May 23, 2011

Memorandum to the Docket Listing Additional Information to Update and to Enhance the Risk Assessment, 

New Toxicological Benchmarks, and EPA Exposure Guidance

1. New human health toxicological benchmarks have been developed since the preparation of EPA‟s 2010 Risk 

Assessment. Benchmarks used in the 2002 risk screening, “Constituent Screening for Coal Combustion 

Wastes,” were updated in 2002 and the benchmarks used in the 2010 Risk Assessment were updated in 2009. 

EPA is considering new values in accordance with the hierarchy outlined in the EPA Office of Solid Waste and 

Emergency Response 2003 Human Health Toxicity Values in Superfund Risk Assessments Memorandum 

(Directive 9285.7-53) available on-line at: www.epa.gov/oswer/riskassessment/pdf/hhmemo.pdf. 

a. Integrated Risk Information System (IRIS) benchmarks, available on-line at: www.epa.gov/iris/.

b. Provisional Peer-Reviewed Toxicity Values (PPRTVs), available on-line at: 

http://hhpprtv.ornl.gov/quickview/pprtv_papers.php.

c. An IRIS cancer slope factor (CSF) for arsenic is still under revision. As well as using the current IRIS 

benchmarks for arsenic, EPA is considering using an updated CSF used in the 2010 proposed rule‟s RIA at: 

www.regulations.gov (EPA-HQ-RCRA-2009-0640-0003). This CSF is based on National Research 

Council„s (NRC) Arsenic in Drinking Water (1999) and NRC Arsenic in Drinking Water: 2001 Update. 

These documents are available at http://www.nap.edu/openbook.php?isbn=0309063337&page=R1 and 

http://www.nap.edu/catalog.php?record_id=10194 respectively.

d. An oral CSF for chromium (VI) is being developed by IRIS. To evaluate this endpoint, EPA is considering 

using a New Jersey Department of Environmental Protection CSF as a Tier III value. NJDEP 2009. 

“Derivation of Ingestion-Based Soil Remediation Criterion for Cr+6 Based on the NTP Chronic Bioassay 

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

OFFICE OF

SOLID WASTE AND EMERGENCY

RESPONSE
Data for Sodium Dichromate Dihydrate.” Available in the docket supporting this Notice (EPA-HQ-RCRA2011-0392) and on-line at: http://www.nj.gov/dep/dsr/chromium/

2. EPA is considering updating ecological toxicity benchmarks based on: 

a. EPA‟s ecological soil screening levels for soil receptors available on-line at: www.epa.gov/ecotox/ecossl/.

b. EPA‟s ambient water quality criteria for aquatic receptors available on-line at: 

http://water.epa.gov/scitech/swguidance/standards/current/index.cfm.

c. EPA is also considering the use of the National Oceanic and Atmospheric Administration‟s SQuiRTs 

(Screening Quick Reference Tables) available in the docket supporting this Notice (EPA-HQ-RCRA-2011-

0392) and on-line at: http://response.restoration.noaa.gov/book_shelf/122_NEW-SQuiRTs.pdf.

d. One commenter, the Utility Solid Waste Activities Group (USWAG), provided an ecological benchmark for 

boron (See Appendix 20, pages 4-13 and 4-14 of EPA-HQ-RCRA-2009-0640-10483.1 available at 

www.regulations.gov). 

3. New EPA human exposure guidance has become available. 

a. Guidance on Selecting Age Groups for Monitoring and Assessing Childhood Exposures to Environmental 

Contaminants, 2005 (EPA/630/P-03/003F) available on-line at: www.epa.gov/raf/publications/guidance-onselecting-age-groups.htm.

b. Child-Specific Exposure Factors Handbook, 2008 (EPA/600/R-06-096F) available on-line at: 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=199243.