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2021 Supplemental Environmental Impact Statement (SEIS)

The 2021 SEIS builds upon the findings of the 2010 DEIS by accounting for changes that have occurred to land use, traffic, demographics, and natural resources within the study area. To account for these changes, new field studies for all resources, including but not limited to wetlands, streams, threatened and endangered species, noise, communities, and hazardous materials within the project study area have been completed for the 2021 SEIS. A new traffic analysis was completed for the 2021 SEIS using the latest version of the Charleston Area Transportation Study (CHATS) Travel Demand Traffic Model (2019) to analyze alternatives. The 2021 SEIS reanalyzed all 39 preliminary alternatives evaluated in the 2010 DEIS, which resulted in an updated set of Reasonable Alternatives. While most of the 39 preliminary alternatives remained the same, some alternatives required design modifications to account for changes in the study area and incorporate comments from the public, resource agencies, and local governments since the 2010 DEIS. This 2021 SEIS evaluated the updated set of alternatives and their impacts to revalidate the studies and findings of the 2010 DEIS. The 2021 SEIS identified Alternative G as the Recommended Preferred Alternative.

The 2021 SEIS was published for review online, at physical locations within the community, at Community Meetings, and at the Public Hearing. See the Public Hearing page for details. The public was encouraged to comment on the SEIS through October 15, 2021. SCDOT is fully evaluating the public comments received before the selection of the Preferred Alternative is finalized.

The SEIS was also available for review in hard copy at:

  • SCDOT Headquarters (955 Park Street, Columbia, SC 29202) - To schedule an appointment, call 855-467-2368.

  • SCDOT District 6 Office (6355 Fain Boulevard, Building A, North Charleston, SC 29406)

  • Cynthia Graham Hurd/St Andrews Regional Library (1735 N Woodmere Drive, Charleston, SC 29407)

  • West Ashley Library (45 Windermere Boulevard, Charleston, SC 29407)

  • John’s Island Regional Library (3531 Maybank Highway, Johns Island, SC 29455)

  • James Island Library (1858 S Grimball Road, Charleston, SC 29412)

Mark Clark Extension 2021 Supplemental Environmental Impact Statement

01 Cover_Signature Page_Environmental Commitments_Summary

02 Table of Contents_Aconyms

03 Chapter 1_Introduction

04 Chapter 2_Purpose and Need

05 Chapter 3_Alternatives Development

06 Chapter 4_Public Involvement and Agency Coordination

07 Chapter 5_Environmental Consequences

08 Chapter 6_Recommended Preferred Alternative

09 List of Preparers, Glossary, Index

Appendices

Appendix A_2010 DEIS

Appendix B_2016 Reevaluation

Appendix C_Agency Coordination and Public Involvement Plan

Appendix D_Travel Demand Modeling

Appendix E_NEPA 404 Merger Coordination Letters

Appendix F_Alternative Analysis

Appendix G_Traffic Noise Report and Detailed Noise Report_Part 1

Appendix G_Traffic Noise Report and Detailed Noise Report_Part 2

Appendix G_Traffic Noise Report and Detailed Noise Report_Part 3

Appendix G_Traffic Noise Report and Detailed Noise Report_Part 4

Appendix G_Traffic Noise Report and Detailed Noise Report_Part 5

Appendix G_Traffic Noise Report and Detailed Noise Report_Part 6

Appendix H_Community Impact Assessment

Appendix I_Historic Resources Survey

Appendix J_Agency Coordination_Part 1.1

Appendix J_Agency Coordination_Part 1.2

Appendix J_Agency Coordination_Part 2.1

Appendix J_Agency Coordination_Part 2.2

Appendix J_Agency Coordination_Part 3.1

Appendix J_Agency Coordination_Part 3.2

Appendix J_Agency Coordination_Part 4

Appendix J_Agency Coordination_Part 5

Appendix K_Draft Section 4(f) Evaluation

Appendix L_Farmland Conversion Impact Rating

Appendix M_Natural Resources Technical Memorandum

Appendix N_Supplemental Land Use Documentation

Appendix O_Model Output Differences

Appendix P_SEIS Public Involvement Materials

Appendix Q_USCG Navigation Study

Appendix R_Hazardous Materials-Waste Survey Technical Memorandum

Appendix S_Conceptual Relocation Report

Appendix T_Floodplains Checklist

Appendix U_Visual Impact Assessment Checklist

Appendix V_2012 Public Opinion Survey

Appendix W_Comments and Reponses for the 2010 DEIS

Appendix X_Biological Assessments

What did we hear during the 2021 Public Hearing comment period?

Below is a summary of the number and type of comments received during the 2021 SEIS Public Hearing comment period (August 18 to October 15, 2021).

Document Archive