United States Environmental Protection Agency

Washington, D.C. 20460

Office of Solid Waste and Emergency Response

April 2, 1993

Debra K. White

Chief Inorganic Scientist

Enseco Technology Group

Enseco, Inc.

4955 Yarrow Street

Arvada, Colorado 80002

Dear Ms. White:

Thank you for your letter of March 18, 1993 concerning the November 24, 1992 Federal Register notice on revisions to the Toxicity Characteristic Leaching Procedure (TCLP).

In response to your first question regarding the conditions under which the method of standard additions (MSA) must be run for metallic contaminants in TCLP samples, both conditions listed in the FR notice must be met before MSA is required. These criteria are linked together. Unless both are met, MSA is not required. The intent here is to lighten the burden on laboratories. If a waste is clearly hazardous or clearly non-hazardous further testing is unwarranted. It is those cases where the analyte is near the regulatory limit that additional work is required to prove its "true" concentration.

Your second question concerns the proper procedure for administering the method of standard additions, when MSA is required. You should do the full 4-point procedure as stated in the Federal Register notice. This overrides the QC procedures for MSA found in Method 7000 and 6010.

I hope that this information will be of use to your analytical program. If you have any further questions, please feel free to call me at (202) 260-4778.


Oliver Fordham

National Inorganic Program Manager for RCRA