Conceptual Site Model - Argonne National Laboratory

WVDP Phase 1 CSAPthe area to enter the Old Sewage Treatment Plant. An estimated 0.5 Ci gross beta and 0.05 Ci ofSr-90 was released. The Old Sewage Treatment Plant and its outfall drainage were contaminatedto 1 mR/h, with effluent concentrations subsiding after the leak was repaired. Affected outfallswere located in WMA 6 and included the Old Sewage Treatment Plant drainage channel witheventual discharge to Erdman Brook (DOE 2009 Table 2-17; DOE 2010 Section 3.11.5).In addition, during the 1960s and 1970s, the Old Sewage Treatment Plant experienced severalother contamination events, some of which were expressed as radioactivity increases in thetreated effluent. The Old Sewage Treatment Plant outfall drainage extends approximately 650feet south of a culvert near the Old Warehouse (also in WMA 6), and flows into the first culvertunder the railroad tracks on the South Plateau (in WMA 6), and then to Erdman Brook (inWMA 6 and WMA 12 South). Actions were taken to find and repair a suspected sewage lineleak, but when the line near the south side of the Process Building was excavated, radiation levelsfrom soil contamination hampered the project.A 1982 gamma radiation survey of the Old Sewage Treatment Plant drainage channel showedlevels three feet above the surface ranging from 110 to 500 μR/h on a section of the channel thatextended approximately 200 feet south of the discharge culvert. The contaminated portion of thearea was about 15 feet wide and 600 feet long, the northern 200 feet of which exhibitedsignificant contamination in sediments represented by an 800 pCi/g Cs-137 sample result fromthe channel sediments, and up to 1 mR/hr near the surface of the drainage channel. The sedimentlayer was estimated to be at least a foot thick. In order to prevent further contaminant transportdownstream, a new drainage channel was excavated to the west of the contaminated channel, andthe spoil was placed over the old channel. At least three feet of soil covers the old drainagechannel sediment (DOE 2009 Section 2.3.2).F.5 Existing DataExisting data sets for this area include:• In 1982, static direct exposure readings were collected across the WVDP premises(WVNSCO 1982). All of WMA 6 was covered by these measurements on a 10-m grid.Figure F.10 shows these results color-coded by the exposure readings encountered, withthe data overlain on a 1977 aerial photograph. Interpretation of these data in the vicinityRev. 1 F-7