region 3)
Onsite Wastewater Expert Panels
● TN BMPs in Onsite Systems
● Attenuation of TN and TP
Maryland Gap Closer Analysis
● Statewide plan for reducing nitrogen from existing onsite systems for ChesBay WIP
OWTS BMP Panel Charge
Initially convened in January 2012
Review available science on the nitrogen removal performance of treatment practices
Provide concise definitions and percent reductions for nitrogen load reduction practices
Provide a definition for each treatment practice and qualifying conditions
Only address treatment technologies, not soil “attenuation”
ChesBay Expert Panel: Baseline Load Recommendations
ChesBay WQ model assumes zero TP load from septic systems throughout watershed
ChesBay Expert Panel: Residential System with BMP
ChesBay WQ model assumes zero TP load from septic systems throughout watershed
Best Management Practices
Proprietary BMPs
• Manufacturer responsible for design, installation, management
• Standardized design and construction and little variability
• Recommend two-step credit assignment protocol: provisional testing (e.g., NSF Standard 245) followed by third-party field testing
• TN reduction credit of 50 percent, unless managed according to min. EPA Level 3
Nonproprietary BMPs
• Designed on case-by-case basis for each site using nonspecific and readily available materials and mechanical equipment
• Local design and material variations common
• Two-step protocol for new systems goes through WWTWG
Expert Panel: Nitrogen Removal Mgt. Practices
Insitu practice
Exsitu practice
Conventional
baseline
Shallow pressure
dosed
Elevated mound
Septic tank baseline 4.0 kg/p/yr (0%) 2.5 kg/p/yr (38%) 2.5 kg/p/yr (38%)
Intermittent Filters 3.2 kg/p/yr (20%) 2.0 kg/p/yr (50%) 2.0 kg/p/yr (50%)
Constructed Wetland 3.2 kg/p/yr (20%) 2.0 kg/p/yr (50%) 2.0 kg/p/yr (50%)
IFAS 2.0 kg/p/yr (50%) 1.25 kg/p/yr (69%) 1.25 kg/p/yr (69%)
Recirculating Filter 2.0 kg/p/yr (50%) 1.25 kg/p/yr (69%) 1.25 kg/p/yr (69%)
Two-stage approval protocol for proprietary systems.
Exsitu BMPs
Insitu BMPs
12
System with BMPs
This is what we
care about!
Attenuation
OWTS Attenuation Panel Charge
Initially convened in May 2014
Determine whether Bay TMDL model can be improved for TN
● Currently, constant 60% total nitrogen (TN) attenuation rate across watershed.
● Can we develop attenuation rates that vary based on soil, site and system characteristics.
Determine whether 100% removal of TP is warranted.
● Should it be changed and should TP removal should be variable based on site/system characteristics?
OWTS Attenuation Factors
Soil texture
Soil geochemistry
Soil wetness/water table depth or depth to restrictive horizons
System proximity to surface waters and surface water-groundwater interactions
Hydrogeological setting, groundwater recharge, and groundwater residence time
System age, maintenance, and biomat formation
Riparian buffers
Water use, wastewater, and source water chemistry
Topographic conditions between system and surface water
Higher order stream miles
Other factors
NC Piedmont Nutrient Load Reducing Measures
Data-based nutrient load reduction credits for Falls and Jordan Lake watershed management measures
2 “wastewater”, 4 “stormwater”
Onsite wastewater measures
● Remedy malfunctioning septic systems
● Remedy discharging sand filters
Project Deliverable
Technical report
● Define load reducing measures and identify practices
● Evaluate feasibility and benefits of measures
● Develop accounting methods and tools
● Estimate load reductions for designs across a range of NC Piedmont field conditions
● Science-Policy-Implementation
Jordan and Falls Lake Watershed Water Quality Monitoring Locations
NC Piedmont System Performance
Equivalent “effluent” concentrations: 2.0 mg/l TN, 0.2 mg/l TP
Equivalent reductions: 96% TN, 98% TP
Septic-Generated
Nutrients Measured Load in
Stream
Percent Septic Load Delivered
to Stream
Basin Stream Order*
TN (lb/d/mi2)
TP (lb/d/mi2)
TN (lb/d/mi2)
TP (lb/d/mi2)
TN (%)
TP (%)
Rhodes Creek unk. - - 0.57 0.012 - -
Seven-Mile Creek 4th 30.4 3.9 0.139 0.0068 0.46 0.18
Cabin Branch 8th 30.2 3.86 0.57 0.0178 1.89 0.46
Crooked Creek 2nd 27.0 3.45 1.53 0.0286 5.67 0.83
Beaverdam Creek unk. 3.83 0.42 0.20 0.024 5.1 5.7
New Light Creek unk. 4.68 0.60 0.37 0.033 8.0 5.4
Honeycut Creek unk. 15.5 1.99 0.33 0.025 2.2 1.3
Cedar Creek unk. 29.7 3.81 0.66 0.039 2.2 1.0
AVERAGE 20.2 2.6 0.55 0.023 3.6 2.1
Data from:
NCDENR 2010
Berkowitz 2014
USGS Study
Nutrient measurement and source identification in three
Durham streams, including septic-dominated Cabin Branch
Tributary and two urban waterways
Monthly water quality samples over one calendar year – 9
baseflow, 3 stormflow (falling limb based on work of Ferrell,
USGS)
Cabin Branch had lowest nutrient concentrations and source
tracking showed no samples with a wastewater signature
(McSwain, K. 2013. Nitrate Sources in Urban Surface Waters Feeding Falls and
Jordan Lakes, Durham, NC. Unpublished soil science seminar presented
September 11, 2013 and Personal Communication)
Wastewater Measures Performance Summary Properly functioning onsite: 97% TN, 100% TP reduction
● Jordan Lake Watershed Model calibration results
● Denitrification rate calculation
● Water quality data
Malfunctioning onsite (soil treatment) system: 67% TN reduction, 70% TP reduction
● Delivered load varies temporally
● Population of malfunctioning systems changes – track malfunction rate
Discharging system: 0-60% TN, 0-50% TP reduction
● Illicit discharges (straightpipes)
● Gravity-dosed single pass filters with or without regular discharges
● Recirculating filters and TS-II equivalent treatment systems
Conclusions and Recommendations: Focus on Problematic Systems
PTRC/DWR project results suggest that:
● Properly functioning systems in the Piedmont are very effective
at reducing nutrients
● Malfunctioning systems deliver substantially more nutrients than
properly functioning systems
● Discharging systems deliver far more nutrients than properly
functioning or even most malfunctioning systems
Otherwise high-risk systems
● Poorly sited
● Proximate to surface waters
● Very old
● etc.
Wastewater Measures - Conclusions and Recommendations
Inventory
● GIS data, permit data, field reconnaissance
Prioritize
● Indicators include: proximity to water, soil characteristics, system age, etc.
Manage
● Onsite system improvements, cluster systems, sewer
Risk Indicators
● system age
● soil suitability
● proximity to streams
● proximity to lakes and ponds
● proximity to Bay tidal waters
● watershed vulnerability
● housing density
Conclusions and Recommendations: Inventory, Prioritize and Manage
Conclusions and Recommendations: Inventory, Prioritize and Manage
Mgt. Indicators
● parcel size
● proximity to collection systems
● proximity to large parcels
Wastewater Measures - Conclusions and Recommendations
Do more research
● More intensive monitoring of septic-dominated watersheds to include ground and surface water, temporal variability, landscape effects
● Attenuation in ditches, riparian areas, lower order streams
● Don’t research exsitu systems – lots of data exist and State has approval mechanism (plus they don’t help reduce nutrient loads in the Piedmont)
Work together
● Local (county) health departments and municipal utilities
– Implement new malfunctioning system survey program
– Manage decentralized systems
● DWR should make discharging system standards consistent with DEH
● Financial assistance program for homeowners
Additional information
Victor D’Amato, PE
919-485-2070
Chesapeake Bay Expert Panel Final Report: http://www.chesapeakebay.net/documents/Final_OWTS_Expert_Panel_WQGIT_approved_07142014.pdf
Maryland Decentralized Wastewater Management Gap Closer Research and Analysis: http://www.mde.state.md.us/programs/Water/TMDL/TMDLImplementation/Documents/Binder/Gap_Closer_Report_3-10-11.pdf
PTRC/DWR Nutrient Load Reducing Measures Report: http://www.nccgl.net/c/document_library/get_file?uuid=9a09a876-e498-4136-8ee8-fd23beb00eaf&groupId=38364