Consolidated Edison Company of New York, Inc., Hudson Avenue Generating Station
Posted on June 12, 2015
Client: Consolidated Edison Company of New York, Inc.
Project Type: Comprehensive Oil Spill Investigation/Remediation Program
Project Period: March 2004 - Ongoing
Project Cost: $2.1 Million
Work Elements Completed
Phased Remedial Investigation/Feasibility Study
Engineering Services During Remedial Construction
Analytical QA/QC Activities
Health and Safety Plan Development and/or Review
The services provided by D&B Engineers and Architects, P.C. in support of the Comprehensive Spill Management Plan for the Hudson Avenue Generating Station were completed under contract with Consolidated Edison Company of New York, Inc. (Con Edison) on budget and within the project schedule. When D&B undertook the project in 2003, there were a total of 45 “open” New York State Department of Environmental Conservation (NYSDEC) spills as defined by Article 12 of the New York State Navigation Law associated with the Station. Through D&B’s remedial efforts over the last 10 consecutive years, there remain only 3 “open” spills as of February 2010. In 2006, the firm was tasked by Con Edison with the design and implementation of several remediation systems in targeting the remaining “open” spills. As of February 2010, D&B continues to operate two remedial systems at the Hudson Avenue Generating Station as well as monitor 60 on-site monitoring wells on a monthly basis.
Site Description and Background
The Hudson Avenue Generating Station (the Station) was constructed in 1922 and is currently serving as a steam and peak capacity electric generating plant that is owned and operated by Con Edison. The 13-acre facility, located in the Vinegar Hill section of Brooklyn, New York and fronting on the East River, manages over 10 million gallons of petroleum storage capacity including No. 6 fuel oil, No. 2 fuel oil and kerosene. The Station supplies nearly 3 million pounds of steam an hour to Manhattan, as well as electric power for customers throughout Con Edison’s service area.
The majority of petroleum is stored within the on-site Tank Farm that is comprised of four 2.75 million gallon storage tanks. The four rectangular steel tanks are located side-by-side in an east-west alignment. Each tank is located within a reinforced concrete dike. There is an 8-foot wide sand-filled annular space between the ends of the tanks and the dike. The concrete walls are 25 feet high and extend an additional 17 feet below grade. The tanks rest on an 18-inch thick concrete pad. Note that although the tanks are located partially below grade, the top of the Tank Farm is approximately 25 feet higher than the surrounding area.
In 2003, Con Edison entered into an Order on Consent with the NYSDEC to address 45 “open” spills that had occurred at the facility since 1988. In response, Con Edison retained the services of D&B in 2003 to develop and implement a Comprehensive Spill Management Plan for the Station.
A preliminary investigation was completed by D&B to determine existing conditions of the site and to determine if the site posed a risk to human health and the environment. In addition, an assessment was made at this stage of the project as to the likely need for remedial action. The firm conducted a detailed review of the numerous reports and documents associated with prior environmental investigations and remediations that were completed at the Station prior to D&B’s involvement. D&B also reviewed facility drawings and site plans for the Station in order to understand how the Tank Farm was constructed and to identify potential routes for subsurface contaminant migration.
Based on the records review findings, the firm developed a preliminary investigation scope of work involving the inspection and redevelopment of the existing monitoring well network at the Station, along with undertaking a 7-day tidal study designed to determine groundwater flow patterns at the site.
Based on the completed tidal survey, it was determined that all site wells outside the Tank Farm experience some tidal influence. However, there is no tidal influence on water levels within the Tank Farm itself. Furthermore, the preliminary investigation revealed that water levels within the Tank Farm are significantly higher than water levels in the immediately surrounding area. There are also significant differences in the water levels among the four vaults of the Tank Farm. This data inferred that there exists a poor hydraulic communication between the Tank Farm and the surrounding area, as well as among the four tank vaults that comprise the Tank Farm.
Due to the greater hydraulic head within the Tank Farm, water from precipitation, as well as any No. 6 fuel oil which has collected within the Tank Farm, will tend to “seep” into the surrounding subsurface through weep holes, cracks/fissures and joints within the concrete walls, as well as where piping enters the Tank Farm. Evidence of this process includes a slow and steady drop in the water levels within the Tank Farm during dry periods, as well as the highly localized mounding of the water table immediately north of the northwest corner of the Tank Farm.
Phased Remedial Investigation/Feasibility Study
Scoping of the Remedial Investigation/Feasibility Study
A Comprehensive Site Investigation Work Plan was developed incorporating the findings of the preliminary field investigation in conjunction with the initial information review. The objectives of the site investigation program presented in the work plan included:
- Collect environmental data required to adequately assess the current nature and extent of petroleum and dielectric fluid (DEF) contamination and to assess the potential effectiveness of remedial technologies.
- Investigate “open” spills and determine the need for additional investigation and/or remediation.
- Identify the potential migration pathways of petroleum/DEF contamination from the point of discharge to soil, groundwater, underground utilities and surface water.
- Identify potential human and environmental exposure pathways associated with petroleum/DEF contamination.
- Site Characterization (Remedial Investigation)
- In order to meet the site investigation objectives, the following investigation activities were performed:
- Storm Water Sewer Assessment – This assessment included a television inspection and physical walkthrough of the site sewer system, and collection and analysis of sediment samples.
- Tank Farm Utility Clearance Test Pits – Excavation of eight test pits to the water table using a vacuum excavation or the “Guzzler” method to confirm the presence or absence of underground utilities entering the Tank Farm.
- Soil Borings and Subsurface Soil Sampling – Advanced 33 on-site soil borings, including 12 within the Tank Farm. Due to the dense network of underground utilities at the Station, a vacuum truck was utilized followed by a Hollow Stem Auger (HAS) drill rig in order to complete the majority of the borings and wells. However, due to the difficulty of utilizing a drill rig on top of the Tank Farm, the firm was able to install all 10 soil borings and monitoring wells in the Tank Farm using vacuum excavation technology. In addition, 65 subsurface soil samples were collected for laboratory analysis.
- Groundwater Monitoring Well Installation and Sampling – Installed and developed 18 on-site monitoring wells, including 10 within the Tank Farm, and ranging in depth from 15 to 30 feet below grade. D&B also completed baseline gauging and collection of groundwater or NAPL samples from all new wells for analysis.
- Groundwater Sampling of Existing Monitoring Wells – Completed the gauging and collection of groundwater or NAPL samples for analysis from 29 monitoring wells.
- Groundwater Monitoring – Monitoring of all site wells for free-product/NAPL.
- All utility clearance procedures necessary during the investigation were completed in accordance with Con Edison’s Utility Clearance Process for Intrusive Activities.
- All intrusive activities were accompanied by air monitoring for dust and volatiles utilizing a site-specific Community Air Monitoring Plan (CAMP).
- A qualitative human health and ecological exposure assessment was prepared by D&B and used as the basis for evaluating the need for remediation of the site. Of major interest were the proximity of site contamination to the East River and the implication of any potential natural resources damages.
A Site Investigation and Remedial Plan (SIRP) was prepared by D&B and reviewed by the NYSDEC. The report included descriptions and documentation of field activities; site setting; tabulated analytical results by environmental medium and area of concern; identification of standards, criteria and guidelines (SCGs) for comparison to analytical results; findings and conclusions by environmental medium and contaminants of concern; assessment of the potential risk to human health and the environment based on identified contaminants of concern.
Key findings of the SIRP include:
- The fill unit, found to be 15 to 25 feet thick on-site, exhibited the vast majority of the observed petroleum/DEF contamination.
- No. 6 fuel oil impacted soil, often at saturated conditions, was present in the interstitial space throughout the soil column between the northern walls of each tank and the concrete dike wall. Existing and newly installed monitoring wells within this area of the Tank Farm exhibited measureable free phase NAPL.
- Seepage of No. 6 fuel oil from the Tank Farm was observed during test pit excavation along the outside of the north end of the Tank Farm.
- No. 6 fuel oil contamination was observed at and immediately below the water table north/down gradient of the Tank Farm.
- Further north near the East River, a major area of residual soil contamination was observed in the vicinity of former gas turbines and an inactive kerosene tank, with high VOC concentrations in soil and free-phase NAPL present in monitoring wells.
- An area near the East River where a large historical spill of No. 6 fuel oil was documented exhibited oil contamination at and below the water table, including several inches of LNAPL in a newly installed monitoring well.
The exposure assessment found there are no direct exposure pathways for human receptors to site-related contaminants. However, the potential for free-phase or dissolved phase contamination to discharge to the East River with the flow of groundwater was found to exist. In addition, the SIRP recommended that, based on the Site Investigation, the NYSDEC close 14 of the 25 open spills associated with the site. However, 11 of the spills should remain open pending remedial activities. Accordingly, a remedial technology assessment and recommendations for further evaluation of certain technologies were included in the SIRP. Based on a review of the SIRP, the NYSDEC agreed to close 13 of the 25 open spills, leaving 3 remaining open spills pending remedial activities.
Remedial Alternatives Evaluation and Screening
The SIRP included an evaluation of a number of remedial alternatives that focused on closure of remaining open spills. Technologies for the remediation of soil and groundwater impacted by No. 6 fuel, No.2 fuel oil, as well as kerosene were identified. The identified technologies were screened by D&B on a preliminary basis by evaluating each technology or process with respect to its ability to meet the project’s remedial action objectives, its technical implementability, and its short-term and long-term effectiveness. Remedial technologies that were screened for soil and groundwater included: hydraulic control, soil excavation and off-site disposal, steam enhanced nonaqueous phase liquid (NAPL) recovery, in-situ chemical oxidation; in-situ bioremediation, in-situ oxygen enhanced bioremediation, monitored natural attenuation and free-phase NAPL recovery.
Based on the evaluation of the above listed technologies, D&B recommended that hydraulic containment be utilized to remediate the No. 6 fuel oil present in the Tank Farm. Based on the fact that the Transformer Gas T
urbine Area contained dissolved phase No. 2 fuel oil and kerosene, D&B recommended that a bio-sparge/bio-vent pilot study be undertaken in this area to assess the effectiveness of this technology at reducing overall VOC concentrations in soil and groundwater.
Remedial technologies were compared and evaluated based on development of capital costs, and operation and maintenance (O&M) costs for the soil and groundwater components of each remedial alternative being evaluated. The capital and O&M costs were compared to assess the cost-effectiveness of each remedial alternative based on 30-year present worth.
Selection of Remedy
Based on extensive investigation studies completed by D&B, it was determined that the Tank Farm contained residual No. 6 fuel oil contamination within the interstitial space between the Tank Farm vault and steel tank walls. Given water levels inside the Tank Farm vaults were at higher levels than the surrounding land due to infiltrating precipitation, it was concluded that the residual contamination inside the Tank Farm would continue to seep out into surrounding soil and groundwater. Based on the Tank Farm construction, the nature of the contamination and the analysis of feasible remedial technologies performed by D&B as part of the SIRP, it was recommended that a dewatering system be installed in the Tank Farm. The goal of this remedial system would be to dewater the interstitial space between the concrete tank vault wall and the steel tank wall and equalize the water levels inside the Tank Farm with groundwater levels outside the Tank Farm. A secondary objective of the dewatering system would be to recover any No. 6 fuel oil that may be present.
The Transformer Gas Turbine Area contained dissolved phase No. 2 fuel oil and kerosene, D&B recommended that a bio-sparge/bio-vent pilot study be undertaken in this area to assess the effectiveness of this technology at reducing overall VOC concentrations in soil and groundwater. As stated above, since the pilot study was conducted over a period of 5 weeks, beginning with the installation of three soil vapor extraction (SVE) wells, three air sparge (AS) wells and six vapor monitoring points. The pilot study included a stepped SVE test, a stepped AS test and several rounds of continuous testing utilizing differing air sparge and extraction rates. Field measurements, as well as air and groundwater samples, were collected periodically to monitor the system.
Based on the findings of a completed Bio-Sparge/Bio-Vent Pilot Study, D&B recommended that the remedy of the Transformer Gas Turbine Area should first focus on the recovery of the free-phase No. 2 fuel oil that was discovered in this area by D&B during the completion of the Pilot Study. Based on experience with similar sites, D&B selected a pumping system that selectively recovers only light nonaqueous phase liquids (LNAPLs) such as No. 2 fuel oil and kerosene for the Transformer Gas Turbine Area.
Plans and Specifications
D&B prepared detailed plans and specifications for the Tank Farm dewatering system. D&B worked closely with Con Edison’s Engineering Department to ensure that the system would be compatible with the complex network of Tank Farm piping and equipment. D&B also specified the type of LNAPL recovery system utilized in the Transformer Gas Turbine Area based on experience with similar projects and the review of vendor technical information. D&B worked with the vendor to customize their equipment for the intended site-specific application.
Detailed Cost Estimates
D&B developed detailed construction cost estimates for the above described systems (Tank Farm Dewatering System and Gas Turbine Area LNAPL System) based on the developed plans and specifications and our extensive experience with similar projects. In addition, the firm developed estimated costs related to the long-term operation and maintenance of the systems.
Engineering Services During Remedial Construction
At the inception of the construction phase services portion of the assignment, D&B developed a detailed project schedule and coordinated the scheduling of all construction activities with Con Edison facility management and the selected remedial contractor. Given the “active” status of the facility, it was critical that the construction activities did not interfere with the daily operations of the facility since it is responsible for generating and conveying nearly 3 million pounds of steam per hour to lower Manhattan. This required daily coordination with various business units within the Con Edison organization.
As discussed above, the remedial action recommended for the Tank Farm consisted of a dewatering system. The remedial system was constructed to dewater the interstitial space between the concrete tank vault wall and the steel tank wall and equalize the water levels inside the Tank Farm with groundwater levels outside the Tank Farm. A secondary objective of the dewatering system was to recover any No. 6 fuel oil that may be present. The system consists of four piston pumps that were installed inside existing monitoring wells. The piston pump design was selected for this application given their ability to pump highly viscous fluid such as No. 6 fuel oil. The recovered water/oil mixture is conveyed to two 17,500- gallon storage tanks that are periodically pumped out by Con Edison and transported and disposed in accordance with all applicable re
gulations. As of February 2010, a total of 45,000 gallons of the water/oil mixture have been recovered from the Tank Farm. The system has been in operation since September 2009.
D&B field directed the installation of the LNAPL recovery system in nine 4-inch diameter groundwater monitoring wells. The system consists of, in each well, a portable skimmer pump that can selectively recover No. 2 fuel oil. The recovered oil is pumped to a 55-gallon drum that is periodically removed for the Station by Con Edison for recycling. As of February 2010, the system has been in operation for approximately 18 months. To date, a total of 500 gallons of LNAPL, consisting of a mixture of No. 2 fuel oil and kerosene, has been recovered from the Transformer Gas Turbine Area.
Bidding and pre-award services were not required for this project given Con Edison approved the use of a contractor recommended by D&B based on their experience and proven track record with similar projects. However, to ensure construction costs were reasonable, D&B reviewed the contactor’s costs and compared them to known benchmarks before Con Edison authorized the contractor to proceed with the work.
Attend and Participate in Pre-Construction Meeting
Pre-construction and regularly scheduled on-site meetings were held with the contractor to review progress and plan future activities. For each meeting, D&B prepared a detailed agenda to focus the discussion and minutes to document the resolution of each action item along with a schedule for completion.
Review of Contractor Submissions
The remediation contractor provided D&B with equipment and product information for materials and supplies utilized in the construction of the dewatering system. These submittals were evaluated by D&B for consistency with the design documents before use and/or installation. The technical reviews completed by D&B assured a high level of quality assurance/quality control with regard to the installation of the remedial equipment on site.
The remedial design included a requirement for the remediation contractor to prepare and implement a site-specific health and safety plan (HASP) that was reviewed by D&B and ultimately approved by Con Edison, with D&B input, prior to undertaking the construction phase of the assignment. In addition, during installation of the remedial system, D&B provided full-time engineering oversight to ensure a high degree of quality assurance/quality control.
Applications for payment submitted by the contractor to Con Edison were reviewed by D&B with respect to the work specified and completed, as well as the unit pricing established in the contract documents. Exceptions to the payment applications were noted where appropriate and were resolved prior to payment.
At the request of Con Edison, full-time engineering inspection was undertaken by D&B to ensure compliance with the approved work plan and contract documents (plans and specifications) throughout all phases of the dewatering system installation, start-up and “shakedown.”
“As built” drawings of the installation of the remediation/dewatering system at the Tank Farm were prepared by the remediation contractor, and reviewed and approved by D&B, after careful evaluation. Ultimately, the “as-built” drawings were incorporated into the O&M manual prepared by the contractor and reviewed and approved by D&B.
Technical support was provided regarding the review of the single change order request submitted by the remediation contractor. It is important to note that the only change order requested by the contractor was related to field modifications to the approved design for the Tank Farm dewatering system that were requested by Con Edison.
Construction Records and Reports
Daily field activities were documented during the construction activities including personnel on-site, arrival and departure times, daily weather conditions, equipment and materials on-site, activities conducted, problems and solutions and documented field changes. Photographic documentation of all aspects of the installation of the remediation system was also provided.
D&B conducted daily inspections of the contractors work to ensure compliance with the contract documents (plans and specifications) throughout all phases of the dewatering system installation, startup and “shakedown.”
Site Management Plans
The remedial design included a site-specific health and safety plan (HASP) that was reviewed by D&B prior to undertaking the construction.
An operations and maintenance (O&M) manual was drafted by the contractor and reviewed by D&B. The O&M manual included procedures and protocols related to the performance of short-term operation and maintenance of the Tank Farm dewatering system to achieve the specified performance objectives. In addition, the O&M manual included detailed procedures and protocols related to the long-term monitoring and maintenance of the dewatering system.
Analytical Quality Assurance/Quality Control Activities
A site-specific quality assurance/project plan (QAPP) was prepared and implemented by D&B for the project in accordance with USEPA and NYSDEC requirements. The QAPP plan described data quality objectives, procedures to be utilized for sample collection, equipment decontamination, equipment calibration, sample custody, laboratory analysis, and data reporting and data validation. The QAPP was reviewed and approved by D&B’s QA Officer, as well as the NYSDEC. The data validation process included review of sample holding times and results of QA/QC samples (method blanks, trip blanks, matrix spikes and matrix spike duplicates) to evaluate data usability in comparison to data quality objectives. Data collected during the site investigation was validated by the QAO. The results of the data validation process were summarized in a Data Usability Summary Report (DUSR).
Site Response Activities/Interim Remedial Measures
Based on the findings of a completed Bio-Sparge/Bio-Vent Pilot Study, D&B recommended that the remedy for the Transformer Gas Turbine Area focus on the recovery of the free-phase No. 2 fuel oil that was discovered in this area by D&B during the completion of the Pilot Study. Based on experience with similar sites, D&B selected a pumping system that selectively recovers only light nonaqueous phase liquids (LNAPLs) such as No. 2 fuel oil and kerosene for the Transformer Gas Turbine Area. D&B field directed the installation of the LNAPL recovery system in nine 4-inch groundwater monitoring wells by the system manufacturer. As of January 2010, the system has been in operation for approximately 17 months. To date, a total of 500 gallons of LNAPL, consisting of a mixture of No. 2 fuel oil and kerosene, has been recovered from the Transformer Gas Turbine Area.
The firm completes twice monthly monitoring of all site wells for free-product/NAPL. In addition, D&B conducts weekly performance monitoring of the Tank Farm dewatering and the LNAPL recovery systems described above. D&B submits quarterly reports to the NYSDEC summarizing the results of the monitoring.
Health and Safety Plan Development and/or Review
A site-specific health and safety plan (HASP) for the project was prepared and implemented by D&B in accordance with Occupational Safety and Health Administration requirements for hazardous waste sites. The HASP was prepared by a Certified Industrial Hygienist and implemented by the D&B Field Operations Manager. The HASP was also reviewed and approved by Con Edison.
The remedial design included a requirement for the remediation contractor to prepare and implement a site-specific health and safety plan (HASP) that was evaluated by D&B and ultimately approved by Con Edison, with D&B input, prior to undertaking the construction phase of the assignment. In addition, during installation of the remedial system, Con Edison requested that D&B provide full-time engineering oversight to confirm compliance with the project documents including the HASP.
For more information about this service, email us at firstname.lastname@example.org.