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UZIG-News - December 1996 - Issue 6

edited by John R. Nimmo (jrnimmo)

Newsletter of the Unsaturated Zone Interest Group (UZIG) of the US Geological Survey. The purpose of this newsletter is to enhance communication within the UZIG. It should not be quoted or cited as a publication. Send desired changes in the mailing list to jrnimmo.

Please contact authors or other people mentioned in UZIG-News with any questions, comments, or suggestions. For contact from outside the system, append @usgs.gov to the internal USGS email addresses given.

Contents:

Line 35    News and Information

Line 75    Summary of the Unsaturated-Zone Interest Group Meeting,
           September 24-26, 1996, Las Vegas, NV, by Rick Healy
           (rwhealy)

Line 152   Recent Activities in the Office of Ground Water, by Bill 
           Alley (walley)

Line 224   CFC Degradation near the Water Table, Mirror Lake, New
	   Hampshire, by Dan Goode (djgoode)

News and Information

++ VS2DT Workshop ++

A 3-day workshop, led by Rick Healy, on use of the Survey's unsaturated flow and transport model VS2DT is being offered January 7-9, 1997 in Menlo Park and February 11-13 in Denver. The workshop will cover the underlying theory on which the model is based, and all aspects of model use and application. The number of attendees will be limited to about eight. The Menlo workshop is filled, but there are a couple of slots open for the one in Denver. If there is additional interest another workshop may be arranged in Atlanta or Reston. If you wish to attend the workshop, please go through appropriate channels to obtain approval, and also contact Rick (rwhealy).

++ Hydrology Days ++

The 17th Annual Hydrology Days will be held April 15-18 at Colorado State University, Fort Collins. In addition to talks on a wide range of hydrologic topics, there will be a special session "Hydrology of Watersheds in Arid or Semi-Arid Regions." The conference is dedicated to Herman Bouwer, Jan van Schilfgaarde, Donn DeCoursey, and Glendon Gee. Bouwer and Gee will give talks in the arid-region special session, tentatively titled, respectively, "Role of Recharge and Reuse in Integrated Water Management" and "Aquifer Recharge Estimation in Deserts." There will be other invited talks, including some from the USGS. The deadline for submission of an abstract is January 24, 1997. For abstract guidelines contact Hubert Morel-Seytoux (morelsey). For a full paper in the Proceedings (optional, not required) the deadline is March 7. Contact Hubert for guidelines and blank mats. Additional information is available from the AGU web site: http://www.agu.org/meetings/hd97top.html or the Hydrology section site: http://www.esd.ornl.gov/societies/AGU/Hydrology.

Summary of the Unsaturated-Zone Interest Group Meeting, September 24-26, 1996, Las Vegas, NV

by Rick Healy (rwhealy)

Approximately 60 people attended the UZIG meeting in Las Vegas. There was great interest in the talks that covered a wide range of topics on the first two days. A number of talks were related to waste-disposal issues, at Yucca Mountain, Hanford, Beatty, the Idaho National Engineering Laboratory, and elsewhere. Others addressed such topics as unsaturated-saturated zone interactions, and instrumentation for measuring gas flux and matric potential. The field trip on the 26th was a great opportunity to enter the Yucca Mountain Tunnel to see firsthand the deep unsaturated-zone rocks of the proposed waste repository, and also to see the arid-region radioactive waste disposal site at Beatty, NV.

Discussions were lively and productive. John Nimmo (jrnimmo) talked about the history of the unsaturated-zone interest group. John agreed to continue his work as editor of the UZ newsletter and solicited more contributions. John also raised the idea of the UZIG setting up its own web page which would have advantages for accessibility, archiving, and presentation of graphics. Anyone with ideas or suggestions should contact John by email or phone (415-329-4537).

Brian Andraski (andraski) summarized responses to UZIG-News queries about the possibility of UZIG members collaborating on a handbook devoted to unsaturated-zone field methods. Several opinions were voiced during the ensuing discussion; many highlighted the need to maintain a focused approach to meet the needs of a specific target audience and to ensure timely completion. Responses to the UZIG-News queries indicated the need for a unified handbook, in the form of a Techniques of Water Resources Investigations (TWRI) report. This would serve as a reference and guide for District projects that necessarily require proven methods and quick answers because of their typically short duration (<= 3 years). The next steps in development of such a handbook include identifying additional contributors and developing a miniproposal for headquarters review. Please follow up with Brian regarding any additional input by email or phone (702-887-7636).

Bill Herkelrath (wnherkel) presented some work that he and Terry O'Neal have done on developing a graphical input system for computer program VS2DT.

Herb Buxton (hbuxton) gave a rundown on the Toxics Hydrology Program, including descriptions of new programs such as the Abandoned Mine Lands Initiative, and new emphasis on toxic substances such as mercury, MTBE (a gasoline derivative), and pesticides used in growing cotton. Herb also led a separate discussion of the possibility of suppporting an Amargosa Desert research site (including the Beatty waste-disposal area) through the Toxics Program.

Ed Weeks (epweeks) presented a summary of unsaturated-zone work that is being conducted through the Thrust Programs. It appears that these programs are not funding nearly as much UZ work as in the past. It was noted that there is very little such work being performed through the NAWQA program. On the other hand there is still a growing number of District projects that are involved with the unsaturated zone. Funding for these projects comes from various sources including coop funds, OFA, and Toxics.

The date and location of the next UZIG meeting was tossed around. Most people felt that 2 years from now would be a good target to shoot for. Possible locations include Albuquerque NM, Menlo Park CA, and Ithaca NY.

All of the speakers deserve thanks for their excellent presentations. Special thanks to Alan Flint for making all the arrangements for the meeting and for the trip to Yucca Mountain. Thanks also to Brian Andraski and Dave Prudic for conducting the tour of the Beatty disposal site.

 

Recent Activities in the Office of Ground Water

by Bill Alley (walley)

Several activities are underway in the Office of Ground Water that should be of interest to the Unsaturated Zone Interest Group. Two that I will note here are efforts to develop a strategic plan for ground-water modeling in USGS, and restructuring of the Hydrogeology of Critical Aquifers Program. The new Office of Ground Water home page can now be accessed through the WRD Internal home page at http://h2o.usgs.gov/usgs

1. Ground-Water Modeling

The Office of Ground Water is in the process of developing a strategic plan to guide our future efforts in development of ground-water models and related programs. We are currently undertaking two efforts to help in this regard. First, we have developed a questionnaire which is being sent to NRP researchers involved with modeling and to the Regional Ground-Water Specialists. The Regional Specialists have been requested to send it to District Ground-Water Specialists and key District scientists and managers involved in ground-water modeling projects. If you have not received a copy of the questionnaire and are interested in participating, please request a copy from Arlen Harbaugh (harbaugh). Responses are due back to OGW by January 1, 1997.

Secondly, a workshop to assess the status and future directions of ground-water modeling in USGS is being organized. Workshop organizers are Arlen Harbaugh, Dave Pollock, Stan Leake, Paul Hsieh, Dave Parkhurst, Ward Sanford, Rick Healy, Terrie Lee, Mary Hill, and Wes Danskin. The workshop is scheduled for March 18-20, 1997, in Denver. Attendance at the workshop will be limited to about 50 people to ensure an environment conducive to dialogue. Arlen Harbaugh can provide more information.

2. Ground-Water Resources Assessment Program

Quantitative assessments of 25 major regional aquifers were produced by the Regional Aquifer-System Analysis (RASA) Program from 1978-1995 and this work has been continued through the Hydrogeology of Critical Aquifers Program in FY 1996 and 1997. Current plans are to restructure the Hydrogeology of Critical Aquifers Program to develop an adaptive program oriented to providing an ongoing assessment of the Nation's ground-water resources.

The program, renamed the Ground-Water Resources Assessment Program, would include development of a National Hydrogeologic Framework and Database, Regional Assessment, and Research and Methods Development. The National Hydrogeologic Framework and Database would be a digital spatial database that contains up-to-date information on aquifer properties, water levels, and geochemical characteristics for major aquifer systems of the United States. It would build upon the National Ground Water Atlas. The Regional Assessment component of the program would address major issues on a rotating basis in different regions of the country as priorities evolve. Example issues include recharge, interactions of surface water with ground water, saltwater intrusion, subsidence, areas of major water-level decline, and studies of specific settings such as karst or fractured rock. The Research and Methods Development component would continue similar to that under the RASA program. The intent of the new structure is to provide a flexible framework focused on ground-water resources that could be added to over time. We are taking steps to reorient the Hydrogeology of Critical Aquifers Program in this direction in FY 1998 and working on this concept as a budget thrust for FY 1999 or future years.

 

CFC Degradation near the Water Table, Mirror Lake, New Hampshire

by Dan Goode (djgoode)

The Mirror Lake fractured rock research site is adjacent to the Hubbard Brook Experimental Forest, where the Northeast Research Station of the USDA/Forest Service and the Institute of Ecosystem Studies have coordinated long-term research on many aspects of forests. For example, the impact of acid rain on North American forests was first documented here. Tom Winter (tcwinter) and his colleagues have shown that ground water has an important role in determining the chemistry of Mirror Lake, and that a significant portion of lake outflow is through glacial sand deposits. Paul Hsieh (pahsieh) and Allen Shapiro (ashapiro) are leading multi-scale multi-disciplinary investigations of fluid flow and chemical transport in the fractured crystalline rock, with primary support from the Toxic Substances Hydrology Program and the National Research Program. Several widely-applicable field and interpretive methods have been developed for fractured rock studies, including tracer tests and geophysical methods.

Several environmental tracers derived from atmospheric sources are being used to estimate large-scale transport properties of the fractured rock as well as the overlying glacial deposits. Niel Plummer (nplummer) and Ed Busenberg (ebusenbe) have demonstrated the use of several different forms of ChloroFluoroCarbons (CFC-11, CFC-12, and CFC-113; also known as Freon-11, etc.) to date shallow ground waters. Atmospheric concentrations of these man-made volatile organic compounds have been steadily increasing for about 50 years. The concentrations of these slightly soluble gases in water are proportional to the atmospheric concentration. Hence, the CFC concentration in a ground water sample can be used to estimate the time at which that water was isolated from air. Unfortunately, ground-water ages in samples from isolated bedrock zones do not follow readily apparent spatial patterns at Mirror Lake, and there is some disagreement between ages determined from CFCs and tritium. This article describes preliminary results of a study of factors controlling CFCs in recharge at Mirror Lake.

CFC and dissolved oxygen (DO) concentrations in piezometers screened near the water table suggest that significant anaerobic degradation of CFCs is occurring either in the unsaturated zone above the water table, or in the shallow saturated zone. Anaerobic degradation of CFCs has been documented in laboratory studies and in other recent field studies. If organic carbon is available, and if DO levels are close to zero, then CFC-11 and CFC-113 are likely to be significantly degraded. CFC-12 also degrades but at a slower rate. At Mirror Lake, several samples with zero DO also have zero CFC-11 and CFC-113, and CFC-12 levels are about 1/3 of modern equilibrium concentrations. However, several samples with low DO, but not low enough to be biologically anaerobic, also have significantly reduced CFCs. Many of these samples fall on a linear mixing line for both CFCs and DO, suggesting that the samples are a mixture of two end members: (1) waters saturated with oxygen and containing CFCs in equilibrium with the modern atmosphere, and (2) zero-DO waters containing no CFC-11 or CFC-113, and containing about 1/3 of modern CFC-12. Other evidence of active anaerobic biodegradation includes wells with high methane and ample iron (Fe-II) and sulfate, and generally low DO. In samples from anaerobic drift piezometers, Don Vroblesky (vroblesk) has measured hydrogen gas concentrations consistent with methanogenesis or sulfate-reduction as the terminal electron-accepting process.

Unsaturated-zone conditions at Mirror Lake are being monitored to support future simulations of tracer transport. Gaseous diffusion in the air phase depends on air and water contents, and the CFC equilibrium concentration in water depends on temperature. Measurements include water content by time-domain reflectometry, temperature by thermocouple, and water pressure by tensiometers. Conditions last summer were relatively wet in June and July, and moisture contents remained high throughout the relatively thin (1-5 m) unsaturated zone. During several dry weeks in August, streamflow, ground-water levels, and moisture contents went down. Evapotranspiration caused diurnal fluctuations in the ground-water levels and water contents. Temperatures followed the expected conduction-controlled response to seasonal changes, except when heat was advected with infiltrating water during intense thunderstorms. Soil gas sampled at multiple depths and locations will be analyzed for CFCs. These data will be used in models of nonisothermal multi-phase transport; preliminary simulations show that CFC concentrations at a shallow water table may be elevated above those in equilibrium with the atmosphere at the mean annual temperature due to the nonlinear dependence of equilibrium concentration on temperature.

CFCs in ground water at Mirror Lake will apparently not be easily used to identify large-scale transport properties because the concentrations in at least some areas are significantly reduced by anaerobic biodegradation. Perhaps the relative degradability of CFC-12 can be used in conjunction with other tracers to estimate field biodegradation rates, although current evidence suggests that the biodegradation varies spatially and probably temporally. Thus it may not be easily quantified at the basin scale. Interested scientists are invited to visit the Mirror Lake site to learn more about this and other ongoing research. Collaborative research in fractured rock hydrology is particularly encouraged.


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Last modified: Mon Mar 1, 2013