National Cost of Compliance With a Drinking Water <scp>MCL</scp> for Hexavalent Chromium

ABSTRACT With the publication of the toxicological review for hexavalent chromium, Cr(VI), the US Environmental Protection Agency may be initiating the process to develop a Maximum Contaminant Level (MCL) for Cr(VI) in US drinking water. This study developed national costs of compliance with Cr(VI) MCLs between 5 and 20 μg/L. All California water systems were excluded from the costs for MCLs of 10 μg/L and greater since California already adopted an MCL of 10 μg/L. For a national MCL of 10 μg/L, the minimum non‐California capital cost is projected to be between $3.8B and $8.2B, with the minimum annual O&amp;M cost ranging from $340M/year to $720M/year in 2024 dollars. The total population impacted by this MCL is projected at 4.36 million people. For communities smaller than 101 people, the minimum 2024 household cost for this MCL may have a 5th percentile value of $566/year and a 95th percentile value of $1611/year.