Arvin Farid

Effects of Electromagnetic Stimulation on Soil’s Hydraulic Conductivity

Jonathan Rocha et al. — Wed, 30 Nov 2011 13:41:22 PST

Our research involves the identification of the different effects that electromagnetic (EM) stimulation has on varying soil properties; properties such as hydraulic conductivity. This work could prove to be of importance in furthering our understanding of the effects of EM stimulation with regard to the hydraulic conductivity of soil. A positive correlation between EM stimulation and an increase in hydraulic conductivity could have broad applications for environmental contaminant mitigation in soils and for various geotechnical construction applications such as minimizing soil setup during pile driving operations. EM waves can be used to enhance soil and groundwater remediation in a way that no heat is generated, yet the desired mechanisms in soil are stimulated. Our approach in this project involved the construction of a customized permeameter that enabled us to measure the change in hydraulic conductivity given a tuned EM wave from an antenna. An EM wave with a fixed frequency and varying power output was sent through the permeameter while the hydraulic conductivity was measured in real time. Tests performed for the research project were successful in showing a correlation between hydraulic conductivity and EM stimulation.

Mapping the Electric Fields for Geotechnical Applications

Sara Kaster et al. — Wed, 30 Nov 2011 13:41:19 PST

Volatile Organic Compounds (VOC’s) such as gasoline are contaminating our country's groundwater. From leaky underground tanks to hazardous spills, which put our groundwater at risk and will potentially contaminate our drinking water. Air sparging is used to clean up these harmful chemicals. However, air sparging is a slow process taking months or even years to reach acceptable contaminate levels. Air sparging uses an air injection well to pump air into the contaminated ground water. The harmful chemicals are volatilized as the air rises to the surface and removed with soil vapor extraction wells.

Tunnel detection using cross borehole radar

Clay Kurison et al. — Wed, 30 Nov 2011 13:41:17 PST

Shallow tunnels present both military and homeland security threats. Smugglers with intentions of avoiding border security have turned tunnels into transit routes for trafficking weapons, people, drugs and other illegal materials. Shallow tunnels are also used by prisoners to escape prisons. While drug and human trafficking have long been border concerns, the threat of international terrorism has transformed the effort to detect tunnels into a national security priority. Imminent threats include assailants entering military fortifications by burrowing under buildings, detonation of high grade explosives from foundations of high security facilities, and high level prisoners escaping detention centers through tunnels. Real-time monitoring of the ground surrounding prisons across the country is a desired solution to this problem.

An Experimental Setup for Electromagnetic Stimulation of Air Sparging

Arvin Farid et al. — Thu, 15 Sep 2011 08:59:54 PDT

The task of cleaning leakage from aging underground tanks along with surface spills of gasoline and other hazardous chemicals is of utmost importance to federal and state agencies. Minimally disruptive remediation techniques, such as air sparging, have become more attractive in the past decade compared with more traditional ex-situ remediation technologies. However, formation of air channels and slow airflow between them can make air sparging and similar methods less effective. The existing methods to stimulate airflow, such as pulsating air sparging systems, are time-consuming and not as effective.

Using radio frequency (RF) stimulation can expedite the remediation by affecting the formation, shape and size of air channels, and increasing air diffusion between these channels. To study the diffusion and RF stimulation, different cases will be studied within a clear acrylic box with: (i) water as the medium and an inert dye as the diffusive matter, and (ii) a water-saturated glass bead medium with air as the diffusive matter. A high power (75W) electromagnetic (EM) field is radiated through the saturated medium using two parallel copper plates (antennae), one connected to the amplifier, and the other grounded. The alternating electric field oscillates the dipole water molecules, which in turn, enhances the airflow. The first case studies the effect of the stimulation on diffusion. In the second case, in addition to the effect of the electric field on air diffusion, its effect on air channel formation is studied.

An Experimental Setup for Electromagnetic Stimulation of Geoenvironmental Applications

Arvin Farid et al. — Thu, 15 Sep 2011 08:59:52 PDT

Cleaning contaminated soil/groundwater is important to federal and state agencies. Traditional contaminant removal methods are costly and impractical for large sites. Less disruptive remediation techniques (e.g., air sparging) are attractive but limited by the restriction of airflow in soil. The use of electromagnetic (EM) stimulation to expedite airflow, diffusion, and control air channel formation is investigated. The diffusion of an inert dye as the diffusive matter within water and the effect of EM waves on the diffusion are experimentally modeled. To study the effect on air sparging through saturated soil, a clear acrylic box filled with a water‐saturated glass bead medium and air as the diffusive matter is used. The effects of the electric field on air channel formation in the second case (i.e., glass‐bead medium) are studied. It is expected that the stimulation of the water increases the diffusion of air between air channels and expands the air channel volume. The EM field is made possible using a dipole antenna connected to an RF source. The alternating electric field emitted off the antenna into the medium, oscillates the dipole water molecules. The stimulation helps enhance diffusion and enlarge the formed air channels.

Electromagnetic Waves in Contaminated Soils

Arvin Farid et al. — Tue, 12 Jul 2011 13:50:12 PDT

Soil is a complex, potentially heterogeneous, lossy, and dispersive medium. Modeling the propagation and scattering of electromagnetic (EM) waves in soil is, hence, more challenging than in air or in other less complex media. This chapter will explain fundamentals of the numerical modeling of EM wave propagation and scattering in soil through solving Maxwell’s equations using a finite difference time domain (FDTD) method. The chapter will explain how: (i) the lossy and dispersive soil medium (in both dry and fully water-saturated conditions), (ii) a fourth phase (anomaly), (iii) two different types of transmitting antennae (a monopole and a dipole), and (iv) required absorbing boundary conditions can numerically be modeled. This is described through two examples that simulate the detection of DNAPL (dense nonaqueous-phase liquid) contamination in soil using Cross-well radar (CWR). CWR —otherwise known as cross-borehole GPR (ground penetrating radar)—modality was selected to eliminate the need for simulation of the roughness of the soil-air interface. The two examples demonstrate the scattering effect of a dielectric anomaly (representing a DNAPL pool) on the EM wave propagation through soil. The objective behind selecting these two examples is twofold: (i) explanation of the details and challenges of numerical modeling of EM wave propagation and scattering through soil for an actual problem (in this case, DNAPL detection), and (ii) demonstration of the feasibility of using EM waves for this actual detection problem.

Cross-Well Radar I: Experimental Simulation of Cross-Well Tomography and Validation

Arvin Farid et al. — Mon, 21 Sep 2009 11:02:40 PDT

This paper explains and evaluates the potential and limitations of conducting Cross-Well Radar (CWR) in sandy soils. Implementing the experiment and data collection in the absence of any scattering object, and in the presence of an acrylic plate (a representative of dielectric objects, such as DNAPL (dense non-aqueous phase liquid) pools, etc.), as a contrasting object in a water-saturated soil is also studied. To be able to image the signature of any object, more than one pair of receiving and transmitting antennas are required. The paper describes a method to achieve repeatable, reliable, and reproducible laboratory results for different transmitter-receiver combinations. Different practical methods were evaluated for collecting multiple-depth data. Similarity of the corresponding results and problems involved in each method are studied and presented. The data show that the frequency response of a saturated coarse-grained soil is smooth due to the continuous and dominant nature of water in saturated soils. The repeatability and potential symmetry of patterns across some borehole axes provide a valuable tool for validation of experimental results. The potential asymmetry across other borehole axes is used as a tool to evaluate the strength of the perturbation on the electromagnetic field due to hidden objects and to evaluate the feasibility of detecting dielectric objects (such as DNAPL pools, etc.) using CWR. The experimental simulation designed for this paper models a real-life problem in a smaller scale, in a controlled laboratory environment, and within homogenous soils uniformly dry or fully water-saturated, with a uniform dielectric property contrast between the inclusion and background. The soil in the field will not be as homogenous and uniform. The scaling process takes into consideration that as the size is scaled down; the frequency needs to be scaled up. It is noteworthy that this scaling process needs to be extensively studied and validated for future extension of the models to real field applications. For example, to extend the outcome of this work to the real field, the geometry (antennas size, their separation and inclusion size) needs to be scaled up back to the field size, while soil grains will not scale up. Therefore, soil, water and air coupling effects and interactions observed at the laboratory scale do not scale up in the field, and may have different unforeseen effects that require extensive study.

Cross-Well Radar II: Comparison and Experimental Validation of Modeling Channel Transfer Function

Arvin Farid et al. — Mon, 21 Sep 2009 11:02:39 PDT

Close agreement between theory and experiment is critical for adequate understanding and implementation of the Cross-Well Radar (CWR, otherwise known as Cross-Borehole Ground Penetrating Radar) technique, mentioned in a previous paper by the authors. Comparison of experimental results to simulation using a half-space dyadic Green’s function in the frequency domain requires development of transfer functions to transform the experimental data into a compatible form. A Channel Transfer Function (CTF) was developed to avoid having to model the transmitting and receiving characteristics of the antennas. The CTF considers electromagnetic (EM) wave propagation through the intervening media only (soil in this case), and hence corresponds to the simulation results that assume ideal sources and receivers. The CTF is based on assuming the transmitting antenna, soil, and receiving antenna as a cascade of three two-port microwave junctions between the input and output ports of the Vector Network Analyzer (VNA) used in the experimental measurements. Experimentally determined CTF results are then compared with computational model simulations for cases of relatively dry and saturated sandy soil backgrounds. The results demonstrate a reasonable agreement, supporting both the model and CTF formulation.