Most systems that fail a Time of Transfer inspection were never broken in the usual sense. They were just old enough, or neglected enough, for something specific to give. Iowa Code 455B.172 requires an inspection before nearly every sale or deed transfer in the state, and the inspector isn’t guessing. They’re checking a short list of known failure points, in order, because those are the points that actually fail.
Age sets the clock, but it isn’t the cause by itself
A system doesn’t fail because it turned 25. It fails because 25 years gave corrosion, root intrusion, and soil compaction time to finish the job. Knowing the expected service life tells you where to look first.
Concrete tanks, 20 to 40 years
Concrete holds up well structurally, but the gas space above the liquid line is where hydrogen sulfide gas converts to sulfuric acid on contact with moisture. That acid eats concrete from the inside out. An inspector checks the underside of the lid and the tank walls above the waterline for spalling, exposed aggregate, or a baffle that’s thinned to nothing. A tank can look solid from the top and still be failing there.
Steel tanks, 15 to 25 years
Steel tanks are rarer in newer installs but still common on older properties in Warren and Madison counties. They rust from the outside in, and the failure point is usually a hole low in the tank wall or a collapsed lid, not a slow leak you’d notice from the yard.
Baffles corrode and collapse, and inspectors know exactly where to look
The inlet and outlet baffles are what force wastewater down below the scum layer instead of letting it flow straight through the tank. When a baffle corrodes through or breaks off, solids and scum pass straight into the drain field instead of settling out first. That’s one of the fastest ways to shorten a drain field’s life, and it’s also one of the easiest things for an inspector to catch. They’re looking directly at the outlet baffle with a camera or a mirror, checking for a missing tee, a broken slot, or scum sitting at or above the outlet line. If they see effluent riding high with no baffle stopping it, that’s a fail, not a gray area.
The drain field is where most failures actually live
Tanks get replaced. Drain fields get diagnosed as a problem and then argued about, because the fix is bigger and the cause is less obvious from the surface.
Biomat that’s outlived its working life
Every drain field trench develops a biomat, a layer of anaerobic bacteria and solids that lines the trench bottom and actually helps treat effluent. That’s normal. The problem starts when the biomat thickens past what the soil can still pass water through. Effluent stops infiltrating, backs up in the pipe, and eventually surfaces in the yard or backs into the house. An inspector reads this through standing effluent in the inspection pipes, sluggish drainage during a dose test, or wet, spongy ground over the field even in dry weather.
Clay soil the system was never matched to
Central Iowa’s glacial till clay is a real factor here, not a footnote. Clay has low permeability to begin with, and a field sized off a percolation test that ran a little optimistic will show biomat problems years earlier than the same design in sandier soil. When a drain field in Jasper or Marion county fails at 15 years instead of 25, the soil is usually part of the story, not just the age.
Systems undersized for the household from the start
Iowa’s sizing tables run off bedroom count and design flow, and that number gets locked in at install. A system sized right for a three bedroom house holds up fine until a finished basement adds two more people, or a family simply grows into the house differently than the original design assumed. Nobody upsizes a drain field because the household got bigger. The system just runs closer to its limit every year, and an inspector sees that as a field that’s stressed well before its expected age, sometimes with signs of hydraulic overload that don’t match how old the system actually is.
No pumping schedule means solids reach the field
A tank that’s never pumped on schedule eventually fills past its working capacity, and solids that should have settled in the tank get carried out into the drain field instead. Once solids reach the field, they don’t leave. They accelerate biomat buildup and shorten the field’s life for good, and there’s no fixing that after the fact the way you can fix a maintenance gap in the tank itself. An inspector checks scum and sludge depth with a measuring stick or sludge judge, and a tank that’s clearly overdue is one of the more common, and most preventable, reasons a system shows up as marginal.
Catching this before you list beats discovering it mid-sale
A failed Time of Transfer inspection during an active sale puts the repair cost, the timeline, and the negotiating leverage all on the buyer’s side of the table. Get the same information two months before you list, and the same $250 baffle repair or $2,500 drain field rehab is just routine maintenance you handled on your own schedule, not a closing-day scramble. That’s the entire difference.
The system doesn’t fail the inspection out of nowhere. It fails because a specific, checkable thing finally gave, and most of those things show warning signs for years first.