Lead and copper 90th percentile calculator
Put tap sample results in order and find the 90th percentile the way 40 CFR 141.80(c)(3) describes it, then compare it with the lead and copper action levels in the 2024-revised rule.
90th percentile, 2024-revised Subpart I Our calculation
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Enter at least one result.
Dates
This tool follows Subpart I as revised in 2024. Systems must comply with it no later than November 1, 2027, except where the rule says otherwise:
“Community water systems and non-transient non-community water systems must comply with the requirements of this subpart no later than November 1, 2027, except where otherwise specified in §§ 141.81, 141.84, 141.85, 141.86, and 141.90, or where an exemption in accordance with 40 CFR part 142, subpart C or F, has been issued by the Administrator.”
Until then, the earlier text applies, with listed additions:
“Between October 30, 2024, and November 1, 2027, community water systems and non-transient non-community water systems must comply with 40 CFR 141.2, 141.31(d), and 141.80 through 141.91, as codified on July 1, 2020,”
Which results go in the list
The count above follows 141.80(c)(3)(i), for systems whose sites are all Tier 3, 4 or 5. Systems with enough Tier 1 and 2 sites use (c)(3)(ii), which counts the same way but says which result per site goes in the list:
“For lead, water systems must include the higher of the first-liter and fifth-liter lead sample results at each Tier 1 and 2 site (or first-liter lead sample if tiering is based on premise plumbing) taken during the tap sampling period in paragraphs (c)(3)(ii)(B) through (D) of this section.”
A study aid, not a compliance determination. It does not cover (c)(3)(iii) (too few Tier 1 and 2 sites), the sample eligibility rules in § 141.86(e), or State decisions. Your State may set stricter requirements.
A study aid, not legal or compliance advice. goraedu does not certify water operators, and our questions are not a state operator certification exam. Not affiliated with or endorsed by the U.S. EPA, any state drinking water program or any operator certification body. Spot an error? Tell us.