The headline number turns up in OPB, the Mail Tribune, and every Southern Oregon water-quality conversation: roughly 44% of tested Jackson County wells have detectable arsenic (Pure Water Solutions citing USGS-referenced data). That's not a scare statistic — it's a geology statistic, and it's why OSU College of Health is running the 4,000-household Be Well project specifically in this county.
The geology
Arsenic in Southern Oregon groundwater is almost entirely natural. Two lithologies drive it. The first is the Western Cascades volcanic sequence — the andesitic and basaltic rocks that underlie most of Jackson County east of the valley floor. Volcanic glass and secondary minerals release arsenic slowly into groundwater over geological time. The second is the Klamath Mountains gold-belt lithologies — the Galice and Applegate formations around Jacksonville, Ruch, Forest Creek, and Kanaka Flats. These rocks carry arsenopyrite (FeAsS), the same arsenic-bearing mineral that accompanied the Jackson County gold that was mined from 1852 through 1959 (DOGAMI — Jackson County Mining). Historical placer mining in Jackson Creek, Rich Gulch, Daisy Creek, and Sterling Creek disturbed those same rocks and left legacy mercury in the stream gravels too.
Documented exceedances of the 10 ppb federal Maximum Contaminant Level in this county include Gold Hill 11.7 ppb, Grants Pass 18.1 ppb, and Jacksonville 32.1 ppb — the last at 3.2 times the federal limit (Pure Water Solutions). In July 2024, OPB documented that the Rogue Meadows mobile-home-park public system in nearby Shady Cove exceeded the arsenic MCL in 2020, 2021, and 2023, with one sample at twice the federal limit (OPB 2024).
Why private wells are the story
Public water systems are regulated. Medford Water is non-detect for arsenic at both its Big Butte Springs and Rogue River entry points. The city of Medford, Central Point, Eagle Point, Jacksonville, and Talent all buy from Medford Water and have arsenic-free finished water.
Private wells are not regulated by the EPA. In Oregon, the only required testing is at property transfer — arsenic, nitrate, and total coliform — and the test may be a decade old by the time a contaminant changes. The homeowner owns the problem entirely.
Speciation: As(III) vs As(V)
Arsenic in groundwater exists as two species. Arsenate (As V) is charged, easier to capture, and removable by most certified technologies. Arsenite (As III) is uncharged, much harder to capture, and needs an oxidation step to convert to As(V) before most treatment media work. A lab test that reports only "total arsenic" without speciation can push a household toward the wrong treatment. On wells where we find arsenic above trace levels, we specify speciation testing before we design the system — not after.
Two answers: point-of-use vs whole-house
For a Jackson County well with a detection, there are two technically sound paths:
Point-of-use reverse osmosis at a single drinking tap. RO rejects 95%+ of arsenate at the membrane. Paired with a carbon prefilter and optional remineralization cartridge, it's the cheapest effective solution for households where only drinking and cooking water needs treatment. It doesn't help the shower, the laundry, or the outdoor hose — but arsenic is a dietary concern, and dermal absorption is minor.
Whole-house adsorptive media — iron-based Bayoxide E33, GFH (granular ferric hydroxide), or titanium dioxide. These sit in a point-of-entry tank and treat every gallon going into the home. They require periodic media replacement (typically 2-5 years depending on concentration and flow), but remove the need to remember which tap is treated. For wells above 20-30 ppb or households with small children, the whole-house path is the more defensible one.
Anion exchange is a third option for low-sulfate water, but it's rarely the first choice in this county's geochemistry.
When to test, and what to order
CDC, EPA, and OSU Extension all recommend the same cadence for private wells: bacteria and nitrate annually; arsenic, lead, radon, fluoride, uranium, pH, hardness, iron, and manganese every 3-5 years; VOCs and pesticides as the surrounding land use indicates; plus a full panel after any event — flood, fire, neighboring construction, earthquake, pump replacement, or a taste or smell change (OSU Well Water Program).
OSU's Be Well project is currently enrolling Jackson County well owners and provides free testing as part of the study. Outside the study, we run a full well panel on-site plus certified lab follow-up for arsenic and anything else the geology or history calls for.
The short version
44% isn't noise — it's geology. If you're on a well anywhere in Jackson County and your last arsenic test is more than five years old (or you've never had one), it belongs on your next panel.