A septic lagoon is the odd one out among Oklahoma's four home systems. There are no lateral lines and no sprinkler heads: wastewater leaves the house, passes through an ordinary septic tank, and then runs into a shallow, fenced pond that holds it. DEQ lists the lagoon beside the conventional field, the evapotranspiration/absorption field and the aerobic unit as one of the four home treatment types (DEQ sewage treatment). The rules for building one fill their own subchapter of OAC 252:641.
Who can have a septic lagoon
Mostly people with land. Under DEQ's lot-size table a lagoon needs at least two and a half acres, whether the house is on a well or on public water, and it can't go in Zone 1, the land within 300 feet of a listed lake's highest normal pool or a stream bed. Its draw is that it can be designed without a soil test: with no testing at all, the rule leaves two choices, a lagoon or an aerobic spray system sized as if the yard were solid clay (OAC 252:641-3-1). That makes it an option on big lots with heavy clay, where a lateral field may not pass. Our septic system type tool runs your lot size, water source and soil result against the same tables, and the Oklahoma septic rules guide covers the paperwork that comes before any digging.
What the rule makes the installer build
| Part | What OAC 252:641 subchapter 15 says |
|---|---|
| First stop: a tank | All sewage has to pass through a septic tank for primary settling before it reaches the lagoon (15-1). |
| Holds everything | Lagoons are total retention (15-1). Nothing but sewage may be put in, and sludge can't be disposed of from the lagoon before DEQ approves. |
| Shape and depth | Essentially square or round, no islands or peninsulas, at least 7 feet deep in total, and no smaller than 10 by 10 feet at the bottom or 15 feet across if round (15-2). Sizing follows DEQ's Appendix H figures. |
| Bottom | Level, built of thoroughly compacted homogeneous clay, the same clay on the inside slope of the dike (15-3). |
| Leakage test | At final inspection, 6-inch test holes are presoaked for four hours and then watched for an hour. If any hole drops more than an inch in 60 minutes, the lagoon gets 12 inches of compacted clay, bentonite or a synthetic liner and is retested (15-3). |
| Dikes | Topsoil stripped, homogeneous clay in 6 to 9 inch compacted lifts, no steeper than 1 foot rise per 3 feet run, a top at least 4 feet wide, and at least a foot above the surrounding ground to turn runoff away (15-4). |
| Inlet pipe | Solid pipe, anchored, ending in the center of the lagoon on a concrete pad of at least a square foot. On a gravity system the tank outlet sits at least 6 feet above the lagoon bottom (15-5). |
| Wind and sun | Not located where trees or terrain block the wind or shade the water during the day (15-1). |
| Fence | At least 4 feet high, woven wire or equal, with a gate wide enough for mowing equipment, unless the whole property is fenced with controlled access (15-6). |
Due for a pump-out, or the alarm is buzzing? Call us and tell us your town.
(405) 546-2064Living with one
A gravity-fed lagoon has no air blower, spray pump or timer to wear out, which is why DEQ's homeowner guide rates aerobic systems higher than conventional or lagoon systems in yearly upkeep (DEQ guide). That doesn't make it maintenance-free. The rule requires a fence with a gate, has the dike top graded so it can be maintained, forbids putting anything but sewage into the lagoon, and puts any sludge removal behind DEQ approval. The tank ahead of it still fills, and it's the part we can reach: see septic tank pumping and how often to do it in the pumping schedule guide. A wet, soft or leaking dike, a fence down, or water rising toward the top is a repair call: septic repair sorts out who handles it.
Buying a house with a lagoon
Ask for the original inspection report from DEQ and look at the fence, the dike and the water level yourself. A pre-purchase septic inspection includes the tank in front of the lagoon, and DEQ certifies installers in a lagoon category of their own, which you can check on its installer list (DEQ certified installers).
Frequently asked
How much land does a septic lagoon need in Oklahoma?
At least two and a half acres under DEQ's lot-size table, and it cannot go in Zone 1, within 300 feet of a listed lake or stream bed.
Does a septic lagoon still need a septic tank?
Yes. OAC 252:641-15-1 says all sewage entering a lagoon must first pass through a septic tank for primary settling.
Does a septic lagoon need a fence in Oklahoma?
Yes, at least 4 feet high with a gate for mowing equipment, unless the entire property is fenced and access is controlled (OAC 252:641-15-6).