Drip Dispersal Septic Systems: Tubing, Treatment, and Upkeep

The buried tubing is only one part of the system. Tennessee requires secondary treatment before wastewater reaches a drip field. A septic tank alone does not provide that level of treatment. An approved aerobic treatment unit (ATU) is one option: it adds air so microorganisms can break down more of the waste.

So a typical Tennessee drip system is a chain: septic or trash tank, treatment unit, dosing tank, filter, pump, controller, zone valves, then the tubing. Each link has a job, and the drip field only stays healthy if every link ahead of it does its job. That's the reason the state ties drip to a lifetime maintenance contract.

Drip sizing follows the soil, and the arithmetic is simple enough to check a designer's numbers.

Tennessee designs a home for 150 gallons per bedroom per day, so a 3-bedroom house is planned at 450 gallons a day. The soil consultant digs pits (at least two per acre for drip, described to 36 inches, rock, or fragipan, whichever is shallower) and records the soil's texture and structure, meaning how the soil clumps together. Perc tests aren't allowed for drip. Each soil type has a loading rate in the rule, the gallons a square foot of field can take each day.

Take a silt loam with moderate blocky structure, rated 0.30. Divide 450 by 0.30 and you need 1,500 square feet of field. Tennessee divides the unadjusted area by 2 to get the minimum tubing: 750 feet, normally laid in lines 2 feet apart. On a 10 to 20% slope with a restrictive layer at 23 inches or less, the rule adds 15% to the area. The minimum tubing calculation still uses the unadjusted area, while spacing and layout must cover the larger footprint. And you need room for a full duplicate field, the reserve area kept clear for a future replacement.

Plan on $15,000 to $30,000 or more in Maury County for the whole system, treatment unit included. That's this site's editorial planning range, which means it's a budgeting number and you should get written bids before relying on it.

National guides use different scopes: Fixr lists $4,000 to $10,000 as materials only, while HomeGuide lists $6,500 to $15,000 for drip distribution. Neither figure establishes the cost of your complete Tennessee design. Ask whether the quote includes pretreatment, tanks, electrical work, controls, tubing, startup, and site restoration.

Slope is one reason a designer may consider drip. Tennessee won't allow a mound on a slope steeper than 12%, and an LPP field stops at 30%. Drip goes to 50%. Those are slope limits, not promises of approval. The site still has to meet soil, area, setback, and other permit requirements.

Drip still can't make soil out of rock, and around here rock is often the limit. The rule wants a foot of undisturbed soil under the tubing, and the pits have to show it. If they don't, no amount of tubing fixes it. TDEC's Columbia Environmental Field Office reviews drip permits for the county, so the soil consultant's report, not a supplier's brochure, is where the decision starts.

Drip emitters are tiny, and slime, mineral scale, or fine grit that a gravel trench would shrug off can slowly choke them. Filter backwashing cleans the filter. Line flushing scours the tubing. They're two separate jobs, and the controller should log both.

A useful service report shows the filter pressure before and after cleaning, the flow in each zone, which flush cycles ran, and any alarms. A slow drop in zone flow over a year tells you more than "looked fine" ever will. Leave cleaning chemicals to the provider; the wrong product can kill the bacteria in the treatment unit.

If you're unhappy with a provider, you can switch. Tennessee bars drip manufacturers from refusing replacement parts or technical help to any approved maintenance provider. Just don't let the contract lapse. If an owner cancels or doesn't renew, the provider has to tell TDEC within 30 days.