Water Quality, Testing, and Contaminant Response
This domain tests what to test for in Massachusetts, what the numbers mean, and what you actually do when a result fails. The exam favours the state's characteristic contaminants: arsenic, radon, uranium, nitrate from septic systems, and PFAS.
The standard picture
- Bacteria: total coliform and E. coli; any positive is a construction, seal or disinfection problem first.
- Arsenic MCL 10 µg/L, common in bedrock wells in central and northeastern Massachusetts.
- Nitrate MCL 10 mg/L as nitrogen; septic systems and fertilizer are the usual sources.
- Lead action level 0.015 mg/L and copper 1.3 mg/L; often plumbing, not the aquifer.
- Iron 0.3 mg/L and manganese 0.05 mg/L are secondary aesthetics, not health emergencies.
- PFAS6 - the sum of six PFAS compounds - has a Massachusetts standard of 20 ng/L, among the strictest in the country.
- Radon in water is addressed by a MassDEP guidance level around 10,000 pCi/L, with aeration as the effective treatment.
Worked example
A bedrock well returns nitrate at 14 mg/L as N. Do not order treatment first. Resample to rule out error, then walk the property: a failing septic system, a manure pile, or a cracked casing seal can all explain it. If the source is the septic system, fixing it is the remedy; if nitrate is genuinely formation-wide, point-of-use reverse osmosis or anion exchange reduces it, but the homeowner must understand that treatment hides a symptom unless the source is controlled.
Traps
Treating arsenic with a water softener; ignoring a positive coliform as seasonal; sampling through a filter or a softened line; and forgetting to resample before quoting treatment.