7.  Agencies Studying Water Chemistry Now, Part B

7.3  The US DOE Yucca Mountain Project

The US DOE Yucca Mountain Project has been studying the regional hydrology and geochemistry around Yucca Mountain for over 25 years.  Until the 1990’s, very slow water penetration through Yucca Mountain was assumed, just as with the NTS.  In fact the DOE’s Environmental Assessment in 1986 estimated that groundwater travel through Yucca Mountain from the repository to the accessible environment would take an average of about 40,000 years, with a maximum of 80,235 and minimum of 9,485 years.  The travel time through rock unsaturated with water (i.e. above the water table) accounts for all but about 140 years.[1] 

In the early 1990s, evidence[2] was uncovered that indicated a much faster water transport mechanism than previously assumed by the DOE.[3]  As a result of this evidence, the DOE modified its water transit model considerably, from an unsaturated zone travel time minimum of about 9,000 years, to figures ranging from tens to about 1,000 years.[4]  More current estimates of water travel times show that approximately 20% of unretarded technicium-99[5] would take an average of about 300 years (with a range of 20 to 40,000) to reach the water table from the repository horizon.[6]  The wide range of times is an indication of the DOE’s expected duel mechanisms for water transport: the historically assumed slow diffusion through the rock strata, and the more recently realized fast fracture flow pathways. 

The wide range of water travel times also underscores uncertainties inherent in knowledge of the water movement and expected arrival of contamination in Amargosa Valley.  For example, if there is a catastrophic failure of the disposal casks, radionuclides could arrive within 550 years by the DOE’s own estimates.[7]  Subsequent isotopic analysis for chlorine-36 have not been able to fully duplicate the 1995 results, and the question of whether the chlorine-36 in Yucca Mountain is from atmospheric nuclear weapons tests is not sufficiently resolved, so the DOE continues to assume that the fast pathways exist.[8] 

Currently, there is no radionuclide contamination at Yucca Mountain, and the focus of the work there has been to understand how radionuclides will migrate from the proposed repository to the accessible environment.  As can be seen in Figure 7.3, the DOE has drilled numerous boreholes in the immediate vicinity of Yucca Mountain for various purposes.  Most are not dedicated to water characterization; although geochemistry characteristics are well known.[9]

7.4  Nye County Early Warning Drilling Program (EWDP)

Nye County, as part of its Independent Scientific Investigations Program (ISIP) has an ongoing Early Warning Drilling Program (EWDP) conducting routine water baseline analysis.  The objectives of the ISIP are: 

1. collection of baseline data on a comprehensive suite of chemical parameters,
2. the identification of potential flow paths from Yucca Mountain to potential receptors in Amargosa Valley, and
3. the development of a defensible groundwater chemistry monitoring network, downgradient of Yucca Mountain suitable for long-term performance confirmation monitoring.[10] 

Currently, the EWDP analyzes the following parameters:

·         in the field:

§         pH, electrical conductivity, temperature,

§         turbidity, dissolved oxygen, and oxidation-reduction potential;

·         by testing laboratories:

§         major anions and cations, total dissolved solids, and field indicator parameters

§         approximately 20 trace elements (See Figure 7.4.2)

§         nutrients, including total phosphate, nitrite plus nitrate, and ammonium

§         stable isotope analyses of nitrogen and oxygen in  nitrate, oxygen and hydrogen in water, and carbon in stable inorganic matter

§         tritium and radiocarbon

§         gross alpha and beta radiation

Previous studies dated from 1999 have also analyzed chlorine-36, stable isotopes of oxygen and sulfur in sulfate, and isotopes of uranium, strontium, and lead.  Discussions with Nye County staff revealed that these radioisotopes were dropped from analysis largely from cost considerations, and found unnecessary for the County’s interests.[11] 

The strategy of Nye County, as understood by HþME, is to establish a baseline, and investigate anomalies that arise; such as, elevated alpha or beta radiation counts.  At that point, further and more detailed testing of water would be pursued to determine if there is a need to take action to protect residents from contamination.  Inspection of the well monitoring locations (see Figure 7.4.1) and general underground water flow patterns (Figure 4.1.1), shows a clear line of intersection of downgradient water from Yucca Mountain, but not of water moving from some of the underground testing areas such as Pahute Mesa.  If the analysis contained in the Citizen Alert report is correct, then radioactive contamination could slip past both the NTS and Nye County early warning monitoring wells, leaving a gap in the early warning system.

7.5  Summary of the Sampling Programs

Overall, despite the extensive resources that have been dedicated to studying and attempting to understand the movement and contamination of groundwater in the region including and surrounding the NTS and Yucca Mountain, as well as detection of radioactive isotopes potentially migrating off the NTS, significant uncertainties still exist. 

Figure 7.4.1.  Existing and proposed EWDP well locations.

(Source:  Nye County Dept. of Natural Resources and Federal Facilities, Nuclear Waste Repository Project Office, “Final Nye County Proposal for Additional Independent Scientific Investigations Program Activities for fiscal Years 2002-2006,” February 2002.)

Figure 7.4.2  Nye County EWDP Water Chemistry Analysis

Source: Nye County Nuclear Waste Repository Project Report, Workplan 11,

“Groundwater Chemistry Sampling and Analysis”, Rev. 09/28/03 WP4