Project Description

BACKGROUND

Two gasoline stations (the Sites) were operated on the southeast and southwest corners of Old Country Road and Plainview Road in the 1950’s until the early 2000’s. These stations had underground storage tank (UST) systems dispensing gasoline and fuel oil for use in their commercial operations. Gasoline and oil are petroleum products that contain hydrocarbon compounds. These hydrocarbon compounds have been found in the soil and groundwater beneath these Sites indicating that there were leaks or spills at some point during the operation of the gas stations. Because of this, in 1997 and 2002, respectively, the New York State Department of Environmental Conservation (NYSDEC) created environmental cases for each of these Sites that are still under investigation. Environmental investigations of the groundwater were begun and continues under the direction of the NYSDEC. A third gasoline service station was located on the northwest corner of this intersection and also had a environmental case assigned but has not been found to have contributed to this particular contamination plume.

During operation of the gas stations, at unknown times, petroleum products entered the subsurface at each of the two former stations (Sites) via leaking UST systems. Once released, hydrocarbons moved down through soil toward the water table. Once the hydrocarbons met the water table, they mixed into the groundwater under the Sites and then started slowly moving downgradient along with normal groundwater flow to the southeast of the Sites. Even after the gas station infrastructure (USTs, piping, etc.) was removed and the leaks stopped, some hydrocarbons remained in the soil and migrated to the southeast.

Groundwater in the area is encountered about 70 feet (ft.) below ground surface (bgs), which is the “top of the water table”. Because the groundwater in the area flows to the southeast of the Sites, over the years a groundwater monitoring well network of over 200 monitoring wells was installed (click on the tab for the Study Area map). The location of these wells now covers an area approximately 3,000 ft. long by 1,500 ft. wide southeast of the Sites which comprise the “Project or Study Area”. This monitoring network consists of monitoring wells that were installed to the water table and even deeper in order to collect groundwater samples at different depth intervals that are then analyzed for hydrocarbon compounds. As groundwater travels from the area of the Sites, it moves hydrocarbons with its flow to the southeast, but also drops lower in the ground meaning that the hydrocarbons dive deeper the farther they get from the Site.

Once environmental releases at the gas stations were discovered, they each separately performed different investigations and active remediation at their respective Sites. After the gas stations were closed (in 1997 and 2005), cleanup was largely successful on the properties, but the NYSDEC recognized that operations from both gasoline stations appeared to have contributed to the groundwater hydrocarbon plume southeast of the Sites. At that time, investigation and remediation responsibilities at both Sites were transitioned to Resource Environmental, LLC (RELLC) in 2011. RELLC is an independent organization formed by several major oil companies that specialize in responding to and managing the clean-up of such releases of petroleum fuels into the ground from retail sites, pipelines, terminals, and other petroleum fuel related facilities throughout the United States.

Regular Project Area-wide groundwater sampling has been conducted on existing and newly drilled wells since 2003, and, since taking over Project Area activities in 2011, RELLC has overseen continued investigation work including soil and groundwater sampling, drilling and installing additional monitoring wells, and groundwater computer modeling work. Additionally, tests have been conducted to evaluate if conditions exist for contamination to be degraded by naturally occurring bacteria in the soil.

One primary goal has been to find the limits of environmental impacts, or to delineate the plume, in each horizontal direction as well as vertically, to see how wide and how deep it is. As is typical of a diving groundwater plume, the depth where contamination ends is different, and generally deeper, as the plume moves away from the Sites. Starting in 2017, with NYSDEC agreement RELLC moved forward with the installation of several monitoring well clusters that extended deeper and further from the Sites. These groundwater plume delineation activities have continued through 2024. With these additional monitoring wells, data has shown that the plume margins were largely identified by the end of 2023, except for the farthest area to the southeast. This area will be targeted in 2024.

Another goal has been to prove that biodegradation is occurring in the Project Area, where bacteria consume hydrocarbon impacts and change it into less harmful by-products. Chemical analysis of the groundwater and of physical tests for actual bacteria counts have provided data to support the conclusion that this is occurring in the Project Area.

ENVIRONMENTAL SITUATION AND PATH FORWARD

Through extensive assessment work conducted from 2011 through present, RELLC has developed a model that predicts how the groundwater hydrocarbon plume will likely behave in the present and into the future. The behavior of the hydrocarbon plume is affected by the geology in the Project Area. Long Island geology consists of complex layering of sands, silts, and clays that were naturally created and influenced by the action of the Atlantic Ocean, surrounding waters, and coastal forces. The Project Area geology is important to understand because it influences the flow of groundwater and any attendant hydrocarbon plume formation. Specific conditions in areas of the Project Area were identified by soil samples and other test results during drilling operations. These results were studied and combined with data from other locations in the Project Area to create a coherent model of the geology. With this geologic model, predictions can be made about the current and future location of hydrocarbon impacts and a plan can be proposed and agreed upon with the NYSDEC concerning the most effective remediation program.

Groundwater is the drinking water supply for most of Long Island and it is pumped from the Magothy Aquifer from depths of approximately 400-600 ft. bgs. There are many water districts that supply drinking water, and both the Plainview Water District (PWD) and the Bethpage Water District (BWD) serve the Project Area. The closest downgradient water supply wells are PWD Plant No. 5 and BWD South Park Drive Well. These two water supply wells are the primary receptors of concern for the Project Area. Both of these wells have activated carbon or air stripping or other treatment processes in use already which are designed to remove any hydrocarbons that may be present in the influent groundwater. There is an upgradient water supply well, PWD Plant No. 1, north of the Plainview Road and Old Country Road intersection where the Sites are. The groundwater flows to the southeast from this plant and so contamination from the Sites is not expected to flow north and should not affect this water supply location.

ADDRESSING EXISTING HYDROCARBON IMPACTS

Once delineation of the hydrocarbon plume extent is completed, the monitoring well network will be in place to reliably monitor the location of hydrocarbon impacts and confirm that the developed computer groundwater model can adequately predict the behavior of the hydrocarbon plume. Under NYSDEC guidance, several alternative plans will be considered to close the environmental cases at both sites and then a path forward for both Sites will be agreed upon. The NYSDEC has strict criteria that they will use in accepting any plan which prioritizes any contamination impacting the water districts and therefore public health.

There are many factors that are being considered in developing a plan to close these environmental cases.

The plume location is in highly developed, residential, and commercial area.
The depth to contamination is great and varies from approximately 70 to 360 feet below ground surface.
The hydrocarbons of concern can be readily biodegraded.
The existing plume conditions indicate that biodegradation is naturally occurring. Bacteria and other naturally occurring processes are working to breakdown the constituents of concern over time (natural attenuation). This has been established by the results of several different groundwater tests, computer modeling, and mass calculations of the plume.

Much new information was obtained in 2023. The overall sequence of the path forward is to complete delineation of the hydrocarbons in groundwater; use groundwater data to complete an updated model and present this to the NYSDEC; propose and implement a remedy including a long-term groundwater monitoring plan to confirm the remedy is satisfying NYSDEC mandated remediation goals.

CONCLUSIONS

The groundwater plume originated from both historical service stations’ USTs and associated dispenser and piping leaks. Original sources of hydrocarbon release have been eliminated through the removal of service station USTs, piping, equipment, and near-surface impacted material (soil) to the greatest extent possible within the former station parcels. During station operation and after closure, active remediation was conducted at both properties. RELLC continues to monitor and evaluate groundwater conditions throughout the plume, with a specific focus on the 350 to 500 ft. bgs zone to the south and southeast of the Sites, at the toe of the plume. Additional well installations to delineate the plume edges at the south edges are planned.

There is no health concern at or near the surface for any residential or commercial properties in the area, and more work is being done to model and simulate the potential extent of future plume migration. Advanced modeling and analysis tools have been and will be applied to studying the data from the plume. Ultimately, it is thought that the plume constituents of concern will naturally attenuate and become insignificant within the groundwater with time. Until agreements can be reached with NYSDEC regarding a final remedy, RELLC will remain diligent with its ongoing investigation and monitoring activities.

Several times a year, meetings are held with the NYSDEC to summarize work performed, discuss preliminary results, and discuss planned work. These sessions involve deliberations on future plans and address any problems or concerns that may arise. Testing results continue to be reported on a regular basis by RELLC to the NYSDEC. Key stakeholders include private entities with whom RELLC has executed access agreements and on whose properties RELLC maintains monitoring wells. They are kept informed when active field sampling or well drilling activities occur and are regularly updated on the project status.

TIMELINE & STATUS

Environmental assessment activities are continuing until all necessary evaluations are completed, as judged by the NYSDEC. Activities are typically performed Monday through Friday, during business hours, as approved by the NYSDEC, Town and County officials, and relevant property owners.