ML20027C023
| ML20027C023 | |
| Person / Time | |
|---|---|
| Site: | 02700039 |
| Issue date: | 09/20/1982 |
| From: | Siefken D NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Hawkins E NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| References | |
| NUDOCS 8210120320 | |
| Download: ML20027C023 (6) | |
Text
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R JBMartin DTM 613-8 REBrowning DLSiefken DOCKET 27-39 EFHawkins RAScarano JAShaffner MEMORANDUM FOR:
Edward F. Hawkins, Section Leader s
Low-Level Waste Licensing Branch c r EG. III Division of Waste Management BChasnoff, IL St.
P. Gustafson FROM:
David L. Siefken Low-Level Waste Licensing Branch Division of Waste Management
SUBJECT:
NOTES OF STEERING COMMITTEE MEETING FOR SHEFFIELD TRITIUM MIGRATION STUDY, WEDNESDAY, SEPTEMBER 8, 1982 ATTENDEES:
David Ed, IDNS Thomas Borecki, Office of Attorney General, State of IL Keros Cartwright, ISGS James Foster, USGS Rick Healy, USGS John Fischer, USGS Larry Toler, USGS Ronald Caynor, US Ecology David Siefken, US NRC PURPOSE: The purpose of the meeting was to discuss the results of the Phase II portion of the tritium migration study and to determine the need for, and to plan if appropriate, any additional investigations to be performed as Phase III of the tritium migration study.
DISCUSSION: The meeting began with a presentation by the USGS of the results of the Phase II investigations. Well locations of the Phase II wells (nos. 587_594) are shown on Exhibit 1.
Reported tritium concentrations for wells in which tritium has been detected are presented in Exhibit 2.
Based on these reported tritium concentrations, the area of tritium contamination in the sand aquifer has been cross-hatchured on Exhibit 1.
These results confirm previous indications that the tritium is migrating in a very narrow channel, probably of significantly higher permeability, within the sand aquifer. Potentiometric levels in the aquifer and preliminary results of the ground temperature survey confirm this interpretation.
DFC FLAME :
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i DOCKET 27 39/DLS/82/9/14 Discussion then centered on the three main questions to be answered by the tritium migration study, namely:
- 1) the extent of migration (3-dimensionally in space)
- 2) the nature of migration (concentration)
- 3) the source.
With respect to the first question, the tritium plume has been well-defined ~in all directions except to the east, where wells 560 and 561 show no tritium but are not located along the narrow channel. Wells even further to the east also show no tritium but are not located along the narrow channel. Since the ground temperature survey has provided reasonable correlation of the channel location with boring data and flow paths interpolated from potentiometric levels, additional wells located on the basis of the ground temperature survey should define the eastern extent of migration in the narrow channel.
With respect to the nature of migration, the latest reported tritium concentrations, if confirmed by subsequent samples, appear to indicate two tritium peaks rather than only one tritium peak as indicated by the Phase I results. This change in interpretation has resulted from measured concentration in wells 575 and 592. Whereas most wells have shown nearly constant tritium concentrations, well 575 has shown a marked decrease (46 to 18 nci/l in 5 samples collected over 6 months) and well 592 has shown a marked increase (19 to 36 nci/1 in the two samples collected). Additional wells east of well 592 and additional samples from all wells should resolve the question on the number of tritium peaks. Based on present data, the peak concentration appears to be associated with the trailing peak and is less than 100 nci/l (3 percent of MPC).
With respect to the source, the potentiometric surface map for the sand aquifer indicates that the centerline of the flow system trends north to south under trenches 26, 25C, 24 and 23; then, bends to a nearly east to west course as marked by the tritium plume shown on Exhibit 1.
It probably will not be possible, or necessary, to determine releases from individual trenches since the tritium appears to be the result of one or more slug releases rather than a continuous release. The slug releases (s) probably occurred when significant quantities of water entered the trenches, such as when the trenches were cpen and being filled or in 1979 when sinkholes developed in the trench cap covers.
Determination of ground-water velocities from continued monitoring of the lpFC :
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_3-tritium plume should permit re-construction of approximately when the slug release (s) occurred.
It was decided that pumping tests in the area of the tritium plume under B6967 should be delayed until next spring so as to not interfere with the tritium migration study.
Additional work to be performed includes the following:
- 1) four wells, two at approximately 50 and 100 feet south of well 560, one along the channel approximately 85 feet east of well 592, and the fourth to be located farther east based on the results of the ground temperature survey (USGS).
- 2) borehole geophysical logging in all wells, including the US Ecology site well, within the next two weeks (USGS).
- 3) additional ground temperature survey on Friday, September 10 (ISGS).
- 4) borehole ground-water velocity measurements in the wells with measured tritium concentrations (USE).
Based on completion of these studies, including at least three samplings of the new wells, the next meeting of the tritium migration study working group will be on December 8,1982. At that time, the three questions should be adequately answered and a preliminary report will be prepared by the working group. Additional monitoring of the tritium plume will continue in order to increase the amount and length of the data base and to confirm the results presented in the preliminary report.
_ Original SignedBF David L. Siefken Low-Level Waste Licensing Branch Division of Waste Management
Enclosure:
As stated l
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