ML20029A411
| ML20029A411 | |
| Person / Time | |
|---|---|
| Issue date: | 02/14/1991 |
| From: | Surmeier J NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Matthews M ENERGY, DEPT. OF |
| References | |
| REF-WM-54 NUDOCS 9102220005 | |
| Download: ML20029A411 (9) | |
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wAsHINGiON D. C. 20566 Ico a 4 199l Mr. Mark Matthews.
Project Manager Uranium Mill. Tailings Remedial Action Project Office U.S. Department of Energy-Albuquerque Operations 0ffice P.O. Box 5400 Albuquerque, NH 87115
Dear Mr. Matthews:
We have reviewed the U.S. Department of Energy's (DOE) submittal dated February 1, 1991, providing responses to the open issues identified in our draft Technical Evaluation Report for the Grand Junction, Colorado, site. Additional information pertinent-to erosion protection issues (submitt_ed by letter dated January 17, 1991)Lwas also reviewed.
Your cover letter appears to indicate that you are seeking immediate resolution of only issues 2, _13, and 14 1.e. those you have identified as having direct-impact on the' placement of init.ial lifts of tailings within-the disposal cell.
However, based on a reading of the individual issue responses and discussion between rqy staff and yours, we understand that you actually seek resolution
- of-issues l' 2, 8.- 9,13, and 14 These are the issues that you have
' identified as-impacting the activities planned for this construction season.
Those activities are:'1) placing and compacting tailings in.the disposal cell, and 2) processing rock to be used for the erosion-protection on the top and sides of the cell.
Based upon our review of the information provided. the NRC staff concludns that DOE has accurately'identif e the issues needing resolution prior to the planned construction activities. 'Furthermore, the staff concludes that issues 1, 2, 8. 9, and 14t have been resolved by the information provided, and issue 13 has been sufficiently. resolved to allow the construction activities to proceed.
p Therefore, the NRC staff has no: objection to DOE's proceeding.with the H
-construction activities planned.to begin on March 1, 1991.
.The enclosure provides a discussion of the staff's conclusions regarding DOE's.
response'to each. issue. This discussion should be used'in'the. resolution of the remaining open issues and development of the final Remedial-Action Plan
-(RAP).
Since constr::ction will be starting shortly,'I would hope that DOE resources continue to be focused on placing high priority on resolving the-I remaining open issues on Grand Junction and submitting a final RAP. As you g
know, our formal concurrence cannot be given unti1~the final RAP is received and-has been reviewed to ensure that the information from the response documents on the open issues have been incorporated into the RAP.
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ORIGINALStGNED By j
t John J. Surmeier, Chief
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REVIEW 0F RESPONSES TO OPEN ISSUES GRAND JUNCTION, COLORADO SITE
!ssue 1.
Information provided in ihe subcontract documents indicates that ' c supporting calculations do not reflect the current excavation plan, i.e. an additional 6 feet of excavation into the Mantos shale. DOE needs to address the effect of this design change on slope stability in the Final Remedial Action Plan.
DOE has identified that this issue needs resolution prior to tailings placement, and therefore, has revised the slope stability calculations to reflect both the additional excavation and a revised cover design (response to erosion protection issues). Procedures identical to those of the previous analysis were used for the revised analysis. The factors of safety for all conditions decreased very slightly due to the revised cover design, but all remained above the required minimum values. The staff concludes that this issue has been adequately addressed.
Issue 2.
The supporting calculations do not reflect the current excavation plan.
UUE needs to address the Offect of this design change on the settlement / cracking analysis in the Final Remedihl Action Plan.
DOE has identified that this issue needs resolution prior to tailings plccement, and therefore, has revised the slope stability calculations to reflect both the additional excavation and a revised cover design (response to erosion protection issues). The resulting total and differential settlement actually decreased due to the cover design change (load reduction).
The staff concludes that this issue has been adequately addressed.
Issue 3.
The selected gradation requirements in the specifications appear to allow for radon /infiltra+ ion barrier material that is inconsistent with the expected design permeability. Furthermore, it is not exactly clear what value is proposed for the design permeability 1.e., 5.02E-8 cm/sec as given in the sumary of design parameters, or 1E-7 cm/sec as given in the water resources protection strategy.
In order to bring clarity to this aspect of the radon barrier design, DOE needs to provide a discussion that presents the expected material make-up of the radon barrier, the design permeability, the basis for selection of the permeability, the resulting gradation specifications, and justification of how the specifications will ensure a radon barrier with the design permeability.
DOE has elected to defer resolution of-this 1-ssue since it involves the radon barrier which would not ba affected by hauling and placing tailings.
- However, DOE has provided discussion that they propose to incorporate into the RAS to resolve this we. The staff does not agree with the resolution DOE's discussion 1*
atesghattheradonbarrierwillbeoclaymaterialwith permeability sx10' cm/sec, and refers to page 172 of the material properties calculation for range of particle size.
Consistent with the proposed material, this table shows CL material with an average of 70% passing the number 200 sieve (minimum 40%). However, DOE's discussion further indicates that the gradation
specifications are correct in specification 02228, part 2, 2.1.A.I.
This specification only= requires the radon. barrier material to have 205 passing the number 200 sieve, with allowance for every fifth test to have as low as 15%.
This specification appears centrary to the test data and design.
L Issue 4 The. RAS indicates that the layer immediately above the radon barrier is to be a six-inch-thick sand bedding / drain layer, intended to drain water laterally-off the cell and protect the radon barrier from the riprap. The gradation specifications and drawings show two separate materials, a drain-material and a bedding material. The RAS does not clearly identify the design basis for the two different materials, and the calculations do not clearly lay out how the gradations are established from the design criteria (permeability, filtercriteria). DOE needs to clarify these aspects of the cover design in the final RAP.
DOE has elected to defer resolution of this issue since it involves cover layers that would not be affected by hauling and placing tailings.
- However, DOE has provided discussion that they propose to incorporate into the RAS to resolve the issue. The staff agrees that the proposed discussion will resolve the issue, Issue 5.
The calculations provide the basis for the gradation design of the choked rock layer.
However, the resulting gradation is not consistent with the gradation presented in the construction specifications. There is no basis for the gradation provided in the specifications. D0E needs to resolve this discrepancy in the final RAP.
00E has indicated that the choked rock layer is no longer a part of the design and all references to it_will be removed from the RAP documentation. This
_ issue _is no longer applicable.
l Issue 6.
00E needs to address two additional aspects of the disposal cell construction in the RAIP, The specifications indicate that compaction requirements for the bedding, drain, and choked rock layers are method (number of passes) rather than numerical (% maximum density). The RAIP should contain discussion of the plans to inspect and document the placement of these-materials. The specifications also include requirements for placement of the t
i rooting soil, rock mulch, and vegetation. The RAIP should contain plans to l
inspect these aspects of the cover.
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DOE has elected to defer resolution of this issue since it involves cover layers that would not be affected by hauling and placing tailings. However, DOE has indicated that they will revise the RAIP to address placement of drain and bedding layers; the other layers have disappeared with the revised cc er design..-
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Issue 7.-
It does not appear that care was taken to ensure consistency between the specifications and the RAIP. DOE needs to review the specifications, making appropriate revisions to ensure consistency with the RAIP.
DOE' indicates, and the staff agrees, that there are no inconsistencies involving the tailings placement. Therefore, they elect to defer this issue. The specifications'and RAIP will be reviewed by DOE for inconsistencies and revised as necessary.
Issue 8.
DOE needs to provide a redesign of the eror n protection for the top slopes of the' disposal cell, addressing flow concentra W n considerations, or provide additional justification for the design proposed.
Issue 9.
DOE needs to prm :de a redesign of the erosion protection for the side slopes of the disposal cell, revising assumptions for peak flows and dispersion
_by the 20-foot rock cover extension, or provide additional justification for the design proposed.
DOE has identified that issues 8 and 9 need resolution to allow processing of erosion protection material. DOE revised the design to include rock riprap protection..for these slopes rather than s vegetated cover. The staff reviewed these designs and has concluded that they meet the criteria suggested in the NRC Staff Technical position on Design of Erosion Protection Covers.
Based on the adequacy of these designs, it is acceptable for DOE to proceed with construction of these features.
-Issue 10. DOE needs to provide a redesign of the crosion protection for the toes and aprons of the disposal cell, consider _ing: revised-peak flows from the side slopes and potential _for gully headcutting, or provide additional justification
- for the design proposed.
Issue 11.- DOE needs to provide a redesign of the erosion protection for the.
diversion channel, considering erosion protection at the channel outlet,
--potential for: gully' inflow to the channel, and clogging / sedimentation, or provide additional justification for the proposed design.
DOE has elected to defer resolution of issues 10 and 11 since they involve final site grading and erosion protection features not affected by hauling and
-placement of tailings.
However, DOE has provided.information directed toward
-future resolution of these issues. The staff has reviewed the design of the toe ~and off-pile swale, and concluded that the designs are not acceptable.
In the toe design, DOE has not assumed appropriate flow concentrations that would be expected to occur in the immediate area of the toe. The staff concludes that the riprap size will likely have to be increased in order to meet the longevity standards of 40 CFR 192.
For the design of the off-pile swale, DOE has not used appropriate assumptions.
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in the-design of the riprap on the embankment slope imediately adjacent to the swale.
Further, DOE has not correctly evaluated shear stresses and velocities that would be expected to occur in the area.
The design will likely need to be revised significantly, including the design of the swale outlet area, since inappropriate assumptions have been made regarding the configuration of the gully likely.to be formed at the outlet.
As' discussed with DOE / TAC /RAC staff in a February 1, 1991, telephone
. conference call on the erosion protection issues, DOE needs to provide revised designs for these features of the design. Construction of these features should not proceed, until the designs have been reviewed and approved by the NRC staff.
Issue 12. DOE needs to demonstrate that by deferring groundwater cleanup at the Grand Jiinction processing site public health and safety will not be affected.
DOE needs to take additional water quality samples from the Colorado River (especially at low flow) and test for all hazardous constituents.
Further, DOE needs to define the area potentially affected by the present contamination, and the grc='twater usage (not just for drinking purposes) within that area.
DOE has elec ed to defer responding to this issue until submittal of the final RAP. Since re heating.the tailings will not prevent DOE from resolving this issue, and DOE has proposed an approach to resolve the issue, the NRC staff agrees.that DOE can defer responding to this issue until submittal of the final RAP.-
-DOE's proposed approach to resolving this issue involves collecting edditional surface-water quality data'from the Colorado River during low flow to demonstrate that contaminaris reaching the river are adequately diluted. 00E-has:also proposed to reanalyze the' extent of the contamination plume, at the site, through the use of off-site wells, and they propose to undertake a well inventory.
The following general comments are offered to assist DOE in closing this open
-issue when the final RAP is submitted:
1.
DOE needs to explain their rationale for.
'eting wells for inclusion in the inventory. As ' stated in the open issue, SE needs to define the area potentially affected by the present contamincion; this information should-be the basis for including or excluding wells from the inventory; 2.
DOE needs to provide well construction information (such as zones that they are withdrawing from) and water use information on the wells included in the inventory. Water use should.not be strictly defined as consumption use only; and -
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DOE needs to demonstrate that all water users will not be affected by contamination as a result of deferring groundwater cleanup.
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Issue 13. DOE needs to clearly state in the RAP exactly what the supplemental standard is. DOE also needs to demonstrate that their proposed supplemental standards come as.close to meeting the otherwise applicable standards as is reasonable under the circumstances.
DOE needs to provide a list of the concentration _ limits-of the hazardous constituents that they have identified.
DOE has determined that since this issue is integral to the groundwater compliance strategy, a resolution of the issue cannot be deferred.
In response to the issue, DOE has revised the RAS to present a clear narrative supplemental standard.
' DOE is not proposing concentration limits for the designated hazardous constituents since they are not proposing to do any monitoring at the Joint of compliance (P0C); however, DOE has identified concentration limits of lazardous constituents that are the applicable standards that the supplemental standard is supposed to come as close to meeting as is reasonable under the circumstances.
The NRC staff considers DOE's response to this issue adequate to allow relocation of the tailings to proceed. While the NRC staff considers DOE to have adequately stated their proposed narrative supplemental standard, and have adequately demonstrated that the remedial action will protect human health and the environment and come as close as is reasonable to meeting the otherwise applicable standards, the NRC staff has the following concerns with the proposed concentration limits identified by DOE:
1.
DOE has proposed to use the maximum detectable limit (MDL) for antimony, beryllium, and nickel. According to 40 CFR 264.94, DOE must use either background, MCL, or an alternate concentration limit as the concentration limit-for hazardous constituents; therefore, maximum detectable limit should be correctly identified as the background concentration for these constituents; 2.-
DOE has proposed to use a concentration limit of 44 mg/l for nitrate; this should be changed to 10 mg/l (as measured for nitrogen) as referenced in 40 CFR 192.02(a)(3)(ii) of the draft EPA rules; and 3.
DOE has proposed concentration limits for aluminum, copper, cobalt, cyanide, sulfide, strontium, vanadium, and zine; however, since-they are not listed in the standards as hazardous constituents, they can be eliminated.
If DOE desires to keep these on the list, the proposed concentration limits that they have indicated are appropriate.
These concerns should be addressed as part of the resolution of this issue in the final RAP submitted by 00E..
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Issue 14 DOE needs to perform additional vertical permeability testing on the foundation material, at the final excavation depth. The permeability tests should be performed on compacted Mancos Shale material, since it is likely that the heavy, moist tailings will compact the friable shale material.
DOE has concluded that this issue must be resolved at this time since additional testing will not be able to be performed once the tailings are relocated to the cell.
DOE has provided results from SDRI and falling head tests which provide information on the saturated vertical and horizontal conductivity of the foundation material. These tests show that the foundation material is more permeable than the design saturated hydraulic conductivity of the barrier; therefore, a "bathtubbing" effect should not occur within the cell. 00E did not perform the infiltrometer tests on compacted foundation material as suggested by HRC staff because they concluded that the geostatic load from the tailings should be less than the original geostatic load from the overburden material; therefore, tailings are not expected to significantly compact the friable material.
Based upon DOE test results, the NRC staff agrees with DOE's conclusion that the foundation material should be more permeable than the design for the barrier, even at the lower depths within the Mancos Shale. The SDR1 tests show a saturated vertical hydraulic conductivity of the foundation material that is at least an order of magnitude greater than the design saturated hydraulic conductivity of the barrier.
The NRC staff does not agree w th DOE's conclusion that because the geostatic load on the Mancos Shale will be less than under previous conditions, significant compaction should not occur.
By exposing the unweathered Mancos Shale to the surface environment, the shale has become chemically unstable resulting in its friable nature.
In its current friable condition, the combination of moisture and load will likely compress the upper surface of this material into a clay.
However, the NRC staff accepts DOE's test results because the information provided s %ws that vertical flow in the unweathered Mancos Shale is strt,,1 gly contrciled by fractures several feet into the formation. Most of the flow out of the base of the cell will occur through the unweathered Mancos Shale because of the topographic gradient of the base. Once moisture moves below the initial thin layer of compacted material, flow will be largely controlled by the fractures within the upper few feet of the formation.
If we assume that the compacted surface will have a conductivity one or two orders of magnitude less than the underlying material, the conductivity of the base (i.e., the area controlling discharge) will be greater than or equal to the designed saturated conductivity of the barrier.
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Issue 15.-DOE.needsto-correct-theRawlsmethod(long-termmoisture) calculations, and provide discussion of.the_ basis for not factoring the results of the Rawls method into the selection of the-design long-term moisture.
DOE'has elected to defer resolution of this issue since it involves design of the radon barriet which would not be affected by hauling and placing tailings.
-However, DOE has indicated that they have corrected the Rawls calculation and has provided discussion that they propose to-incorporate into the RAS to-resolve the. issue _The staff agrees that the proposed discussion will resolve the issue.
-Issue 16.-_ The_ concept of adjusting the average Ra-226 concentration values for the design is acceptable to the NRC staff; however, the Standard Error of-the Mean does not_-adequately-represent the variability of the data. DOE needs to reevaluate parameter adjustment to better represent the variability of the data.- The range of Ra-226 for=the main tailings and off-pile materials should be added to Table 6.3.
D0E has elected to defer resolution of this issue since it involves design of the_ radon barrier which would not be affected by hauling and placing tailings.
DOE also has provided proposed discussion pertinent to future resolution'of this issue.- Review of revised calculations not provided remains open.
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