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Subsurface Investigation, Large Underground Storage Tank Closures, Large Remedial Soil Excavation, A

Location: Gloversville, NY

Project Duration: 6 months

Impact Characterization: Release of various petroleum products, resulting in an adverse impact to the subsurface soil, groundwater, and surface water regimes, including the presence of light non-aqueous phase liquid. Sensitive receptors included the adjacent Cayadutta Creek.

Technical Overview: Light non-aqueous phase liquid (LNAPL), petroleum impacted soil and groundwater were encountered during the reconstruction of an adjacent City bridge. Following the discovery PES initiated its site involvement by deploying both harbor boom and absorbent boom within the Cayadutta Creek to capture LNAPL leaching from the creek bank and prevent additional down-stream impacts.

Following the deployment of the boom and assisting the City with management of the impacted soil generated during the bridge construction, PES initiated a subsurface investigation into the environmental quality of the site’s soil and groundwater through the installation of a network of soil borings and monitoring wells. All drilling aspects were performed utilizing PES’s limited access direct-push soil sampling system.

The subsurface investigation identified a large area with significant concentrations of volatile and semi-volatile organic contamination within the soil and groundwater as well as the presence of several underground storage tanks (USTs) ranging in capacity from 15,000 – 20,000 gallons. In addition to the absorbed and dissolved phase impacts an LNAPL plume greater than one foot thick was identified at a monitoring location immediately adjacent to Cayadutta Creek.

An evaluation of the investigative data and possible remedial alternatives was conducted and presented to the NYS DEC. The implementation of a contaminated soil excavation, UST closure, and groundwater treatment program was selected. The remedial action required:

  • The design, installation, and removal of a sheet pile and grout wall along a 250-foot section of the Cayadutta Creek.

  • Redirection, removal, and replacement of approximately 150 feet of 24-inch diameter Gloversville sanitary sewer utility.

  • Closure of five 20,000-gallon USTs and one 15,000-gallon UST.

  • Excavation of impacted soil and backfill to depths in excess of twenty feet below grade.

  • Transportation and disposal of all impacted materials to a permitted facility.

  • Construction dewatering to depths greater than 10 feet below the average static water table elevation and treatment of groundwater.

  • Restoration and installation of erosion control measures along affected portion of Cayadutta Creek bank.

In order to maximize the volume of soil available to the excavation process, a sheet pile wall was designed to boarder a 250-foot section of the property that was adjacent to the Cayadutta Creek. Prior to completing the design several geotechnical soil borings and groundwater monitoring wells were installed by Aquifer Drilling and Testing, Inc. under the supervision of PES geologic staff utilizing hollow stem auger drilling and standard split spoon soil sampling methodologies. The purpose of the borings and wells were to provide site-specific geotechnical data to be utilized in the final sheet pile wall design specifications.

The sheet pile wall was designed to provide a groundwater/surface water cutoff and to provide soil/creek bank integrity along the creek side of the wall. This engineered control was necessary due to the fact that contaminated soil was targeted for removal from the site (property) side of the sheeting wall to depths of ten to fifteen feet below the base of Cayadutta Creek. In order to achieve this goal the sheets were designed to be set into a layer of glacial till and terminated at a depth of approximately thirty-two feet below grade.

At the midpoint of the sheet pile wall a transition to a grout slurry wall was designed to provide a groundwater/surface water cutoff at the location where a 100-year old 24-inch diameter clay pipe sanitary sewer main, one of two mains servicing the City of Gloversville, transected the property and intersected the Cayadutta Creek.

The remedial action phase of the project began in the spring of 2006 with the installation of the sheet pile and grout slurry walls. The initial phase of the sheet pile wall installation involved utilizing a 60-ton crawler crane, approximately eighty-five 50-foot lengths of AZ-36 tongue and groove steel sheeting, and a vibratory hammer to reach the glacial till interface. Subsequent to reaching the till the vibratory hammer was removed from the crane and substituted with a 50-foot diesel hammer in order to drive the sheets and penetrate the stiff glacial till to the designed depth.

Remote vibration monitoring of several nearby structures was performed on a continuous basis during the installation of the sheet-pile wall to ensure structural integrity of the neighboring buildings.

Following completion of the sheet pile wall the grout slurry wall was installed in the vicinity of the sewer main to complete the groundwater cutoff wall. A chemical grout was injected at several points around the sewer main enveloping the utility and sealing the pore space within the soil thus creating a subsurface wall capable of retaining the Cayadutta Creek from the scheduled excavation.

The final preparations for the remedial action involved the redirection of the flow of the sanitary sewer main that transected the property. The redirection was necessary in order to allow for the removal of the utility and the impacted soil in its vicinity. An inflatable test plug was installed within an up gradient sewer manhole to block the flow through the subject sewer main and direct all of the City’s sanitary service through a secondary main. A temporary alternative sanitary sewer system was designed and installed for the Nethaway’s site building for the duration of the remedial action.

Following completion of the preparations, PES initiated the remedial action with the closure and removal of the 15,000-gallon and five 20,000-gallon USTs. Several technical challenges were present during the tank removal process as five of the six USTs were filled with concrete. The entire top half of each of the five 30-foot long and 10-foot diameter steel USTs was removed in order to excavate the concrete from the tanks and allow for the removal of the USTs and the impacted soil below. The construction, contents, and condition of each UST and the environmental quality of the soil and groundwater in the vicinity of each tank was recorded during the closure process in order to determine and document the possible source(s) of the impacts observed across the site.

Subsequent to the closure of the USTs, PES personnel initiated the remedial soil excavation phase of the project utilizing cut and fill excavation methodology. Regular field screening utilizing a photo-ionization detector (PID) and headspace methods during the excavation process allowed the uncontaminated material to be removed and temporarily staged alongside the excavation prior to the excavation of impacted soil. The uncontaminated material was then reapplied later as borrowed backfill material. During the contaminated soil excavation process soil samples were continuously collected and field screened utilizing a PID and headspace field screening methods for excavation direction and documentation purposes. Documentation of the end result of the excavation on the environmental quality of the site’s soil was provided through the regular collection of soil samples for laboratory analysis. Resulting data was used to confirm compliance with NYS DEC regulations.

Due to the large volume of soil requiring removal, the considerable area that the excavation would impact, and the depth to which excavation was anticipated, the excavation was performed utilizing two excavators and one backhoe. The primary excavator was equipped and tasked for the sole purpose of excavation and loading of contaminated material for transport and disposal. The secondary excavator had a dual purpose; backfilling and excavating. The secondary excavator was equipped with a vibratory plate compactor attachment and dozer blade for backfill and compaction purposes. In addition, the second excavator was supplied with an excavating bucket for the purpose of assisting the primary machine with the excavation process at depths, which exceeded one machine’s capability, and with removal of the USTs. Finally, the backhoe was tasked with providing onsite soil transportation services and assisting the secondary excavator with backfilling operations.

While performing the contaminated soil excavation project approximately 150 feet of the City of Gloversville’s 24-inch diameter clay pipe sanitary sewer main that transected the Nethaway’s property and an associated brick manhole was surveyed for location and pitch, removed, and plugged to allow for the complete excavation of the impacted soil in its vicinity and future replacement.

Large scale construction dewatering during the excavation project was performed on a daily basis. Construction dewatering involved transferring groundwater that infiltrated into the excavation utilizing high volume (3-inch and 6-inch diameter) trash pumps across the Cayadutta Creek via a temporary bridge to a manifold set of 21,000-gallon fractionation tanks staged on an adjacent property. Following settling of the sediment within the tanks, the water was transferred from the tanks through a high volume groundwater treatment system comprised of bag filtration and four vessels each filled with 1,000-pounds of granular activated carbon (GAC). The system was designed to absorb the contaminants of concern from the impacted groundwater prior to being discharged to the Cayadutta Creek. PES performed daily monitoring and regular sampling of the groundwater treatment system was performed to ensure that all treated groundwater was discharged in compliance with the standards set forth by the NYS DEC.

More than 12,500 tons of petroleum impacted material was encountered during the excavation process and loaded directly into Part 360 permitted dump trailers or temporarily staged on a layer of polyethylene sheeting prior to being loaded and delivered to the Fulton County Landfill in Johnstown, NY for re-use as daily cover.

Upon completing the remedial soil excavation project the section of the sanitary sewer main and manhole that was removed during the excavation was replaced and upgraded to 24” diameter HDPE with a pre-cast concrete manhole. The sanitary sewer service to the newly installed section of the main for the Nethaway’s site building and main flow for the City of Gloversville was re-established. The sheet-pile wall was also dismantled and sheets removed utilizing the same equipment as during the installation to allow the groundwater gradient to return natural static conditions. Additionally, a site-specific rip-rap stone slope and curb plan was designed and enacted in order ensure that the areas of the creek bank and property adjacent to the top of the creek bank which were disturbed by the excavation are protected from future erosion.

Site Progression Specifics: PES performed the majority of the work including all the investigation, remedial action planning, and the remedial action. In instances where specialized services were required such as the design and installation of the sheet pile wall and sanitary sewer system, subcontractors were solicited and overseen by PES as the general contractor.

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