Wells over 50 feet deep, and with past negative test results, can probably wait longer between tests. Bulletins WQ 3 "How To Take A Water Sample" and WQ 1 "Water Testing Laboratories" give further ...

The WQ bulletin "Why Test Your Water?", available at your extension office, may be helpful in determining which tests to run. After selecting the tests, choose a lab to test the samples. See WQ 1, ...