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EXPLANATION OF SIGNIFICANT DIFFERENCES: ONONDAGA LAKE BOTTOM SUBSITE OF THE ONONDAGA LAKE SUPERFUND SITE, MODIFIED PROTECTIVE CAPS
U.S. EPA, 30 pp, 2018

This ESD documents the basis for modified cap design and construction in the vicinity of the Onondaga County Metropolitan Wastewater Treatment Plant deepwater outfall pipeline and in portions of Remediation Areas (RAs) B, C, and D. The 2005 ROD defined the caps as a mixing layer, a ≥12-in chemical isolation layer, and a ≥12-in habitat/erosion protection layer. Cap stability and settlement evaluations concluded that a ROD-complaint cap would affect the integrity of the outfall pipe. A thinner modified erosion-resistant cap (MERC) design was implemented. The MERC consisted of 6 in of gravely sand amended with granular activated carbon (GAC). Revisions to cap design were necessary for the 3 RAs due to soft sediment localized on relatively steep slopes causing disturbances in the already-placed cap. Caps were designed to resolve specific issues in each RA and generally consisted of a habitat/erosion protection layer on top of a sand and GAC layer thinner than the ROD-compliant cap. Post-construction physical and chemical monitoring will be conducted in the MERC and RA areas to ensure the remedy meets the related goals specified in the 2005 ROD. https://www.dec.ny.gov/docs/remediation_hudson_pdf/olmpcesd0318.pdf



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