Complex sentence: In 2006, the State Water Resources Board took samples from domestic wells in Tulare County; they found that 40% of 181 domestic wells had nitrate levels above the 10 mg/L legal limit.
Split into simpler sentences: In 2006, the State Water Resources Board took samples from domestic wells in Tulare County. The results indicated that 40% of 181 domestic wells had nitrate levels above the 10 mg/L legal limit.