New York State Department of Environmental Conservation 123 Post Avenue Site

Posted on June 15, 2015

Client: New York State Department of Environmental Conservation
Project Type: 123 Post Avenue Site

Major Components

  • Remedial Investigation
  • Feasibility Study
  • Bench-scale Treatability Study

Project Description


The services provided by D&B Engineers and Architects, P.C. in connection with the 123 Post Avenue Site, which are described below, were completed on time and within budget. The work was initiated in October 2000 and completed in June 2004. D&B is presently preparing design/contract documents to implement the selected remedy program (in-situ chemical oxidation).

Site Description

The 123 Post Avenue Site is an active dry cleaning facility located in the Village of Westbury in Nassau County, New York. The site is approximately 0.2 acre in size and is occupied by the dry cleaner building. The site is surrounded by residential and commercial buildings, and the Long Island Rail Road (LIRR). The off-site study area is, for the most part, densely populated and residential in nature, with some commercial properties along the west side of Post Avenue.

Site History

On-site Activities

  • The 123 Post Avenue Site building was constructed in 1949, with at least one expansion in 1957. The building has been occupied by a dry cleaner since at least 1957.
  • The building was connected to the municipal sanitary sewer system in 1979 or 1980. Prior to that time, wastewater generated on-site was apparently discharged to an on-site sanitary system.
  • In July 1995, an inspection by the Nassau County Department of Health (NCDH) revealed the presence of two floor drains in the western portion of the building. Based on this finding, the site was referred to the U.S. Environmental Protection Agency (USEPA) for action under the Underground Injection Control (UIC) program. The USEPA approved a UIC Closure Plan for the floor drains in June 1998.
  • In December 1997, the NYSDEC issued a Notice of Intent to Designate a Potential Hazardous Waste Disposal Site for the 123 Post Avenue Site. The site was placed on the New York State Registry of Inactive Hazardous Waste Sites in December 1998.
  • In July 1998, the NCDH discovered that soil samples had been collected from the floor drains in January 1996 by a consultant for the property owner. Dry cleaning solvent tetrachloroethene (PCE) and its breakdown product trichloroethene (TCE) were detected in the soil beneath the drains at concentrations up to 5,800,000 micrograms per kilogram (ug/kg) and 40,000 ug/kg, respectively.
  • Based on these results, contaminated soil was removed from beneath both floor drains in August 1998. Due to concerns about undermining the building, some contaminated soil was left in place, and a soil vapor extraction system began operation in May 2001 to address this residual contamination.
  • In March 1999, three monitoring wells were installed at the site to evaluate groundwater quality. Sample results showed PCE at concentrations up to 20,000 micrograms per liter (ug/l) in groundwater immediately downgradient of the dry cleaner.

Previous Off-site Activities

  • Shallow groundwater samples collected as part of a 1997 property transfer investigation at 117 Post Avenue (immediate south of the LIRR tracks that form the southern boundary of the 123 Post Avenue Site) contained concentrations of volatile organic compounds (VOCs), primarily PCE, as high as 15,000 ug/l. The investigation report concluded that the 123 Post Avenue Site was the source of the detected VOCs.123post1
  • In May 1998, TCE was detected in Westbury Water District Well No. 11, located approximately 2,000 feet south-southwest of the 123 Post Avenue Site, at a concentration of 1.0 ug/l (the New York State drinking water standard for TCE is 5 ug/l). Due to the absence of PCE detections and the depth of Well No. 11 (screen zone of 474 to 535 feet below ground surface), no conclusion could be made about whether the 123 Post Avenue Site was the source of the TCE.
  • A shallow water supply well at a car wash located approximately 2,000 feet south of the 123 Post Avenue Site was sampled in October 2000 by the NCDH. Water from this well is used for car washing only, and potable water is supplied to the car wash by the Westbury Water District. The car wash well contained PCE at 1.3 ug/l (the New York State groundwater standard for PCE is 5 ug/l).

In October 2000, D&B was issued a work assignment by the NYSDEC to conduct a Remedial Investigation and Feasibility Study to evaluate groundwater quality off-site and downgradient of the 123 Post Avenue Site. The study area extended from just north of the 123 Post Avenue Site to just south of Old Country Road, and from Post Avenue on the east to approximately 2,500 feet west of Post Avenue.

Responsibilities of the Firm

Remedial Investigation

The work assignment from the NYSDEC tasked D&B with conducting a Remedial Investigation for the off-site groundwater contamination and preparing a Feasibility Study Report that developed and evaluated remedial alternatives for the identified off-site contamination. The field activities that were conducted as part of the Remedial Investigation (RI) for off-site groundwater included the following elements:

  • Preparation of a site-specific RI Work Plan, including a site-specific Health and Safety Plan and Quality Assurance/Quality Control Plan;
  • Existing well survey;
  • Direct push soil conductivity logging and geophysical logging of monitoring well boreholes;
  • Plume delineation through direct push vertical profile sampling;
  • Installation of permanent monitoring wells;
  • Monitoring well sampling; and
  • Well surveying.

Each of the field activity elements, including the element results, is described in detail below.

Existing Well Survey: A review of NYSDEC files was conducted to identify water supply wells within and in the vicinity of the study area. The only wells identified within the study area were Westbury Water District Well No. 11 and the car wash well. Outside of the study area, identified wells included a cemetery irrigation well located approximately 1,800 feet east of Post Avenue, and Roosevelt Field Water District Well No. 5, located approximately one mile south of the 123 Post Avenue Site. Samples from both of these wells were found to contain VOCs, including PCE and TCE, but the source(s) of the contamination could not be identified.

Soil Conductivity Logging and Geophysical Logging: Continuous soil conductivity logging was conducted at two locations and each of the boreholes for the five permanent monitoring wells was geophysically logged, to evaluate subsurface geologic characteristics within the study area. In general, the lithology of the study area is comprised of fine to coarse or fine to medium sand to a depth of approximately 115 feet below ground surface. Below that depth, several apparently discontinuous clay layers were identified, especially in the southern portion of the study area. While these clay layers may impede the vertical migration of contamination, since they are not continuous, it is unlikely that vertical migration of contamination of contamination will be prevented by them.

Plume Delineation Through Direct Push Vertical Profile Sampling: Direct push groundwater samples were collected at 20 locations throughout the study area. At each location, vertical profile samples were collected from the maximum depth achievable (ranging from 80 to 120 feet below ground surface) to the water table (approximately 40 feet below ground surface) at 20-foot intervals. Each sample was analyzed for VOCs.123post2

Based on previous on-site and off-site investigations and the historic site use, three chlorinated VOCs typically associated with dry cleaners, PCE and its breakdown products TCE and 1,2 dichloroethene (1, 2 DCE) were identified as representative contaminants of concern for the 123 Post Avenue Site. The total concentration of these contaminants detected in off-site groundwater ranged from non-detect to approximately 11,300 ug/l, with the greatest concentrations detected in shallow groundwater nearest the 123 Post Avenue Site, at and immediately south of the 117 Post Avenue property. Concentrations of total targeted VOCs decrease to the south-southwest, downgradient of the site. In addition, the depth of the zone most highly impacted by the targeted VOCs increases with distance downgradient of the site. The concentration of total targeted VOCs in the sample collected north/upgradient of the 123 Post Avenue Site was 11 ug/l, verifying that the site is the predominant source of the detected chlorinated VOCs.

Based on these results, a narrow contaminant plume, comprised predominantly of PCE, was identified in groundwater downgradient of the 123 Post Avenue Site. The plume extends toward the south-southwest and becomes deeper with distance from the site. In the southern portion of the study area, the vertical migration of the plume appears to be limited by the presence of discontinuous clay layers.

Installation, Sampling and Surveying of Permanent Monitoring Wells

Five permanent monitoring wells were installed within the study area. The well locations were selected based on the results of the direct push groundwater samples to provide permanent monitoring points for temporal assessment of the plume conditions. As a result, the wells were installed in a generally linear pattern within the identified plume.

Sample results from the monitoring wells confirmed the results of the direct push groundwater sampling program.123post3

The permanent monitoring wells were surveyed to establish their horizontal locations and vertical elevations.

Following completion of the field investigation, the data were validated and evaluated, and a qualitative human health exposure assessment was prepared. A Remedial Investigation Report was then prepared. The report described the activities that had been conducted summarized conditions within the study area and presented the analytical results in tabular form and on figures. The report also included the human health exposure assessment, including identification of current and future potentially-complete exposure pathways, and provided conclusions and recommendations regarding the source and extent of off-site groundwater contamination and the potential for adverse impacts to human health. Although the report concluded that there currently was little potential for adverse impacts to human health, it was recommended that evaluation of remediation technologies be conducted in a Feasibility Study to mitigate continued downgradient migration of the contaminant plume.

Bench-scale Treatability Study, Development of Remedial Alternatives, Selection of Remedy and Preparation of Feasibility Study Report

Based on review of potential remedial technologies for remediation of VOC-contaminated groundwater, it was determined that in-situ chemical oxidation and ozone-enhanced air sparging, among others, could be effective. However, in order to obtain the data necessary for detailed screening of in-situ chemical oxidation and ozone-enhanced air sparging, it was concluded that additional testing was required. As a result, D&B prepared documents to obtain proposals to conduct a bench-scale treatability study for chemical oxidation and a field-scale pilot test of ozone-enhanced air sparging. However, due to receipt of an insufficient number of responsive bids for the ozone-enhanced air sparging pilot test, only the bench-scale treatability study for chemical oxidation was implemented.

The bench-scale treatability study was conducted to evaluate the effectiveness of chemical oxidation utilizing sodium permanganate. Soil and groundwater collected within the most highly contaminated portion of the off-site plume was utilized for the study. Three samples with different ratios of soil to oxidant were used during the test, to allow determination of the optimal oxidant application rate for full-scale implementation. A control sample with no oxidant was also prepared for comparison purposes. The results of the treatability study showed that sodium permanganate effectively oxidized the contaminants of concern, with VOC concentrations reduced to non-detectable levels in each of the three samples. As a result, this technology was maintained for further evaluation.

Other potential remedial technologies were identified and screened on a preliminary basis, based on implementability and effectiveness. These other technologies included institutional controls, groundwater extraction and treatment, air sparging, in-well air stripping, in-situ bioremediation, reactive wall, chemical reduction, funnel and gate systems and natural attenuation. Based on preliminary screening of these technologies for technical effectiveness and implementability, bioremediation, ozone-enhanced air sparging and chemical oxidation were retained for further consideration. A “no action” alternative was also evaluated further, to serve as a baseline against which to compare the other alternatives.

The retained technologies were combined into four remedial alternatives, which included:

  • No action with long-term groundwater monitoring;
  • In-situ chemical oxidation with long-term groundwater monitoring;
  • In-situ bioremediation with long-term groundwater monitoring; and
  • Ozone-enhanced air sparging with long-term groundwater monitoring.

A detailed evaluation of each of these alternatives was performed according to the following criteria:

  • overall protection of human health and the environment;
  • compliance with standards, criteria and guidelines;
  • short-term impacts and effectiveness;
  • long-term effectiveness and performance;
  • reduction of toxicity, mobility or volume;
  • implementability;
  • cost; and
  • regulatory agency and community acceptance.

Based on the detailed evaluation of the four alternatives, in-situ chemical oxidation with long-term groundwater monitoring was ranked highest. A Feasibility Study (FS) Report was prepared to document the preliminary screening of remedial technologies, treatability study results and development and evaluation of remedial alternatives. The FS Report also included detailed cost estimates for each alternative, including capital costs, engineering fees and present worth operation, maintenance and monitoring costs.

The Record of Decision (ROD) listed in-situ chemical oxidation with long-term groundwater monitoring as the selected remedy for Operable Unit 2 (OU2). The selected remedy included the following components:

  • remedial design program to verify the components of the conceptual design;
  • installation of groundwater and soil monitoring points to evaluate the effectiveness of the action and to determine the potential for soil vapor impacts;
  • injection of chemical oxidants into the northern portion of the contaminant plume to act as a pilot test to determine the effectiveness of the oxidant;
  • evaluation of the pilot test results, assessment of the oxidant’s effectiveness to remediate the remainder of the plume and modification of the design as appropriate;
  • injection of oxidant into the remainder of the contaminant plume as described in the Remedial Design documents; and
  • long-term monitoring to evaluate the effectiveness of the remediation.

In 2005, D&B was issued a work assignment by the NYSDEC to prepare remedial design documents for implementation of the remedy selected in the ROD. The assignment included supplemental soil vapor and groundwater sampling, implementation of an in-situ chemical oxidation pilot study, preparation of plans and specifications for public bidding of the full-scale remedy, and bid assistance for selection of a remedial contractor.

Citizen Participation

The following Citizen Participation activities were conducted by D&B:

  • Preparation of a site-specific CP Plan as part of the site-specific OU2 RI/FS work plan. This plan included the identification of national, state and local elected officials; potentially affected governmental and citizen groups and organizations; potentially affected individuals; local media; and state and local government contacts. The name and address of each party was listed to create a site-specific mailing list for distribution of public notices and information related to the project. The site-specific CP Plan also included identification of the repositories for documents generated during the RI/FS activities and a description of the citizen participation activities planned for the project, including public meetings and preparation and distribution of site-related fact sheets.
  • Preparation of presentation materials for, and participation in, public meetings to describe the work plan and the Proposed Remedial Action Plan for the site.

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