Formatted Title
Electrical Resistance Heating at an Active Food Industry Site Optimized by High-Resolution 3-D Conceptual Site Model
Background/Objectives
In situ thermal remediation (ISTR) using electrical resistance heating (ERH) was selected as the remedy for an active food grade industrial site in Brazil that was contaminated with chlorinated volatile organic compounds (CVOCs). The soil in the treatment volume is highly heterogeneous and composed of plastic silty clay layers up to 10 meters (m) below grade surface (bgs). In Brazil, risk-based remediation targets are derived based on the local contamination levels and specific site use. This industrial site revealed maximum concentrations of PCE and its degradation products in the order of 3,500 mg/kg in soil and 10,000 µg/L in groundwater. A large part of the treatment area was located below an active production building that was densely occupied by sensitive equipment and personnel. Facility production was not allowed to be interrupted or greatly interfered with during construction or operations which set special boundary conditions that required the highest level of precision and care in planning and execution of the thermal system.
Approach/Activities
A combination of high-resolution site characterization (HRSC) tools such as membrane interface hydraulic profiling (MIHPT) and conventional drilling methods were implemented to delineate the 5,400 cubic meters target treatment zone (TTZ) and the characteristics of the aquifer within it. Buildings and structures on and around the 860 square meter (m2) target treatment area were surveyed with a terrestrial laser scan (TLS) to develop a high-resolution three-dimensional (3-D) Conceptual Site Model (CSM) as a precision planning tool. Fifty-nine electrodes and co-located vapor recovery wells were installed in the TTZ at a depth of up to 9 m bgs. The electrode cable and vapor recovery piping were installed below grade during planned downtimes of the site owner to allow continuous site operations and prevent production interferences. Special hygiene requirements had to be considered. For example, drilling and construction activities performed within the food grade facilities had to be completely isolated and enclosed from facility operations. Physical barriers and engineering controls were used to perform this work. Remediation targets were proven by confirmatory soil and groundwater samples. The site is currently in the cool-down phase.
Results/Lessons Learned
The benefits of the high-resolution 3-D CSM as a detailed planning tool will be demonstrated in the presentation. For example, the 3-D CSM assisted in providing an accurate mass estimation and clearly defined request for proposal. It was also used as a tool for efficient dimensioning of the treatment system so that costs and schedule could be optimized during planning and met at the end of the treatment phase. Sharing the 3-D CSM as a 3D-PDF file and in virtual reality strongly enhanced comprehension and unambiguous communication between all stakeholders. This digital aspect was a major advantage considering the international project team and project implementation during the Corona virus pandemic. Additionally, the presentation will address specific challenges and findings encountered during installation and operation of a thermal remediation system in a highly active industrial site with sensitive receptors.