Evaluation of groundwater monitoring results at the Hanford Site 200 Area Treated Effluent Disposal Facility

Abstract

SummaryThe Hanford Site 200 Area Treated Effluent Disposal Facility (TEDF) has operated since June 1995.Groundwater monitoring has been conducted quarterly in the three wells surrounding the facility since 1992, with contributing data from nearby B Pond System wells.Cumulative hydrologic and geochemical information from the TEDF well network and other surrounding wells indicate no discernable effects of TEDF operations on the uppermost aquifer in the vicinity of the TEDF. The lateral consistency and impermeable nature of the Ringold Formation lower mud unit, and the contrasts in hydraulic conductivity between this unit and the vadose zone sediments of the Hanford formation suggest that TEDF effluent is spreading laterally with negligible mounding or downward movement into the uppermost aquifer.Hydrographs of TEDF wells show that TEDF operations have had no detectable effects on hydraulic heads in the uppermost aquifer, but show a continuing decay of the hydraulic mound generated by past operations at the B Pond System. Comparison of heads in the uppermost aquifer immediately northwest of the TEDF with the head in a well in the same area which is screened in the Rattlesnake Ridge Interbed (upper basalt confined aquifer), indicate that hydraulic heads in the two aquifers are converging as the hydraulic mound at the B Pond System subsides. Further southeast, near TEDF, an upward hydraulic gradient may already exist, making potential of incursion of groundwater fiom the upper basalt confined aquifer to the unconfined aquifer (uppermost aquifer beneath TEDF) more likely. This condition would further hamper downward movement of effluent of TEDF into the uppermost aquifer, particularly if no substantial groundwater mound is created beneath the TEDF.Comparison of groundwater geochemistry fiom TEDF wells and other, nearby RCR4 wells suggests that groundwater beneath TEDF is unique; different from both effluent entering TEDF and groundwater in the B Pond area. Tritium concentrations, major ionic proportions, and lower-than-background concentrations of other species suggest that groundwater in the uppermost aquifer beneath the TEDF bears characteristics of water in the upper basalt confined aquifer system. This report recommends retaining the current groundwater well network at the TEDF, but with a reduction of samplinghnalysis frequency and some modifications to the list of constituents sought.iii

Revised Hydrogeology for the Suprabasalt Aquifer System, 200-East Area and Vicinity, Hanford Site, Washington

“…Gephart et al (1976) and Hartman (1999) discuss the influence of wastewater discharge at the 216-B-3 Pond (B-Pond) and associated lobes. Barnett (1998) discusses the influence of wastewater discharge at the 200-East Areas Treated Effluent Disposal Facility (TEDF).…”

“…The Tri-Party Agreement (TPA) milestone M-17-00A defined the schedule to discontinue disposal of contaminated liquids into the soil column and cease all liquid discharges to hazardous waste land disposal units (ponds, cribs, and ditches) at the Hanford Site by 1995 (Ecology et al 1989). By 1997, all discharge to the B-Pond disposal had ceased, and some of the former B-Pond effluent streams were rerouted to the TEDF (Barnett 1998). Concurrent with the decreased waste-water discharge in the 200-East Area and B-Pond facility since the late 1980s, the water table (and the potentiometric surface) near B-Pond has declined.…”

Groundwater Monitoring Plan for the Hanford Site 216-B-3 Pond RCRA Facility

“…This feature suggests that tritium, and presumably effluent from the B Pond, may not have migrated southeast of this line. In fact, low level analyses for tritium from wells at the TEDF indicate levels of tritium below natural background for the uppermost aquifer (Barnett 1998), thus suggesting a relatively old age for groundwater at this location. Analyses for tritium in these wells have been performed since 1992 or earlier.…”