Conceptual Site Model - Argonne National Laboratory

WVDP Phase 1 CSAP• There are also limited groundwater data for WMA 6 within ELIMS. Figure F.13 showslocations with groundwater results color-coded by Sr-90 activity concentrations. FigureF.14 shows the same for tritium. The detection limits for Sr-90 and tritium varied widelyamong ELIMS samples. 10 pCi/L and 500 pCi/L were selected as thresholds for Sr-90andtritium, respectively, because based on ELIMS data results above these activityconcentrations were consistently above method detection limits and so indicative ofcontamination impacts rather than simply measurement error.The highest groundwater contamination was in the northernmost portion of WMA 6,immediately down gradient of the presumed 1968 Process Building subsurface release. Inaddition there were low level elevated Sr-90 results along the WMA 2 border, with theProcess Building the presumed source.The tritium above-background activity concentrations identified in Figure F.14 just eastof the Railway Spur were in the early 1990s and appeared to be transitory. There are onlytwo groundwater samples with Sr-90 results for this same location, both from the early1990s. For both samples, the Sr-90 results were around 30 pCi/l, indicating Sr-90impacts. There is a fairly continuous set of gross beta information for this location thatappears to indicate on-going elevated gross beta levels over the years, presumablyassociated with Sr-90 impacts. This location is directly east of the Old Sewage TreatmentPlant outfall channel discharge culvert; contamination associated with discharges fromthat culvert may be the source of the groundwater impacts.The cluster of groundwater sampling locations immediately south of the SewageTreatment Plant had what appeared to be very low level gross beta above-backgroundactivity concentrations in the early 1990s along with some tritium results that weremarginally detectable and above background conditions. Any groundwater impacts in thisvicinity would presumably be from Sewage Treatment Plant activities.F.6 Planned Phase 1 DP ActivitiesFor a more complete description of planned Phase 1 DP activities, see the Phase 1 DP, Section3.1 and Section 7.7.Rev. 1 F-9