All research projects supported through the WRRI culminate in a final report which is published as part of the Institute’s technical completion report series. The reports are disseminated to public libraries throughout the state of New Mexico and are available at no charge, while supplies last, from the WRRI.

The WRRI homepage (http://wrri.nmsu.edu) contains a list of all published completion reports along with each report’s abstract. In the near future, the Institute hopes to provide, via its homepage, the full text of each new report.

Four completion reports were published recently. For copies of the reports, contact the WRRI at 646-1813.

• Spatial and Temporal Distribution of Mercury in Caballo and Elephant Butte Reservoirs, Sierra County, New Mexico by Colleen Caldwell and Christopher Canavan, New Mexico State University (Report No. 306): This study looked at the concentrations of inorganic and organic aqueous mercury in Caballo and Elephant Butte reservoirs. The two-year study (1995-1997) was conducted to characterize the combined effect of selected physiochemical characteristics of water (pH, alkalinity, hardness, dissolved oxygen, conductivity, and temperature) and reservoir volume on the presence and availability of total mercury (THg) and monomethylmercury (MMHg).The researchers found elevated concentrations of both organic and inorganic forms of mercury in the upstream portion of Caballo Reservoir, and this finding lead to a continued investigation of Elephant Butte Reservoir and Rio Grande water coming into Caballo Reservoir. High levels of biologically available methylmercury in the upper section of Caballo Reservoir are attributed to the discharge of anoxic Elephant Butte waters to the Rio Grande.The study determined a potential source of mercury in the Rio Grande basin to be atmospheric deposition. Further study is needed to describe Hg concentrations in runoff from the Black Range watershed entering the Rio Grande and Caballo Reservoir and to determine the influence of Elephant Butte Reservoir on the Hg cycle in Caballo Reservoir.
• Arsenic Remediation in Drinking Waters Using Ferrate and Ferrous Ions by Christopher Vogels and Michael Johnson, New Mexico State University (Report No. 307): As groundwaters used for municipal water supplies become increasingly contaminated with arsenic and as the U.S. Environmental Protection Agency (EPA) acceptable threshold limits decrease (currently at 50 parts per billion but may decrease to 1 ppb), new methods for inexpensive arsenic removal are needed.Dr. Michael Johnson and his graduate assistants have developed new chemical procedures using ferrate [iron(VI)] to remove extremely low concentrations of arsenic and arsenic-containing compounds from water. This report describes the method used by the researchers to determine the ability of ferrate to remediate arsenic. The method provides an inexpensive approach to meet new drinking water regulations where acceptable levels of arsenic may reach as low as 2 ppb.
• Determination of Agricultural Chemical Impacts on Shallow Groundwater Quality in the Rio Grande Valley: Las Nutrias Groundwater Project by Robert Bowman and Jan Hendrickx, New Mexico Tech (Report No. 308): A comprehensive assessment was made of water and chemical relationships at a commercial farm in the central Rio Grande Valley during 1994-1996. The Las Nutrias Groundwater Project included a highly instrumented 15-acre tile-drained field used to collect areally averaged data on recharge rates and nitrate and pesticide leaching to shallow groundwater.Based on the information collected during the Las Nutrias Groundwater Project, typical agricultural cropping, water, nutrient, and pesticide management practices do not appear to pose a broad threat to shallow groundwater in the Rio Grande Valley. Due to large dilution by ambient groundwater (whose source includes mountain-front recharge, infiltration losses from the Rio Grande, and recharge from other agricultural fields), temporary spikes in field drainage chemical concentrations are rapidly diluted below regulatory levels.
• Temporal Variability of Diffuse Groundwater Recharge in New Mexico by Anne Kearns and Jan Hendrickx, New Mexico Tech (Report No. 309): The ability to make accurate predictions of groundwater recharge from precipitation may help us make more responsible decisions concerning the allocation of declining groundwater resources. This project’s objective was to verify the possibility of significant quantities of diffuse precipitation recharge.One hundred years of actual precipitation data collected from Las Cruces were used as an input to a one-dimensional numerical model to explore this concept. Four soil textures were simulated in soil profiles, some barren and some vegetated. Climate conditions supporting the initiation of recharge include both single, very large rainfall events and gradual soil moisture content increases. Recharge periods ended if two consecutive years had below average rainfall. El Nino conditions did not correlate well with the five recharge periods studied, but Eastern Pacific cyclones were responsible for the two single, largest rainfall events, both of which initiated major recharge periods and may be responsible for the continuance of other periods as well.