A Spreadsheet-Based Multi-Layer Vadose Zone Leaching Model
Phillip C. de Blanc, Groundwater Services, Inc., Houston, TX

Use of SEVIEW Software in Determining Groundwater Impacts at POCs
Michael R. Kulbersh, US Army Corp of Engineers, Concord, MA

A Permanganate Natural Oxidant Demand Kinetic Model
Laura Jones, University of Waterloo, Waterloo, ON, Canada

A Proposal for a Quantitative Petroleum Weathering Model to Replace Today's Qualitative or Descriptive Categories
Michael J. Wade, Wade Research, Inc., Marshfield, MA

Evaluating the Impacts of Uncertainty in Geomorphic Channel Changes on Predicting Mercury Transport and Fate it the Carson River System, Nevada
John J. Warwick, Desert Research Institute, Reno, NV  

BIOSCREEN, AT123D, and MODFLOW/MT3D, a Comprehensive Review of Model Results
Robert A. Schneiker, P.G., Environmental Software Consultants, Inc., Madison, WI

A Spreadsheet-Based Multi-Layer Vadose Zone Leaching Model  

Phillip C. de Blanc, Ph.D., P.E., Groundwater Services, Inc., 2211 Norfolk St., Ste. 1000, Houston, TX 77098, Tel: 713-522-6300, Fax: 713-522-8010

Environmental professionals routinely use one-dimensional models to simulate the leaching of contaminants from vadose zone soils to underlying groundwater.  These models solve the one-dimensional form of the advection-dispersion-reaction (ADR) equation to determine the concentration of a constituent as a function of time and depth within the soil column.  Many commonly-used models of contaminant leaching from vadose zone soils are numerical models that require an input file and post-processing.  While these models are flexible and accurate, they require training for the user to take full advantage of the model capabilities, even if the user possesses all of the knowledge of the underlying physical principles.  An alternative to numerical leaching models is to solve the ADR equation analytically.  Because the ADR equation is linear, superposition can be used to simulate leaching from multiple layers by adding the solutions for each individual layer.  By specifying the correct boundary conditions for each layer, leaching from any number of layers can be simulated without having to resort to numerical models.  Because the analytical solutions are exact, time-step limitations and numerical dispersion are eliminated.  In addition, because all calculations are performed in a spreadsheet, there is no need for qualified professionals to learn how to use new software; their knowledge can be applied directly with a tool that is nearly universally used by environmental practitioners.   Currently, the leaching model simulates the processes of liquid phase advection, liquid and air phase diffusion, liquid phase dispersion, and first-order reactions.  Each layer can have a different thickness and initial concentration of a single constituent.  Breakthrough curves and concentration profiles computed by the model match those computed by a popular numerical model.  The capability of simulating layers with different physical properties by using dimensionless scaling factors is in progress.

Use of SEVIEW Software in Determining Groundwater Impacts at POCs

Michael R. Kulbersh, P.HG., C.G., R.G,  U.S. Army Corp of Engineers, 696 Virginia Road, Concord, MA 01742, Tel: 978-318-8088, Email: Michael.R.Kulbersh@USACE.Army.Mil

As part of soil and groundwater investigations at hazardous waste sites across the country organic and inorganic compounds are readily detected in surface soils.  At many of these sites the current protocol is to use readily available soil impact to groundwater standards or use the SESOIL model coupled with the Summers dilution model to determine impacts at points of compliance (POCs).   However, the Summers model cannot address multiple areas of discrete (patch) sources or contiguous areas of contamination not aligned parallel to groundwater flow. 

SESOIL in combination with AT123D, a 3-D analytical transport model may be used to simulate impacts from either a patch or contiguous sources and can account for contaminants loading to groundwater not parallel to groundwater flow.  Unfortunately neither SEVIEW nor RiskPro software packages that run SESOIL/AT123D in a GUI environment presently simulate impacts from multiple sources arrayed in various configurations as part of a single run. 

USACE worked with the SEVIEW developer, Environmental Software Consultants, Inc. to modify the existing version of SEVIEW to be able to pull in multiple loads from SESOIL (presently 15) into one AT123D run.  A beta version was developed and tested extensively by USACE and the developer.  The benefits of being able to pull the SESOIL loads into a single run will reduce model runs/contractor costs.  The beta version of SEVIEW now allows a user to toggle on/off a SESOIL load and immediately determine its impact on the POC.  The user can view the soil loads impact to groundwater in both an areal view (2D array graphic) and through a time concentration plot at the POC for all loads.   The net result is that at a site only certain areas may require soil remediation/excavation in order to be protective of groundwater standards.

A Permanganate Natural Oxidant Demand Kinetic Model

Student Presenter

Laura Jones, Department of Civil and Environmental Engineering, University of Waterloo, 200 University Ave West,    Waterloo ON, Canada N2L 3G1, Tel: 519-888-4567 Ext 33821, Fax: 519-888-4349, Email: lj3jones@engmail.uwaterloo.ca
Xiuyuan Xu, Department of Civil and Environmental Engineering, University of Waterloo, 200 University Ave West,      Waterloo ON, Canada N2L 3G1, Tel: 519-888-4567 Ext 33821, Fax: 519-888-4349, Email: xxu@engmail.uwaterloo.ca
Neil R. Thomson, Department of Civil and Environmental Engineering, University of Waterloo, 200 University Ave West, Waterloo ON, Canada N2L 3G1, Tel: 519-888-4567 Ext 32111, Fax: 519-888-4349, Email: nthomson@civmail.uwaterloo.ca

The presence of naturally occurring reduced species associated with aquifer materials exerts a significant permanganate demand thereby reducing the mass of oxidant available for the destruction of the contaminant(s) of concern as well as reducing the oxidation rate.  Recent laboratory efforts indicate that this demand is not a single-valued quantity, but is kinetically controlled and depends on the parameters of the test system and type of reduced aquifer material species present.  A comprehensive model that captures the kinetic behaviour of permanganate consumption by aquifer materials was formulated by using data collected from well-mixed batch reactor and column systems.  The batch experiments were based on the theoretical derivation of the stoichiometric reaction of permanganate with bulk aquifer material reductive components, and consisted of excess permanganate mass experiments and excess aquifer material mass experiments.  A typical experimental column trial consisted of flushing an aquifer-material packed column with the permanganate source solution until sufficient permanganate breakthrough was observed.  Aquifer material from several representative sites across North America was used.  We assumed that the dichromate chemical oxygen test results could serve as a surrogate for the overall aquifer material reduction capacity.  The developed kinetic model consists of three reactive components associated with the aquifer material: a fast component, an intermediate component, and a slow component.  The fast and intermediate components were observed in the batch experiments, while the slow component was observed in the column breakthrough curves.  Evidence of passivation was apparent in the data and confirmed by manganese oxide coating on grains.  This presentation will include a discussion of the underlying processes, and a description of the experimental data and aspects of the developed kinetic model.  In addition, the impact of permanganate consumption kinetics on source zone treatment will be demonstrated.

A Proposal for a Quantitative Petroleum Weathering Model to Replace Today's Qualitative or Descriptive Categories

Michael J. Wade, Ph.D., Principal Scientist, Wade Research, Inc., 110 Holly Road, Marshfield, MA 02050-1724, Tel: 781-837-5504, Email:  mjwade@waderesearch.com

Assessment of the extent of petroleum weathering in today's environmental forensics community can be described as qualitative at best and at worst as slipshod. Descriptive determinations of chemical analysis results such as "moderately weathered" or "extensively weathered" are routine. Up until now there has been no quantitative model proposed to actually measure the various stages of natural weathering of petroleum products such as gasolines and distillate fuels.

Such a quantitative weathering model is proposed to the forensics community. The model is based upon today's analytical ability to accurately quantify numerous different types of petroleum hydrocarbons, such as paraffins isoparaffins, alkylaromatics and the like in gasolines and distillate fuels. Following the progress of natural environmental weathering by measuring the changes in selected alkylaromatics and paraffins, for example, will allow an accurate (quantitative) assessment of the progress of environmental weathering in modern gasolines and distillate fuels.

Illustrations of how to calculate quantitative indices of today's contemporary gasolines and distillate fuels are provided. Specific project examples where such calculated values have been used to distinguish among the different weathering stages of petroleum products are presented.

It is proposed that such quantitative descriptions of environmental weathering of petroleum products should replace today's much more vague and descriptive approach in common use today.

Evaluating the Impacts of Uncertainty in Geomorphic Channel Changes on Predicting Mercury Transport and Fate it the Carson River System, Nevada

John J. Warwick, Ph.D., Environmental Engineering, Executive Director, Desert Research Institute, Division of Hydrologic Sciences, 2215 Raggio Parkway, Reno, NV 89512, Tel: 775-673-7379, Email: John.Warwick@dri.edu
Rosemary Carroll, M.S., Hydrology, Research Scientist, Desert Research Institute, Division of Hydrologic Sciences, 2215 Raggio Parkway, Reno, NV 89512

The Carson River is one of the most mercury contaminated fluvial systems in North America. Most of its mercury is affiliated with channel bank material and floodplain deposits, with the movement of mercury through this system being highly dependent on bank erosion and sediment transport processes. Mercury transport is simulated using three computer models: RIVMOD, WASP5, and MERC4. Model improvements include the addition of a bank package that accounts for flow history. The rates at which river stages are rising or falling will, in turn, impart time-dependant and vertically variable MeHg concentrations within the channel banks along the Carson River. Also, Lahontan Reservoir’s geomorphic characteristics have been refined along with the explicit tracking of a temporally and spatially varying colloidal fraction. The augmented and refined modeling approach results in more accurate and realistic simulation of mercury transport and fate. An extensive uncertainty analysis, involving characterizing the co-variance of two calibration parameters used to define bank erosion and overbank deposition, will define the degree of expected variation in model predictions relative to limitations posed by available field data.

BIOSCREEN, AT123D, and MODFLOW/MT3D, a Comprehensive Review of Model Results

Robert A. Schneiker, P.G., Environmental Software Consultants, Inc., P.O. Box 2622, Madison, WI 53701-2622, Tel: 608-240-9878, Fax: 608-241-3991, Email: rschneiker@seview.com  
Liliana Cecan, P.E., Ph.D., McLane Environmental, LLC, 707 Alexander Road, Suite 206, Princeton, NJ 08540, Tel: 267-685-1828, Fax: 267-685-1801, Email: lcecan@mclaneenv.com 

The Domenico equation is commonly used to evaluate risks associated with contaminated groundwater. Numerous groundwater models are based on it, including BIOSCREEN and BIOCHLOR. Results from such Domenico equation based models are considered conservative and are readily accepted by most regulatory agencies. In fact many regulatory agencies even require that Domenico equation based methods be used.

This paper compares the results from the BIOSCREEN, AT123D and MODFLOW/MT3D groundwater models, and shows that there is little correlation between BIOSCREEN and the other models. As expected the BIOSCREEN model consistently produced the highest peak groundwater concentration. However these peak concentrations are identical for everything from benzene to polycyclic aromatic hydrocarbons. Although all the predicted concentrations produced by BIOSCREEN are identical, contaminant mobility varies significantly. Travel times discrepancies between BIOSCREEN and the other models increased as hydraulic conductivity is reduced. These travel time discrepancies range from insignificant to almost 40,000 years for benzene in a clay aquifer. The influence of biodegradation is also evaluated. The amount of biodegradation is controlled by the time it takes to reach a point of compliance. As such, inclusion of biodegradation further increases discrepancies between BIOSCREEN and the other models. Discrepancies in contaminant concentrations increased as hydraulic conductivities are reduced, reaching many orders of magnitude for benzene in a clay aquifer.

Correlation between the AT123D and MODFLOW/MT3D models is very good in that they produce nearly identical peak concentrations and travel times. Unlike BIOSCREEN, results vary significantly based on contaminant and aquifer properties as should be expected.

Although BIOSCREEN produces the highest maximum concentration, it underestimates consistently the mobility of the contaminant, and thus exposure. Inclusion of biodegradation only increases discrepancies between BIOSCREEN and the other models, thus making BIOSCREEN the least conservative model tested.  Given that AT123D and BIOSCREEN use almost identical input parameters it is difficult to explain the use of BIOSCREEN and other Domenico equation based models.

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