City of Virginia Beach Uranium Mining Impact Study Energy Advisory - - PowerPoint PPT Presentation

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City of Virginia Beach Uranium Mining Impact Study Energy Advisory Committee September 29, 2011 Uranium Mill Tailings Original Concept 119 million # of uranium (0.06% ore) 100 million pounds of yellow cake Open-Pit, 76 MCY of

SLIDE 1

City of Virginia Beach Uranium Mining Impact Study Energy Advisory Committee September 29, 2011

SLIDE 2

Uranium Mill Tailings

 Original Concept –119 million # of uranium (0.06% ore)

100 million pounds of yellow cake
Open-Pit, 76 MCY of tailings

 Dec 2010 plan – 60 million # of uranium (0.11% ore)

50 million pounds of yellow cake
Deep Shaft, 20 MCY of tailings
About 1/3 returned to mine shafts, 2/3 stored in 8

surface tailings impoundments

Surface tailings impoundments will be 40 acres

(maximum) and store about 1.5 – 2.0 MCY, each

 Mount Trashmore in Virginia Beach is 20 acres and 1.3

million cubic yards

SLIDE 3

Project Description

Coles Hill

SLIDE 4

SLIDE 5

Near PMP Storms in Virginia

 Examples:

Nelson County –

August 1969

 27 – 31 inches in

8-hours (Hurricane Camille)

Madison County –

June 1995

 30 inches in 14

hours

SLIDE 6

Virginia Beach Disaster Simulation Study

 Model and estimate the water quality impacts

from a storm-based breach of a uranium mill tailings confinement structure, which results in a large release of mill tailings downstream to the Banister or Roanoke Rivers

 Provide the results to the National Academies of

Sciences Committee on Uranium Mining for consideration as part of its study due Dec 2011

SLIDE 7

Study Qualifiers

 The study simulated a rare event that

regulations are supposed to prevent

 Conservative Worst Case Scenario

based on above ground impoundments

 The model does not address the issue

f whether there will be a catastrophe

– it only simulates the outcome if one did occur

SLIDE 8

Aftermath of a Tailings Release

 Tailings separate into particulate (80-90%) and

dissolved (10-20%) components

 Particulates tend to remain above Kerr Dam –

in the reservoirs, river beds and flood plains

 Dissolved contaminants tend to move

downstream with the water and flow into and then out of Kerr Reservoir, into and then out of Lake Gaston, thru Roanoke Rapids Reservoir, and ultimately downstream

SLIDE 9

Impacts From a Tailings Release

 Radioactivity in the water is initially very high,

but declines as the particulates settle and the dissolved contaminants flow downstream

 Radioactivity of the sediments remains high on

a long-term basis

 Subsequent high flows re-suspend some settled

particulates and move them incrementally downstream – much smaller effect

 Most particulates will remain in the flood plain,

river beds, or reservoirs upstream of Kerr Dam

SLIDE 10

Fate of Radiological Contaminants in the System after One Year

Banister River, Various Modeling Scenarios Roanoke River, Various Modeling Scenarios

Percent of Radioactivity Leaving the System (Flowing Downstream as a Dissolved Contaminant)

5-11% 11-19%

Percent of Radioactivity Remaining in the Water Column

0-2% 0-2%

Percent of Radioactivity Remaining in the System (In the Flood Plain, River Bed or Kerr Reservoir)

89-93% 78-87%

SLIDE 11

5 10 15 20 25 30 35 40 45 50 50 100 150 200 250 300 350 400

Radioactivity Concentration (pCi/L) Time (Day) Radioactivity Concentration in the Water Column from Radium-226 and Thorium-230 Banister + Dam 15m + CSW3 50% + HYD2 1% + GSC1 + RAD2

Node 286 - At Mouth of Kerr Reservoir Node 397 - At Kerr Dam MCL for Combined Radium-226 and 228 10 20 30 40 50 60 70 80 90 100 50 100 150 200 250 300 350 400

Radioactivity Concentration (pCi/L) Time (Day) Radioactivity Concentration in the Water Column from Radium-226 and Thorium-230 Roanoke + Dam 15m + CSW3 50% + HYD2 1% + GSC1 + RAD2

Node 311 - At Mouth of Kerr Reservoir Node 420 - At Kerr Dam MCL for Combined Radium-226 and 228

SLIDE 12

Model Limitations – Flushing Time

 Kerr Reservoir was modeled as a large, one-

dimensional channel – a giant river

 Reasonable during flood periods. During normal

and drought periods, Kerr Reservoir will act more like a lake

 Dissolved contaminants will experience mixing,

dispersion, stagnation. May add to flushing time

 Lake Gaston has a volume equal to about half of

Kerr Reservoir which will add to flushing time

SLIDE 13

Flushing Time in Kerr and Gaston

 Retention time for Kerr and Gaston combined:

 About one month during severe flooding  About six months during normal flows  About one year during droughts

 It can take one or two retention times to

completely flush dissolved/suspended contaminants from a large water body

 Depending upon whether it is wet or dry

following a contamination event, it could take two months or two years to flush dissolved and suspended contaminants from both reservoirs

SLIDE 14

Conclusions – Phase 1

 If there is a storm-based release of tailings, the

particulates will settle in the river and reservoir beds, dissolved contaminants will move downstream

 Radiation in the water column rises significantly

then will subside

 River and reservoir beds are significant long-term

trap for particulates which are the bulk of tailings

 Impacts upstream of Kerr Dam are greater and

potentially longer lasting than downstream

SLIDE 15

Impact Study – Phase 2

 2D model for Kerr and Gaston  1996 (Hurricane Fran): 100-year storm in

Banister River, 30-50 year storm in remainder

f Basin, followed by 2002 drought year

 Second lowest impoundment level (15 M)  More precise data on tailings properties

(radiation, grain size distribution, partition coefficients)

 Study is behind schedule – Current target is

for end of the year

SLIDE 16

Kerr Reservoir 1D Channel Model

SLIDE 17

Kerr Reservoir: 2D Model Grid

SLIDE 18

Lake Gaston: 2D Model Grid

59 blocks

SLIDE 19