Onsite systems nutrients and the wakulla springshed
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Onsite Systems, Nutrients, and the Wakulla Springshed. By Eberhard Roeder, Ph.D., P.E. Bureau of Onsite Sewage Programs FL Dept. of Health, Division of Environmental Health. Wakulla Symposium May 12, 2005. Outline of the Presentation. How do septic/onsite systems work?

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Onsite systems nutrients and the wakulla springshed

Onsite Systems, Nutrients, and the Wakulla Springshed

By Eberhard Roeder, Ph.D., P.E.

Bureau of Onsite Sewage Programs

FL Dept. of Health, Division of Environmental Health

Wakulla Symposium

May 12, 2005

Outline of the presentation
Outline of the Presentation

  • How do septic/onsite systems work?

  • What can be done about nutrients?

  • What are best management practices?

  • What are suggestions for the Wakulla Springshed?

How do onsite systems work
How do onsite systems work?

Septic Tank

Aerobic Treatment Unit

Performance Based Treatment System

2 feet between bottom

of drainfield and

seasonal high water



What can be done about nutrients
What can be done about nutrients?

  • 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:

    • Recycle to plants (drip-irrigation, generally in conjunction with an ATU)

    • High-performance 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)

Karst study
Karst Study

  • Manatee Springs State Park Bath Houses

    • Rapid transport of tracers

    • Nitrate concentrations in excess of drinking water standards at many monitoring wells

    • Phosphorus elevated

    • Few fecal coliform observations

Upland (On top of cave)

River Front

Conceptual flow model upland








Conceptual Flow Model: Upland

~60 feet

Sue Sink

Average Nitrate

Concentration (mg/L)







Manatee Spring


Conceptual flow model river front

M-1 Core

M-2 Core

M-3 Core

M-4 Core

M-4 Core


4.5 fine, medium sand

6.5 wackestone

6.0 fine, medium sand





6.6 poor recovery

rubbly limestone









8.0 medium sand

K=1.5E-5 cm/s



K=1.4E-5 cm/s

Screen 7’-17’

3 ft of washout 6.5’-11.5’

8.6 packstone

10 medium sand


K=failed due to channeling

8.4 fine, medium sand

Screen 10’-20’

K=5.0E-6 cm/s

K=1.7E-4 cm/s

12.5 packstone

11.7 packstone


K=2.8E-4 cm/s

Screen 16.2’-26.2’

washout, poor recovery

15 medium sand

17 wackestone

19 medium sand


K=9.6E-5 cm/s

K=4.4E-4 cm/s

Screen 19.3’-29.3’


poor recovery

22.5 packstone

25.7 packstone

K=5.7E-5 cm/s

25.5 packstone

K=3.2E-5 cm/s

26.5 wackestone


25 wackestone




K=4.0E-4 cm/s

K=3.3E-5 cm/s

30.0 packstone

31.5 packstone

poor recovery, washout

30 medium sand

34.4 packstone

35 wackestone

Conceptual Flow Model: River Front

~30 feet

Suwannee River

Average Nitrate

Concentration (mg/L)






M-1 Core

M-2 Core

M-3 Core







Nitrogen in the wakulla springshed
Nitrogen in the Wakulla Springshed

Delta N-15 as indicator of N-source in residential drinking water wells in the Wakulla Springs area

<3 artifical fertilizer

>10 animals/sewage

Data from Chellette, Pratt and Katz, 2002

Wakulla Springs

What are florida s management practices
What are Florida’s management practices?

  • Standard Septic Systems:

    • Homeowner education

    • Design and construction (water table separation, soil textures) standards

    • Missing: regular inspection and maintenance requirement

  • Aerobic treatment units:

    • Units third-party tested to meet performance criteria.

    • Operating permit requires homeowner contract with qualified maintenance entity.

    • Regular inspection required

  • Performance-based treatment systems:

    • Engineer-designed and in most cases third-party tested

    • Operating permit requires homeowner contract with qualified maintenance entity

    • Regular inspection and sampling required

  • Some demonstration/pilot projects have exploredsewer districts with authority over onsite systems to achieve reliable maintenance and monitoring. EPA emphasizes this solution.


Some suggestions for the wakulla springshed
Some Suggestions for the Wakulla Springshed

  • What is the problem? Nutrient contributions to groundwater (22% for TN) or possible pathogen indicator contributions to stormwater from failing systems

  • Where is natural attenuation ineffective?Spring vulnerability mapping and groundwater monitoring to confirm priority (unconfined) areas for protection

  • What is an effective mix of approaches?

    • Nnutrient-reducing treatment in vulnerable areas by either onsite systems, DEP package plants or connection to a larger WWTP.

    • A funding and coordinating entity will be necessary, especially to involve onsite systems, which serve mostly populations in the urban fringe and rural areas (counties)

  • Further information about onsite research http://www.doh.state.fl.us/environment/ostds/research/researchreports.htm