August Mack Newsletter | April, 2019

Electrical Resistance Heating Case Study
by Chris Abel & Bryant Hoffer

Contaminated properties have various liability implications so it is important that stakeholders involved with such matters are informed of the various options available to address contamination, prevent exposure, and manage liability. The approach to environmental cleanup and closure has changed and evolved over the years. There is a renewed focus on clean-up of source areas, which typically have the highest contaminant levels at a site and likely present the greatest threat to human health and the environment.

The ability of a technology to remediate soil and groundwater impacted by chlorinated solvents and petroleum hydrocarbons regardless of lithology proves to be beneficial over conventional in situ technologies that are dependent on advective flow. These conventional technologies include soil vapor recovery, air sparging, and pump-and-treat, or the delivery of fluids to the subsurface such as chemical oxidization and bioremediation.  Electrical resistance heating (ERH) is an in situ thermal treatment for soil and groundwater remediation that can reduce the time to clean up volatile organic compounds (VOCs) from years to months. The technology is now mature enough to provide site owners with both performance and financial certainty in their site-closure process. The technology is very tolerant of subsurface heterogeneities and actually performs as well in low-permeability silts and clay as in higher-permeability sands and gravels. ERH is often implemented around and under buildings and public access areas without upsetting normal business operations. ERH may also be combined with other treatment technologies to optimize and enhance their performance.

Electrical resistance heating passes an electrical current through the soil and groundwater that requires treatment. Resistance to this flow of electrical current warms the soil and then boils a portion of the soil moisture into steam. The natural resistance of the subsurface to this flow of electrical current creates uniform heating throughout the treatment area, regardless of whether it is saturated or unsaturated (vadose). This in situ steam generation occurs in fractured or porous rock and in all soil types, regardless of permeability. Electrical energy evaporates the target contaminant and provides steam as a carrier gas to sweep VOCs to vapor recovery (VR) wells. After the steam is condensed and the extracted air is cooled to ambient conditions, the VOC vapors are treated using conventional methods, including granular activated carbon (GAC) or oxidation.

Electrodes are usually placed in the subsurface throughout the remediation area using standard drilling techniques. Electricity may be directed to groups of electrodes, or electrode intervals, either simultaneously or sequentially depending on the depth of impact, or the size of the volume being treated, or the desired heating pattern. The electrodes also serve as vapor and steam-recovery points, or can operate as multiphase extraction wells for the recovery of vapor, steam, water, and NAPL from the subsurface; in fact, it is best to think of an electrode as a well that has the added capability of directing electrical current to the proper depth for subsurface heating.

A power control unit (PCU) is used to direct conventional three-phase electricity from municipal power lines to the electrode field using cables. The PCU control computer is used to both monitor and control site activities and may be accessed directly or remotely. Subsurface temperature, voltage, vacuum, airflow, and subsurface pressure data are collected on set schedules and uploaded daily to the PCU control computer.

The type of contaminant and the desired cleanup goal affect the energy, time, and cost to remediate a site. To date, most applications of ERH have focused on contaminant source area treatment and, in particular, the remediation of DNAPLs and LNAPLs. Direct in situ volatilization provides a mechanism to rapidly and efficiently extract contaminants with low boiling points, such as PCE, TCE, and cis-1,2-dichloroethene (cis-DCE) from the subsurface.

Compared to other technologies, ERH provides higher assurance of source-area contaminant removal at attractive costs per pound removed. However, when contemplating applying ERH on dissolved-phase plumes, the costs per weight of contaminant treated become less attractive. Remediation cost accounting, no matter what technologies are employed, is site-specific and typically dependent on one or more of the following: the size, depth and volume of the treatment area, the target contaminants and level of contaminant reduction required, site geology, depth to groundwater, groundwater velocity, and total organic carbon content in soil.

Case Study – Former Dry Cleaner

The facility consists of the main building of approximately 2,600 square feet. The project Site is situated in a mixed industrial and commercial portion of town with a buffer zone on all four (4) sides of industrial and commercial property. Historically, dry cleaning operations have occurred at the Site for several decades and tetrachloroethylene (PCE) was reportedly used starting in 1959. Impacts identified in both soil and groundwater are attributed to dry cleaning operations, product storage, and waste handling practices.

Historical, pre-remediation soil and groundwater investigation identified the vast majority of contaminant mass to be PCE with limited breakdown products including trichloroethylene (TCE), cis-1,2- dichloroethene (cis-1,2-DCE), trans-1,2-dichloroethene (trans-1,2-DCE) and vinyl chloride (VC). Numerous subsurface investigations have been conducted at the Site and near off-Site properties to evaluate Site lithology, determine potential preferential pathways, to collect confirmatory samples for laboratory analysis, and to fully delineate subsurface impacts.

The initial remediation approach began in 2002 and utilized chemical injections to reduce the known contamination at the Site. Based on the poor performance of the initial injection treatability study, a new remediation approach of Enhanced Vacuum Extraction (dual-phase extraction system) was installed and started operation in November 2007.

August Mack was contracted in 2012 to further evaluate the impacts identified at the Site and determine if a new remediation approach was appropriate to more rapidly reduce Site impacts. Based on the Site lithology, limited potential exposure pathways, expected future Site usage, and project stakeholder goals, an in-situ ERH was the recommended remedial option. The primary goal of the ERH was rapid source reduction concentrating on known impacts near and beneath the on-Site building and maximizing contaminant mass removal with limited residual impacts leading to an expedited Site closure.

An RWP and Site-specific Conceptual Site Model (CSM) outlining the ERH process was submitted for regulatory review in March 2016 and approved in July 2016. The RWP outlined the goal to reduce the subsurface impacts in soil by 99.99% and listed Site-specific remediation closure levels.

August Mack and Environmental Field Services, Inc. (EFS) personnel mobilized to the Site in November 2015 to initiate the subsurface installation of ERH system components. The subsurface installation consisted of the following:

  • Installation of forty-seven (47) co-located electrodes and vapor recovery (VR) points,
  • Installation of eight (8) temperature monitoring points (TMPs)/pressure monitoring points (PMPs), and
  • Installation of five (5) deep vapor recovery (VR) wells.
 

Uninterrupted ERH system operation started in March 2016 and ran for a total of 189 days while utilizing utilized a total of 1,928,238 kilowatt hours (kWh). During operations, routine activities (i.e. health and safety (H&S) checks, off-gas sampling ambient air monitoring, etc.) was conducted, and in September 2016 the ERH system was shut-down. To assist in vapor recovery during the initial cool-off period, the vapor recovery system was allowed to operate for an additional week. Based on the laboratory analysis of the ERH system effluent air, approximately 10,000 pounds of VOCs were removed from the treatment volume during system operation.

In an effort to collect representative media using standard sampling protocols, both soil and groundwater samples were collected from the Site after the subsurface temperature decreased from approximately 190 degrees Fahrenheit (achieved during system operation) to 120 degrees Fahrenheit (or less) in each previously installed temperature monitoring probe. The cooling of the subsurface media was evaluated periodically following system shutdown, and the target subsurface temperature was reached in October 2017.

The 16 confirmatory soil borings were advanced in November 2017 using a Geoprobe® Direct Push Sampling System. Laboratory analysis of soil samples collected during the confirmatory sampling indicated all VOCs in each soil sample were reported below their respective Site Specific Remediation Goal. In November 2017 the first of the eight (8) routine (i.e. quarterly) groundwater monitoring events were initiated. As of April 2019, low-level impacts in groundwater remain above their respective Site Specific Remediation Goal in one (1) monitoring well in the southwest portion of the Site, just outside of the treatment area.

Exposure concerns from these residual detections will be managed by the following:

  • A Vapor Intrusion (VI) mitigation system is planned to address any VI exposure concerns from detections above Site Specific Remediation Goal to any potential receptors.
  • An Environmental Restrictive Covenant (ERC) will be recorded on the property, restricting future residential use of the property and the advancement of drinking water wells to limit exposure for these scenarios.
 

August Mack anticipates requesting regulatory closure in Fall 2019, following collection of two (2) additional rounds of quarterly groundwater sampling and implementation of the engineering and institutional controls outlined above.

For more information on this topic, sign up to attend our webinar on June 5, 2019.


Chris Abel is a Senior Manager/Chemist for closure services with August Mack Environmental, Inc. in the Indianapolis, Indiana office. He has over 23 years of experience in environmental engineering, chemistry, and project management. He has extensive experience managing residential, commercial, and industrial site assessments, site investigation, and remediation system design, construction, operation and maintenance. He has performed a wide range of engineering and project management related work on hazardous and non-hazardous sites including retail, chemical manufacturing plants, natural gas collection and compression stations, and a former nuclear weapons manufacturing site. He is a Certified Hazardous Materials Manager (CHMM).  Chris can be reached at 317.916.3107 or via e-mail at cabel@augustmack.com

Bryant Hoffer is a senior manager for August Mack Environmental, Inc. in its Indianapolis, IN office. He has more than ten years of experience with extensive knowledge regarding geological and hydrogeological investigations, monitoring well installation and abandonment, soil and groundwater sampling, vapor intrusion evaluation and mitigation, tank management, and environmental site assessments. He graduated with a Bachelor of Arts degree in Geology from Indiana University – Purdue University. Bryant can be contacted at 317.916.3163 or via e-mail at bhoffer@augustmack.com.


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