August 20, 2019 Ms. Amanda Killeen CT Department of Energy
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Norwalk Power LLC One Manresa Island Avenue South Norwalk, CT 06854 An NRG Energy company August 20, 2019 Ms. Amanda Killeen CT Department of Energy & Environmental Protection 79 Elm Street Hartford, CT 06106 Subject: Sediment Remedial Action Plan Norwalk Harbor Generating Station, Manresa Island Avenue, South Norwalk, CT Dear Ms. Killeen: Norwalk Power LLC (“Norwalk”) respectfully submits this Remedial Action Plan (RAP) for the Norwalk Harbor Generating Station (the “Site”), located in South Norwalk, Connecticut to the Connecticut Department of Energy & Environmental Protection (CTDEEP) for your review and approval. This RAP presents proposed activities to remediate sediment in freshwater and saltwater wetlands at the subject Site. Public notice will be issued for this document after CTDEEP issues approval to do so. Aptim Environmental & Infrastructure, LLC (APTIM; formerly CB&I) prepared and submitted the draft Wetland Sediment RAP to CTDEEP in October 2014 for review and approval prior to Public Notice. CTDEEP temporarily postponed concurrence to initiate Public Notice pending the completion of a pilot test. The pilot test details were agreed upon by the CTDEEP and the U.S. Environmental Protection Agency (USEPA). Norwalk successfully performed the pilot test and prepared and submitted the Wetland Sediment Remediation Pilot Test Data Evaluation Report to CTDEEP in February 2019. The report included the following summary and conclusion: “Per the pilot test plan, the pilot test sample results were evaluated to determine whether the draft Sediment RAP was verified by the pilot test (i.e., new backfill sediment concentrations less than TCCs). A nonparametric bootstrap method was used to calculate 95 percent UCLs of the mean for COCs in sediment at the wetland test cells (Tables 4 and 5). For each COC at each test cell, the 95 percent UCL of the mean is less than the corresponding TCC. In accordance with the pilot test plan, the pilot test is considered successful and no further statistical evaluation is required. The pilot test plan stated that if any of the 95 percent UCL of the mean were greater than the corresponding TCC, that further statistical evaluation was required, specifically to compare the lined versus unlined test cells. However, as stated in the previous paragraph, both tests were successful so the liner is not needed. Thus, per the pilot test plan, the draft Sediment RAP will continue with the 1 foot depth with no liner and no confirmation samples. The October 2014 draft Sediment RAP will only be modestly revised with things such as updated dates and schedule, updated site plans (e.g., 2016 wetland re-delineation, new wells, etc.), pilot test construction lessons learned regarding wetland access, staging, and backfill specification, project permitting, new signatures, etc. and submitted to CTDEEP as draft for approval to issue public notice.” USEPA and CTDEEP concurred with the conclusions of the final pilot test report in an email from USEPA dated March 25, 2019. As such, this revised Sediment RAP is consistent with the October 2014 version with updated dates and schedule, updated site plans (e.g., 2016 wetland re-delineation, new wells, etc.), pilot test construction lessons learned regarding wetland access, staging, and backfill specification, project permitting, and new signatures. REMEDIAL ACTION PLAN FOR WETLAND SEDIMENTS NORWALK HARBOR GENERATING STATION MANRESA ISLAND AVENUE SOUTH NORWALK, CONNECTICUT Prepared by: APTIM 150 Royall Street Canton, Massachusetts Prepared by: Reviewed by: Aptim Environmental & Infrastructure, LLC Aptim Environmental & Infrastructure, LLC Andrea E. Steele Andrew D. Walker, LSP, LEP Project Scientist Project Manager Licensed Environmental Professional Project No. 631003718 August 2019 P:\NRG\Norwalk Harbor\Final 19\Reports\sediment RAP\sediment RAP text_Aug2019_to CTDEEP.docx Remedial Action Plan for Wetland Sediments August 2019 Norwalk Harbor Generating Station, South Norwalk, Connecticut Page i TABLE OF CONTENTS 1.0 INTRODUCTION .............................................................................................................................. 1 2.0 SITE DESCRIPTION ........................................................................................................................ 1 2.1 Wetlands .......................................................................................................................... 2 2.1.1 Wetland W-1 .................................................................................................... 2 2.1.2 Wetland W-2 .................................................................................................... 2 2.1.3 Wetland W-3 .................................................................................................... 3 2.1.4 Wetland W-4 .................................................................................................... 3 2.1.5 Wetland W-5 .................................................................................................... 3 2.1.6 Wetland W-6 .................................................................................................... 3 2.2 Sediment .......................................................................................................................... 4 2.3 Surface Water .................................................................................................................. 4 2.4 Groundwater .................................................................................................................... 4 2.5 Biological Resources ....................................................................................................... 5 2.6 Current and Potential Future Site Uses ........................................................................... 6 2.7 Site Regulatory History .................................................................................................... 6 3.0 CONTAMINANT FATE AND TRANSPORT ..................................................................................... 6 3.1 Fate and Transport .......................................................................................................... 6 3.2 Groundwater Model ......................................................................................................... 7 4.0 RISK ASSESSMENT ....................................................................................................................... 8 4.1 Sediment Ecological Risk Assessment ........................................................................... 8 4.2 Surface Water Ecological Risk Assessment .................................................................... 9 4.3 Groundwater Ecological Risk Assessment .................................................................... 10 4.4 Human Health Risk Assessment ................................................................................... 11 5.0 WETLAND REMEDIATION OBJECTIVES .................................................................................... 11 5.1 Groundwater .................................................................................................................. 12 5.2 Surface Water ................................................................................................................ 12 5.3 Sediment ........................................................................................................................ 12 6.0 SEDIMENT REMEDIATION........................................................................................................... 13 6.1 Sediment Remedial Action Alternative Evaluation ........................................................ 13 6.1.1 Initial Sediment Remedial Action Technology Screening .............................. 14 6.1.2 Detailed Sediment Remedial Action Alternative Identification ...................... 15 6.1.3 Selection of the Proposed Remedial Action .................................................. 16 6.2 Proposed Sediment Remedial Action ............................................................................ 17 6.2.1 Location and Quantity of Sediment ............................................................... 18 6.2.2 Remedial Action Design – Sediment Removal ............................................. 18 6.2.2.1 Site Preparation ........................................................................ 18 6.2.2.2 Excavation ................................................................................. 20 6.2.2.3 Dredging .................................................................................... 20 6.2.2.4 Sediment Dewatering ................................................................ 21 6.2.2.5 Water Management ................................................................... 23 P:\NRG\Norwalk Harbor\Final 19\Reports\sediment RAP\sediment RAP text_Aug2019_to CTDEEP.docx Remedial Action Plan for Wetland Sediments August 2019 Norwalk Harbor Generating Station, South Norwalk, Connecticut Page ii TABLE OF CONTENTS (continued) 6.2.2.6 Solids Disposal .......................................................................... 23 6.2.3 Remedial Action Design - Wetland Restoration ............................................ 23 6.2.3.1 Soils ........................................................................................... 23 6.2.3.2 Hydrology .................................................................................. 24 6.2.3.3 Vegetation ................................................................................