What are the 90th percentile values, and what are they for?
The 90th percentile is a statistical calculation performed on all compliance sampling data taken over an established monitoring period. These calculations establish the system specific value which is used to help evaluate compliance with the action levels. The goal is to ensure that no more than 10 percent of the population served has Lead or Copper present in amounts above the action level by comparing it to the calculated 90th percentile value.
