INTRODUCTION 

Ocala is a City of 50,000, located in North Central Florida. The area is best known for its

thoroughbred industry, second only to Kentucky in breeding and training of champions. The

Ocala area has experienced dynamic growth over the last 20 years with the resulting demand for

infrastructure expansion.

The topography of this area is generally low rolling sand hills. The well-drained surficial

soils are underlain by intermittent clays and fractured limerock. The only surface water features

in the area are spring fed streams and small ponds. Silver Springs, on the east side of Ocala, is

the world’s largest Artesian spring producing over 300 million gallons per day of crystal-clear

water.

The City of Ocala has provided sewer service since the 1940’s. The traditional method of

disposal for reclaimed water has been percolation ponds. The constant hydraulic loading of

these ponds tend to weaken the underlying limerock and cause collapses or sinkholes. These

failures allow direct surface connection to the Floridan Aquifer from which all of Central

Florida’s drinking water is drawn.

In the mid 1980’s, the Florida Department of Environmental Regulation (FDER) had

seen enough effluent dumped to the aquifer through sinkholes and hit Ocala with a moratorium

on sewer connections until the City developed alternate reuse/disposal methods. This shot over

the bow precipitated the hiring of a new water and sewer consultant and a new City Engineer and

staff. The new team went to work designing one of the most diverse and innovative reuse

systems in place in America today. The system includes traditional uses such as irrigation of

golf courses, recreation facilities, and landscaping. On the more innovative side are an airport

firefighter training facility, a dedicated agricultural site, and the two subsurface reuse sites

SUBSURFACE REUSE OVERVIEW

 The subsurface systems constructed in Ocala consist basically of a filter and a drainfield.

The filters are little more than large pool filters to minimize clogging of emitters and pipes with

solids. The distribution fields are some form of plastic pipes placed 8” to 12” below the surface

delivering the water to the soil.

This description is deliberately vague, as many of the subsurface irrigation systems

available are proprietary. The engineer has the option to do a detailed design of the system,

which would exclude some proprietary systems and bidders, or to performance spec the systems

for design build. Ocala chose the latter course with specified performance and durability criteria

and an extended maintenance line item. The successful bidder was qualified by presenting a

system, which met the specified criteria and selected on present worth of the proposed system.

Russell Daniels Irrigation built the Ocala airport project. The system installed was a GEO

FLOW tubing emitter system with FLOW Guard sand filters and HARDIE irrigation controllers.

The system is designed to deliver up to 500 gpm to a 44 acre wetted area.

The Ocala airport system is operated 16 to 20 hours per day in wet weather. In dry

weather it normally operates less than eight hours as other sites need the reclaimed water for

irrigation.

The system has operated essentially maintenance free for it’s first three years with very

limited operational effort required.

PERMITTING

FAA

The permitting of wastewater facilities at airports was prohibited by a letter from the

FAA Atlanta Regional Office in the early 80s. The potential to attract birds and wildlife and mist

from conventional irrigation was the basis for the wastewater ban.

To overcome this hurdle, a different approach was required for permitting. As with most

reuse, the positive effect of reclaimed water must be preached to overcome the “no sewage in my

backyard” mentality. In this case the sandy soils around the runway posed a minor dust and

erosion hazard for aviation. Subsurface reuse was a perfect fit. The underground system did not

create ponding, which FAA was concerned could attract animals. There was no mist or odor from

the system. Non seed bearing grasses were chosen to minimize the bird attraction. The irrigated

grass forms a thick mat minimizing erosion and dust problems around the runways and the system

and maintenance were provided at no cost to the airport.

With minor changes to meet FFA construction requirements local and regional FAA

Offices approved the “Ocala Airport Dust Reduction Project”.

FDEP

In 1991, when Ocala ventured into testing underground reuse systems the FDEP was

justifiably skeptical. By 1996, Ocala had a track record with five years logged on two test

systems. While operation of the test systems had been far from smooth, Ocala had gained

enough experience and FDEP had gained enough confidence to proceed with a full-scale project.

One of the major advantages of an airport location is permitting. The property around

Ocala’s airport is primarily commercial and industrial with some low income housing. When the

permit was filed and noticed there was no objection filed, no public outcry, and no bad press.

The permit slid through without a hitch.

FEASIBILITY

The subsurface system in Ocala was installed for $1.25 per gallon. This is considerably

higher than the $.75 to $1.00 per gallon range for traditional irrigation on similar local projects.

In the case of airport reuse, the big savings up front is the land. In Ocala where land

values are low, the cost of property for dedicated reuse sites runs from $4,000 to $8,000 per acre

or the equivalent of $.50 to $1.00 per gallon. The land at an airport is generally publicly owned

and the property in the clear zones has no value for other uses. Even at Ocala’s small regional

airport, the zones cover almost 400 acres. This “free land” makes the capital costs very

competitive for subsurface.

In the long term, the savings of subsurface reuse are on the operation and maintenance

end. The only moving parts are the operating valve and filter backwash valves. The system all

runs on reuse main line pressure so no additional pumping is required. The power demand is

 requirement is a weekly inspection. As a result, the operation and maintenance costs are

approximately half of that required for fixed gun or center pivot installations.

The relative present worth costs of traditional vs. airport subsurface irrigation are

summarized in Table 1.

DEDICATED REUSE SITE COSTS PER GALLON

TABLE 1

MAINTENANCE

 The cost to operate and maintain a subsurface reuse system is much less than a

conventional irrigation system. Once a week maintenance personnel visit the site to visually

inspect the irrigated area and equipment. The site is remotely monitored from the water

reclamation facility so the visit is to ensure everything is operating correctly and that there are no

problems the SCADA system may not detect.

Once a year the filter system and controller are taken off line so the components can be

inspected and tested. Sand is added to the filter and control components replaced as needed.

Spare emitter tubing couplings and relays are all that are required to be kept on hand for spare

parts.

For purposes of comparison Ocala’s “conventional system” is a mixed center pivot, fixed

sprinkler irrigation site. The subsurface system per gallon uses approximately 1/2 of the

operating manpower, 1/4 of the electric power, needs less than 1/4 of the maintenance effort, and

requires less than 1/5 of the value of stocked parts.

Ocala’s wastewater operators are “amazed” by how easy and inexpensive the site has

been to maintain. Since setup the system has basically operated maintenance free without any

problem significant enough to shut it down.

REUSE OR DISPOSAL

Many would contend that irrigation of an airport clear zone is not really “reuse”.

Limited constructive use is made of the heavy water use and groundwater withdrawal is not

offset. The Ocala area, however, is the prime recharge area for the Floridian Aquifer providing

drinking water for much of Florida so recharge is considered reuse.

One of the major challenges and expenses of reuse has proven to be the balance between

reusers and storage or dedicated disposal sites. Airport systems provide dedicated wet weather

disposal that can reduce expensive storage requirements. In Ocala’s case, the dedicated sites

have a peak capacity equal to plant flow eliminating the need for storage. In fair weather, the

golf course and irrigation users draw up to 90% of the reclaimed water resting the dedicated sites

for rainy days.

OCALA SYSTEM SPECIFICATIONS

Background

 Soils coarse to fine sands          10 feet to 30 feet thick

Groundwater                            25 feet to 40 feet below surface in fractured limerock

Site                                          48 acres

Wetted Area                            44 acres

Flows

Design maximum           500 gpm,          720,000 gpd                4.2 in/wk

Permitted average                                 512,000 gpd                3.0 in/wk

Current loading                                     500,000 gpd

System

GROUNDWATER DATA

 No extensive analysis of nutrient loading was performed in permitting this project or

drafting this paper. The reclaimed water applied at this site meets advanced secondary standards

for public access reuse. The quality of effluent meets or exceeds the requirements for most

groundwater monitoring criteria. The diluting effects of rainfall, groundwater flow and minor

losses from nutrient breakdown combine to reduce applied concentrations to well below

permitted levels. 

NITRATES                - average loading                                  10 ppm reclaimed water

   background levels                              2 ppm to 4 ppm

   average monitoring well levels            5 ppm to 6 ppm

 TDS                            - startup average                                   200 ppm

   current average                                  less than 100 ppm

 CHLORIDES             - startup average                                   10 ppm

   current average                                  15 ppm

      Note: background well showing high concentrations, cause not identified.

PH                               - startup range                          5.2 to 11.7

   current range                                     5.4 to 10

FECAL COLIFORM - none detected for three years.

TOTAL COLIFORM - one hit of nine in three years.

TURBIDITY - no clear pattern.

CONCLUSION

permitting and construction of reuse projects than most other areas industrial.

allows the site to be virtually invisible once in operation.