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April 29, 2005
Tracking groundwater radiation unpredictableBEATTY, AMARGOSA VALLEY WATER SUPPLY A CONCERN
By PHILLIP GOMEZ From the point of view of hydro-geologists and computer programmers studying regional underground aquifer flows, it's reliable field data - or the lack thereof - that puts limits on making accurate predictions about radiated water showing up in the "capture zones" of private wells. "We believe that we don't have enough data to make computer models to predict movement (of underground water)," said Genne Nelson with the Community Advisory Board for the Nevada Test Site underground test area committee. The Nye County Federal Impacts Advisory Board met with the committee last week to get an update on its monitoring of groundwater on and near the Test Site. Making and interpreting computer models to predict the flow of underground water contaminated on the Test Site during 908 underground nuclear detonations, from 1951 to 1992, has been the abiding goal of the committee since its inception in 1989. The detonations took place in shafts and tunnels at depths ranging from 89 feet to 4,764 feet. One-third of the tests occurred near or below the water table, resulting in groundwater radiation contamination. The Community Advisory Board and Underground Testing Area Committee peer review concern is the potential for off-site migration of contaminated groundwater. The committee wants to have a strategy in place to give early warning and protect down-gradient communities like Beatty and Amargosa Valley, home to the largest dairy operation in the state; half of the milk purchased in Nevada comes from the Ponderosa Dairy in Amargosa. The Pahrump Valley is thought to be unaffected due to westerly gradient flows off the Spring Mountains and the blocking of southerly flows by the Nopah divide north of Pahrump. Additionally, the bi-entity committee wants to verify computer model predictions of the contaminant boundary for a period of 1,000 years around detonation points. There are probably as many factors involved in identifying all the possibilities in the movement of water through the earth, as there are abbreviations in the peer-review oversight and the federal alphabetic terminology describing regional geologic activity. Some 50-60 underground nuclear detonations occurred beneath or near the water table surface of Pahute Mesa in the northwest area of the Test Site, the area closest to human habitation. Radiation contaminants within the "glass melt" of a nuclear test cavity leach out slowly over time and are transported in groundwater through crevices by incompletely understood earth forces. The committee's strategy is to improve its capability to detect changes in groundwater brought on by those multifarious factors - water velocity, gradient slope, faulting, fractures and uplifted landforms, to name a few - early enough for corrective action to be taken. Therefore, groundwater flow paths and their velocities must be understood in scientific terms. That means validated, repeatable field data collected in the appropriate areas off the Nevada Test Site. The data only comes from test well drilling. Exploratory tests are now being conducted to sample the water in Pahute Mesa's volcanic rocks. Also important today is monitoring of transition zones where known contaminated water merges with the larger flow patterns in the region as theoretically established by computer modeling. This area is considered one of high probability for early detection and is the focus of increased study and drilling for data. Fully half of all new wells drilled in recent years have been off the former volcano of Pahute Mesa, according to Nelson. The committee's objective now is to mine more data in order "to reduce uncertainties in northwest Pahute Mesa," where the steepest slope - and hence the greatest velocities - for groundwater exists. To that end, "sentinel wells" will be drilled, beginning in 2009 at the soonest and pending approval by the state. Again, questions remain regarding the sentinels' ability to detect contaminant migration before it gets to somebody's downgradient well, the nearest receptors to the Test Site for water coming off Pahute Mesa. These "fast path" flows threaten the Oasis Valley and Beatty in particular - especially given the four-year time lag before the new wells are drilled and obtain data samples. By then, the contaminated water could be all the way to the aquifer discharge area of Badwater in Death Valley, marking perhaps an appropriate ending to the experiments. But it's hoped that computer predictions, based on past science and augmented by new scientific data from the new wells, will turn up evidence in time to intercept the contaminant plume of migration before it reaches private wells off the Test Site. In one recent test, at the TYBO Test Well, plutonium showed up in the water, having migrated from its earlier known location in the BENEM Test Well 0.8 mile to the north. Now the joint committee wants to drill another well south of TYBO; a second well is planned for a mid-way location between the two, and a third one for the bench up-gradient from the BENEM Well, to see if water there is being contaminated as well. The federal program is expected to extend to the year 2030 and cost an estimated $2.23 billion over its lifecycle. Remediation alternatives for corrective action from underground testing at the Test Site have ranged from pumping of the contaminated water to excavation of an open-pit mine. The latter, assuming its technical feasibility, would cost an estimated $7.3 billion. A 1997 estimate of the cost for a complete cleanup of the subterranean environment went as high as $7 trillion. But the federal government does not intend to clean up the contamination; it intends only for DOE to assume long-term stewardship and maintenance of the Nevada Test Site. That includes the modeling, testing and prediction activities of the joint committee in order to set boundaries and restrict access to known contaminated areas in perpetuity. The path forward now is to continue its task of making recommendations to stakeholders in Nye County and to the Department of Energy on the everlasting legacy of the nation's nuclear weapons' testing in Nevada. |
