Colorado Soil Evaluation Values (CSEV) and EPA Regional Screening Levels (RSL)

Update on the Division's New Approach to Soil Screening Numbers

For the last few years, the Division has published health-based screening numbers in its Colorado Soil Evaluation Values (CSEV) table, the most recent version dated July 2011. Historically, numbers in the CSEV table were calculated using a mix of both EPA and Colorado specific methods and assumptions used for assessing risk and calculating soil screening numbers. However, in light of the fact that a) with each passing year, Colorado adopted more of the EPA approach, and b) in recognition of EPA's decision to harmonize the Region 3, 6 and 9 numbers into a single table, the Division was faced with the question of whether it was worthwhile maintaining the CSEV table considering that the differences between it and the national table were relatively small. After considering the benefits of adopting the EPA Regional Screening Levels (RSL) table versus the cost in time and money having to maintain Colorado's version of that table, a decision was made to be consistent with the nation and use the EPA RSLs to determine whether levels of contamination found at a site may warrant further investigation or cleanup, or whether no further investigation or action may be required.

Rather than delay this change, after November 28, 2012 the Division will use the RSL and CSEV tables in the following fashion:

Screening Levels for Residential and Industrial Worker Exposure Scenarios

From this point forward, the Division will be using the direct exposure levels for residential and industrial exposure scenarios listed in the EPA RSLs. This table, which EPA updates on a regular basis, can be found at:

http://www.epa.gov/reg3hwmd/risk/human/rb-concentration_table/Generic_Tables/index.htm

Please use one of the links to the Summary Table in the top row of links.

Another benefit of adopting the national approach to calculating screening levels is that EPA also has a Calculator that can be used to adjust the input parameters for the purpose of coming up with site-specific RSLs. A link to this feature is provided on the web page referenced above. A useful background document and User's Guide identifying the toxicity values, equations and exposure assumptions used to calculate RSLs is also provided on this web page.

Screening values presented in the RSL table are based on human health risk from the combined exposure of direct soil ingestion, dermal contact with soil, and inhalation of vapors or particulates associated with soil. Other pathways, such as indoor air or food chain effects, may need to be consdered on a site-specific basis. Users should also be aware that some sites in sensitive ecological settings may need to be evaluated for potential ecological risk. In addition, please continue to take into consideration the following:

Colorado Department of Public Health and Environment-specific toxicity values such as an inhalation Reference Concentration (RfC) of 7.0 ug/m³ for 1,1-dichloroethylene (1,1-DCE) and an oral Reference Dose (RfD) of 0.0011 mg/kg/day for diisopropyl methylphosphonate (DIMP).
For facilities where multiple non-carcinogenic chemicals are present, HQ values should be divided by a factor of 10 to account for additivity. If adjusted tables values are exceeded, consultation with a toxicologist is recommended to assess likely impact on specific target organs.
For lead, consideration of site-specific inputs to the IEUBK or ALM lead models and consultation with a toxicologist is strongly recommended for facilities with lead levels in soil that exceed the residential or worker table values. Contact the Division for additional information about details of the lead models and site-specific considerations.
For workers at facilities where soil-intensive use is anticipated, additional analysis and consultation with a toxicologist will be required to determine appropriate site-specific inputs to the risk equations.

Screening Levels Protective of Groundwater Quality

The Division will continue using the Groundwater Protection Level and Leachate Reference Concentration columns in the CSEV table, the last column in that table identifying the water standard used in the calculations which are based on standards and methods established and employed by the Water Quality Control Commission.

Colorado Soil Evaluation Values (CSEV) Table pdf file

These two columns should be consulted when reviewing site data because in some cases, decisions on whether or not further evaluation or remediation are needed may be based on the mobility of constituents and their potential to reach and degrade groundwater quality.

Air Screening Concentrations

Although the method by which the Division calculates air exposure screening numbers is identical to the method used by EPA, there are a few differences between our Air Screening Concentration Table and air columns listed in the RSLs. You are therefore advised to continue using the Division's air table.

Air Screening Concentrations Table pdf file

Target indoor air concentrations for those chemicals not included on the Division's list may be found in the EPA RSL table.

Next Steps

When time permits, the Division will modify the CSEV table to only show the Groundwater Protection Level, Leachate Reference Concentration and the Water Standard columns, relying entirely on the EPA RSLs for the direct exposure soil concentrations. The groundwater protection numbers for certain constituents will need be modified in light of the recent changes approved by the Water Quality Control Commission that go into effect on January 31, 2013.

If you have questions about the derivation or application of these table values, please contact the Division by email sent to comments.hmwmd@state.co.us . Please be sure to put "Avramenko" in the subject line.