Service
Post-Mitigation Testing in San Diego County
Verification testing that proves a system worked, rather than assuming it did because the fan is running.
Installing a mitigation system without testing afterward is like taking medicine without ever checking whether the symptoms improved. The fan running is evidence of mechanical operation, not of reduced exposure.
Post-mitigation testing closes the loop. It documents the new indoor concentration under the same closed-house conditions used for the original measurement, which makes the before-and-after comparison meaningful.
It also catches the uncomfortable cases: the system that reduced radon from 12 to 6 pCi/L and stopped, or the one that improved the living room while a back bedroom over a separate slab stayed elevated. Those situations are fixable, but only if someone measures.
Why this work matters
- It is the only proof that mitigation achieved its purpose.
- It establishes the performance baseline against which future tests are compared.
- It identifies partial success early, while the installer is still engaged and correction is straightforward.
- It produces documentation that supports a future sale or refinance.
Signs this service applies to your building
- A newly installed mitigation system that has run at least 24 hours.
- A fan that was recently replaced.
- A system repair, added suction point, or new sealing work.
- An existing system with no verification test on record.
- A major remodel, foundation repair, or HVAC replacement after mitigation.
- Two years elapsed since the last verification test.
How the process works
- 1
Wait for stabilization
The system runs continuously for at least 24 hours so sub-slab conditions reach steady state before measurement begins.
- 2
Restore closed-house conditions
The same conditions used for the original test are re-established so the comparison is apples to apples.
- 3
Place devices to match the baseline
Detectors go in the same locations used originally, in the lowest lived-in level, so any difference reflects the system rather than the placement.
- 4
Measure for at least 48 hours
A continuous monitor logs hourly data across two full cycles, revealing whether reduction is stable or only intermittent.
- 5
Compare and document
Before and after averages, percent reduction, and manometer reading are recorded together in a single report.
- 6
Adjust if needed
If the result falls short, diagnostics identify whether added suction points, additional sealing, or a different fan curve is required.
Equipment and materials involved
Continuous radon monitor
Hourly data showing whether the reduction holds through daily pressure and weather cycles.
Alpha track detector
Optional long-term follow-up to confirm the annual average, not just the test window.
Digital manometer
Documents system vacuum at the time of testing for correlation with the result.
Comparative report template
Places baseline and post-mitigation data side by side for a clear record.
What you get out of it
- Confirmed protection rather than assumed protection.
- A documented performance baseline for future comparison.
- Early detection of partial reductions while correction is easy.
- Records that answer inspector and buyer questions later.
- Confidence that the money spent produced the intended result.
San Diego County considerations
San Diego's mild weather makes it tempting to test with windows open, which will produce a flatteringly low post-mitigation number that does not reflect closed conditions.
Seasonal soil moisture shifts across the county mean a system verified in dry September should be rechecked during the wet winter months for a fuller picture.
Homes with additions, very common in older San Diego neighborhoods, are the most likely to show partial reduction, so testing in more than one area of the home is worthwhile.
Because many local homes are single story on slab, post-mitigation devices go on the main living level rather than in a basement, and placement away from the kitchen and bathrooms matters more in an open floor plan.
Frequently asked questions
How soon after installation should I test?+
After the system has run continuously for at least 24 hours, and ideally within 30 days of installation. Waiting the initial 24 hours allows sub-slab pressure to stabilize so the measurement reflects steady-state performance rather than the transition. Testing within 30 days keeps the verification close enough to installation that the installer is still engaged if adjustments are needed.
What result should I expect?+
Well-designed systems commonly finish below 2.0 pCi/L and frequently below 1.0 pCi/L. A result under 4.0 pCi/L meets the EPA action level, but since risk is continuous rather than threshold-based, the practical aim is to get as low as the building reasonably allows. A reduction from 15 to 3.8 pCi/L technically passes and still deserves a conversation about whether more can be done.
What if the level is still high after mitigation?+
It is a diagnostic problem with known causes: insufficient pressure field extension, unsealed major openings, a separate slab section left untreated, or an undersized fan. The correction is usually an added suction point, additional sealing, or a fan better matched to the measured static pressure. A reputable installation treats a failed verification as unfinished work rather than an unlucky outcome.
How often should I retest after the initial verification?+
Every two years under normal circumstances, and additionally after fan replacement, foundation repair, significant remodeling, HVAC replacement, or converting space to living area. If the manometer ever shows level columns, retest after the repair regardless of when the last test was performed.
Should the post-mitigation test be done by the installer?+
It can be, and it commonly is. Some homeowners prefer an independent test to remove any appearance of conflict, which is a reasonable choice, particularly during a real estate transaction where the result affects the deal. Either way, insist on a continuous monitor test under documented closed-house conditions rather than an informal reading.
Related reading
Related services
Available throughout the county
- Post-Mitigation Testing in San Diego
- Post-Mitigation Testing in La Jolla
- Post-Mitigation Testing in Del Mar
- Post-Mitigation Testing in Carlsbad
- Post-Mitigation Testing in Encinitas
- Post-Mitigation Testing in Poway
- Post-Mitigation Testing in Escondido
- Post-Mitigation Testing in Chula Vista
- Post-Mitigation Testing in El Cajon
- Post-Mitigation Testing in La Mesa
- Post-Mitigation Testing in Santee
- Post-Mitigation Testing in National City
- Post-Mitigation Testing in Coronado
- Post-Mitigation Testing in Imperial Beach
- Post-Mitigation Testing in Pacific Beach
- Post-Mitigation Testing in Mission Valley
- Post-Mitigation Testing in Clairemont
- Post-Mitigation Testing in Mira Mesa
- Post-Mitigation Testing in Rancho Bernardo
- Post-Mitigation Testing in Rancho Peñasquitos
- Post-Mitigation Testing in Carmel Valley
- Post-Mitigation Testing in University City
- Post-Mitigation Testing in Point Loma
- Post-Mitigation Testing in Hillcrest
- Post-Mitigation Testing in North Park
- Post-Mitigation Testing in South Park
- Post-Mitigation Testing in Ocean Beach
Not sure where to start?
Testing is the first step. Send a note describing your home, its foundation type, and any test results you already have.