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8. Remedial Measures

8.1 RDS Source Control System

The Final Remedy for the RDS source area was installed during 2003 and 2004. The source area containment measures consist of a grout curtain in the bedrock, a soilbentonite wall in the soil layer, and a multi-layered capping system. The grout curtain and soil-bentonite wall are together referred to as the barrier wall. Monitoring of these measures was performed in 2020 in accordance with the Site Management Plan (Cornell University, October 2014).

8.1.1 Water Testing Results

Seven monitoring wells surrounding the RDS barrier wall were tested quarterly for paradioxane. Four of these seven wells were also tested annually for tritium, carbon-14 and strontium-90. These analytical results are summarized in tables 6-1 and 6-2.

Paradioxane is the primary chemical tracer for evaluating the effectiveness of the RDS barrier wall in containing the source area contaminants. The table below presents a summary of the paradioxane data for 2020 compared to the three years before the barrier wall was installed.

Paradioxane Concentration in Selected Wells (μg/L)
Well Location 2000 - 2002 Average 2020 Average % Reduction
RDS-1WS West side of disposal area 7832 809 90%
RDS-2WS West side of disposal area 891 349 61%
RDS-3WS South side of disposal area 2329 486 79%
RDS-4WS East side of disposal area ND 285 0%
RDS-6WS East side of disposal area 113 178 0%

As shown on the table above, paradioxane concentrations have significantly decreased along the south and west sides of the disposal area since the installation of the barrier wall. Average paradioxane results along the east side are similar to those observed in 2019.

Strontium-90, Tritium and Carbon-14 were detected in one or more wells (Table 6-2).  However, these results are typically lower than results from previous years (Appendix B).

8.1.2 Operation, Repair, and Maintenance

Maintenance and repair activities at the CDS and RDS, including the RDS Source Control System, for 2020 were similar to 2019. Cap inspections were conducted quarterly during 2020. The cap was observed to be in generally good condition with good vegetative cover and no significant areas of erosion or poor drainage. Cornell performed routine maintenance for the RDS including soil placement and seeding at monitoring well areas; mowing of cap, side banks and security fenceline; repairs to the site fencing; proactive tree work; rodent controls; and drainage system improvements as needed.

8.1.3 Conclusions

The RDS source control system remained in-place. While paradioxane concentrations in groundwater have decreased on the west side of the disposal area, the decrease has not been as significant on the east side of the disposal area. It remains unclear whether this is related to migration of residual contamination located outside the barrier wall or is indicative of transport around or through a portion of the barrier.

8.1.4 Future Plans for Source Control

Operation, maintenance, and monitoring will continue in accordance with the Site Management Plan.

8.2 RDS Groundwater Recovery System

8.2.1 Chemical Evaluation

Influent from the RDS Groundwater Recovery System was sampled and analyzed for paradioxane on a monthly basis in 2020. Results are provided in Table 8-2. The range of paradioxane in the influent varied from 44 (J) ug/L in September to 128 μg/L in December.

In addition, samples were collected from the active RDS extraction well (RW-111) quarterly in 2020. Results are provided in Table 6-1. Paradioxane concentrations in the pumping well varied from 63.1 μg/L in September to 124 μg/L in March.

8.2.2 Conveyance Line Inspections

Conveyance line inspections were conducted quarterly. Infiltration of surface water into the tie-in manhole and inspection sumps occurred occasionally during 2020; dewatering was required following especially heavy rain or snow melt.

8.2.3 Operation, Repair and Maintenance

Cornell University continued to operate RW-111 throughout 2020.

Maintenance and repair activities related to the recovery system included repair of cover drains, placement of fabric and stone, mowing and pumping of infiltrated surface water from the tie-in manhole and conveyance line inspection sumps.

8.2.4 Recommendations and Future Plans

Monitoring of the groundwater plume at strategic locations north and south of Snyder Road will continue during 2021 in accordance with the Site Management Plan to document the effectiveness of the barrier system and the groundwater recovery system.

Cornell University will continue pumping operations from recovery well RW-111 in 2021. Groundwater monitoring data will be evaluated to assess whether modifications to the pumping strategy may be warranted. Cornell University will operate the groundwater recovery system until the paradioxane concentration in groundwater monitoring wells south of Snyder Road (RDS-11WS and RDS-13WS) remains below 50 μg/L for four (4) consecutive quarters.

Cornell University will utilize a contract driller in 2021 to re-develop RW-111 and MW-11WS using physical and chemical processes.

8.3 CDS Source Control System

8.3.1 Hydraulic Evaluation

The hydraulic head differential across the groundwater barrier wall was measured using four pairs of wells (couplets), each consisting of a piezometer located within the area enclosed by the groundwater barrier wall and a monitoring well located just outside the groundwater barrier wall (Figure 2-2). Groundwater levels were obtained from these piezometer couplets weekly.

The on/off level set points of the pumping wells inside the source area are designed to maintain an inward hydraulic head differential (i.e., a hydraulic flow potential of groundwater from outside the groundwater barrier wall to inside the groundwater barrier wall). Operating guidelines call for maintaining a minimum inward head differential of one foot, which minimizes the potential for releases of contaminants underneath or through the groundwater barrier wall.

Table 8-1 reports the range in head differentials. A head differential of at least one foot was maintained along all sides of the CDS throughout 2020.

In addition to creating an influence on the horizontal hydraulic flow potentials, the SCS affects the vertical hydraulic flow potential. Pumping from the extraction wells creates a vertical hydraulic head potential in the upward direction. This minimizes the potential for downward migration of dissolved contaminants beneath the CDS.

8.3.2 Chemical Analysis Volatile Organic Compounds in System Influent

Grab samples analyzed for VOCs were collected monthly from the SCS groundwater influent to the treatment plant. VOC influent results are presented in Table 8-2. Benzene, 1,2-Dichloroethene, 1,2-Dichloroethane (DCA), 1-4, Dioxane, and trichloroethylene (TCE) were present at the highest concentrations.  Concentrations of VOCs observed in the influent from the SCS were generally consistent with what has historically been observed. Volatile Organic Compounds in Groundwater

Concentrations of VOCs in monitoring wells adjacent to the CDS source area (monitoring wells MW-8 through MW-12, Table 7-1) remained consistent with recent monitoring during 2020, yielding no evidence of significant leakage of groundwater from inside the CDS.

8.3.3 Conclusions

The CDS source control system was effective during 2020 in preventing discharges or exposures from site-related contaminants. An inward hydraulic gradient across the barrier wall was maintained throughout the year.

8.3.4 Recommendations and Future Plans

Operation, maintenance, and monitoring will continue in accordance with the Site Management Plan.

8.4 CDS Plume Collection System

The Plume Collection System includes two groundwater collection systems:

  1. A shallow system consisting of three scavenger wells and a collection trench in the glacial till deposits and upper few feet of bedrock (known as the PCS-Shallow recovery system), and
  2. A deeper system consisting of seven extraction wells capturing groundwater flow in the fractured shale deposits 10 to 40 feet below ground surface (known as the PCS-Deep recovery system).

Portions of the Trench Upgrade (PCS-Deep) Performance Monitoring sampling were continued in 2020, including collection of samples from selected wells for VOC analysis.  Operation of the PCS-Shallow system and extraction well EW-3 were discontinued in 2020 after monitoring data showed contamination levels were consistently below NYSDEC's ambient water quality standards.

8.4.1 Hydraulic Evaluation

Water level measurements provide the primary means for verifying that the PCS is working properly. The potentiometric surface contours indicate that the groundwater flow potential from the CDS is toward the southwest, and that the plume collection system is maintaining hydraulic control in the fractured shale unit.

Sampling of the individual PCS-Deep extraction wells over a period of several years indicated minimal levels of contaminants were present at the ends of the extraction well alignment (i.e. EW-1, EW-2, EW-6 and EW-7). Similarly, EW-3 operations were discontinued in March 2020.  In order to focus the groundwater extraction process on the zone of contaminant migration, only wells EW-4 and EW-5 were operated during continuously during 2020.

8.4.2 Chemical Analysis Volatile Organic Compounds

The concentrations of VOCs in monthly grab samples of the influent from the PCS-Deep recovery system are summarized in Table 8-2. Compounds detected and the ranges of concentrations were similar to previous years. The average concentrations of the total VOCs detected in the PCS-Deep influent streams were similar to 2019 (Appendix G).

In addition to the samples from the PCS-Deep influent streams, an annual sample was taken from each of the operating PCS-Deep extraction wells (EW-3 through EW-5). The results are summarized on Table 7-1. The highest concentration of total VOCs in the plume collection system extraction wells was detected in a sample from EW-4 (30 μg/L). This well is in the center of the plume collection system. VOCs detected in samples from the extraction points in 2020 were similar to previous years (Appendix E).

PCS-Deep recovery system monitoring included quarterly sampling of monitoring wells MW-27D, MW-30D, MW-33D and MW-35D. Concentrations of volatile organic compounds over time in wells MW-30D (center of plume), MW-35D (within the PCS well alignment), and MW-33D (downgradient of PCS), are plotted on Figure 7-2. The large variations in VOC concentrations at well MW-30D (center of plume) seen on the chart are the result of seasonal factors affecting groundwater flow and recharge.

8.4.3 Operation, Repair and Maintenance

Maintenance and repair activities at the Plume Collection System for 2020 were similar to 2019.

8.4.4 Conclusions

The PCS maintained consistent hydraulic control of the groundwater plume on the airport property during 2020. Concentrations of VOCs at down gradient well MW-33D and surface water location SW-41 were within the range typically seen since monitoring began at these locations in 1998 (Appendix F).

8.4.5 Recommendations and Future Plans

Monitoring of the Plume Control System will continue in 2021 in accordance with the Site Management Plan. Hydraulic and water quality conditions near the collection trench will continue to be evaluated, and the active PCS-Deep recovery system extraction wells (EW-4 and EW-5) will continue to be monitored to ensure prompt resolution of any problems with the operation of the groundwater pumps and associated equipment.

Cornell University has also developed and submitted a work plan to NYSDEC to pulse the PCS-D system.  This pulsing effort is intended to determine whether the PCS-D system has reached asymptotic conditions and to evaluate whether a transition to monitored natural attenuation is warranted.

8.5 Groundwater Treatment Plant

8.5.1 Flow Evaluation

The Groundwater Treatment Plant processed over 2 million gallons of groundwater from the CDS and RDS during 2020 (Table 8-3).

8.5.2 Laboratory Analysis Volatile Organic Compounds and Paradioxane

As reported in the Discharge Monitoring Reports submitted monthly to the NYSDEC, all final effluent volatile organic chemical concentrations were within the effluent requirements (Table 8-4). Metals

Quarterly samples from the Groundwater Treatment Plant are analyzed for 18 metals, while monthly samples are analyzed for 6 of these metals. All effluent metal concentrations were below their respective effluent discharge limitations with the exception of manganese in March (Table 8-5). Radionuclides

The substantive Part 380 Radiation Control permit requires the submission of annual activity report that includes the number of days the treatment plant operated, the total volume of water discharged, and the total RDS-related activity (Appendix D).

8.5.3 Hazardous Waste Generated

Spent bag filter and carbon waste was generated in 2020.  Ten drums of spent carbon waste were shipped offsite for reactivation and returned in 2020.

8.5.4 Repair and Maintenance

Maintenance and repair activities at the CDS and RDS, including the Groundwater Treatment Plant, for 2020 were similar to 2019. Maintenance and repair activities related to the Groundwater Treatment Plant included response to system alarms.

Routine activities included items such as scheduled feed pump, peroxide pump, unit heater, GAC vessel, treatment system and compressor maintenance and repairs; ball valve/ball check replacement; activated carbon placement, painting and cleaning, hydrogen peroxide, potable water and propane delivery, ridge vents properly infilled and insulated, light fixture lamp replacement (LEDs), pH probe sensor cleaning/calibration/replacement, pump controls desiccant replacement, changing of bag filters and exterior building/lighting improvements.

8.5.5 Conclusions

The Groundwater Treatment Plant was operational throughout 2020 and treated over 2 million gallons of water.

8.5.6 Recommendations

Monitoring and maintenance activities at the Groundwater Treatment Plant will continue in 2020 in accordance with the Site Management Plan.  In addition, sampling for low-level 1,4-dioxane analyses will continue, as requested by NYSDEC.

8.6 Summary of Operations, Recommendations for 2021, and Future Plans

The RDS Source Area containment has minimized infiltration and prevented release of VOCs and radionuclides from the disposal site via air or surface water. Cornell will continue to monitor and evaluate the paradioxane concentrations near the disposal area to determine if any changes in the Site Management Plan are warranted. The RDS Groundwater Recovery System continued to control and treat the paradioxane groundwater plume near Snyder Road.

The CDS Source Control System is working as designed, preventing migration of contaminants from the site via groundwater by maintaining hydraulic control within the disposal area. The cap has been effective at preventing direct contact with waste and reducing infiltration into the waste. The CDS Plume Collection System operated as designed and maintained hydraulic control throughout the year. Operation, maintenance and monitoring of the CDS and RDS remedial measures will continue in 2021.

Plans for 2021 include continued performance monitoring of the remedial measures in accordance with the Site Management Plan. In addition, groundwater monitoring wells and other infrastructure no longer in use may be decommissioned.