ML20196K182
| ML20196K182 | |
| Person / Time | |
|---|---|
| Issue date: | 06/27/1988 |
| From: | Lohaus P NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Arthur W ENERGY, DEPT. OF |
| References | |
| REF-WM-74 NUDOCS 8807060534 | |
| Download: ML20196K182 (19) | |
Text
ts UMTRA74 75/6/22/88 1
? 7 :ris W. John Arthur, III, Project Manager Uranium Mill Tailings Project Office Department of Energy P.O. Box 5400 Albuquarque, Naw Mexico 87115
Dear Mr. Arthur:
Enclosed are NRC Staff coments on the draft Remedial Action Plan (dRAP) and draft Environmental Assessment (DEA) for Belfield and Bowman, North Dakota i:
sites.
As a result of our review, we find that DOE has not demonstrated complianc'e with the proposed EPA groundwater protection standards, due to deficiencies in the hydrogeologic characterization presented for the two sites. The staff also notes a lack of correlation between specific design parameters and the geotechnical test results provided in the dRAP text and Appendices.
Of additional concern are numerous deficiencies and inconsistencies identified in the review of the geologic logs, cross sections and borehole location maps.
While minor, they raise a recurrent quality control problem the Staff have comented on in a number of previous UMTRA document reviews.
In conclusion, no fatal flaws were identified through our review, however our coments should be addressed in development of the final RAP or design. Should you have any questions on these co ments please contact Susan Bilhorn of my staff at FTS 492-0573..
Sincerely, l
Paul H. Lohaus, Chief L
Operations Branch l
Division of Low-Level Waste Management i
and Decomissioning l
l cc:
F. Bosijevac, DOE /AL D. Mount, N.D. State Dept. of Health l
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NRC STAFF COMMENTS ON THE BELFIELD/B0WMAN, NORTH DAK0TA DRAFT REMEDIAL ACTION PLAN AND DRAFT ENVIRONMENTAL ASSESSMENT Groundwater Hydrology BELFIELD 1.
dRAP, General - Groundwater restoration.
DOE has not provided any discussion regarding restoration of groundwater contamirated by past milling activities at the site, as required under Subpart B of 40 CFR Part 192. The NRC staff, however, considers that groundwater cleanup may be deferred until after EPA promulgates final groundwater protection standards provided that DOE demonstrates that disposal and cleanup activities may proceed independently. DOE should explain in the final RAP why restoration at the Belfield site can be separated from disposal to defer this demonstration.
If the NRC staff finds the demonstration acceptable, DOE need only submit a conceptual plan for restoration in the final RAP. When the final EPA groundwater protection standards are promulgated, DOE should submit for NRC review complete information on the groundwater cleanup standard, cleanup demonstration, and cleanup monitoring program as required in 40 CFR 192 Subparts B and C.
At this time, the NRC staff will review for adequacy the information provided in the dRAP on site characterization, including background water quality, hydrogeologic characterization, and extent of contamination.
2.
dRAP, Appendix 0 - Characterization of lower lignite zone.
(a) Page D-166 - Background water quality.
DOE has not characterized background quality of grouncNater in the lower lignite zone of the uppermost aquifer system (Sentinel Butte Aquifer) because none of the three existing wells screened in this unit are upgradient of the Belfield site. Considering that contamination has extended to the base of this transmissive lignite unit (page 0-168),
characterization of ambient water quality is important to demonstrate restoration of this unit to background levels or some other specified concentration in accordance with 40 CFR Part 192, Subpart B.
In addition, EPA standards in 40 CFR 192.02(a)(3)(iv) require that a monitoring program be established that is adequate to determine background levels of listed constituents.
NRC staff recomends that DOE install at least one upgradient monitoring well screened in this unit in order to establish background water quality of the lignite zone, as well as sample any existing upgradient domestic wells tapping this unit.
2 (b) Page 0-166 - Determination of hydraulic conductivity of lower lignite zone.
DOE has not adequately characterized the lower, transmissive lignite zone of the uppermost aquifer. Only three wells are conpleted in this unit, and only a single value of hydraulic conductivity was obtained. Due to this lack of data on hydraulic conductivity and effective porosity, DOE has not estimated average linear velocity of groundwater in the lignite zone. Before DOE can perform transport modeling in support of groundwater restoration and monitoring activities at the Belfield site, aquifer parameters of the lignite unit need to be characterized spatially and areally by installing additional wells (both upgradient and downgradient) and performing slug tests, and if required, pump tests so that groundwater restoration of the contaminated lignite unit can be successfully demonstrated.
(c) Page 0-168 - Extent of groundwater contamination.
Due to the lack of wells, DOE has not provided contaminant concentration distributions of identified constituents in the transmissive lignite zone.
flRC staff recommends that DOE install additional wells in the lignite zone to1)determinebackgroundwaterquality;2)bettercharacterize groundwater flow directions; and 3) define extent of downgradient contamination in the transmissive lignite unit.
3.
dRAP, Page D-165 - Characterization of groundwater flow in uppermost aquifer unit.
DOE indicates in the dRAP that groundwater flow direction in the uppermost unit of the Sentinel Butte Aquifer System in the vicinity of the Belfield site is to the south (Figure D.5.5), based on groundwater elevations in wells completed in the shallow sediments.
However, DOE stated that local flow directions were to the east and northeast in the final CADSAR (DOE, 1987).
In addition, FBDU, Inc., (1981), reports that regional groundwater flow direction is to the north, and discusses potential impacts to downgrodient domestic wells to the north of the site. DOE should offer explanations in the final RAP why flow in this uppermost unit is in the opposite direction of what was previously reported.
In addition, examination of Figure 0.5.1 reveals that there is an absence of wells completed in this upper unit to the east and south of the Belfield site, probably because groundwater flow was originally thought to be to the north and northeast. NRC staff recommends that DOE: 1) install additional wells to the east and south of the site in order to better characterize flow patterns and directions and to characterize the extent of downgradient contamination in this uppermost contaminated unit; 2) collect water level information from well 523 at the same time the other wells are sampled so that the potentionetric map shown in figure 0.5.5 can be revised to include water table elevation from all available wells; and 3) collect water level data from the 16 or more domestic wells located within one mile of the site (FBDU,1981), nany of which are likely completed in this uppermost unit.
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4.
dRAP, Page 0-165 - Determination of hydraulic gradient.
00E has not provided quantitative values of horizontal and vertical gradients in the claystone/ sandstone unit and lignite units of the uppermost aquifer.
00E should provide information on hydraulic gradients in order to perform transport calculations in support of aquifer restoration, as required in 40 CFR Part 192 Subparts B and C.
In addition, 00E has not described hydraulic interactions that may exist between the Sentinel Butte Aquifer and underlying aquifer systems. 00E should provide in the final RAP information on hydraulic interactions between the upper and lower aquifers to identify all possible pathways for contaminant migration to successfully demonstrate aquifer restoration.
5.
dRAP, Page D-165 - Effect of local pumping on groundwater flow.
00E states that local variations in the potentiometric surface shown in Figure D.5.5 may result from pumping of several domestic wells in the area, among other causes.
If pumpage of local wells in the area affect directions and patterns of groundwater flow away from the Belfield site, DOE should discuss the effects of such wells on future cleanup activities, when information is provided on groundwater restoration.
In addition, DOE should provide in the final RAP a complete discussion of the potential effects of pumping on movement of contaminated water from beneath the Belfield site toward domestic or municipal wells.
6.
dRAP, Page 0-177 - Discussion of water use.
Because of differing reports on groundwater flow direction in various references (see consnent # 3), DOE needs to adequately characterize the nature and extent of downgradient contamination resulting from past milling activities at the Belfield site. Of particular concern is a report from FBOU (1981) that many livestock and domestic wells tap the uppermost aquifer formation, and as many as 35 domestic or municipal wells are located within 2 miles of the Belfield site.
DOE should conclusively determine groundwater flow direction so that an accurate assessment of the extent of contamination of affected wells can be made.
- 7. dRAP, Figure 0.5.4 - Hydrogeologic cross-section.
00E has provided only a single cross-section to depict hydrostratigraphic relationships. A single cross-section does not provide meaningful representations of groundwater flow relationships. At least one additional crcss-section perpendicular to the existing cross-section would be helpful and should be included in the final RAP.
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dRAP, Figures D.5.8 thrcugh D.5.11 - Isopleth ar.d potentiometr.ic maps.
In Table 0.5.5, DOE provides water quality data for domestic wells number 524 through 531, but neglects to incorporate this water quality information in the contaminant distribution maps shown in Figures D.5.8 through D.5.11.
The close proximity of these domestic wells to the Belfield site (Figure D.5.2) would make water level and water quality data quite useful in refining a potentiometric surface and characterizing the extent of contamination.
DOE should incorporate water level and water quality data collected from these domestic wells into the potentiometric and isopleth maps in the final RAP.
9.
dRAP, Table D.5.5 - Contamination of downgradient domestic well Examination of Table D.5.5 reveals that well 528, a domestic well located downgradient of the site, exceeds the Maximum Concentration Levels (MCLs) listed in 40 CFR Part 192 for chromium, molybdenum, and nitrate, and particularly for lead.
Inclusion of water quality data for lead in Figure 0.5.11 alters significantly the isopleth map, given that well 528 has the second highest reported value for Lead for all the wells sampled.
In the final RAP, DOE should discuss possible health effects due to concentrations of lead and other contaminants in excess of the MCLs if the well is in use.
In addition, in the groundwater restoration pla'n, DOE should define the complete extent of downgradient contamination in domestic wells resulting from past milling activities, and should discuss how domestic well contamination will be dealt with prior to and during groundwater restoration activities.
10, CRAP, Figure 0.5.11 and Table D.5.5 - Inconsistent value for lead from background well 533.
DOE illustrates in Figure 0.5.11 a value for lead of 0.03 mg/l reported for July, 1987, while Table D.5.5 reports a value of 0.06 og/l for the same sampling period.
Because well 533 is used as a background well, accurate characterization and reporting of ambient concentrations of lead and other contaminants is particularly important. DOE should clear up this discrepancy in the final RAP.
- 11. dRAP, Table D.5.5 - Analysis of gross-alpha.
Gross-alpha particle activity was not included in Table D.5.5, but is an identified hazardous constituent in 40 CFR Parts 264.93 and 192.12(c).
DOE should analyze for gross-alpha in future monitoring and should incorporate the results in Table D.5.5 of the final RAP.
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5 BOWMAN 22.
dRAP, General - Grcundwater protection standard.
00E has not specified a groundwater protection sti.ndard for the Bowman site as required in 40 CFR Part 192.02. The groundwater protection standard should contain three components: 1) a list of hazardous constituents expected to be at the site, which includes radium, uranium, molybdenum, nitrate, and gross-alpha;
- 2) a corresponding list of concentration limits for the listed constituents; and 3) a point of compliance. DOE should provide information adoressing these components prior to submittal of the final RAP.
- 13. dRAP, General - Performance analysis.
In accordance with 40 CFR 192 Subpart A, DOE should demonstrate through analyses that the conceptual design of the disposal unit and the performance of the disposal unit are adequate to comply with the site-specific groundwater protection standard.
With respect to the design analysis of the disposal unit, DOE has not demonstrated in the dRAP that engineered features designed to limit infiltration and prevent groundwater contamination required in 40 CFR Part 192.20(a)(2) are adequate to protect groundwater resources.
In the final RAP, DOE should specify in their design analysis the design necessary to achieve compliance with the groundwater protection standard, and discuss specific aspects of the design, such as: 1) estimated inventory of residual radioactive material and hazardous constituents, 2) elimination of free liquids, 3) stabilization of radioactive material, and 4) infiltratiun through the cover (fromNRCdraftBTP,1988).
l With respect to the performance assessment of the dispesal unit provided in the of the current design (gh D-179), DOE has not demonstrated that the performance dRAP (pages D-177 throu l
infiltration / radon barrier with saturated hydraulic l
conductivity = 1 E-7 cm/s) is adequate to comply w(ith the groundwater i
protection standard required in 40 CFR Part 192.02 a)(3). Predicted hazardous
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constituent concentrations are ebove the EPA Maximum Concentration Limits (MCL's) as far as 820 feet downgradient from the stabilized embanbnent after 1000 years. While DOE has indicated in the dRAF that alternative designs, such as a geochemical barrier, sodium-amended cover, and geomembrane are currently being evaluated for' their feasibility, the performance of these alternative designs has not been assessed and compared to the groundwater protection stancards.
l In addition to evaluating alternative design features, DOE is evaluating whether predictions made by S0ILMOIST of the saturated hydraulic conductivity l
of the cover are too conservative (K = 1 E-7 cm/s), and is also testing the cover to determine if a lower hydraulic conductivity is achievable through t.ompaction. Based on the results of the performance assessment, a 1cwer hydraulic conductivity of the cover would facilitate compliance with the MCL's j
at the toe of the embanbnent. DOE shculo submit the proposed final design
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necessary to assure compliance witn the groundwater protection standards and accompanying assessment of disposal unit perfurmance to demonstrate compliance with40CFRPart192.02(a)(3).
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6 14 dRAP, General - Closure perforrance standard, t
In accordance with Ne closure performance standard in 40 CFR Part 192.02(a)(4), DOE has not dernonstrated that the proposed disposal aesign 1) minimizes the need for further maintenance as required in 40 CFR Part 264.111(a) and 2) controls, minimizer, or eliminates releases of hazardous constituents to groundwater as required in 40 CFR Part 264.111(b).
To comply with the closure performance standard relating to groundwater protection (40 CFR Part 264.111(b)) DOE needs to specify the design required to meet the groundwater protection standards and assess that the performance of the disposal unit is adequate to protect groundwater resources as required in,40 CFR 192.02(a)(3) (see connent #13).
To comply with the requirement for minimizing maintenance (264.111(a)), DOE needs to demonstrate compliance with the long-term stability standards in 40 CFR Part 192.02(a).
In the final RAP, DOE should demonstrate through analysis that the proposed design Satures for groundwater protection do not rely upon maintenance to comply with the groundwater protection standard. A potentially significant concern at the Bowman site is flooding of the stabilized pile due to the placement of the embankment in a low lying area having an extremely shallow water table (6 feet from surface).
Flooding and ponding could compromise the ability of the cover to minimize infiltration, resulting in increased leaching and subsequent failure to comply with the long-term stability standards in 40 CFR Part 192.02(a).
In their analysis, DOE should address the effects of potential flooding and ponding'on the need to rely upon maintenance to assure compliance with the groundwater protection standards.
- 15. dRAP, General - Groundwater neonitoring and corrective action.
DOE has not described in the dRAP how monitoring will be conducted before, during and after disposal activities at the Bcwman site adequate to demonstrate that the initial performance of the disposal unit complies with groundwater protection and closure performance standards under 40 CFR Parts 192.02(a)(3) and(4).
DOE should propose a conceptual monitoring plan in the final RAP that will be adequate to confirm initial performance of the disposal unit.
In addition, DOE should provide in the final RAP an evaluation of alternative corrective actions that could be implemented if the monitoring program indicates that the dispscal unit or the ertankment are not performing adequately.
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- 16. dRAP, General - Groundwater restoration.
DOE,has not provided information on cleanup of groundwater contaminated by past milling activities at the Bowman site, as required under Subpart B.of 40 CFR Part 192. 'The NRC staff considers that groundwater cleanup may be deferred until after EPA promulgates final groundwater protection standards, provided that DOE adequately demcnstrates that disposal may proceed independently of cleanup. DOE has not demonstrated in the dRAP that the proposed disposal activities at the Bowman. site will not preclude successful demonstration and implementation of future cleanup activities adequate to comply with 40 CFR Subparts B and C.
DOE should either select and present to NRC complete information on the groundwater cleanup standard, cleanup demonstration, a'd n
cleanupmonitoringprograminthefinalRAP(including)howplannedcleanus activities will be integrated with disposal activities, or demonstrate w1y cleanup can be defe.rred until'after promulgation of the final EPA standards.
- 17. dRAP, Page D-172 - Characterization of groundwater flow in upper aquifer unit.
DOE states in the dRAP that potentiometric data are not sufficient to construct a potentiometric surface of the uppern,ost aquifer system (only three wells tap this unit). However, DOE assumes a hydraulic gradient of 0.005 to estimate an average linear velocity and subsequently predict downgradient concentrations of hazardous constituents. Although a potentiometric map has not been constructed, NRC staff infers a hydraulic gradient of approximately 0.01 from the water level data reported in Table 0.5.8 and the well location map in Figure 0.5.14.
If the higher gradient it used te calculate average linear velocity, the velocity value essentially is doubled, which would change the predictions of downgradient contaminant concentrations. NRC staff recommends that DOE install additional monitor wells corpleted in this upper unit to 1) better define' rates and directions of groundt,ater flow to verify predicted concentrations of hazardous constituents, and 2) better characterize background concentration of the upper unit.
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18.
dRAP, Page 0-172 - Inaccurate description of uppermost aquifer unit.
DOE refers in the dRAP to the uppermost aquifer unit above the lignite zone as having "relatively low hydraulic conductivity." However, examination of Table D.S.9 reveals that measured hydraulic conductivity values range from 0.15 to 2.97 f t/ day, which are not "relatively low" values. To justify their conclusion. DOE should install additional wells completed in this upper aquifer to establish rates and direction of flow. Alternately, DOE should more accurately describe the upper unit in the final RAP as having a relatively high hydraulic conductivity, steep gradient, and shallow and fluctuating water table.
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- 19. dRAP, Page D-172 - Characterization of hydraulic conductivity of lower lignite zone.
DOE states in the dRAP that monitor wells completed in the four foot lignite zone recharged too rapidly during the slug test to calculate a numeric value of hydraulic conductivity. However, DOE reports in Table D.5.9 values of hydraulic conductivity of 23.55 and 2.37 ft/ day for the lignite unit, which is inconsistent with the test.
In either case, DOE has not adequately characterized hydraulic conductivity of the lignite zone and is unable to estimate average linear velocity of for this unit. Adecuate characterization of this unit may be important to predict downgradient concentrationx of hazardous constituents in the performance assessment.
To assess tha performance of dispsoal and cleanup activities, NRC staff recomends that DOE install additional wells in this unit and perform pump tests if needed to calculate numeric values of hydraulic conductivity.
- 20. dRAP, Page 0-175 - Extent of contamination.
DOE indicates in the dRAP that due to lack of wells downgradient of the Bowman site (Figure 0.5.12), the extent of contamination offsite toward the east and southeast has not been completely characterized. DOE indicates that additional wells could be installed in all three aquifer zones downgradient from the site.
NRC staff recomends that DOE install additional wells to the east and to the south of he Bowman site to: 1) cdequately characterize the full extent of contamination, 2) better characterize groundwater flow, and 3) define a potentiometric surface for the uppermost aquifer unit.
- 21. dRAP, Page 0-179 and DEA pages C-7 and C Inconsistent information reported on probability of Bowman site achieving EPA MCLs.
DOE reports in the dRAP and DEA that there is a very low probability that the existing disposal design will meet the EPA groundwater maximum concentration limits (MCLs) within the mixing zone beneath the site.
DOE also reports in the dRAP that if the cover design of the enbankment is modified to reduce saturated hydraulic conductivity by one order of magnitude, or if it can be demonstrated that the barrier is unsaturated, the disposal site will be in compliance with the proposed EPA MCLS. However, this is inconsistent with information in the oEA on page C-71, which indicates that if hydraulic conductivity of the cover is modified by one order of magnitude, or if it can be demonstrated that the barrier is unsaturated, there is a low probability that the disposal site would achieve compliance.
Finally, DOE reports on page C-7 of the DEA that if the hydraulic conductivity of the cover is reduced by one order of magnitude, there is a low probabilit.y that the site would achieve compliance, but if it is demonstrated that the infiltration barrier is not saturated, there is a good probability of achieving compliance.
DOE should resolve these inconsistencies in information reported in the final RAP.
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22.
dRAP, Page D-178, and supplemental information provided on the Domenico and Robbins model, 1985.
00E has not justified several of the assumptions and input parameters used to calculate contaminant concentrations downgradient from the disposal site; these calculations were parformed to assess whether the disposal site will comply with proposed EPA standards. For example, 00E uses the mean value of hydraulic conductivity measured from two wells to calculate average linear velocity in the upper aquifer unit below the embankment. Cue to the minimal hydraulic conductivity data available for this unit, 00E shoulo conservatively use the highest measured value of the two to calculate velocity. In addition, DOE, assumes a hydraulic gradient of 0.005 for this upper unit, while there is insufficient data to support use of this vclue. Otherconcernsinclude1)use of a value of 20 feet for the thickness of the mixing zone below the embankment, when DOE reports in the dRAP (page 0-178) a mixing zone thickness of 15 feet, and 2) selection of dispersion coefficient values, which are not referenced or explained.
Finally, DOE states in the DEA that, ".... contaminants would disperse horizontally and vertically through the groundwater in the fine grained sediments of the upper zone unit reaching the more transmissive lignite zone, where substantial dilution should occur..." However, the lignite zone does not appear to have been considered in the transport calculation. DOE should justify in the final RAP why the transmissive lignite zone is not considered a potential pathway for contaminant migration and shoulo justify use of all input parameters used in the Demenico and Robbins model, t
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10 Geotechnical Engineering
- 23. dRAP, Page 17, Section 3.2.2 - Belfield, Radiation levels and concentrations.
The description of the excavation operations to remove contaminated seils from the Belfield site should be expanded to cover: (1) the anticipated configuration (plan with top and bottom of slopes, bottom elevations) of the excavation when completed; (2) the measurements (type, equipment to be used, frequency of readings) to be made to ensure that all contaminated materia,1s are removed; and (3) the specific grading plan for restoring the excavated area after removal of the contaminated soils.
24 dRAP. Page 29, Section 3.4.1 - Processing sites.
Copies of the logs for the test pit explorations in the Griffin Borrow site (Figure 3.11) have nut been provided. The logs should be available to evaluate this potential borrow source for radon barrier materials, particularly to understand the problems with avoiding the lignite layers. The borrow excavation operations should be described to cover (1) the field method to be used to ioentify acceptable radon barrier materials,)(2) the method of (3 the anticipated excavation (willthesoilsoverdepthbemixed?)[4)thespecificgradingplan configuration of the excavated borrow area, and for restoring the excavated area.
- 25. dAAP, Page 37, Section 3.4.2 - Infiltration / radon barrier and random fill.
Provide the support for the statement that the Griffin borrow soils exhibit good properties for radon barrier material by specifically identifying all the laboratory test data upon which this statement is based.
It would be helpful if all the pertinent data were graphically surinarized for each important engineering characteristic (e.g. low permeability, good radon diffusion properties) and the selection design parameter was shown in relation to the available data.
With respect to Table D.4.7, is back pressuring the sample in the triaxial cell the cause of the change in density from the initial to the final condition?
Because the final densities are significantly higher than the densities to be required in compaction control, the resulting hydraulic concuttivity values provided on Table D.4.7 may not be conservative.
Please disetss the potential effect of using these non-cunservative values, spe;ifically with regard to redon barrier design.
In addition, on Table D 4.7 it is indicated that samples were taken from a depth interval of 2.0 to 8.0 feet. Will actual excavation operations duplicate this mixing of materials with depth?
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- 26. dRAP, Page 37, Section 3.4.2 - Erosion protection materials.
The description of the sand and gravel materials from the Bowman borrow site needs to be expanded to describe (1) the subsurface conditions (areal extent, soil layering, depths of available borrow quantities), (2) the anticipated method of borrow excavation, (3) the method of sampling used and the test results on gradation and material quality and durability (refeunced to specific test data) and (4) the design details demonstrating h w the appropriate filter criteria has been met.
27.
ORAP, Page 37, Section 3.4.2 - Erosion protection materials.
Description of the plans for borrowing at the Rhame site should include (1) the rock source (areal extent and depths), (2) the anticipated range and distribution of rock sizes and how this range was determined, (3) potential problems with excluding deleterious materials or in obtaining the required volume, and (4) the specific criteria and test results that demonstrate suitable material quality and durability.
- 28. dRAP, Page 42, Section 3.5.2 - Groundwater movement.
Provide the location of the spring on Figure D.5.16.
- 29. dRAP, Page 63, Secton 4.3.9 - Conceptual design.
There is very little factual information provided on the stability analyses of the disposal embankment slopes. As suggested in the NRC Standard Review Plan (SRP), the information to be provided should include: (1) cross-sections and profiles with representative engineering properties (density, shear strengths) for the embankment and in situ materials; (2) discussion uf the procedures used to select the conservative soil properties and profiles for analyses from the available field and laboratory data; (3) a description of the groundwater conditions assumed in the stability analyses (including any effects from flooding or ponding assumed to occur from design bases events); (4) stability calculttions from both static and dynamic loading conditions including the design issumptions (e.g. boundaries of the various types of embankment and foundation soils, dynamic and water pressures acting within the slope); and (6) faiiure surfaces corresponding to the lowest factors of safety.
- 30. dRAP, Page 63, Section 4.3.9 - Conceptual design.
Soils that are compacted to only 90 percent of Standard Proctor are not so dense to be unquestionably safe against liquefaction type failure. Also, the level of compactive effort to be required for cohesionless filter and bedding materials has not been provided and therfore, the ability of these materials to
12 resist liquefaction needs to be eddressed with supporting information. The discussion on resistance of the site's soil to liquefaction should be expanded in the final RAP to address concerns with 90 percent compacted soils and the cohesionless soils, and clearly describe the water conditions that could conservatively be assumed to develop in the long-term fur both the embankment and foundation sofis.
- 31. dRAP, Page 64, Section 4.3.9 - Conceptual design.
Only concluding staternents on the effects of settlement are provided.
A, discussion on settlement needs to provide essential information (refer to SRP for guidance on type of information) and should include calculaitons with the supporting technical basis for corcluding that differential settlement will not be a problem (e.g. cracking of the radon barrier cover layer). The discussion should also address the anticipated non-uniform placement of organics and debris in the embankment and how the presence of these materials has been considered in the slope stability and settlement analyses. What controls will DOE require in construction on the placement of organics and debris (other than on maximum percent) to ensure conditions more severe than those assumed in design will not occur?
It would be worthwhile when describing the results of the settlement study to tie in the settlement and displacement monitoring that is planned for the surveillance and maintenance program that is intended to verify that the completed disposal site is functioning as designed.
32, dRAP, Page 65, Sc-tion 4.3.9 - Design criteria.
What compactive effort and moisture control is to be required for the filter and bedding layers? Are the windblown materials (Figure 4.3) to be compacted the same as the contaminated materials? What laboratory test results are available for the windblown materials to understand their engineering characteristics? Recognizing that cohesive soils when compacted dry of optimum may, upon wetting, exhibit significant compressibility, are there valid design considerations for compacting the contaminated materials as dry as five percent below optimum as proposed? What construction controls other than on compaction and moisture (e.g. maximum size, maximum or minimum percent fines, soil classification,, lift thichness, plasticity, quality and durability) are to be required for the radon barrier materials, random fill and filter and bedding layers? Have the practical considerations for construciton placement of an approzimately 30-inch wide layer been considered? (This results from a 6-inch thick layer on a 5H to IV slope).
33, dRAP, Page 65, Section 4.3.10 - Design criteria.
This paragraph notes that the radcn cover thickness needs to be determined during final design. The final RAP should discuss the specific test results used in final design, the technical bases for selecting the final design parameters and also provide the pertinent calculations supporting the final design thickness, l'
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- 34. dRAP, Page 67, Section 4.3.11 - Toe protection rock sizing: conceptual design.
Excavating to a depth of seven feet below ground surface for the rock apron could at some locations result in extending the excavation below the upper water surface. What provisions are planned to permit performing this work in the dry? The design of rock toe apron should address protection measures (filter critera) needed to prevent the migration of fines from the natural soils into the rock apron.
In addition, what design provisions have been considered to prevent ponding in the rock apron from adversely affecting the stability of the final embankment. What specific drainage measures are planned to remove water that is collected in the rock toe apron?
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Surface Water Hydrology
- 35. dRAP, Civil engineering calculation t B0W-12-87-08-05-00 and #
B0W-12-87-05-03-00.
We note from our review of the civil engineering calculations that the water surface profile calculations for the disposal site were based on the use of normal depth procedures. Normal depth procedures were also used to assess the erosion protection requirements for the side slopes of the rendiated embankment.
Based on an examination of the topography and the overall site location adjacent to railroad and highway embankments, we conclude that calculations using normal depth procedures may not be appropriate at this location.
It appears that the highway embankment will probably act as a constriction and/or cownstream control, causing flood runoff to pond on the entankment side slopes.
Depending on culvert capacity (which should probably be ignored due to clogging), it appears that flood runoff will cvertop the roadway, causing at least several feet of ponding on the embankment. Since the culverts are likely to become clogged during major flood events, little or no flow should be assumed to occur in these structures.
A more appropriate method of computing water surface profiles would be to use standard-step backwater models, such as the U. S. Army Corps of Engineers HEC-2 model. Such models can account for flow occurring over and under roadway embankments which act as constrictions.
In using models such as HEC-2 at this location, it may be necessary to begin the water surface profile calculations some distance downstream of the reacway embankment to determine that the embankment is acting as a control section for various flow rates up to and including the Probable Msximum Flood (pMF). Due to other constricitons and/or topography upstream of the pile, it ray also be necessary to determine that flood flows from adjacent drainages will not spill over into the East and West Drainages or that these drainages will not spill over into each other during major flood events.
The velocities and flow depths derived using HEC-2 may then be used to determine riprap requirements for the pile side slopes.
For any part of the pile where the ground slope is very small or non-existent, the ground slope should not be used to determine the shear stress and riprap requirements.
Rather, the slope of the energy grade line, as computed by the HEC-2 model, shoulo be used in these areas to determine the slope to be used in calculating riprap requirements on various areas of the pile.
(We note from the calculations that some areas have practically no slope, and using such slopes is not representative of the forces which may act during a flood event).
,-,------,-,---,g
,----,y--,-e,.y
4 15
- 36. dRAP, Section 4.3.8 and Figure 4.1 - Slope stability.
We note from the pile layout that it will be located in a relatively low-lying area adjacent to several small drainages.
It also appears that it will be located in a poorly-drained area, as evidenced by the occurrence of ponded water in low-lying areas.
It further appears that the culverts / bridges under the highway embankment may not provide adequate drainage during and after flood events on the adjacent small streams.
It appears that there is a potential for significant pending to occur on the embankment. This may have some effect on slope stability and there is a potential that groundwater quality could be affected by any increases in leaching rate caused by the ponding on and adjacent to the pile.
will not adversely affect slope stability (yses to demonstrate that ponding The RAP should provide discussions and anal see comment # 34) or goundwater quality (see connent # 14). Alternately, the RAP should justify that ponding will not occur in the area of the embankment. Such justification should address the capacity of the culverts and ponding en the pile during both routine and extreme flood events, particularly if they become clogged and cannot be naturally flushed out.
- 37. dRAP, Sections 4.3.5 and 4.3.8 - Embankments.
We note that some credit has been taken for the presence of man-made structures (highway and railroad entanksnents) in reducing tie potential for lateral Unless it can be shown that erosion of streams adjacent to the proposed pile.,for a these structures will survive without maintenance 200-1000 year period, no credit should be taken for their presence in reducing the potential for geomorphic changes to occur.
Particularly for the embankments which may reduce flow velocitics adjacent to the pile, more conservative assumptions regarding their survivability should be used. Additional backwater calculations should be performed with the embankments removed (for whatever reason) to determine that the erosion protection on the pile has been designed for the most critical case.
Additionally, the embankments should be assumed to be removed in the assessment of potential geomorphic changes (see also Geology connents).
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16 Geology 38, dRAP, Page 28 - Bowman, Geomorphic hazard.
Paragraph one under section 3.3.4, Geomorphic hazard, states, "Based on the present man-made interferences with the drainage, lateral erosion and gullying is not likely to occur.
Because ponding provides a water source for cattle and conserves farm topsoil, changes to the drainage are not expected."
Because the potential for erosion must be assessed, the duration of the,
man-made interferences with the drainage need to be shown to be expected to last 200 to 1000 years. Otherwise, it should be demonstrated that if man-made interferences are removed that no lateral erosion or geomorphic changes could occur in a 200 to 1000-year period that could adversely affect pile stability.
- 39. dRAP, Page 28 - Bowman, Geomorphic hazards.
Paragraph one under section 3.3.5, Potential impact on future natural rescurce development, indicates that groundwater is not a significant resource at the Bowman site location. As the disposal site for all the tailings, the groundwater quality and quanity at the Bonnan site is important to evaluating the impacts of the proposed action. No references were given in this section to support the conclusions made on the resource potential of groundwater at Bowman. Full documentation or references for the conclusions made about the Bowman site groundwater should be provided in this section.
40.
dRAP, Page 0 Bowman, Geomorphic hazards.
Paragraph two under section 0.3.7.1, Geomorphic hazards, refers to erosion along the stream on the west side of the Bowman Site. The final document should be amended to specifically define the location of this stream on a suitable topographic map so its potential impacts may be adequately assessed.
41, dRAP, Page 0 Bowman, Geomorphic hazards.
Paragraph 4 under section 0.3.7.1, Geomorphic hazards, states that the Bowman area is susceptible to wind erosion. This paragraph concludes by stating that standard repository designs, including a gravel cap, should prevent wind erosion of contaminated materials.
If high wind conditions exist, it is not clear why standard repository designs intended for areas with less wind should be expected to prevent wind erosion of contaminated material at this location.
00E should discuss particular features of the Bowman site design that are intended to prevent erosion for the specific conditions in the region or should reference other sections of the document which provide a thorough discussion of the ability of the design to resist wind erosion.
4 17 42, CRAP, Page 0-164 - Belfield, Hydrogeologic environment.
Section 0.5.3.2, Hydrogeologic environment, paragraph 2, refers to a claystone of undetermined thickness. The hydrologic significance of' the claystone which is below a permeable 15' thick lignite zone needs to be explained. The approximate thickness of the claystone and b& sis for the value used should be provided.
- 43. dRAP, Geologic Logs, Cross Sections, and Borehole Plot Maps.
There are many problems, most minor, with the geologic logs, cross sectio's and n
borehole plot maps. When taken as a whole, these problems impair the ability to review the information. Some of the problems found during the review are as follows:
Bowman -
Figure 3.10 shows monitor wells 518 and 511 numbered and spaced differently than Figure D.5.14.
Figure 3.10 shows monitor well 517 in a different location than in
~
Figure D.5.14.
Figure 3.10 shows monitor wells 513 and 515 numbered and spaced differently than in Figure D.S.14 Figure D.5.15, Hydrogeologic Cross Section A-A' Bowman Processing site-Griffin, North Dakota, and Figure 0.3.9, Geologic Cross Section of the Bowman Processing Site, has 3 logs from monitor wells used to construct the lithology on the cross sections. The data for monitor well 502 cannot be verified because the log for this well is not included in the log section (Addendum 03). Therefore, assessment of the Bowmar. Site Hydrogeologic Cross Section for the Bowman Site is based on only two well logs.
Addendum D3 includes a log for hole #580 but there is no map showing the location of this hole.
Monitor wells 501 and 503 are shown on Figures D.5.12, D.5.14, and 3.10, but logs of these wells are not included in Addendum D3.
Belfield -
Hole #581 has a log included in Addendum D3 but there is no map showing the location of this hole.
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s 18 1
Although the number 240 appears on Figure 3.7, there is no legend applied to the map which plots the location and type of borehole represented by the number 240.
Boreholes 206, 221, 236, and 237 appear on Figure 3.7 but no logs for these holes are included in Addendum 03.
Fioure 0.5.4 shows a hydrogeologic cross section.
The log for monitor well 540 appears more complex in the upper 30' than indicated on the hydrogeologic cross section.
On Figures D.5.1 and 3.9, wells 537 and 540 have different loca'tions.
Figure 3.9 shows the location of hole 521, but this hole is not included in the logs in Addendum 03.
Figure D.5.3 shows a borehole symbol plotted north and slightly west of #542. This borehole has no numerical label.
The discrepancies and deficiencies noted above should be corrected in the final RAP, with proper information provided.
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