Roger L. Jacobson

Stable isotopic study of precipitation and spring discharge in southern Nevada

Abstract Precipitation was collected in southern Nevada on a semi-regular monthly basis at 14 locations for 6 years for stable isotopic analysis. The total elevational range of the collection sites was 1270 m and the total geographic range was 65 km. The average yearly difference in δ 18 O of precipitation from all sites was smallest and amounted to only 2.3‰, whereas the average difference based on location (elevation) was only 3.7‰. The largest difference in δ 18 O was between enriched summer and depleted winter precipitation and amounted to more than 13‰. The precipitation record shows two time-based regimes. For the first 3 years of collection, the precipitation was highly variable with several large events and several dry periods. During the last 3 years of collection, the precipitation was much more even with no large events. However, there is no correlation between the variability of the amount of precipitation and the stable isotopic composition of precipitation. In addition, the δ 18 O composition and discharge of two springs, Whiterock Spring and Cane Spring, issuing from perched water tables, were monitored for 5 years on a similar basis as for the precipitation. During the first 2.5 years of collection, both volume of discharge and δ 18 O responded to large precipitation events. However, during the last 2.5 years of collection when precipitation moderated in amounts, but not in stable isotopic composition, the springs displayed not only less variation in discharge, but in stable isotopic composition as well. Summer precipitation may be involved in groundwater recharge, as during the first 3 years of collection, some of the events to which the springs responded were summer events. Moreover, the average δ 18 O of winter precipitation is less than that of the spring discharge, even when the water from large summer events is absent from the spring discharge.

Radionuclide migration using a travel time transport approach and its application in risk analysis

The travel time transport approach for radioactive elements undergoing sorption and decay is employed in assessing the potential health risk at possible locations of human receptors. The principal entity in approach presented is a travel time probability density function conditioned on the set of parameters used to describe different transport processes, like advection, dispersion, sorption, and decay. The importance of accounting for parameter uncertainty and possible correlation between them is described and demonstrated in the study of risk analysis at the Nevada Test Site (NTS), which is located in the southwestern part of the state of Nevada. Because of the lack of sorption, the migration of tritium is found to provide the largest health risk to the accessible environment. Inclusion of the sorption process indicates that the parameter uncertainty and especially negative correlation between the mean velocity and the sorption strength are important in evaluating the arrival time of radionuclides at the prespecified accessible environment. The results from the risk-based screening analysis suggest that tritium, which does not sorb and has a short effective half-life (both physical and biological), is responsible for about 90% of the total risk.

A stable isotope study of bank storage mechanisms in the Truckee river basin

Abstract River, ground water, and snow samples were collected in the Truckee river drainage basin in northern California and Nevada to determine the mechanisms of bank storage. Lake Tahoe, the source for the Truckee river, has a σD of −57 and σ 18 O of −5.5. These compositions are more enriched than the average local precipitation, calculated to be −117 in σD and −15.8 in σ 18 O , due to continued evaporation during the long residence time of the water in the lake. Thus, Lake Tahoe water can be easily recognized allowing for easy tracing as bank storage. An enrichment threshold value was developed to explain the stable isotopic ratios observed in the Truckee river. The σD value of −85 was determined as being the threshold value, below which evaporation can explain the isotopic composition observed in the Truckee river, and above which the presence of Lake Tahoe water is required. There does not appear to be a direct relationship between the σD value of the Truckee river and the discharge to the river from Lake Tahoe, at least in the upper reaches of the basin. The rise in σD of the river to a value similar to that of the lake appears to move progressively upstream and is thought to be related to the discharge of the bank-stored Lake Tahoe water.

Comparison of drilling and mining as methods for obtaining microbiological samples from the deep subsurface

Abstract Ashfall tuff samples for microbiological analysis were obtained by mining and drilling within a 400 m deep tunnel system at Rainier Mesa, Nevada Test Site. Comparison of microbiota revealed that bacteria recovered from the core samples were similar to those recovered from the mined samples in abundance, diversity, evenness of distribution, and the numbers of distinct colony types. Cluster analyses based on the characterization of one of each distinct bacterial type from cored and mined samples indicated morphological and physiological similarities between some of the microbiota that were recovered. Drilling fluid microbiota were more abundant, and were distinct from those recovered from cored or mined samples. Storage of both the mined and cored samples for 1 week at 4°C led to the recovery of increased numbers of culturable cells, but with decreased diversity. The presence of bromide tracer indicated penetration of drilling fluids into the cored rock samples, a problem not encountered with mining. However, abundance and diversity values, and isolate characterization indicate that valuable information can be obtained from cored rock samples.

Heterogeneity of deep subsurface microorganisms and correlations to hydrogeological and geochemical parameters

Nineteen samples were obtained from a 21‐m3 section of zeolitized volcanic ash‐fall tuff, 390 m below the surface of Rainier Mesa, Nevada. Rock mined aseptically from the walls of deep subsurface tunnels provided pristine samples for microbiological and geochemical analyses. Microbiological parameters measured on all samples included direct counts and the abundance, diversity, morphology, and metabolic traits of culturable organisms. Physical and chemical parameters measured included ionic and nutrient chemistries, mineralogy, porosity, moisture content, and permeability. The results indicate that the culturable microbiological community size and composition exhibit random spatial variability within the geologically/geochemically homogeneous rock section. The relative abundance of microorganisms testing positive for nitrate reductase demonstrated a spatial trend along the vertical and front‐to‐back axes of the rock section by gradient analysis. The porewater concentration of nitrate correlated with number...

Pilot study risk assessment for selected problems at three U.S. Department of Energy facilities

Abstract Objective and realistic human health risk assessments were performed for environmental problems at the Savannah River Site (SRS), the Fernald Environmental Management Project (FEMP), and the Nevada Test Site (NTS). At the SRS, cancer mortality risks were analyzed for projected public exposures to 3 H and 137 Cs released into the Savannah River. For annual human exposures to SRS tritium in Savannah River water, calculated incremental individual lifetime risks in two human receptor populations were small (8×10 −7 ; upper 95 percentile point of the distribution). The 95th percentile point of the distribution for incremental individual lifetime risks from one years exposure to 137 Cs is less than 10 −8 . No deaths are expected in either population as a result of exposures to tritium or cesium released to the Savannah River from the SRS. Routine releases of radon and radon progeny from the K-65 silos at FEMP resulted in individual lifetime risks greater than 1×10 −4 only for onsite workers and fenceline residents. Population risks were less than 1.0 for all identified receptor populations. Assessment of risks from exposure to uranium in ground water released by the FEMP predicted no toxic effects for human receptors. All estimated cancer risks were small. The largest predicted individual lifetime risk was for a well close to the facility (1.3×10 −5 ). For the various above-ground shot sites at the NTS, the highest predicted lifetime cancer risks are for a resident farmer, assuming a loss of institutional control, and exceed 1×10 −4 at the 95th cumulative percentile level. At 50 000 and 100 000 y in the future, the predicted cancer risks are all below 10 −6 . In the assessment of exposure to radionuclides in ground water at the NTS, for an individual onsite near the site boundary, the geometric mean of the maximum potential excess lifetime risk of cancer mortality for an individual is 7×10 −3 . For an individual using water offsite, the geometric mean of the maximum potential excess lifetime risk of cancer mortality is 7×10 −7 .

Empirically Driven Computer Simulations of Solar Thermal Systems for Space Heating and Domestic Hot Water

The Desert Research Institute (DRI) has developed a Renewable Energy Deployment and Display Facility (REDD) which utilizes solar and wind to create a net zero energy residence for research, education, and outreach. The facility is a demonstration of the integration of many renewable energy technologies into a residential setting such that technology developers can show proof-of-concept, students and trade workers can get hands-on experience, and public organizations can see renewable energy components implemented into a residential setting. A major technological aspect of the facility is the use of solar thermal energy to provide space heating, Domestic Hot Water (DHW), and solar cooling. Data are monitored from three separate solar thermal systems, each with their own hot water storage, to evaluate optimized utilization of solar thermal energy into residential applications.The three solar thermal systems differ in their working fluids. System 1 uses a conventional mixture of glycol and water in 200 ft2 of ground mounted collector area, System 2 uses DHW in 210 ft2 of roof mounted collector area, and System 3 uses air in a 578 ft2 collector built into the roof. Each system is configured to be used for space heating and DHW. Systems 1 and 2 are built into the HVAC system of the 1200 ft2 house, and System 3 is built into the HVAC system of the 600 ft2 detached workshop. Data collected from each system provide the basis for year-long energy and economic simulations using TRNSYS for comparison. The results from the simulations are used to demonstrate the effectiveness of site-built solar air collectors, which have the advantage of using conventional materials, and avoid the issues of liquid collectors associated with boiling and freezing. This paper describes the experimental setup of the solar thermal systems, how the data are used as inputs to the computer simulations, and the configuration of the computer simulations.The REDD Facility, as well as the use of TRNSYS will continue to be used by DRI researchers to investigate not only the most feasible integration of components for a solar thermal residential system, but also as a tool to properly size and implement solar thermal systems.Copyright

Enhancing Engine Operations in Off-Grid Renewable Energy Applications Through the Additional Use of Hydrogen

The current renewable energy transformation taking place around the world has led to drastic advances in technology that relates to the issue of climate change. Although many solutions have been found and/or created, there has yet to be one that can, on its own, solve the problem of finding an environmentally friendly energy source. This leads to the challenge of creating an integrated system which relies on several components with different types of energy. It has been the goal of this study to further enhance an off-grid renewable energy power system to supply economical, secure, and continuous electrical power, in an environmentally conscious way, for various types of loads. The previous power system consisted of a mobile unit with inverters, batteries, hydrogen generator, hydrogen storage, propane storage and an internal combustion engine generator that was connected to photovoltaics and wind turbines while being controlled and monitored by a single computer unit. The only pollutants emitted from this power system were the result of the use of propane as a backup fuel, when renewable energy was insufficient. Even though propane is a fossil fuel, its use in this study allowed the system to be simpler and more cost effective. With the assistance of Southwest Gas Corporation, a more efficient and reliable internal combustion engine was acquired. The three cylinder engine, with a 10,000 hour maintenance interval, was converted from natural gas to combust either hydrogen or propane. The engine provides mechanical power to a belt driven alternator supplying electricity to the load and other components of the system. Initial testing of the engine achieved engine dynamometer efficiency of over 40% using propane at wide open throttle and 45% using hydrogen at wide open throttle. The output under these conditions was roughly 20 HP using propane and 10 HP using hydrogen. The current system is not mobile but has the potential to be mobile by using an existing KOH electrolyzer for hydrogen generation with a larger output and hydrogen storage capacity.© 2010 ASME

Natural Nitrate Occurrence in Closed Basins in Southwestern United States

Abstract Expanding development of groundwater supplies in the closed basins of the southwestern United States has led to increasing reports of high nitrate levels in the water. Many of these nitrates appear to be from natural sources. Data indicate that playa areas have substantial quantities of nitrogen that is mobilized to water supplies. Documented areas include Clark and Lyon Counties in Nevada where water supplies have been adversely impacted with nitrate levels reaching 100 mg/l as N. Several other playa areas have soil nitrate levels up to 20,000 mg/kg. Field and laboratory studies are progressing on the origin and process of concentration of nitrogen in the playa areas. Potential sources include solution and transport from bedrock, fixation from the air by organisms and photochemical reactions, and old buried shallow lake deposits of organic or evaporite material. Better understanding of the occurrence of natural nitrates is necessary in order to access the impacts of man on present and future development of groundwater supplies.