ERH in Soil and Groundwater San Diego, California

Project Summary

TRS Group, Inc. designed and implemented an electrical resistance heating (ERH) system to reduce concentrations of chlorinated volatile organic compounds (CVOCs) in soil and groundwater at a site in San Diego, California. Chlorinated solvents including 1,1,1-trichloroethane (TCA) and trichloroethene (TCE) had impacted the soil and groundwater beneath the site. The clean-up objective for the remediation was to reduce CVOC concentrations in soil and groundwater in the ERH remediation area by 90 percent from existing concentrations. A combination of sheet pile and bored electrodes were implemented at a depth of 30 feet below ground surface (ft bgs) over an area of approximately 36,740 square feet (ft2) resulting in a remediation volume of 34,018 cubic yards (yd3). The ERH remediation was highly successful, with a total of 47,105 pounds of contaminant mass being physically removed from within the remediation area or remediated in-situ through hydrolysis, reducing CVOC contaminant concentrations in soil by greater than 99 percent, with final concentrations of less than 10 mg/kg at each of the 20 confirmation soil boring locations and at each depth sampled.

Background

The site is located in a light industrial area and is bordered to the northwest and southeast by commercial properties. A railroad right-of-way and a wetlands area borders the southwestern portion of the site. The property is approximately 3.7 acres in area with an approximately 31,000 square foot concrete tilt up building situated on it. The site was developed in 1963 and was used for the manufacturing of ceramic capacitors from the late 1960’s until 1986 when the property was vacated. In 1990, the property was leased to a printing company and was sold in 2004 to a development group. The property was re-sold in 2007 and in 2013. The property is currently in use as office space and the parking lot is used for vehicle storage. The site is currently occupied by one building, with the remainder of the property covered as an asphalt and concrete parking lot, driveways, and planter areas as depicted in site aerial photo, Figure 1. A chain link fence surrounds the entire property, with the exception of a portion of the southeast parking lot. In order to complete the installation and operation of the ERH remediation system, multiple permits were required by and obtained from multiple agencies.

Hydrolysis Remediation of TCA and TCE in Soil and Groundwater

Figure 1. Site Overview

Figure 1. Site Aerial

TRS SOR15 ShortV ProjEx 031815 acf © 2015, TRS Group, Inc. All rights reserved.

Site Characteristics & Design Parameters

TRS designed and implemented the ERH remediation system on the property to remediate chlorinated volatile organic compounds (CVOCs) in soil and groundwater. The investigative and remedial activities were performed as a voluntary cleanup under the County of San Diego Department of Environmental Health (DEH) for approximately 20 years. In light of a non-potable-use aquifer, the remedial goals established with the DEH were a stable or shrinking plume, no significant adverse health risks to human or ecological receptors, and source reduction. Prior to initiating the ERH remedy, the property owner, tenant, and the neighboring property owners and property managers were briefed on and provided written notice of the remediation activities. Property owners and managers were provided contact information in the event that they required additional information regarding the ERH remediation.

TCE, TCA, and various other volatile compounds detected in soil and/or groundwater at the site were the subject of the ERH remediation process. Provided in Table 1 below is a list of the maximum historical (prior to 2012), pre- ERH concentrations of the VOCs detected in soil and groundwater at the Site.

Table 1. Historical Contaminant Concentrations (pre-2012 Sampling)

VOCs Soil (mg/kg) Groundwater (µg/l)

1,1-Dichloroethane 0.410 46,000

1,2-Dichloroethane 12 51,900

1,1-Dichloroethene 459 35,300

cis-1,2-Dichloroethene 19.8 78,400

1,1,1-Trichloroethane 10,200 202,000

Trichloroethene 2,500 65,600

Vinyl chloride 11.7 7,300

Total Xylenes 510 3,310

Ethyl Benzene 187 567

Total 13,900 490,377

Although TCA concentrations exceeded TCE in the subsurface, TCA hydrolyzes in situ converting to 1,1-DCE, which can be removed much more rapidly from soil in comparison to TCE. Therefore, TCE was the controlling contaminant used to model the site-specific ERH remediation design since it is more difficult to remove than TCA or 1,1 DCE.

System Construction and Operations

The ERH remediation area covered 36,740 square feet (ft2) with a volume of 34,018 cubic yards (yd3). Depth of remediation was on average, 30 ft bgs. The remediation area was situated behind the existing building at the facility and extended from the northern property boundary, along the western property boundary and close to the southern property boundary.

To maintain use of the property during the remediation, the majority of the ERH remediation area was designed as a below-grade completion, with electrodes, VR piping, electrode cables, groundwater conveyance piping, and temperature monitoring components below-grade. Subsurface components transitioned to the surface within the “cable corridor” along the property boundary adjacent to the railroad easement. The “cable corridor” (Figure 2) facilitated surface conveyance piping and electrode cabling from the remediation area back to the ERH equipment compound.

The basis of the ERH remediation primary design was to accelerate the volatilization and steam stripping of CVOCs by heating the subsurface to the point where water transitions into steam. Heat was generated in the subsurface by passing an electrical current through the soil between subsurface electrodes throughout the ERH remediation volume. A vapor recovery and VOC removal system connected to a network of vapor recovery screens collected the resulting steam and VOC vapors generated by the ERH system.

Figure 2. Cable Corridor

TRS SOR15 ShortV ProjEx 031815 acf

A total of 82 electrodes were used to deliver electrical energy from the PCUs to the remediation volume. Seventy-six of the electrodes were vibratory-driven sheet piles (Figure 3). The remaining six electrodes were dual-bored electrodes. Using a dual-bored electrode design provided a less disruptive installation adjacent to the building to preserve its structural integrity.

The vapor collection system where VOCs were recovered from the vapor stream by directing it, subsequent to removal of steam, through a Steam Regenerated Granular Activated Carbon (SRGAC) unit (Figure 4), followed by vapor polish through carbon.

The energy milestone was achieved on November 27, 2013. At the request of the Principals, ERH application continued for an additional 28 days to achieve even further reductions in CVOC concentrations in soil and groundwater. Extended ERH operations were complete on December 25, 2013. Vapor recovery operations (i.e. vapor recovery from the ERH remediation volume and collection of VOCs from recovered vapors with no power applied to the subsurface) continued for 14 days after completion of ERH application. The ERH system was completely shut down on January 8, 2014.

Project Results

Mass Removed TRS analyzed two metrics to estimate the quantity of mass destroyed or removed from the ERH remediation volume, influent vapor concentrations and liquid-phase VOCs generated from the SRGAC system. Ultimately, the vapor concentration data provided the most consistent data set for estimating mass destroyed or removed. Based on the evaluated data, TRS estimates that a minimum of 47,105 pounds of VOC mass was recovered or destroyed in situ via hydrolysis, during the ERH remediation. An estimated 43,490 pounds of the mass removed or destroyed in situ were CVOCs. The average VOC mass removal rate through the vapor recovery system was approximately 113 pounds per day. Although, the ERH system was designed and optimized for CVOC remediation, the ERH system also provided a significant reduction in the other VOCs encountered during the remediation. Figure 5 is a graphic depiction of the compounds removed, including non-chlorinated VOCs such as xylenes and ethylbenzene.

1,1-DCE

Hydrolyzed TCA

VC1,1-DCA

cis-1,2-DCE

1,1,1-TCA1,2-DCAHeptane

TCE

1,4-Dioxane

Toluene PCEEthylbenzene

m,p-xylenes o-xylenes

Figure 3. Sheet Pile Electrode Installation Figure 4. Steam Regenerated Granular Activated Carbon (SRGAC)

Figure 5. Mass Removed by Compound

TRS SOR15 ShortV ProjEx 031815 acf

Groundwater CVOC Contaminant Reductions After the first groundwater sampling event in late August 2013 (approximately two months after the start of ERH operations), CVOC concentrations in groundwater met the objective of a 90 percent reduction in total CVOC concentrations, reaching a reduction of 98.5 percent. After the final sampling event in November 2013, analytical data indicates a 99.5 percent reduction in total CVOC concentrations in groundwater. Soil CVOC Contaminant Reductions Prior to ERH remediation, the remediation volume average CVOC contaminant concentration in soil was 708 mg/kg. The maximum CVOC concentration reported in baseline soil data was 12,103 mg/kg (SB-4 at 28 ft bgs). CVOC concentration in the soil of the suspected source area averaged 4,075 mg/kg. The maximum CVOC concentration post-ERH was 7.9 mg/kg. The average CVOC concentration in the remediation volume post-ERH was 0.83mg/kg, which equates to an average CVOC reduction of 99.93 percent. In the suspected source area, the average post-ERH CVOC concentration was 1.9 mg/kg, which equates to a 99.95 percent reduction of CVOC concentrations in this area. Pre- and post-ERH results in source area are shown in Figure 6. CVOC reductions will continue to occur within the remediation volume until the residual heat in the subsurface returns to natural conditions, one year or more from the date of this report.

Summary

TRS Project Manager/Senior Project Manager: Miles Stumbaugh/Greg Knight

TRS Project Engineer Michelle Nanista

Site Geology and Hydrology: Sand, clay and clay lenses, silt and gravel in 2 zones divided by a silt/clay aquitard. Groundwater: variable, 6 ft bgs average

Treatment Area Size, Volume, and Depth: 36,740 ft2; 34,018 yd3; surface to approx. 30 ft bgs

Beginning Contaminant Concentrations: Average CVOCs in soil in ERH treatment area: 4,075 mg/kg Average CVOCs in groundwater in ERH treatment area: 158,143 µg/l

Remedial Goal(s): Reduce CVOC concentration sin soil and groundwater by 90%

Actual Cleanup Achieved: Groundwater: CVOC reduction of 99.5% Soil: CVOC reduction, average 99.93%; source area 99.95% Removed 47,105 pounds of contaminant mass, including non-chlorinated VOCs

Period of Performance: June – December 2013; 186 operation days

Contract Terms: Standard Fixed Price Remediation (SFPR)

TRS Contact Information Mr. David Fleming, (425) 396-4266, dfleming@thermalrs.com, www.thermalrs.com

Figure 6. Soil Results

TRS SOR15 ShortV ProjEx 031815 acf

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

SB-1 SB-4 SB-5 SB-6 SB-12 SB-13 SB-14 SB-15

0.0000 0.0426 0.0000 7.2950 7.9200 0.0000 0.0317 0.0038

4,035.8

12,103.0

8.9

11,686.0

36.3

4,708.0

17.7 11.8

mg/

kg

Sample Location

Post-ERH

Pre-ERH