Human and Ecological Risk Assessment - Earthjustice

Appendix CSite DataHydrologicRegionNumber ofCCWPlantsRegional Surface Water pH Distributions. (continued)No. ofMeasurementsNo. of AnnualMedianValuesAnnual Median pH(triangular distribution)Minimum MaximumWeightedAverageAverageMedian pH7 20 234,589 39 7.6 8.1 7.9 7.88 2 171,643 39 6.9 7.8 7.1 7.29 1 23,038 38 7.5 8.4 7.9 7.910 20 269,570 39 7.6 8.2 8.0 8.011 8 311,768 39 7.4 8.1 7.8 7.812 6 178,990 39 7.0 7.9 7.8 7.613 0 35,355 39 7.0 8.1 8.0 7.914 5 77,041 39 7.9 8.3 8.1 8.115 4 75,145 38 7.7 8.3 8.0 8.016 1 68,581 38 7.5 8.3 8.0 8.017 0 293,909 39 6.9 8.0 7.5 7.418 2 182,049 38 7.4 8.6 7.8 7.8Data source: Legacy STORET database.C.6.4 Distance to Surface WaterBecause the CCW plant locations were not accurate in terms of locating the WMUs, anational empirical distribution of distances between the WMU and the nearest downgradientsurface waterbodies (discussed in Section C.2.1) was developed using manual measurements ononline maps and aerial photographs for a random selection of 30 CCW landfills and 29 CCWsurface impoundments. Scaled USGS maps and aerial photographs were obtained from theTerraserver Web site (http://www.terraserver.com) by entering each plant’s longitude andlatitude. Labels on the maps, features on the photographs, and best professional judgment wereused to identify the power plant and the surface impoundment or landfill in question, along withthe nearest downgradient waterbody.The nearest waterbody matching one of the following descriptions was used in theanalysis:• Lakes or rivers beyond the facility boundary• Streams originating in or passing through the facility boundary and then coursingdownstream beyond the property boundary• Streams with an order of 3 or greater (i.e., fishable waterbodies).Stream order was determined by tracing the convergence of tributaries with order 1 assigned tothe furthest upstream segment indicated on the map (both ephemeral and perennial streams wereassigned as order 1). Topography on the map was used to determine if the waterbody wasdowngradient of the plant. Many CCW WMUs in the sample were located on a large waterbody.April 2010–Draft EPA document. C-20