Every septic inspection in Pierce County is filed with the health department, so what follows is what inspectors actually recorded in Bonney Lake rather than a rule of thumb.
| Measure | Figure | What it covers |
|---|
| Inspections filed in Bonney Lake, 2015–2025 | 9,610 | Every inspection is filed with the health department |
|---|
| Inspections that found a problem | 18.0% | 2.3 points above the Pierce County average |
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| Carried out at the point of sale | 3,569 | Of which 14.8% found a problem |
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| Partial rather than full inspections | 25.9% | Region-wide, partial inspections find a problem more often |
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| Past due for an inspection | 50.4% | Of the 752 whose system type is on record |
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| Past twice their interval | 30.9% | A subset of the row above |
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| Properties on septic in Bonney Lake | 5,618 | System type recorded for 752 of them (13%) |
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Of the inspections filed in Bonney Lake over the decade to 2025, 18.0% recorded a deficiency — 2.3 points above the Pierce County average. A deficiency is an inspection filed with a status of Deficient, and the records carry no severity field, so it covers everything from a missing riser lid to a failed drain field. It is not the same thing as a broken system.
Roughly 37% of the inspections here happened because a property was changing hands, and 14.8% of those found something. Washington requires an inspection at sale whatever the system type, so that group is a complete count of a defined event rather than a sample.
How often you are due depends on what kind of system you have, so this can only be measured where the type is on record. In Bonney Lake that is 752 of the 5,618 septic properties — 13%. Of those, 50.4% have no inspection filed within their interval and 30.9% are past twice it. The rest cannot be assessed either way, and nothing here should be read as a finding about them.
That recorded share is low, so treat the percentage as indicative rather than precise: it describes 752 properties, not the whole of Bonney Lake, and there is no reason to assume the unrecorded majority behave the same way.
One further caveat. Pierce County allows eligible owner-occupied gravity systems to move from a three-year cycle to a five-year one, and approvals are not visible in the filings, so some properties counted here as past due are legitimately on the longer cadence.
If you do not know where your own system stands, we can tell you: there is more on what an inspection covers, who is allowed to carry one out and what the records show region-wide on our septic inspections page.