Following the table across, the action level is a concentration that triggers some type of control or treatment. The AL for lead and copper is based on the 90 percent rule - 90 percent of all samples taken must be below the AL. Buckley's 90th percentile result was .5 parts per million for copper and less than 2 parts per billion for lead. Maximum contamination level is the limit below which there is no known or expected risk to health. Buckley did not violate the lead and copper rule.