Arsenic-in-groundwater certified-lab testing route (private wells) — Chaco-Pampean Plain, Argentina.

How this work is done

A documented method, so this packet comes out the same whoever does it.

Bring

• A certified laboratory (state-certified/accredited for arsenic in drinking water via EPA Method 200.8 or 200.9), or a New Mexico Environment Department free water test fair where available
• The lab's own sample bottle and collection instructions
• A way to record local geologic context (known volcanic/granitic/sedimentary bedrock, prior area test results) if known
• A chain-of-custody form for a paid-lab sample

Steps

1. 1. Confirm the source is a private well (the owner IS the water system, same law as this library's private-well-annual-screen standard) rather than a utility connection already covered by a Consumer Confidence Report.
2. 2. Select a certified laboratory that specifically uses EPA Method 200.8 (ICP-MS) or 200.9 (GF-AAS) for arsenic — confirm the method before sending a sample, since EPA withdrew approval of the older ICP-OES methods (200.7 / Standard Methods 3120B) for arsenic specifically because their detection limit could not reliably measure compliance at the 10 µg/L MCL. Where a state agency runs a free water test fair using one of these methods (for example New Mexico's roughly 10-per-year, first-100-well-owners program), that counts as an equally valid route.
3. 3. Collect the sample exactly per the lab's own bottle and preservation instructions (arsenic samples are typically preserved with nitric acid to prevent adsorption to the container) and complete a signed chain-of-custody form for a paid-lab sample.
4. 4. Record any known local geologic context — volcanic or granitic bedrock, prior test results from nearby wells, a documented regional arsenic pattern — as context only, never as a substitute for this household's own current result.
5. 5. When the result returns, report it in µg/L (ppb) and compare it explicitly to the EPA 10 µg/L MCL; never write a household 'safe' or 'unsafe' verdict.
6. 6. If the household is in or approaching a drought period, note that as context (Lombard et al. 2021 found drought conditions can raise the probability of an elevated result) and coach a retest rather than relying on an older, pre-drought number.
7. 7. Route any result at or above 10 µg/L per the decision rules; this packet never recommends a specific treatment technology or product.

What counts as done

• Certified laboratory named, with a signed chain-of-custody form for the sample
• Analytical method recorded and confirmed capable of reliably measuring at the 10 microgram/L level (the level a consumer field kit cannot reach)
• Arsenic result reported in micrograms per liter (ppb) and compared explicitly to the 10 microgram/L EPA/WHO-aligned standard, never to the higher 50 microgram/L endemic-region allowance
• The Chaco-Pampean Plain's documented geogenic arsenic context recorded as regional stewardship framing, never treated as a substitute for this household's own lab result
• Any result at or above 10 micrograms/L routed per the decision rules, with the routing recorded

Proof is measured against these, not judged by taste.