ML20235M794
| ML20235M794 | |
| Person / Time | |
|---|---|
| Issue date: | 07/06/1987 |
| From: | Fliegel M NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Weber M NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| References | |
| REF-WM-62 NUDOCS 8707170316 | |
| Download: ML20235M794 (25) | |
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REVIEW OF RIFLE DRAFT DRAP U,
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>'1 JUL 0 61987 c
l MEMORANDUM FOR: Myron H. Fliegel, Section Leader Operations Branch Division r; Low-Level Waste Management and Decommissioning FROM:
Michael Weber, Acting Section Leader Technical Branch Division of Low-Level Waste Management and Decommissioning
SUBJECT:
REVIEW 0F THE RIFLE DRAFT REMEDIAL ACTION PLAN AND DRAFT ENVIRONMENTAL IMPACT STATEMENT In accordance with your request, the Siting Section, LLTB, has reviewed the Draft Remedial Action Plan (DRAP) and Draft Environmental Impact Statement (DEIS) for the Uranium Mill Tailings Remedial Action sites at Rifle, Colorado.
Based on our review, we conclude that the DRAP does not demonstrate compliance with reasonable assurance with the EPA standards in 40 CFR Part 192 in the review areas of long-term stability, geologic stability, and groundwater protection.
Our review indicates that erosion protection of DOE's preferred disposal site, Estes Gulch, may be difficult because of steep slopes adjacent to the site and the need to divert upstream surface water flows around the site.
DOE's design requires the use of steep, heavily-armored diversion ditches that will probably require long-term maintenance to ensure satisfn oy performance of erosion protection measures. Because of the extensive and elaborate measures required to protect this site, we have serious reservations about the effectiveness' of these' measures with respect to tailings stabili::ation for 200 to 1,000 years.
Our review of the DEIS indicates that less costly and possibly more viable disposal alternatives have.been identified for the Rifle tailings. While we do not necessarily endorse the use of any one alternative, the DEIS indicates that tetter sites than Estes Gulch may be reasonably available near the Rifle site. Therefore, we suggest that DOE re-examine the selection.of the Estes Gulch disposal alternative, especially in light of the possibility that compliance with the EPA standards may be difficult to achieve at this site.
In addition, the dRAP does not demonstrate that the design basis is consistent with the site geologic setting.
In many areas, the dRAP's hydrologic and geologic information is inconsistent and incomplete. These deficiencies preclude independent verification of DOE's conclusions by the NRC staff.
8707170316 070706 PDR W AST E g
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JUL 0 6 BB7 REVIEW OF RIFLE DRAFT DRAP 2
j As per your guidance, the enclosed comments have not been produced using the.UMTRA comment format.
Kristin Westbrook will provide additional editorial comments to George Pangburn by July 8,1987, for communication to D0E.
This review was performed by Joel Grimm (geomorphology), Ted Johnson (surface I
water hydrology), Kristin Westbrook (geology), Michael Blackford (seismology),
and Michael Young (groundwater hydrology). Please contact Ms. Westbrook if you have any comments or questions about our review.
1 Original Signed By Michael Weber, Acting Section Leader Technical Branch Division of Low-Level Waste Management and Decommissioning
Enclosures:
As Stated m
COMMENTS RIFLE RAP
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JUL 0 6 ME7 SITING SECTION COMMENTS ON THE RIFLE DRAFT REMEDIAL ACTION PLAN AND DRAFT ENVIRONMENTAL IMPACT STATEMENT Surface Water:
SW1. RAP: Page 87 (Design of Rock Apron).
.The design of the rock apron for the southern end of the remediated pile may not be adequate to protect the pile against flooding and erosion.
It appears that several key factors have been overlooked in the assessment:
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i A.
The apron has been designed to prevent gully intrusion to a maximum depth of 15 feet. However, other sections of the RAP ('page 72 1
l and Appendix D) indicate that the potential exists for additional, future downcutting. Since 15-foot gullies already exist, the apron design should account for the expected addi.tional erosion.
If the additional erosion cannot be quantified, it may be necessary to design the apron assuming that erosion.could occur to the depth of competent bedrock. The apron should be re-designed accordingly to account for the additional, expected downcutting.
1 B.
The rock for the apron has been sized assuming that' sheet flow occurs on a IV on 2H slope. The assumption of sheet. flow on a plane slope is not valid because a new rock channel will be formed when the rock apron collapses into the gully. Therefore, the apron should be designed under the assumption that flow in a channel will occur over the apron with a channel slope of IV on 2H.
The apron design should be modified, and all assumptions and calculations should be carefully documented.
The RAP should be revised to provide these improved designs or should justify that the proposed design is adequate to protect against long-term flooding and erosion.
COMMENTS RIFLE RAP -
SW2. RAP: Page 85 (Design of Diversion Ditches - Upstream End).
The diversion ditches at the extreme upstream (northern) end of I
the pile may not be adequate to protect against. flooding and 4
erosion. Concentrated flow in the natural channel immediately north'
.I of the pile could cause excessive erosive forces to occur in specific, j
undefinable locations. The natural channel should transition l ~
smoothly into the extreme upstream portions of both the east and
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l' west channels to assure even flow distribution across the channel i
cross-sections. Therefore, the channel design should be revised to l
include a rock protected transition section extending upstream into the natural channel. At a minimum, such a section should assure that:
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(a) flows are evenly distributed across the channel, so that flows in the east and west channels do not exceed their design flows; (b) concentrated flows will not impinge directly on the south side slopes of the channels; and (c) hydraulic jumps or significant energy dissipation will not occur.
1 SW3. RAP: page 87 (Design of Diversion Ditches - Upstream End).
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Very high velocities and large amounts of sediment and debris appear j
to be a potential problem at the upstream end of the diversion ditches.
Topographic maps (Fig. 4.3) indicate that the slope of the natural j
channel in this area is greater than approximately 20 percent. A slope of this steepness will produce very high velocities in the natural channel Such velocities are capable of moving large amounts of debris and sediment, which will likely be deposited at the upstream end of the diversion channels.
It appears that debris deposition could be of such magnitude that long-term maintenance will be needed to assure adequate performance of the channels. Therefore, this site may not meet EPA standards due to the need for active maintenance.
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i In-order to demonstrate that epa standards are met by the proposed design, the RAP should be revised to (1) modify the design of the channels to avoid the need for long-term maintenance or (2) demonstrate the following:
(a) Demonstrate that the material eroded by the natural stream does not-deposit in the diversion channels, or that if it is deposited, the d
channels will always be self-cleaning. Show that transitioning a p
20 percent slope (natural channel) to a much flatter slope (diversion channel) is feasible without debris deposition (see comment SW2).
(b) Demonstrate that' debris flows caused either by alluvial forces (gullying and erosion)mr landslides will not reduce the 4
capacity of the channels. The existing debris flow (Fig. 4.3)
I should be characterized in support of this justification.
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(c) Demonstrate that the position and alignment of the natural channel (upstream of the diversion channels) is likely to be constant over a long period of time, particularly in light of the potential for erosion and debris deposition.
Show that the proposed design accounts for any such expected changes.
SW4. RAP; Page 85 (Design of Diversion Ditches).
The alignment of the diversion ditches shown in Figure 4.1 and in the
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supporting hydraulic calculations indicates that there will be several locations where channel bends will occur. However, these bends, with the J
associated increase in shear stress, have not been accounted for in the l
design of the riprap.
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The RAP should be modified to provide a revised design that (1) alters the alignment of the ditches to eliminate the bends and/or (2) increases the riprap size to accommodate the increase in shear stresses or demonstrates that the proposed rock sizes are adequate to resist the i
shear forces produced at the channel bends.
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COMMENTS RIFLE RAP,
q SW5. RAP: Page 85 (Design of Diversion Ditches - Down' stream End).
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The diversion ditch outlets at the south end of the pile have been designed assuming that the diversion ditches discharge into natural channels with trapezoidal cross-sections and bottom widths of 35 and 100 feet. Since the bottom widths of natural channels observed at i
the site appear to be much smaller than the assumed 35-100 feet and
_I are not. trapezoidal in cross section, it appears that the ditches j
may have been inappropriately designed. The proposed design may not be effective in preventing headward erosion since velocities will be higher in a smaller channel. Additionally, the assumption of sheet flow over the rock will not be valid, as described in Comment SW1 4
above; the rock should be designed for channel flow on a IV on 2H slope. A rock layer keyed tnto competent bedrock would appear to be I
the most effective erosion protection approach.
The RAP should be revised to modify the diversion ditch design to protect against headward erosion or to demonstrate that the proposed designs are adequate.
SW6. RAP: Page 85 (Design of Diversion Ditches).
The diversion ditches have been designed using a manning's 'n' value computed using the equation n =.0395(D50)
Recent research and technical assistance performed for the NRC staff by Colorado State University (NUREG/CR-4651) have indicated that a more accurate equation for computing the 'n' value at low flow depths in rock-lined channels is n =.0456 (D50. S)*
where S = the channel slope.
Use of this equation may result in increased depths of flow which may, in turn, increase the riprap size required to protect the diversion ditches.
The RAP should be revised to modify the calculation of Manning's 'n' or to demonstrate the adequacy of the 'n' values proposed. Additionally, changes to generic design procedures should incorporate this new information.
SU7. RAP: Page D-327 (Rock Durability).
The RAP should be revised to include rock durability specifications and design criteria.
The informat~ ion should include durability specifications and the design criteria that will be applied to rock sizing and gradation.
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COMMENTS RIFLE RAP-.
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SW8. DEIS: Page 29.
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1 One of the major design considerations affecting siting of alternatives
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1 included long-term stability and the ability to withstand flooding and erosion. NRC staff review indicates that long-term stability may be a significant problem at the Estes Gulch site. The long-term maintenance problem, in conjunction with the need to provide extensive and elaborate
. l hydraulic design features, hava resulted in a design that' may not satisfy i;
the EPA long-term stability. standards given 40 CFR 192. The use of such
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elaborate and expensive hydraulic design measures may not be feasible or cost-effective and may not provide the required confidence in oredicting long-term performance. Based on these deficiencies, the EIS should be revised to assess the other disposal alternatives at'more favorable sites.
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COMMENTS RIFLE RAP
- Ground Water:
GW1. dRAP, General, Near-Surface Saturation at Estes Gulch Although fully saturated strata exist at 270 feet below ground level, DOE has not evaluated the potential for near-surface saturation of material existing on i
an intermittent basis in the alluvium. Shallow ground water could interact j
with the stabilized tailings.
NRC staff are concerned that a situation similar l
to the Lakeview, OR, UMTRA site may occur, in which shallow seeps breached the compacted clay walls and began flooding the tailings embankment. This natural process resulted in substantial design modifications to minimize the interaction of the water with tailings material. The current design at Estes Gulch does not address this potential.
For example, the rock lined ditch in the proposed design is not incised enough into the alluvium to route significant amounts of water away frorr the base of the tailings embankment.
Also, if water ponded in the ditch, a line source would be formed increasing the possibility that potentially large volumes of water could flow into the j
tailings embankment.
'Although the deeper saturated layers may not be directly affected by this flooding, perched ground water could enhance contaminant leaching and migration from the stabilized tailings. DOE should investigate this possibility and alter embankment designs appropriately so that near-surface seeps will not result in saturation of tailings material.
GW2. dRAP, D-342, Estes Gulch Travel Time DOE calculated the 230 year and 800 year travel times for leachate eminating from the base of the tailings embankment to reach 75 feet and 270 feet, respectively. These calculations and results are non-conservative.
The hydraulic conductivity value used in the calculation is for compacted clay / radon barrier material, which equals 3.13 E - 07 cm/s.
Thus, DOE non-conservatively assumed that compacted clay material comprises the full l
thickness of foundation soil down to the water table. A more appropriate 1
assumption is to assume that the hydraulic conductivity of the foundation soil j
equals the highest conductivity measured for material beneath the disposal site. In this case, the appropriate conductivity value for determining the travel time would be 1.2 E - 05 cm/s, found in Table D.5.4.
For example, using j
this assumption, a unit gradient, and the effective porosity for sandy-clay
'j material of 18%, mure conservative travel time values for leachate to percolate I
down to saturated layers equal 1.1 years for 75 feet and 3.9 years for 270 f
J feet. The dRAP should be revised to provide conservative analyses of ground-water flow and contaminant transport at the Estes Gulch site to demonstrate adequate protection of ground-water resources.
GW3. dRAP, General, Fate of Leachate DOE has not evaluated the fate of leachate eminating from the pile after stabilization of the tailings at Estes Gulch. Such evaluations are important because leachate may emerge from the embankment in surface drainage features i
within a relatively short distance from the tailings disposal area.
NRC staff j
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COMMENTS RIFLE RAP.
4 is concerned that the proposed disposal design may promote discharge of water from the tailings.may be relatively low, infiltration of.f original pore leachate into the surface environment. Although the drainage o i
rain and snowmelt will eventually recharge the pile and percolate downward.
Leachate percolating through the bottom layer will probably flow southward along the
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bottom layer in the general direction of lithologic and topographic dip.
l Thus, leachate may emerge as diffuse seeps in areas topographically and geologically downgradient from the tailings or as more concentrated seeps in i
the deeper incised gulleys located just south of the proposed disposal area.
Although deeper ground-water resources may not be threatened, direct discharge i
of leachate to the surface may be difficult to solve after construction of the i
embankment. DOE should assess the likelihood of the occurrence of this ii scenario for the proposed design and evaluate whether design modifications are necessary to minimize emergence erf leachate steps. The dRAP should be revised to include a design that addresses this potential problem or justifies how the current design will minimize lateral movement and emergence of leachate.
GW4. dRAP, Page 57, Hydraulic Conditions at Old Rifle i!l DOE asserts that hydraulic conditions at Old Rifle will preclude or at least j l minimize the potential for downward migration of contaminated leachate from 4 '
alluvium into the Wasatch Formation. The dRAP, however, does not demonstrate
!li the validity of this assertion.
Based on limited site information, it appears that significant downward migration of leachate into the Wasatch Formation is
'I occurring. The following factors provide the technical basis for NRC's j i conclusion:
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A.
On Page D-333 of the dRAP (and on Figure D.7.9), DOE used water level measurements in wells 597 and 598 (alluvial) and well 620 (Wasatch) to determine an upward hydraulic gradient from the Wasatch Formation to the alluvial aquifer. Although NRC staff do not dispute these data, these wells are located approximately 4000 feet east of the pile and do not represent hydraulic conditions near the tailings. Water level data from well 584 (alluvium) and well 624 (Wasatch), although collected 40 days apart, show that the head in the alluvial aquifer (5306 feet) is 46 feet higher than head in the Wasatch Formation (5260 feet), indicating that a significant downward hydraulic gradient exists. Because these wells are only 800 feet east of the pile, water levels in them are considered by NRC staff to better represent conditions in the hydrogeologic system near the tailings than water levels in wells 597, 598 and 420.
B.
On Page 0-336, DOE claims that water quality from downgradient wells is similar to background wells. However, water quality analyses from well 645, located south of the Colorado River and downgradient of the Old Rifle pile, indicate anomalously high values of ammonium, chloride, gross beta,
.i sodium and total dissolved solids, relative to upgradient water quality.
DOE has not provided an explanation for why constituent levels are so high j
in this well.
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COMMENTS RIFLE RAP.
C.
Water quality results from well 623 (located 800 feet east of the pile) show elevated levels of chloride, iron, sulfate and TDS relative to background quality. These data indicate contamination of ground water in the Wasatch Formation upgradient of the pile. Because no wells exist north of the Colorado River (downgradient of the pile), DOE cannot evaluate whether water quality in the Wasatch Formation adjacent to and downgradient of the tailings has been affected.
Based on these observations, NRC staff considers that ground water in the Wasatch Formation has been contaminated due to downward migration of tailings j
leachate. The extent, significance, and rates of contaminant migration cannot be evaluated because DOE has not adequately characterized the hydrogeology of the formation. Also, the level of characterization of the Wasatch Formation is below the minimum specified in DOE's Technical Approach Document. The dRAP j
should be revised to characterize the hydrogeology of and the extent of j
contamination in the Wasatch Formation at Old Rifle or demonstrate that additional characterization is not necessary.
GW5. dRAP, General, Background Water Quality The dRAP provides estimates of background ground-water quality for the both the Old and New Rifle sites. Based on data contained in the dRAP and dEIS, however, NRC staff conclude that DOE has not established background ground-water quality. Therefore, NRC staff cannot confirm DOE's conclusions on the extent of ground-water contamination caused by uranium and vanadium recovery operations in the Rifle area. DOE's ground water sampling program was inadequate to characterize spatial and temporal variability of ground-water quality, which may be expected to be relatively large for the transient, alluvial systems encountered at Rifle. DOE collected ground-water samples only once from the majority of wells at the Rifle sites; no wells were sampled more than twice. Based on the level of sampling thus far, DOE cannot assess potentially significant seasonal changes in ground-water quality in the transient alluvial aquifer systems.
Conclusions about background ground-water quality should be based on a minimum of four samples collected quarterly to account for seasonal changes.
DOE needs to establish background ground-water quality adequately to determine the extent and significance of ground-water contamination at the Rifle sites. The dRAP should be revised to characterize background ground-water quality or to demonstrate that the present characterization is adequate to define the extent of contamination and assess its significance.
GW6. dRAP, General, Organic Contaminants DOE did not characterize the extent of organic contamination of ground water at the Rifle sites.
Dissolved organic carbon in alluvial ground water at New Rifle was detected at levels up to 310 mg/1, which indicates the presence of organic contamination. Such high organic concentrations, the diversity of extraction procestes, presence of vanadium pits and other ponds used to separate various extraction fluids, and the on-site storage of a variety of 55 gallon drums and solvent tanks indicates the strong possibility that ground i
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water has been contaminated with organic constituents.
The dRAP should be revised to characterize the extent and significance of organic contamination in ground water at the Rifle sites.
I GW7. dRAp, General, Extent of Contamination Figures in the dRAP describe the lateral extent of ground-water contamination in the alluvial and Wasatch Formations at the New and Old Rifle sites. NRC staff conclude, however, that DDE has not adequately characterized the lateral-or vertical' extent of contamination at the Rifle sites and that the figures provided are ambiguous. The following points support this conclusion:
A.
DOE has not collected any ground-water samples since January 1986 j
for some wells and June 1985 for remaining olde wells. Any conclusions presented in the dRAP can be valid only for the periods from 1985 to 1986.
i The transient nature of the alluvial aquifer systems suggest that the flow l
system and location of plumes will change over time. Therefore, current decisions about remedial actions may be based on out-dated information.
B.
The plume maps provided in the dRAP are not valid because the
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i concentration levels from samples collected during the characterization period were averaged. Averaging of samples'tends to smooth out j
heterogeneities that the characterization program is attempting to assess.
j Therefore, the lateral extent of the contaminant plumes may be considerably underestimated.
C.
The lateral extent of the sulfate plume in the alluvial aquifer at New Rifie is unknown because the leading edge of the plume is hydraulically downgradient of monitor wells furthest from the pile.
D.
DOE has not constructed monitoring wells downgradient of the tailings in the Wasatch Formation at the Old Rifle site. Although DOE asserts that the Wasatch Formation has not been affected by the tailings, data in the dRAP indicate the unit is being contaminated (see coniment GW4).
The deficiencies preclude DOE's characterization and NRC's verification of the extent of ground-water contamination at the New and Old Rifle sites. DOE should institute a monitoring program to supplement historical concentration levels through collection of additional data. The program should include the i
construction of additional wells to monitor areas pr'esently unmonitored, i
sampling of ground water from strategically located wells, analyses of samples for constituents known or suspected of being dissolved in ground water, and the collection of an adequate number of samples to characterize the spatial and temporal variability of water quality and the extent of contamination. The dRAP should be revised to assess these data and to characterize the extent of l
ground-water contamination.
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GW8. dRAP/dEIS, General, Discrepancies The dRAP and dEIS contain sa many inconsistencies and discrepancies between text and tables, text and figures,.and between text sections that NRC's documentation of each one is inappropriate. These inconsistencies complicates independent verification of DOE's conclusions with regard to ground-water i
i protection.
It also may indicate quality control problems with failure to ensure that information is accurately documented. The. examples below illustrate the deficiencies:
A.-
Page E-104 of the dEIS claims that New Rifle alluvium well 581 has i
the highest level of uranium, but uranium concentrations are not contained in the water quality table for this unit (Table E.2.24).
4 B.
Page E-115 of the dEIS claims that alluvial ground-water j
contamination at Old Rifle extends 800 feet downgradient, yet page E-127 claims that contaminated ground water extends only 300 feet downgradient 4
from the pile in the alluvial aquifer.
C.
Page D-332 of the dRAP claims that the hydraulic gradient in the Old' Rifle alluvium is 0.005. Table D.7.5 (Page D-369) indicates that the i
gradient is 0.003, and from Figure D.7.8 (Page D-351), NRC staff calculated a range of gradients from 0.0033 - 0.0064.
I D.
Page D-386 of the dRAP provides water levels measurentents of monitor wells completed in the Wasatch Formation at New Rifle. Page E-50 of the dEIS contains the same table, but water level measurements taken on May 13, 1986, for several wells differ greatly from those presented in the dRAP.
The dRAP and dEIS should be revised to resolve these and other discrepancies through internal review of the documents prior to their release.
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GW9. dRAP, Page D-339, Restoration.
I DOE justified the decision not to implement ground water restoration actions at the Rifle sites based on the following points: 1) restoration costs ($18 million) exceed the value of the resource, 2) no known users of potentially contaminated ground water, 3) measures other than restoration will ensure that no health effects occur from ingestion, 4) the State of Colorado would institute controls, and 5) citizens wishing to use ground water should be required to treat it.
Based on NRC staff review, however, the staff concludes that DOE has not adequately supported these assertions. The following points support this conclusion:
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A.
DOE did not provide a technical basis or methodology from which the
$18 million restoration cost was derived. ~ DOE cannot accurately calculate-restoration cost because (1) the extent of contamination is not known and (2) EPA has not yet promulgated ground-water protection standards.
Without a cost estimation methodology, NRC staff cannot independently j
verify DOE's cost estimate. Therefore, the restoration cost estimates have not been adequately supported in the dEIS/dRAP.
i B.
Although at least 47 wells exist within a two-mile radius of the Rifle sites, DOE asserts that none of the wells are expected to be l
affected by contaminated ground water.
Figure D.7.20 identifies several 4
wells located just north of;the. tailings piles. DOE's assertion with q
respect to potential impacts cannot presently be supported because the extent of ground-water contamination is not known, the possible seasonal changes in flow direction have not been established, and DOE hhs not i
estimated the rate and direction of contaminated ground-water migration.
l C.
According to Colorado Department of Health staff, the State of l
Colorado currently does not have statutory authority to control ground-water use. Therefore, DOE cannot rely upon state imposed institutional controls to preclude ground-water use or to require testing of ground water by residents prior to use.
D.
The dRAP does not demonstrate how measures other than aquifer restoration will ensure protection of health for residents who ingest contaminated ground water.
It would appear likely that ingestion of contaminated water may cause health impacts to the population, regardless of the institutional measures designed to minimize or preclude consumption. DOE should revise this statement appropriately.
The dRAP should be revised to reassess the need for ground-water restoration or to substantiate assertions about ground-water restoration based on assessments that can be independently verified.
GW10. dRAP, Pages D-369 - D-372, Hydraulic Conductivity The dRAP presents a rummary of hydraulic conductivity (K) values determined during site characterization. All K values were included in the dEIS (Tables E.2.7,E.2.9,E.2.11,E.2.13).
The dRAP summary, however, omits hydraulic conductivity values recorded in well 641 (Wasatch, Old Rifle). The dRAP does not explain why this K value was omitted in the summary. Although this value of 99 ft/ day is higher than other values for the Wasatch Formation at Old Rifle, the higher K value may indicate the existence of preferential pathways for contaminant migration beneath the site. Because lithologic logs in the dRAP are either absent or ambiguous, NRC staff cannot assess unique characteristics of each well that could result in the higher K value. The dRAP should be revised to include the K value from well 641 in the summary or to justify why it should not be included.
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GW11. dRAP,'Page D-534, Suitability of Ground Water.
DOE indicates.that natural ground water derived from the alluvial aquifer at Old Rifle is unsuitable for domestic consumption. Water quality data from wells 601 and 602 in the alluvial aquifer, however, indicate that ground water is suitable'for domestic use because TDS levels and other contaminant a
concentrations are below drinking water standards. Although the dRAP states I
that ground water is used primarily for livestock and. irrigation, the f
possibility exists that domestic consumption will occur. The dRAP should be revised to state that alluvial ground water of background quality at Old Rifle q
is suitable for domestic consumption or to demonstrate why it is unsuitable.
GW12. dRAP, Page D-382, Precipitation Rate i
DOE stated that an annual average of 11.02 inches of rainfall and 41.1 inches of snowfall are recorded at Rifle, CO. These averages may not be 1
1 representative of precipitation at the Estes Gulch disposal area because the elevation is 600 feet higher than the town of Rifle. Orographic influences q
could create a microclimate in which substantially higher rainfall and snowfall could occur. This difference in precipitation could result in larger infiltration rates than expected, thus enhancing leachate generation and migration. The dRAP should be revised to characterize precipitation at the Estes Gulch site based on site-specific information or to demonstrate its comparability to precipitation rates at Rifle.
1 GW13. dRAP, Page D-341, Estes Gulch Water Quality DOE conducted a field characterization program at Estes Gulch, which included the construction of 10 ground-water monitoring wells. Despite this program, DOE has not been able to characterize background ground-water quality or hydrogeologic conditions at the Estes Gulch site. Only one well was drilled deep enough to intercept the saturated zone and allow collection of water samples.
The other nine wells were completed at shallower depths above the water table. DOE sampled ground water once in well 963 and found the pH level to be 11.6, which is elevated due to grout contamination in the borehole.
Thus, DOE has not characterized baseline or background ground-water quality at the Estes Gulch site. The dRAP shoulo be revised to characterize ground-water quality and the hydrogeologic system at Estes Gulch or to justify why additional characterization is not necessary.
I GW14. dEIS, Page E-115, Ground-Water Restoration DOE determined that contaminated ground water at the Old Rifle site would be restored naturally in 1.9 years. Based on NRC staff review, this restoration period is highly non-conservative.
Specifically, NRC staff questions the assumption that additional contaminants will not be released to the ground water via dissolution and desorption of contaminants.
If dissolution and I
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! desorption occur, the amount of water flux required to restore the contaminated aquifer. would be. expected to exceed the one pore volume assessed in the dEIS.
Numerous rese' arch programs have shown that several pore volumes'of ground water are needed to clean-up. contaminated aquifers because of dissolution and mobilization of constituents sorbed onto the porous media (e.g. NRC, 1985).
In-addition, NRC staff questions the assumption.that contaminants migrate at 1
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.one-half the ground-water flow rate. Some of the contaminants would be.
L expected to be mobile and thus migrate at the same velocity as groucd water.
L Migration of. other contaminants, however, may by considerably retarded as a result of sorption and precipitation / dissolution reactions which result in a wide variability of contaminant migration rates relative to ground-water flow rates. The dEIS should be revised to assess natural restoration using-conservative assumptions and calculations to present a reasonable range of restoration rates.
Reference:
U.S. NRC, 1985, Methods of Minimizing Ground-Water Contamination From In-Situ Leach Uranium Mining, NUREG/CR-3709, prepared by Battelle Pacific-Northwest Laboratory.
GW15. dEIS, Page E-87, Source Term j
DOE used concentration levels of constituents in neutralized ground water.in i
subsoils beneath the tailings as the' source term for contamination. This j
method underestimates the potential source term because contaminant concentrations in neutralized solutions are generally much lower than in I
solutions that are in contact with the tailings.
In addition, the source term at the Rifle sites may be considerably higher than at other UMTRAP sites because of the recent operation of raffinate pits and other on-site activities creating a range of potential contaminants. DOE should collect representative samples of tailings material and/or tailings pore water. The dEIS should be revised to characterize the contaminant source term.
GW16. dEIS, Page E-111, Irrigation DOE claims that irrigation water is no longer percolating through the tailings, thereby inferring that irrigation of the pile has ceased. However, during a site visit on 11 June 1987, NRC staff observed the New Rifle pile being irrigated at a rate of 700 gallons per minute. The staff were also told that irrigation occurred for about 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> a day. Therefore, additional leachate may be percolating downward into the alluvial ground-water system at New Rifle. The dEIS should be revised to indicate that irrigation is ongoing and i
that additional leachate is being produced.
GW17. dEIS, Page E-115, Impact Assessment DOE claims that sufficient data are not available for calculating natural restoration rates for aquifers at New Rifle. Natural restoration represents, i
in part, the no action case for assessing environmental impacts associated with tailings stabilization at Rifle.
If impacts associated with natural l,
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-restoration cannot be assessed, then DOE cannot compare impacts to water quality for tailings stabilization. The dEIS should be revised to characterize the ground-water systems at the New Rifle site sufficient to assess natural restoration and to evaluate environmental impacts.
GCh1. dRAP, General, Geochemical Characterization q
Review of the dRAP and dEIS indicates that DOE has not adequately considered geochemistry in evaluating environmental transport of contaminants for the remedial action proposed at the Rifle sites. The subject documents do not characterize the geochemistry of the site soil and hydrochemistry, which includes a description of the baseline conditions, contaminant source term, and the supporting quantitative and representative site-specific geochemical data (e.g. dispersion coefficients, attenuating capacities) as required for site l
characterization by the DOE's Technical Approach Document (TAD). Such j
characterization is necessary to assess transport of contaminants in ground water to ensure protection of ground water resources from significant degradation of quality. This deficiency should be corrected in the final dRAP and/or dEIS.
GCh2. dRAP, General, Salt Disequilibria Similar to comments on the Green River, UT UMTRA Project site, DOE has not adequately considered potential dissolution of salts within the tailings pile and resulting contaminant transport and physical instability of the pile during the design life of 200-1000 years. Following the review of DOE's response to NRC comments on the Grand Junction dRAP, NRC staff agreed in principle with DOE that salt dissolution and transport due to geochemical disequilibria leading to failure of the disposal cell and radon barrier could be moderated under certain site conditions. These conditions include, but are not limited to: a water table sufficiently below the bottom of the pile to preclude upward movement of water into the tailings, salt concentrations in the tailings low enough so that dissolution will not rcomote settlement of the pile, and a sufficiently moist cover system which will preclude the development of strong upward hydraulic gradients.
The dRAP should be revised to assess the effects of salt dissolution and related processes on contaminant transport and tail.ings stability during the design life of 200-1000 years. Specifically, DOE should determine representative salt concentrations in the tailings and evaluate the potential for shallow ground water accumulating beneath the pile.
Further, DOE should demonstrate that hydraulic gradients in the tailings will be downward.
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- Geology:
G1. dRAP: Mass Wasting and. Geologic Hazards at Estes Gulch The dRAP's site geology section (p. D-67) provides a presentation of observations and information regarding colluvial deposits and mass wasting near the proposed disposal area. The dRAP states (p. D-80) that only minor slope failures in the disposal area presently affect the dt c.. However, the NRC staff consider that DOE's conclusions are premature and that sufficient observations have not been presented to demonstrate that mass wasting will not present a significant geologic hazard in the next 1000 years.
First, the dRAP states that massive debris flow deposits north of the area.have i
not been active since late Pleistocene time. However, evidence has not been 1
provided to demonstrate this interpretation. Also the potential
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reactivation of the deposits has not been considered during the design life q
of the tailings embankment.
l Secone, landslides southwest of the disposal area appear to be caused by hillslope failure along bedrock dip and fractures. Even though mass wasting at this location does not presently affect the proposed disposal area, DOE has not demonstrated that continued and accelerated slumping will not occur nor that it will not affect long-term stability of the tailings embankment that is proposed less than 1000 feet from the scarp.
Finally, DOE has not demonstrated that local debris flows will not affect long-term stability of the tailings pile.
Specifically, local debris flows could damage erosion control structures by entraining riprap from the cover, by choking the riprap pore spaces with fines, by filling and blocking drainage diversion ditches, or by altering natural drainage patterns near the site.
In conclusion, contrary to conclusions drawn in the dRAP, the staff considers that mass wtsting may be an important geologic hazard at Estes Gulch. DOE should revise the RAP to assess the extent and significance of future mass wasting including potential seismic impacts and to revise embankment designs to mitigate potential impacts.
G2. dRAp; general, Site Geology and Conceptual Design The dRAP does not explain how the site's detailed geologic setting and conceptual design will complement one another to assure long-term site stability.
First, the proposed pfle layout (p. 71) identifies 10 feet as the optimum depth for site excavation prior to tailings emplacement. This proposed depth will result in a tailings' foundation composed of " pediment alluvium," "old alluvial fan" deposits, as well as Eocene bedrock. The design does not appear to take into consideration the potential differences in engineering properties of these foundation materials, nor the potential for stratigraphic contacts to serve as hydrculic pathways of contaminated tailings leachate.
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Secondly, DOE concludes (p. 75) that no liner will be required to protect
. ground water resources because the proposed Estes Gulch ' disposal area is
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underlain by more than 300 feet of unsaturated Eocene bedrock. ~ The proposed design, however, will also result in up to.30 feet of Quaternary deposits remaining above bedrock. The design does not appear.ts consider downward migration of leachate.through the alluvium to the bedrock contact, then lateral (southward) movement to surface outcrops above Government Creek.
e Fina118, the DRAP does not consider that fractured and~ steeply inclined strata f
may affect ground water protection from the tailings. Although the water.
j table may be more than 300' feet deep, inclined sandstone layers and fractured
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mudstones in the Wasatch Formation may serve as preferential pathways for j
contaminant migration. Despite this potential significance, DOE has not characterized bedrock dip nor the stratigraphic distribution of mudstones and
.i sandstone below the disposal area.
In addition, the site's locatio'n in the j
limb of the Grand Hogback monocline results in dramatic decreases in dip as one moves southward. Thus, pathways formed by Eocene strata could potentially>
conduct contaminated groundwater. laterally offsite toward Government Creek.
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'The RAP should be revised to assess the significance of these deficiencies or '
1 demonstrate that hydraulic and geotechnical properties of the foundation' materials will not affect the long-term stability and ground water protection provided by the tailings embankment at Estes Gulch.
G3.
dRAP; general, Estes Gulch Logs DOE's logs of wells drilled at Estes Gulch contain so many errors, omissions, and ambiguities that the logs are inadequate to support geologic characterization of the site.
None of the logs contain such basic information as method and date of. drilling. The logs contain background information such as "strat, order" and "N-value" (blowcounts?), but do not explain the meaning of these values. The logs do not explain abbreviations used for sampling methods.
Furthermore, abbreviation of soil classes include notations which are not conventionally used in the referenced Unified Soil Classification System.
Finally, the level of data and observations cited in the logs do not provide an adequate basis to differentiate surficial deposits and bedrock.
Based on the log deficiencies, the dRAP does not provide adequate information to characterize site geology and fcundation materials beneath the proposed tailings embankment. Such information is necessary to assess site suitability with respect to ground-water protection and long-term foundation stability.
DOE should revise the logs to incorporate accurate observations based on the field logs and lab samples, or provide other information to characterize site geology.
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G4. dRAP; PP. D-66 and D-107 DOE's geologic site characterization at Estes Gulch has identif'ied several major surficial deposits. However, no data have been provided in the dRAP to explain the differentiation or indicated distribution of these units.
Narrative descriptions of the units are general and vague. No sedimentologic data are provided for pediment deposits. (map unit "pa").
No information is j
provided to explain the stratigraphic, genetic, and age relationships between.
alluvial fan deposits (map unit " oaf") and unit pa. Furthermore, data in the dRAP's well logs do not demonstrate the differenti.ation between clayey alluvium and bedrock (see comment G2). Thus, the thickness and distribution of Quaternary deposits is apparently unknown.
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Such data are necessary because the deposits are proposed as the foundation for stabilization'of the contaminated materials. The dRAP lacks key.
1 information needed to demonstrate that surficial deposits at Estes Gulch are i
suitable with respect to foundation stability and ground-water protection. The dRAP should be revised to characterize the distribution and characteristics of:
unconsolidated materials at Estes Gulch or to demonstrate that such data are
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not necessary to assess site suitability.
G5. dRAP: P. D-68 This section of the draft RAP indicates that a gully is actively cutting head-ward toward the west side of the proposed tailings pile. Although Figure 4.3 shows the major geomorphic features at Estes Gulch, it does not show any gully on the west side of the proposal enbankment. Gully formation may promote erosion of the stabilized tailings pile. DOE should revise Figure 4.3 to indicate the large gully west of the proposed enbankment an'd assess its significance with respect to erosion protection.
G6. dRAP; PP. D-105 and D-107 DOE's Technical Approach Document (TAD) states that part of the site conceptual design process includes preparation of surficial and bedrock geologic maps extending to a i km radius around the site. DDE should provide a 1 km radius surficial and bedrock geologic map of the site or demonstrate that maping at this scale is not necessary to assess geologic suitability.
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- G7.
dRAP; P: 30
-This section;of the draft RAP indicates that Uranium - Vanadium' deposits occur in the Navajo and Entrada sandstones about'two miles east of the Estes Gulch site. The presence *of considerable faulting and fracturing may have some
' bearing on the unusual concentration of these ore deposits.
Faulting and l
fracturing can provide preferential pathways for contaminant migration in
-j ground water.
In addition,: seismic activity could reactivate faults in the l
. site area and impact the stability of the pfle. DOE should revise the RAP to assess.the significance of the ore bodies near the site with. respect to
. geologic stability and groundwater protection.
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G8. dRAP; P. 27 This section of the draft RAP indicates that there are features within an-j unspecified vicinity of the site identified by Kirkham and Rogers (1981) as Quaternary faults. DOE concluded, based on field inspection, that these features were collapse features in Quaternary volcanic flows. The RAP, however, does not characterize these features or provide information necessary:
to assess their genesis.
Recent faulting, as suggested by Kirkham and Rogers (1981), could impact the seismic design basis for the stabilized tailings pile.
The RAP should be revised to characterize the " collapse" features and provide the basis for concluding that these features are the result of collapse.
G9. dRAP; P. D-41 This section of the draft RAP places the floating earthquake 15 km from the Estes Gulch site. This floating earthquake is presumably in the Colorado Plateau seismo-tectonic province as indicated on page D-40.
Page D-45 makes it clear that the Estes Gulch site is on the northeastern edge of the Colorado
COMMENTS, RIFLE RAP
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Plateau.- Figure D.3.1 shows the Estes Gulch site just outside the boundary of the Colorado Plateau in the Southern Rocky Mountains. However, Figure D.3.13 shows the Estes Gulch site as being within the Colorado Plateau'on the border of the Western Mountain seismo-tectonic province.
In addition, Figure D.3.14 shows the Estes Gulch site as straddling the boundary of the Colorado' Plateau i
and Western Mountain seismo-tectonic provinces.
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The determination of the floating earthquake is important to the seismic design bases for the stabilized tailings pile.
If the Western Mountain province is used (at 15km), a FE acceleration of 0.26. is determined (Campbell 1981),
9 which is greater than the 0.21g FE acceleration determined for the Colorado Plateau.
It appears that the Western Mountain seismo-tectonic province should be-considered in determining the floating earthquake for the Estes Gulch site.
j The RAP should be revised to state clearly the host seismo-tectonic province i
for the Estes Gulch site and to reassess the design acceleration associated with the floating earthquake.
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Reference:
Campbell, K. W.1981.
"Near-Source Attenuation of Peak Horizontal Acceleration," Bulletin of the Seismological Society of America, Vol. 71, pp. 2039-2070.
G10. dRAP: P. D-67 Under the " Site Geology" heading, this section of the draft RAP indicates a small debris flow at the west side of Estes Gulch. The dRAP does not assess the potential for occurrence of debris flows elsewhere at the site or potential impacts to the stabilized tailings pile. The RAP should be revised to characterize the potential for debris flows at the Estes Gulch site and to demonstrate that the tailings embankment has been designed to mitigate potential impacts associated with debris flows.
Gil. dRAP; P. D-55 This section of the Draft RAP indicates that rapidly eroding Tertiary sandstones and shales are significant causes of slope failure at the Estes Gulch site. The Tertiary Wasatch Formation is a sequence of sandstones, siltstones and shales, and an important part of the foundation beneath the i
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proposed tailings embankment at Estes Gulch., In addition, gullies at Estes.
Gulch have' already eroded into the Wasatch Formation.. The RAP should be L
revised to assess the influence of the Wasatch Formation on the-erosional l
l stability of the Estes Gulch site or to demonstrate that' erosion of the Wasatch Formation will not affect pile stability; L!
- G12. dRAP; P. D-67' I
Figure 3.27 shows estimated bedrock contours for the. Estes' Gulch site. However,-
this' figure.does not show locations and numbers of the borings used in preparing the figure..The configuration of the bedrock contact may significantly affect 3
groundwater flow beneath.the site. ~Also, the configuration of the bedrock
- contact may significantly affect embankment design (e.g., keying the erosion.
protection apron.into completed bedrock) and foundation preparation. The RM -
should be. revised to state the basis for Figure 3.27 explicitly by showing I
boreholes used to prepare the figure.
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G13. dRAP: P. Addendum D-5.1 I
Many of the borehole logs, for example,: Logs BH-920, BH-954 BH-956, BH-958 and BH-963, contain information which may indicate unsuitable foundation materials below the proposed tailings location at Estes Gulch. Terms like
" highly weathered", " calcareous", " soft", "slickensides", " zones of major fractures", " crumbled zones" and " highly fractured" can be found describing various intervals (including but not limited to the upper portion) of the.
Wasatch Formation beneath the proposed tailings embankment. The RAP should be-revised to assess the potential impacts of these foundation conditions on the stabilized embankment, including potential disolution of materials by acidic tailings solutions, occurrence of failure zones beneath the tailings,- and preferential pathways for contaminant migration.
G14. dRAP: P. D-86 Paragraph 3 states that "...the probability of occurrence of a magnitude 6.5
~4 event within any nine-mile (15 km) radius within the region is 0.06 x 10 The recurrence interval of an ME earthquake within any nine-mile radius is 1
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l COMMENTS RIFLE RAP l
thus 166,700 years." The bases for the calculated results on earthquake-probability and recurrence interval are not clearly stated and cannot be verified by NRC staff based on the information given. Calculation of earthquake recurrence interval is important with respect to selecting the seismologic design basis for the stabnized tailings embankment. The RAP should be revised to provide the detailed calculations used to determine the.
recurrence of the ME earthquake for the Rifle area.
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GIS. dRAP; P. D-88' This page indicates that the threshold magnitude that would result in the propagation of a fault rupture to.the earth's surface in a tectonic plate.
j interior can be determined by setting fault rupture length equal to zero in.
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the Bont11a, 'et al. (1984) equation and solving for the magnitude. Such a; process is in error mathematically because the equation requires tiking the-I log of the fault rupture length and taking the log of zero is a undefined number. The process is also in error because the assumption of a zero, or 1
very small, surface rupture length is an insupportable extrapolation of the j
,Bonilla, et al. (1984), data. The RAP should be revised to justify the I
assumption of a.zero, or very small, surface rupture length and to demonstrated that this assumption provides conservative estimates of the potential for surface rupture of a fault in the Rifle area.
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Reference:
J Bont11a et al. (M. G. Bonilla, R. K. Mark, and J. J. Lienkaemper),1984.
" Statistical Relations Among Earthquake Magnitude, Surface Rupture Length and Surface Fault Displacement," Bulletin of the Sehmological Society of America, Vol. 74, No. 6, pp. 2379-2411.
G16. dRAP: P. D-88 Section 0.3.6.2 of the DRAP entitled " Colorado Plate.ac Seismotectonic Province" has no mention of a large earthquake that occurred on November 8, 1882 (Stover, et al., 1984)." The exact location of this earthquake is difficult to fix..The location suggested by Stover et al., (1984) is the Piceance Basin with a maximum intensity of VII. Therefore, this large earthquake ray have occurred in the same basin (Piceance) in which Estes Gulch site is located.
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An oblique reference to a large earthquake in '1882 is made on page.D-94 under
-t Section D.3.7.5 entitled " Fault Compilation". This section of the DRAP suggests the 1882 carthquake occurred on a northwest trending graben (Nu'mber 10 on Plate D.3.1) that shows late Quaternary and possibly Holocene movement on the South.
- fault (McGuire, et al.,1982). The graben (Number 10 on' Plate D.3.1), however, could have been displaced by the Rio Blanco (5-17-1973) nuclear explosions f
13-km to the south of the Graben. These nuclear explosions mean that any 1
conclusions about geologic movement in Quaternary time would have to be based
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on pre-1973' studies because the explosions could be responsible for observed displacements.
- i The implications of the 1882 earthqua'e are-important to determining the k
floating earthquake (FE) which is being used for design purposes. The 1882 earthquake would be a magnitude 6.3 rather than the 6.2 FE being used for design purposes in the DRAP. The RAP should be revised to characterize.the y
location and significance of the 1882 earthquake with respect to design of the tailings embankment.
Referencesi Stover, C. W. Reagor, B. G., and Algermissen, S. T., 1984, " Seismicity map of the State of Colorado," U.S.G.S. Miscellaneous Field Studies map MF-1694'.
R. K. McGuire, A. Krusi, and S. D. Oaks,1982.
The Colorado Earthquake of November 7, 1882: Size, Epicentral Location, Intensities, and Possible Causative Fault," The Mountain Geologist, Vol. 19, No. 1, pp. 11-23.
G17. dRAP: P. D-88 This page states "The site area lies along the approximate trace of lineament 2."
Actually, the Estes Gulch and Rifle sites appear to lie closer to the trends of lineaments 3 and 4 (see Figure D.3.16) than lineament 2.
The
. lineaments have the potential for impacting the seismological assessments used in support of the seismologic design basis for the proposed tailings embankment. The RAP should be revised to assess the proximity of the site to lineaments and the potential significance of the proximity to stability of the tailings embankment.
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G18. dRAP: P. D-88 It is unclear how the earthquake recurrence rates. in Figure D.3~.19 were determined. The recurrence rates shown in Figure 0.3.19 are considerably less than the rates derived from the data shown in Figure D.3.13 and tabulated in j
. Table D.3.7.
The earthquake recurrence rates are important to the assessments.
needed for the seismologic design bases for the stabilized tailings' embankment.
'i The recurrence rate information on the above referenced figures and table needs to be clarified in the RAP.
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G19. dRAP: P. D-43 1
I The' text indicates that soils at'Estes Gulch may collapse upon wetting.- Due to the potential significance of the soil collapse to the stability of the.
. tailings embankment, the RAP should De revised to characterize the-engineering l
characteristics of soils at Estes Gulch site and assess their significance
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with respect to stability of the proposed tailings embankment.
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