Remedy Malfunctioning Septic System
North Carolina Piedmont Nutrient Load Reducing Measures Technical Report Project Update Victor D’Amato Jonathan Smith Andrew Anderson and Natalie Carmen
Project Approach Schedule Activity Task 1 Selection of Measures - Kick off and NSAB meeting Task 2 Data Sources - Data protocol - Data collection - Data assessment - Data summary Task 3 Technical Report - Method/tool development - Draft report - NSAB presentation - Final report
May
June
July
August
September
Project Approach – Tasks Task 1. Selection of Measures ● May 13th NSAB meeting: kick off/presentation attended by Vic, Jonathan ● Will begin putting together data protocol (Task 2) in preparation ● Prepared to discuss key questions to be addressed prior to data collection ● Coordination with PTRC/DWQ
Task 2. Data Sources ● Data protocol technical memo (by May 20th) – criteria for accepting data – NC Piedmont applicability – Data QA/QC and other characteristics
● Data collection – collect data sources/references ● Data assessment – assess sources versus acceptance criteria ● Data summary (by June 14th) – summarize assessment and recommend data sources to use
Project Approach – Tasks
Task 3. Technical Report ● Method/tool development – data processing and analysis ● Draft report (by August 9th) ● NSAB presentation (September 6th) – Summarize draft report, comments received and proposed revisions and other actions to be taken
● Final report (by September 20th)
Today’s Presentation
For each measure: ● Orientation to and summary of content in draft report ● Major issues identified ● Remaining work to finalize report
● Question/answer
Executive Summary Background and Introduction ● Project Parties and Roles ● Project Overview
Data Sources and Assessment ● (Load Reducing Measure)
(Load Reducing Measure) ● Background ● Baseline Load Characterization ● Potential Management Practices ● Management Practice Performance Summary and Validation ● Other Recommendations
Program Implementation Recommendations
References
Remedy Malfunctioning Septic System – Background
“Malfunctions” and load delivery characteristics vary spatially and temporally
New malfunctions occurs as old malfunctions are remedied Malfunction types ● Illicit septic tank effluent discharge ● Illicit graywater (e.g., from laundry) discharge ● Demonstrated drainfield malfunction
Remedy types ● Repair to properly functioning septic system ● Repair with properly functioning TS-II (nitrogen-reducing) onsite system ● Connection to permitted major NPDES system ● Replacement with a discharging TS-II system
Credits awarded based on rates of different types of malfunctions and remedies implemented
Remedy Malfunctioning Septic System – Program Elements
New “survey program” for jurisdictions to establish malfunction rates and accounting for malfunctions and remedies ● 20% of systems inspected per year ● Normalize seasonal differences ● Apply malfunction rate improvement to all systems in jurisdiction
Remedies resulting from malfunctions identified via traditional methods (complaints, required inspections, home transfers)
Systems (functioning and malfunctioning) otherwise eliminated by connection to sewer
Averaging across multiple systems captures expected range in malfunction intensity and remedy performance
Remedy Malfunctioning Septic System – Malfunction Types
Illicit septic tank effluent discharge ● TN load of 11 lb/yr-person (assumes no reduction in septic tank) ● TP load of 1.8 lb/yr-person
Illicit graywater (e.g., from laundry) discharge ● TN load of 0.70 lb/yr-person ● TP load of 0.98 lb/yr-person ● Based on published data post detergent phosphate reduction
Demonstrated drainfield malfunction ● TN load of 1.1 lb/yr-person ● TP load of 0.036 lb/yr-person
● Based on combination of Piedmont water quality data and malfunction accounting methodologies used in other watershed studies
Remedy Malfunctioning Septic System – Remedy Types
Repair to properly functioning septic system ● TN load of 0.55 lb/yr-person (95% reduction of STE load) ● Zero TP load (100% reduction)
● Based on combination of Piedmont water quality data, Chesapeake and others ● Currently conducting additional literature review and review of Piedmont water quality data to estimate functioning and malfunctioning system loads
Repair with properly functioning advanced (TS-II) onsite system ● TN load of 0.22 lb/yr-person (60% + 95% = 98% reduction of STE load) ● Zero TP load (100% reduction in soil)
Connection to permitted NPDES system ● Assume all load transferred to point source sector, but awaiting DWQ input
Replacement with TS-II equivalent discharging system ● TN load of 4.4 lb/yr-person ● TP load of 1.8 lb/yr-person
Remedy Malfunctioning Septic System – Credit Summary TN load reduction credits Remedy (R)
Properly functioning septic system (R1)
Properly functioning TS-II system (R2)
Connection to major NPDES system (R3)*
(lb/cap/year)
(lb/cap/year)
Connection to a TSII Discharging System (R4)
M alfunctioning System (M)
(lb/cap/year)
Direct STE discharge (M1)
10.45
10.78
11.0
6.6
Direct graywater/laundry discharge (M2)
0.15
0.48
0.70
--
Dem onstrated drainfield m alfunction (M3)
0.55
0.88
1.1
--
Properly functioning septic system (R1)
Properly functioning TS-II system (R2)
Connection to major NPDES system (R3)
(lb/cap/year)
(lb/cap/year)*
Connection to a TSII Discharging System (R4)
(lb/cap/year)
TP load reduction credits Remedy (R)
M alfunctioning System (M)
(lb/cap/year)
Direct STE discharge (M1)
1.8
1.8
1.8
--
Direct graywater/laundry discharge (M2)
0.98
0.98
0.98
--
Dem onstrated drainfield m alfunction (M3)
0.036
0.036
0.036
--
(lb/cap/year)
Remedy Discharging Sand Filter – Background
Describes several different types of systems with varying characteristics Only a portion have actually been identified and permitted Accounting can be done on a system-by-system basis but there are benefits for jurisdictions to combine program with that for septic systems
Discharging system types ● Gravity-dosed single pass sand filters with regular discharges ● Gravity-dosed single pass sand filters with no or infrequent discharges
● Recirculating filters and TS-II equivalent treatment systems ● Malfunctioning (surface failing) systems
Remedy types ● Upgrade to recirculating filters or TS-II treatment systems
● Connection to major NPDES system ● Replacement with properly functioning septic system ● Replacement with properly functioning TS-II onsite system
Remedy Discharging Sand Filter – System Types
Gravity-dosed single pass sand filters with regular discharges ● TN load of 7.4 lb/yr-person (33% load reduction) ● TP load of 1.8 lb/yr-person (no load reduction) ● Based on Durham/DWQ data and some published data
Gravity-dosed single pass sand filters with no or infrequent discharges ● TN load of 7.4 lb/yr-person (33% load reduction) ● TP load of 0.9 lb/yr-person (50% load reduction)
Recirculating filters and TS-II treatment systems ● TN load of 4.4 lb/yr-person (60% load reduction) ● TP load of 1.8 lb/yr-person (no load reduction)
Malfunctioning systems ● TN load of 7.4 lb/yr-person (33% load reduction)
● TP load of 1.8 lb/yr-person (no load reduction)
Remedy Malfunctioning Septic System – Remedy Types Upgrade to recirculating filters and TS-II treatment systems ● TN load of 4.4 lb/yr-person (60% load reduction) ● TP load of 1.8 lb/yr-person (no load reduction)
Connection to major NPDES system ● Assume all load transferred to point source sector, but awaiting DWQ input
Repair to properly functioning septic system ● TN load of 0.55 lb/yr-person
● Zero TP load
Repair with properly functioning advanced (TS-II) onsite system ● TN load of 0.22 lb/yr-person ● Zero TP load
Remedy Malfunctioning Septic System – Credit Summary
TN load reduction credits Alternative (A)
Discharging System (D)
Upgrade to TS-II treatm ent system (A1)
Connection to m ajor NPDES system (A2)* (lb/cap/year)
(lb/cap/year)
Replacem ent w ith properly functioning septic system (A3) (lb/cap/year)
Replacem ent w ith properly functioning TS-II onsite system (A4) (lb/cap/year)
Single-pass filter with regular discharges (D1)
3.0
7.4
6.9
7.2
Single-pass filter with no or infrequent discharges (D2)
3.0
7.4
6.9
7.2
TS-II or equivalent treatment system (D3)
--
4.4
3.9
4.2
Malfunctioning discharging systems (D4)
3.0
7.4
6.9
7.2
Remedy Malfunctioning Septic System – Credit Summary
TP load reduction credits Alternative (A)
Discharging System (D)
Upgrade to TS-II discharging treatm ent system (A1)
Connection to m ajor NPDES system (A2)* (lb/cap/year)
Replacem ent w ith properly functioning septic system (A3) (lb/cap/year)
(lb/cap/year)
Replacem ent w ith properly functioning TS-II onsite system (A4) (lb/cap/year)
Single-pass filter with regular discharges (D1)
--
1.8
1.8
1.8
Single-pass filter with no or infrequent discharges (D2)
--
0.9
0.9
0.9
TS-II or equivalent treatment system (D3)
--
1.8
1.8
1.8
Malfunctioning discharging systems (D4)
--
1.8
1.8
1.8
Stormwater Measures – Improved Street Sweeping
Chesapeake Bay Expert Panel Recommendation Summary • Credit approved in March 2011 • Primarily based on Law, 2008 • Two credit methods: • Mass loading approach • Qualifying street lanes approach • *CBP reconvening in August 2013 to update protocol • Updated performance • Expanded credit for less frequent sweeping
Stormwater Measures – Improved Street Sweeping
Street Sweeping Pollutant Removal Performance Background • First studies in 70’s -80’s • Technology of the time limited to mechanical broom • Initial research indicated no impact (NURP, 83) • Poor pick-up performance of small particulates • Improvements to sweeper design in last 30 years have resulted in significantly increased performance • Many studies on pick-up performance, few on impact of sweeping to downstream WQ
Stormwater Measures – Improved Street Sweeping
Credit Protocol: Direct Measurement • Maintain records of collected “sweepings” mass • Conduct analysis of N and P content of collected materials • Alternative: Apply standard rates Lbs of TN = 0.0025 pounds of dry weight sweeping solids Lbs of TP = 0.001 pounds of dry weight sweeping solids
• Concerns: • Little research supporting impact of street sweeping on downstream water quality • Nitrogen processing prior to discharge
Stormwater Measures – Improved Street Sweeping
Credit Protocol: Miles swept method • Estimate annual Nutrient load to road surface • Apply removal performance per frequency and type of sweeper technology Frequency
TP
TN
Monthly
4%
4%
Biweekly
5%
6%
Weekly
5%
6%
Stormwater Measures – Improved Street Sweeping
Credit Protocol: Miles swept method • Concerns • Road dirt load and constituents highly variable • Age/type of roadway surface • Traffic load/type • vegetation/seasonal effects • Climate • Sweeping obstructions
Stormwater Measures – Improved Street Sweeping
Credit Protocol: Miles swept method • Sweeping program criteria • No parking or other obstructions • Sweeper type: regen/vac • Primary and secondary roads only
Stormwater Measures – Stream Restoration/Enhancements
• Stream Restoration Credit Protocols • Prevented sediment • In-stream nutrient processing • Floodplain reconnection • Regenerative Stormwater Conveyance (RSC)
Stormwater Measures – Stream Restoration/Enhancements
“Prevented Sediment” Protocol • Evaluates the reduction in nutrients delivered to receiving waters associated with the reduction in streambank erosion and relies on computation of three factors:
• Pre-project annual sediment load • Nutrient content (N and P) of streambank soil • Net efficiency (%) of restoration in reducing bank erosion
Stormwater Measures – Stream Restoration/Enhancements
Prevented Sediment: Pre-Project Annual Sediment Load • Option 1: Estimate sediment loss rate based on pre-project monitoring of streambank erosion rates via cross-section surveys and bank pins. • Requires pre-project monitoring • Monitoring stations must be representative of reach
Stormwater Measures – Stream Restoration/Enhancements
Prevented Sediment: Pre-Project Annual Sediment Load • Option 2: Estimate sediment loss rate based on the application of the Bank Assessment for Non-Point Source Consequences of Sediment (BANCS, Rosgen 2001, Doll, 2004) method. The BANCS method relies on two common bank erodibility estimation tools which have seen widespread application in North Carolina • Bank Erosion Hazard Index (BEHI) • Near Bank Stress (NBS) • Concerns: • Variation among practitioners • Erosion rate curves specific to region
Stormwater Measures – Stream Restoration/Enhancements
Prevented Sediment: Nutrient content of eroded sediments • Option 1: Conduct monitoring of streambank sediment characteristics within the reach of interest
• Concerns • Sediment monitoring protocol • Distribution of sampling locations
Stormwater Measures – Stream Restoration/Enhancements
Prevented Sediment: Nutrient Content of eroded sediments • Option 2: Use default nutrient concentration values representative of urban streams within the region Source
Phosphorus
Nitrogen
Content (lb/tn)
0.46
1.26
• Concerns • Variability between reaches • Representative values not published for NC
Stormwater Measures – Stream Restoration/Enhancements
Prevented Sediment: Net efficiency • Incorporates the efficiency of the restoration to reduce streambank erosion • Concerns • Efficiency may range widely between projects • Should also consider delivery of nutrients to downstream resources
Limited data was discovered supporting the selection of a restoration efficiency in NC Net Efficiency= 50%
Stormwater Measures – Stream Restoration/Enhancements
In-stream Nutrient Processing Protocol • Applies to projects or components of projects in which in-stream design features promote nutrient processing specifically de-nitrification within the “Hyporheic” zone • Protocol: • Determine appropriate reach length for credit • Identify “hyporheic box” • Apply unit denitrification rate
Stormwater Measures – Stream Restoration/Enhancements
In-stream Nutrient Processing Protocol • Concerns • Hyporheic box/exchange • Bed material/bedrock can limit vertical extent of box • Slope • Substrate • Very limited on headwater streams • Denitrification rate • No published values for NC • Net reduction depends on bulk density of bed material
Stormwater Measures – Stream Restoration/Enhancements
Floodplain Reconnection • Applies to projects in which stream restoration results in frequent overbank flooding and provides temporary storage and treatment of overflows
.
Stormwater Measures – Stream Restoration/Enhancements
Floodplain Reconnection Protocol • Estimate net storage volume of floodplain reconnection • Estimate N and P load/concentration delivered to the floodplain* • Estimate N and P removal performance to floodplain reconnection • Compute Net N and P reduction
*Since this credit applies to N and P contained in stormwater runoff, the load estimation should account for the performance of any upland BMPs.
Stormwater Measures – Stream Restoration/Enhancements
Floodplain Reconnection • Estimate of net volume of floodplain reconnection • Survey or computation of floodplain treatment storage volume • Computation of fraction of annual runoff which will be “captured” by floodplain storage • Requires detailed hydrologic and hydraulic analysis
Stormwater Measures – Stream Restoration/Enhancements
Floodplain Reconnection • Estimate of N and P Load delivered to the floodplain • Determine total N & P load delivered to watershed • < 40 acres JFLSLAT • > 40 acres • Falls: WARMF model • Jordan: Jordan Lake Model Compute net load delivered to floodplain by multiplying total load by fraction of runoff treated
Stormwater Measures – Stream Restoration/Enhancements
Floodplain Reconnection • Estimate N and P removal performance of floodplain reconnection • Compute load reduction by applying stormwater wetland effluent values (JFLSLAT) to reconnection volume
Stormwater Measures – Stream Restoration/Enhancements
Regenerative Stormwater Conveyance • Dry Channel RSC Protocol • Compute treated volume (filtered, infiltrated, retained) • Compute N & P load per JFLSLAT • Apply effluent values for treated volume per Dr. Hunts ongoing research (use Sand Filter in interim) • Concerns • Unproven BMP in NC
Project Approach Schedule Activity Task 1 Selection of Measures - Kick off and NSAB meeting Task 2 Data Sources - Data protocol - Data collection - Data assessment - Data summary Task 3 Technical Report - Method/tool development - Draft report - NSAB presentation - Final report
May
June
July
August
September
Project Approach – Tasks Task 1. Selection of Measures ● May 13th NSAB meeting: kick off/presentation attended by Vic, Jonathan ● Will begin putting together data protocol (Task 2) in preparation ● Prepared to discuss key questions to be addressed prior to data collection ● Coordination with PTRC/DWQ
Task 2. Data Sources ● Data protocol technical memo (by May 20th) – criteria for accepting data – NC Piedmont applicability – Data QA/QC and other characteristics
● Data collection – collect data sources/references ● Data assessment – assess sources versus acceptance criteria ● Data summary (by June 14th) – summarize assessment and recommend data sources to use
Project Approach – Tasks
Task 3. Technical Report ● Method/tool development – data processing and analysis ● Draft report (by August 9th) ● NSAB presentation (September 6th) – Summarize draft report, comments received and proposed revisions and other actions to be taken
● Final report (by September 20th)
Today’s Presentation
For each measure: ● Orientation to and summary of content in draft report ● Major issues identified ● Remaining work to finalize report
● Question/answer
Executive Summary Background and Introduction ● Project Parties and Roles ● Project Overview
Data Sources and Assessment ● (Load Reducing Measure)
(Load Reducing Measure) ● Background ● Baseline Load Characterization ● Potential Management Practices ● Management Practice Performance Summary and Validation ● Other Recommendations
Program Implementation Recommendations
References
Remedy Malfunctioning Septic System – Background
“Malfunctions” and load delivery characteristics vary spatially and temporally
New malfunctions occurs as old malfunctions are remedied Malfunction types ● Illicit septic tank effluent discharge ● Illicit graywater (e.g., from laundry) discharge ● Demonstrated drainfield malfunction
Remedy types ● Repair to properly functioning septic system ● Repair with properly functioning TS-II (nitrogen-reducing) onsite system ● Connection to permitted major NPDES system ● Replacement with a discharging TS-II system
Credits awarded based on rates of different types of malfunctions and remedies implemented
Remedy Malfunctioning Septic System – Program Elements
New “survey program” for jurisdictions to establish malfunction rates and accounting for malfunctions and remedies ● 20% of systems inspected per year ● Normalize seasonal differences ● Apply malfunction rate improvement to all systems in jurisdiction
Remedies resulting from malfunctions identified via traditional methods (complaints, required inspections, home transfers)
Systems (functioning and malfunctioning) otherwise eliminated by connection to sewer
Averaging across multiple systems captures expected range in malfunction intensity and remedy performance
Remedy Malfunctioning Septic System – Malfunction Types
Illicit septic tank effluent discharge ● TN load of 11 lb/yr-person (assumes no reduction in septic tank) ● TP load of 1.8 lb/yr-person
Illicit graywater (e.g., from laundry) discharge ● TN load of 0.70 lb/yr-person ● TP load of 0.98 lb/yr-person ● Based on published data post detergent phosphate reduction
Demonstrated drainfield malfunction ● TN load of 1.1 lb/yr-person ● TP load of 0.036 lb/yr-person
● Based on combination of Piedmont water quality data and malfunction accounting methodologies used in other watershed studies
Remedy Malfunctioning Septic System – Remedy Types
Repair to properly functioning septic system ● TN load of 0.55 lb/yr-person (95% reduction of STE load) ● Zero TP load (100% reduction)
● Based on combination of Piedmont water quality data, Chesapeake and others ● Currently conducting additional literature review and review of Piedmont water quality data to estimate functioning and malfunctioning system loads
Repair with properly functioning advanced (TS-II) onsite system ● TN load of 0.22 lb/yr-person (60% + 95% = 98% reduction of STE load) ● Zero TP load (100% reduction in soil)
Connection to permitted NPDES system ● Assume all load transferred to point source sector, but awaiting DWQ input
Replacement with TS-II equivalent discharging system ● TN load of 4.4 lb/yr-person ● TP load of 1.8 lb/yr-person
Remedy Malfunctioning Septic System – Credit Summary TN load reduction credits Remedy (R)
Properly functioning septic system (R1)
Properly functioning TS-II system (R2)
Connection to major NPDES system (R3)*
(lb/cap/year)
(lb/cap/year)
Connection to a TSII Discharging System (R4)
M alfunctioning System (M)
(lb/cap/year)
Direct STE discharge (M1)
10.45
10.78
11.0
6.6
Direct graywater/laundry discharge (M2)
0.15
0.48
0.70
--
Dem onstrated drainfield m alfunction (M3)
0.55
0.88
1.1
--
Properly functioning septic system (R1)
Properly functioning TS-II system (R2)
Connection to major NPDES system (R3)
(lb/cap/year)
(lb/cap/year)*
Connection to a TSII Discharging System (R4)
(lb/cap/year)
TP load reduction credits Remedy (R)
M alfunctioning System (M)
(lb/cap/year)
Direct STE discharge (M1)
1.8
1.8
1.8
--
Direct graywater/laundry discharge (M2)
0.98
0.98
0.98
--
Dem onstrated drainfield m alfunction (M3)
0.036
0.036
0.036
--
(lb/cap/year)
Remedy Discharging Sand Filter – Background
Describes several different types of systems with varying characteristics Only a portion have actually been identified and permitted Accounting can be done on a system-by-system basis but there are benefits for jurisdictions to combine program with that for septic systems
Discharging system types ● Gravity-dosed single pass sand filters with regular discharges ● Gravity-dosed single pass sand filters with no or infrequent discharges
● Recirculating filters and TS-II equivalent treatment systems ● Malfunctioning (surface failing) systems
Remedy types ● Upgrade to recirculating filters or TS-II treatment systems
● Connection to major NPDES system ● Replacement with properly functioning septic system ● Replacement with properly functioning TS-II onsite system
Remedy Discharging Sand Filter – System Types
Gravity-dosed single pass sand filters with regular discharges ● TN load of 7.4 lb/yr-person (33% load reduction) ● TP load of 1.8 lb/yr-person (no load reduction) ● Based on Durham/DWQ data and some published data
Gravity-dosed single pass sand filters with no or infrequent discharges ● TN load of 7.4 lb/yr-person (33% load reduction) ● TP load of 0.9 lb/yr-person (50% load reduction)
Recirculating filters and TS-II treatment systems ● TN load of 4.4 lb/yr-person (60% load reduction) ● TP load of 1.8 lb/yr-person (no load reduction)
Malfunctioning systems ● TN load of 7.4 lb/yr-person (33% load reduction)
● TP load of 1.8 lb/yr-person (no load reduction)
Remedy Malfunctioning Septic System – Remedy Types Upgrade to recirculating filters and TS-II treatment systems ● TN load of 4.4 lb/yr-person (60% load reduction) ● TP load of 1.8 lb/yr-person (no load reduction)
Connection to major NPDES system ● Assume all load transferred to point source sector, but awaiting DWQ input
Repair to properly functioning septic system ● TN load of 0.55 lb/yr-person
● Zero TP load
Repair with properly functioning advanced (TS-II) onsite system ● TN load of 0.22 lb/yr-person ● Zero TP load
Remedy Malfunctioning Septic System – Credit Summary
TN load reduction credits Alternative (A)
Discharging System (D)
Upgrade to TS-II treatm ent system (A1)
Connection to m ajor NPDES system (A2)* (lb/cap/year)
(lb/cap/year)
Replacem ent w ith properly functioning septic system (A3) (lb/cap/year)
Replacem ent w ith properly functioning TS-II onsite system (A4) (lb/cap/year)
Single-pass filter with regular discharges (D1)
3.0
7.4
6.9
7.2
Single-pass filter with no or infrequent discharges (D2)
3.0
7.4
6.9
7.2
TS-II or equivalent treatment system (D3)
--
4.4
3.9
4.2
Malfunctioning discharging systems (D4)
3.0
7.4
6.9
7.2
Remedy Malfunctioning Septic System – Credit Summary
TP load reduction credits Alternative (A)
Discharging System (D)
Upgrade to TS-II discharging treatm ent system (A1)
Connection to m ajor NPDES system (A2)* (lb/cap/year)
Replacem ent w ith properly functioning septic system (A3) (lb/cap/year)
(lb/cap/year)
Replacem ent w ith properly functioning TS-II onsite system (A4) (lb/cap/year)
Single-pass filter with regular discharges (D1)
--
1.8
1.8
1.8
Single-pass filter with no or infrequent discharges (D2)
--
0.9
0.9
0.9
TS-II or equivalent treatment system (D3)
--
1.8
1.8
1.8
Malfunctioning discharging systems (D4)
--
1.8
1.8
1.8
Stormwater Measures – Improved Street Sweeping
Chesapeake Bay Expert Panel Recommendation Summary • Credit approved in March 2011 • Primarily based on Law, 2008 • Two credit methods: • Mass loading approach • Qualifying street lanes approach • *CBP reconvening in August 2013 to update protocol • Updated performance • Expanded credit for less frequent sweeping
Stormwater Measures – Improved Street Sweeping
Street Sweeping Pollutant Removal Performance Background • First studies in 70’s -80’s • Technology of the time limited to mechanical broom • Initial research indicated no impact (NURP, 83) • Poor pick-up performance of small particulates • Improvements to sweeper design in last 30 years have resulted in significantly increased performance • Many studies on pick-up performance, few on impact of sweeping to downstream WQ
Stormwater Measures – Improved Street Sweeping
Credit Protocol: Direct Measurement • Maintain records of collected “sweepings” mass • Conduct analysis of N and P content of collected materials • Alternative: Apply standard rates Lbs of TN = 0.0025 pounds of dry weight sweeping solids Lbs of TP = 0.001 pounds of dry weight sweeping solids
• Concerns: • Little research supporting impact of street sweeping on downstream water quality • Nitrogen processing prior to discharge
Stormwater Measures – Improved Street Sweeping
Credit Protocol: Miles swept method • Estimate annual Nutrient load to road surface • Apply removal performance per frequency and type of sweeper technology Frequency
TP
TN
Monthly
4%
4%
Biweekly
5%
6%
Weekly
5%
6%
Stormwater Measures – Improved Street Sweeping
Credit Protocol: Miles swept method • Concerns • Road dirt load and constituents highly variable • Age/type of roadway surface • Traffic load/type • vegetation/seasonal effects • Climate • Sweeping obstructions
Stormwater Measures – Improved Street Sweeping
Credit Protocol: Miles swept method • Sweeping program criteria • No parking or other obstructions • Sweeper type: regen/vac • Primary and secondary roads only
Stormwater Measures – Stream Restoration/Enhancements
• Stream Restoration Credit Protocols • Prevented sediment • In-stream nutrient processing • Floodplain reconnection • Regenerative Stormwater Conveyance (RSC)
Stormwater Measures – Stream Restoration/Enhancements
“Prevented Sediment” Protocol • Evaluates the reduction in nutrients delivered to receiving waters associated with the reduction in streambank erosion and relies on computation of three factors:
• Pre-project annual sediment load • Nutrient content (N and P) of streambank soil • Net efficiency (%) of restoration in reducing bank erosion
Stormwater Measures – Stream Restoration/Enhancements
Prevented Sediment: Pre-Project Annual Sediment Load • Option 1: Estimate sediment loss rate based on pre-project monitoring of streambank erosion rates via cross-section surveys and bank pins. • Requires pre-project monitoring • Monitoring stations must be representative of reach
Stormwater Measures – Stream Restoration/Enhancements
Prevented Sediment: Pre-Project Annual Sediment Load • Option 2: Estimate sediment loss rate based on the application of the Bank Assessment for Non-Point Source Consequences of Sediment (BANCS, Rosgen 2001, Doll, 2004) method. The BANCS method relies on two common bank erodibility estimation tools which have seen widespread application in North Carolina • Bank Erosion Hazard Index (BEHI) • Near Bank Stress (NBS) • Concerns: • Variation among practitioners • Erosion rate curves specific to region
Stormwater Measures – Stream Restoration/Enhancements
Prevented Sediment: Nutrient content of eroded sediments • Option 1: Conduct monitoring of streambank sediment characteristics within the reach of interest
• Concerns • Sediment monitoring protocol • Distribution of sampling locations
Stormwater Measures – Stream Restoration/Enhancements
Prevented Sediment: Nutrient Content of eroded sediments • Option 2: Use default nutrient concentration values representative of urban streams within the region Source
Phosphorus
Nitrogen
Content (lb/tn)
0.46
1.26
• Concerns • Variability between reaches • Representative values not published for NC
Stormwater Measures – Stream Restoration/Enhancements
Prevented Sediment: Net efficiency • Incorporates the efficiency of the restoration to reduce streambank erosion • Concerns • Efficiency may range widely between projects • Should also consider delivery of nutrients to downstream resources
Limited data was discovered supporting the selection of a restoration efficiency in NC Net Efficiency= 50%
Stormwater Measures – Stream Restoration/Enhancements
In-stream Nutrient Processing Protocol • Applies to projects or components of projects in which in-stream design features promote nutrient processing specifically de-nitrification within the “Hyporheic” zone • Protocol: • Determine appropriate reach length for credit • Identify “hyporheic box” • Apply unit denitrification rate
Stormwater Measures – Stream Restoration/Enhancements
In-stream Nutrient Processing Protocol • Concerns • Hyporheic box/exchange • Bed material/bedrock can limit vertical extent of box • Slope • Substrate • Very limited on headwater streams • Denitrification rate • No published values for NC • Net reduction depends on bulk density of bed material
Stormwater Measures – Stream Restoration/Enhancements
Floodplain Reconnection • Applies to projects in which stream restoration results in frequent overbank flooding and provides temporary storage and treatment of overflows
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Stormwater Measures – Stream Restoration/Enhancements
Floodplain Reconnection Protocol • Estimate net storage volume of floodplain reconnection • Estimate N and P load/concentration delivered to the floodplain* • Estimate N and P removal performance to floodplain reconnection • Compute Net N and P reduction
*Since this credit applies to N and P contained in stormwater runoff, the load estimation should account for the performance of any upland BMPs.
Stormwater Measures – Stream Restoration/Enhancements
Floodplain Reconnection • Estimate of net volume of floodplain reconnection • Survey or computation of floodplain treatment storage volume • Computation of fraction of annual runoff which will be “captured” by floodplain storage • Requires detailed hydrologic and hydraulic analysis
Stormwater Measures – Stream Restoration/Enhancements
Floodplain Reconnection • Estimate of N and P Load delivered to the floodplain • Determine total N & P load delivered to watershed • < 40 acres JFLSLAT • > 40 acres • Falls: WARMF model • Jordan: Jordan Lake Model Compute net load delivered to floodplain by multiplying total load by fraction of runoff treated
Stormwater Measures – Stream Restoration/Enhancements
Floodplain Reconnection • Estimate N and P removal performance of floodplain reconnection • Compute load reduction by applying stormwater wetland effluent values (JFLSLAT) to reconnection volume
Stormwater Measures – Stream Restoration/Enhancements
Regenerative Stormwater Conveyance • Dry Channel RSC Protocol • Compute treated volume (filtered, infiltrated, retained) • Compute N & P load per JFLSLAT • Apply effluent values for treated volume per Dr. Hunts ongoing research (use Sand Filter in interim) • Concerns • Unproven BMP in NC
