ML20138D954
| ML20138D954 | |
| Person / Time | |
|---|---|
| Issue date: | 08/30/1985 |
| From: | Higginbotham L NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Themelis J ENERGY, DEPT. OF |
| References | |
| REF-WM-48 NUDOCS 8510240516 | |
| Download: ML20138D954 (9) | |
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PD W MKnapp v-U.'S. Department of Energy JGreeves Albuquerque Operations Office LNL TJohnson pistribet on:
P.O. Box 5400 MFliegel Albuquerque, New Mexico 87115 i
RDSmith, URF0 U
EHawkins, URF0
Dear Mr. Themelis:
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We have reviewed the draft RAP, SCR, and DSCR and the preliminary final EIS for the mill tailings site at Durango, Colorado. Our specific coments on the draft RAP and D,SCR are provided in the enclosure to this letter. Some of our general concerns are provided below.
.The draft RAP has two design features that DOE needs to consider very carefully in order to meet EPA standards. The first is long-term erosion protection.
In
. general, we believe that the erosion protection proposed for the drainage
, ditches and_for the prevention of gully intrusion has not been adequately designed, due to flawed application of shear stress models and rainfall distributions. Adequate rock sizes and quantities for the ditches and for gully erosion protection appear to be much larger than the sizes.and quantities proposed.- In addition, recent meetings with the National Weather Service have indicated that short duration rainfall intensities need to be significantly increased above the intensities used in DOE's analyses for the erosion protection for the top and sides of the pile. These increases will affect the rock size for the top and sides of the pile and will also further affect the rock size in the perimeter ditches and gullies.
-The second questionable design feature is the use of a lime addition for the radon barrier to compensate for soil deficiencies with regard to dispersivity and swell potential. We are uncertain of the long-term effectiveness of the lime and the construction techniques to assure a. uniform mixture for the quantities needed.
We have no coments on the preliminary final EIS. Detailed coments were made on the draft EIS. Therefore, our' review of the preliminary final EIS, which does not need NRC concurrence, was primarily to determine if items were of such significance that we would reconnend DOE not issue the EIS. We do, however,
-have reservations regarding DOE's ability to provide a suitable design at Bodo
~ Canyon (as discussed above and in the enclosure). Of the.three alternative sites provided, all have significant siting problems in our view. We are not comfortable with any of the alternatives, but agree that the Bodo Canyon site does seem the best of those alternatives available. For this reason we do not object to issuance of the final EIS. However, the final design will need to be engineered very carefully to meet EPA regulations.
If a suitable design is 0510240516 850830 PDR WASTE WPt-48 PDR
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unattainable due to a lack of adequate rock or. coils, or because of cost considerations, DOE would then need to consider other alternative locations.
If you have any questions regarding our review, please contact me or Mark Haisfield nf my staff.
Sincerely,
/s Leo B. Higginbotham, Chief Low-Level Waste and Uranium Recovery Projects Branch
~
Division of Waste Management, NMSS
Enclosure:
As stated cc: John E. Baublitz, w/ encl.
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NRC COMENTS ON THE DURANGO DRAP AND DSCR 9
Surface Water Hydrology and Erosion Protection DRAP 1.
Use'of Average Shear Stresses for Channel Design Our review of the information presented in the RAP and in the backup calculations indicates that average shear stresses were used to design the riprap to be placed in the perimeter ditches surrounding the remediated.
pile.
The NRC staff does not consider this to be an acceptable method' for designing. erosion protection for drainage channels similar to those proposed for this site. The proposed V-shaped channels are relatively inefficient and tend to produce shear forces which are very low on the
. sides and v' ry high in the center of the channel,' where the channel is the n
e most efficient.
One acceptable method for resolving these concerns is to assume that the hydraulic radius (R) in the design equation is equal to the depth of flow in the center of the channel. This will assure that the rock is designed i
for local velocities, as recommended in most standard hydraulic design e-methods. Another acceptable method is to provide a channel design where O'
shear stresses are distributed more uniformly across the channel section.
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(Because the average 'R' is about 1/2 of the 'R' that should be used for design purposes in V-shaped channels, the NRC staff expects that the D50 rock sizes needed will be approximately twice as great as the sizes proposed. Also, see comment 5, below).
2.
. Gully Erosion Protection The basis for providing erosion protection for the existing on-site gullies need to be more clearly defined. As presented in the RAP and supporting calculations, it is not clear how the erosion protection will prevent further gully erosion and headcutting. Our review indicates that the following additional considerations need to be factored into the design and/or addressed in the revised RAP:
A)
Provide detailed plan views and cross-sections in the areas where
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. gully erosion protection is provided and in those areas where the perimeter ditches merge and transition into the gully erosion protection.
B)
Because of the high velocities and supercritical flow in the ditches, consideration must be given to further increasing rock sizes in the ditch-to-gully transition areas, in the ditch junctions, and in those areas where hydraulic jumps will occur. These increases will be needed in addition to the increases noted in Comment 1, above, and comment 5, below. Additional analyses should be performed to determine the increase in shear forces and the need for additional erosion protection at these locations.
C)
Based on the information presented, it appears that the design of the gully erosion protection should be based on the velocities which will occur in the perimeter ditches or in the existing gullies. There is no basis for the assumption that uniform sheet flow will occur over the gully erosion protection blanket (as assumed in the backup-calculations).
It appears that the rock ~provided for gully protection should be at least as large as the rock in the perimeter ditches. The slopes of the blankets appear excessively steep and the basis for providing such blankets should be further explained.
It is difficult to determine the effectiveness of such a design when the existing erosion features in the area indicate that gully protection should extend for some distance downstream and stabilize the gully cross-sections as they now exist to prevent further erosion both laterally and headward.
D)
Based on the infonnation presented, it is not clear what drainage areas were used to compute peak runoff rates to the ditches and gullies.
For example, the north gully erosion protection is designed for the runoff from a drainage area of 31 acres. However, it appears that flow from the north ditch, with a drainage area of about 25 acres should be combined with the flow from the existing north gully, which appears to have a drainage area much greater than 6 acres.
Further analyses and possible re-evaluation of the drainage areas should be provided. A map should be provided which outlines the drainage areas for each ditch segment and gully.
3.
Based on the configuration of the proposed pile, it appears that the concave shape (Figure B.1.12) will be conducive to the concentration of runoff at the toe of the pile. This phenomenon should be factored into the design of the erosion protection for the sides of the pile, or the pile configuration should be modified such that flow concentration is u-
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' prevented. The basis for computations should be provided along with revised analyses which document the degree to which flow concentration will occur for the final design selected.
4.
Provide a discussion of the rock that is available at the potential borrow areas cited in the RAP.
Information should be provided regarding the amounts and types of rock that are available in the sizes needed.
In addition, the feasibility and practicability of crushing rock from various sources to meet the required gradation should be discussed.
5..
The rainfall distributions used to compute peak rates of runoff in the ditches and gullies is not considered acceptable. As stated in previous comments at other sites, the rainfall distributions given in Hydrometeorological Report No. 49 should be extrapolated and used for design purposes.
The NRC staff recently met with the National Weather Service (NWS) staff.
Based,on NWS recommendations, the,following rainfall distribution should be used for the Bodo Canyon site and for any future site in the region covered by HMR 49:
Duration (minutes)
Percent of 1-hr PMP 5
45 I
10 61 15 74 30 89 60 100 Based upon these distributions, it will be necessary to re-compute peak rates of runoff used to design the riprap erosion protection for the top and sides of the pile, and for the perimeter ditches and gullies.
6.
In order to document that flow concentration will not occur, discussions and/or analyses should be provided to show that differential settlement will not be a problem. As discussed in recent meetings between NRC and TAC, a commitment should be provided.to take necessary measures (such as surcharge loading, compaction of slimes, etc) that will ensure that differential settlement will be minimized over the 1000-year stability f
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. period. Otherwise, consideration must be given to flow concentration for sizing the rock for the tops and sides of the pile.
Geology and Seismology DSCR 7.
Page 6, Section 2.5.1; The DSCR should provide the field reconnaissance, low sun reconnaissance and trenching data to support the conclusion that the " Ridges Basin Fault" dries out south of the site.
8.
Page 8 of Appendix B; The DSCR states that the zone of crustal extension bounding the Colorado Plateau appears to be growing and that the marginal zone of increased seismicity associated with it is increasing as well. 'Is the increase in seismicity an increase in areal extent of the zone of seismicity, an increase in the size of the earthqbakes occurring in the zone, or both? How was this increase of seismicity taken in account,in the determination of the MCE for the Durango site considering the 1000 year criteria? Similarly, is the maximum earthquake defined for the Dulce, New Mexico area sufficient considering the potentially increasing
.effect of the Rio Grande Rift intb the Colorado Plateau over the next 1000 years?
Geohydrology DRAP 9.
Page 30 and 32, Sections 4.4 and 4.5.2; It is evident from these sections that the proposed remedial action for contaminated ground water underlying the processing site is natural flushing to the Animas River. Please provide a discussion of the time that will be required for contaminants to be flushed from the system. Additionally, provide a discussion detailing what protective measures will be utilized during this period of time to prevent usage of the water.
- 10. 'Page 32, Section 4.5.2 indicates that the potential need for deep aquifer restoration beneath the raffinate ponds cannot be determined until additional water quality data become available.
It is recommended that the final RAP contain a characterization of the ground-water contamination within the Menefee and Point Lookout formations together with a proposed remedial action plan. Proposed remedial action should take into consideration present and future use of the ground water, availability and A
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characteristics of alternative water supplies, institutional controls on
-use, and the value of the resource evaluated against the cost of proposed remedial actions.
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- 11. Page 53 of the DRAP indicates that the ground water systems underlying the Bodo Canyon alternative site are presently being utilized upgradient.
It
.must therefore be assumed that at some time in the future, these systems could also be utilized at some point downgradient from the proposed disposal site. The goal of the DOE should be zero degradation of the Bodo Canyon ground-water regime. The worst case estimate for ground-water contamination at Bodo Canyon (pp. B B-89) is too conservative. Even concentrations that are 200% less than indicated in Column 3 of Table B.3.5 (p. B-88) would result in unacceptable concentrations of some hazardous constitutents. The estimate should be revised taking into account the permeabilities and attenuative capacities of the clay liner and cover and the unsaturated subsurface materials.
DSCR
- 12. Page 35, Section 5.1; The hydraulic conductivities presented here should have negative signs in the exponents. Additionally, in order to adequately evaluate the aquifer hydraulic properties derived, a discussion should be provided detailing the types of tests performed and the aquifer analysis nethods used to determine the hydraulic conductivities.
- 13. Page 37, Section 5.2; The second and third paragraphs of this section should be revised to be consistent with the last paragraph on page 26 of the DRAP (i.e., the DSCR should be updated to reflect the findings of the recent sampling program of the shallow Menefee and Cliff House aquifers).
Radon Barrier and Radiological Safety DRAP
- 14. Page 51, Section 5.5.4, and Page B-33, Section B.1.3.1 The actual value for the radon barrier cover thickness must be supplied to the NRC for concurrence prior to cover construction.
In addition, the adverse effects of frost on the integrity of the clay cover should be addressed.
- 15. Page B-38 and Table B.1.6; The emanating fraction, as estimated for the contaminated material, appears to be low.
For estimating purposes, a default value of 0.35 should be used.
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- 16. Page B-44, Section(s) 8.1.3.3 and B.1.3.5; Is the long term moisture content of the material obtained from Bodo Canyon the same for both materials (see related comment No.18 on Bodo Canyon DSCR)? Please compare the long term moisture content to the equivalent bar water retention value.
- 17. Page D-19, Section D.3.7.b; Please clarify which radionuclide(s) would be analyzed for during a whole body count. Also, is it not necessary to conduct the baseline whole body counting of all employees prior to working in a controlled area. Those enployees that exhibit high urinalysis values
.during remedial action could then be whole body counted upon employment termination and the results compared to the baseline previously determined.
It would probably be most meaningful to whole body count for radium-226.
'DSCR
- 18..Page 83,.first full paragraph; Please provide the~ actual calculations performed to obtain the long term moisture contents as estimated via' the conceptual procedures outlined in this paragraph. Please compare this estimate to the 15 bar water retention value.
Geotechnical DRAP
- 19. Page 50; Table 6.5 of NUREG/CR-2642 indicates that a petrographic examination provides the better overall assessment of rock quality than standard rock durability tests such as the freeze-thaw test. The information provided by the petrographic examination, such as chemical composition and fracture density, is especially important when the long-term durability of the rock is being evaluated. The rock durability i
testing should therefore include a petrographic examination.
- 20.,Page 63; The radiological survey plan indicates that excavation of contaminated soil underlying the existing site would continue until the EPA radium standard was met. While this is necessary, it should be noted that excavation depths may need to be determined based on chemical contamination (i.e., arsenic,etc.). The survey plan should be revised to state that an evaluation of the extent of chemical contamination will also be performed.
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- 21. Page B-40; It is proposed to add lime to the onsite soils to be used for the radon barrier to attempt to compensate for serious deficiencies of the i
. soil with regard to dispersivity and swell potential. The proposed approach raises several critical concerns which must be addressed.
- First, can the longevity of the soil-lime matrix remain effective for at least 200 years? Explain in detail the effects of dissolution on the effectiveness of the lime over long-time periods.
Infiltration of rainfall will occur and will in fact be increased due to the presence of the rock layer. Further, the onsite soils are expected to have a rather high residual moisture content which may affect the lime. Second, explain in detail a mixing and quality assurance program which will assure that the required percentage of lime is consistently attained for all radon barrier material. This is extremely important as even small areas not meeting specifications could seriously impact the stability of the cover.
These critical issues could result in a need to identify an alternative borrow source. This comment also applies to the DSCR, pages 80-82.
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