Lecture 30

Case Studies

Study Problem - Potentiometric Surface

Yucca Mountain northwest of Las Vegas, Nevada, is an area being considered as a

potential high-level radioactive-waste repository (figure 1). To determine the direction and magnitude

of ground-water flow at the proposed repository, water levels were measured in 1993 in 28 wells

(Tucci and Burkhardt, 1995) (figure 2).

The proposed repository is located in the Great Basin portion of the Basin and Range

physiographic province. Yucca Mountain is composed of a thick sequence of extrusive volcanic

rocks that overly Paleozoic carbonate rocks. The volcanic rocks are estimated to be up to 3,000

feet deep under Yucca Mountain. At Yucca Mountain, the uppermost saturated zone is in the

Tertiary age volcanic rocks.

1) Plot the measured water-level altitudes from table 1 on figure 2.

2. Contour the potentiometric surface. All of the wells are completed in confined portions

of the volcanic aquifer.

 

3. Describe how and why the magnitude of the hydraulic gradient changes over the

Solitario Canyon fault.

 

4. Place flow lines on your potentiometric surface map and describe what direction ground

water is flowing under Yucca Mountain, Jackass Flats, and Fortymile Wash.

References

Tucci, P. and D.J. Burkhardt, 1995. Potentiometric-surface map, 1993, Yucca Mountain and

vicinity, Nevada, Water-Resources Investigations Report 95-4149, U.S. Geological Survey,

15 p.

Key for Yucca Mountain Study Problem

1) and 2) See the potentiometric surface map of Yucca Mountain and vicinity, 1993

(Tucci and Burkhardt, 1995).

3. The Solitario Canyon fault appears to act as a barrier to ground-water flow, causing

water to mound on the upgradient side of the fault. There is a steep hydraulic gradient across

the fault zone. Also, there is thought to be a zone of higher permeability across the fault. Other

researchers have theorized that the fault may create a semi-perched zone.

 

4. Assuming that the volcanic rocks are homogeneous and isotropic, ground-water flows

toward Fortymile Wash and then to the south towards Death Valley.

Location of Yucca Mountain and vicinity.

Map showing locations of wells in the vicinity of Yucca Mountain.

Summary of selected wells monitored for water levels at Yucca Mountain.

[Water-level altitude is 1993 mean value unless otherwise indicated. Depths are in

meters below land surface. Altitude is in meters above sea level.]

^{1Water-level altitude for uppermost interval of well. Other interval(s) also monitored.}

^{2Water-level altitude based on 1989 data. Data not available for 1993.}

^{3Water-level altitude for Paleozoic carbonates. Does not represent water level in the}

^{uppermost flow system.}

^{4Calico Hills}¾ abbreviation Calico Hills Formation.

⁵Topopah Spring¾ abbreviation Topopah Spring Tuff.

⁶Water-level altitude from Waddell and others (1984).

⁷Water-level altitude from Robison (1984).

⁸Estimated water-level altitude.

Key for sample problems.

Portsmouth Gaseous Diffusion Plant, Piketon, Ohio

Environmental Effects of potential discharges are monitored through comprehensive

analysis of air water soil and sediments.

The Portsmouth Facility is located in South-central Ohio (figure 1). It is still used to

process uranium.

Summary of ground water, surface water, soil and sediment monitoring

Geology: site located in an ancient river valley

Ancient river, "the Teays" once had a northerly flow

Pleistocene glaciation reversed the Teays flow creating the current Scioto River

which flows southerly into the Ohio River (figures 2 and 3)

Scioto River has downcut bedrock to the west leaving a perched ancient river

valley (figure 4)

Near-surface soils: clay, silt and sand (avg. 25 to 35 feet thick)

underlain by bedrock consisting of: the Sunbury shale, Berea sandstone, and

the Bedford shale. (figure 4)

Two aquifers beneath the Plant:

Shallow unconfined aquifer in the unconsolidated near-surface sediments 15

to 25 feet below surface.

Confined bedrock aquifer in the Berea sandstone --confined by the Sunbury

shale.

Ground-water flow in the Berea sandstone is radial away from the center of the

facility towards the edges of the facility (figure 5).

Only the shallow aquifer is contaminated

Plume extent remains under the plant

Ground-water monitoring

Quarterly sampling of over 100 wells and 11 offsite private wells

voc's, metals, specific chemicals and radioactive isotopes

Primary contaminant is TCE

Also, chromium and low levels of technetium and uranium

Surface-water sampling

• Liquid discharges at 21 locations
• 5000 samples taken annually at various intervals (weekly, daily,

quarterly or monthly)

• In compliance 96% of the time
• No indication so far that contaminants have left the site (ex. Little Beaver

Ck. found with TCE and a trench was built to intercept contaminated water for treatment)

Soil and Sediment Sampling

Radioactive impacts tested in soil and vegetation (including Scioto River

sediments)at 35 locations up to ten miles from the plant

Some Current Treatment Strategies (figure 6)

• X-611-A Lime sludge Lagoons
• X-701B Contaminated Ground-water plume
• X-705 A/B Incinerator Storage Lot
• X-749/X-120 South Ground-water plume

X-611-A Lime sludge Lagoons

• Cooling water was treated with a chromium rust inhibitor and disposed of in sewage

lagoons

• Most promising treatment alternative is to turn the lagoons into a wetlands habitat

X-701B Contaminated Ground-water plume

Interceptor trench and three extraction wells for ground-water treatment

X-749/X-120 South Ground-water plume

Slurry wall to contain plume movement

X-705A/B Incinerator Storage Lot

• Soil around lot contaminated with uranium and has higher than background

levels of radiation

• Soil washing : chemicals concentrate and remove uranium from Soil.
• Uranium is disposed of as low level radioactive waste
• Soil is reused at site or placed in a sanitary landfill

South of X-326 process building

• Area was previously waste oil biodegradation plots (allows for the natural

biodegradation of organic waste).

• In-situ soil treatment from thermal enhanced vapor extraction (TEVE)
• Prevents excavation and storage of contaminated soils

The Treatment Process

• In-situ a boring tool with an eight foot diameter augarhead air injected

under pressure

• Aids "desorption" of volatile organics(mostly degreasers ie TCE)
• Volatile organics are removed to depth of 22 feet
• Off gases are captured in a metal shroud and vacuum-filtered through

a mobile treatment unit

Chosen as the best alternative between 1)solidification 2) ambient air

3) thermally enhanced soil vapor extraction 4) peroxidation

Figure 1. Scioto River basin and pertinent features in the Piketon area.

Figure 2. Map showing ancestral Ohio River.

Figure 3. Teays stage and post-Teays stage (Newark River) valleys in southern

Ohio (from Stout and others, 1943).

Figure 4. Schematic geologic cross section of plant site.

Figure 5. Site-wide Berea Ground-water flow.

Figure 6. Map showing operable units at Portsmouth.

Tuba City UMTRA Site

(Uranium Mill Tailings Remedial Action), Tuba City Arizona

About the Site:

• Located south of US Hwy. 160 approximately (5 mi.) 8 km east of

Tuba City, Arizona (85 mi.)140 km northeast of Flagstaff, Arizona, on the Navajo

Indian Reservation (figure 1).

• 1800m NW and 90-190m elevation above Moenkopi Wash, an intermittent

stream that drains into the Little Colorado River (figure 2).

• Situated on a sloping veneer of unsconsolidated dune sand and pediment gravels (figure 3).
• Water in the wash is used seasonally to supply water to cattle, within 3 km radius

of site are a shallow domestic use well and a spring, four deeper wells used to supply

processing plant are north of the site.

• Net evaporation rate for area(evaporation minus rainfall) = (80 inches)204 cm/year

Site History

• Uranium Mill operated by Rare Metals Corporation of America from 1956 to 1962

and merged with El Paso Natural Gas Company which ran the site until 1966.

• Processed 800,000 tons of uranium ore over the 10 year span.
• From 1956 to 1962 avg. 300 tons/day were processed using sulfuric acid leaching

(3-5 tons of water used/ ton of ore).

• 1963-1966 avg. 200 tons/day processed with sodium carbonate in an alkaline process

(2-3 tons of water used/ton of ore).

• Water discharged to with mill tailings to mill tailings pond and to evaporation ponds.
• Four productions wells supplied this water.
• Propriety was turned over to the Navajo Tribe, although this is currently being contested

in court by the nearby Hopi Tribe who have had long going boundary disputes with the

Navajo Tribe

Geology at the Tuba City Site (figure 3)

0-20 m(0-60 ft.) of unconsolidated dune sand and pediment gravels

20 - 150 m (60- 490 ft) Navajo Sandstone weakly cemented medium to fine grained

sandstone with lenticular beds of cherty limestone (major aquifer- depth to water 10 -20 m (30-60 ft.)

150-170m (490-890 ft.) Kayenta Formation siltstone, mudstone and sandstone

170-339m (890-1140 ft.) Moenave Formation Sandstone and silt with an abundance of

calcareous cement

Water stored in ponds during processing has leached into aquifer, plume contains sulfate,

nitrate and chloride (projected percolation rates on 3-4)

Contamination due to Uranium processing activities

source: tailings piles and processing activities

began in 1956 and ended in 1966

transient drainage had contributed to ground water contamination

UMTRA project field activities

• drilled and installed a series of monitoring wells form November 1984 to August 1985 (figure 4)
• slug tests and water elevations
• ground water samples
• conceptual site model (figure 5)
• contaminants from tailings include: molybdenum, nitrate, selenium, strontium, sulfate, and

uranium contamination in ground water at least 450 m down-gradient to depth 20 m below water table

The Disposal Cell:

• Tailings disposed by stabilization in place (SIP), this includes wind blown

contaminated soils

• Progressively less contaminated materials toward top
• Radon emissions and infiltration of water reduced by compacted clayey sand

layer on the surface

• Erosion Reduced by graded layers of durable rock placed over pile
• No liner beneath cell to retard leakage

Hazards(risk evaluation)

(Plume currently poses no threat to human health and the environment)

Analysis of ground water quality show 18 constituents in ground water beneath and

down-gradient from site exceed MCLS or background levels; these are ammonium,

cadmium, calcium, chloride, chromium, iron, magnesium, manganese, molybdenum,

nitrate, potassium, selenium, sodium, strontium, sulfate, tin, uranium, and zinc.

• High TDS, with a lower pH and reduction/oxidation potential than

background water in the center of the plume.

• Nearby domestic drinking water wells have not yet been reached.
• Livestock will be threatened by continued movement toward Moenkopi Wash.

Nitrate is the most significant hazard:

It’s easily absorbed by infants stomach lining and prevents transportation

of oxygen in the blood.

Sulfate and uranium are also at toxic levels

Sulfate gives diarrhea

Uranium concentrations increase the risk of cancer to 1 in 1000 above the

EPA acceptable risk of 1 in 100,000

The Aquifer:

• Ground water in Navajo Sandstone is unconfined; depth to ground

water is 6 to 45 m(DOE, 1989a)

• Water flows generally to the Southeast (figure 6)
• Water levels and land surface elevations declining towards Moenkopi Wash

Aquifer parameters as determined from slug tests in observation wells and pumping

tests in production wells (DOE, 1986)

• avg. linear ground water velocity = 0.l6 - 30 m(2-100 ft.) / year;
• k= 4.6 x 10^-5 to 8.6 x 10^-4 cm/s(0.13 to 2.4 ft./day)
• hydraulic gradient = 0.009 to 0.03
• effective porosity = 0.25

Plume velocity averages16 m(50 ft.)/year(mounding of pile may have created an artificially

high initial gradient)

Region is a discharge zone for the Navajo Sandstone Aquifer

Moenkopi Wash shows perennial vegetation, seeps, and springs

Two Interpretations of Regional Flow Conditions:

1) Navajo Sandstone is a more or less uniform body well connected vertically

2) the Navajo Sandstone is divided into somewhat isolated water bearing

intervals divided by clay and chert beds

Figure 1. Tuba City UMTRA site location map (after DOE/AL/62350-161, 1995).

Figure 2. Physiographic setting for Tuba City UMTRA site (after DOE/AL

/62350-161, 1995).

Figure 3. Generalized stratigraphic cross-section, Tuba City UMTRA site,

Tuba City Arizona (after DOE/AL/62350-161, 1995).

Figure 4. Ground-water monitor well locations, Tuba City UMTRA site,

Tuba City Arizona (after DOE/AL/62350-161, 1995).

Figure 5. Diagram of the Conceptual Site Model, Tuba City UMTRA site,

Tuba City Arizona (after DOE/AL/62350-161, 1995).

Figure 6. Potentiometric surface of the Navajo Sandstone Aquifer,

Tuba City UMTRA site, Tuba City Arizona (after DOE/AL/62350-

161, 1995).

The Hanford Environment

Structure (Figure 1)

Located in the Yakima fold belt

Hanford site in the Pasco Basin, a syncline in the fold belt

Stratigraphy (Figure 2)

1- Local surficial Holocene eolian deposits

2- Hanford formation: Pleistocene sand and gravel catastrophic flood deposits

0 to 24 m(80 ft.) thick, <23 Ma

3- Ringold Formation, up to 185 m (600 ft.) thick; sedimentary deposits

consisting of interbedded clay, silt, fine to coarse sand, and gravel:

Late Miocene to mid Pliocene , <8.5 to >3.5 Ma

4- Columbia River Basalts; basalts flows and interbeds that have been

warped and folded: Miocene, 17 to 6.5 Ma

Hydrogeology

• vadose zone 20 to 23 m thick
• vadose is highly permeable cobbles, gravel and sand
• includes the top few feet of the Ringold
• occasional perched groundwater over silty sand and gravel lenses
• Ringold contains the upper unconfined aquifer with variable conductivity

(.03 to 183 m/day) (Figure 2)

• base of aquifer believed to laterally continuous paleosols and clay-rich

overbank deposits

• Lower parts of the Hanford Formation are locally saturated
• The confined aquifers, particularly in the Columbia River Basalts have

received very little contamination due to an upward hydrologic gradient

(also protected by the confining layer)

• Ground-water flow generally north and northeast toward the Columbia River

Flora and Fauna

• 240 species of plants
• 100 areas mostly cheatgrass and riparian plants
• 300 species of terrestrial and aquatic insects
• 16 species of amphibians and reptile
• 125 species of birds (horned lark and meadowlark)
• wastewater ponds are important habitats for songbirds, shore birds, ducks

and geese

• 300 species of mammals: muskrats, porcupines, muledeer
• Columbia River has a large diverse community of planktonic and benthic

invertebrates

• 44 species of fish in the Hanford reach of the Columbia River

Columbia River "Class A as designated by the state of Washington"

• domestic and industrial water supply
• stock watering
• fish and shellfish migration, rearing, spawning and harvesting
• wildlife habitat
• recreation
• commerce and navigation

Landuse around Hanford

• irrigated and dry land farming
• Saddle Mountain Wildlife Refuge

Ground-water use

• nearest domestic ground-water use is 16 km (10 mi.) upgradient

Human uses

• 8 archeological sites in the 100 N area
• historical gold mine tailings and homestead sites
• no residents on site

Figure 1. Geologic structure of the Hanford Site.

Figure 2. Generalized Southwest-Northeast geologic cross-section.

100-NR-2

Radioactive discharges "strontium and tritium" at Hanford

Site History

100-N: divided into two clean-up units 100-N-1 and 100-N-2

N-reactor located at this site (figure 1)

1)production of special nuclear fuel

2) by-product-- steam for power generation

contamination sources

unplanned spills of liquid waste (radioactive effluent) (figure 2)

• coolant
• tank farm leaks
• crib tank overflow and leaks
• pump/pipe leaks
• trench leaks and spills

Strontium and Tritium detected in springs along Columbia River boundary

with the 100-N unit and in the river channel

Geology (figure 3)

• one deep well in the upper most aquifer for site characterization (figure 4)
• cable tool drilled due to gravel, cobbles and boulders
• residuals easily controlled
• sampled with spilt spoon samples and core barrel
• samples @ 1.5 m intervals and lithologic changes
• well completed in upper 3 m of confined/semi-confined aquifer

Structure

Yakima fold belt

site in the Pasco Basin, a syncline in the fold belt

Stratigraphy (figures 3, 5, and 6)

1- Local surficial Holocene eolian deposits

2- Hanford formation: Pleistocene catastrophic flood deposits, <23 Ma

3- Ringold Formation: Late Miocene to mid Pliocene , <8.5 to >3.5 Ma

4- Columbia River Basalts: Miocene, 17 to 6.5 Ma

Hydrogeology (figure 6)

• vadose zone 20 to 23 m thick
• vadose is highly permeable cobbles, gravel and sand
• includes the top few feet of the Ringold
• occasional perched groundwater over silty sand and gravel lenses

Upper most aquifer in Ringold (figures 6 and 7)

• 12 to 15 m thick
• base of aquifer believed to laterally continuous paleosols and overbank deposits
• T = 1000 to 6000 ft²/day
• K_h = 0.02 to 0.11 cm/s (50 to 300 ft./day)
• K_v = 3.5 x 10^-5 to 0.02 cm/s (0.1 to 70 ft./day)... lab data from split spoon sample
• S_Y = 0.1 to 0.3
• water flows north and east @ Hanford
• discharges into Columbia River
• water in 100-N area flows north and northwest
• in the 100-B area Columbia River recharges aquifer

At high river stage water flows into aq. from river

Seasonal river stages affect aq. up to 300 m inland

Daily variations affect ground-water up to 230 m inland

Ground-water levels in 100-N area vary doe to artificial recharge from liquid waste disposal

-affect ground-water flow directions

-leads to ground-water mounds

Contaminants

Arsenic, cadmium, chromium VI, fluoride, manganese, tritium, strontium 90

Highest concentrations are the radioactive tritium and strontium 90 (others are at

minor levels)

Strontium 90 (figures 8 and 9)

• found in unconfined aquifer
• not found deeper than top of aquifer
• sorbs onto soil impeding downward movement
• max. conc. = 6,160 pCi/L

Tritium (figures 10 and 11)

• doesn’t sorb in soil
• moves unimpeded with ground-water
• MCL = 20,000 pCi/L; max. conc. 90,400 pCi/L

Nitrate (figure 12)

Preliminary corrective Action Technology

treatment options

-large scale movement of contaminated material coupled with soil washing

-waste containment

• capping with suitable cover
• horizontal grout barrier pressure injected into closely spaced holes
• vertical grout barriers injected into a regular pattern of drilled holes

-waste treatment

• physical
• in situ vitrification: placement of electrodes in the soil (soil graphite mix to

enhance conductivity

• immobilizes contaminants (heavy metals and radionuclides)
• chemical
• stabilization/solidification
• uses pozzolonis and polymers; chemically react with or encapsulate heavy metals

Figure 1. Hanford Site Area Designations.

Figure 2. Map of 100-N area at Hanford.

Figure 3. Conceptual Geologic and Hydrogeologic Column.

Figure 4. Location of Monitoring Wells and Geologic Borings in the 100-N Area.

Figure 5. Location of Cross Sections A-A’, B-B’, and C-C’.

Figure 6. Cross Section A-A’.

Figure 7. Water Levels at the 100-N Area on June 24, 1988.

Figure 8. Strontium-90 activity in 100-N area ground water during February, 1990.

Figure 9. Strontium-90 concentrations in ground water in February-March, 1993.

Figure 10. Tritium activity in 100-N area ground water during February, 1990.

Figure 11. Tritium concentrations in ground water in February-March, 1993.

Figure 12. Nitrate concentrations in ground water in February-March, 1993.

ENV 302 - Lectures