GJT-6

PHASE II - TITLE I

ENGINEERING ASSESSMENT OF

INACTIVE URANIUM MILL TAILINGS

DURANGO SITE

DURANGO, COLORADO

November 1977

Prepared For

DEPARTMENT OF ENERGY

GRAND JUNCTION, COLORADO

Contract No. E(05-l)-1658

By

FORD, BACON AND DAVIS UTAH INC. 375 Chipeta Way Salt Lake City, Utah 84108

FB&DU 130-05 CHAPTER 2

SITE DESCRIPTION

The purpose of this chapter is to describe the Durango site and the characteristics of the tailings materials present on the site.

2 LOCATION

The Durango millsite is located just outside of the city lim­ its of Durango, La Plata County, in southwest Colorado. (See Fig­ ure 2-1.) The site is bordered on the east by the Animas River, on the north by Lightner Creek, and on the southwest by Smelter Mountain. More specifically, the site is in Sections 29 and 30, Township 19 South, Range 70 West, Sixth Principal Meridian, at 37 deg 15 min 54 sec north latitude, and 107 deg 53 min 04 sec west longitude.

2.2 TOPOGRAPHY

The site is located in the valley of the Animas River. The elevation of the river in this location is 6,470 ft above sea level with the valley floor varying in elevation from 6,500 to 6,650 ft above sea level. The area contains mesas, steep cliffs, and mountainous terrain typical of the western slopes of the Rocky Mountains. The surrounding San Juan Mountains rise to elevations up to 9,000 ft. Vegetation varies from sagebrush, juniper, and pinion pine on the south to pine and fir in the San Juan National Forest to the north.

There is a large and a small tailings pile on the approxi­ mately 147-acre site. These tailings piles cover about 21 acres. The base of the piles is about 30 ft above the river and the piles lie against Smelter Mountain which rises on the southwest part of the site. The piles are relatively flat on top, but have steep slopes varying from 2-to-1 to a 1.5-to-1 slope. The small pile, just north of the large pile, is about 90 ft high and contains approximately 325,000 tons of tailings on 7 acres. The large pile covering 14 acres is about 230 ft high and contains approximately 1,230,000 tons of tailings. The piles are visible from almost any point in the city.

The millsite and ore storage area, adjacent to the large pile on the southeast, cover approximately 8 acres. The 9-acre raffi­ nate pond area is located about 0.5 mi southeast of the large pile. Figure 2-2A is a topographic map of the tailings and mill­ site area and Figure 2-2B contains a topographic map of the raffi­ nate ponds area.

2.3 OWNERSHIP

In 1976 and 1977 the Ranchers Exploration and Development

2-1 Corporation purchased the entire site except for two small parcels which were deeded to the Colorado Highway Department and the La Plata Electric Co. In Figure 2-3, the land ownership of the site is shown.

2.4 HISTORY OF MILLING OPERATIONS AND PROCESSING(l)

The mill was built on the site of an old lead smelter by United States Vanadium Corporation (USV) in 1942 to furnish vana­ dium to the Metals Reserve Company, a company set up by the fed­ eral government for the purchase of strategic materials needed during World War II. Retreatment of the vanadium tailings for the recovery of uranium was begun by USV in 1943 for the Manhattan Project. The early mill operated until 1946, then was shut down until 1949 when the Vanadium Corporation of America (VCA) contrac­ ted to sell uranium to the AEC. The VCA leased the property then later purchased it. Plant operation continued until March 1963 when the mill was shut down permanently. The VCA retained owner­ ship of the millsite and adjoining property until 1967 when VCA was merged into Foote Mineral Company.

The initial milling capacity of about 175 tons of ore per day was expanded to 430 tons/day by 1956 and to 750 tons/day by 1958. Ore averaging 0.29% u3o8 and 1.60% v2o5 was delivered to the Durango mill from mines of the Uravan M~neral Belt, Dry Valley, Carrizo, Cove Mesa, Placerville, Hermosa Creek, Lightner Creek, and Monument Valley. The company also purchased ore from indepen­ dent operators and processed ore and upgrader products from com­ pany-controlled properties. All mill feed was hauled to the Durango mill by truck.

Concentrates from the company upgrader plants and ores were salt-roasted. The calcines were quenched in carbonate solutions, then treated by countercurrent washing. Pregnant solutions were treated to precipitate the uranium and filtered. The filtrate was processed further to recover vanadium. Tailings from the carbonate leaching operation were retreated to recover additional uranium and vanadium by means of acid-leaching. The pregnant acid-leach liquor then was treated by solvent extraction to recover both ura­ nium and vanadium. (2)

2.5 PRESENT CONDITION OF THE SITE

Because of the steepness of the tailings pile slopes, they have not been stabilized with earth cover. However, vegetation has been planted directly on the piles with some success. This is an experimental stabilization program under Part VIII, State of Colorado Regulations (See Appendix B). A report of the results on the stabilization program is furnished to the state annually. The vegetation requires constant irrigation during the summer and

(l)see end of chapter for references.

2-2 tailings maintenance is required all year to prevent canyon winds from eroding the tailings.

Snow fencing and other types of physical restraints presently in use provide some surface stability. Diversion ditches have been dug above the piles on Smelter Mountain to divert water run­ off away from the tailings.

Nevertheless, some ongoing erosion is evident. In particu­ lar, the southern exposure of the large pile is eroding badly. The top of the pile and the northern and northeastern slopes ap­ pear stable. The small pile appears well stabilized except for a major gully below an excavation, where tailings were removed for a heap leach test in New Mexico, on the northeastern slope of the pile, and for some erosion on the southeastern part of the pile near the contact of the pile with Smelter Mountain. Some of this eroded material has reached Lightner Creek and the Animas River in spite of the ditches and catchment areas between the piles and the river. A recent improvement to the access road which runs along the toe of the piles should assist in ensuring that surface drainage coming off the slopes of the piles will not drain direct­ ly into the Animas River.

The slope stability of the pile could be of concern because the tailings represent a uranium, thorium, and radium reservoir that could introduce radionuclides into the Animas River if large­ scale erosion or a sudden mass movement were to occur. The tail­ ings are stratified horizontally and are somewhat vertically zoned. They increase in fines against the slope of Smelter Mountain. As the tailings have dried, th~ stability of the piles has improved. According to a recent study(3) the slopes of the piles are stable. However, disturbances of the piles, such as cutting the toe or redistribution of the tailings, could lead to slope instability and potential slippage into the Animas River.

A recent highway improvement 'included a cut below the large tailings pile. (4) (See Figure 2-4.) The cut was evaluated and the tailings were reported to be stable. The realignment of the river channel has reduced the millsite area.

Raffinate was channeled to the raffinate ponds during opera­ tions from 1959 to 1962 through a l/2 mi long ditch which has since been filled with soil. In the early 1970's these raffinate ponds were filled, covered with local soils~ and graded. The area was seeded and vegetation typical of the vicinity is now estab­ lished. Figures 2-5A and 2-5B are descriptive maps of the tail­ ings and raffinate pond areas, respectively. Included in the figures are the locations of drill holes used for sampling and radiation measurements. To supplement the description of the site, cross-section profiles of the tailings piles are shown in Figure 2-6.

2-3 2.6 TAILINGS AND SOIL CHARACTERISTICS

Several types of materials make up the Durango tailings piles: uranium tailings, vanadium tailings, lead smelter slag, rubble and contaminated earth. The types, volumes, and weights of materials presently on the site are summarized in Table 2-1. The Durango tailings consist of gray, finely ground sands with a low-clay cont-ent. The calculated average bulk density of the tailings is 98.3 lb/ft3. The bulk density and pH of soil samples from on-site test holes are given in Table 2-2. The pH of the samples is in the neutral range. Assays of composite uranium and vanadium tailings samples are shown in Table 5-l, Chapter 5.

Analyses of borings and samples indicate that the tailings were not deposited uniformly in the piles. This nonuniformity can be attributed to differing ores processed and to the differ­ ential deposition and migration of slimes from the discharge points.

The millsite and the toe of the large tailings pile are in part located on a man-made shelf consisting of vitreous fractured slag from the old lead smelter that operated from 1880 to 1930. Beneath the slag and the tailings piles is a 1 to 30 ft layer of unconsolidated riverbed material. The bedrock at the site con­ sists of dark gray shales with interbedded light-brown, fine­ grained, and highly fractured sandstones.

2.7 GEOLOGY, HYDROLOGY, AND METEOROLOGY

2.7.1 Geology

The Durango site is confined to a shelf between the Animas River on the northeast and the sharply rising Smelter Mountain on the southwest. The Mancos Shale is exposed on Smelter Mountain in outcrops above the tailings piles and is evident in borings through the tailings piles. The Mancos Shale primarily consists of gray to dark.gray mudstones but there are many thin sandy lime­ stone lenses and limestone concretions throughout the unit. This easily weathered formation is capped by the Point Lookout Sand­ stone Member of the Mesa Verde Sandstone Group. South of Durango the Lewis Shale, which is similar in appearance to the Mancos Shale, overlies the Mesa Verde Group.

At the millsite, the strata dip 5 to 10 deg toward the south­ east. The Mancos Shale is hundreds of feet thick beneath the tail­ ings and acts as a barrier to the downward and upward migration of ground waters. A simplified stratigraphic column of the rock formations is shown in Figure 2-7.

2.7.2 Surface Water Hydrology

The flowing surface waters near the site consist of Lightner Creek and the Animas River. These streams merge immediately up­ stream from the tailings. Lightner Creek has sufficient channel

2-4 capacity to carry minor floods without significant property darn­ age, although major floods have caused substantial damage in the Lightner Creek drainage.

The Animas River at the site area is a swiftly flowing stream with a narrow flood plain and relatively limited flood carrying capacity. The river has no flood plain along the west bank in the reach containing the tailings. Rather, the stream is con­ tained by a near-vertical bank cut within 70 ft east of the base of the tailings. The location of surface waters and flood-prone areas is given in Figure 2-8. Areas covered by an intermediate regional flood and by a standard project flood are indicated by different shading in the figure. The lowest elevation of either tailings pile is along the northwest toe of the small tailings pile at 6,490 ft. Flood waters associated with either an inter­ mediate regional flood (100-yr flood) at about 6,484 ft or a more severe standard project flood at about 6,488 ft would not reach the piles. Riprap protects the river bank against a 50-yr frequen­ cy event. The slag material underlying the large pile provides excellent protection for the toe of the pile. Flood waters have not removed tailings materials from the site. Contamination of surface waters near the piles could occur by physical transport of the tailings in overland runoff and by seepage from the piles. The degree of physical transport of the tailings by overland flow has been reduced by the construction in 1965 of a flash flood diversion ditch on Smelter Mountain above the tailings piles. Since then, the ditch has survived heavy rainfalls; however, two sections appear inadequate to contain the flow from the drainage. In general, though the overland flow onto the piles is limited almost entirely to the rain that actually falls on the piles. Flow of water through the piles is not evi­ dent from any surface seepage along the west bank of the river.

2.7.3 Ground Water Hydrology

The tailings generally lie directly on Mancos Shale outcrops or are at most separated from the shale strata by less than 15 ft of unconsolidated material. The Mancos Shale is relatively impermeable, is not a major aquifer, serves as a confining layer over the Dakota Sandstone and thus prevents downward migration of contaminants. At Durango, water in the Dakota Sandstone is under artesian pressure and moves in a southeasterly direction. Al­ though the Dakota Sandstone is a potential aquifer and would be capable of yielding dependable small quantities of water for stock, it is not tapped in the Durango area because of availability of surface waters. The unconfined aquifers in the Durango area consist of waters within the recent valley alluvium and glacial deposits. Most of the tailings rest almost directly on bedrock separated at most by only a few feet of intervening unconsolidated material. There is little potential for ongoing seepage through the pile. However,

2-5 it is possible that ground waters flowing through the unconsoli­ dated material could be contaminated by any such seepage. Water for the City of Durango comes from the underflow of the Animas River via infiltration galleries installed in the alluvium up­ stream of the tailings piles. Records in the State Engineer's Office show no registered wells at a hydraulically lower gradient than the base of the piles within 2 mi of the tailings site.

2.7.4 Meteorology

High-intensity rainfall such as thunderstorms can ~e yxpected an estimated 15 times in the Durango area each summer. ( ' 7 These storms have caused physical erosion of the tailings. Snowmelt is not of major concern because it generally does not result in rapid runoff and consequent erosion. Average annual precipitation totals approximately 19 in. Large rainstorms occur usually from May through October. A rainfall of 6-hr duration totaling 1.3 in. has a probability of occurring once in five seasons. A high­ intensity cloudburst at the site would result in serious erosion of the less stabilized areas of the piles.

Very little direct information exists regarding the frequen­ cy, duration, and intensities of winds in the immediate vicinity of the tailings. The weather data for Durango have been gathered primarily at the airport southeast of the city outside the rela­ tively narrow section of the Animas Valley, which controls the winds at Durango. The strongest winds are those which blow up or down the valley as depicted in Figure 2-9. A wind rose from the Durango airport, located on a mesa, is given in Figure 2-10. The wind records from the airport indicate a predominance of winds from the southwest quadrant. Valley winds flow up the Animas Val­ ley and are channeled past the tailings to where the valley widens. Tailings have been carried north and northwest from the piles as a result of these strong winds eroding the semi-stabilized south­ ern exposure of the large pile.

2-6

APPROXIMATE RIVER ELEVATION 6464 FT

SEWAGE PLANT

NOTE MAP DEVELOPED FROM COLORADO STATE DEPARTMENT OF HIGHWAYS MAP AND FB&DU DATA LOGGED APRIL 5, 1976

0 100 200 300 FT kM.+o;J I ! INTERVAL 2 FT)

EDGE OF TAILINGS

FIGURE TOPOG IC MAP OF NGS AREA 130·05

2-8 ~~;EDEVELOPED FROM C~~~~:~~ S'ATE DEPARTMENT OF H D M~P AND FB&DU DATA LOGGE APRIL5,1976

LEGEND em LIMIT OF RAFFINATE PONDS

0 100 200 300 400 FT

TO BODO (CONTOUR INTERVAL 2FT) CANYON

FIGURE 2B. PHIC AP OF NOS AR 130-05

2-9 &

CITY OF DURANGO SEWAGE PLANT

RANCHERS EX DEVELOPMENTPLORATION AND CORP.

LIMITS OF COLO WILDLIFE PROPtR~~O DIVISION OF

LA PLATA ELECTRIC CO.

COLORADO HIGHWAY DEPARTMENT

UNMARKED ARE ~~~iRSHIP OR I~SC~~~ IN PRIVATE SHIP, oo: :::NSPORTAT7~~~~EPART­ THEM FOR HID BEING AQUIRED NER­ GENERALL y ~:WAY PURPOSES BY ANIMAS RIVER RALLELING THE

0!! liil!!!l2iZO!!O!!i!401;0;;6~0~~800FT

130-05 3. LAND HIP MAP

2-10 I I I I ' ',, I I \ \ , NARROW GAUGE RR DEPOT I I • I I \ I I \ \ \ \ \ \ \ \ \ PROP. R.O. W. \ \ ' I ~~\ '\ \\ ' '\'\ DURANGO 16'1 ' \ ' tOF DIKE ' ' ' \ \ -~~,' \ \ ORIGINAL GROUND LINE \ --- \ \ \ I \ I I / MILLSITE 'r 'I / '>- I ~I ~I :X:j C:JI RIVER FLOW LINE fXI Ii?, f?t Q..l 72 1 I I I I I I TYPICAL CROSS-SECTION OF BANK NEAR LARGE PILE I I I I I I I I I I I I DURANGO SEWAGE PLANT I I I I I t I l 0 100 200 300 400 500 FT

GURE 2-4. CHANN GE R E HIGHWAY CON U ON PROJECT 'OU NGO SO 130-05

2-ll ~ ...... ---!"'---­ _,, ,'......

TEST PIT

SUDDEN CHANGE IN SLOPE (D EDGE 0 OWNWARD) F PILE + HOLE LOCATION· AND DEVELOPME~; ~OYR~A:~~~~SBY EXPLORATION FB&DU ~C-.20

FIGURE 2- 5A OF TAILINGS AR 130-05

2-12 Jnc.

NOTE

' (' ... .. \

___ ...... ~ ...... ROAD __.=..------::::::~··· ,_-- HAUL ------·· HOLEDC L OCATION ...----::--___- ,-o____ ,.,ccsnto.s"';::::::::::::-.;:::-----===:::--""-----===------..------==-"'=------=------.·· .. . BY FB&DU

0 100 200/ 15i~!iiiiiiiiiiiii~~~300 FT

FIGURE 2- 58 . DESCRIPTIVE MAP OF RAFFINATE PONDS AREA 130-05

2-13 LIGHTNER CREEK EDGE OF TAILINGS ----\·-)----EDGE OF TAILINGS

BASELINE SEE FIGURE __j EDGE :s- LOWER EDGE BASELINE SEE FIGURE 2-5A OF TAILINGS

SECTION AT SMALL TAl LINGS PILE SECTION AT LARGE TAILINGS PILE

PLAN

6725 6725

6675 6675

6625 6625

6575 6575

6525 6525

RIVER 6475 6475

6425 6425 PROFILE 0+00 2+00 4+00 6+00 8+00 10+00 FIGURE 2-6. CROSS-SECTIONS SMAll AND LARGE TAILINGS PILES 130-05

2-14 Jnc.

POl NT LOOKOUT SANDSTONE MEMBER OF THE MESA VERDE GROUP (POTENTIAL AQUIFER) MAXIMUM THICKNESS ABOUT 400FT TAILINGS PILE

MANCOS SHALE (AQUICLUDE) MAXIMUM THICKNESS ABOUT 2,400 FT

FIGURE SIMP FlED RATIGRAPHIC COLUMN

130·05

2-15 & 'IDa~ts Jnc.

\

GRAVEL PIT

-...... 6800

INTERMEDIATE STANDARD REGIONAL PROJECT FLOOD FLOOD

RAFFINATE ---4---t----11-1 PONDS AREA

GURE 8. F 00 NE 130-05

2-16 :eacon & 'IDal?is Jnc.

LEGEND

400+ FT ABOVE VALLEY RELATIVE MAGNITUDE OF WINDS :=LOOR DEPICTED BY LENGTH OF ARROWS

200-400 FT ABOVE VALLEY Ml FLOOR

GURE 2-9. WIND MAP 130-05

2-17 J'"oro, :13acon &. IDa"ts Jnc.

N

E

s

FIGURE RANGO AIRPORT SURFACE WIND ROSE (CUMULATIVE DATA FROM 1970 THROUGH 1972) 13o-os

2-18 TABLE 2-l

TAILINGS SITE MATERIALS ======·-----

Volume Weight * Material (yd3) (tons) Uranium Tailings 1,200,000 (@ 98.3 lb/ft3 ) 1,555,000 3 Slag 68,000 (@ 130 lb/ft ) 120,000 Millsite and Tailings Area Contaminated 3 Earth 215,000 (@ 110 lb/ft ) 307,000 Off-site Contaminated Earth 27,000 (@ 100 lb/ft3) 41,000 3 Rubble, Stack, Buildings 300 (@ 150 lb/ft ) 600

TOTAL 1,467,000 2,023,600

*Weight based on average existing field densities, which include moisture.

TABLE 2-2

PHYSICAL PROPERTIES OF THE URANIUM TAILINGS

Percent . a Bulk Density pH Samp l e Locat1on Moisture (lb/ft3) ( 5% water by wt)

DC ll 95.0 6.2

DC 26 12.47 101.6 8.2

2-5A

2-19 CHAPTER 2 REFERENCES l. "Phase I Report on Conditions of Inactive Uranium Millsite and Tailings at Durango, Colorado"; AEC; Grand Junction, Colorado; 1974.

2. R. C. Merritt; The Extractive Metallurgy of Uranium; Colo­ rado School of Mines Research Institute; Golden, Colorado; 1971.

3. "Stability of Tailings Piles at Durango, Colorado"; unpub­ lished report prepared for Foote Mineral Company; Woodward - Clyde and Associates; Denver, Colorado; 1968.

4. Final Environmental Impact Statement; Project F 019-2 (14) Durango South, La Plata County; prepared by the U.S. Depart­ ment of Transportation, Federal Highway Administration, and Colorado Division of Highways; FHWA-Colo-EIS-73-09-F; 1975.

5. "Flood Plain Information, Animas River and Tributaries, Durango, Colorado"; prepared for the Animas Regional Planning Commission, La Plata County and the City of Durango; U.S. Corps of Engineers; Sacramento, California; 1974. (In addi­ tion, an updated edition was issued in Hay 1977.)

6. L. Hjermstad, Meteorologist; personal communication; Durango; Colorado; 1976.

7. "Meteorology Affecting Uranium Tailings at Durango, Colorado"; unpublished report; URS Company; Denver, Colorado; Jun 1976.

2-20