Manganese – Of the 51,028 wells sampled between September 2002 and April 2007, 9,890 or 19% of the wells exceeded the secondary standard for manganese. Manganese concentrations ranged from 0-2300 µg/l.
Figure 9: Percent of Wells with Results that Exceeded the Recommended Upper Limit for Secondary Parameters (Of 51,028 wells)
Percent of Wells Exceeding Secondary Standards
P E R C E N T
50 45 40 35 30 25 20 15 10 5 0
What are the data telling us about private wells?
This report is based on 55,749 samples that were submitted between September 2002 and April 2007 to the Private Well Testing Act Program collected from 51,028 individual wells throughout the State. A total of 6,369 wells (13%) exceeded one or more of the MCLs developed for primary drinking water contaminants (i.e., arsenic, mercury, nitrate, total coliform and fecal coliform, gross alpha particle activity, and volatile organic compounds). One well exceeded 6 MCLs; 3 exceeded 5 MCLs; 3 exceeded 4 MCLs; 48 exceeded 3 MCLs; 692 exceeded 2 MCLs; and the remaining 5,622 exceeded one MCL.
Figure 10 depicts the percentage of wells that passed the primary standards; lead results are discussed separately because of problems encountered with the test results for lead.
With the exception of lead, the greatest percentage of private wells that exceeded a primary drinking water standard were naturally occurring contaminants: arsenic and