Septic aerator and pump replacement in St. Louis County, Missouri

Because the county requires one. The county plumbing code says all water-carried sanitary sewage shall pass through an approved mechanical sanitary sewage treatment plant before it goes into the soil, and that an individual system consists of that plant discharging into an approved sub-surface disposal field. The plain tank and gravity field most people picture is not the standard design here.

Septic ground in this county is its western and southern edge, the parcels outside the MSD sewer service area. Where that boundary runs, and what connecting costs if a sewer reaches you, is covered on the metro page at /st-louis-septic/.

The unit is sized by an engineer, never smaller than 120 gallons per bedroom per day or 1,000 gallons, whichever is greater, and its access has to be brought within 14 inches of finished grade. That access rule is what makes component work practical: the compressor, the pump chamber and the floats are meant to be reachable by taking a lid off, not by bringing a machine.

It supplies air, and that is the whole job. An aerobic system injects oxygen into the treatment tank, and the added oxygen is what raises the bacterial activity the design counts on. The aerator delivers it: a small compressor or blower in a housing on or beside the tank, running nearly all the time on household current.

When it stops, the added oxygen stops with it, and the effluent leaving the unit is no longer treated the way the design assumed. Nothing dramatic happens on the first day, which is why these failures run for months before anybody looks.

• Silence. A running unit hums, and you stopped hearing it years ago. Stand over the tank. If the sound is gone, that is your finding.

• A light or a buzzer at the control panel, usually on the house wall or on a post near the tank.

• A tripped breaker or a kicked GFCI outlet. Check this first: most common cause, least work to rule out, nothing to lose by looking.

• A sour or sewage smell around the unit or the field that was not there a month ago.

• A compressor that runs but moves no air, from a split diaphragm, a plugged intake filter or a cracked air line. A running motor is not proof of a working aerator.

• Wasps, ants or mice in the housing, or an intake filter packed with lawn dust. A common reason a motor cooked itself.

• A breaker that resets and then trips again within minutes. That is a motor or a wiring fault, not a nuisance trip, and it wants a contractor rather than a second reset.

Wet ground, odor, gurgling drains and a slow backup are the four symptoms a homeowner reads as a dead field. Every one of them can come instead from a stopped motor, a failed pump or a hung float, and the component is the likelier cause, because it is the part with moving pieces in it.

One rough test separates them. If the field is the problem, water has nowhere to go but up, so the ground over the trenches is soft, wet or oddly green in a dry week. If the pump side is the problem, water backs up inside the tank and the yard stays dry.

A backup that clears for a day after the tank is pumped and then returns is a downstream problem, the pump side or the field, not the tank. A backup at one fixture only, with the rest of the house draining normally, is a house drain problem and never the field.

Rule the cheap component out before anyone prices a new field. What replacing a field involves, and what it costs to permit, is set out on the installation page.

The connection runs one direction only. A unit that has not aerated for months pushes poorly treated effluent and solids out to the field, which is how a component failure becomes a field failure. That argues for fixing the cheap part fast. It does not argue for replacing the field.

Not every system moves water by gravity. Where the field sits above the treatment plant, or too far from it, treated effluent is lifted by a pump in a chamber at the end of the unit, a pump tank or lift station. Floats switch it: one starts the pump, another stops it, and a separate high-water float does nothing but set off the alarm. These are the parts that put a system on a shorter inspection cycle. EPA puts alternative systems with electrical float switches, pumps or mechanical components at generally once a year.

Start at the float, because it is the cheapest thing in the chamber to check and the fastest to rule out. A float can hang on its own cord, on the riser wall or on grease. Stuck high, it reads a full tank as an empty one and the pump never starts. Stuck low, the pump runs dry and burns itself out, which turns a float job into a pump job.

The order that saves money runs breaker, float, pump. A pump that hums but moves no water is usually jammed or has lost its check valve. A pump that is silent with power confirmed at the panel is usually the switch, not the motor. A check valve stuck open lets each dose drain back into the chamber, so the pump lifts the same water over and over, and the first sign of it is a power bill, not a smell.

The alarm is the one part built to warn you before sewage reaches a floor. Silencing the buzzer while the light stays on is fine. Ignoring it for a week is how a repair becomes a cleanup. When it sounds, stop sending water down the drains and call an independent local septic contractor, not a plumber whose pump work is basement sump pumps, which is a different trade on different equipment.

The emblem on the equipment is the thread to pull. The county code requires every individual mechanical treatment plant serving a home to be approved to NSF Standard 40 Class I and to carry an NSF emblem on the equipment for inspection. It requires one more thing that matters far more 15 years later: manufacturers and distributors have to show proof that repair parts and a qualified service company are available.

Read that for what it is. The county made parts and service a condition of letting the equipment go in the ground. It is a duty on the manufacturer at approval, not a promise attached to your tank for life. Some units here were approved by companies that no longer exist.

That does not make a unit unfixable. A stopped aerator is a compressor, an air line and a diffuser. A dead pump is a pump. A company that services aerobic units can usually match a part once it knows what is in the ground. What stalls these jobs is nobody knowing what the unit is.

• Photograph the nameplate and the NSF emblem: make, model, serial number. Do it before you need it.

• Note whether the control panel runs on one circuit or two, and which breakers feed it.

• Measure the air line and note the fitting size. A generic compressor of the right output often fits where a discontinued one came out.

• Ask the county's plumbing office whether a design for your address is on file, with the address and year built ready when you call.

Ask the county, and here is why the answer is not obvious. Missouri defines a major modification or major repair as relocating the system or part of it, replacing the septic tank, or constructing a new absorption field. A compressor, a pump or a float is none of those three, so the state's permit trigger is aimed at much bigger work than a component swap.

The state permit rule is not absolute in the other direction either, and pages that state it flatly are overstating it. Section 701.046 opens "except as provided in section 701.031", and 701.031 excludes the owner of a single-family residence lot of three acres or more, and a residential lot of 10 acres or more meeting a separation and density test, from sections 701.025 to 701.059 and the rules made under them. Every condition is load-bearing: the exclusion does not reach lots adjacent to lakes operated by the Corps of Engineers or by a public utility, all points of the system have to sit more than 10 feet from any adjoining property line, and no effluent may enter an adjoining property, contaminate surface water or groundwater, or create a nuisance.

Do not read that as a free pass. A county may regulate under its own ordinance regardless of the state exclusion, and that is what the collar counties do. St. Louis County runs its own plumbing code, permits under it, and requires anyone repairing a private sewage system to hold the state credential and be a master drainlayer or work under one. On a three-acre lot here you are still dealing with the county. Put the question to your permit authority before work starts, not after.

A few questions sort a component job from a system job, and they cost nothing on the phone. This site explains the rules and routes requests to independent local septic contractors; it does not check anyone's credentials, so the full list of what to ask before hiring, credentials and insurance included, is on the metro page at /st-louis-septic/.

One item belongs on the calendar rather than the call. A machine in the yard needs a standing service interval, and what a maintenance agreement should cover is on the maintenance page at /septic-maintenance-contract-missouri/.

• Is the ground over the field wet right now? If it is dry, why are we discussing the field.

• Is the aerator drawing power at the panel, and did the breaker hold after a reset.

• Was the high-water alarm float tested on its own, separately from the pump float.

• Are you replacing a compressor, a pump, a float, or the whole treatment plant, and which office is issuing anything on that. Missouri DHSS lists two permit authorities here: the St Louis County Plumbing Dept. on (314) 615-0330 and the county Department of Public Health on (314) 615-1600.