Former Harrison MGP Site Remediation

Significant Project Features

• In-situ soil stabilization via deep soil mixing (auger) and shallow mixing with excavator.
• Pre-excavate 275,000 tons of soil/debris (concrete, timbers) to a depth of 7-ft. to create platform for ISS work.
• Clear obstructions down to depths of 25-ft. BGS to facilitate ISS work.
• ISS of 105,000 CY via deep auger mixing down to maximum depth of 45-ft. BGS.
• ISS of 315,000 CY via excavator down to a max depth of 40-ft. BGS.
• Process soils with reagent to comply with T+D facility requirements.
• Control odors and vapors using 300,000 gallons of RUSMAR odor suppressant foam (short and long term) and 60,000 gallons of SLSUPER odor neutralizing agent.
• Demolish existing site buildings and perform Hazardous Abatement.
• Dewatering for treatment via 200 GPM WWTP.
• Install 2,200 LF Hydraulic Barrier Wall (HBW) to depths down to 100-ft. BGS using DeWind One Passing Trencher.
• Jet grout termination at HBW interface/existing gas lines.
• Install utility corridor consisting of 16-in. and 36-in. gas lines.
• Restore 330,000 SF with 130,000 tons of clean import fill.

Project Gallery

History & Location Details

The Harrison Former MGP Site is located in Harrison, New Jersey. The site encompasses 32 acres. The site is bounded on the east by a roadway; the west by an Amtrak and PATH rail line; the south by the Passaic River; and the north by property owned by PATH. The site was acquired by PSEG and its predecessors from 1884 through 1924 and used for various operations including oil and manufactured gas storage. The MGP plant was constructed in 1924 and operated as a base load plant until 1963 when it was converted to a peak shaving status facility until retired from service in 1987. In 1992 the MGP was decommissioned. Buildings and structures were removed to grade. MGP foundations, pipes, and other remnants remained below grade. In 1998, PSEG began remedial work to define and address the extent of soil and groundwater contamination. Concurrent with ongoing studies and investigations, PSEG performed a variety of IRMs in 2004, 2009, 2010, 2012 and 2017. The site is currently used by PSEG for various operations. The site is planned for redevelopment. Sevenson’s contract, Phase 1 Gas Plant Remediation, was awarded on a competitive proposal basis. This project requires Sevenson to clear subsurface obstructions; pre-excavate soils and remove debris; perform ISS; install a hydraulic barrier wall; install a utility corridor; demolish site structures; and perform restoration activities.

Project Description

Mobilization and Site Preparation

Upon receipt of the Notice to Proceed Sevenson initiated mobilization and site preparation activities. Over 54 pieces of company-owned equipment necessary to execute the scope of work was mobilized in less than one month.

Site preparation required Sevenson to:

• Perform existing conditions topographic survey, and GPR survey.
• Mobilize temporary office trailer(s) and personnel decontamination facilities.
• Establish temporary utilities, such as power, water, and sanitary facilities.
• Implement health & safety measures including PSE&G’s site-specific training.
• Demarcation of work zones, mark-out and protection of subsurface/overhead utilities, and initiation of breathing zone monitoring.
• Install temporary fence, barricades, and traffic controls.
• Setup truck wash/decon pads.
• Setup truck weigh scale.
• Setup stormwater/decon water tanks.
• Install construction entrances, staging areas, and access roads.
• Install erosion controls.
• Establish dust/odor suppression controls.

Building Demolition

Site structures required demolition prior to initiating remediation. Sevenson self-performed building demolition activities. A licensed subcontractor performed abatement of asbestos and hazardous building materials. Utilities were deactivated and removed prior to initiating demolition. This phase of the project included:

• Conduct Safety Evaluations.
• Install Temporary Barriers to Limit Access.
• Perform Asbestos Abatement.
• Collect and Package Hazardous Materials (light, ballasts, etc.).
• Conduct a Hazardous Waste Clearance Survey.
• Demolish Site Structures.
• Segregate and Size Materials.
• Recycle and Load out Debris for Disposal.

Demolition began at one end of each building and proceeded lengthwise. For each building, the roofing material was removed first and lowered, and then the exterior walls followed by structural steel. Concrete slabs and foundations which remained from earlier demolition work were removed using a hoe ram, concrete muncher, and universal processor.

Excavation Support

Two areas of the site required excavation support prior to initiating excavation. One was along a stretch of Frank E. Rogers Blvd; the other along the Amtrak-Path Right of Way. A soil mix was installed for support.  Vibration monitoring controls were used to establish safe vibration levels for structures and utilities within a 200-ft radius if the installations.

Excavation and Debris Removal

Excavation and debris removal was required prior to initiating ISS operations. Sevenson sequenced excavation to direct load soil from each the cell between 5-ft to 6.5-ft bgs to prepare the ISS platform. Underground obstructions were removed concurrent with excavation. ISS crews mobilized to the excavation cell as the excavation and debris removal progressed to set up and begin in-situ stabilization. Sevenson implemented both auger mixing and bucket mixing techniques. A total of 275,000 tons of soil and debris were removed. Equipment used included conventional excavators and excavators with a hoe ram, grapple, shear and similar attachments. Exclusion zones with signage and safety fencing were established to alert personnel of the need for appropriate PPE. Sevenson provided an off-site disposal coordinator to ensure all work was performed to local, state, and federal requirements. The offsite disposal coordinator worked closely with Sevenson’s onsite Project Manager to ensure that excavation operations adhered to transportation schedules and all regulatory requirements. Backfill and compaction of the excavation areas was done daily. Placement of clean fill was done using dedicated clean equipment to prevent the potential for cross contamination. Groundwater collection sumps were installed, as necessary, to dewater existing or infiltration water. Excavation dewatering, construction water and decon water was collected and stored onsite for pretreatment and off-site disposal.

Odor and Vapor Control

Odor, vapor and dust control during execution of the work was critical to maintain an uninterrupted flow of work. PSE&G’s performance objective for odor and vapor control was stringent. Sevenson was required to control, eliminate, or mask any odors during active work. This included during excavation, soil management, ISS, barrier wall installation, backfilling operations, and load out for disposal.

Sevenson employed the following dust and vapor control methods:

• Install and operate a perimeter drip system prior to performance of intrusive work.
• Setup, staff, test and operate Rusmar and Biosolve odor control systems prior to performance of any intrusive work.
• Minimize the footprint of remediation areas. Removing clean, or overburden soils “just in advance” of remediation activities assured that any releases of odors were minimized to the maximum extent possible.
• Apply odor control foam continuously to the active excavations.
• During inactive periods (e.g. overnight or on weekends) long duration foam was applied.
• Applied short duration foam to the auger to ISS rotary mixing.
• Applied short duration foam to swell material.
• Applied short duration foam to the excavator bucket during loading of MGP soil and prior to tarping soil, and/or removed from the excavation
• Backfill approved remediation areas with clean fill as soon as possible. Dust was controlled by using a water truck over the footprint of the site.

In-situ Stabilization

Sevenson self-performed both ISS bucket mixing and ISS auger mixing of MGP impacted material. The conventional excavator bucket soil mixing method was used within areas of the site that were less than 27-ft to 28.5-ft below pre-existing ground surface. A slurry mixture of cement, slag, and water was blended into the impacted soil to achieve the target treatment parameters. The ISS bucket mix area was laid-out into a series of rectangular cells approximately 25-feet wide by 15-feet long (defined by the effective reach of the mixing excavator).  Adjacent cells were overlapped to ensure complete treatment of the target soil. A total of 145,000 CY of soils was stabilized by bucket mixing.

For ISS the primary soil mixing rig used was a Bauer BG45 track mounted rotary drilling rig that was modified to accept large diameter mixing tools with the capability to pump fluid through the Kelly bar and mixing tool. The ISS rig utilized a 10-foot diameter mixing tool. This auger and rig combination was capable to produce a well-mixed homogeneous soil mix material. The ISS rig was equipped with a mast inclination system with automatic mast adjustment to maintain vertical alignment. This assured that the soil mixed columns were installed within strict vertical tolerances. The rig is fitted with a computerized drill parameter monitoring system capable of monitoring:

• Verticality
• Penetration Depth
• Penetration Rate and Withdrawal Speed
• Rotation Rate
• Drilling Resistance
• Injection Rate and Pressure

Grout was prepared in a batch plant on a continuous basis. Columns were located by Sevenson’s engineer using a GPS based system. During ISS swell generated was contained in an area adjacent to the drill rig in a 4-ft deep pit. A total of 230,000 CY of soil was solidified through auger mixing. This equated to 3200 columns drilled to depths of up to 45-ft BGS.

Hydraulic Barrier Wall Installation

Sevenson installed a HBW around the perimeter of the M&R Station to contain clean soils which did not require remediation. The HBW was installed utilizing the DeWind One Pass Trenching system. This technology incorporates the in-situ mixing of or other in-place soils with dry bentonite (or additional reagents) and water to create the barrier wall. An independent lab conducted treatability to develop the reagent mix. The HBW trench alignment was surveyed and staked.  Sevenson pre-trenched along the alignment to remove obstructions. To reduce trench spoils generated during installation, crews excavated a key trench 2.5 ft. wide by 3 ft. deep. Reagents were placed in the trench. Additional reagents were injected through an auger delivery system as necessary. The depth of the trench ranged from 82 ft to 98 ft BGS. Crews managed all spoils from the operation.  Sevenson’s QC Manager performed compliance inspections of the bentonite and HBW installation to ensure mixing met the design specifications. During installation, mix water was fed through the water line into the cutting chain as necessary to maintain a slump of 6 – 7 inches. The One-Pass trencher homogenized the native soils and dry bentonite to the specified depths. Barrier wall depths were maintained using a laser guidance system mounted on the mixing boom and controlled by the Trench operator. A secondary measurement of the boom length was also documented to ensure the wall depth at each station or elevation change. The HBW measured 2140 LF and approx. 179,805 VSF.

36-inch RCP Storm Sewer Replacement

Sevenson installed a new 36-inch storm sewer. Sevenson’s installation of the new storm sewer required:

• Excavation of the area immediately west of the existing 52-inch storm sewer to the elevation of the ISS platform.
• Performed ISS (by auger method) of the area of the proposed new clean utility corridor.
• Installed a temporary 36-inch storm sewer piping within the proposed clean utility corridor footprint.
• Removed the existing 52-inch storm sewer piping.
• Installed a cementitious earthen support wall.
• Performed ISS in the area beneath new 36-inch RCP storm sewer.
• Installed new 36-inch storm sewer and 12-inch sanitary sewer.
• Backfilled clean utility corridor sanitary sewer.

Water Treatment

Sevenson construct a 200-GPM on-site WWTP to pre-treat to PVSC requirements.  The plant treated all water encountered during remediation. Sevenson’s WWTP included the following components:

• Influent equalization ModuTank or frac tanks
• Pre-treatment bag filtration
• Organoclay
• Carbon filtration
• Post-treatment bag filtration

Sevenson initially pumped, stored and treated all water encountered during field work onsite. Water was tested in batches per PVSC requirements. Once it was determined that Sevenson met treatment standards continuous discharge was allowed. Sevenson’s dewatering system consisted of sumps.

Site Restoration

Upon completion of remediation, Sevenson restored the site to pre-construction conditions. Site restoration included:

• Placement of crushed stone and perform any final surface grading to the limits identified on the drawings.
• Construction of a clean utility corridor.
• Installation of a new 36-in storm sewer and 12-in sanitary sewer.
• Installation of a M&R cap.
• Decontaminated and demobilized from the site all steel piling and bracing systems, and all heavy equipment.
• Removed and dispose construction entrances, decontamination stations, and laydown areas.
• Removed temporary fencing and install permanent fencing.
• Dismantled and removed from the site all temporary facilities and utilities, temporary water storage tanks, office trailers, temporary power panels, and site signage.

Challenges

Working in an active an active PSE&G Gas Facility required re-sequencing of work to accommodate gas operations. Working in close proximity to highly populated residential and commercial area required controlling odors, vapors, and noise. Waste characterization sampling and facility approval required the site to be 60% pre-characterized prior to mobilization. Deep excavation and obstruction removal below 10-ft. created a punctured meadow mat. The magnitude of

subsurface obstructions was greater than anticipated, with large concrete footings and 60-in. diameter piping. This required the mobilization of a PC1250 and Liebherr 976. Unstable work platform for the 400,000 lbs. drill rig. Sizing of grout plants required a larger auger to increase output. Auger layout and deep soil mixing required depth greater than 20-ft. and evaluation long runs to optimize production and debris laden areas.

Innovations

Sevenson primed for deep soil mixing via auger mixing. Sevenson purchased two new BG 45 Bauer Rigs and three CMS MAT Batch Plants. The Work Platform was enhanced. Traditionally, the industry standard for progressing auger mixing is to retreat from auger mixed holes and work off of undisturbed stable ground. Due to logistical limitations, Sevenson developed a plan that allowed stabilization of material upfront by advancing timber mats over previously mixed columns to create a stabilized work platform. This allowed production to be expedited and minimized downtime.

V-bottom Frost Buckets were introduced to facilitate removal of hard soils and obstructions as well as to maximize productions for bucket mixing. Sevenson modified sticks to maximize depths of bucket mixing and prevent damage to equipment during mixing, and added reinforcement to struts to drill bits to mitigate damage during deep auger mixing. Insitu soil rendering was required and Portland slurry was introduced from batch plants to stabilize/render soils to be shipped offsite. This method helped to mitigate dust and increased reaction time to expedite offsite disposal. Better control of amendment reagents for cost reduction. Transferred high-dollar exotic/haz material to ISS monolith to reduce disposal cost to client. Treated portions of exotic/haz material with MAECTITE™ to reduce T+D cost to client.

Sevenson was granted approval to perform ISS from higher mixing platform to reduce T+D cost for client and maximize revenue of ISS work. Utilized swell to construct mixing bins for bucket/auger mixing in lieu of clean/native fill.