1. Summary of Conceptual Design Site 3 Causeway Landfill Culvert Stabilization Marine Corps Recruit Depot Parris Island (CTO JM38) 19 August 2014

2. BACKGROUND Causeway provides vehicular access to Marine Corps Recruit Depot Parris Island Causeway constructed over closed landfill (Site 3), with Land Use Controls in place

3. BACKGROUND Sinkholes noted above two sets of concrete culverts beneath the 3rd Battalion Causeway

4. POTENTIAL REMEDIES TO BE CONSIDERED Partial Excavation of Problem Areas/Depths Injection of Expanding Polyurethane Grout (from above and/or from within) Installation of Engineered Lining System Some Combination of Various Remedies Conducted limited pre-design investigation in March 2014 for additional information to select remedy

5. LIMITED PRE-DESIGN INVESTIGATION MARCH 2014 Geophysical Survey FINDINGS  2 Types of Anomalies Detected Immediately above culverts = very loose soils, representative of sink hole Away from culverts = loose soils, not representative of sink hole

6. LIMITED PRE-DESIGN INVESTIGATION MARCH 2014 Geotechnical Study FINDINGS –Medium dense silty sand to 4 feet, followed by geosynthetic liner (no liner above culverts) –Very loose to medium dense silty sand and debris from 4 to 20 feet –Soft clay from 20 to 30 feet –Loose to dense silty sand from 30 feet to terminal depth –Groundwater encountered at approximately 10 feet –No evidence of contamination (visible, odors, photoionization detector utilized)

7. LIMITED PRE-DESIGN INVESTIGATION MARCH 2014 Geotechnical Study FINDINGS –Sink Holes Apparent as chimney-like voids Immediately above/adjacent to culverts Majority exist in unpaved shoulders Several (including beneath road) identified as not yet open at surface Result of very loose soils to depths of 10 to 15 feet below ground surface Attributed to vertical migration of sands to voids (debris and lifting holes) Additional and larger sink holes are likely

8. LIMITED PRE-DESIGN INVESTIGATION MARCH 2014 Geotechnical Study FINDINGS –Dips Broad roadway settlement issue away from culverts Attributed to long-term settlement of soft clays at depth and compression of landfill debris No voids in dip areas away from culverts Unlikely will develop into new sink hole features

11. PRE-DESIGN LAND SURVEY JUNE 2014 South Carolina Department of Health and Environmental Control-Ocean and Coastal Resource Management Critical Line located Located and obtained elevations of key site features Identified locations of soil borings from Pre-Design Investigation, used to coordinate location of anomalies Located utilities where possible Construction control points established

12. CONCEPTUAL DESIGN Objective Repair existing sinkholes Mitigate development of future sinkholes (to extent possible) Minimize impacts to landfill Preferred Remedy Internal inspection Internal repairs (from inside culverts) Grouting of voids (from road surface) Roadbed replacement Approach avoids sheet piling/significant dewatering

13. CONCEPTUAL DESIGN Anticipated Construction Sequence Establish traffic control/install erosion control Demolish docks Install culvert plugs on upstream side, dewater culverts, remove weirs, and remove debris Conduct internal video inspection to verify conditions During low tide (from inside culvert), seal lifting holes, gaps, and cracks with polyurethane grout and repair spalls and exposed rebar with cement grout Inject cement compaction grout from road surface to no less than 2 feet below culverts, utilize 6 foot by 6 foot grid spacing Excavate 4 feet below road surface over culvert area, install geogrid, and restore road bed and surface

14. CONCEPTUAL DESIGN - SITE PLAN

16. CONCEPTUAL DESIGN RESTORED ROAD FILL SECTION

17. TYPICAL SIDE SLOPE RESTORATION

18. CONCEPTUAL DESIGN SLOPE RESTORATION ADJACENT TO CULVERTS

19. NEXT STEPS Draft Conceptual Design completed and submitted for review by Marine Corps Recruit Depot Parris Island Partnering Team Once approved, Remedial Action Contractor Contractor to prepare Final Design Drawings