Where the arsenic and radon in a well come from
Neither one is pollution. The Highlands bedrock that wells up here are drilled into is Precambrian gneiss and granite, and rock that old carries trace amounts of arsenic along with the uranium that decays into radium and then into radon gas. Groundwater moves through fractures in that rock, sits against mineral surfaces for a long time, and picks up whatever dissolves. That's the entire mechanism. No spill, no leaking tank, no septic system, no bad neighbor.
Arsenic sits in sulfide minerals like arsenopyrite and in the iron oxide coatings on fracture faces. Whether it ends up in your glass depends on the chemistry a few hundred feet down, mostly pH and how much dissolved oxygen is present. Water that's low in oxygen and on the alkaline side releases arsenic more readily. That's why one well produces a measurable number and the well four hundred feet away produces almost nothing. Each well intersects its own fractures.
Radon behaves differently because it's a gas. It dissolves into the groundwater, rides up the drop pipe with everything else, and comes out of solution the second the water is agitated. A shower, a dishwasher, a washing machine, a faucet hitting the bottom of a sink. That's what separates radon from every other line on a lab report. It doesn't stay in the water once the water is in your house.
One practical consequence: geologic numbers don't swing much year to year. A bacteria result can be clean in June and positive in October. Arsenic and radon come from the rock, so one good test tells you a great deal.
What New Jersey already makes you test
The Private Well Testing Act requires raw, untreated water to be tested when a property served by a private well is sold, and rentals get tested every five years. Arsenic is on the required panel for wells in the northern counties, Passaic, Sussex, Bergen and Morris included, and so are gross alpha and uranium. The state didn't put those parameters on the list because it suspects contamination up here. It put them there because it knows what this bedrock is made of.
Radon in water is not on that panel. If you want to know your number, you order the test yourself. A certified lab runs radon in water as its own test, and it's a separate bottle with its own handling rules, so ask for it by name. Nobody will hand you that result as part of a real estate transaction.
If you're not selling and not renting, nothing requires you to test anything, ever. That's the actual gap. Houses in West Milford and Vernon change hands once in thirty years, and the family living there in between has never seen a number on paper. A reasonable schedule for a private well is the full panel including arsenic once, then again every three to five years, plus bacteria and nitrate annually. Radon in water is worth running once, and again if the pump gets set at a different depth, because a different part of the fracture system can give a different result.
Radon in your air and radon in your water are two different tests
People conflate these constantly, and the confusion costs money. An air test measures radon gas in the lowest lived in level of the house, with a charcoal canister sitting out for two to seven days or a continuous monitor over a longer stretch, and the result is picocuries per liter of air. A water test measures radon dissolved in the water, in a sealed vial filled with no air bubble at all, drawn with the aerator off and any treatment bypassed, and delivered to the lab fast because the hold time is short. The units share a name and mean nothing alike.
The rough transfer factor the industry works with is about ten thousand to one. On average, roughly 10,000 picocuries per liter in the water contributes on the order of 1 picocurie per liter to the air inside the house. That ratio is why water radon matters most in two situations: when the water number is genuinely large, or when the air number is already sitting close to the level at which EPA recommends fixing a house, which is 4 picocuries per liter in air. In most northern New Jersey basements, the bulk of the radon in the air came up through the slab as soil gas, not out of the shower head.
So the order of operations is air first. Test the air, and if it's high, that's a sub slab depressurization system installed by a radon mitigation contractor certified in New Jersey. That's a different trade from ours and we'll say so. Then test the water and find out whether the water is adding anything meaningful on top. Treating the water does nothing about soil gas coming through the foundation, and a contractor who sells you a water system to fix an air problem has sold you the wrong thing.
Treating arsenic
Arsenic comes in two forms and the difference decides the equipment. Arsenate, sometimes written as arsenic five, adsorbs readily onto treatment media. Arsenite, arsenic three, does not, and it has to be oxidized first with chlorine, an air injection step or a manganese dioxide filter before anything downstream will hold it. A lab can speciate the sample and tell you which you have. Skipping that step is how people end up with a system that tests fine on day one and fails a year later.
The rest of the water chemistry matters just as much. Iron in the raw water helps adsorption. High pH, silica and phosphate hurt it. Sulfate competes for sites on anion exchange resin, so a system that works in one town does poorly two ridges over. This is why a full raw water panel comes before the quote. The test is the specification.
For whole house treatment, the common approach is an adsorptive media tank at the point of entry, generally an iron based granular media, and it is a significant install, not a filter you screw on. Media replacement comes every one to three years depending on tank size, water use and how loaded the water is, and it is a recurring cost you should ask about before you buy the tank, not after. Anion exchange is an alternative where sulfate is low, but it can release accumulated arsenic in a slug if the resin exhausts unnoticed, so it wants monitoring.
The cheaper correct answer for a lot of houses is reverse osmosis at the kitchen sink, a small fraction of a whole-house system, with a modest yearly cost in membranes and prefilters. Arsenic is an ingestion concern, not something you take in through the skin in a shower, so treating only the water you drink and cook with is a defensible choice rather than a compromise. The tradeoffs are real: it treats one tap, it produces reject water, and it fills slowly. Either way, test the treated water after installation and on a schedule, because adsorptive media exhausts quietly and gives you no warning at the faucet.
Treating radon in water
There are two methods and the level decides which one. Aeration is the workhorse. Water enters a small vented tank where air is bubbled or sprayed through it, the radon comes out of solution, a blower pushes it out a vent line that terminates above the roofline, and a small pump repressurizes the treated water for the house. Removal runs in the high nineties as a percentage. It is the most expensive option on this page, and it is the right one when the radon numbers are high enough to justify it. It needs electricity, floor space, a vent route to the outdoors and annual cleaning, and iron, manganese or iron bacteria will foul the tank, so pretreatment is part of the design and not an upsell.
Granular activated carbon is the other option. Water passes through a carbon tank and the radon adsorbs onto the carbon. It's considerably cheaper, with no blower, no vent and no power draw. The catch is what happens inside the tank. Radon decays into solid daughter products, so the carbon slowly accumulates radioactivity and the tank becomes a low level source you don't want against a finished bedroom wall or where people sit. Spent carbon disposal has rules attached. For that reason carbon suits lower radon levels, and aeration is the standard choice once the water number gets large. If a contractor proposes carbon on a very high result, ask him to explain that decision in writing.
Both systems get sized off flow rate and peak household demand, not off square footage. Ask where the vent will run before you sign anything, because on some basements the honest answer is a long pipe chase through finished space. Ask what annual service costs, which for an aeration unit is realistically a few hundred dollars a year.
Who decides what your number actually means
The lab report is the authority on your result. A certified lab prints your value next to the current state limit for that parameter, and that comparison column is the one to read. New Jersey's arsenic standard is tighter than the federal one, and the way radon in water is handled in New Jersey is not the same as a parameter with a hard enforceable limit, so let the report and the state tell you where you stand rather than a number somebody quotes you over the phone.
We're a well contractor. We won't tell you what a result means for your health, and you should be suspicious of anyone selling equipment who does. The environmental health office at your county health department, Passaic, Sussex, Bergen or Morris, answers private well questions for homeowners and does it without a product to move. NJDEP publishes the current guidance. If you're worried about exposure for someone in the house, that conversation belongs with a physician.
What we handle is the water system side. Drawing a proper raw water sample from the right tap with the aerator off and the treatment bypassed, checking the well cap, casing and grout while we're there, reading the full panel to work out what a treatment system actually has to deal with, then installing and servicing that equipment. Part of that job is telling you when an under sink unit is enough, which is the answer more often than the industry admits.
Call 973-853-1550 with the report in front of you and read the numbers off the page.