Supersized Onsite Solution Chosen Over Lengthy Sewer Run

Dual split treatment trains with big tanks and drainfields handle a heavy flow for a new Florida convenience store

Supersized Onsite Solution Chosen Over Lengthy Sewer Run

An electrician hired by Dykstra Construction runs power to the control panel. Dustin Osbron, a Tampa Septic technician, installs conduit in a riser for lift station electrical, while technicians Nick Whittington and Ryan Near discuss hooking up the control panel wiring to the lift station components.

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A corporation wanted to add another convenience store and service station to its chain of facilities, but the distance to the municipal sewer was greater than 1,000 feet. Opting for an onsite system, executives hired John Katsantonis, a professional environmental scientist and owner of JK Environmental Services in Minneola, Florida, to design it.

Hydraulic flow at the Okeechobee location totaled 7,000 gpd, triggering a required variance in the Innovative System Permit application. However, Katsantonis could avoid the variance if he kept system flow below 5,000 gpd, and a split low-pressure dosing system did just that.

Because this high profile job was Katsantonis’ first with the company, he consulted with Greg Mayfield, president of Southern Water and Soil in Dade City, Florida. Based on the soils, Mayfield recommended the GeoMat Leaching System from Geomatrix Systems to optimize space. He also had installed seven such systems with Tyler Chancey, owner of Tampa Septic in Dade City.

“Our code states that every linear foot equals 4.56 square feet,” says Mayfield. “A 39-inch-wide roll of GeoMat has a 3.25-foot-wide treatment core, but we get credit for 4.56 square feet.”

Even with the credit, the two drainfields totaled 6,000 square feet. The system took a month to install and went online as scheduled in May 2022.

Site conditions

Soils are muck and wet sand with a loading rate of 0.60 gpd per square foot. Depth to limiting factor on the flat 4.80-acre lot is 44 inches.

System components

Katsantonis designed System 1 to treat 3,720 gpd; System 2 handles 3,360 gpd. Tanks, risers and lids (TUF-TITE) are H-20 traffic rated. Major components include the following:

  • Two 1,050-gallon concrete grease interceptor tanks set in series from Sebring Precast Products
  • Two 5,000-gallon, dual chamber concrete septic tanks with PL-525 effluent filter (Polylok). Tanks from Florida Septic.
  • Two 3,000-gallon concrete dose tanks
  • Four 1 hp FL102M-2 effluent pumps (Liberty Pumps)
  • 2,904 feet GeoMat 3900 Flat Leaching System (Geomatrix Systems)
  • 1,620-cubic-yards septic and system sand
  • Four RF9858 1.5 hp SoilAir blowers with microprocessor controller (Geomatrix)
  • Two control panels CP-2BL2P2F (Geomatrix Systems)

System operation

Piping is PVC Schedule 40.

The 4-inch pipe in System 1 carries wastewater 122 feet to the septic tank. For System 2, wastewater flows 169 feet to another septic tank. Liquid from the grease interceptors drains into the first system. Effluent from the septic tanks gravity flows to the dose tanks in which each alternating pump run eight times per day. Each of four drainfields in two systems are 1,495 square feet and measure 64.5 by 23 feet.

System 1 sends 232.5 gallons per dose through a 2-inch force main 97 feet to the first drainfield and 102 feet to the second drainfield. The low-profile drainfield leaching system has a 1-inch-thick nylon core of fused, entangled filaments covered by a hygroscopic geotextile fabric bonded to one side of the core and containing the distribution pipe.

System 2 sends 210 gallons per dose 49 feet to the first drainfield and 92 feet to the second drainfield. Each zone has an 18-foot-long, 2-inch manifold feeding six 1.25-inch distribution laterals 62.5-feet long on 4-inch spacing. The pipes have 13 3/16-inch perforations. These holes and those in the aeration laterals are spaced 5 feet apart at the 5 and 7 o’clock positions. Pipe holes and orifice shields face down so the water hits the shields and disperses uniformly.

Adjacent to every distribution pipe is a 2-inch aeration lateral with 1/2-inch holes. Each zone has an air bleed valve (Schrader) and a blower pushing 7 to 8 psi inside the membrane. “If there isn’t enough cover on the fabric, it will raise up from the air,” says Mayfield.


General contractor Darry Dykstra of Dykstra Construction hired Tampa Septic, Mayfield’s sister company, to install the system. Chancey was the foreman and Mayfield the septic inspector.

Because the building plumbing was 4.5-feet deep, code specified H-20 traffic-rated tanks. Sebring Precast delivered and set the grease traps, but the 14-foot-deep excavations for the septic and dose tanks filled with abundant groundwater. Chancey hired Able Dewatering to drill dry points around the area and dewater. The pump ran for a week, discharging to a retention pond.

With the groundwater at bay, Florida Septic delivered the four main tanks, but didn’t have a heavy enough crane to set them. Chancey hired Beyel Brothers Crane & Rigging and they did the job in four days.

The drainfield locations had remnants of asphalt parking overlaying 16 inches of limestone road base on bad soil, requiring excavations 40 to 70 inches deep. Chancey rented a Doosan DX140LC excavator-crawler from Synergy Equipment (DEVELON) and used his Bobcat T64 compact track skid-steer and E85 tracked compact excavator to stockpile the suitable material for backfill. They shot elevations with a LL400 Laser Level (Spectra Precision/Trimble).

Dan Borkowski, Geomatrix’s senior project manager, oversaw the installation and provided technical support as to wiring the blowers and piping the aeration lines.

Digging out and rebuilding each drainfield took a week because of the distance between quarry and site. Dump trucks hauled in 70 loads (1,260 cubic yards) of septic sand and 20 loads (360 cubic yards) of C-33 system sand. Workers replaced the excavated area with a bed of septic sand topped with 12 inches of system sand. Installing the 100-foot rolls of GeoMat took two days per field, with each zone using 726 feet.

“It’s easy to install,” says Mayfield. “Just be sure the system sand layer is perfectly level. Also, overlap the membrane and staple the ends together, then seal everything around the distribution pipe to keep out sand and groundwater.” 


Tampa Septic holds the maintenance contract and Borkowski monitors the system remotely. A technician inspects the system and cleans the filters quarterly. Tanks are inspected annually and pumped as required.


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