A number arrived and it is bigger than you expected. Before anything else: this is a solved problem, the fix is neither exotic nor especially expensive, and nothing about it is an emergency measured in hours.
What the number means
The EPA and NJDEP action level is 4.0 pCi/L. At or above that, fixing it is recommended. Between 2 and 4 pCi/L New Jersey suggests you consider mitigating, on the basis that no level of radon is known to be risk-free. Below 2, current guidance is that reduction is generally not warranted.
The band between 2 and 4 is where most of the difficult decisions live, and it is also where a long-term test earns its money — more on that below.
Step one: check the test was valid
A short-term test requires closed-house conditions: windows and external doors shut except for normal entry and exit, for at least twelve hours before and throughout the test, which itself runs at least 48 hours. The detector belongs at the lowest level you live in or reasonably might, away from drafts, exterior walls and heat. If a window was open, if a fan was running, if the detector sat on a radiator, the number is not describing your house.
Weather matters too. Readings tend to run higher in winter and during storms, when the pressure difference between the house and the ground beneath it is greatest. A high February reading is real, but it is not the same as a high annual average.
Step two: decide whether you need a second measurement
If the result was well above 4.0 and the test was properly conducted, there is not much to be gained by measuring again — the answer is going to be the same and you can move to fixing it. If it landed in the 2 to 4 band, or if two short-term tests disagreed, a long-term detector left in place for 90 days to a year returns an annual average rather than a snapshot, and that is a much better basis for a decision about a house you are going to live in for years.
The exception is a sale. Long-term testing does not fit a closing date, which is why real-estate transactions run on short-term tests and why the argument in a transaction is usually about the validity of the test rather than the length of it.
Step three: get the design done by measurement, not by eye
This is the step that gets skipped. Before deciding where a suction point goes, a contractor can measure how far suction actually travels under your slab — communication testing at test holes, pressure-field readings, sometimes a smoke pencil to find where air is moving. In Hunterdon that matters more than it does in most places, because thin soil over rock and additions built on separate footings are both common here, and both limit how much of a floor one point can serve.
Step four: install, then prove it worked
A clearance test is run no sooner than 24 hours and no later than 30 days after the fan is switched on, under the same closed-house conditions as the original. Without it, all anyone knows is that there is now a pipe on the side of the house. Ask, before you sign, whether the clearance test is in the price.
What not to do
Do not seal cracks and hope. Sealing helps an active system work efficiently; on its own it rarely gets a house below the action level and there is a long history of it being sold as though it would. Do not accept a design with no diagnostic work behind it. And do not take a result from an uncertified tester in a New Jersey transaction — testing for a fee here requires NJDEP certification, and measurement is certified separately from mitigation.
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Get free quotes →General information for Hunterdon County, NJ property owners — not a diagnosis, not a quote, and not a reading for any particular building. Every property is different; a certified professional confirms specifics on site.