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7. CDS Monitoring Results

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7.1 Groundwater Monitoring

Groundwater monitoring focuses on the fractured shale unit because past monitoring has shown this is the primary zone of contaminant migration.

7.1.1 Chemical Analysis

The groundwater sampling schedule followed for 2020 is summarized in Table 4-1. 2020 VOC concentrations in monitoring wells, piezometers and extraction wells are included in Table 7-1. Recent historical groundwater sampling results, including results from 2020, are included in Appendix E.

  • Areal Extent of Plume in Fractured Shale: Figure 7-1 depicts the approximate extent of the contaminant plume from the CDS, as derived from the concentration of total VOCs in the fractured shale monitoring wells in September (See Table 7-1). Paradioxane is not included in the total VOCs summarized in Table 7-1 or on Figure 7-1. The highest concentrations of total VOCs were found in monitoring wells MW-22D,MW-30D, and 9D.
  • Temporal Variations – As in previous years, VOC concentrations exhibited a seasonal variation.
  • Most Frequently Detected Contaminants: Trichloroethylene (TCE) remained the compound detected most frequently and in the highest concentrations in monitoring wells in 2020. Other compounds frequently detected in monitoring wells and piezometers in 2020 included 1,2-dichloroethane, cis-1,2-dichloroethylene, 1,2-dichloropropane and chloroform, similar to previous years (Appendix E).
  • Exceedances of Groundwater Quality Standards: One or more volatile organic compounds were detected in concentrations exceeding water quality standards or guidance values in 6 monitoring or extraction wells in 2020 (Table 7-1). Compounds detected in concentrations above water quality standards or guidance values included 1,2-dichloroethane, cis-1,2-dichloroethylene and trichloroethylene.

7.1.2 Conclusions

Peak VOC concentrations in the center of the CDS plume were similar to those seen during 2019 and remained lower than the typical values seen during the several years prior to completion of the CDS remedial actions. The plume remained similar in terms of location and areal extent.

7.2 Surface Water

7.2.1 Chemical Analysis

Surface water samples are collected semi-annually from the drainage ditch north of the Airport runway (SW-41). Results are summarized in Table 7-3. Trichloroethene was detected at SW-41 at a concentration below NYSDEC standards and guidance values. Toluene was also detected. Historical surface water sampling results are included in Appendix F.

7.2.2 Conclusions

Surface water sampling at SW-41 indicate the presence of low levels of Trichloroethene, and Toluene at concentrations below NYSDEC standards and guidance values.

7.3 Recommendations for 2021

Groundwater and surface water sampling will continue in 2021 in accordance with the Site Management Plan.  Conduct additional sampling for low-level 1,4-dioxane analyses, as required by NYSDEC.

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