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None of the parameters had a significant effect on the results of the ruggedness test. 9.2 Precision. Many TCLP precision (reproducibility) studies have been performed, and have shown that, in general , the precision of the TCLP is comparable to or exceeds that of the EP toxicity test and that method precision is adequate. One of the more significant contributions to poor precision appears to be related to sample homogeneity and inter-laboratory variation (due to the nature of waste materials) . 9.2. 1 Metals - The results of a multi -laboratory study are shown in Table 6, and indicate that a single analysis of a waste may not be adequate for waste characterization and identification requirements. 9.2.2 Semi -Volatile Organic Compounds - The results of two studies are shown in Tables 7 and 8. Single laboratory precision was excellent with greater than 90 percent of the results exhibiting an RSD less than 25 percent. Over 85 percent of all individual compounds in the multi -laboratory study fell in the RSD range of 20 - 120 percent. Both studies concluded that the TCLP provides adequate precision. It was also determined that the high acetate content of the extraction fluid did not present problems (i .e. , column degradation of the gas chromatograph) for the analytical conditions used. 9.2.3 Volatile Organic Compounds - Eleven laboratories participated in a collaborative study of the use of the ZHE with two waste types which were fortified with a mixture of VOCs. The results of the collaborative study are shown in Table 9. Precision results for VOCs tend to occur over a considerable range. However, the range and mean RSD compared very closely to the same collaborative study metals results in Table 6. Blackburn and Show concluded that at the 95% level of signifi - cance: 1) recoveries among laboratories were statistically similar, 2) recoveries did not vary significantly between the two sample types , and 3) each laboratory showed the same pattern of recovery for each of the two samples. 10.0 REFERENCES 1. Blackburn , W.B. and Show, I . "Collaborative Study of the Toxicity Characteristics Leaching Procedure (TCLP) . " Draft Final Report, Contract No. 68- 03-1958, S-Cubed, November 1986. 2. Newcomer, L.R. , Blackburn, W.B. , Kimmel] , T.A. "Performance of the Toxicity Characteristic Leaching Procedure. " Wilson Laboratories, S-Cubed, U.S. EPA, December 1986. 3. Williams , L.R. , Francis, C.W. ; Maskarinec, M.P. , Taylor D.R. , and Rothman, N. "Single-Laboratory Evaluation of Mobility Procedure for Solid Waste. " EMSL, ORNL, S-Cubed, ENSECO. CD-ROM 1311- 23 Revision 0 July 1992