Formatted Title

Lessons Learned from Multiple ERH Implementations: Design Considerations and Challenges

Background/Objectives

This presentation describes the technical hurdles associated with the implementation of two electrical resistive heating (ERH) systems. It focuses on the full-scale operation and limitations of the designs: the variables that affect heat up rate, the ability to reach the boiling point of water, mass removal rates, and the importance of maintaining hydraulic control.

The first Site involved the use of nine electrodes and monitoring points while the second Site included two orders of magnitude more subsurface infrastructure. The soils at both Sites (saturated and unsaturated zones) consisted of heterogeneous fine-grained sediments and chlorinated VOCs were the primary contaminants. Though remediation was required to be performed to the “limits of the technology” at both Sites, asymptotic mass removal was the only prescribed remedial goal at the smaller Site. At the larger Site, a combination of heating levels, asymptotic mass removal, and the collection of confirmatory soil samples was required by the regulators. The similarities (and differences) between the two Sites, afforded a unique perspective to compare the design, implementation, efficacy, and applicability of this technology.

Approach/Activities

Significant delays due to permitting hurdles at the local level were realized by both projects as local permitting authorities were unaware of how to evaluate and permit the technology. To balance infrastructure costs with the desired power density, a wider electrode spacing was designed for the larger Site. Neither system design included supplemental hydraulic control or temperature monitoring outside the heated zone, necessitating implementation of chemical oxidation on a fast-track basis to control the increase in downgradient VOC concentrations caused by the ERH remedy at the smaller Site. A hydraulic control system was incorporated into the remediation at the larger site mid-implementation.

Results/Lessons Learned

Successful remediation at both Sites resulted in regulatory closure of the ERH remedies. The smaller Site heated up much faster (reaching temperatures up to the boiling point of water) with vigorous mass removal - 1,000 pounds of VOCs removed in 5.5 weeks. The larger system removed the same mass from an area which was 70-times larger and in which concentrations were more diffuse, over the course of 6 months. Design modifications including closer electrode spacing, hydraulic control infrastructure, temperature monitoring outside the heated zone, and achievement of the boiling point of water across the entire treatment zone (both laterally and vertically) would have decreased the remedial timeframe at the larger site and provided more streamlined operation. That said, increasing the power density at larger sites may prove cost prohibitive; therefore, both the financial and technical requirements need to be fully considered during the design phase.