WEKIVA BASIN ONSITE SEWAGE TREATMENT 

AND DISPOSAL SYSTEM STUDY 

Bureau of Onsite Sewage Programs 

Division of Environmental Health 

Florida Department of Health 

December 1, 2004 

John O. Agwunobi, M.D., M.B.A., M.P.H. 

Secretary, Department of Health 

Jeb Bush

Governor
i 

TABLE OF CONTENTS 

Executive Summary 1

Introduction 3

Impact of Onsite Sewage Treatment and Disposal Systems 

 on Public Health and the Environment 4

The Process of Nitrogen Removal Using Onsite Sewage Treatment 

 and Disposal Systems 6

The Treatment Results of Nutrient-Removing Onsite Sewage Treatment 

 and Disposal Technologies in Florida 7

Operational Management of Onsite Sewage Treatment Disposal Systems, 

 Costs, and Management Program Models 12

Priority Areas within the Wekiva Basin, Characterization 

 of Environmental Sensitivity, and Sewering Decision-Making 18

Recommendations 19

References 21

Front Cover Photo: The Wekiva Springs “boil” looking downstream. 
ii 

FIGURES 

Figure 1: Total numbers of septic tanks by county and the number 

of systems within the Wekiva Study Area 1

Figure 2: A sample of Florida limestone from a karst area 

3

Figure 3: Relative contribution from inventoried nitrogen sources to 1990-1999 average 

nitrogen loading in semi-confined and unconfined portions of Leon and Wakulla 

Counties 5

Figure 4: Relative contribution from anthropogenic sources to 1990-1999 average 

nitrogen loading in semi-confined and unconfined portions of Leon and Wakulla counties 6

Figure 5: Image showing the layout of a conventional onsite sewage treatment and 

disposal system 7

Figure 6: The mean (±) the standard deviation for nitrogen data 11

Figure 7: A typical, conventional septic tank 12

Figure 8: The Wekiva Area Aquifer Vulnerability Assessment map for nitrogen 18

Figure 9: A conceptual view of the recommended nitrogen treatment 

and drip irrigation disposal system 19

TABLES 

Table 1: Treatment process power consumption and cost data, Phase II 16

Table 2: Operation and Maintenance Activities Needed 17

.
1 

EXECUTIVE SUMMARY 

This study was prepared for the Governor and the Florida Department of Community Affairs in 

response to section 369.318, Florida Statutes (F.S.). The statute requires the Department of 

Health to study onsite disposal system standards needed to achieve nitrogen reductions 

protective of groundwater quality within the Wekiva Study Area. The department is required to 

consider a more stringent level of wastewater treatment to reduce the level of nitrates and 

implementation of a maintenance and inspection program, including the upgrading of existing 

systems and funding mechanisms. 

The Wekiva Study Area is underlaid by a karst geology characterized by limestone or dolostone 

bedrock with caves and springs. Conventional septic tank and drainfield systems have been 

used in the area as a relatively low-maintenance, low-cost method of safely treating and 

disposing of human waste. The estimated numbers of septic systems by county are shown in 

Figure 1. 

Figure 1: Total numbers of septic tanks by county and the number 

of systems within the Wekiva Study Area 

48,468

54,044.00

50,344

19,786.00

25,586

13,228.00

0

20,000

40,000

60,000

80,000

100,000

120,000

Orange Lake Seminole

Wekiva

Remaining

Based on recent in-state research it is now known that conventional septic tank and drainfield 

systems discharge nitrogen into the ground waters of karst regions like the Wekiva basin. Using 

existing Florida research data, a family of four will discharge 25 pounds of nitrogen per year into 

the drainfield of a conventional onsite sewage treatment and disposal system. A conventional 

system costs from $5,500 to $7,500. A comparable nutrient reduction system costs from $7,500 

to $9,000. In areas where development densities are low, the overall costs of onsite sewage 

treatment and disposal systems are less than sewering. Onsite sewage treatment and disposal 

systems can provide protection of the environment and the public health that is comparable to a 

central sewer system. 

The Department of Health recommends the following: 

• Set a discharge limit of 10 milligrams per liter of total nitrogen for new systems, systems 

being modified, and for existing systems in the primary and secondary Wekiva Study 

Area protection zones. 

• Prohibit the land-spreading of septage and grease trap waste in the Wekiva Study Area. 

Septage waste would be required to be disposed of at wastewater treatment plants. 
2 

• Evaluate the economic feasibility of sewering versus nutrient removal upgrades to 

existing onsite sewage treatment and disposal systems. A phased-in approach to 

replacing the remaining existing systems should be developed with a target completion 

date of 2010. 

• Establish new regional wastewater management entities or modify existing ones to 

oversee the maintenance of all wastewater discharged from onsite sewage treatment 

and disposal systems in the study area. These programs should take the privatization 

approach and contract with existing licensed septic tank contractors. 
3 

INTRODUCTION 

This study was prepared for the Governor and the Department of Community Affairs in 

response to section 369.318, Florida Statutes (F.S.). The statute requires the 

Department of Health, “to study the efficacy and applicability of onsite disposal system 

standards needed to achieve nitrogen reductions protective of groundwater quality within 

the Wekiva Study Area including publicly owned lands.” By March 1, 2005, it also 

requires the department to, if appropriate, “initiate rulemaking to achieve nitrogen 

reductions protective of water quality or recommend legislation for any additional 

statutory authority needed to implement the report recommendations.” The study will 

consider: 

(a) For new developments within the Wekiva Study Area and any existing 

development within the Wekiva River Protection Area using onsite disposal 

systems, a more stringent level of wastewater treatment, including, but not 

limited to, the use of multiple tanks to combine aerobic and anaerobic treatment 

to reduce the level of nitrates. 

(b) The implementation of a septic tank maintenance and inspection program 

which includes upgrading certain onsite disposal systems permitted prior to 1982 

to meet minimum Department of Health standards; replacement of failing 

systems and systems not meeting current standards; and providing funding 

mechanisms for supporting a septic tank inspection and maintenance program. 

The Wekiva Study Area is underlaid by karst geology, which is characterized by limestone 

(Figure 2) or dolostone bedrock with caves and springs. 

Figure 2: A sample of Florida limestone from a karst area. Note its porous nature. 

Conventional septic tank and drainfield-type onsite sewage treatment and disposal systems 

have been used in the area for many years as a relatively low maintenance, low cost method of 

safely treating and disposing of human waste. The estimated numbers of septic systems by 

county are shown in Figure 1. Based on recent in-state research, it is known that conventional 
4 

septic tank and drainfield-type onsite sewage treatment and disposal systems discharge 

nitrogen into the ground waters of karst regions like the Wekiva basin. Using existing research 

data from Florida, a family of four will discharge just under 25 pounds of nitrogen per year into 

the drainfield of a conventional onsite sewage treatment and disposal system. Although more 

expensive than conventional septic tank and drainfield systems, nitrogen–removing, onsite 

sewage treatment and disposal systems are now available. 

Even with the added costs of nutrient removal technologies, onsite sewage treatment systems 

remain a viable option for wastewater disposal. In areas where development densities are low, 

the overall costs of onsite sewage treatment and disposal systems are less than sewering. 

Onsite sewage treatment and disposal systems can provide protection of the environment and 

the public health comparable to central sewer. 

THE IMPACT OF ONSITE SEWAGE TREATMENT AND DISPOSAL SYSTEMS 

 ON PUBLIC HEALTH AND THE ENVIRONMENT 

Human sewage waste contains disease-causing viruses, bacteria, and parasites. Preventing 

sewage contamination of drinking water has been the primary way that public health officials 

have prevented the epidemics that occurred in early United States (U.S.) history. Sewage also 

contains nutrients, such as nitrogen and phosphorous, that can adversely impact the ground 

and surface water quality. Nitrogen levels in the environment as low as one milligram per liter 

(mg/L) have been shown to degrade the aquatic environment in Florida’s springs. Nitrogen 

levels of 10 mg/L or more have been found to cause blue baby syndrome (methemoglobinemia) 

in infants. 

Onsite sewage treatment and disposal systems have been used for many years as a relatively 

low maintenance, low cost method of safely treating and disposing of human waste. The 

typical, conventional onsite sewage treatment and disposal system consists of a septic tank 

distribution piping, and drainfield. The treatment process begins in the septic tank. The septic 

tank is designed to skim off fats, oils, and greases; settle out the larger solids; and partially treat 

the sewage through breakdown by anaerobic bacteria. The waste then leaves the tank through 

the distribution piping and is distributed into the soil by the drainfield. Unsaturated soil 

surrounding the drainfield is extremely effective at removing disease-causing viruses, bacteria, 

and parasites. In 1983, the department adopted a requirement that there be two feet of 

unsaturated soil beneath the drainfield to achieve effective removal of these disease-causing 

agents. 

The conventional septic system is generally less effective at removing nutrients, particularly 

nitrogen. Onsite sewage system treatment and disposal system research has shown that 

certain environments have a higher capability of naturally removing the nitrogen once it leaves 

the drainfield. In a 1999 study done by the department, nitrogen levels reached the ambient 

background levels before reaching surface waters surrounding Saint George Island. In the karst 

environment, such as the Wekiva Study Area, nitrogen responds differently. The department 

just concluded a study designed to measure the influence of a conventional onsite sewage 

treatment and disposal system on the groundwater in Karst areas. In this study, nitrogen levels 

were found as high as 60 mg/L in the groundwater adjacent to the drainfield, indicating that 

there was little or no removal. 
5 

Figures 3 and 4 show the relative nitrogen contribution of onsite sewage treatment and disposal 

systems in a karst environment that is similar to the Wekiva Study Area.1

 

Figure 3: Relative contribution from inventoried nitrogen sources to 1990-1999 average 

nitrogen loading in semi-confined and unconfined portions of Leon and Wakulla Counties. 

Sinking 

Streams 3%

Livestock 6%

WWTF 14%

OSTDS 11%

Atmospheric 

Deposition

49%

Residuals 

Disposal, 6%

Commercial 

Fertilizer 12%

 

1

 Chelette, Angela and Pratt, Thomas R. “Nitrate Loading as an Indicator of Nonpoint Source Pollution in 

the Lower St. Marks-Wakulla Rivers Watershed,” Water Resources Special Report 02-1, Northwest 

Florida Water Management District, 2002. 
6 

Figure 4: Relative contribution from anthropogenic sources to 1990-1999 average nitrogen 

loading in semi-confined and unconfined portions of Leon and Wakulla counties.

Residuals 

Disposal 

12%

Commercial 

Fertilizer 

25%

Livestock 

12% OSTDS 22%

WWTF 29%

THE PROCESS OF NITROGEN REMOVAL USING ONSITE SEWAGE TREATMENT 

 AND DISPOSAL SYSTEMS 

Removal of nitrogen from the onsite sewage treatment and disposal system waste stream is 

achieved through the enhancement of natural biological processes. The plumbing from a home 

delivers waste to the system with nitrogen in the form of ureic acids and proteins. In a 

conventional septic tank and drainfield system as shown in Figure 5 on the following page, the 

nitrogen is converted to ammonia in the septic tank. The ammonia in the waste stream is then 

carried into the drainfield and surrounding soil where it is converted to the nitrate form. This 

process is called nitrification. Unfortunately, nitrate is highly mobile in groundwater. That 

mobility is enhanced by the rapid movement of groundwater seen in a karst environment such 

as the Wekiva Study Area. Nitrate is also a form of nitrogen that is readily available to plants. 

As discussed earlier, levels of nitrate as low as one mg/L can result in degradation of the 

aquatic environment of Florida’s springs. 
7 

Figure 5: Image showing the layout of a conventional onsite sewage treatment and 

disposal system. 

To reduce nitrate from the waste stream, additional treatment is necessary. That step involves 

taking the nitrified sewage and placing it in an environment where there is no dissolved oxygen 

present, where facultative anaerobic bacteria live, and where food for bacteria is available. 

When these conditions occur, the bacteria remove the oxygen from the nitrate as part of their 

living processes and the nitrogen is converted to a gas. This nitrogen gas escapes from the 

treatment system into the air where it is harmless to the environment. Nitrogen gas naturally 

makes up some 78 percent of the air we breathe. A number of different treatment systems that 

remove nitrogen using these processes are available today, many of which are currently used in 

the Florida Keys. Some of these processes are described in the following section. 

THE TREATMENT RESULTS OF NUTRIENT-REMOVING ONSITE SEWAGE TREATMENT 

 AND DISPOSAL TECHNOLOGIES IN FLORIDA 

Extensive research has been conducted on nutrient-removing systems in the state of Florida. 

These nutrient-removing systems are classified as performance-based treatment systems 

(PBTS) by current rules. As part of a two-phase research project in the Florida Keys, five 

different treatment processes were studied to determine their effectiveness at removing 

nutrients.2

 A synopsis of the study results follows. 

 

2 Ayres Associates, “Phase 2 Addendum, Florida Keys Onsite Wastewater Nutrient Reduction 

Systems Demonstration Project,” a report prepared for the Florida Department of Health, April 

2000.
8 

System Descriptions 

Process System 1: Recirculating Sand Filter/Anoxic Biofilter/Subsurface Drip Irrigation

Process Description - System 1 consisted of a septic tank (ST-1) followed by a recirculating 

sand filter (RSF) and then an anoxic biofilter (ABF). Effluent from the system is discharged to 

an unlined drip irrigation bed. Treatment occurred through digestion and settling in the septic 

tank, and physical, chemical, and attached growth aerobic biological processes in the RSF. 

Adsorption by the RSF media removes limited quantities of phosphorus. The nitrified RSF 

effluent is mixed with anoxic septic tank effluent in the recirculation chamber (RC) to encourage 

denitrification. The effluent also undergoes nutrient reduction by plant uptake in the drip 

irrigation bed, as well as by adsorption on the drip field media. 

The unlined drip irrigation bed utilizes a subsurface drip irrigation (SDI) system for effluent 

distribution to the sod root zone. The SDI consists of 15 5/8-inch drip irrigation lines spaced at 

four-inch centers. The effluent is discharged via pressure emitters spaced every two feet within 

the lines. Each emitter discharges at a rate of 0.6 gallons per hour (gph). Three treatment 

media are evaluated in this treatment unit: 1) locally available sand; 2) an expanded clay 

aggregate from Norway, commercially known as LECATM; and, 3) crushed brick material from 

Cherokee-Sanford Brick Company in Sanford, North Carolina. Collection pans are placed at the 

bottom of each bed. A peristaltic pump is used during sampling to pull water quality samples 

from each collection pan. Grab samples are collected from each pan and labeled as USAND, 

ULECA, and UBRICK. 

System Modifications - In January 1999 the sand media in the RSF was replaced with 2-4 

millimeter LECATM media. Also, two lines were routed from the recirculation chamber (RC). 

One line was routed to septic tank 1 (ST-1) and the other one to the anoxic biofilter (ABF). 

These lines were installed in an attempt to provide enhanced denitrification within ST-1 and add 

biological oxygen demand (BOD) as a carbon source for additional denitrification in the ABF. 

Also, two stainless steel suction lysimeters were installed in the unlined sand and unlined 

crushed brick beds in an effort to improve sample collection from these locations. 

Process System 2: Septic Tank/Lined Drip Irrigation Bed

Process Description - This system utilized a relatively passive technology consisting of a 

septic tank (ST-2) followed by a lined drip irrigation bed. The septic tank effluent is distributed 

to the root zone via pressurized drip emitters in the same manner as the unlined bed described 

above. Septic tank effluent, which is not discharged, is recycled back to the influent side of ST2. Reduction of nutrients and other parameters is accomplished by preliminary digestion and 

settling in the septic tank with additional physical, chemical, and biological treatment processes 

occurring in the lined irrigation field and by plant uptake. Under proper conditions, the effluent 

undergoes nitrification in the upper unsaturated (aerobic) portion of the drip bed and 

denitrification in the saturated (anaerobic) lower portion of the drip bed. 

The lined bed is constructed in a similar manner and with the same treatment media as the 

unlined bed. The exception is that each treatment media is hydraulically separated from each 

other and the groundwater by an impermeable liner. The final effluent from the lined beds is 

collected by an underdrain system, which flows, by gravity into three effluent chambers for 

sampling and flow monitoring. 
9 

System Modifications - In January 1999, the original drip irrigation system was replaced with a 

system by GeoflowTM. The design details of the GeoflowTM system include the following: 

• Eleven, 33-foot long, subsurface, drip irrigation lines. 

• Drip-line spacing = 0.5 foot. 

• Total number of emitters = 681. 

• Emitter flow rate = 0.5 gallons per hour. 

• 24 doses per day at approximately two minutes per dose. 

In addition, the system is equipped with flush valves to flush the lines and filters on a scheduled 

basis. 

The LECATM Material in the lined drip irrigation bed was replaced with Filterlite-P, an advanced 

form of LECATM. The old sod was removed and new sod was placed on top of the lined, drip 

irrigation bed. In July 1999, a trickling filter was installed in association with the ST-2 to aid in 

denitrification. 

Process System 3: Bio-Microbics FASTTM/Anoxic Biofilter

 

Process Description - The principal treatment unit in this system is a proprietary unit known as 

the Bio-Microbics FASTTM aerobic unit. This unit utilizes fixed-film activated sludge treatment 

(FAST), which uses a combination of suspended growth and attached growth aerobic biological 

processes. The aeration process also provides circulation of wastewater to increase contact 

with aerobic bacteria. Also, anaerobic zones within the FAST chamber result in denitrification. 

This system provides a nitrified effluent prior to discharge. 

The FAST treatment tank is separated into two chambers. The first chamber receives dosed 

influent and provides primary treatment. Wastewater overflows via a six-inch diameter orifice in 

the partition wall to a second chamber where secondary treatment is provided by the FAST unit. 

A blower mounted outside on top of the treatment tank provides the air source for the FAST 

aeration. Treated wastewater then flows by gravity into an effluent chamber where it is pumped 

to an anoxic biofilter treatment unit. 

System Modifications

In May 1998, the FAST system was modified replacing the original mushroom shaped top of the 

unit with a low profile top, which can be buried to provide a more aesthetic appearance. In 

addition, during the course of the operation the timing sequence for aeration was modified three 

times. The modified timing sequences were: 

• Initial timing sequence: 4.5 hours of aeration followed by 1.5 hours off. 

• June 1999: 1.0 hour aeration followed by 1.0 hour off. 

• August 1999: 1.0 hour of aeration followed by 1.5 hours off. 

Supplemental Carbon Feed Process (an add-on treatment process)

Process Description - This system consists of a proprietary treatment unit known as the 

“NiteLess” denitrification system. The technology of this system is based on the automatic 

addition of dry-carbon and freeze-dried denitrifying bacteria. Delivery of the products is via a 

closed product hopper with opening and closing valves, a vibrator, drop-tube drier, a hopper 

desiccant, and a master timer. The unit is adjustable from one to 15 dosing cycles per day and 
10 

the volume of product dispensed may be increased or decreased based on system 

requirements. The “Niteless” system was added to the anoxic biofilter located downstream from 

the FAST unit to provide additional denitrification of effluent received from the FAST. These 

samples were labeled FAS-ABF. 

Process System 4: Advanced Environmental Systems BESTEP

Process Description - This system consists of a proprietary treatment unit known as the AES 

BESTEP-IDEATM system, an aerobic/anaerobic, suspended growth biological treatment 

process, which operates as a continuous feed cyclic reactor (CFCR). The process operates 

similarly to a sequencing batch reactor (SBR), but is unique in that it allows continuous flow 

while using only one process tank. Aeration to the system is cyclical, which causes alternating 

aerobic and anoxic conditions. This process results in nitrification followed by denitrification for 

nitrogen removal and promotes uptake of phosphorus by the activated sludge biomass. 

System Operation Performance/Observations - This system operated on a limited basis 

during the Phase II test period. Problems encountered with this system included erratic controls 

and failure of the system to properly decant the wastewater during the settling period. 

Process System 5: Klargester BiodiscTM/ABF

Process Description - This system consists of a proprietary treatment unit known as the 

Klargester BiodiscTM, which is a rotating biological contactor (RBC), followed by an anoxic 

biofilter (ABF). The RBC is an attached growth, aerobic, biological treatment process that 

provides biochemical oxygen demand and suspended solids removal and limited nitrogen 

removal via an internal cycle of nitrified effluent to the primary clarifier for denitrification. It 

produces nitrified effluent, which is discharged to an ABF for additional nitrogen removal. 

Influent from the dose pot is directed down into a primary settling tank. The wastewater flows 

up into the secondary treatment area where the RBC is located. The RBC is divided into three 

media disk banks with eight disks in each bank. As the wastewater flows through the RBC it 

empties into a final settling tank, which discharges by gravity into the ABF. A pump placed in 

the final settling tank recycles sludge to the primary tank every hour for 30 seconds, at a flow 

rate of 10 gallons per minute. The RBC effluent flows through three stages of submerged 

plastic filter media in the ABF and then into a sump area. 

System Modifications - Modifications were made to this system to allow the second stage of 

the RBC rotor to receive flow from the first stage at a fixed rate, and provide a stable organic 

and hydraulic load to the treatment process. This modification was achieved by modifying the 

opening between the first and the second stage of the unit. 

The modifications also incorporated a carbon-feed arrangement whereby a small amount of 

wastewater containing biochemical oxygen demand was collected from the front of the RBC 

rotor and fed to the submerged anoxic reactor of the denitrification module. This organic 

carbon, in the form of biochemical oxygen demand provides nutrient to the bacteria performing 

the denitrification. 

Summary of Treatment Process Results 

The concentrations of nitrogen and phosphorus in sewage effluent showed significant variation 

among the different processes. The influent total nitrogen (TN) concentration during Phase II 
11 

testing was significantly higher than Phase I with a mean concentration of 47.98 mg/L, 

representing an approximately 25 percent increase in TN. This, in combination with increased 

flow, resulted in a much higher loading of TN to the systems in Phase II of the study. The 

increases in untreated sewage concentrations of TN, however, were insignificant in comparison 

to the increase in loading rate. This indicated that the systems achieved a higher removal 

percentage under increased nitrogen loading. 

The FAST system showed the best efficiency with mean effluent TN concentration of 11.51 

mg/L, followed by the RBC-ABF system with a mean value of 14.9 mg/L. These results are 

encouraging as they were obtained without supplemental carbon addition to enhance 

denitrification. The effluent concentrations for the other three systems ranged from 26.23 mg/L 

for RSF/ABF to 31.29 mg/L for the SDI system with LECATM media (LLECA). 

The results obtained from the “Niteless” denitrification unit (FAS-ABF) used in series after the 

FAST indicated that the Florida Keys’ standard of 10 mg/L could be achieved with the addition 

of supplemental carbon. Phase II results indicated a mean effluent TN concentration of 7.09 

mg/L for this system. 

Figure 6 presents the mean plus or minus (±) the standard deviation for the nitrogen data. The 

FAST unit provided the most consistent nitrogen removals over the study period. Supplemental 

nitrogen removal processes would be required for all the systems tested for effluent TN 

concentrations to meet the Florida Keys’ effluent standard of 10mg/L. 

Figure 6: The mean (±) the standard deviation for nitrogen data. 

Figure 6: Effluent TN Concentrations (Mean ± Std. Dev.) 

Other Technologies: The summary above is not a comprehensive list of all available 

technology. Many treatment options are available with new processes being developed 

0.00

5.00

10 .0 0

15 .0 0

20.00

25.00

30.00

35.00

40.00

RSF- ABF LBRICK LLECA FAS FAS- ABF RBC- ABF

Treatment Unit

TN Concentration (mg/L)

Mean Plus Standard Deviation Mean Mean Minus Standard Deviation

Florida Ke ys Standard
12 

continuously. Some examples include: peat biofilters, fixed-film vertical-downward filtration, 

vertical-upward filtration, fluidized-bed sand filtration, and constructed wetlands. 

OPERATIONAL MANAGEMENT OF ONSITE SEWAGE TREATMENT DISPOSAL SYSTEMS, 

 COSTS, AND MANAGEMENT PROGRAM MODELS 

The purpose of a maintenance and inspection management program is to ensure that onsite 

systems continuously meet their performance requirements, especially in an environmentally 

sensitive area such as the Wekiva Study Area. A maintenance and inspection program would 

provide for continuous oversight to ensure systems are properly functioning and operating. 

Currently, an operational management program already exists in all portions of the state for 

aerobic treatment units (ATU) and performance-based treatment systems (PBTS). Owners of 

ATU and PBTS are required by statute to have a contract with an approved maintenance entity. 

The approved maintenance entity is required to obtain a two-year operating permit for a fee of 

$100.00 from the local county health department for each system under maintenance contract. 

The state operational management program is limited in the fact that it does not require 

mandatory pumping for these types of systems. No maintenance requirements are mandated 

by law or rule for conventional septic tank systems. 

However, the department recommends a septic tank should not require pumping more than 

once every 3 to 5 years based on the daily sewage flow and individual household wastewater 

characteristics. It is also recommended that the tank be inspected to determine the depth of the 

accumulated sludge and grease, which could have an adverse effect on the functioning of the 

system, if excessive. (See Figure 7) 

Figure 7: A typical, conventional septic tank. 

The current procedures require the county health department to inspect the systems with 

operating permits on an annual basis for residences and two times per year for commercial 

business. In addition, the approved maintenance entity must inspect the system two times per 

year for residences and four times per year for commercial businesses. These systems require 

regular routine monitoring, because they are more advanced than the simple septic tank and 
13 

have filters and moving parts, such as motors and pumps that require routine servicing and a 

greater level of user knowledge. 

In addition, commercial wastewater systems, such as those serving restaurants, and systems 

located in industrial/manufacturing zones or the equivalent require operating permits from the 

department and are inspected annually. It is estimated that less than 0.5 percent of the systems 

located in the Wekiva Study Area currently have an operating permit. It is also estimated that 

this number would increase 25 to 50 percent if systems located in the primary and secondary 

protection areas are required to be retrofitted with nitrogen-reducing systems. 

National Model Management Programs 

The U.S. Environmental Protection Agency (EPA) has developed five model guidelines for 

management of systems. The state has already incorporated some of these guidelines into the 

onsite sewage system laws and regulations. These models are represented as a progressive 

series in which the management requirements of onsite systems become more important as the 

system technologies become more complex and/or as the sensitivity of the environment 

increases. The EPA believes that these goals are best achieved through the performance 

standards for individual systems that have been developed to protect the water quality of the 

receiving watershed and/or aquifer. The models list management objectives and are 

benchmarks for a state or local unit of government. These models are listed and summarized to 

indicate more options that are available for management of onsite systems as follows:

Model Program 1: System Inventory and Awareness of Maintenance Needs 

This model relies on educating the system owner about how to properly maintain their system. 

It is designed as a minimum level of management. Model Program 1 is a suitable management 

program where conventional onsite systems are owned and operated by individual property 

owners in areas of low environmental sensitivity, that is, no restricting site or soil conditions 

such as drinking-water wells in close proximity. This level of management is being met through 

the state of Florida with Chapter 64E-6, Florida Administrative Code (F.A.C.), and Section 

381.0065, F.S.

Model Program 2: Management Through Maintenance Contracts

This model is designed as the minimum necessary where more complex system designs are 

employed to enhance the capacity of conventional systems to accept and treat wastewater, 

because of small lots, slowly permeable soils, or shallow seasonal water tables. This program 

may also be appropriate for areas that supply water to public water systems (for example, 

source-water or wellhead protection areas). The objectives of this program build on Model 

Program 1 by ensuring that maintenance contracts with trained operators are maintained by the 

property owner. This level of management is being met through the state of Florida with 

Chapter 64E-6, F.A.C., and Section 381.0065, F.S., for aerobic treatment units and 

performance-based treatment systems.

Model Program 3: Management Through Operating Permits

This model is designed for areas where the onsite system must provide treatment to achieve 

specific water quality criteria. Examples include shellfish growing areas, situations where a 

source-water assessment has identified onsite/decentralized systems as threats to drinking 

water supplies. The objective of the management program, in addition to the previous levels, is 

to ensure that the onsite systems continuously meet their performance requirements. 

Treatment systems that are designed to meet specific effluent limits are less dependent on site 
14 

characteristics and condition. Therefore, they can be used safely in more sensitive 

environments, but only if their performance can be ensured continuously. Limited term 

operating permits are issued to the property owners, which are renewable for another term if the 

owner demonstrates that the system is in compliance with the terms and conditions of the 

permit. The permit provides the management program a mechanism for continuous oversight of 

system performance, and negotiating corrective actions or levying penalties if compliance with 

the permit is not maintained. To comply with these performance standards, the property owner 

should contract with a maintenance provider, as in Model Program 2. This level of management 

is being met through the state of Florida with Chapter 64E-6, F.A.C., and Section 381.0065, 

F.S., for aerobic treatment units and performance-based treatment systems.

Model Program 4: Utility Operation and Maintenance 

This model is designed for performance-based systems where the sensitivity of the environment 

is high, and there is a need for continuous monitoring and reliable operation and maintenance. 

For example, this approach may be applicable where monitoring of a drinking-water supply has 

detected pathogens or elevated levels of nutrients, and a source-water assessment has 

identified onsite/decentralized systems as sources of concern. The objective of the program is 

to achieve greater control over compliance by issuing the operating permit to a utility instead of 

the property owner. This allows the use of performance systems in more sensitive 

environments than Model Program 3. The utility takes responsibility of the operation and 

maintenance of systems owned by subscribers for a service fee. This reduces the number of 

permits and the necessary administration by the management program. System failures are 

also reduced as a result of routine maintenance. Ownership of the system remains with the 

property owner. The operating permit system is identical to Model Program 3 except that the 

permittee is a public or private utility. 

Model Program 5: Utility Ownership and Management 

This model is a variation of the utility operation/maintenance concept in Model Program 4, 

except ownership of the facilities is no longer with the property owner. The designated 

management entity both owns and operates the onsite systems in a manner analogous to a 

conventional wastewater utility. Under this approach, the utility maintains total control of all 

aspects of management, not just operation and maintenance. The model is appropriate in 

similar environmental or public health conditions as is Model Program 4, but provides a 

somewhat higher level of control and reduces the likelihood of disputes between the system 

operator and the property owner. The utility can also more readily replace existing systems with 

high-performance units where necessary. The EPA recommends implementation of Model 

Program 5 in cases where new, high-density development is proposed in the vicinity of sensitive 

receiving waters. 

Existing Management Programs in Florida

Several counties in Florida have enacted local ordinances requiring management of onsite 

systems on a limited basis. Polk and Lake Counties have ordinances requiring all onsite 

systems located in the Green Swamp to be pumped and inspected every five years. Escambia 

and Santa Rosa Counties have similar ordinances requiring septic tanks to be pumped, 

inspected, and upgraded to repair standards at the time of real estate transactions or prior to the 

sale of an existing house. To encourage routine maintenance, the City of Tallahassee provides 

septic tank pump-out services without charge. Charlotte County has currently drafted a local 

ordinance to require mandatory maintenance pumping every five years in a specific 

environmentally sensitive area of the county located near Charlotte Harbor. In Monroe County 

the state law requires advanced nutrient reduction systems (nitrogen and phosphorus) to protect 

the sensitive ecosystem from nutrients. These systems are performance-based treatment 
15 

systems and require an annual operating permit, maintenance contract, and annual inspection 

from the county health department. Brevard, Charlotte, Citrus, Franklin, and Volusia Counties 

have county ordinances requiring aerobic treatment units in specific circumstances and in 

environmentally sensitive areas. As with the performance-based treatment systems, these 

systems require annual operating permits from the county health department, maintenance 

contracts, and annual inspections from the department. 

System Installation Maintenance and Operational Costs

Installation Costs – The department contacted licensed contractors and engineers that design 

and install nutrient-reducing systems in the area. They reported that a conventional septic tank 

and drainfield costs from $5,500 to $7,000 for a three-bedroom home. A comparable nitrogenreducing system with a drip irrigation drainfield costs from $7,500 to $9,000. 

Operational Costs – Many of the nitrogen removing systems use pumps or blowers to treat the 

sewage. Nitrogen reducing systems also require an operating permit from the department. 

Operating permit fees are $100 every two years and partially cover the costs of conducting an 

annual inspection. In addition to the operating permit, nitrogen-removing systems require 

additional routine maintenance and, in some cases, electricity to operate properly. For 

reference, the operational costs of nitrogen-removing systems in the Florida Keys are shown in 

Table 1 on the following page. The systems described are the same as those described 

previously. An electricity cost of $0.10/kilowatt-hour was used to determine the daily electric 

cost. 

Chemical/Material Consumption Results – The “Niteless” denitrification unit located in series 

after the FASTTM unit was the only process tested during Phase II that required a chemical 

addition. This process required the addition of a carbon/bacteria-media mixture to an ABF unit 

and was tested on the FASTTM effluent stream. It was observed that an application rate of 20 

ounces or 0.57 kilograms (kg) of media per day resulted in an average of 7.1 mg/L, or less, of 

total nitrogen in the effluent during Phase II testing. Based on this, the cost of the 

carbon/bacteria media is estimated to be approximately $100.00 per year. 

Operation and Maintenance Cost – At the onset of the study a list of recommended operation 

and maintenance activities was prepared based on the experience with the treatment systems 

and review of the manufacturers’ installation guidelines, operation manuals, and sales 

information. A summary of semi-annual and annual operation and maintenance activities for the 

systems comparing Phase I and Phase II is presented in Table 2 on page 15. Also, an estimate 

of time to perform the activities is presented. 

In addition to the operation and maintenance activities listed in Table 2, the following activities 

are also anticipated for the treatment systems: 

• Removal of accumulated sludge every five years for septic tanks and approximately every 

three years for aerobic units. 

• Effluent water quality monitoring of advanced waste treatment (AWT) parameters [chemical 

biological oxygen demand5 (CBOD5), total suspended solids, total nitrogen, total 

phosphorus) for compliance with treatment performance requirements. 
16 

Table 1: Treatment process power consumption and cost data, Phase II 

(January 27, 1999 to December 17, 1999) 

Process 

System 1: 

Recirculating 

Sand Filter 

Process System 

2: Septic Tank/ 

Lined Irrigation 

Bed 

Process 

System 3: 

Fast System 

Process System 5: 

Rotating Biological 

Contactor 

Number of Days in 

Monitoring Period 270 324 324 324 

Net Electric Use (kwhrs) 1006 309 1514 821 

Average Daily Electric 

Use (kw-hrs/day) 3.7 1.0 4.7 2.5 

Average Daily Electric 

Cost ($/day)1 $0.37 $0.10 $0.47 $0.25 

Average Monthly 

Electric Cost ($/month)2 $11.18 $2.86 $14.02 $7.60 

Average Yearly Electric 

Cost ($/year) $136.00 $34.81 $170.56 $92.49 

1

 Mean electrical use is based on the period of time from March 22, 1999 to December 17, 1999. 2

 Average Electrical Costs Calculated on $0.10/kw-hr. 

3

 Monthly costs calculated on a 30-day cycle. 

Notes: Process System 4 values are not included due to the system being inoperative. Net power usage for the five process 

streams was monitored following system modifications for a period of 324 days. The average daily power use ranged from 1.0 kwhr/day for the SDI (Process Stream 2) to 4.7 kw-hr/day for the FASTTM (Process Stream 3). The average electrical usage for 

Process System 1 was calculated based on 270 days (March 22, 1999, to December 17, 1999). An unusual spike in electrical 

usage was observed during the period between February 17, 1999, to March 22, 1999, for Process System 1, and data collected on 

power usage during this period was not considered. The cause of the electrical spike, however, could not be determined. Process 

System 2 showed a decrease in power cost due to the installation of a smaller blower unit in Phase II. The blower was also 

connected to a timer that cycled on and off in an effort to increase nitrogen removal. These items reduced energy consumption 

considerably from Phase I. 
Table 2: Operation and Maintenance Activities Needed 

System Activity Performed 

SemiAnnual* 

(2X/year) 

A

(1

Inspect recirculation pump operation, high water alarm system, and float operation. X Inspect sand filter surface (LECATM surface, during Phase II). X Observe sprayer operation. Clean spray heads. Flush out distribution lines. Record operational data (pump run time, dosing meter). Compare data to past records. X Calibrate pump and recirculation ratio. 

RSF 

Check sludge depth in septic and recirculation tanks. 

Inspect irrigation pump operation, high water alarm system, and return flow from irrigation beds. X Increase return flow and pressurize lines to flush out emitters and dripper lines. Clean effluent screen in septic tank and filter cartridges in SDI pump unit. Check pressure differential across dripper line. Adjust. Inspect bed surface for exposed dripper lines and signs of effluent surfacing. Check sludge depth in septic tank and SDI tanks. X 

SDI 

Record operational data (flow meters and pump timers). Measure return and forward flow rates. 

Compare data to past records. X Check sludge depth, primary tank. Check inspection port for aeration and blower screen. Clean filter. X 

FAS 

Check system performance with respect to blowers, controls, mixed liquor color, and system odors. 

Measure DO and collect mixed liquor sample and conduct settleable matter test. X 

Check timer clock and decant pump operation. X Check alarm system and float operations. X Remove cover; observe air compressor aeration and mixer operation. Measure DO and collect mixed liquor sample and conduct settleable matter test. X Wash off control floats and decant float. 

CFCR 

Clean air compressor filter and effluent screen from flow inducer tube. 

Remove cover, check disk operation, and biomass growth. X Check sludge recirculation pump in secondary tank and recycle dipper bucket. X Remove surface scum from primary tank. Check sludge depth in primary and secondary tanks. 

RBC 

Replace nylon bushings on rotator gear. 

ABF Check biomass growth and DO in the tank. X 

*Number of times required by manufacturer. RSF = recirculating sand filter; SDI = subsurface drip irrigation; FAS = fixed activated sludge; CFCR = continuous feed cyclic reactor; RBC = rotating biolo
18 

PRIORITY AREAS WITHIN THE WEKIVA BASIN, CHARACTERIZATION 

 OF ENVIRONMENTAL SENSITIVITY, AND SEWERING DECISION-MAKING 

The Florida Geological Survey developed a groundwater sensitivity map for nitrogen in the 

study area called the Florida Aquifer Vulnerability Assessment (FAVA). The map shows less 

vulnerable, vulnerable, and more vulnerable protection zones. The Wekiva Study Area falls in 

the vulnerable and more vulnerable FAVA protection zones. A more detailed Wekiva Aquifer 

Vulnerability Assessment (WAVA) of the groundwater sensitivity in the Wekiva Study Area 

further breaks down the sensitivity to three categories, the primary protection zone, the 

secondary protection zone and the tertiary protection zone. Figure 8 shows the WAVA 

protection zones. The department has nearly completed a spatial inventory of existing onsite 

sewage treatment and disposal systems within the study area. This information will be 

combined with the WAVA protection zone map to highlight priority areas for sewering. When 

completed, the mapping will be available for local land-use planners. The highest priority for 

sewering should be given to areas with high densities of systems in the primary and secondary 

protection zones. Areas where densities are too low to support a viable central sewer system 

should use nitrogen-removing onsite sewage treatment and disposal systems. 

Figure 8: The Wekiva Area Aquifer Vulnerability Assessment map for nitrogen 

Relative Vulnerability

Water Features

Wekiva Study Area

Primary Protection Zone

Secondary Protection Zone

Tertiary Protection Zone 10 0 10 5 Miles

10 0 10 5 Kilometers

μ Hydrography
19 

RECOMMENDATIONS

The department is required by section 369.318, F.S., to make recommendations about a 

number of items including a more stringent level of wastewater treatment to reduce levels of 

nitrates, the replacement of failing systems, and the implementation of a maintenance program: 

Nitrate Treatment Levels:

The Department recommends a discharge limit of 10 mg/L of total nitrogen for new systems, 

systems being modified, and for existing systems in the primary and secondary WAVA 

protection zones. This level of treatment has been shown to be achievable through existing 

wastewater treatment technologies and would reduce the levels of nitrogen introduced into the 

environment by onsite sewage treatment and disposal systems by approximately 75 percent. In 

addition, the department also recommends that wastewater be discharged into a shallow drip 

irrigation drainfield (Figure 9) to maximize plant uptake of nitrogen, to reduce lawn fertilization, 

and to reduce lawn watering needs. 

Figure 9: A conceptual view of the recommended nitrogen treatment 

and drip irrigation disposal system 

The department recommends that to protect the aquifer confining layer, the practice of removing 

severely limited soil layers (dig outs) be prohibited in the entire study area. 
20 

The department recommends the prohibition of the land-spreading of septage and grease-trap 

waste in the study area. Septage waste would be required to be disposed of at wastewater 

treatment plants. 

The department recommends that state and local planning agencies evaluate the economic 

feasibility of sewering versus nutrient-removal upgrades to existing onsite sewage treatment 

and disposal systems. Areas with high densities of development will be better suited to central 

sewering, and lower density areas more suitable for nitrogen-removing onsite sewage treatment 

and disposal systems. Since environmental and public health protection can be achieved by 

both options, sewage disposal costs should be the determining factor as to which disposal 

method is used. Existing systems in the primary and secondary WAVA protection areas should 

not be required to upgrade to the 10 mg/L nitrogen limit if central sewer will be made available 

by 2010. 

A policy for a phased-in approach to replacing the remaining existing systems should be 

developed after opportunity for citizen and local government input. A target date for phase-out 

would be 2010. 

Replacement of Failing Systems: 

The department recommends that failed or modified systems located in the Wekiva Study Area 

be upgraded to meet new system standards.

The department’s permit program currently addresses the repair-permitting for systems that are 

malfunctioning, defective, and “failing” or creating a sanitary nuisance. The department’s 

permitting program also addresses the inspection of, or modification to, existing systems. A 

failure is defined in Chapter 64E-6, F.A.C., as; “a condition existing within an onsite sewage 

treatment and disposal system, which prohibits the system from functioning in a sanitary 

manner and which results in the discharge of untreated or partially treated wastewater on the 

ground surface, into surface water, into ground water, or which results in the failure of building 

plumbing to discharge properly.” Current repair standards are less stringent than new 

standards. The year of the original installation determines the permitting requirements with 

regard to the septic tank capacity, drainfield size, and set-backs to wells, surface water, and 

property lines. 

An existing system inspection is conducted, or permit issued, when an applicant is changing 

like-for-like residences on their property, such as the replacement of a mobile home with one 

that has the same number of bedrooms and building area. If this is a system that was 

previously approved by the department, it has remained in satisfactory operating condition, and 

it does not show signs of failure, it would be approvable without modifications. A modification 

permit is required when there is an increase in sewage by adding bedrooms or square footage 

to the building. Where modifications are proposed, the existing system is evaluated to 

determine if the tank and drainfield would need to be upgraded due to the increased flow. 

Establishment of a Maintenance Program: 

The department recommends that new regional wastewater management entities be 

established or that existing ones be modified to oversee the maintenance of all wastewater 

discharged from onsite sewage treatment and disposal systems in the study area. The 

management entities would be a part of county or city governments, or a special taxing district. 

The management entities would be responsible for implementing a Program Model 4 

management program as described previously. Maintenance of nitrogen-removing systems is 

critical to assure that the recommended 10 mg/L discharge limit is met. 
21 

It is further recommended that these programs take the privatization approach to the 

maintenance of onsite sewage treatment and disposal systems. Under this approach, the 

governmental management entity would contract with existing registered septic tank 

contractors, licensed plumbers, or licensed wastewater treatment plant operators for inspection 

and maintenance services. The management entity would be responsible for assuring that 

required inspections and maintenance are conducted and that the discharge limits specified by 

the operating permits issued by the Department of Health are met. Funding for the 

management entity program would be generated through user service fees, much the same as 

central sewer users pay a monthly sewer bill. 

REFERENCES 

Ayres Associates, “Phase 2 Addendum, Florida Keys Onsite Wastewater Nutrient Reduction 

Systems Demonstration Project,” a report prepared for the Florida Department of Health, April 

2000. Copy available on the Internet at: 

http://www.doh.state.fl.us/environment/ostds/research/researchreports.htm. 

“Operating Onsite Disposal Systems Management,” Guidance Specifying Management 

Measures for Sources of Nonpoint Pollution in Coastal Waters, U.S. Environmental Protection 

Agency publication number 840-B-92-002, January 1993. Copy available on the Internet at: 

http://www.epa.gov/owow/nps/MMGI/Chapter4/ch4-5b.html. 

“Septic Systems: Information for State and Local Government Officials,” U.S. Environmental 

Protection Agency web site located at: http://cfpub.epa.gov/owm/septic/officials.cfm, last 

accessed December 1, 2004. 

“Septic Systems: Guidelines and General Guidance,” U.S. Environmental Protection Agency 

web site located at: http://cfpub.epa.gov/owm/septic/guidelines.cfm#7478, last accessed 

December 1, 2004. 

”Septic Systems Funding Sources,” U.S. Environmental Protection Agency web site located at: 

http://cfpub.epa.gov/owm/septic/linkresult.cfm?link_category=12&view=link, last accessed 

December 1, 2004. 

Chelette, Angela and Pratt, Thomas R. “Nitrate Loading as an Indicator of Nonpoint Source 

Pollution in the Lower St. Marks-Wakulla Rivers Watershed,” Water Resources Special Report 

02-1, Northwest Florida Water Management District, 2002. Available at: 

http://www.state.fl.us/nwfwmd/pubs/nitrate/nitrate.zip. 

“National Small Flows Clearinghouse Resources,” National Environmental Services Center web 

site located at: http://www.nesc.wvu.edu/nsfc/, last accessed December 1, 2004.