The link above will take you to the most recent version of the Regional Screening Levels (RSLs) Summary Table (TR=1E-06, HQ=1). The TR=1E-06, HQ=1 means that the values in the table were calculated using a Target Cancer Risk of One (1) in a Million and a Target Hazard Quotient of 1.0. We now exclusively use the EPA RSLs as cleanup levels/screening levels for all environmental media except water, where the EPA RSLs are secondary to the Water Quality Control Division’s Regulation 41.
We use the “Resident Air” and “Industrial Air” sub-columns within the main “Screening Levels” column of the EPA RSL Summary Table when evaluating the results of indoor air samples to determine whether there is a potential human health impact via the air pathway.
We will continue to use the “Resident Soil” and “Industrial Soil” sub-columns within the main “Screening Levels” column of the EPA RSL Summary Table as screening levels to determine whether levels of soil contamination at a site warrant further investigation or cleanup.
We use the “Protection of Groundwater SSLs” that are found in the rightmost column of the most recent version of EPA RSL Summary Table (TR=1E-06, HQ=1)” as Screening Levels Protective of Groundwater Quality in Colorado. Some constituents have two different Protection of Groundwater SSLs. If the ground water beneath, and down gradient of, the Facility is used for drinking water, or is likely to be used in the future, the lowest (most-conservative) value of the “MCL-Based SSL” sub-column and the “Risk-based SSL” sub-column will be applicable as the Protection of Ground Water SSL. Facilities and their consultants are encouraged to work closely with their division project manager to determine the correct Protection of Ground Water SSL to use. We will continue to use standards and method established and employed by the Colorado Water Quality Control Commission as the primary source of surface water and groundwater cleanup levels. EPA RSLs for water may be used when there is no Colorado water standard for a chemical, or in other very specific circumstances.