Fixed price remediation of tetrachloroethene in soil & groundwater

Seattle, Washington

Project Summary

TRS Group, Inc. (TRS) designed, installed and operated an electrical resistance heating (ERH) source area remediation project at a former commercial laundry and dry cleaning facility in the rapidly growing area of South Lake Union in Seattle, WA. The scope of the remediation was to treat tetrachloroethene (PCE) as dense non-aqueous phase liquid (DNAPL) underlying, and adjacent to, the area of the site where underground storage tanks (USTs) were located. The site is being purchased by a biotech real estate investment trust (REIT) for future development. The consultant evaluated soil vapor extraction, chemical oxidation, excavation and disposal, enhanced reductive dechlorination (ERD) and ERH for site remediation. The final cleanup strategy included using ERH in the source area to reduce PCE in soil to concentrations below the hazardous waste threshold allowing the owner to dispose of the cleaned soil from the excavation for a future underground parking garage. The ERH remediation reduced PCE concentrations in soil and groundwater by approximately 98% which saved the owner approximately $10M in landfill disposal fees. The PCE concentrations in groundwater during the ERH remediation were reduced low enough that the client is considering the use of ERD as a groundwater polish. The project required execution on a very fast schedule with portions of install and characterization occurring simultaneously. System install commenced April 2013 and operations were completed December 2013. TRS contracted with Frontier Environmental Management to operate the ERH system until either the remedial objective (1,000 µg/L PCE in groundwater), or the design energy of 6,640,000 kilowatt hour (kWh) had been applied to the treatment volume, whichever occurred first. The overall ERH treatment volume of the site was determined using the 1,000 µg/L PCE contour in groundwater. The site was sub-divided into two treatment regions. The overall treatment area was approximately 37,500 sq. ft. and within that treatment region, a “hot spot” was defined as an area of approximately 7,500 sq. ft. The hot spot was centered on and somewhat hydrologically down gradient of the former UST locations. The hot spot was treated from a depth of 4 to 40 feet below grade surface (ft bgs). The remainder of the treatment area was treated from a depth of 10 to 40 ft bgs.

Background

The Site currently is an unoccupied city block, located at 700 Dexter Avenue North, in Seattle, Washington. The site was formerly occupied by a commercial laundry facility, a parking garage, and an automotive repair facility. The total area of the site was approximately 44,000 square feet. All structures were demolished prior to installation and operation of the ERH remediation system. This resulted in an approximately 50 foot high wall from the treatment area ground surface up to the level of Dexter Avenue North. The eastern and western sides of the site sloped down to the east from the elevation of Dexter Avenue North to the street level at 8th Street. The outer building structural walls bordering Dexter Avenue North, Roy Street and Valley Street were left in place and supported with steel shoring beams; this was done to ensure that the streets did not collapse into the void left by removal of the buildings (see Figure 1).

Figure 1. Site Post-Demolition

DEX29 ProjEx 110314

Site Characteristics & Design Parameters

In the immediate Site vicinity, surficial deposits have been mapped as anthropogenic fill, Vashon-age recessional sand, glacial till, ice-contact deposits, advance sand deposits, pre-Fraser Olympia beds, and pre-Fraser undifferentiated glacial and nonglacial deposits (Troost et al. 2005). The Vashon recessional outwash deposits in the vicinity of the Site are generally discontinuous and consist of loose to very dense layered sand and gravel, which are generally well sorted (poorly graded). Layers of silty sand and silt are less common. The Vashon recessional lacustrine deposits consist of layered silt and clay, which range in plasticity from low to high and may contain localized intervals of sand or peat. The recessional lacustrine deposits may grade into recessional outwash deposits (Troost et al. 2005). Site subsurface conditions:

• Silt in vadose and saturated zones • Till encountered toward Dexter Ave • Unconsolidated soils encountered towards 8th Ave • Groundwater depth 1 – 10 ft bgs • Total Organic Carbon – 0.25%

Site characterization was conducted by the client’s consultant, Sound Earth Strategies (SES), prior to, during and after ERH operations. Figure 2 shows the source zone area targeted by ERH with the remaining outlying areas of contaminantion and downgradient plume targeted for the bio polish post ERH.

Figure 2. Site Investigation (courtesy SES)

DEX29 ProjEx 110314 ©2014- TRS Group®, Inc. All rights reserved.

System Construction/Operations

The ERH system was designed and installed by TRS to remediate the VOCs present in soil and groundwater beneath the site. The ERH treatment area measured approximately 37,500 square feet in surface area. A total of 165 electrodes with co-located vapor recovery (VR) wells were installed. 40 dual element electrodes were installed in the “hot spot” area with treatment intervals of 4 to 21 feet below grade for the upper interval, and 25 to 40 feet below grade for the lower interval. The remaining 125 electrodes were installed in the remaining treatment area with a heating interval of 10 to 40 feet below grade. The resulting treatment volume was approximately 43,000 cubic yards. Subsurface temperatures within the treatment volume were measured at 16 temperature monitoring points (TMPs) containing thermocouples vertically spaced at 5, 10 ,15 20, 25, 30 ,35 and 40 ft bgs at each location. Construction of the below grade components of the system began on April 29, 2013 and was completed on June 6, 2013. Installation of above grade components and equipment began on June 6, 2013 and were completed on July 31, 2013 as shown in Figure 3.The city of Seattle required a third party inspection of all electrical components and connections prior to issuing an authorization to start operations. The third party inspection, along with system startup testing, and addressing the inspection findings occurred between July 31, 2013 and August 19, 2013. Figure 3 displays the site during ERH operations. TRS began continuous operation of the ERH system on August 19, 2013. On December 13, 2013 the system was de-energized after a total of 6,706,000 kilowatt hours (kWh) of energy was applied to the treatment region, and confirmatory groundwater sample results indicated that the remedial objectives had been achieved. The ERH system was in operation for 116 days.

Figure 3. ERH Site Operations and Aerial View

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Results

All existing monitoring wells at the Site were removed prior to ERH installation. New wells were installed at the ERH TMP locations and were not sampled prior to ERH operations since percent removal was not a remedial objective. During active heating groundwater elevations were reduced to the point where samples could not be collected from all of wells due to either absence of water or the depth to water exceeding the pump capabilities. The concentration of PCE in confirmatory groundwater samples collected from two performance monitoring wells following ERH was reduced to within 10% of the 1000 µg/l goal. TRS estimates approximately 12,373 pounds of total VOCs, (of which approximately 12,113 pounds was PCE) were removed from the subsurface during the remediation. TRS successfully achieved the contracted remedial goals. Figure 4 displays the PCE in groundwater analytical results for the two monitoring wells which contained groundwater.

Figure 4. PCE in groundwater within ERH treatment area.

Summary

Site Geology and Hydrology Sand, silt and clay with minor amounts of gravel, groundwater 1 to 10 ft bgs

Treatment Area Size, Volume, and Depth 37,500 ft2; 43,000 yd3; 4 to 40 ft bgs (variable)

Beginning Maximum Contaminant Concentrations PCE groundwater: 140,000 µg/l

Remedial Goal(s) Groundwater: 1000 µg/l

Remedial Goal Achieved PCE reduced to within 10% of goal in wells that contained water. Follow on bioremediation deemed appropriate

Period of Performance August 19, 2013 – December 13, 2013 (116 days)

Contract Terms Standard Fixed Price Remediation

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

0

10000

20000

30000

40000

50000

60000

70000

MW-F13 MW-G12

Before ERH After ERH

µg/l

DEX29 ProjEx 110314 ©2014- TRS Group®, Inc. All rights reserved.