Groundwater Control, Inc. had extensive experience which is now part of Southeast Trenching Technologies, LLC. Listed below are examples of some of the projects completed by GCI. Please feel free to contact us to discuss any of these in detail.

Highway Groundwater Underdrain System Eastern Transportation Corridor Project Irvine, CA

Groundwater Control, Inc. (GCI) was contracted to install a highway groundwater underdrain system as part of the Eastern Transportation Corridor Project. The system consisted of approximately 30,000 linear feet of a trenched gravity collection system. The collection system trenches depth ranged from eighteen feet to nine feet and was equipped with a six inch diameter corrugated HDPE collection line. The collection line was perforated with nominal 1/8 inch slots. The trench was backfilled with a washed coarse-grained silica sand to provide an efficient dewatering interface with the surrounding formation.

The project was originally designed for construction of the underdrain system utilizing conventional techniques, to be constructed at the same time as the early stages of the highway road base construction. However, due to above normal El Nino rainfall, the site needed to be dewatered prior to starting the earthwork. As a result, GCI installed the dewatering system prior to the excavation of the highway subgrade.

Interceptor Trench Installation NWIRP Dallas Dallas, TX

Groundwater Control, Inc. (GCI) installed a series of groundwater interceptor trenches for the remediation of a chromium plume emanating from past operations at the Naval Weapons Industrial Reproduction Plant (NWIRP) located outside Dallas, Texas.

There were a total of six trenches constructed, each equipped with its own individual six inch diameter HDPE collection sump. The depth of the trenches varied from ten feet deep up to twenty-six feet deep depending upon the lithologic conditions. Normally, this range of installation depths would require two one-step trenching machines. However, in order to minimize mobilization costs associated with two machines, GCI benched down as much as four feet in order to accommodate the depth requirements of the project with one machine. A 22 foot maximum depth installation machine was utilized for the project

The design called for the installation to provide complete interception coverage for approximately 1,250 linear feet. This was accomplished using the six trench segments by overlapping each segment by fifteen feet, with an offset distance of approximately five feet. In all, 1,309 linear feet of collection trench was constructed, with the longest run being 327 linear feet and the shortest being 158 linear feet. A four-inch diameter perforated HDPE collection pipe was utilized with a gravel-sized pack material for the trench construction. All of the trenches were installed using a nominal eighteen inch wide trench utilizing the one-step installation approach. The gravel was placed from approximately six inches below the base elevation of the four inch diameter collection pipe, to the top of the water table.

Collection System Installation Lang Superfund Site Browns Mills, NJ

Groundwater Control, Inc. (GCI) constructed a collection system designed by R.E. Wright Environmental, Inc. The horizontal collection trenches were installed to supplement an existing collection system. The horizontal collection trenches for this project were only five feet deep. However, due to the high water table, contamination and flowing sands, a conventional installation approach was not cost effective.

Three trenches were installed which were all tied into a single sump. Once each run was approximately fifteen feet away from the collection sump, the runs were aligned to be parallel to each other. The three trenches were 225 feet, 200 feet and 150 feet in length. They were all constructed out of six inch diameter perforated collection pipe covered with a geo-fabric filter sock and installed on a 0.5 percent grade. Three-eighths inch washed gravel was utilized to pack the trenches to land surface. A single twenty-four inch diameter HDPE collection sump was installed to eight feet below land surface.

Groundwater Capture System McConnel Air Force Base Witchita, KS

Groundwater Control, Inc. (GCI) worked on the McConnel Air Force Base project. The project was designed to capture a down-gradient movement of groundwater contaminant plume associated with a closed disposal site (LF-11).

Two overlapping trenches, each with a length of 200 linear feet were installed between twenty-two and twenty-four feet deep. The horizontal collection line was a six inch diameter HDPE perforated pipe. The base of the two trenches were constructed approximately one foot into the top of an underlying bedrock unit composed of a mixture of gypsum and shell. The trenches were packed with a high hydraulic conductivity washed sand and each run was equipped with a twelve inch diameter HDPE sump. The lower portions of the sumps were perforated with 0.01 inch slots for additional collection capacity.

Recovery Trench Installation Chemical Waste Management Corpus Christi, TX

The Corpus Christi Project was constructed for OHM Remediation Services by Groundwater Control, Inc. (GCI). The installation depth of the project was thirty-one to thirty-eight feet below land surface. The installation was done with a twenty-four foot deep one-step trencher, the design depths were achieved with the aid of a seven to fourteen foot deep bench. Installation using a bench was possible on the site due to the presence of a thick vadose or unsaturated zone above the water table and the presence of an unobstructed installation corridor. The bench was cut approximately 18 feet wide to allow for the operation of the trencher and graded to match the

installation depth of the collection line. This installation bench also served to contain the spoils from the trenching operation, which were left on the top of the bench after the installation and backfilled in place.

The collection line consisted of a six inch diameter perforated HDPE pipe. A total length of 900 linear feet was installed and backfilled with a 3/8 inch diameter washed pea gravel. The collection line was attached to a 12 inch PVC collection sump.

The purpose of the system was to intercept a contaminant plume up-gradient to a river in order to prevent the contaminant from entering the surface water body.

Gypsum Stacks Trench Drains Faustina Plant – Agrico Chemical Company St. James, LA

Groundwater Control, Inc. (GCI) constructed five 18 inch wide gravity trench drains for the Faustina Plant in St. James, Louisiana. They were installed to control dike seepage and thus increase stability of the dikes using the one-step trenching process. The gravity trench drains discharge into a perimeter ditch and were installed in 21′ wide levees between ponds prior to their conversion to gypsum stacks. The dikes were constructed out of gypsum placed in lifts. Hardness of the gypsum can vary significantly depending upon the degree of dehydration.

Approximately, 6,000 linear feet of six inch HDPE slotted corrugated collection line with polypropylene filter fabric wrap was installed at a nominal depth of eighteen feet below the top of the dike. The entire collection line trench was packed with non-reactive silica washed concrete sand pack. The pack was installed from six inches below the collection line to a minimum of four feet above the top of the pipe. Additionally, approximately 4,200 linear feet of six inch diameter solid HDPE piping was installed with the one-step trencher to act as a conveyance line to tie in the collection piping with the perimeter ditch.

Gypsum Stack Closure Project Agrico Chemical Company Uncle Sam, LA

Groundwater Control, Inc. (GCI) completed one of its largest projects to date for Agrico Chemical Company in Louisiana. GCI installed approximate 61,000 linear feet of an eighteen inch wide packed collection drain trench using the one-step process to a depth of eighteen to nineteen feet below the working platform. The majority of the installation used a six inch diameter HDPE collection line, however, drain line as large as twelve inches in diameter was installed. The entire installation was completed in seventy-seven days of actual construction. This equates to almost 800 feet per day of drain line installation in gypsum of varying hardness.

The purpose of the project was to provide a multi-level seepage collection system for the closure of a gypsum disposal area, referred to in the industry as a “gyp-stack”. All of the drain lines were placed on the design grade to facilitate gravity drainage to a perimeter ditch system and were equipped with intermediate HDPE manholes. All of the lines were packed with a non-reactive washed concrete sand from six inches below the collection pipe to a minimum of four feet above the pipe overt.

Seepage Relief Drain CF Industries Gypsum Stack Expansion Plant City, FL

Groundwater Control, Inc. (GCI) installed approximately 6,500 linear feet in the construction of two groundwater collection trench segments. The collection trench was installed to depth of between eight and twelve feet below land surface with GCI’s one-step trencher system cutting a nominal eighteen inch wide trench. A six inch interior diameter HDPE collection line was installed simultaneously at the base of a four foot thick gravel layer. Two – 48 inch diameter concrete manholes were installed on either end of the collection system lines and access ports or clean-outs were installed on the interior ends of the runs. The clean-outs allow for future access to the collection system lines should maintenance to the lines be required.

Both collection lines were installed at the top of a well-defined clay unit in order to drain an overlying interbedded sand, silt and clay unit. The four foot thick gravel unit allows the collection system piping to effectively tap the interbedded lenses of higher hydraulic conductivity sand, thus allowing for an efficient dewatering of the overlying strata. CF Industries needs were to dewater the up-gradient perimeter of a new gypsum stack cell expansion to allow for the placement of a large HDPE liner system. The work was completed in twelve days, including the installation of the sumps.

Groundwater Collection System Risser Petroleum Co., Lake City, FL

Groundwater Control Inc. (GCI) installed three innovative multi-functional trenches that ranged in depth from four to sixteen feet along the down-gradient end of a petroleum plume that originated from several sources. Two of the trenches were constructed using GCI’s proprietary installation process that simultaneously installs an impermeable HDPE membrane on one side of the trench and a groundwater collection system on the other side. The lengths of the trenches ranged from 145 to 225 feet. The purpose of the collection system trenches was to capture a dissolved phase BTX plume for above-ground treatment purposes. The impermeable barrier was installed on the down-gradient side of the collection system portion of the two trenches in order to minimize the pumpage of uncontaminated groundwater into the collection system and to divert free product migration into a separate LNAPL collection system. The two impermeable barrier walls were constructed out of six foot wide, 80 mil HDPE panels that extended from the base of the trench to land surface. The HDPE panels have a hydraulic conductivity of 1×10^-13 cm/sec. The purpose of the panels was to block the flow of groundwater into the trench from the up-gradient side. All three of the trenches were completed with a groundwater collection system that consisted of six inch diameter sumps, four inch diameter collection piping and a full depth 3/4 inch gravel pack.

The groundwater collection trenches were selected for the remediation of the site based on their ability to obtain significant yields from the thin layer of unconsolidated low hydraulic conductivity strata. The system is currently operating at levels that exceed the design parameters.

Horizontal Recovery Well Lockheed Martin Missiles Complex Orlando, FL

Groundwater Control, Inc. (GCI) was contracted by Lockheed Martin to install a horizontal recovery well. The well was constructed for recovery of a DNAPL source plume using GCI’s one-pass trencher approach. The trenched approach for the construction of the horizontal recovery well was selected because of its ability to yield significant groundwater flow from low hydraulic conductivity formations. The site lithology is characterized by a relatively low yield sand/silt unit of less than 20 feet thick, which is underlain by a semi-confining clayey silt unit.

GCI installed a five hundred-foot long horizontal recovery well to a depth of 15 feet below land surface on the clean-out end of the well and 17 feet below land surface on the sump end. The well was installed after a twenty-foot wide by two-foot deep bench was prepared along the trench alignment. The purpose of the bench was to the contaminated soils generated as a result of the trenching operation. This allowed the contaminated trenching spoils to be left in the bench instead of having to be removed from the site. The well consisted of a collection sump constructed of 12 inch diameter HDPE connected to a 6 inch diameter corrugated HDPE collection screen. The trench was packed with 3/8 inch limestone gravel from approximately six inches below the base of the collection screen to approximately six feet above the top of the collection screen.

Groundwater Recovery System Project SCM Glidco, Inc. Jacksonville, FL

In 1995, Groundwater Control, Inc. (GCI) installed a groundwater collection system for the recovery of a on-site multi-phase contaminant plume underlying an industrial chemical facility. The facility is located adjacent a tidal tributary and one of the primary objectives of the project was to prevent migration of the contaminant plume into the surface water body. The other objective was to capture the contaminants for above ground treatment.

Woodward Clyde and Associates designed the collection system. It consists of five separate collection trenches that were installed using a six inch diameter perforated HDPE collection pipe tied into five – 60 inch diameter concrete manholes, which serve as collection sumps. The total length of the collection system was approximately 1,900 linear feet. The installation depth of the collection pipe was twenty-one feet for trench 2 and 5, nineteen feet for trench 4, sixteen for trench 3 and nine for trench 1. All of the trenches were constructed with a 1/4 to 1/2 inch diameter pea gravel backfill to increase the collection efficiency of the system and to draw in the LNAPL fraction of the plume.

Permeable Reactive and Impermeable Barrier Walls Industrial Site Northern Vermont

Groundwater Control, Inc. (GCI) working in conjunction with the project engineers, adapted the one-step trenching process to the installation of the largest in-situ funnel and gate treatment system. The purpose of the system was to provide passive treatment of a dissolved phase chlorinated solvent groundwater plume that was migrating toward property boundaries, and subsequently threatening an adjacent public park. The overall length of the funnel and gate system was approximately 1,600 linear ft. The depth of the system varied from eight feet to twenty-one feet below land.

The barrier wall portion of the project consisted of 1,150 linear ft. of 60 mil HDPE panels in five separate barriers with a total installed wall area of approximately 15,000 square feet. The panels are interconnected using watertight interlocking joints. The purposes of the barrier was to block groundwater flow through the surficial permeable sand and silt, and direct it to the in-situ flow-through treatment gates. The entire barrier wall was keyed into the clay unit a minimum of two feet. As part of the one-step installation process, the barrier wall trench was backfilled and sealed with a bentonite add-mix of 3 percent to the native material. The bentonite was mixed with the native strata by the trencher and returned to the trench after the barrier wall was pulled out of the delivery apparatus all in one step.

The gate portion of the funnel and gate system, was made up of permeable iron filings for in-situ

dechlorination of the contaminants. In all there were four permeable iron gates that varied in depth from approximately eight feet to twenty feet and from 64 feet to 169 feet in length. The gates were installed in a one step process, with a trencher pulling a iron delivery box behind the trencher. The greatest challenge of the project was to install the largest gate, which had a variable iron concentration with respect to depth. The lithology of the site was a coarsening upward sequence, with clay at the base, overlain by a silt sequence and finally a sand unit. Because of this coarsening upward sequence, the highest hydraulic conductivity strata occurred at the top, in the sand unit. The vast majority of the flow occurred in the upper sand unit, so the design allowed for the installation of the highest percentage of iron in the upper sand unit. The variable iron concentration with respect to depth was installed by making two parallel passes installing two parallel gates. The first one was approximately 14 inches wide with a depth of 14 feet, and the second pass was 30 inches wide with a depth of 8 feet. The two parallel gates were tied together with steel sheeting to prevent any groundwater flow from short circuiting the second gate. Approximately 750 tones of permeable iron was installed in 416 linear feet of iron walls. The project was completed within the original budget, despite the fact that 1998 provided the region with the highest annual rainfall total for the 117 years of record. The record rainfall did present a number of operational problems that would have brought most conventional installation contractors to a halt.

Groundwater Barrier Wall Koppers Texarkana Site Texarkana, TX

Groundwater Control, Inc. (GCI) installed 240 linear feet of 80 mil barrier wall to a depth of 16 feet below land surface. The wall was constructed out of interlocking HDPE panels with a width of six feet. Each panel is interlocked with the next using water proof joint system that incorporates a hydrophilic seal that swells upon hydration, thus locking the profiles together.

The barrier wall was constructed to block the migration of a LNAPL plume. The panels were installed using the one-step trencher method. Installation with the trencher allows for the panels to be joined inside of the installation boot that is pulled behind the trencher. The base of each of the HDPE panels was keyed into a underlying low hydraulic conductivity confining bed with the trencher. The key was sealed using a one foot thick cement-bentonite slurry. The purpose of the seal was to prevent the underflow of groundwater and contaminates from the up-gradient side.

GCI also installed two HDPE “boots”to facilitate for the penetration of utilities through the wall. GCI installed the wall in conjunction with Tetra Tech NUS of Houston, Texas.

Vertical Barrier Wall Installation Wisconsin Power and Light Company Fond Du Lac, WI

Groundwater Control, Inc. (GCI) installed three hundred linear feet of GundWall Vertical Barrier Panels to a depth of seventeen feet using a delivery system incorporated into a one-pass deep trencher system. The panels were constructed out of 80 mil HDPE and were five feet wide by fifteen feet long. The wall was approximately 4,500 square feet in size and was composed of sixty panels. The advantage of installing HDPE panels in this manner is that the trencher cuts the strata allowing the panel delivery system to install the panels in a protected manner when compared to a driven or vibratory installation directly in subsurface strata. The interlock profiles are connected inside of the evacuated delivery system boot before it is pulled from the boot and backfilled as the trencher and boot move forward. This is advantageous when compared to making these connections while having to simultaneously displace the strata. The purpose of the barrier system was to block contaminant plume from down-gradient movement. An up-gradient collection system was used in conjunction with the barrier wall.

Another advantage of the trencher installation of the panels for this project was to use the trencher to remove obstacles such as cobbles and boulders from the barrier wall alignment. Numerous cobbles and boulders were encountered during the installation that would have prohibited a vibratory installation process. The only way to have completed the project as vibratory installation, would have required the pre-trenching of the alignment to remove the obstructions, leaving behind fine grained unconsolidated strata.

Vertical Barrier Wall for LNAPL Containment DOD Site Pacific Island

Groundwater Control, Inc. (GCI), working in conjunction with a remedial contractor, installed a 500 foot HDPE vertical barrier wall on the down-gradient side of a horizontal collection system for the recovery of fuel oil. The horizontal collection system was installed after the installation of the barrier wall. The vertical barrier wall was composed of 80 mil thick HDPE constructed from interlocking watertight panels that were 4 feet wide. The panels were installed to an installation depth of approximately eighteen feet below land surface.

The installation working platform was limited by the steel sheet pile harbor bulkhead and upland facilities landward. The vibratory installation approach allowed the operation to take place in the limited work platform.

Groundwater Barrier Wall Koppers Texarkana Site Texarkana, TX

Groundwater Control, Inc. (GCI) installed 240 linear feet of 80 mil barrier wall to a depth of 16 feet below land surface. The wall was constructed out of interlocking HDPE panels with a width of six feet. Each panel is interlocked with the next using water proof joint system that incorporates a hydrophilic seal that swells upon hydration, thus locking the profiles together.

The barrier wall was constructed to block the migration of a LNAPL plume. The panels were installed using the one-step trencher method. Installation with the trencher allows for the panels to be joined inside of the installation boot that is pulled behind the trencher. The base of each of the HDPE panels was keyed into a underlying low hydraulic conductivity confining bed with the trencher. The key was sealed using a one foot thick cement-bentonite slurry. The purpose of the seal was to prevent the underflow of groundwater and contaminates from the up-gradient side.

GCI also installed two HDPE “boots” to facilitate for the penetration of utilities through the wall. GCI installed the wall in conjunction with Tetra Tech NUS of Houston, Texas.

In-situ Iron Filings Treatment Wall Industrial Manufacturing Site Manning, SC

Groundwater Control, Inc. (GCI) installed a 325 foot long by twenty-seven deep iron filings wall. The wall width is twelve inches wide and was composed of a mixture of iron filings and sand. This site is the first full-scale installation of an iron-sand mixture. GCI’s one-pass trenching technique was employed to deliver the mixture in a controlled environment. GCI’s patented trenching equipment was vital to the project’s success by providing a cost-effective method of installation. State-of -the art “smart systems” were used to ensure that the proportions of iron/sand and the delivery depths were maintained. The performance data is instrumental for future applications of this exciting passive in-situ technology.

The installation was accomplished utilizing a 24 feet deep one-pass trencher operating in a three foot deep bench. The bench not only served to allow a greater trench depth to be achieved, it also acted as a containment area for the displaced trench spoils. The trench spoils were left in the bench after the installation, thus eliminating the costly disposal of contaminated spoils

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