Ohio VAP Groundwater Standards - Metals

Overview

Ohio’s VAP establishes unrestricted potable use standards (UPUS) for metals in groundwater under OAC 3745-300-08. The UPUS is the lower of the risk-based groundwater concentration and the Safe Drinking Water Act MCL for each contaminant. For most metals, the MCL is the governing standard because it’s lower than the risk-based number.

The values below are from the current CIDARS database (February 2025 version, accompanying the VAP rules effective February 16, 2025).

Key point: The VAP UPUS applies when groundwater is classified as a potable use resource. If groundwater is classified as non-potable (based on yield, TDS, urban setting designation, or other criteria under OAC 3745-300-07), different standards may apply.

Unrestricted Potable Use Standards - Metals

Practical Notes for Consultants

Arsenic - The Number Everyone Gets Wrong

Arsenic is the metal that causes the most confusion at Ohio sites. The MCL is 10 µg/L, which is what the UPUS uses. But the risk-based groundwater number is 0.5 µg/L - twenty times lower. This matters because:

• If you’re doing a property-specific risk assessment (PSRA) under OAC 3745-300-09 instead of using generic standards, the 0.5 µg/L risk-based number is the starting point, not the MCL.
• Natural background arsenic concentrations in Ohio groundwater frequently exceed the risk-based value of 0.5 µg/L, and sometimes exceed the MCL of 10 µg/L, particularly in western Ohio glacial deposits.
• If your site has arsenic above the MCL, you’ll need to determine whether it’s attributable to the site or represents natural background. Ohio EPA’s Technical Guidance Manual for groundwater monitoring has guidance on background characterization.

Hexavalent Chromium - The Speciation Trap

The VAP has three separate entries for chromium: Cr(III) at 22,000 µg/L, Cr(VI) at 0.35 µg/L, and total chromium at 100 µg/L. The standard you use depends on whether you perform speciation analysis.

If you analyze for total chromium only and the result is below 100 µg/L, you’ve met the MCL. But if there’s any reason to suspect hexavalent chromium (plating operations, industrial sites), you should run speciation - because total chromium at 50 µg/L could pass the total Cr MCL while the hex chrome fraction alone could exceed the 0.35 µg/L risk-based standard by orders of magnitude.

In practice, request dissolved metals analysis (field-filtered through 0.45 µm) alongside total metals, and add chromium speciation (EPA Method 218.6 or 218.7) if the site history warrants it.

Lead - Not a Simple MCL

Lead and copper are regulated under the Lead and Copper Rule (LCR), not through traditional MCLs. The 15 µg/L value is an action level measured at the consumer’s tap, not a health-based MCL in the traditional sense. The VAP uses this value as the UPUS for lead, but be aware that EPA has revised its residential soil screening level for lead to 200 mg/kg (down from 400 mg/kg), which may eventually influence how Ohio handles lead at cleanup sites.

For lead specifically, the VAP also provides a fixed GDCSS for soil (200 mg/kg residential) that is not calculated from the standard risk equations - it’s set by rule.

Dissolved vs. Total Metals

When collecting groundwater samples for metals analysis, the distinction between dissolved and total metals matters. For VAP compliance:

• Total metals (unfiltered) is the default for comparison to UPUS unless the site-specific evaluation justifies dissolved results
• Dissolved metals (field-filtered through 0.45 µm) should be collected alongside total metals - this helps distinguish between dissolved-phase contamination (mobile, bioavailable) and particulate metals (from turbid samples, not necessarily representative of aquifer conditions)
• High turbidity in monitoring well samples can artificially elevate total metals concentrations. If your total metals results seem anomalously high, check the turbidity - values above 10 NTU suggest the sample may not be representative

Low-flow sampling (as described in our groundwater sampling guide) minimizes turbidity and produces more representative metals results.

Related Resources

• Ohio VAP Soil Standards - Metals - Companion soil standards for metals
• Ohio VAP Groundwater Standards - VOCs - VOC groundwater standards
• Ohio VAP Program Overview - How the VAP works
• Low-Flow Groundwater Sampling Guide - Sampling procedures that produce valid metals results
• Cleanup Levels vs. Screening Levels vs. MCLs - Why the arsenic MCL and risk-based value diverge, and how that affects site decisions