Chesapeake Bay Watershed and North Carolina Piedmont Project Experiences

Transcription

1 Reducing Nutrient Loading from Onsite Wastewater Systems Chesapeake Bay Watershed and North Carolina Piedmont Project Experiences Victor A. D Amato, PE

2 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

3 Nutrient Removal in Onsite Systems Exsitu treatment Insitu treatment Attenuation

4 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 noncoastal areas; little indication that sorptive capacity is an issue

5 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

6 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

7 ChesBay Expert Panel: Baseline Load Recommendations ChesBay WQ model assumes zero TP load from septic systems throughout watershed

8 ChesBay Expert Panel: Residential System with BMP ChesBay WQ model assumes zero TP load from septic systems throughout watershed

9 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

10 Expert Panel: Nitrogen Removal Mgt. Practices Insitu practice Conventional baseline Shallow pressure dosed Elevated mound Exsitu practice 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.

11 Exsitu BMPs

12 Insitu BMPs 12

13 System with BMPs This is what we care about! Attenuation

14 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?

15 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

16 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

17 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

18 Jordan and Falls Lake Watershed Water Quality Monitoring Locations

19 NC Piedmont System Performance Septic-Generated Nutrients Measured Load in Stream Percent Septic Load Delivered to Stream TN TP (%) (%) Basin Stream TN TP TN TP Order* (lb/d/mi 2 ) (lb/d/mi 2 ) (lb/d/mi 2 ) (lb/d/mi 2 ) Rhodes Creek unk Seven-Mile Creek 4 th Cabin Branch 8 th Crooked Creek 2 nd Beaverdam Creek unk New Light Creek unk Honeycut Creek unk Cedar Creek unk AVERAGE Equivalent effluent concentrations: 2.0 mg/l TN, 0.2 mg/l TP Equivalent reductions: 96% TN, 98% TP Data from: NCDENR 2010 Berkowitz 2014

20 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 Nitrate Sources in Urban Surface Waters Feeding Falls and Jordan Lakes, Durham, NC. Unpublished soil science seminar presented September 11, 2013 and Personal Communication)

21 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

22 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.

23 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

24 Conclusions and Recommendations: Inventory, Prioritize and Manage Risk Indicators system age soil suitability proximity to streams proximity to lakes and ponds proximity to Bay tidal waters watershed vulnerability housing density

25 Conclusions and Recommendations: Inventory, Prioritize and Manage Mgt. Indicators parcel size proximity to collection systems proximity to large parcels

26 Wastewater Measures - Conclusions and Recommendations Do more research More intensive monitoring of septicdominated 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

27 Additional information Chesapeake Bay Expert Panel Final Report: QGIT_approved_ pdf Maryland Decentralized Wastewater Management Gap Closer Research and Analysis: Documents/Binder/Gap_Closer_Report_ pdf PTRC/DWR Nutrient Load Reducing Measures Report: Victor D Amato, PE victor.damato@tetratech.com