IDEM vs. EPA Cancer Risk Targets - What the Difference Means for Your Site

IDEM (the Indiana Department of Environmental Management) builds its published screening levels for carcinogens around a target excess cancer risk of 0.00001 (one in one hundred thousand). EPA’s default target for its Regional Screening Levels (RSLs) is 0.000001 (one in one million). That single order-of-magnitude difference in acceptable risk drives most of the cases where an Indiana published level is numerically higher than the corresponding EPA RSL for the same chemical and land use. Here is what that framework looks like and what it means when you are comparing results to IDEM’s tables.

Why the Two Agencies Land at Different Numbers

EPA’s RSLs are screening tools, not cleanup standards. They are calculated at a 0.000001 excess lifetime cancer risk target and are intended to flag sites that may warrant further evaluation, not to define what a state program must require as a cleanup endpoint. States set their own risk targets within a range that EPA considers protective, and IDEM has chosen 0.00001 as its program target for the Risk-based Closure Guide (WASTE-0046-R2). That choice is documented in the R2 guidance itself. Neither target is inherently “wrong” - they reflect policy decisions about where to draw the line on acceptable incremental risk.

The practical result is that IDEM’s published levels for carcinogens are generally higher than EPA RSLs for the same scenario. A consultant screening Indiana soil or groundwater data against EPA RSLs will sometimes see exceedances that would not trigger action under IDEM’s own tables. The reverse is also possible for non-carcinogens, where hazard quotient calculations and reference doses drive the number rather than a cancer risk target, but the cancer risk difference is the most common source of confusion when comparing the two sets of tables.

What This Means When You Are Working an Indiana Site

Voluntary Remediation Program and State Cleanup Sites

If you are working under Indiana’s Voluntary Remediation Program (VRP) or the Indiana State Cleanup Program, the applicable screening levels are IDEM’s published levels, not EPA RSLs. Comparing your analytical results to EPA RSLs and reporting exceedances without noting that IDEM’s own levels may not be exceeded can create unnecessary alarm for clients and reviewers. Always run your data against the current IDEM published levels tables for the correct land use and medium. The IDEM R2 Walkthrough guide on this site covers how those tables are structured.

CERCLA and RCRA Corrective Action Sites

Federal programs at Indiana sites may apply EPA’s 0.000001 risk target rather than IDEM’s 0.00001 target. At a CERCLA site, EPA’s remedial project manager will typically use EPA RSLs as preliminary remediation goals, and the acceptable risk range for a Record of Decision is defined in the National Contingency Plan, not in IDEM’s R2 guidance. If you are working a site with both state and federal oversight, confirm which risk target governs each decision point before you finalize cleanup levels.

Reporting and Risk Communication

When you present screening-level comparisons in a report, state which table you used and what risk target it reflects. A result that is 3x the IDEM published level for a carcinogen is a different finding than a result that is 3x the EPA RSL. Clients and reviewers who see both sets of numbers without context will draw incorrect conclusions about the severity of the exceedance.

Ohio note: Ohio’s Voluntary Action Program (VAP) uses its own risk-based standards published in CIDARS (Chemical Information Database and Applicable Regulatory Standards). Ohio’s generic standards are derived at a 0.00001 (one in one hundred thousand) cancer risk target under OAC 3745-300-08 - the same target IDEM uses, not EPA’s RSL default. The two states’ published levels still differ chemical by chemical because of different exposure assumptions and toxicity inputs, so if you work across the Ohio-Indiana border, do not assume the values are interchangeable for any chemical.

Bottom Line

The tenfold difference between IDEM’s 0.00001 and EPA’s 0.000001 cancer risk targets means Indiana’s published levels for carcinogens will often be numerically higher than EPA RSLs for the same chemical and land use. Screening Indiana data against EPA RSLs without accounting for this difference overstates exceedances under the applicable state standard. Always identify which risk target and which table governs the decision at hand, and document that clearly in your report. For a detailed walkthrough of how IDEM’s published levels tables are organized, see the IDEM R2 Walkthrough and the How to Read IDEM Published Levels Tables guides on this site.