these estimates is caused by the need to make certain assumptions, such as the thickness of the contaminated layer. However, for the period evaluated, the trends in parameters suggest a relatively constant level of contamination, but with some variability. At the 618-11 sub-region, monitoring results since 1999 show decreasing tritium concentrations at wells closest to the source and variable concentrations at wells along the downgradient migration pathway. This plume has not reached the Energy Northwest water supply wells, nor the Columbia River. At the 316-4/618-10 sub-region, COPC are currently at levels below the drinking water standards, except for very recent samples from two wells near the 316-4 cribs excavation site that show concentrations near the 30-ug/L standard for uranium. A revised strategy for categorizing waste constituents in groundwater as a COC or COPC, along with the implications for remedial actions and regulatory decisions, is proposed. As a result, the lists developed during the remedial investigation have been shortened, primarily because of improving conditions and lack of evidence suggesting unacceptable risk. Conceptual Site Model for 300 Area Uranium. The 300 Area uranium plume can be characterized as persistent, i.e., the area and concentrations have remained similar to early 1990 conditions. There has been variability in spatial and temporal distribution patterns, primarily as a consequence of (a) cessation of liquid waste disposal to the ground, (b) large-scale source excavation activities, (c) unusually high and prolonged water table conditions during 1996 and 1997, and (d) seasonality because of river-stage fluctuations. During the most recent years, the plume appears to be relatively stable, with evidence showing gradual downgradient migration to the Columbia River. The highest concentrations observed currently are along the shoreline, and probably reflect the last significant input from beneath former major waste sites, such as the 316-5 process trenches. Uranium is lost from the plume via discharge to the river and groundwater withdrawal at a water supply well. Some amount of re-supply to the plume is believed to occur as a consequence of long-term release of uranium that has been sequestered on vadose zone and aquifer solids. The mobility of uranium and controls on dissolved concentrations are influenced by the geochemistry of the original waste effluent, the receiving sediment, and pore fluids, all of which vary in the 300 Area environment. The compositional and spatial variability leads to complexity in computer models designed for predicting plume behavior. The heterogeneity in conditions also drives the need for more field data on the locations, inventory, and geochemical characteristics of uranium in potential source zones. Conceptual Site Model for 618-11 Tritium. The tritium plume associated with the 618-11 sub-region has apparently been created by episodic release of tritium gas from irradiated materials in the burial ground. The gas interacts with moisture in the vad...

I 20. I A BD-7400-172-2 (04/94) GEF097 21. DOE APPROVAL iir required) U Approved Approved u/ccmnerits tl Disapproved w/connnts Ctrl. No.

This report catalogs geophysical borehole data acquired between January 1, 1958 and April 8, 1980 for nearly 800 wells on and around the Hanford Site. These data have been placed in a format that can be easily adapted to a computerized data management system. Maps are provided for quick identification of specific wells. Each well is classified according to the amount of geophysical logging data available. A cross reference between common well name and the Hanford grid name is given to eliminate confusion among various sources of data.

This document presents a groundwater quality assessment monitoring plan, under Resource Conservation and Recovery Act of 1976 (RCRA) regulatory requirements found in WAC 173-303-400, and by reference, requirements in 40 CFR 265(d)(3) and (d)(4), for three RCRA sites in the Hanford Site's 200 East Area: 216-A-10, 216-A-36B, and 216-A-37-1 cribs (PUREX cribs). The objectives of this monitoring plan are to combine the three facilities into one groundwater quality assessment program and to assess the nature, extent, and rate of contaminant migration from these facilities. A groundwater quality assessment plan is proposed because at least one downgradient well in the existing monitoring well networks has concentrations of groundwater constituents indicating that the facilities have contributed to groundwater contamination. The proposed combined groundwater monitoring well network includes 11 existing near-field wells to monitor contamination in the aquifer in the immediate vicinity of the PUREX cribs. Because groundwater contamination from these cribs is known to have migrated as far away as the 300 Area (more than 25 lan from the PUREX cribs), the plan proposes to use results of groundwater analyses from 57 additional wells monitored to meet environmental monitoring requirements of U.S. Department of Energy Order 5400.1 to supplement the near-field data. Assessments of data collected from these wells will help with a future decision of whether additional wells are needed. The near-field network wells will be sampled semiannually except for three wells (one near each facility) that will be sampled quarterly. Groundwater samples from the near-field wells will be analyzed for turbidity, phenols, ICP metals, anions, gross alpha, gross beta, alkalinity, ammonium ion, arsenic, 12?, 3H, %r, and the field parameters pH, specific conductance, temperature, and turbidity. Far-field network wells will be sampled annually for anions, 3H, 12?, and the field parameters pH, specific conductance, temperature, and turbidity. A recently installed well (699-37-47A) will be sampled quarterly for one year to assess the initial water quality for that specific well and then will be scheduled for semiannual sampling like the other near-field network wells.

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process dmlosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, m mmendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.