(Figures 1-3, modified for size, are above. #1- uppermost, #2 - middle, #3 - bottom. They are from the USGS, Circular 1245. Links for Figures 4-5 are below the text document and are from the Piedmont Environmental Council.)Uranium Mining and Extreme Flooding in Virginia
The Need for a Sediment Transport/Water Quality Model and PMP Failure Analysis
by
Thomas M. Leahy
July 1, 2009
Extreme Flooding in VirginiaFigure 1 is a map of the United States showing the location of approximately 23,000 past and present USGS stream flow gauges. Figure 2 is the same map showing only those stream flow gauges (about 3,000) that have recorded extreme flooding events. The screening criteria that the USGS used to define an extreme flooding event was 100 to 300 cubic feet per second (cfs) per square mile for small water sheds (less than 1000 square miles) and 50 to 100 cfs per square mile for large watersheds (1,000 squaremiles and greater). The average stream flow for watersheds in Virginia and adjacent states is about 1.0 cfs per square mile. Therefore, Figure 2 shows the locations where stream flows have been recorded that were at least 50 to 300 times greater than the average normalized stream flow in Virginia.
For the contiguous 48‐states, Figure 2 shows that other than the west coast, extreme flooding occurs mostly in the southeast quadrant (south of the 40th parallel and east of the 100th meridian). Moisture for the precipitation that fuels these events is provided by the warm waters of the Gulf of Mexico and the Atlantic Ocean. These floods can be represented by three primary clusters.
The first is the central mid‐west and lower Mississippi Valley which includes eastern Kansas and Oklahoma, Missouri, Arkansas, Louisiana, Mississippi, and western Tennessee and Alabama. These regions have been nicknamed Tornado and Dixie Alleys due to the frequency and magnitude of tornados that result from intense thunderstorms known as super-cells, formed by the collision of cool dry Canadian air with warm humid Gulf of Mexico air.
The other two clusters of extreme flooding events are southern Texas and the eastern ridge of the Appalachian/Blue Ridge Mountain chain from Georgia to Maine, including a distinct concentration in Virginia. The USGS determined that these regions are prone to extreme flooding because topography provided by mountain ranges and escarpments can rapidly lift moisture laden air into the cooler upper atmosphere:
“Within the eastern conterminous United States, the pattern of large flows closely corresponds to the proximity of subtropical moisture derived from the Gulf of Mexico and the Atlantic Ocean. Finer‐scale patterns within this region, however, are clearly linked to topography. Orographic lifting of moisture from the Gulf of Mexico triggers convective instability and has caused concentrations of large floods at topographic features such as the Balcones Escarpment in south central Texas, the Ozark Mountains of western Missouri, and along the eastern edge of the Appalachians on the eastern seaboard. The important role of topographic relief is also illustrated by the lack of exceptional discharges in Florida, and along the coastal plain of the southern and eastern tier States. Despite being closest to the moisture sources and subject to frequent landings of major hurricanes, these relatively flat areas have few stations that have recorded flows exceeding the large‐flow criteria . . .”
--Large Floods in the United States: Where They Happen and Why, USGS Circular 1245, 2003, p.9. Emphasis added.
Figure 2 also shows that there are very few extreme flow events in the western states or in the northern mid‐west. Where they do occur, they are mostly confined to very small watersheds. This is the result of a lack of an available moisture source and/or cooler air temperatures, both of which limit the moisture content in the air.
Probable Maximum Precipitation [PMP] in VirginiaThe screening criteria for identifying the extreme flows depicted in Figure 2 ranged from 50 to 300 cfs per square mile. However, depending upon duration, a Probable Maximum Precipitation (PMP) event in Virginia and surrounding areas will deluge an area with 1,000 to 7,000 cfs per square mile.
Figure 3 is the same as Figure 2, except that the locations of storms with precipitation approaching the PMP have been shown. Figure 3 also includes the location of the proposed Coles Hill uranium mine, in Pittsylvania County, VA. In the eastern US, the locations of the near‐PMP events mimic the location of the extreme flooding events identified by the USGS: Tornado and Dixie Alleys, southern Texas, and the eastern ridge of the Appalachian and Blue Ridge Mountains.
In fact, Figure 3 shows a string of at least 8 near‐PMP storms east of the Blue Ridge Mountains from North Carolina to Maine. These events occurred along a corridor that cuts a path right through the uranium ore deposits in Pittsylvania County and the ore deposits in four counties west of Fredericksburg.
Two of the storms occurred in Virginia ‐ one in 1969 in Nelson County about 60 miles from the Pittsylvania uranium deposits (Figure 4), and the other in 1995 in Madison County, one of the four counties west of Fredericksburg where uranium ore deposits have been identified (Figure 5).
The Need for a Sediment Transport and Water Quality Model and Failure AnalysisAs a consequence of the topographic relief provided by the Blue Ridge Mountains and the subtropical moisture provided by the Gulf of Mexico and the Atlantic Ocean, the Piedmont region in Virginia just east of the Blue Ridge Mountains is prone to extreme flooding and has a much higher likelihood of experiencing catastrophic precipitation events than many other areas in the country. However, this is also the same location of the uranium deposits in Pittsylvania County and west of Fredericksburg.
Stakeholders concerned about the potential impacts of uranium mining have asked to be shown locations and examples of uranium mines and mill tailing cells that occur in areas that have similar climate, geography, and population density as Virginia. This may be problematic ‐ there may not be any other locations where uranium mines and milling operations, an unlimited source of hot humid air, topographic/orographic lifting potential, and high population density all intersect.
Even if a uranium mine and milling operation located in a relatively wet climate (i.e., 45‐inches per year of precipitation) could be identified, that location might not be prone to extreme precipitation events due to its particular meteorological and physiographic characteristics. It is even less likely that a uranium mine or milling operation will be indentified that has ever experienced a PMP event similar to the two that have occurred in Virginia (about thirty inches of rain in six‐hours).
Therefore, it is important to assess what the potential consequences would be if a storm similar to the Nelson County or Madison County storms were to strike a mining and milling operation and transport a significant load of mill tailings downstream to the receiving rivers and reservoirs. This will require an engineering study that includes a sediment transport and water quality model.
The model must be able to accept as input, various precipitation events ranging from severe hurricanes and nor’easters that strike Virginia relatively frequently to a probable maximum precipitation (PMP) event. The modeling of the fragmentation of a mill tailing dewatering facility, storage area, or confining cell will be a difficult task, subject to much debate. So, initially, the model should be designed to accept as input, assumptions of various amounts of mill tailings that might be released as the result of a catastrophic precipitation or flood event that would strike the proposed Cole’s Hill mining operation.
The model would then predict the downstream transport and fate of the mill tailings in terms of location and quantity beginning with the Banister River, through Kerr Reservoir, through Lake Gaston and Roanoke Rapids, and downstream through the Roanoke River and flood plains, and into Albemarle Sound.
After the model has determined the location and quantity of the transported mill tailings, a water quality component will predict the increased radioactivity and other contamination that will result in the downstream waters for any given amount of mill tailings released. The water quality parameters that will be considered are gross alpha, gross beta, radium isotopes, radon, and uranium. Other toxic substances typically associated with mill tailings will also be considered.
The model will also include an assessment of how long the increased radioactivity or other contamination would persist given normal weather and flow patterns.
Figure 4:
http://www.pecva.org/anx/index.cfm/1,557,2133,0,html/Properties-with-Former-Uranium-Mining-Leases-and-Downstream-Water-Supplies-Southside-RegionFigure 5:
http://www.pecva.org/anx/ass/library/19/downstreamflow_counties_wtr.pdf
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