ML20003H664
| ML20003H664 | |
| Person / Time | |
|---|---|
| Issue date: | 04/09/1981 |
| From: | Scarano R NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Hazle A COLORADO, STATE OF |
| References | |
| REF-WM-34 NUDOCS 8105060598 | |
| Download: ML20003H664 (40) | |
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NUCLEAR REGULATORY COMMISSION a f W ASHINGTON, D. C. 20555 o
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APR 9 1981
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S-i Mr. Albert Hazle, Director Q
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Denver, Colorado 80220
Dear Mr. Hazle:
The Nuclear Regulatory Comission with the technical assistance of Geotechnical Engineers, Inc. (GEI) has completed an evaluation of the Union Carbide Corporation's proposed in-place reclamation alternative for existing tailings (including the next two years of operation) at the Uravan disposal site located at Uravan, Colorado. The attached assessment contains our conclusions, and recomendations regarding long-tem stabi'.ity and isolation of the proposed reclamation plan for the existing tailings.
We are currently reviewing Union Carbide's alternative sites. study and expect our evaluation regarding these sites to be completed in the near future. Questions regarding the attached assessment should be directed to Dr. LeRoy Person of my staff (301-427-4540).
Sincerely, Ross A. Scarano, Chief Uranium Recovery Licensing Branch Division of Waste Management
Attachment:
As stated cc:
K. Weaver, CDH R. Turnbull, GEI i
S 8305oe0593,
1 ASSESSMENT OF THE IN-PLACE TAILINGS RECLAMATION ALTERNATIVE FOR THE
)
UNION CARBIDE URAVAW MILL SITE Introduction l
This assessment was performed by Geotechnical Engineers Inc. (GEI) in response to a request to NRC's Uranium Recovery Licensing Branch from the State of Colorado Department of Health, and is an evaluation of the Union Carbide Corporation's Phase III Tailings Reclamation Plan submitted to the State of Colorado on May 30,1980 (crtained in References 1, 2, and 11), in support 4
of an application for renewal of State of Colorado Material License SUA-673.
The mill which generates tailings at the site is part of the Union Carbide Uravan Uranium Project and is located in Montrose County, Colorado. A map of 4
this portion of Colorado is provided in Figure 1.1-1. Location of the mill l
and tailings area relative to the town of Uravan is shown on Figure 1.1-2.
Two large tailings piles are located at the Uravan Mill. Pond 2, which includes the old Pond 1, consists of about 57 surface acres of tailings located on a bench above the. San Miguel River. The southern toe of the stabilization bem for Pond 2 is less than 200 ft immediately north of the Uravan Mill. Pond 3, which consists of about 22 surface acres of tailings, is located along a bench above Hieroglyphic Canyon. The eastern edge of Pond 3 is less than 1000 ft west of the Uravan Mill. Under the Union Carbide proposal, these two ponds would be stabilized in place by cutting back the slopes of the existing ponds to SH:1V. This would require removal of about 60". of the tailings to a site which is immediately adjacent to the northwest side of Pond 2.
The ponds and the adjacent disposal site are in Section 33, T48N, R17W.
l Inasmuch as the Uravan tailings disposal areas have only limited storage capacity remaining (it is estimated that sufficient volume may be available for approximately two more years of mill operation), NRC, at the request of the State of Colorado Department of Health (CDH), has also contracted GEI to review Union Carbide's alternative sites study for the location of a new impoundment for disposal of future tailings and possible disposal of existing tailings if in-place reclamation of existing tailings is not found acceptable.
This evaluation of the alternative sites study will be available in the near future. However, the objective of the current assessment is to make reconnen-dations which will enable a determination of whether the existing) tailings (including the tailings from the two remaining years of operation can be reclaimed in-place (or must be moved to a new site) in a manner which will protect the public health, safety, and the environment over the long-tem.
Technical Criteria used to Evaluate In-Place Reclamation at the existing site The reclamation alternatives that can be implemented at the Uravan tiilings disposal site are limited due to the fact that the tailings have been in place for over 50 years. New NRC regulations (45 FR 65521) recognize the
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fact that it may not be practicable to provide the same measures of conserva-tism for existing tailings areas as can be done at new sites. However, there are certain requirements in the regulations which represtrit " minimum levels of protection" that must be met in all cases. Accordingly, these facts are taken into consideration in this assessment of the proposed in-place reclamation of the existing tailings disposal area.
Appendix A of 10 CFR Part 40 contains technical crittria against which tailings management plans and disposal sites are to be evaluated. The applicable criteria from Appendix A of 10 CFR 40 used in this assessment to evaluate Union Carbide's proposed plan for in-place reclamation of existing tailings are summarized below:
Technical Criteria 1.
Isolation of the tailings and associated contaminants from man and the environment for thousands of years, with consideration of the following:
a.
Eliminate the need for an ongoing monitoring and maintenance program following successful reclamation b.
Remoteness from population centers c.
Hydrologic and other natural conditions as they contribute to continued immobilization and isolation of contaminants from usable groundwater sources d.
Minimize erosion, disturbance and dispersion by natural forces over the long term 1.
minimization of upstream external drainage area
- 11. wind protection provided by topography iii. minimization of embankment and cover slopes l
iv. establishment of a self-sustaining vegetative or a rock cover v.
impoundment should not be located near a capable fault 2.
Minimization of seepage of toxic materials to the maximum extent reasonably achievable.
3.
Application of sufficient earth cover, but not less dian three meters, to provide assurance against long term erosion, to reduce radon exhalation from the tailings to less than 2 picocuries per square meter per second, and to reduce gamma exposure to background level s.
The purpose of this assessment is to determine the extent to which these technical criteria are met by the in-place long-term reclamation j
plan proposqd by the Union Carbide Corporation (UCC).
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. 1.0 EXISTING ENVIRONMENT 1.1 METEOROLOGY 1.1.1 Temperature The monthly mean and extreme tremperatures recorded at Uravan are indicated in Table 1.1-1.
Extreme temperatures recorded at Uravan during the period of record (August 1972 through December 1977) show a minimum of -23.3oC
(-loof) which occurred in January 1974 and a record neximm of 41. loc (106oF) which occurred in July 1976.
At Grand Junction, located about 55 miles north of Uravan, the tenperature exceeds 32.30C (90cF) on about 64 days per year and fails to reach 0.00C (320F) on or about 25 days per year. Temperatures at Grand Junction fall to 0.0 C (32 F) or below on about 138 days per year and will fall to -17.80C (00F) on about 7 days per year. Annual mean temperatures for Uravan are very similar to those for Grand Junction; however, Uravan experiences a larger diurnal temperature variation than does Grand Junction.
1.1.2 Precipitation Annual and mnthly average precipitation values, and monthly and daily extreme precipitation values from Uravan are listed in Table 1.1-2.
The annual average tctal precipitation received at Uravan from 1973 through 1977 was 25.6 cm (10.1 in.). An annual maximum of 31.1 cm (12.2 in.) of precipitation was reccrded in 1975, and an annual minimum of 20.4 cm (8.0 in.) was recorded in 1976. The maximum monthly precipitation recorded at Uravan was observed in October 1972 when 14.9 cm (5.9 in.) were recorded, and the minium monthly precipitation was received in June 1974 when only 0.07 cm (0.03 in.) were l
recorded. During the period of record, the greatest single daily precipitation amount was 3.2 cm (1.25 in.), occurring on July 24, 1977.
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l 1.1.3 Winds Winds at Uravan are strongly influenced by the San Miguel River. The river at the site runs from the southeast to the northwest and, accordingly, the highest frequency wind directions are from the east-southeast through south-southeast. Winds from these directions were observed 59% of the time during the period of record. These winds represent i.he drainage flow of air that occurs generally during the night and early morning hours. The highest speed winds flow up the river valley from the west-nortnwest and are observed 24.9% of the time. These winds generally occur during the late morning and afternoon or after a frontal passage. The annual mean wind speed is 1.95 m/s (4.4 mph). Table 1.1-3 gives the percent frequency of wind direction by wind speed intervals and mean wind speeds.
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. 1.2 TOP 0 GRAPHY The tailings ponds and adjacent disposal site are located on gently sloping, moderately dissected benches set back from the cliffs bordering the San Miguel River and Hieroglyphic Canyon. Tailings pond 2 is located on a gently sloping bench on the west side of the San Miguel River about 340 ft. above the river and the town of Uravan. Natural ground elevations at the Pond 2 site range from about 5300 to 5500 ft. ms1 from east to west across t!M pond. The T.ailings are contained by a natural ridge on the west and scuth sides and by a tailings embankment on the north and east sides. At present, the maximum height of the embankment is about 140 ft.; by 1983 this edankment will be at about El 5503 ft. for a final maximum height of about 200 ft, Final embankment slopes before reclamation will be about 2.5H:1Y with a flat bench about 100 ft. wide at El 5440 ft. After reclamation, the Pond 2 etankment slopes would be cut back to 5H:1V. The toe of the eastern portion of the reclaimed embankment would generally be about 400 ft. from the steeper slopes of the San Miguel River Canyon. However, at one point along the edankment, the toe would be only about 50 ft. from the head of a steep drainage leading into the San Miguel River Canyon.
Tailings Pond 3 is located on a gently sloping bench above the north side of Hieroglyphic Canyon, about 300 ft. above the caryon floor. Natural ground elevations at the site range from about 5420 to about 5540 ft. from southeast to northwest across the pond. The tailings are contained by a natural ridge on the northwestern side of the site and by a tailings embankment on the southeastern side. At present, the maximum height of the embankment is about 105 ft.; by 1983 this embankment will be about El 5535 ft. for a final maximum height of about 115 ft. Final embankment slopes before reclamation will be 3H:1V with benches at Els 5450 and 5500 ft. After reclamation, the Pond 3 embankment slopes would be cut back to SH:1V. The toe of the southern portion of the reclaimed embankment would generally be more than 200 ft. from the steep cliff walls of Hieroglyphic Canyon. However, the southeasternmost corner of the reclaimed embankment would be only about 125 ft. from the edge of the canyon, and a nearby section of the embankment would be located on top of a drainage leading to the canyon.
The topography at the disposal site adjacent to the north side of Pond 2 is similar to the natural topography at the Pond 2 sita. iiround elevations range from about 5350 to 5550 ft. ms1 from northeast to southwest across the adjacent site.
1.3 GEOLOGY The Uravan site is underlain by Mesozoic
- sedimentary strata that generally strike northwest-southeast and dip 1 to 2 degrees to the northeast. Tailings Ponds 2 and 3 and mie adjacent disposal site are sited upon the Salt Wash
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- Geologic time scale is presented in Table 1.3-1.
. Sandstone Member of the Morr'.w Formation. The Salt Wash Ment)er is reported to range in thickness from 2t~ to 350 ft. in the region. At the site this formation extends from the ground surface to a depth of about 60 ft. The Salt Wash Ment)er consists credominantly of sandstones which are variously colored white, gray, b"
tan, and reddish-brown.
Interbedded with the sandstones are red to addish-brown shales and green and red mudstone layers.
The sandstones are mostly fine-grained, cross-bedded, and massive and consist largely of calcium carbonate-cemented quartz grains. The shale and mudstone layers also contain some calcium carbonate and range in hardness from soft to hard.
The sandstone exhibits a distinct near-vertical fracture set, which strikes approximately parallel to the strike of the formation. A secondary vertical set is orthogonal to the primary fracture set. The sandstone contains numerous highly fractured zones in the upper 20 to 30 ft., but below 30 ft.
the sandstone generally grades to only slightly fractured.
Permeabilities of the rock strata, determined using packer pressure tests in the field and laboratory tests on core samples, are presented in the Environ-mental Report (Ref. 2). Permeabilities determined from packer pressure tests ranged from 2.3 x 10- cm/sec in an 8 -ft.-thick interval of shale and claystone to 1.3 x 10 3 cm/sec in a 7-ft.-thick fractured sandstone interval.
Permeabilities detgrmined in the laboratory ranged from 2.9 x 10- cm/sec in shale to 7.2 x 10- cm/sec in sandstone.
Samples with interbedded coarse and fine-grained rocks showed intermediate permeabilities. Several sandstone samples with secondary 7 cementation and staiging had much reduced permeabilities ranging from 5.8 x 10- cm/sec to 8.7 x 10- cm/sec, generally lower than the other sandstones.
Below the Salt Wash Sandstone and exposed in the walls of the canyon of the San Miguel River are, in descending sequence, the Summerville Formation, the Entrada Sandstone, the Carmel Formation, and the Navajo Sandstone. The l
top of the Kayenta Formation is exposed at the lowest level in the canyon floor. The Kayenta Formation is conposed of interbedded shale, siltstone, and well-cemented fine to coarse sandstone and is about 200 ft. thick.
Soils at the site consist of thin residual and windblown deposits which range in thickness from 0 to 3 ft. TLey consist of red, red-brown, and brown silty clays and silty fine sands. The canyon floors are generally covered with thin alluvial deposits which consist primarily of silty fine sand, fine sand and poorly graded gravel. Small deposits of terrace gravels occur at scattered locations along the side of the canyons.
According to Kirkham and Rogers,1978 (Ref. 6) no faults exist at the Uravan disposal site, and the nearest fault, which is inactive, is about 2 miles due north of Uravan.
. 1.4 GEOMORPHOLOGY Rates of erosion and mass wasting in the Uravan area were estimated by Smith (Ref. 10). By comparison with average rates of river incision as measured for other tributaries of the Colorado River, downward erosion rates along the San Miguel River and in Hieroglyohic Canyon were estimated to be about 1 ft.
per thousand years. Mass wasting rates were estimated by attempting to date fractures formed in sandstone blocks as they were undercut and began to separate from the cliffs. The maxinum estimate of local rates of mass wasting and cliff retreat is atos.t 4 ft. per thousa.,d years. Recession rates of active gullies could not be determined, however they probably exceed cliff retreat rates. Therefore, headward erosion of iocal gullies is assumed to occur at a rate greater than about 4 ft. per year. GEI believes that the conclusions reached by Dr. Smith are reasonable. Dr. S. Shum of Colorado State University, following review of the Smith study at the request of the NRC, has independently found Dr. Smith's conclusions to be reasonable (Ref. 8).
1.5 SEISMICITY The region surrounding the Union C2rbide Uravan uranium mill has exhibited relatively little historic seismic activity and, in fact, the entire Colorado Plateau province is considered to be a relatively quiescent seismic region.
Significant damaging earthquakes have occurred only at relatively large distances from the site, primarily to the far west along the Wasatch frontal faults of the intermountain seismic belt. The Southern Rocky Mountains province has experienced low to moderate seismicity.
The Environmental Report (Ref. 2) indicates that there have been 140 seismic events of Richter magnitude 4.0 and greater within 200 miles (320 km) of the site between December 1,1853 and January 5,1976; the report also indicates that there have been 22 seismic events of Richter magnitude 2.0 and greater within 100 miles (160 km) of the site between November 10, 1882 and January 30, 1975. Epicenters are plotted on Figure 1.5-1.
The zone of highest seismicity in the region is the north-south-trending intermountain seismic belt which lies about 200 miles (320 km) west of the site. The largest earthquake associated with this zone within 200 miles (320 km) of the site was a magnitude 6.7 event in 1901, whose epicenter was about 185 miles west of the site.
No strong relationships exist between earthquake epicenters and specific tectonic structures throughout most of the region. The strongest zone of seismicity is the north-south trending intermountain seismic belt which lies on the west margin of the region. Earthquake activity in this zone falls along a series of faults which bound the east margin of the basin and range province. Diffuse earthquake activity occurs in the north-northeast trending Colorado mineral belt. Most events seem to have been within 50 miles of
. post-oligocene extrusives (Ref. 5). Diffuse, low to moderate level activity elsewhere outlines the Colorado Plateau. Scattered, low-level seismic activity occurs within the Colorado Plateau; these epicenters do not correlate with specific tectonic features.
A review of the historic seismicity, seismotectonic relationships and geology of the region indicates that there are two potential sources for generating the maximum credible earthquake at the site. Faults which flank the Ucompahgre Uplif t are the first potential source that could generate such an earthquake.
Regional studies have not been of sufficient; detail to evaluate the capability of these faults; however, since their actisity is in qaestion, the Environmental Report assumed that the faults are potentially capable. The closest major fault lies 9 miles (14 sk) northeast of Uravan. The Environmental Report, using data presented by Slemmons (Ref. 9), calculated a design earthquake of magnitude 6.8 for this fault. Using attentuation relationships developed by Schnabel and Seed (Ref. 7), UCC expects an event of this magnitude to produce a maximum ground acceleration of 'approximately 0.35 to 0.40g on bedrock at the site. GEI believes that the values obtained for the design earthquake magnitude (Richter 6.8) and the maximum ground acceleration (0.35 to 0.43) are reasonable based on the assumptions and methodology used by UCC.
The second potential source for the maximum earthquake is a random earthquake of a maximum magnitude typical of those which occur in the eastern Colorado Plateau. The maximum measured event is of magnitude 4.6.
However, the seismic record is short and a magnitude 5.0 was assigned to the maximum random event for the purposes of this report. Assuming that a magnitude 5.0 earthquake occurred two miles directly under the site, a mean peak ground acceleration of 0.2g is estimated in the Environmental Report. GEI believes that the values assumed here are reasonable, and although it is conceivable that a larger earthquake could occur at a shallower depth, the resulting maximum ground accelerations would still be less than those associated with the fault nine miles away as discussed in the paragraph above.
l 1.6 SURFACE WATER The total upstream catchment areas above Ponds 2 and 3 are estimated to be about 50 and 51 acres, respectively. The design storm rainfall over the watershed areas above the tailings ponds is estimated to be 20.7 inches based on combined rainfalls considering the general PMP stonn and the 100-year storm (Ref. 2). The total storm runoff within each watershed above tailings Ponds 2 snd 3 that would result from the design storm rainfall is estimated to 20.3 irches, conservatively assuming two ' percent rainfall losses to evaporation and groundwater infiltration.
The sites are more than 300 ft. above the maximum potential flood levels on the San Miguel River and in Hieroglyphic Canyon.
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. 1.7 GROUNDWATER As discussed in a previous section, the site is underlain by, in descending sequence, the Salt Wash Member of the Morrison Formation, the Sununerville Formation, the Entrata Sandstone, the Carmel Formation, and the Navajo Sandstone which are all exposed in the walls of the canyon of the San Miguel River. Groundwater in these strata, which lie topographically above the San Miguel River, occurs in erratic discontinuous minor perched zones. Groundwater movement is generally toward the San Miguel River as evidenced by groundwater and tails solution discharge along the canyon walls. The San Miguel River probably controls the base groundwater level for the area.
These formations are poor aquifers in the area due to their low primary permeability and their topographically high position. No wells are known to tap these formations in the Uravan area.
The Kayenta Fonnation, which is exposed at the lowest level of the canyon floor, is a poor aquifer in itself, but is tapped by several wells in the vicini ty.
The Wingate Sandstone is the primary aquifer in the area and is tapped by several wells. This formation consists of fine-grained, thick-bedded to massive sandstone, about 250 ft. thick. This formation is estimated to be about 800 ft. below the site.
l Only three operational wells are reported within 5 miles of the site.
l These wells have been constructed for water supply for the Uraven mill and i
town. No other public water supplies are located within 10 miles of the si te. The staff believes this site to be reasonably isolated frca usable groundwater sources.
1.8 SEEPAGE Observations at the sita (Ref. 4) indicate that seepage is occurring from the tailings ponds into the underlying sandstones. Seepage has been observed exiting out of the San Miguel River canyon wall at several locations.
In the winter, tailings fluid seepage appears as greenish ice patches and is more visible than the wet spots observed during warmer periods.
2.0 UNION CARBIDE'S PROPOSED TAILINGS DISPOSAL PLAN Under UCC's proposed in-place stabilization plan (Ref. 2 and Ref.1) the disposal of tailings into the ponds would cease in 1983 leaving approxi.;ately l
10 million tons of tailings impounded in Ponds 2 and 3.
The ponds would be allowed to drain a sufficient amount of time to drop the phreatic surface in the tailings to a level below the point at which the pile would be cut back to a 5H:1V slope upon reclamation. Contaminated waste material from the Club i
Ranch, River Ponds, Atkinson Creek storage area, l
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. plant area clean up, and the Club Mesa spray system would be placed in the rear of Pond 2.
The dry tailings above the elevation of the buttress would be cut back and moved to the rear of Pond 2 to cover the contaminated wastes from the areas just described. The slopes of Ponds 2 and 3 would be cut back to 5H:1V. This would involve cutting off the rockfill buttress and pushing some of the tailings back tovards the rear of the ponds. About 60% of the tailings would be moved to a new lined fill area proposed to be built immediately adjacent to the northwest side of Pond 2.
The rock salvaged from the buttress would be stored for use in the final covering. The reclaimed tailings areas would be covered with 4.5 ft. of Mancos shale which UCC estimates would reduce the radon emanation rate to 2 times the background rate, and would reduce gamma to background. To protect against erosion, the shale would be covered with 2 ft. of mine run rock with an approximate top size of 12 inches. Soil or clay would be dumped into the voids betweeen the rocks in an attempt to minimize drying out the clay Cover.
3.0 EVALUATION OF PROPOSED RECLAMATION PLiN AGAINST TECHNICAL CRITERIA 3.1 ISOLATION OF THE TAILINGS AND ASSOCI ATED CONTAMINANTS FROM MAN AND THE ENVIRONMENT FOR THOUSANDS OF YEARS 3.1.1 Remoteness From Population Centers NRC objectives with regard to siting require that tailings disposal areas be located remote from population areas in order to minimize population doses both during operations and following reclamation. In the cata of an existing tailings pile, such as at Uravan, it must be shown that once reclaimed, the pile will not present an undue hazard to nearby populations. Although the proposed reclamation area is located approximately 400 feet from the town of l
Uravan, the reclaimed pile should not present an undue hazard to the town provided that the reclaimed pile satisfies the criteria discussed below for isolation of tailings from the environment over the long term.
In addition, since Uravan is a conpany town, it will probably only exist over the remaining life of the mill (approximately 20 years).
Hydrologic and Other Natural Conditions As They Contribute to Continued 3.1.2 ~Imootlization an'a Isolation of contaminants from usable Grounowater Sources Groundwater below the site occurs in discontinuous perched zones. Geologic formations below the site but above the San Miguel River are poor aquifers due to their relatively low permeability and their topographically high position. No wells are reported to tap the:a fomations in the Uravan area.
The Kayenta Fomation, which is exposed at the lowest levels of the canyon floor, is a poor aquifer in itself, but is tapped by several wells in the vi cini ty. The Wingate Sandstone is the primary aquifer in the area and is tapped by several wells. This aquifer is estimated to be about 800 ft. below
. the site. Three wells are reported within 5 miles of the site and they are used for water supply for the Uravan Mill and town.
Because of the relatively large depth to usable groundwater sources, and the presence of many relatively impermeable strata between the site and the primary aquifer (the Wingate Sandstone), the staff believes this site to be reasonably isolated from usable groundwater sources.
1 3.1.3 Eliminate the Need for An Ongoing Monitoring and Maintenance Program Following Successful Reclamation Monitoring and maintenance will probably not be required following reclamation provided the UCC plan is suppleriented by the reconinendations made in this assessment. These recommendations have been based on state-of-the-art geotechnical engineering methods and techniques, and sound engineering judgment to minimize the potential for long-tenn disruption of the tailings piles without planned maintenance. Erosion protection materials will be selected to ensure long term erosion protection. A hard rock cover will be relied on for surface erosion protection. The proposed reclaimed slopes are generally gentle enough and protected with a cover sufficient 'to minimize the potential for exposure of the tails through erosion or slope instability.
In general, there are no materials, instruments, or structures utilized in the reclamation plan which would normally require servicing, maintenance, or monitori ng.
Some measure of monitoring for a short finite period (approximately 5 to 10 years) to assure that reclamati<an has been successful will probably be necessary. Ground water levels and gradients in the area should be measured in wells periodically to con'tirm assumptions regarding directions and rates of movement of liquids from the piles. Groundwater and surface water quality should be periodically monitored to ensure that water quality is eventually improving with time, and to permit timely identification of any potential seepage paths from the piles that might degrade local water quality in the long term.
In addition, the condition of the impoundment top, slopes, and cover materials, and gully erosion protection structures should be observed periodically to ensure that the erosion protection schemes are performing as planned.
3.1.4 Minimization of Disruption and Dispersion by Natural Forces 3.1.4.1 Flooding and Water Erosion Protection The existing piles and proposed adjacent disposal site are at elevations which are more than 300 ft. higher than the expected probable maximum flood levels on the San Miguel River and in Hieroglyphic Canyon. Therefore, these rivers pose no potential flood hazard to the reclaimed tailings. The total storm runoff within each watershed above Tailings Fonds 2 and 3 that would result from the design stonn rainfall was estimated to be about 20.3 inches.
In order to ensure that the impoundments and clay cap are protected
. from water erosion due to local storms, UCC plans to cover the piles with 2 ft. of mine run rock with an approximate top size of 12 inches. UCC, however, has not provided specifications on the mine rock to be used. GEI recomends that this cover material be composed of hard, durable rock that will resist wind and water attack through the long-tenn. GEI also recomends that the rock cover be designed with a suitable filter to prevent the erosion of finer materials. GEI further recomends that the relatively flat top of the final impoundment surface be graded to provide for surface drainage, to eliminate areas of surface runoff concentration, to remove runoff from the site, and to provide protection against sheet and gully erosion of the impoundment surface.
Headward erosion of iceal gullies is expected to continue at rates exceeding about 4 ft. per thousand years (Ref.10). GEI recommends that UCC design and submit for review an erosion protection plan for all gullies that head toward the piles or appear to have the potential for advancing headward into the piles as recomended in Dr. Smith's report. This plan should ensure that headward erosion is arrested in gullies adjacent to the toes of the piles, and that the potential for long-tenn headward e osion of gullies back into the piles and threatening their stability is minimized. The staff feels that UCC's proposed plan would not meet NRC criteria with regard to erosion protection unless adequate measures for gully erosion protection are designed and implemented.
3.1.4.2 Wind Erosion Protection The existing tailings ponds and adjacent disposal site are located on gently sloping benches set back from the cliffs bordering the San Miguel River and Hierc, glyphic Canyon. Natural ridges in the west and south sides of Tailings Pond 2, and on the northwest side of Tailings Pond 3 provide a measure of natural erosion protection against winds from these directions.
Properly designed and constructed embankment slopes and tailings cover can provide reasonable assurances of long-tem wind erosion protection for those sections of the reclaimed piles that are not naturally sheltered from the wind. UCC's plan to flatten the slopes to SH:1Y will reduce the potential for wind erosion.
In addition, UCC plans to cover the reclaimed piles with 2 ft. of mine run rock with an approximate top size of 12 inches. GEI recommends that these cover materials (mine run rock) be of hard, durable rock that will resist water and wind erosion over the long-tenn. Shales and other less i
I resistant rock that weather and break down relatively quickly are not to be used. The relative resistance of potential cover materials can be inferred by observing weathering and mass wasting characteristics of bedrock exposures in the field. The site appears to provide adequate wind protection.
1.4.3 Embankment Stability The existing piles and the adjacent disposal site are imediately underlain by the Salt Wash Sandstone Member of the Morrison Formation which, at the present site extends from the ground surface to a depth of about 60 ft.
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, This sandstone is expected to provide adequate bearing strength for the piles through the long-tenn. While foundation conditions at the adjacent disposal site are likely to be similar to foundation conditions beneath the existing piles, GEI recomends that a limited boring, sampling, and permeability testing program be conducted at the adjacent disposal site to establish actual foundation conditions. Particular attention should be paid to local joint orientations with respect to the orientation of the canyon walls of the San Miguel River.
The proposed SH:1V slope for the faces of the reclaimed piles should provide adequate protection against failure of the slopes, provided foundation conditions are properly considered in embankment design, and hea&ard erosion of surrounding drainages is properly checked as discussed in the previous section. However, GEI reconsnends that any suitable material in excess of that neecad for the proposed embankment should be used to flatten slopes to provide additional protection against slope failure and erosion. The downstream force of the embankment should be further protected against erosion by the use of a suitable filter material overlain by 2 ft. of mine run rock as discussed in Sections 3.1.4.1 and 3.1.4.2.
Excessive differential settlement of the embankment due to dra'inage of the tailings and consclidation of slimes in those areas of tailings not to be moved could lead to cracking of the cap and cover materials if they are placed before primary consolidation of the slime tails is complete. Therefore, GEI recomends that UCC design the cap and cover to account for the potential for differential settlement and potential cracking of the cap and cover.
As discussed in Section 1.2, the existing tailings ponds are very close to the cliffs of the San Miguel River and Hierglyphic Canyon. The area is moderately dissected and observations in the field and from photographs indicate that the cliff retreat and headward erosion of gullies are active processes in the area. Smith (Ref.10) estimates maximum rates of cliff retreat to be about 4 ft. per thousand years. Therefore, GEI recommends that the top of the reclaimed piles be set back from the edge of the cliffs at least 4 ft. for each one thousand years considered to constitute the long-tenn; i.e., if the total period of consideration is 10,000 years, the toe of the piles should be set back 40 ft from the edge of the cliffs, if the total period of consideration is 100,000 years, the toe of the piles should be set back 400 ft. Set-backs greater than 50 ft. will require modification of the configuration of the reclaimed piles; the larger set-backs will require greater modification of the piles and the removal of large amounts of tails to the adjacent disposal site.
8 3.1.4.4 Capable Faulting A review of the historic seismicity, seismotectonic relationships and geology of the region indicates that there are two potential sources for generating the maximum credible earthquake at the site. Faults which flank the Ucompahgre Uplif t are the first potential source that could generate such an earthquake.
w..
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i Regional studies have not been of sufficient detail to evaluate the capability of these faults; however, since their activity is in question, the Environmental Report assumed that the faults are potentially capable. The closest major fault lies 9 miles (14 mk) northeast of Uravan. The Environmental Report, using data presented by Slemmons (Ref. 9), calculated a design earthquake of magnitude 6.8 for this fault. Using attentuation relationships developed by Schnabel and Seed (Ref. 7), the applicant expects an event of this magnitude to produce a maximum ground acceleration of approximately 0.35 to 0.40g on bedrock at the site. GEI believes that the values obtained for the design earthquake magnitude (Richter 6.8) and the maximum ground acceleration (0.35 to 0.43) are reasonable based on the assumptions and methodology used by UCC.
The second potential source for the maximum earthquaka is a random earthquake of a maximum magnitude typical of the maximum measured event has been of magnitude 4.5.
However, the seismic record is short and a magnitude 5.0 was assigned to the maximum random event for the purposes of this report.
Assuming that a magnitude 5.0 earthquake occurred two miles directly under the site, a mean peak ground acceleration of 0.2g is estimated in the Environmental Report. GEI believes that the values assumed here are reasonable, and although it is conceivable that a larger earthquake could occur at a shallower depth, the resulting maximum ground accelerations would still be less than those associated with the fault nine miles away as discussed in the paragraph above.
j After the tailings have drained, the reclaimed impoundments would probably withstand the maximum credible earthquake generated by local faults. However, UCC should be required to submit stability analyses for the drained reclaimed pond.
3.2 MINIMIZATION OF SEEPAGE As discussed in Section 4.5, seepage from the ponds is occurring at present, and.it is likely to continue to percolate into local perched groundwaters and surface waters as the ponds drain, and as water enters the existing ponds i
from normal operations, from direct precipitation or through the natural head ridges upgradient from the impoundment systems.
However, once the ponds are allowed to drain and are reclaimed and covered with a relatively impermeable shale cap, infiltration into and seepage from the ponds will be considerably less than the present rate of infiltration and seepage. While reclamation and shale covering of the tailings would not completely eliminate seepage from the piles, they would represent a considerable improvement over present seepage conditions. Seepage would not affect the long-term stability of the tailings piles.
4 r v-,--n---,-,-----
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. Seepage from the tailings emplaced at the new disposal site adjacent to the northwest section of Tailings Pond 2 is expected to be acceptably low for several reasons; first, the new disposal area will be lined. While details i
of the fcundation preparation for the liner, and the liner itself have not been presented, a properly designed and constructed liner will minimize seepage significantly. GEI reconnends that UCC use a shale / clay liner, that meets the following conditions:
1.
The clay liner thickness and permeabilities be determined by seepage analysis using realistic permeabilities for recompacted shales.
2.
UCC submit evidence supporting the conc'iusions that local shale / clay materials can be compacted in the field to provide a continuous liner that has the permeability required as determined in the seepage analysis.
3.
UCC provide test results which ensure that the materials used for the liner will not undergo any increase in permeability characteristics or deterioration of consolidation or stability properties when exposed to tailings solutions over the long-tenn.
4.
UCC submit liner material specifications, compaction criteria, and field compaction procedures.
5.
UCC describe foundation sandstone preparation procedures to ensure that the liner is uniformly of the requirea thickness, and that liner materials are not placed against irregular sandstone surfaces that might threaten the integrity of the liner.
6.
UCC investigate foundation conditions to detennine if the use of filters or other special foundation preparation techniques, such as local grouting, to prevent erosion of liner material into open joints in the foundation is required.
7.
UCC describe source area, material specifications, thickness, and emplacement procedures for protective cover over shale / clay liner.
Second, the tailings to be emplaced at the adjacent site will be stripped from Ponds 2 and 3 after the phreatic surface has dropped below the tails to be moved. Therefore, free liquids in the tailings will he minimized.
Finally, covering the tailings with a relatively impermeable cap will j
l prevent much direct precipitation and runoff from entering the piles and eventually seeping out.
3.3 REDUCE THE RADON EMANATION RATE FROM THE IMPOUNDMENT AREA TO 2 pCi/m -SEC AND GAMMA RADIATION TO BACKGROUND Conclusions reached in the GEIS and later placed in NRC regulations (10 CFR Part 40, Appendix A, Criterion 6) require that sufficient cover be placed over the reclaimed tailings to reduce the radon flux from the tails to 2 pCi/m -sec above background. Union Carbide's proposal to utilize Manchos Shale was evaluated by NRC in order to determine what depth of cover material
. )
is required to meet this criterion. This evaluation shows that a minimum of 9 f t. of cover material will be required to meet this criterion. In any case, it should be pointed out that NRC regulations require a minimum cover thickness of 3 meters (10 ft.) to provide assurance against long-term erosion and to help preclude intrusion by burrowing animals. The placement of sufficient cover to reduce radon exhalation to acceptable levels will r '.ce gamma radiation to essentially background levels. The staff recomends th least 3 meters (10 ft.) of cover be placed over the tailings.
,s.
4.0 MAJOR CONCLUSIONS AND RECOMMENDATIONS Detailed evaluation of Union Carbide's proposed Reclamation Plan and independent review of the existing tailings disposal site at Uravan indicate that tailings at this site can be sucessfully reclaimed in-place with only minimal monitoring required (in the years imediately following cessation of operations) provided that the recomendations contained in this report are carried out. The proposed plan adequately satisfies the aforementioned technical criteria for reclamation of an existing tailings area and meets the minimum levels of protection required for reclamation of tailings piles (45 FR 65521). The site has certain natural features (for example, it has a small upstream catchment area, natural ridges which provide wind protection, and is elevated above the flood plain of the San Miguel River) which will enhance the long-tenn stability and erosion resistance characteristics of the proposed plan. Other features of the site which do not offer desired long-term protectica (headward erosion of gullies and cliff retreat) can be designed against for the long-term.
Major recomendations which must be carried out in order to ameliorate the effects of these later features require that:
(1) Union Carbide submit for review an erosion protection plan for all gullies that head toward the tailings piles or appear to have the potential for advancing headward into the piles; and (2) that Union Carbide set back the top of the reclaimed piles at least 4 ft. for each one thousand years considered to be long-term.
In addition to the above, 3 meters of cover thickness should be placed over the piles in order to reduce radon emanation and gamma radiation to essentially background and to provide erosion protection and a barrier from intrusion.
All of the recommendations contained in this assessment are considered by NRC to be the absolute minimum required for acceptable reclamation of the site.
e-,,
I REFERENCES j
1.
Acres American Incorporated, Uravan Mill Alternative Tailings and Effluent Disposal - Phase IV Report for Union Carbide Corporation, Metals Division, Niagara Falls, N. Y.; January 1980.
2.
Dames and Moore, Environmental Report - Uravan Uranium Project - Montrose County Colorado - For Union Carbide Corporation; Job No. 00822-106-14; 31 August 19/6.
3.
Fenneman, N. M.,1931. Physiography of the Western United States.
McGraw-Hill Book Co., New York.
4.
Geotechnical Engineers, Inc. Safety Evaluation Report Tailings Ponds 2 and 3, Union Carbide Corporation Uravan, Colorado, March 1980.
5.
Hadsell, F. A.,1968.
" History of Earthquakes in Colorado." Hollister, J. S.
and R. J. Weimer, ed., Geophysical and Geological Studies of the Rocky Mcuntain Arsenal Well. Colorado School of Mincs Quart., 63(1):
57-72.
6.
Kirkham, R. M. and W. P. Ro9ers,1978. " Earthquake Potential in Colorado."
Colorado Geol. Survey, Preliminary Draft Report.
7.
Schnabel, P. B. and H.
B., Seed, 1973.
" Acceleration in Rock for Earthquakes in the Western United States." Bull. Seismological Soc. Am., 63(2): 501-516.
8.
Shum, S.
A., 1981. Letter to Dr. John Nelson, Colorado State University.
9.
Slemmons, D. B.1977.
" State-of-the-Art for Assessign Earthquake Hazards in the United States, Report 6; Faults and Earthquake Magnitude."
U. S. Army Corps of Engineers Misc. Paper-S-73-1,
- 10. Smi th, S. V. 1980.
"Long-Term Stability of Union Carbide's Tailings Piles at Uravan, Colorado." Univesity of Houston Final Draft Report.
- 11. Union Carbide Corporation,1980, Proposed Plans and Estimated Costs for l
Tailings Reclamation, Mill Decommissioning and Pond Reclamation at the Uravan Mill - For Surety Purposes.
12.
U. S. Department of Commerce and U. S. Department of the Army, September 1977.
Hydrometeorological Report No. 49, Probable Maximum trecipitation Estimates, Colorado River and Great Basin Drainages.
13.
U. S. Nuclear Regulatory Consission, Final Generic Environmental Impact Statement on Uranium Milling, Project M-25; Office of Nuclear Material Safety and Safeguards, NUREG-0706, September 1980.
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. tan!.E 1.1-1 TEllPEllATuttE DATA ItECORDED AT UltAVAll, Col.0RADO AUGUST 19 72 Tilit0HCil DECEttnEnt 19 7 7 f
tiean Daily Temperatures (*C)
Extreme Temperatures (*C) l Honth flinimum Average llax imum flinimum flaximum Jan
-12.2
-4.5 3.3
-23.3 (1974) 13.3 (l')75')
Feb
-6.7 1.3 9.4
-20.5 (1974) 18.9 (1977) tlar
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-11.6 (1977) 23.3 (1975) j Apr 1.7 10.5 19.4
-7.7 (1977) 28.'8 (1977)
Hay,
6.7 16.7 26.7 0.0 (1975) 37.2 (1974)
Jun 10.6 21.4 32.2 3.3 (1974) 40.0 (1974) i Jul 15.6 25.3 35.0 10.0 (1973) 41.1 (1976)
Aug 13.3 23.0 32.8 7.2 (1977) 38.9 (197,5)
Sept 9.4 18.8 28.3 0.5 (1974) 37.7 (1976)
Oct 2.2 12.2 22.2
-6.6 (1975) 31.1 (1974) tiov
-2.8 5.0 12.8
-16.6 (1976) 23.3 (1973)
Dec
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-16.6 (1972) 15.5* (1975) 1 Year 2.3 11.2 20.2
-23.3 (1/74) 41.1 (7/76) i 4
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PRECIPITATION uATA RICORDED AT URAVAN, COLORADO 1972 THROUGH 1977
'~
Monthly Total Precipitation" (cm)
Maximum 24-hour Month Minimum Average Maximum Precipitation (cm) i
(~
Jan 0.53 (1976) 2.7
'6.4 (1974) 1.6 (1974)
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Feb 0.10 (1974) 0.91 2.2 (1975) 1.1 (1975)
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Mar 0.41 (1976) 2.4 4.9 (1975) 1.2 (1974)
Apr 1.3 (1973) 2.4 6.1 (1975) 0.94 (1974) 3 May 0.10 (1974) 2.0 4.2 (1973) 1.2 (1976) i
.Jun 0.07 (1974) 1.2 4.2 (1973) 2.0 (1973) l
'Jul 0.86 (1973) 4.3 9.0 (1977) 3.2 (1977)
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/ug 0.53 (1974) 2.3 4.8 (1977) 1.0 '(1973)
I Sept 0.96 (1977) 2.8 6.9 (1976) 1.6 (1976) f
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Nov 0.25 (1976) 2.1 3.7 (1977) 2.8 (1977)
F Dec 0.13 (1976) 1.1 2.1 (1972) 1.3 (1972)
P D
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Year.
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- For the period August 1972 through December 197J.
Ud For the period January 1973 through December 1977.
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Mean Total Wind 0-1 1-4 4-10
>10 Occurrence Speed N
0.24 0.67 0.30 0.00 1.7 2.8 NNE 0.80 0.90 0.19 0.00 1.9 1.8 NI 0.40 0.32 0.07 0.00 0.8 1.6 ENE 0.56 0.14 0.01 0.00 0.7 0.8 E
3.72 0.94 0.28 0.00 4.9 1.1
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1.97 1.07 0.13 0.00 3.2 1.2 55W 0.25 0.29 0.01 0.00 0.6 1.3 0.47 0.37 0.06 0.00 0.9 1.4 l:
SW.
WSW 0.15 0.15 0.06 0.00 O.4 1.7 W
1.07 0.87 0.97 0.00 2.0 1.4 l-WNW 1.15 1.97 0.90 0.00 4.0 2.5 P
NW 2.06' 7.71 4.87 0.19 14.8 3.3 I;.
NNW O.76
- 3. 3'6 1.94 0.07 6.1 3.3-lf Annuar Average 47.25 36.81 16.49 0.32 100.0 1.95
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