Human and Ecological Risk Assessment - Earthjustice

Appendix CSite DataOnce the waterbody was identified, the scale provided on the maps and photos was usedto measure the horizontal distance between the CCW impoundment or landfill and thewaterbody. All assignments and measurements were independently checked for accuracy.The two distributions (landfills and surface impoundments) were statistically comparedusing (1) a Wilcoxon Rank Sum Test (to determine whether one distribution is shifted to theright or left of the other distribution) and (2) a Quantile Test (to test for differences, that is,differing numbers of observations) between the two distributions for the values above a givenpercentile. The results of the Wilcoxon test showed a p value of 0.64, indicating no significantdifference in the shape of the distributions. The Quantile Test evaluated every decile from 0.1 to0.9, with adjustments to the lower percentiles to be estimated for large numbers of ties in theranks for the lower end of the data. The nonsignificant p values ranged from 0.33 (for 90thpercentile) to 0.17 (for the 40th percentile). One significant p value indicating differencesbetween the two distributions occurred at the 17th percentile (p value = 0.066), but the remainderof the tests showed no significant differences. Based on these results, the distributions werejudged to be similar and combined to produce the single distribution of 59 values used toproduce a single empirical distribution (previously shown in Table C-2) that was appliednationally to both landfills and surface impoundments at the CCW sites.C.5 ReferencesAller, L., T. Bennett, J.H. Lehr, R.J. Perry, and G. Hackett. 1987. DRASTIC: A StandardizedSystem for Evaluating Pollution Potential Using Hydrogeologic Settings. EPA-600/2-87-035. U.S. Environmental Protection Agency. Office of Research and Development. Ada,OK. April.Carsel, R.F., and R.S. Parrish. 1988. Developing joint probability distributions of soil waterretention characteristics. Water Resources Research 24(5):755–769.Carsel, R.F., R.S. Parrish, R.L. Jones, J.L. Hansen, and R.L. Lamb. 1988. Characterizing theuncertainty of pesticide leaching in agricultural soils. Journal of Contaminant Hydrology2:111–124.Clawges, R.M., and C.V. Price. 1999a. Digital Data Sets Describing Principal Aquifers,Surficial Geology, and Ground-Water Regions of the Conterminous United States.Open-File Report 99-77. U.S. Geological Survey, Rapid City, SD. Available athttp://pubs.usgs.gov/of/1999/ofr99-77/.Clawges, R.M., and C.V. Price. 1999b. Ground-water regions of the conterminous United Stateswith unconsolidated watercourses. Edition: 1.0 (map). In: Open-File Report 99-77(Clawges and Price, 1999a). U.S. Geological Survey, Rapid City, SD. Available athttp://water.usgs.gov/lookup/getspatial?ofr99-77_gwreguw.Clawges, R.M., and C.V. Price. 1999c. Productive aquifers of the conterminous United States.Version 1.0 (map). In Open-File Report 99-77(Clawges and Price, 1999a). U.S.Geological Survey, Rapid City, SD. Available at http://water.usgs.gov/lookup/getspatial?ofr99-77_aquif75m.April 2010–Draft EPA document. C-21