Past Projects

Carlyss, LA

(2015-Present)

Target contaminants: benzene, chlorobenzene, toluene, diphenyl ether, phenol; 1,1,2-TCA; 1,2-DCA; PCE; TCE; Chloroform; cis-1,2-DCE; trans-1,2-DCE; 1,1-DCE; vinyl chloride; 1,1-DCA; and lower concentrations of several other VOC constituents in shallow soils and groundwater

Depth: Approximately 25 – 115 ft bgs

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Project Objective:
Evaluate the efficacy of a TreeMediation® system for providing hydraulic control and remediation of groundwater impacted with high concentrations of VOCs including Dense Non-Aqueous Liquid (DNAPL) impacts. Target treatment depths ranged from 25 to 115 ft bgs.
Implementation:
The TreeMediation implementation consisted of 90 TreeWell® units installed in three different parts of the site over three separate installations. The first installation was performed in December 2015 and consisted of 18 TreeWell units installed on a 20 by 20 foot spacing to approximately 25 ft bgs. A set of hackberry, Russian olive, live oak, and black locust trees were planted in each of the 18 TreeWell units during the first phase of TreeMediation installation. During the 2015 installation the 18 TreeWell units were divided into three subsets with one subset filled with engineered soil with organic matter amendments, a second subset filled with a mixture of soil and zero-valent iron (ZVI), and a third subset filled with a mixture of soil, ZVI, and Daramend® (a proprietary electron donor). In 2017 phase II of the installation commenced with the installation of 18 close-bottomed straw TreeWell units in a second portion of the site. The straw TreeWell units were divided into zones with targeted depths ranging from 44-115 ft bgs. One set of shallow Phase II units were filled with a mixture of soil and ZVI, and the second set of shallow Phase II units and set of deep units were filled with engineered soil with organic matter amendments. Phase III of the installation commenced in 2019 with the addition of 51 straw TreeWell units in a third part of the site. The 2019 units were planted with 35 willow and 25 black locust trees in March 2020. Throughout the installations, a monitoring network consisting of piezometers and camera tubes was constructed to monitor the effectiveness of the TreeWell system at enhancing biodegradation of the COCs in shallow soils and groundwater and exert hydraulic influence on shallow groundwater.
Results to Date:
For the post installation (2016-2021) growing seasons, tree growth and viability were observed to be “very good” for the entire TreeWell unit plantation with no notable indications of plant stress observed. The height and canopy of most of the trees in the TreeWell units continues to increase. To date, no signs of VOC phytotoxicity have been observed.
VOC Concentrations:
Results of vertical profiling of total VOC and chloride concentrations in groundwater within TreeWell units indicate total VOC concentrations decrease as water flows upwards within all TreeWell units installed at the site. Although units with ZVI or ZVI and Daramend® in the backfill exhibited slightly more attenuation than units with only loam soil in the backfill, complete degradation of VOCs was still observed in units without ZVI or Daramend®. Additionally, the groundwater data indicate the straw TreeWell units are functioning as designed by transmitting groundwater from as deep as 115 ft bgs into the TreeWell units, facilitating remediation of VOCs within the TreeWell units.

Danville, IL

(2014-Present)

Target contaminant: carbon tetrachloride

Depth: shallow soils and groundwater (0 to approximately 25 ft bgs)

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Project Objective:
To evaluate the efficacy of a TreeWell® system for treating dissolved-phased contamination and providing hydraulic control of the plume as an alternative to a groundwater pump and treat system.
Implementation:
The site is a former refrigerant manufacturing and packaging facility with carbon tetrachloride impacts in the subsurface. Historically a groundwater pump and treat system was operated as an interim remedy to control the groundwater plume and mitigate potential off-site migration. The initial system implementation consisted of 51 TreeWell units (alternating willow and poplar trees) installed on a 20 by 20 foot spacing to approximately 25 ft bgs. Based on the success of the first installation, a second installation of 28 additional TreeWell units (aspen and Norway spruce) was installed two years later to provide hydraulic capture of the contaminant plume. The secondary planting was performed based on the results of predictive computer modeling of groundwater flow that indicated TreeWell units would be capable of providing complete hydraulic control of the contaminant plume. To monitor system performance and effectiveness, groundwater monitoring wells were installed upgradient, mid-gradient, and downgradient relative to the TreeWell units. Selected wells were equipped with data logging pressure transducers to facilitate continuous monitoring of groundwater elevations. Data loggers were added to select monitoring well locations in the 2016 planting areas during spring 2017. The monitoring wells have also been sampled on a quarterly basis for analysis of VOCs.
Results to Date:
Since installation, overall tree health has been very good with robust growth since planting. Of the trees planted at the site only one tree exhibiting signs of disease and needed replacement. One additional tree was also damaged by deer rub but was pruned and successfully regrew.
Concentrations of 1,4-dioxane in groundwater demonstrate that the shallow groundwater plume shifts towards the TreeWell system during the growing season, indicating that the system is providing hydraulic control of the shallow aquifer and is drawing the shallow zone groundwater towards the trees. Groundwater elevation data since installation of the system indicate an upward vertical gradient between the shallow and deep groundwater zones. Therefore, the TreeWell system is effectively controlling further migration of 1,4 dioxane impacts from the shallow zone to the underlying deep zone.

Ellender Ferry, LA

(2017-Present)

Target contaminants: 1,1,2-TCA, 1,1-DCA, 1,1-DCE, 1,2-DCE, chloroform, chlorobenzene, cis-1,2-DCE, trans-1,2-DCE, TCE, vinyl chloride and lower concentrations of several other VOC constituents.

Depth: shallow soils and groundwater, approximately 20 - 90 ft bgs

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Project Objective:
To evaluate the efficacy of phytoremediation at reducing high concentrations of VOCs in groundwater and providing hydraulic control in shallow (20-25 ft bgs) and deep (90 ft bgs) zones.
Implementation:
The TreeMediation® implementation consisted of 27 TreeWell® units at a site in Ellender Ferry, Louisiana. In October 2017, 22 traditional open-bottomed TreeWell units were installed to 20 ft bgs, and five close-bottomed straw TreeWell units were installed to 90 ft bgs. Black locust trees were planted in the open-bottomed units and cabbage palms were planted in the straw units. Select TreeWell units were completed above grade in four-foot diameter, four-foot-tall pre-cast concrete manhole sections to protect against potential hurricane storm surge. A monitoring network consisting of piezometers and camera tubes were installed to observe the effectiveness of the TreeWell system at reducing COC concentrations and providing hydraulic control of groundwater.
Results to Date:
Over the growing seasons since installation (2018-2021), tree growth and viability were observed to be “very good” for the entire TreeWell unit plantation. The tree health assessments do not indicate any indicators of substantial plant stress. The height and canopy of most of the trees in the TreeWell units have continued to increase.
COC Concentrations:
Groundwater monitoring data indicate the backfill media are effectively reducing VOC concentrations as designed. Additionally, the straw wells are functioning as designed and are effectively transmitting target groundwater from the deep zone into the TreeWell units. Overall, the TreeWell units are performing as designed.

New Stanton, PA

(2014-Present)

Target contaminants: trichloroethene and its degradation products

Depth: Up to 45 ft bgs

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Project Objective:
A Phyto-Integrated® combined-remedies approach that utilized targeted soil excavations, enhanced in-situ bioremediation, and TreeMediation® technologies to reduce concentrations of VOCs in on-site groundwater and mitigate the migration of VOC-impacted groundwater off-site and to downgradient off-site surface water.
Implementation:
A pilot TreeMediation study was installed in September 2014 consisting of 52 TreeWell® units planted with a mix of willow and hybrid poplar trees. The TreeWell units were planted to target migration pathways in shallow surface soils (up to 10 ft bgs) and shallow fractured shale bedrock (up to 45 ft bgs). Based on the success of the pilot study, a full-scale implementation consisting of 166 additional TreeWell units was installed in October 2016 in three plots downgradient from the pilot area. The full-scale installation included 62 shallow units installed to approximately 17 ft bgs, and 112 units installed to depths ranging from approximately 25 to 45 ft bgs. The full-scale installation was planted with alternations of willows, London plane trees, black locusts, and hybrid poplars. Additionally, due to shallow groundwater encountered in a portion of the planting area, 16 of the shallow units were installed as modified TreeWell units; installed to depths of 4.5-7 ft bgs, and planted with red twig dogwoods. Root camera tubes were installed in three of the units to monitor the root systems of each species of tree. Six piezometers and two nested piezometers were installed within individual TreeWell units to equip transducers, with the purpose of monitoring water levels.
Results to Date:
The growing seasons to date for the pilot study include 2014-2021, and the growing seasons for the three downgradient plots include 2017-2021. Tree growth and viability were observed to be “very good” for the entire TreeWell unit plantation. The tree health assessments do not show any indicators of plant stress. The height and canopy of most of the trees in the TreeWell units have continued to increase. Trees are displaying vigorous growth and, based on hydrogeologic monitoring data, are providing hydraulic capture. Preliminary hydrogeologic data suggest they are on track to perform as designed.

Enid, OK

(2012-Present)

Target contaminants: benzene; as well as lower concentrations of several other petroleum hydrocarbons dissolved in groundwater

Depth: shallow soils and groundwater (0 to approximately 25 ft bgs)

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Project Objective:
To evaluate the potential for utilizing phytoremediation to prevent further off-site migration of VOCs by achieving groundwater hydraulic control.
Implementation:
The TreeMediation® implementation consisted of five on-site plots of TreeWell® units which were installed in March 2012 at approximately 20 ft bgs. Three weeks later, alternations of hybrid poplar, sycamore, and willow trees were planted in each unit. Root camera tubes were installed in the main plot, background plot, and hydrocarbon north plot to monitor the root systems of each species of tree. Fifteen piezometers and monitoring wells were installed within individual TreeWell units in the area immediately upgradient and downgradient of the plot, 12 of which were equipped with pressure transducers to measure water levels.
Results to Date:
In the 2012 growing season, herbicide was sprayed in the field where the TreeWell plots were located, resulting in mortality of a large number of trees, willows in particular being negatively affected. In the following years, tree growth and viability were observed to be “very good” for the entire TreeWell unit plantation. The tree health assessments do not show any significant indicators of plant stress. The height and canopy of most of the trees in the TreeWell units have continued to increase. Trees are displaying vigorous growth and, based on hydrogeologic monitoring data, are providing hydraulic capture. Preliminary hydrogeologic data suggest they are on track to perform as designed.

Moss Point, MS

(2017-2019)

Target contaminants: the select primary contaminants of concern (COCs) in the groundwater at the site include [1,2-Dichloroethane, 2-Chloroethanol, 1,4-Dioxane, bis(2-Chloroethoxy)methane, and bis(2-Chloroethyl)ether].

Depth: Approximately 25 ft bgs

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Project Objective:
To evaluate the potential for utilizing phytoremediation to contain the potential off-site flow of COC contaminants in the groundwater through hydraulic control and containment of groundwater (or leachate).
Implementation:
The TreeMediation® implementation consisted of 65 TreeWell® units which were installed in November 2017 at approximately 25 feet below ground surface. Root camera tubes were installed in four of the units to monitor the root systems of each species of tree. Eight piezometers were installed within individual TreeWell units. In January 2018, willow trees were planted in each unit.
Results to Date:
In the first growing season (2018), tree growth and viability were observed to be “very good” for the entire TreeWell unit plantation. In 2019 site maintenance included over-application of herbicide, which resulted in mortality of most trees. Replanting of trees is planned for spring of 2022.

Shelby, NC

(2015-Present)

Target contaminant: Chlorinated VOCs and 1,4-dioxane

Depth: shallow soils and groundwater (0 to approximately 25 ft bgs)

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Project Objective:
To evaluate the efficacy of phytoremediation to control the subsurface migration of CVOCs in groundwater.
Implementation:
The TreeWell® implementation consisted of 150 TreeWell units which were installed in 20 by 20 foot spacing at approximately 25 ft bgs in May 2015. Alternations of willow, London plane, and tulip poplar trees were planted in each unit. Nine piezometers were installed for the utilization of transducers to capture water levels, and eight camera tubes were installed to capture root development data. In spring of 2016, 42 willow and poplar trees were planted to replace the 30% of poplar and London planes which had suffered mortality in the fall of 2015. In the spring of 2017, an additional 10 willow and 6 river birch trees were planted to replace the remainder of the tulip poplars.
Results to Date:
Aside from the 2015 mortality of the poplars (caused by improper storage and a delay in planting due to excessive rainfall), tree growth and viability were observed to be “very good” for the remainder of the TreeWell study. In 2017, an infestation of imported willow leaf beetles consumed most of the leaves of the willow trees, which has not affected the overall growth or vitality. However, any reduction of leaf area or early leaf drop has the potential to reduce the hydraulic function of the system. Due to early spring 2019 detection of the Willow Leaf Beetle, followed by a timely insecticide treatment, there was no additional beetle damage to the Willow trees. The height and canopy of most of the trees in the TreeWell units have continued to increase. Trees are displaying vigorous growth and, based on hydrogeologic monitoring data, are providing hydraulic capture. Preliminary hydrogeologic data suggest they are on track to perform as designed.

Clover, SC

(2017-Present)

Target contaminants: Chlorobenzene; as well as lower concentrations of several other VOC constituents

Depth: shallow soils and groundwater (0 to approximately 40 ft bgs)

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Project Objective:
To evaluate the potential for utilizing phytoremediation in highly contaminated areas and evaluate the remedial and hydraulic impact of the TreeWell® system on chlorobenzene-impacted groundwater and soil.
Implementation:
The TreeMediation® implementation consisted of 19 TreeWell units which were installed in 20 by 20 foot spacing at approximately 30 ft bgs. Subsurface conditions consisted of saprolite soil and weathered rock. One month after the February 2017 installation, alternations of willow and poplar trees were planted in each unit, excluding the four units located in the burn pit area, where both poplar and black locust trees were planted in each unit. Black locusts were planted as a contingency for the possibility of elevated salinity resulting from degradation of the chlorobenzene. A monitoring network consisting of shallow and deep (nested) piezometers, pressure transducers, conductivity sensors, weather stations, and camera tubes were installed to monitor the effectiveness of the TreeWell system to enhance biodegradation of the COC in shallow soils and groundwater and exert hydraulic influence on shallow groundwater.
Results to Date:
For the 2017-2021 growing seasons, tree growth and viability were observed to be “very good” for the entire TreeWell unit plantation. The tree health assessments do not show any significant indicators of plant stress. The height and canopy of most of the trees in the TreeWell units have continued to increase. Overall, the TreeWell units are performing as designed. Chemical data collected from groundwater monitoring wells and from piezometers located in TreeWell units show significant levels of VOCs, particularly chlorobenzene. Data from monitoring wells TW-24, TW-20 and TW-10 show relatively high (25,000 to 50,000 µg/L) concentrations of chlorobenzene. Nested piezometers in TreeWell units 13 and 14 are adjacent to these three monitoring wells and show chlorobenzene concentrations ranging from 230 to 3,200 µg/L suggesting movement of VOCs into TreeWell units with higher concentration typically in the upper water column.

Terneuzen, Netherlands

(2012-Present)

Target contaminants: 1,4-dioxane

Depth: Up to approximately 8 meters bgs (~26 ft bgs)

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Project Objective:
Hydraulic control of a 1,4-dioxane groundwater plume to prevent off-site migration of the plume.
Implementation:
The site historically operated as a chemical plant with operations including the production of 1,4- dioxane. Subsequent releases from the chemical plant resulted in concentrations of 1,4-dioxane in groundwater as high as 31,000 mg/l in the source area and up to 5,900 mg/l in the groundwater plume. To provide hydraulic containment of the plume 240 poplar trees were planted in a combination of shallow and deep TreeWell® units downgradient of a source area at the former chemical plant, which produced 1,4-dioxane. The “deep” zone (4.5 to 8 mbgs) TreeWell units were constructed as straw TreeWell units to focus groundwater extraction within a more permeable sand unit underlying a laterally continuous low permeability layer.
Results to Date:
Overall, the health and growth of the trees have been satisfactory with most trees showing fair or better health. Although some trees have shown relatively poor health, these trees are distributed throughout the installation area and there does not appear to be a correlation of tree health with COC concentrations in groundwater. As with tree health, overall tree growth has also been satisfactory with a clear positive correlation with tree health. Overall, the trees have continued to grow and increase in uptake capacity, thereby increasing treatment effectiveness.
Concentrations of 1,4-dioxane in groundwater demonstrate the shallow groundwater plume shifts towards the TreeWell system during the growing season, indicating that the system is providing hydraulic control of the shallow aquifer and is drawing the shallow zone groundwater towards the trees. Groundwater elevation data since installation of the TreeWell system indicate an upward vertical gradient between the shallow and deep groundwater zones. Therefore, the system is effectively controlling further migration of 1,4-dioxane impacts from the shallow zone to the underlying deep zone. Monitoring of 1,4-dioxane evapotranspiration indicate that the mass of 1,4-dioxane transpired by the trees is substantially lower than anticipated given the water uptake rates of the trees and the concentrations of 1,4-dioxane in the groundwater. Results of a microbiological characterization study show evidence of 1,4-dioxane biodegradation in the root zone of the trees, which may account for the mass difference in the expected vs. measured 1,4-dioxane transpiration.

Past Projects

Carlyss, LA

Danville, IL

Ellender Ferry, LA

New Stanton, PA

Enid, OK

Moss Point, MS

Shelby, NC

Clover, SC

Terneuzen, Netherlands

Past Partners and Clients