The contamination at the Solvents Recovery Service of New England, Inc. (SRSNE) Superfund Site (Site) in Southington, Connecticut is the result of the practices of SRSNE, which began operations in 1955. From approximately 1955 until the facility closed in 1991, spent solvents were received from customers and distilled to remove impurities. Solvents and other wastes were handled and processed by several methods over the operational period, including distillation columns, lagoons, drums, and open pit incineration. Such operations were a source of historical releases of processed materials, solvents and spent fuels, which resulted in the presence of NAPL in the subsurface. The United States Environmental Protection Agency issued the Record of Decision in 2005, which included bedrock/overburden remedial action objectives.
Previous bedrock depth investigations performed by Geoprobe suggested that the bedrock surface varied only slightly across the entire site. Based on this information, the wellfield was designed for three distinct treatment areas, defined by the bedrock depth – 15, 18, and 21 feet below ground surface (ft bgs). Many TerraTherm sites, by contrast, have a defined bottom treatment depth that is consistent throughout the thermal wellfield. To expedite wellfield installation, heater cans, liners, and heaters are typically prefabricated prior to mobilization. As wellfield installation became closer, concerns about the bedrock depth, or possibly weathered bedrock depth, became increasingly problematic. If the actual bedrock depths varied from what was previously thought, modifications to the heater cans would need to occur in the field, real-time, while the borehole was open. Additionally, the occurrence of bedrock deeper than previously expected would result in deeper treatment depths, in turn impacting the electrical design (heater length, circuit layout, and energy needed).
In April 2013, TerraTherm began installation of the thermal wellfield at the site. Working closely with our subcontractor, Cascade Drilling (formerly Boart Longyear), we developed a flexible installation method to definitively identify the actual bedrock surface, and if needed, to modify the heater can(s) without causing downtime to the rig (or project). Because there are several hundred heater wells installed within the SRSNE treatment area, we selected a drilling method known for production – Sonic. The Sonic drilling method provides significant protection against unintended NAPL migration and minimizes water and spoils production during the wellfield installation.
The Sonic method was modified to allow for the advancement of two concentric, smooth-walled casings. The outer casing was advanced to the top-of-rock surface to isolate the overburden, while the inner casing drilled the required “socket” in the top of the rock to facilitate the heater installation into the upper portion of the bedrock – a design requirement to ensure that the bottom of the overburden will be sufficiently heated. Prior to advancing the inner core, the depth to the top of the bedrock was measured and confirmed. While the inner core barrel was advanced approximately four ft into bedrock, TerraTherm modified the heater can length by welding extensions onto each of the prefabricated casings, as needed.
The wellfield took six months to install and consisted of 607 heater wells, 551 vertical vapor extraction wells, 99 temperature monitoring points, 64 combination temperature/pressure and groundwater level monitoring points, and seven groundwater monitoring wells. The actual bedrock surface was on average 4 ft deeper than previously thought. Approximately 20,000 ft of new raw material was needed for extensions to the heater cans, liners, and heaters. There was no downtime caused during wellfield installation due to the deeper bedrock and modifications required in the field.
The operational (i.e., heating) phase of the project began last month and is scheduled to run through the remainder of 2014.
A presentation on the SRSNE project, entitled “In-Situ Thermal Remediation at a Major Multi-PRP CERCLA Site – Establishing Clean Up Levels, Design, and Implementation” by Thompson et al. 2014 (and co-authored by TerraTherm) was made at the Ninth International Conference on Remediation of Chlorinated and Recalcitrant Compounds, May 19-22, 2014, Monterey, CA and provides additional information on this groundbreaking project.
Another great place to find out more about this project is on the official SRSNE Superfund Site website.
For more information on TerraTherm’s drilling capabilities, read Kevin Crowder’s blog, “Drilling and Well Installation at In Situ Thermal Desorption (ISTD) Sites”