Septic Systems: Rumors, Rules, and Research Questions

1
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

2
Black Box Rumors

• If you dont know where the pollution is coming
  from, it is the septic system

3
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

4
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?

5
Floridas Onsite Wastewater Treatment Systems

• gt 2. 3 million septic systems (2001)
• 7.3 million housing units (2000)
• 31 served by septic systems

6
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)

7
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 (50-7k PFU/L)
• Traces of organics, and other elements

8
What is a standard septic system?
2 feet between bottom of drainfield and
seasonal high water table
Groundwater
9
Whats happening in the septic tank?

• Septic tank (anaerobic)
• Collects solids (60lbs/year TSS)-gt 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-1990s

10
Whats happening in the drainfield?

• Drainfield (aerobic)
• Consumes biodegradable material (cBOD5, TSS)
  using oxygen
• Removes/filters pathogens, cBOD, 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
11
Whats happening in an ATU?

• ATUaerobic treatment unit
• Brings sewage (usually pretreated by septic tank)
  mechanically into contact with air for aerobic
  treatment, before discharging to drainfield
• Reduces cBOD and TSS
• Can be used for drainfield size reduction,
  drainfield repair

12
Standard Septic Systems and Aerobic Treatment
Units as secondary wastewater treatment plants

• Primary treatmentsettling of solids
• Secondary treatment removal of oxygen-consuming
  material
• Tertiary treatment removal of nutrients

13
(Average) Treatment Expectations
cBOD5 (mg/L) TSS (mg/L) TN (mg/L) TP (mg/L)
Below drainfield at groundwater interface lt5 lt5 25-40 lt5
Secondary Treatment lt20 lt20
Florida Keys lt10 lt10 lt10 lt1
14
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 (64E-6.001,
  FAC)
• Tracked as number of repair permits divided by
  all systems accounted for

15
Whats happening to nitrogen?

• 1) Ammonification in the septic tank
• Organic N microorganisms -gt NH3/NH4
  microorganisms
• 2) Nitrification in the presence of oxygen
  (drainfield)
• NH4 2O2 -gt NO3- 2 H 2 H2O

16

• 3) The removal step Denitrification
• NO3- organic matter -gt N2 CO2 OH- H2O
• 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

17
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 dont 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)

18
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
19
Karst Study

• Project University Project
• Monitor Groundwater downstream of OSTDS for
  chemical tracers, nutrients and fecal coliforms

On top of Cave System
River Front
20
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
21
Conceptual Flow Model Upland
60 feet
Sue Sink
Average Nitrate Concentration (mg/L)
0.4
0.6
12
21
0.6
0.1
Manatee Spring
Cave
22
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
??? ???
Groundwater
????? ????? ?????
23
OSTDS and Wakulla

• Estimates for number of systems in 2000
• 28,400 in Leon
• 8,900 in Wakulla
• Estimate for Nitrate loading (mid-range of septic
  tank effluent, without accounting for losses in
  groundwater)
• 4kg /year and capita
• 25 lbs/year and household

NW Florida Water Management District Study
(Chellette, Pratt and Katz, 2002)
http//www.state.fl.us/nwfwmd/pubs/nitrate/lowspee
d/nitrate_fig53.pdf
24
Estimated Contributors of anthropogenic Nitrogen
to Wakulla Karst Plain
Livestock 12
OSTDS 22
Missing?
Commercial Fertilizer 27
WWTF 29
Residual Disposal 12
(yearly average 1990-1999 1.3 million kg N)
Data from Chellette, Pratt and Katz, 2002
25
Delta N-15 as indicator of N-Source

• Delta N-15 as indicator of N-source in monitoring
  wells in the Wakulla Springs area
• lt3 artifical fertilizer
• gt10 animals/sewage
• Data from Chellette, Pratt and Katz, 2002

Wakulla Springs
26
How to Manage Onsite Systems?

• EPA March 2003 Voluntary Guidelines provide a
  framework for discussion

http//www.epa.gov/owm/septic/pubs/septic_guidelin
es.pdf
27
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

28
EPAs 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_guidelin
es.pdf
29
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.

30
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 homeowner
  ownership and control to utility ownership and
  control. More complicated systems and higher
  standards require higher levels of management.