12,000

We have over 12,000 students, from over 100 countries, within one of the safest campuses in the UK

93%

93% of Lancaster students go into work or further study within six months of graduating

Home > Research > Publications & Outputs > ERT monitoring of environmental remediation pro...
View graph of relations

« Back

ERT monitoring of environmental remediation processes.

Research output: Contribution to journalJournal article

Published

Journal publication date03/1996
JournalMeasurement Science and Technology
Journal number3
Volume7
Number of pages9
Pages375-383
Original languageEnglish

Abstract

The use of electrical resistance tomography (ERT) to monitor new environmental remediation processes is addressed. An overview of the ERT method, including design of surveys and interpretation, is given. Proper design and lay-out of boreholes and electrodes are important for successful results. Data are collected using an automated collection system and interpreted using a nonlinear least squares inversion algorithm. Case histories are given for three remediation technologies: Joule (ohmic) heating, in which clay layers are heated electrically; air sparging, the injection of air below the water table; and electrokinetic treatment, which moves ions by applying an electric current. For Joule heating, a case history is given for an experiment near Savannah River, Georgia, USA. The target for Joule heating was a clay layer of variable thickness. During the early stages of heating, ERT images show increases in conductivity due to the increased temperatures. Later, the conductivities decreased as the system became dehydrated. For air sparging, a case history from Florence, Oregon, USA is described. Air was injected into a sandy aquifer at the site of a former service station. Successive images clearly show the changes in shape of the region of air saturation with time. The monitoring of an electrokinetic laboratory test on core samples is shown. The electrokinetic treatment creates a large change in the core resistivity, decreasing near the anode and increasing near the cathode. Although remediation efforts were successful both at Savannah River and at Florence, in neither case did experiments progress entirely as predicted. At Savannah River, the effects of heating and venting were not uniform and at Florence the radius of air flow was smaller than expected. Most sites are not as well characterized as these two sites. Improving remediation methods requires an understanding of the movements of heat, air, fluids and ions in the sub-surface which ERT can provide. The Florence site provides an excellent example of using information from ERT to improve a remediation system design. At Florence, the injection well used too long a sand pack in the injection zone which decreased the injection depth and thus the zone of influence of the system. Though in retrospect this is obvious, it would not have been noticed without ERT.