Conceptual Site Model - Argonne National Laboratory

WVDP Phase 1 CSAP• In 1990 and 1991 a second static direct exposure measurement program was conductedacross the WVDP premises (WVNSCO 1992). In the case of WMA 7, this effortprovided systematic coverage of its entire area on a 10-m grid. This data collection useddifferent instrumentation and protocols than the 1982 study, so the results are notquantitatively comparable. Figure G.13 shows these results overlain on a 1995 aerialphotograph.• There are very little soil sampling data for WMA 7 available within ELIMS. In 1993 twosurface samples were collected and two soil cores were obtained. Figure G.14 shows theCs-137 and Sr-90 results for surface samples from these locations. The locations in thenortheastern corner showed Cs-137 and Sr-90 impacts. None of the samples were inlocations where one would expect to see the highest levels of impacts, based on thehistorical gamma measurements. Table G.1 identifies the number of locations analyzedfor each of the 18 primary radionuclides of interest.• There is a fair amount of historical groundwater sampling data available for WMA 7within ELIMS. Figure G.15 shows groundwater sampling locations color-coded byhistorical Sr-90 results. Figure G.16 shows the same for tritium results. In both cases thevarious wells displayed are screened in different geological units. The detection limits forSr-90 and tritium varied widely among ELIMS samples. 10 pCi/L and 500 pCi/L wereselected as thresholds for Sr-90 and tritium, respectively, because based on ELIMS dataresults above these activity concentrations were consistently above method detectionlimits and so indicative of contamination impacts rather than simply measurement error.As is evident from these two figures, there have been groundwater impacts in the vicinityof WMA 7, particularly to the north and northwest. Contaminated groundwater in thisarea is shallow and likely discharges via wetlands, ditches, and seeps to Erdman Brook,which runs along the north edge of WMA 7 and is fed by two drainage featuresoriginating within WMA 7.G.6 Planned Phase 1 DP ActivitiesThe remaining gravel pad associated with the NDA Hardstand will be removed along with the toptwo feet of soil (DOE 2009 Sections 3.1 and 7.8).Rev. 1 G-9