Hector R. Fuentes

Use of Geographic Information Systems (GIS) in water resources: A review

Increasing public awareness, stricter measures and promulgation of new laws in the area of water resources have made the use of advanced technologies indispensable. Geographic Information Systems (GIS) are an effective tool for storing, managing, and displaying spatial data often encountered in water resources management. The application of GIS in water resources is constantly on the rise. In order to stress the importance of GIS in water resources management, applications related to this area are addressed and evaluated for efficient future research and development. Fundamentals of GIS are summarized and the history of the GIS evolution in water resources is discussed. Current GIS applications are presented including surface hydrologic and groundwater modeling, water supply and sewer system modeling, stormwater and nonpoint source pollution modeling for urban and agricultural areas, and other related applications. Future research and development needs are presented, based on these reviews.

A mechanistic modeling of montmorillonite contamination by cesium sorption

Abstract The triple layer electrochemical adsorption model (TIM) was utilized to model adsorption of Cs+ onto Ca-montmorillonite. Input data for the model were obtained via batch adsorption experiments in which Cs+ and mixtures of Cs+ and Sr2+ were added to a Ca-montmorillonite suspension at various conditions of pH and background electrolytes. A best fit of the model was achieved after gradually adjusting the values of the equilibrium constants and adsorption site concentrations. Two types of adsorption sites were considered to be responsible for adsorption in the clay: interlayer and frayed edges. The dominant mechanism of adsorption was identified as specific adsorption in the frayed edge sites, which although composing only 5% of the adsorption sites, they accounted for about 94% of total Cs adsorption. The model predicted precipitation of CsOH at concentrations above 1 mmol Cs/1, this value depending strongly on pH. The TLM successfully represented the adsorption of Cs over a wide range of concentrations, pH, nature of background electrolytes, and presence of competing cations.

Modeling adsorption in multicomponent systems using a Freundlich-type isotherm

Abstract The suitability of a Freundlich-type isotherm, the Sheindorf-Rebuhn-Sheintuch (SRS) equation, to represent the competitive adsorption of Sr, Cs and Co in Ca-montmorillonite suspensions was investigated. Experimental adsorption data were obtained for systems containing these cations as single-component, binary and ternary mixtures. The competition coefficient α ij , which were obtained based on the experimental adsorption data for bicomponent systems, can be viewed as a way to quantify competitive interactions. The competition coefficients obtained for the cations under consideration indicate that their competitive interactions are of similar magnitude, with the cation least affected by competitive effects being Cs, while the adsorption of Co was more significantly affected by the presence of Cs, and Sr by the presence of Co. After α ij -values were substituted in the SRS equation, the adsorption of systems of three or more components could be predicted. To validate the SRS equation, the adsorption values predicted by this equation for the ternary mixture SrCs Co were compared to values determined experimentally. The SRS equation successfully modeled adsorption for the range of concentrations that followed Freundlich behavior.

GIS-Aided Modeling of Nonpoint Source Pollution Impacts on Surface and Ground Waters

An application of GIS-aided modeling is done at an area in South Florida. A Geographic Information System (GIS) is interfaced with a nonpoint source pollution model to facilitate data storage, management and display; derivation of model input parameters; and effective presentation of results. parameters, and to visually present results in maps. Results for current conditions and practices show that sediments, nutrients and pesticides are present in surface runoff and ground water. Two alternatives to minimize pollution levels are evaluated, i.e., reduction of fertilizer application to the minimum required for effective agricultural growth and replacement of fertilizers with sewage sludge. In addition, the impact of urbanization of the agricultural area to the pollutant levels is tested. Both alternatives and the urbanization result in overall reduction of pollution.

A Langmuir isotherm-based prediction of competitive sorption of Sr, Cs, and Co in Ca-montmorillonite

An accurate determination of parameters such as the distribution coefficient Kd (for low concentrations) and the maximum adsorption capacity ST (for high concentrations) is desirable, as these values can be used in contaminant transport modeling. Considering that contaminants would more likely be found as mixtures and not as single components, the effects on Kd and ST values resulting from competitive interactions between the target cation and other cations present in the system were estimated. This study focused on the determination of Kd and ST for suspensions of Ca-montmorillonite and mixtures of the solutes strontium (Sr), cesium (Cs), and cobalt (Co) as analogs of a possible release of contaminants from radioactive waste repositories. Batch experiments were conducted for mixtures of the above solutes at intermediate concentrations at varying pH values and for two background electrolytes, NaCl and CaCl2. The Langmuir isotherm adequately fitted the experimental data and was used to determine Kd and ST. Maximum Kd values were obtained for Sr at pH 6 and for Co at pH 8, while for Cs the pH did not affect the resulting Kd value. The presence of competing ions resulted in a decrease of Kd values depending on the type and concentration of ions in the original mixture. For clay preconditioned with NaCl electrolyte solution, the Na+ partially saturated surface attracted more solutes, leading to greater Kd values than for suspensions preconditioned with a CaCl2 solution. Although the total amount of adsorbed cations (Scum) in either electrolyte solution was nearly constant, a difference in the adsorption of individual cations was observed as an increased percentage of adsorbed Sr and Co in systems preconditioned with NaCl solution.

Assessment of the Mangrove Ecosystem at São Luis, Maranhão, Brazil

The status of the mangrove ecosystem on the eastern part of the island of Sao Luis, Maranhao, Brazil, was assessed during summer and fall of 2005 by a scientific team. The mangroves on the study site cover an area of approximately 926 hectares. They are located in the northeastern Brazilian States of Maranhao, Para, and Amapa, which represent the largest concentration of mangrove forests in the world. The scientific team compiled baseline information that was used to forecast trends in the temporal trajectory of the Sao Luis mangrove ecosystem; information included abiotic and biotic as well as socio-economic indicators. The team then developed an assessment matrix to formulate future scenarios of impacts on the mangrove ecosystem. The mangrove ecosystem of the study area was found to be subjected to abiotic, biotic and socio-economic stressors with varying degrees of magnitude. Human population growth, environmental awareness and local community support, among other considerations, should be part of any long-term strategy for a sustainable mangrove ecosystem and its associated resources. Objective This study provides an independent assessment of the current status of the mangrove ecosystem (approximately 926 acres) immediately south of the existing facilities of Companhia Vale do Rio Doce (CVRD) at Sao Luis, Maranhao, and the potential trajectory of the land use under various scenarios of land management and conservation resources. The assessment was based on review of existing data and published literature, as well as a tour of the study site by a scientific team assembled by the Center for Environmental Studies (CES). The team also conducted interviews

Modeling the mass-transfer rate of radioactive cobalt from a synthetic groundwater to volcanic Tuff media

Abstract The application of a shrinking-core model controlled by macroporous diffusion has been validated for the adsorption kinetics of radioactive Co from a 0.01 N CaCl 2 solution to Bandelier Tuff. This tuff has served as a natural barrier in the disposal of low-level radioactive waste at Los Alamos National Laboratory. The model is validated for duplicate experiments and also in binary and ternary combinations with Sr and Cs. The sorbates were initially in solution at 20 mg L −1 and were contacted with the tuff in bottles agitated in the batch mode at 25°C. The shrinking-core model is compared with traditional models of rate control by chemical reaction, film and particle diffusion. The results have direct implications in the understanding and modeling of the fate and transport of radioactive Co in volcanic tuffs. Volcanic tuff is also being considered as a medium for the location of a high-level nuclear waste respository in the State of Nevada.