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Ithaca Court Street project description

Project Description

Following are the steps most often required by the New York State Department of Environmental Conservation (NYSDEC) in the investigation and remediation of a former MGP site: 

Remedial Investigation/Feasibility Study

Interim Remedial Measures

Record of Decision

Remedial Design and Construction

 

The Ithaca Court Street MGP Site consists of two operable units; operable unit 1 (OU-1) and operable unit 2 (OU-2). 

  • OU-1 consists of the former site property, extending to the sidewalks, and a wooden duct which transported coal tar approximately one-half mile from the site to the Cayuga Inlet Coal Tar Site to the west. 
  • OU-2 consists of any remnants of the wooden duct which may remain west of Meadow Street and all coal tar which has migrated from the site and the wooden duct, along with any associated soil, groundwater and soil gas contamination. 

Discussion of the investigation of the wooden duct is included in the remedial investigation summary for OU-2, which the wooden duct was once considered part of. 

For administrative reasons, the wooden duct is now considered part of OU-1. OU-1 is in the Remedial Design and Construction phase of the process.  OU-2 is in the Remedial Investigation/Feasibility Study phase of the process.

 Remedial Investigation Summary (OU-1):

  • Contaminants detected in soil and groundwater are consistent with those expected for a former MGP Site (primarily BTEX – benzene, toluene, ethyl benzene, and xylenes; and PAHs – polycyclic aromatic hydrocarbons).
  • Coal tar non-aqueous phase liquid (NAPL) was observed to be present in and/or in the immediate vicinity of all former MGP structures, including the wooden duct, one below-grade gas holder, two above-grade gas holders, two tar wells, a tar separator, purification facilities, and the plant building.
  • From the structures identified in the previous bullet, coal tar migrated vertically downward until encountering a less permeable silty clay layer which appears to have acted as a geologic barrier (i.e. confining unit) to further vertical movement of the coal tar. The coal tar appears to have then migrated to the north and the west via gravity flow along the surface of the silty clay layer.
  • Since the entire site is covered with buildings or pavement (at the time of the remedial investigation), exposure to surface soils was not a concern.
  • Subsurface soil in direct contact with and in the vicinity of former MGP structures or related coal tar deposits has been impacted by PAHs or BTEX.
  • Groundwater in the vicinity of coal tar deposits and contaminated subsurface soils has also been impacted by PAHs and BTEX. As with most former MGP sites, groundwater contamination was found only in close proximity to the coal tar, and significant groundwater impacts appear to be limited to an area within 100 feet of coal tar deposits.
  • Soil gas collected from beneath the on-site Markles Flat building contained BTEX at levels ranging from 95 to 1109 micrograms/cubic meter of air.
  • Indoor air samples collected from on-site buildings did not detect any chemicals associated with MGP related contamination except for a detection of toluene in a warehouse building which stored many products that contained toluene.

Interim Remedial Measures (OU-1):

An interim remedial measure was performed at the site in March 2000, prior to the RI/FS process. The goal of the IRM was to remove coal tar and contaminated soil and water associated with two below-ground tar wells in close proximity to the Markles Flat building. The tar wells were uncovered and the liquid contents removed.

A scrubber and a tar separator were also encountered during this operation, and these structures were removed.  A wooden duct was found attached to the tar separator.  This wooden duct was removed to the point where it entered the plant, at which point it was sealed with non-shrink grout.  A trench was excavated to the south of the southern tar well in an attempt to locate the wooden duct between this site and the Cayuga Inlet.  No evidence of this duct was encountered in the trench.

Through review of records from the City of Ithaca DPW, the suspected location of the wooden duct was refined, and later investigated as part of the OU-2 remedial investigation.  A remedial design was performed to remove the wooden duct between Meadow Street and North Plain Street.  The remedial design was completed in three phases from October 26, 2003 to September 9, 2005.

 

Record of Decision (OU-1):

The OU-1 Record of Decision (ROD), issued by the NYSDEC in September 2003, describes the remedial goals and specific remedial requirements for the site to achieve those goals.  For the Ithaca Court Street MGP site, those goals, as summarized in the ROD document, are to eliminate or reduce to the extent practicable:

 

  • The presence of NAPL and MGP related contaminates as the sources of soil, groundwater and soil vapor contamination;
  • Migration of NAPL and MGP related contaminants that would result in soil, groundwater or soil vapor contamination;
  • The release of contaminants from NAPL in on-site soil into groundwater that results in the exceedances of groundwater quality standards;
  • The potential for ingestion of groundwater with contaminant levels exceeding drinking water standards;
  • The potential for ingestion/direct contact with contaminated soil;
  • Impacts to biota from ingestion/direct contact with soil;
  • The release of contaminants from subsurface soil under buildings into indoor air through soil vapor;
  • The inhalation of or exposure to contaminants volatilizing from soil;

Furthermore, the remediation goals for the site include attaining to the extent practicable:

  •  Ambient groundwater quality standards;
  • Recommended soil cleanup objectives in TAGM 4046.

 

The elements of the selected remedy as listed in the ROD document are:

  • Excavation of MGP impacted soil, waste and structures as described below. All excavated material, with the exception of surface soils, will be treated or disposed of off-site. Surface soil will either be treated/disposed of off-site, or, if analytical results show that this soil meets the 500 ppm total PAH remedial objective, it may be used as fill in the excavation below eight feet.

The extent of the excavation will be determined as follows:

  • The entire site will be excavated to a depth of two feet;
  • soils containing individual PAHs above the objectives in TAGM 4046, or which are visibly impacted by coal tar, will be excavated to a depth of eight  feet below ground surface (bgs);
  • soils below 8 feet bgs will be excavated if they contain either total PAHs over 500 ppm or are visibly impacted by coal tar.
  • all former MGP structures will be excavated, including piping.
  • The West Court Street wooden duct, along with impacted soil within 2.5 feet of the duct, will be removed between the plant site and Meadow Street.  All excavated materials will be disposed of or treated at an appropriately permitted facility.  Impacted soils beyond this extent will be mapped and sampled, and will be addressed as part of OU-2, along with any remaining portions of the duct west of Meadow Street.  Approximately 2,500 cubic yards of soil with visual impacts are estimated to be removed in this excavation.
  • All excavation of coal tar impacted materials will be accomplished using appropriate vapor management systems to prevent human exposure to vapors and to minimize nuisance odors.  A Sprung (or equivalent) structure with associated air handling/treatment facilities will be used at the plant site.  The effectiveness of emission controls will be demonstrated with appropriate air monitoring.  A negative pressure air handling and treatment system, including a shroud to direct air from the work zone into the air treatment system would be used during the removal of the wooden duct.  This vapor management system has been field tested at the Binghamton Court Street MGP site demonstrating that it is effective at minimizing odors and meeting the requirements of the Community Air Monitoring Program.
  • The excavation will be backfilled and the site will be covered with a minimum of 2 feet of material complying with NYSDEC TAGM 4046 recommended soil cleanup objectives, including 6-inches of topsoil which will be graded and seeded. Sections of the site may also be paved. All excavation backfill from 2-8 feet will also comply with NYSDEC TAGM 4046 recommended soil cleanup objectives. In the event that portions of the silty-clay confining layer require removal, backfill materials of similar permeability will be placed such that the impermeable barrier remains between the two aquifers after remediation is complete.
  • Following the completion of the site restoration, institutional controls will be implemented to ensure the integrity of the remedy and to prevent contact with the remaining site related contamination.  Development of the site will not be restricted provided that the institutional controls are in place and enforced.  These institutional controls will include:
      1. A site management plan which will address residual contaminated soils.  The plan will require soil characterization and, where applicable, disposal/reuse in accordance with NYSDEC regulations.  The plan will also identify worker and community safety concerns associated with any planned subsurface work, and will provide for the development of a health and safety plan to address these concerns.  
      2. Restrictions to prevent the use of groundwater as a source of potable or process water without necessary water quality treatment, as determined by the Tompkins County Department of Health. 
      3. A requirement that the potential intrusion of soil gas vapors, due to the continued presence of contamination beyond the limits of this operable unit, will be appropriately addressed for any buildings constructed on the site.  This requirement could be modified based on the remedy for OU-2.
      4. The property owner will complete and submit to the NYSDEC an annual certification that the institutional controls put in place, pursuant to the Record of Decision, are still in place, have not been altered, and are still effective.  This certification will continue until the NYSDEC notifies the property owner in writing that this certification is no longer needed.

Monitoring of groundwater contamination at this site will be addressed by OU-2.  Post-remediation monitoring of the groundwater at the site will be initiated as a component of the OU-2 Remedial Investigation, and will be expected to continue as a part of the OU-2 remedy.

 

Remedial Action Design:

  • The remediation will consist of removing and disposing approximately 70,000 tons of coal tar contaminated soil and below grade structures within the limits of the MGP site that are the source of coal tar.
  • A Community Air Monitoring Program will be in place throughout the project to confirm that the community is not exposed to unacceptable levels of air-borne contaminates that might be attributable to the project.
  • The contractor will install a watertight sheet piling wall around the entire excavation area.  In addition sheet piling will be installed dividing the MGP site into six major areas.  Each major area has been sized to fit within the footprint of the temporary fabric structure.  Each major area will have sheet piling wall installed to divide major area in two sections.
  • A temporary fabric structure will be positioned over each proposed excavation area so that it completely encloses the area.  The temporary fabric structure will be moved 6 times to complete the excavations in the major cells.
  • The temporary fabric structure will have a ventilation system to pull air out of the structure and through a filter system prior to release into the atmosphere.
  • Each major area will be dewatered during excavation of each respective area.  All contaminated soil will be treated on-site in the waste water treatment system.  Water will be sampled prior to discharge to the City of Ithaca sanitary sewer for treatment at City of Ithaca wastewater treatment plant.
  • Excavated soils will be transported for off-site disposal or treatment at facilities permitted to accept of treat such materials.
  • Project is estimated to be completed the second quarter of 2010.