Human and Ecological Risk Assessment - Earthjustice

Appendix CSite DataRF1 Reach Types Assigned to CCW Disposal Sites. (continued)RF1Code RF1Name DescriptionReaches with Zero RF1 FlowCGLWCoastal/ContinentalShoreline SegmentGreat LakesShoreline SegmentLake ShorelineSegmentWide-RiverShoreline Segmenta R = river; L = lake.A reach that represents a segment of a shoreline of a gulf,sea, or ocean.A reach that represents a segment of a shoreline of theGreat Lakes.A segment that follows the shoreline of a lake other thanone of the Great Lakes.A reach that represents a segment of the left or right bankof a stream.ReachModelType aNumberof CCWPlantsL 3L 12L 36L 5Stream dimensions were calculated from the flow data as follows. First, the length of themodeled stream segment was set to be the width of the groundwater plume as it enters thewaterbody. Stream width was then determined from flow (Q) using a liner regression equationderived from empirical data by Kocher and Sartor (1997):Width 0.45595.1867Q(C-1)Water column depth (dwc) was derived from width, velocity (V), and flow using the continuityequation:dwcQ (C-2)v WidthC.6.2. Lake Flow Conditions and DimensionsAreas and depths for many of the lakes assigned to the CCW plant sites were not readilyavailable from RF1, Reach File Version 3 (RF3), the National Hydrography Dataset (NHD), orother sources. In addition, many plants were located on very large waterbodies (e.g., the GreatLakes, wide rivers, or coastlines), where applying the simple steady-state, single-compartmentmodel used in this analysis to the entire lake would not be appropriate. For these reasons, amodel lake approach was used to represent all lakes and other nonflowing waterbodies assignedto the CCW disposal site.The model lake chosen was Shipman City Lake in Illinois, a well-characterized 13-acrelake that EPA has chosen as the index reservoir for modeling drinking water exposures topesticides (Jones et al., 1998). The parameter values shown in Table C-8 for Shipman City Lakewere used to model all lakes in this initial analysis. Given that many of the lakes assigned toCCW plants were much larger than 13 acres, this produced high-end risk results. However, giventhat many of the plants were located on very large waterbodies, this necessary simplification isan uncertainty in defining the environmental settings for the CCW risk assessment.April 2010–Draft EPA document. C-16