Conceptual Site Model - Argonne National Laboratory

WVDP Phase 1 CSAPtwo ends of this section are capped. This section was originally used to transfer liquids from theSDA lagoons via a pump house next to the NDA Hardstand to Lagoon 1.Former Lagoon. This lagoon, formerly used by NFS for collecting surface water runoff, waslocated beneath the former Interim Waste Storage Facility floor slab in the northeastern portion ofthe NDA. Around 1972 it was filled with radiologically contaminated soil from cleanup after aHEPA filter was dropped at the NDA during disposal operations.The Interim Waste Storage Facility floor slab was removed in May 2008 as required for theplanned installation of the Geomembrane Cover over the NDA; the Geomembrane Cover wasinstalled in the fall of 2008.Groundwater Barrier Wall. In July 2008, a subsurface groundwater barrier wall was installed onthe southwest and southeast sides of the NDA to minimize groundwater migration into the NFSWaste Disposal Area. This barrier wall is a soil-bentonite slurry wall with a maximum hydraulicconductivity of 1E-07 cm/s that is keyed at least five feet into the underlying unweathered LaveryTill. The slurry wall is approximately 850 feet long, three feet wide, and is 15 to 20 feet deep.Geomembrane Cover. In the fall of 2008 the NDA was covered with XR-5, an ethylene interpolymeralloy geomembrane, to limit infiltration of precipitation into the NFS Waste DisposalArea. During installation of the XR-5 geomembrane, imported backfill was placed on the surfaceof the NDA and the surface was graded to form a suitable foundation for the geomembrane.G.2 Physical SettingThe WMA 7 area is located on the South Plateau, and is bounded by WMA 12 South to the north,WMA 6 to the west, WMA 9 to the south, and WMA 8 to the east.The WMA 7 area was originally relatively flat and farmed prior to site development. After sitedevelopment began, the majority of the WMA 7 area was used for the NDA, or for NDA supportactivities, with the surface reworked several times over the years. In its current configuration, theWMA 7 area includes the capped NDA, a groundwater barrier wall that wraps around the westand south boundary of the NDA, a groundwater interceptor drain that wraps around the north andRev. 1 G-5