Since people seem curious how to analyze this for their locale, the best I could come up with (using the raw data at https://www.epa.gov/sites/production/files/

Since people seem curious how to analyze this for their locale, the best I could come up with (using the raw data at https://www.epa.gov/sites/production/files/2015-09/ucmr-3-occurrence-data.zip https://www.epa.gov/sites/production/files/2015-09/ucmr-3-oc... ) was: 1. Search zipcode in UCMR3_ZipCodes.txt, obtain PWSID. 2. Filter by PWSID in UCMR3_All.txt. 3. Filter that result by rows containing "=" (which means at or above minimum reporting level) 4. Don't panic. 5. Compare AnalyticalResultsValue column to the Reference Concentration in ucmr3-data-summary-april-2016.pdf. If its under the Reference Concentration then you're safe, within the limits of how incomplete their reference concentations are. The document specifically states: > The intent of the following table is to identify draft UCMR reference concentrations, where possible, to provide context around the detection of a particular UCMR contaminant above the MRL. The draft reference concentration does not represent an “action level” (EPA requires no particular action1,2 based simply on the fact that UCMR monitoring results exceed draft reference concentrations), nor should the draft reference concentration be interpreted as any indication of an Agency intent to establish a future drinking water regulation for the contaminant at this or any other level. The minimal reporting level seems to be based on how small an amount is detectable, not harmful. The reference concentration appears to be a best guess at the moment for what a maximum safe amount is. My zipcode for example came up with several of these above the MRL but below the reference concentration. Enjoy. Edit: added link.