ML20214K470
| ML20214K470 | |
| Person / Time | |
|---|---|
| Issue date: | 09/17/1986 |
| From: | Smykowski S NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Haisfield M NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| References | |
| REF-WM-54 NUDOCS 8612020315 | |
| Download: ML20214K470 (9) | |
Text
_ - - -
P i.
,; . g . . .
SEP 171986 SS 9/17/86 N1 HAISEFIELD WM Record Fife WM Praitd [
Dcckct flo.
PDR /
0 U*
NOTE T0: Mark Haisflud ,
Low-Level Waste and Uranium --- L Recovery Projects Branch, WM _._ l -
-C'e t:a to WM,623 SS)
FROM: Steve Smykowski j/
Engineering Branch, WM
SUBJECT:
GE0 TECHNICAL ENGINEERING REVIEW 0F GRAND JUNCTION, COLORADO, DRAFT
. REMEDIAL ACTION PLAN, JUNE 1986 (UMTRAP)
In fulfillment of Technical Assistance Request #WM-86759, we are enclosing geotechnical engineering review draft comments on the Grand Junction Draft Remedial Action Plan (DRAP). We have several major concerns related to the ,
adequacy of the engineered design to meet the required EPA standard. As a result, we will continue to review the RAP in preparation for our scheduled I site visit at the end of this month. At that time, we may have additional review coments which we would discuss with DOE during our site visit and prior to finalizing our comments.
If you have any questions regarding this review, please contact me directly on X74109.
/5 Steve Smykowski Engineering Branch, WM
Enclosure:
As stated Distr 1 Qut. ion: -
SM file: WM-5 W RMSST/f" WMEG r/f JGreeves MNataraja DMartin SSmykowskiIv[Mn/
@FC :WMEG :WM e : : : : :
0____:_____ ____:.. .. ___:____________:____________:____________:____________:___________
QAME :SSr ykowski :MN ja : : : : :
@ ATE :09//f/86 :09/\V86 : : : : :
t
. 't ,.
SS 9/11/86 SLOPE STABILITY l
)
,L GE0 TECHNICAL. ENGINEERING REVIEW 0F THE GRAND JUNCTION .CO.s +
'c DRAFT REMEDIAL ACTION PLAN (RAP) <
prepared by: Engineering Branch, WM ,; .
Section B.4, Slope Stability, Pages B-11 to B-21:
A review of the stability analysis and the parameter values which were used in the analysis raises several questions pertaining to the estimated minimum factor of safety. These concerns are discussed below,
- a. Are the shear strength values shown in Figures B.4.1 and B.4.2 for the tailin materials)gs, thematerial (soil layer 3 low-permeability that(soil liner includes layer fine-grained 4), and the upperslime foundation soils (soil layer 5) based on consolidated-drained (CD) soil conditions? The adopted strengths for the above soils appear to be unreasonably high and use of the drained strength when assessing short-term stability is questionable and possibly unconservative. The staff recommends that short-term stability be assessed using the appropriate unconsolidated-undrained (UU) strength values for each of the slow draining soil layers. For the fill materials, the, shear strength values should be determined by laboratory testing;at-placement densities and moisture contents which fall within the range permitted by the compaction control specifications. n- .
- b. The long-term stability analysis shown in Figures B.4.'3 and B.4.4 use shear strength values for the radon barrier (soil layer 2), and soils 3, 4, and 5 that are based on consolidated-drained (CD) conditions.
These values appear conservative provided the soils do not become wet and saturated _during the design life of the project. What monitoring is planned to check that these soils do not become saturated under which conditions lower shear strengths could be reasonably-,
anticipated? For the long-term condition, if monitoring is.not planned, the staff recommends a conservative approach which would assess stability using the lower of the strengths from either the consolidated-undrained (CU) or the consolidated-drained (CD) shear test results (see NRC Regulatory Guide 3.11). For the fill soils, these strengths should be determined by testing at the planned placement densities and moisture content range permitted by the
! specifications,
- c. Figures B.4.1 to B.4.4 indicate that the surface soil extending from the toe of the pile is soil 4. Will this soil layer meet the same 4
l
SS 9/11/86 SLOPE STABILITY
,2-design requirementsias.the recompacted low. permeability soil layer 4 that will exist under the tailings? If so, what distance will this compacted layer: extend from the toe of the pile. Discussion should be provided on the importance of this design feature.
- d. Figure E.5.3 reports shear strength values for the radon barrier material and the low-permeability liner material from a triaxial compression test performed on the same soil sample and at three different densities and three different moisture contents. The results of these tests are questionable because the lab samples were tested 5t densities and moisture contents which are uvontervatively different from the planned design placement densities and moisture contents. It is standard engineering practice to perf rm triaxial compression tests on several samples of the same matertal and at the same density and same moisture content. The staff recommends that the stability analysis use shear strength values for the radon barrier material and the low-permeability liner material that have been determined by laboratory testing at design densities and moisture contents to be permitted by the compaction specifications.
- e. The staff questions the representativeness of the strength parameter values reported in Table E.6.7 for the tailings material. Based on the staff's experience and typical values reported in the literature, the strengti, values reported in Table E.6.7 are unusually high and may be unconservative for use in a stability analysis. The staff agrees with DOE's reference (Vick, 1983), that typical values for friction angles for drained sands range from 30 to 37 degrees.
However, these are not typical shear strength values for a soft cohesive soil which would include the slime tailings material. A soft cohesive soil could have much lower stren determined by Colorado State University (CSU) gths than testing. The what staffwas is attempting to obtain and review the CSU document which reports these high strength results. The staff plans to check that the materials are similar and were tested under conditions which are expected to exist at the Grand Junction project site. Additionally, in an attempt to better understand the strength properties of the tailings, the staff requests that the laboratory results from all direct shear and triaxial compression tests performed on Grand Junction tailings material be provided for review.
Section B.7, Ground Settlement, Pages B-53/B-54:
A review of the settlement analysis and the parameter values which were used in the analysis raises several questions related to the
SS 9/11/86 SLOPE STABILITY reasonableness of the estimated settlement. These concerns are discussed below.
- a. The consolidation test results shown in Figures E.6.23 and E.6.25
. indicate that the sand and the sand-slime samples had water added after the test was initiated. This same procedure has not been indicated in Figure E.6.24 which shows the consolidation test results for the slime sample. Was the sample of slime material saturated at the start of the test? Since consolidation tests on saturated slime material would likely reflect greater soil compressibility, the omission of wetting the sample would likely result in unconservative results. The test sample for the slime material was also prepared at a much higher density than the DOE proposed design density and at a moisture content greater than the proposed placement moisture content. Because the laboratory preparation and testing procedures do not duplicate anticipated field conditions, the results become questionable and may be unconservative.
- b. Figure E.6.23 indicates that the sand-slime sample was tested at a moisture content greater than the proposed design moisture content?
What is the reason why the sample was not tested at the design moisture content and discuss the effects of the difference in moisture between the lab and actual field placement on the estimates of settlement? Provide discussion that addresses whether the sand-slime material that was tested in the lab is similar (classification, gradation, plasticity) to the material that is expected to be placed at the Cheney Reservoir disposal site allowing for the expected construction operations of excavation, transporting and placement.
- c. The staff questions the magnitude of the estimated immediate settlement (2.45 feet) for the relocated tailings and the time required for this settlement to occur. Section B.7, Ground Settlements, indicates that the immediate settlement in the compacted tailings was calculated using conventional settlement methods which incorporated laboratory test results of the tailings material. The report also indicates that the construction of the final embankment and subsequent placement of the radon barrier is expected to take three years. The staff has several concerns.
First, the analysis completed assumes that settlement will occur immediately after the tailings have been placed. Immediate settlement for the slime and sand-slimes mixture is not a reasonable assumption. Primary consolidation will likely require several years to occur after the fill has been placed. Therefore, it is very
SS 9/11/86 SLOPE STABILITY unlikely that all of the estimated settlement of 2.45 feet will occur prior to placement of the radon barrier. Second, Section E.6.6 indicates that a compression index of 0.13 was used to characterize the tailings for design purposes and that this value corresponds to the sand-slime mixture. Since the slime material is more compressible than a sand-slime mixture, the use of a compression index of 0.13 may be unconservative in estimates of settlements if actual placement operations of the tailings result in segregated placement of slime and sand materials. Discuss the operations which are planned that will result in a uniform blending and placement of tailings material.
In recognition of these concerns, the staff recommends that a settlement monitoring program be implemented which would record actual settlements and permit future settlements to be estimated. This record would indicate where settlements would be within tolerable limits and when placement and compaction of the radon barrier should begin.
Section E.6.5, Compaction Test, Section E.6.6, Consolidation Test, Pages E-134/135:
- For design purposes, the RAP has adopted parameter values for compaction and consolidation that are representative of a sand-slime mixture. No
~
. basis has been provided which would explain why the selection of these 4 specific parameter values are representative of the Grand Junction If the pile material consists of a high percentage of slimes, tailings.
then using a value that may be appropriate for a sand-slime mixture to assess design performance (settlement, stability, etc.) would not be appropriate. The percentage of slimes, sand-slimes, and sands that comprise the tailings material should be identified and the staff recommends that discussion be provided which would justify the use of sand-slime parameter values as being representatn e of the tailings material.
General Comment:
Considering the maximum depth of frost penetration for this area and the thickness of the erosion barrier, what specific design features are being planned to prevent frost heave and frost damage to the radon barrier?
Section B.9.3, Perimeter Apron, Page B-60:
The staff has concerns related to the impact that the perimeter rock apron will have on the engineering properties of the foundation soils as the i
. - - _ = . . _ _ - - _ _ _ - - _-. _ _- - _ _ __ - __ - _ - __ - ._- _ . ___ _- _ _ - _
SS 9/11/86 SLOPE STABILITY apron serves to provide toe protection from surface water erosion. The shear strengths of the foundation soils were based on high blow counts from standard penetration test results where the natural foundation soils have low moisture contents. Since the foundation soils have low natural moisture contents and the in-situ dry densities are relatively low (Table E.4.1), a significant reduction in shear strength and an increase in soil compressibility could result if the soils were to become saturated because of water collected in the rock apron. There is a need to verify by laboratory testing that the foundations soils will retain adequate shear strength and exhibit acceptable compressibility characteristics if they were to become saturated, or to demonstrate that these soils will not
. _ _ _. become saturated. What monitoring provisions will be made to assure that surface water runoff will not collect in the rock apron and cause saturation of the foundation soils?
Section B.6.7, Moisture Content - Radon Barrier, p. B-37:
It is questionable whether the long-term moisture content of the radon barrier soil (17.5%) has been conservatively estimated for several reasons. First, Table E.5.1 indicates that the in-situ moisture content of the radon barrier soil is 10.1% which is significantly lower than the estimated long-term moisture content. Second, if the radon barrier will be placed and compacted at a moisture content of optimum to 3 percent ;
above optimum (RAP, p.B-37), then based on the results reported in Tables E.2.3 and B.6.4, the placement moisture content could be as high as 18%.
Since the annual precipitation at Grand Junction is 8 to 9 inches and high temperatures can be expected during the summer months (RAP, Section "
E.3.3), it would be reasonable to expect the long-term moisture content to i be much lower than the placement moisture content. Third, high blow counts from standard penetration tests in Cheney Reservoir borrow material (RAP, p.32) and the low in-situ moisture contents and densities reported gg in Table E.5.1 indicate a material at moisture contents much lower than the estimated long-term moisture content. As identified in the NRC l Standard Review Plan, it is reconenended that values which have been
- b' measured for the near surface material existing at the borrow site be correlated to the conditions at the actual disposal site to aid in the _"U selection of a conservative long-term moisture value. (seeRAP,p.B-45, paragraph 2). The staf f recommends that a more conservative long-term moisture content be estimated because of these staff comments.
- Section B.6.7, Moisture Content - Radon Barrier, Page B-37:
)
It is unclear which value represents the optimum moisture content of the radon barrier soils. Section B.6.7 states that the optimum moisture v \
a
SS 9/11/86 SLOPE STABILITY 6-content is 19.2%. Tables E.2.3 and B.6.4 report this value as 18.0%, and Table E.5.1 identifies this value as 19.6%. Since the placement moisture content is determined from thit value and certain aspects of the design are based upon this value, claiification of the correct value should be provided.
Section B.2rl, Design Requirements, p. B-7:
- It is unclear whether the materials used to construct the low-permeability layer will be obtained from the foundation materials at the Cheney Reservoir site or whether they will be obtained from another borrow source. The RAP indicates that the soil layer will be placed and
-compacted to a minimum of 90% of the standard Proctor maximum dry density (ASTM D-698). All rock larger than 6 inches will be removed prior to compaction. If the layer is intended to " reduce the amount and rate of contaminant migration" (RAP, p. B-3), then it becomes questionable whether
+he required permeability can be achieved when the soils are placed at this moderately low degree of compaction. Additionally, if the materials contain a large percentage of coarse material, it would be difficult to achieve the low-permeability at the planned density limit. The staff requests that the RAP identify the material type (classification,
.. gradation, plasticity) for the low-permeability soil layer and that the soil be placed and compacted to a minimum of 95% of the standard Proctor maximum dry density. In order to assure that the required impermeability
_ will be achieved,,the. RAP should identify the specification requirements which liuit the percentage of coarse grained material and the field proceduras to be used to control the maximum size and to assure the needed
, gradation. It is recommended that this material require a minimum of 30 7percerit' passinggthe No. 200 mesh sieve to assure impermeability.
Section B.6.8, Radon Emanation, p. B-37: -
As recommer.ded _in the NRC Standard Review Plan, the value of the long-term
~
moisture content'should be factored into the determination of radon m emanation, E. The values of E. reported in Table B.6.5 were determindd for a range of moisture contents and the average value for E was determined.
_The 00E should provide justification ehy this average value_ reflects the
- l'ong-term moisture content that can be expected at this site.
%c Tables B. 2, B.6.'3, B.6.4, E.2.3, Radon Diffusion Coefficients:
What methods were used to obtain the as-tested dry density ar:d moisture content?! Specifically, what procedure was used to compact tLe samples and how were they dried or wetted to obtain the test moisture coritent? In
% y a _ mm
~
r n U p J%.
SS 9/11/86 SLOPE STABILITY order to assure accurate measurements for diffusion coefficients, it is' important that the methods for compacting lab samples be similar to the field compaction methods, and the laboratory procedures for wetting and drying the samples simulate conditions that can be expected in the field.
Tables B.6.2, B.6.3, B.6.4, E.2.3, Radon Diffusion Coefficients:
The staff agrees that the cover diffusion coefficient is one of the most influential parameters used for estimating the cover thickness and the resultant radon flux. The estimate of the Cheney Reservoir cover radoq diffusion coefficient is based on the results of tests performed on ona sample. The RAP indicates that the borrow for the radon cover will be obtained by selective stockpiling of the foundation excavation material (DRAP, p.33). Since the error in the parameter value discussed in Section B.6.13 is a function of the number of samples tested, and since the material properties of the radon barrier borrow soils can be expected to vary over short distances due to the extreme variability of the surficial depcsits in the site area (DRAP, p. E.36), it is recommended that the estimate for cover diffusion coefficient be based on an evaluation of results from several samples. Section B.6.13 (page B-47) mentions that additional diffusion coefficient measurements will be made on borrow material samples once the final borrow site is selected. In recognition of the need for additional test data, the staff is unable to concur in the design cover thickness at this time. Once the testing has been performed, the additional data should be submitted so that a review of the required cover thickness can be completed.
Section B.6.10, Radium Content, p. B-44:
e Were there any radium extraction operations at the Grand Junction processing site that would result in the Ra-226 not being in secular equilibrium with the parent Th-230? If so, to what degree is:the Ra-226 out of equilibrium? How have these operations been considered in the estimate of the tailings radium concentrations listed in Table B.6.1 which would account for the ingrowth of Ra-226 from the parent Th-2307 General Coment:
'~
What provisions are planned for disposing of additional vicinity property material after the radon barrier has been placed on the encapsulation cell?
m em
SS 9/11/86 SLOPE STABILITY t
Section B.6.2. Conceptual Design, p. B-29, Last Bullet:
What does the "30-year floating average" represent?
o . , ,
i e ,,,,
b
.ag 4
4
--muqMb ,p J"' y
' 't
, u.. .
W' l* >w. _ _ _
a..
- - - - , . , - - . - - - ,, ,. ., ,e,,,, ,-,.-w,..-- - - , . ~ - - - - - . , . , _ , , , . - . . , . . . . , - - - - - . . . - , - . . . - - - . - - - . . _ _ , . _ _ , - . . . . - . ..