Iraj Javandel

Citric acid-modified Fenton’s reaction for the oxidation of chlorinated ethylenes in soil solution systems

Fentons reagent, a solution of hydrogen peroxide and ferrous iron catalyst, is used for an in situ chemical oxidation of organic contaminants. Sulfuric acid is commonly used to create an acidic condition needed for catalytic oxidation. Fentons reaction often involves pressure buildup and precipitation of reaction products, which can cause safety hazards and diminish efficiency. We selected citric acid, a food-grade substance, as an acidifying agent to evaluate its efficiencies for organic contaminant removal in Fentons reaction, and examined the impacts of using citric acid on the unwanted reaction products. A series of batch and column experiments were performed with varying H2O2 concentrations to decompose selected chlorinated ethylenes. Either dissolved iron from soil or iron sulfate salt was added to provide the iron catalyst in the batch tests. Batch experiments revealed that both citric and sulfuric acid systems achieved over 90% contaminant removal rates, and the presence of iron catalyst was essential for effective decontamination. Batch tests with citric acid showed no signs of pressure accumulation and solid precipitations, however the results suggested that an excessive usage of H2O2 relative to iron catalysts (Fe2+/H2O2<1/330) would result in lowering the efficiency of contaminant removal by iron chelation in the citric acid system. Column tests confirmed that citric acid could provide suitable acidic conditions to achieve higher than 55% contaminant removal rates.

Hydrodynamics of the Capture Zone of a Partially Penetrating Well in a Confined Aquifer

In the pump and treat approach to the problem of managing a contaminated aquifer, a key problem is to design an effective capture system that collects only the polluted groundwater without allowing any of it to escape. At present, it is customary to design a capture system using fully penetrating withdrawal wells. Very often, however, only part of the vertical thickness of the aquifer is contaminated, so the question may arise whether a more efficient capture system can be achieved using partially penetrating wells. Very little work has been done on the application of partially penetrating wells to this problem. A new semianalytic method that can be used in determining the geometry of the capture zone for steady state flow to a partially penetrating well that is screened from the top (or from the bottom) of a confined aquifer has been developed. By combining the velocity potentials for flow to the well with that for the regional flow field, a three-dimensional velocity potential that can be used in determining the complete geometry of the capture surface has been developed. The results have shown that with a constant pumping rate the maximum horizontal extent of the capture surface at the top (or bottom) of the aquifer increases as the degree of penetration decreases. As one would expect, the maximum vertical extent increases as the depth of penetration increases. Thus, if one knows the actual location of the contaminant plume, an appropriate combination of the degree of penetration and pumping rate can be selected to create an effective capture zone.

Analytical solutions for solute transport in a vertical aquifer section

Abstract Analytical solutions are developed for modeling solute transport in a vertical section of a homogeneous aquifer with steady uniform groundwater flow. The source is assumed to be located at the top (or the bottom) of the aquifer, and the initial concentration is assumed to be zero everywhere in the aquifer. Both constant-flux and constant-concentration sources are treated. For cases of a constant-flux source, we present exact analytical solutions considering the following transport mechanisms: advection in the horizontal direction, dispersions in both horizontal and vertical directions, adsorption, and biodegradation. For cases of a constant-concentration source, we present simplified analytical solutions by neglecting dispersion in the horizontal direction. For both kinds of sources, the solutions for aquifers with a relatively large or small thickness are presented and compared. The solutions for the two different source conditions are also compared for similar cases. The comparisons indicate that simpler solutions, used in appropriate cases, can give the same results as those given by more complex solutions. Example calculations are given to show the movement of the contamination front, the steady-state concentration profiles, and the applications to determine dispersivities. The analytical solutions developed in this study can be useful in site characterization, groundwater monitoring, and remediation.

CHARACTERIZATION OF LEAKY FAULTS : STUDY OF AIR FLOW IN FAULTED VADOSE ZONES

Characterization of leaky faults in vadose zones of large thickness is very important for engineering problems such as high-level nuclear waste disposal. This paper presents analytical solutions for air flow in faulted vadose zones of large or small thicknesses. The focus is on those sites where the fault zone is more permeable than its adjacent rock matrix. On the basis of the assumptions of a two-dimensional air flow in the matrix and a one-dimensional air flow in the fault zone, analytical solutions are presented for a sinusoidal atmospheric pressure variation. A procedure is then provided for extending the application of the solutions to an arbitrary atmospheric pressure variation. The solutions can help determine air permeability of leaky faults in the vadose zone.

Modeling Three-Dimensional Groundwater Flow and Advective Contaminant Transport at a Heterogeneous Mountainous Site in Support of Remediation

Modeling Three-Dimensional Groundwater Flow and Advective Contaminant Transport at a Heterogeneous Mountainous Site in Support of Remediation Strategy Quanlin Zhou, Jens T. Birkholzer, Iraj Javandel, and Preston D. Jordan Ernest Orlando Lawrence Berkeley National Laboratory Earth Sciences Division 1 Cyclotron Road, MS 90-1116, Berkeley CA 94720 USA Abstract A calibrated groundwater flow model for a contaminated site can provide substantial information for assessing and improving hydraulic measures implemented for remediation. A three-dimensional transient groundwater flow model was developed for a contaminated mountainous site, at which interim corrective measures were initiated to limit further spreading of contaminants. This flow model accounts for complex geologic units that vary considerably in thickness, slope, and hydrogeologic properties, as well as large seasonal fluctuations of the groundwater table and flow rates. Other significant factors are local recharge from leaking underground storm drains and recharge from steep uphill areas. The zonation method was employed to account for the clustering of high and low hydraulic conductivities measured in a geologic unit. A composite model was used to represent the bulk effect of thin layers of relatively high hydraulic conductivity found within bedrock of otherwise low conductivity. The inverse simulator ITOUGH2 was used to calibrate the model for the distribution of rock properties. The model was initially calibrated using data collected between 1994 and 1996. To check the validity of the model, it was subsequently applied to predicting groundwater level fluctuation and groundwater flux between 1996 and 1998. Comparison of simulated and measured data demonstrated that the model is capable of predicting the complex flow reasonably well. Advective transport was approximated using pathways of particles originating from source areas of the plumes. The advective transport approximation was in good agreement with the trend of contaminant plumes observed over the years. The validated model was then refined to focus on a subsection of the large system. The refined model was subsequently used to assess the efficiency of hydraulic measures implemented for remediation.

A Multilayered Box Model for Calculating Preliminary Remediation Goals in Soil Screening

In the process of screening a soil against a certain contaminant, we define the health-risk-based preliminary remediation goal (PRG) as the contaminant concentration above which some remedial action may be required. Thus, PRG is the first standard (or guidance) for judging a site. An overestimated PRG (a too-large value) may cause us to miss some contaminated sites that can threaten human health and the environment. An underestimated PRG (a too-small value), on the other hand, may lead to unnecessary cleanup and waste tremendous resources. The PRGs for soils are often calculated on the assumption that the contaminant concentration in soil does not change with time. However, that concentration usually decreases with time as a result of different chemical and transport mechanisms. The static assumption thus exaggerates the long-term exposure dose and results in a too-small PRG. We present a box model that considers all important transport processes and obeys the law of mass conservation. We can use the model as a tool to estimate the transient contaminant concentrations in air, soil, and ground water. Using these concentrations in conjunction with appropriate health-risk parameters, we may estimate the PRGs for different contaminants. As an example, we calculated the tritium PRG for residential soils. The result is quite different from, but within the range of, the two versions of the corresponding PRG previously recommended by the U.S. EPA.

Paul A. Witherspoon (1919–2012)

The hydrologic community lost one of its most charismatic leaders with the death of Paul Witherspoon on 10 February 2012, in Berkeley, Calif. He passed away from complications brought on by his long battle with Parkinsons disease. He was 93. Paul was a dynamic and influential research leader in hydrogeology for more than 50 years. Working from his base at the University of California, Berkeley (UC Berkeley), and later from the Lawrence Berkeley National Laboratory (LBNL), he made significant contributions to the understanding of the flow of fluids in porous media and fractured rock, and he applied his findings to a diverse set of societally important issues, including the development of geothermal energy, use of underground gas storage, and siting and design of nuclear waste disposal facilities. In all these spheres of interest he emphasized the need to marry theoretical studies and field testing. He was especially passionate about the need for large-scale, in situ, underground experiments to guide and corroborate the predictions of theoretically based numerical models.

Pressure-transient testing with a partially penetrating well in a two-layer reservoir

An analytic solution has been derived to investigate the transient pressure response of two-layer reservoirs with cross-flow. Results of the analytic method have been verified using a finite-element model and they reveal important details of pressure transient behavior such as the limiting conditions for detecting a multilayer situation. A procedure has been developed to evaluate the permeability of the producing layer as well as that of the second layer. The method can be applied to both pressure buildup and interference well tests. As has been previously shown from earlier numerical techniques, the early-time response or such a two-layer reservoir producing from a fraction of the thickness of one of the layers closely follows the behavior of a single-layer case. An inflection point in the pressure response can be expected under certain circumstances, and this provides important data. At large times the system behaves like an equivalent homogeneous reservoir.

Hydrogeology and tritium transport in Chicken Creek Canyon, Lawrence Berkeley National Laboratory, Berkeley, California

This study of the hydrogeology of Chicken Creek Canyon was conducted by the Environmental Restoration Program (ERP) at Lawrence Berkeley National Laboratory (LBNL). This canyon extends downhill from Building 31 at LBNL to Centennial Road below. The leading edge of a groundwater tritium plume at LBNL is located at the top of the canyon. Tritium activities measured in this portion of the plume during this study were approximately 3,000 picocuries/liter (pCi/L), which is significantly less than the maximum contaminant level (MCL) for drinking water of 20,000 pCi/L established by the Environmental Protection Agency.There are three main pathways for tritium migration beyond the Laboratory s boundary: air, surface water and groundwater flow. The purpose of this report is to evaluate the groundwater pathway. Hydrogeologic investigation commenced with review of historical geotechnical reports including 35 bore logs and 27 test pit/trench logs as well as existing ERP information from 9 bore logs. This was followed by field mapping of bedrock outcrops along Chicken Creek as well as bedrock exposures in road cuts on the north and east walls of the canyon. Water levels and tritium activities from 6 wells were also considered. Electrical-resistivity profiles and cone penetration test (CPT) data were collected to investigate the extent of an interpreted alluvial sand encountered in one of the wells drilled in this area. Subsequent logging of 7 additional borings indicated that this sand was actually an unusually well-sorted and typically deeply weathered sandstone of the Orinda Formation. Wells were installed in 6 of the new borings to allow water level measurement and analysis of groundwater tritium activity. A slug test and pumping tests were also performed in the well field.