The land surface of the area surrounding the Pantex Plant site is relatively flat with a gentle, regional slope of about 1.5 to 1.9 m/Km (8 to 10 ft/mi) to the southeast. Maximum and minimum (excluding playa floors) elevations at the site are about 1,103 and 1,109 m (3,585 and 3,530 ft) at the northwest and southeast corners, respectively. The most notable feature of the topography is the presence of numerous playa basins ranging up to about 4.02 km (2.5 mi) in diameter with floors as much as 10 m (30 ft) below the general land surface. Within the playa basins, slopes range up to about five percent. Playas are significant because of their role in collecting surface water and, in some cases, concentrating infiltration to recharge the aquifers. These landforms are the result of a series of intermittently active processes, including wind, fluvial erosion and lacustrine deposition, dissolution of soil carbonate, salt dissolution and subsidence, and animal activities, that collectively produced these typically shallow and roughly circular basins on the High Plains. More than 20,000 playas are present on the High Plains of Texas and New Mexico High Plains and are a contributing source of groundwater recharge for the High Plains aquifer.
In 2005, the EPA and the Texas Commission on Environmental Quality (TCEQ) completed technical reviews of investigations for 251 Solid Waste Management Units (SWMUs), including in operational Zones 11, 12, and the Burning Grounds Area. In 2006, the EPA and TCEQ agreed that investigations of Pantex were complete and no further action was necessary for 105 units identified for Risk Reduction Standard (RRS) 1, 2, or administrative closure. The announcement deferred closure for 16 active sites. Negotiation of the Pantex Interagency Agreement (IAG), also known as the Federal Facilities Agreement (FFA), was initiated June 29, 2007. Final negotiations were completed in November 2007. The (Sitewide) Corrective Measures Study/Feasibility Study (CMS/FS)(May 2007) draft final revision has been approved by the TCEQ, with EPA approval pending. The CMS/FS provides an analysis of remedial alternatives, which will be summarized in the CERCLA Proposed Plan. The draft final Proposed Plan is in review, with approval for publication for public notice and comment anticipated in early March 2008.
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