Human and Ecological Risk Assessment - Earthjustice

Appendix CSite DataTable C-5. Hydrogeologic Environments for CCW Disposal SitesHydrogeologic EnvironmentNumber of CCW Sites1 Metamorphic and Igneous 132 Bedded Sedimentary Rock 443 Till Over Sedimentary Rock 174 Sand and Gravel 175 Alluvial Basins Valleys and Fans 36 River Valleys and Floodplains With Overbank Deposit 767 River Valleys and Floodplains Without Overbank Deposits 208 Outwash 49 Till and Till Over Outwash 010 Unconsolidated and Semiconsolidated Shallow Aquifers 2011 Coastal Beaches 112 Solution Limestone 20C.5 Climate DataThe CCW risk assessment selected EPACMTP meteorological (or climate) stations foreach CCW disposal site to collect the climatic data necessary for fate and transport modeling.For each station, the following data were compiled:• Mean annual windspeed• Mean annual air temperature• Mean annual precipitation.With respect to precipitation, EPACMTP uses the climate station, along with soil texture, toselect the HELP-modeled infiltration rates to use in the landfill source model and recharge ratesto use in EPACMTP (see Section 3.2.2). The surface water model uses mean annual windspeedand average air temperature to estimate volatilization losses from the surface waterbodiesmodeled in the analysis.To assign the EPACMTP/HELP climate centers to each CCW site, a GIS was used todetermine the three meteorological stations closest to the plant. These assignments were passedto a meteorologist, who reviewed the closest stations against plots of the CCW sites and theclimate centers on a downloadable map (http://www.nationalatlas.gov) of annual averageprecipitation rates for the period from 1961 to 1990 across the contiguous United States.(Figure C-2). The meteorologist compared the 5-year average precipitation range for eachEPACMTP climate center to precipitation ranges for each plant from the map. In most cases, theprecipitation rate for the nearest climate center fell within the site’s expected precipitation range,and the nearest climate center was assigned in those cases. In some cases, the precipitation ratesfrom the nearest climate center did not fall within the site’s expected range. When this occurred,the second or third closest climate center was examined and matched based on:• A 5-year precipitation average within or close to the site’s predicted precipitation rangeApril 2010–Draft EPA document. C-11