Septic Systems Rumors Rules and Research Questions WSE

Septic Systems: Rumors, Rules, and Research Questions WSE Seminar FAMU/FSU College of Engineering February 25, 2005 By Eberhard Roeder, Ph. D. , P. E. Bureau of Onsite Sewage Programs FL Dept. of Health, Division of Environmental Health 1

Black Box Rumors • If you don’t know where the pollution is coming from, it is the septic system 2

Black Box Rumors • (Failing) septic systems are responsible for pathogen indicators in surface water • Watershed Management Model Version 4. 1 (1998) – 10% of septic systems are failing – Failing septic systems contribute nitrogen and phosphorus, but no pathogen indicators and oxygen demand to stormwater 3

Outline of the Presentation • How many septic systems are there in Florida? • What are septic systems and how do they work? • What about nitrogen? • What is the Karst Study? • How can septic systems be managed? 4

Florida’s Onsite Wastewater Treatment Systems • > 2. 3 million septic systems (2001) • 7. 3 million housing units (2000) • 31% served by septic systems 5

Septic Systems treat Sewage Onsite – wastewater that is treated and disposed of at the location where it is generated (on your property) – In contrast to central sewer – Treatment and Disposal is achieved by an “onsite sewage treatment and disposal system” (OSTDS) 6

What is coming into Septic Systems? • oxygen-consuming material (~300 mg/L measured in carbonaceous oxygen consumption) • suspended solids (~250 mg/L) • Nutrients – nitrogen ~50 mg/L (~23 lbs/year and household of three at 50 gal/cap day ) – phosphorus ~25 mg/L • Pathogens among the Bacteria (~1 billion/L) and virus (~50 -7 k PFU/L) • Traces of organics, and other elements 7

What is a standard septic system? Groundwater 2 feet between bottom of drainfield and seasonal high water 8 table

What’s happening in the septic tank? • Septic tank (anaerobic): – Collects solids (~60 lbs/year TSS) -> must be pumped regularly – Consumes a third of biodegradable material anaerobically (without oxygen) – Nitrogen from protein is converted into ammonia • Rules: Approval testing for water tightness and structural integrity required since mid 1990 s 9

What’s happening in the drainfield? • Drainfield (aerobic): – Consumes biodegradable material (c. BOD 5, TSS) using oxygen – Removes/filters pathogens, c. BOD, suspended solids in the unsaturated zone above groundwater (2 feet minimum separation to water table is foundation of system design) – Converts ammonia to nitrate – Disposes of water • Rules: Built from gravel or alternative materials (chambers, pipes, artificial gravel) Groundwater 10

What’s happening in an ATU? • ATU=aerobic treatment unit – Brings sewage (usually pretreated by septic tank) mechanically into contact with air for aerobic treatment, before discharging to drainfield – Reduces c. BOD and TSS – Can be used for drainfield size reduction, drainfield repair 11

Standard Septic Systems and Aerobic Treatment Units as secondary wastewater treatment plants • Primary treatment=settling of solids • Secondary treatment= removal of oxygen -consuming material • Tertiary treatment= removal of nutrients 12

(Average) Treatment Expectations c. BOD 5 (mg/L) TSS (mg/L) TN (mg/L) TP (mg/L) Below drainfield at groundwater interface <5 <5 25 -40 <5 Secondary Treatment <20 Florida Keys <10 <10 <1 13

What is failure? • System does not function in a sanitary manner: Loss of flush, or discharge of untreated or partially treated wastewater onto ground surface, into ground water, into surface water (64 E-6. 001, FAC) • Tracked as number of repair permits divided by all systems accounted for 14

What’s happening to nitrogen? • 1) Ammonification in the septic tank Organic N + microorganisms -> NH 3/NH 4+ + microorganisms • 2) Nitrification in the presence of oxygen (drainfield) NH 4+ + 2 O 2 -> NO 3 - + 2 H+ + 2 H 2 O 15

• 3) The removal step: Denitrification NO 3 - + organic matter -> N 2 +CO 2 +OH- +H 2 O • Problem: little organic matter left after drainfield (need extra carbon for denitrification) • Solutions: – Recycle nutrients to vegetation via drip-irrigation (generally in conjunction with an ATU, effectiveness unclear) – Tertiary treatment at onsite scale. Recirculate aerated effluent to septic tank or add carbon. • Overall: about 20 -40% of nitrogen is removed from when sewage reaches the septic tank to when effluent reaches the groundwater 16

Nitrogen Management Approaches: technically • No sewage • Limit flow and/or number of OSTDS per acre. This approach has been in Florida OSTDS rules for at least 30 years. • Increased Treatment: – drip-irrigation (generally in conjunction with an ATU) – tertiary treatment at onsite scale (tested in Keys Demonstration Study, proposed for Wekiva). • Natural attenuation: – In some areas, nitrogen and phosphorus decrease subsequent to the drainfield in the groundwater and don’t appear to affect surface water (St George Island Study, Indian River Lagoon Study). – In some areas this natural attenuation process appears to be less important (Lake Okeechobee Study, Karst Study) 17

What is the (OSTDS in) Karst Study • Observations: – karst is widespread and allows rapid groundwater transport (Karst =landscape of dissolving limestone) – Springs experience increasing nitrate-nitrogen concentrations (eutrophication) • Question: What are the impacts of OSTDS on groundwater in karst areas? Wakulla Springs N 18

Karst Study • Project: University Project – Monitor Groundwater downstream of OSTDS for chemical tracers, nutrients and fecal coliforms River Front 19 On top of Cave System

Tracers at Magnolia II M-1: 75 feet from injection point Fl arrival in 2. 5 days M-3: 135 feet from injection point Fl arrival in 1. 4 days 20

~60 feet Conceptual Flow Model: Upland Average Nitrate Concentration (mg/L) 0. 4 0. 6 12 21 0. 6 0. 1 Sue Sink Drainfield Manatee Spring ? ? ? ? ? ? 21 Cave

Conceptual Flow Model: River Front ~30 feet Suwannee River Average Nitrate Concentration (mg/L) 29 23 15 0. 3 Drainfield M-1 Core. M-2 Core. M-3 Core ? ? ? M-1 Core. M-2 Core. M-3 Core M-4 Core ? ? ? K=5. 2 E-7 cm/s 4. 5 fine, medium sand 6. 5 6. 0 wackestone fine, medium ? ? ? sand 6. 6 poor recovery 4. 5 5. 9 K=1. 0 E-7 cm/s K=1. 5 E-5 cm/s K=6. 0 E-3 cm/s 8. 1 ? ? ? 7. 0 K=4. 4 E-4 cm/s 8. 0 medium sand rubbly 7’-17’ limestone ? ? ? Screen K=1. 4 E-5 cm/s ? ? ? 3 ft of washout K=2. 7 E-4 cm/s 6. 5’-11. 5’ 8. 6 packstone 10 K=failed due tomedium channelingsand 8. 4 fine, medium sand Screen 10’-20’ K=5. 0 E-6 cm/s K=1. 7 E-4 cm/s ? ? ? 12. 5 packstone 11. 7 packstone ? ? ? K=1. 3 E-4 cm/s Screen 16. 2’-26. 2’ 19 medium sand. K=3. 4 E-4 cm/s K=9. 6 E-5 cm/s K=2. 8 E-4 cm/s 17 wackestone K=4. 4 E-4 cm/s K=1. 9 E-4 cm/s K=5. 7 E-5 cm/s 25. 7 K=3. 2 E-5 cm/s K=4. 0 E-4 cm/s K=3. 3 E-5 cm/s packstone 25. 5 packstone 26. 5 wackestone. K=5. 2 E-6 cm/s 31. 5 packstone ? ? ? ? ? 30. 0 packstone ? ? ? Groundwater washout, poor recovery 15 medium sand ? ? ? ? ? Screen 19. 3’-29. 3’ ? ? ? poor recovery 22. 5 packstone 25 wackestone poor recovery, washout 34. 4 packstone 30 medium sand 35 wackestone 22

OSTDS and Wakulla • Estimates for number of systems in 2000 • • • 28, 400 in Leon 8, 900 in Wakulla Estimate for Nitrate loading (midrange of septic tank effluent, without accounting for losses in groundwater) • • 4 kg /year and capita ~25 lbs/year and household NW Florida Water Management District Study (Chellette, Pratt and Katz, 232002) http: //www. state. fl. us/nwfwmd/pubs/nitrate

Estimated Contributors of anthropogenic Nitrogen to Wakulla Karst Plain Livestock 12% OSTDS 22% Missing? Commercial Fertilizer 27% Residual Disposal 12% WWTF 29% (yearly average 1990 -1999: 1. 3 million kg –N) Data from Chellette, Pratt and Katz, 2002 24

Delta N-15 as indicator of N-Source Delta N-15 as indicator of Nsource in monitoring wells in the Wakulla Springs area <3 artifical fertilizer >10 animals/sewage Wakulla Springs Data from Chellette, Pratt and Katz, 2002 25

How to Manage Onsite Systems? • EPA March 2003 Voluntary Guidelines provide a framework for discussion http: //www. epa. gov/owm/septic/pubs/septic_guidelines. pdf 26

How to Manage Onsite Systems? • Levels of Management will depend on: – severety of expected impacts (protection zones) – technical complexity of onsite systems, – amount and type of available funding – enforcement capabilities 27

EPA’s Management Models • • Homeowner Awareness Maintenance Contracts Operating Permits Responsible Management Entity Operation and Maintenance • Responsible Management Entity Ownership http: //www. epa. gov/owm/septic/pubs/septic_guidelines. pdf 28

How does Florida manage? • Standard Septic Systems: – Level 1 homeowner awareness; – also: design, construction and training certification and standards, (e. g. water tightness) • Aerobic treatment units: – Level 2/3 operating permit to homeowner requires contract with qualified maintenance entity. Regular inspection required • Performance-based systems: – Level 2/3 engineer-designed; operating permit to homeowner requires contract with qualified maintenance entity. More frequent inspection and sampling required. 29

Summary • About 30% of households in Florida are served by onsite systems • The standard septic system consists of a septic tank and a drainfield. The purpose of such a system is to remove solids, oxygen-consuming material and pathogens from the sewage, and dispose of the water without contacting people. • Standard septic systems and aerobic treatment units remove only some phosphorus and nitrogen. Some additional removal can occur in the groundwater depending on site conditions. Additional technical or institutional measures can further reduce nutrient loads. • The OSTDS Karst Study suggests that nutrients from OSTDS travel quickly and far (~100 feet). Direction depends on local conditions. • Levels of OSTDS management range from homeownership and control to utility ownership and control. More complicated systems and higher standards require higher levels of management. 30