DEVELOPMENT OVER OLD CLOSED LANDFILLS. Brenda S. Clark, PE Darryl Lee, PE, LEED AP

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1 2014 HDR Architecture, HDR, HDR, Inc., all all rights reserved.

2 DEVELOPMENT OVER OLD CLOSED LANDFILLS Brenda S. Clark, PE Darryl Lee, PE, LEED AP

3 Introduction What are old landfills and why do we develop over them What are the concerns and the tools to address Example projects

4 INTRODUCTIONS Brenda Clark, PE o Professional Engineer with over 25 years of solid waste experience o BS in Civil Engineering o South Florida Solid Waste Section Manager for a national engineering consulting firm Darryl Lee, PE, LEED AP o Professional Engineer with over 17 years of environmental consulting and real estate development experience o BS Civil / Environmental Engineering, MBA Real Estate o Development Project Manager for the redevelopment of the former Munisport Landfill (aka Biscayne Landing in North Miami, FL

5 What are old dumps and/or landfills Why would we develop over them

6 IN SOUTH FLORIDA, BORROW PITS WERE HISTORICALLY FILLED WITH WASTE Historical Aerial Photographs help us define their locations

7 HOW DO WE KNOW THE SITE IS AN OLD DUMP? Topography may be a good indication. Confirm with subsurface investigations.

8 HOW DO WE KNOW THEY ARE THERE? If you suspect the site was historically a dump, perform a Site Investigation Don t find by accident, such as when you start construction

9 NOW THAT YOU HAVE FOUND ONE WHO REGULATES THE ACTIVITIES OVER OLD LANDFILLS WHAT DOES FDEP REGULATE? Waste Disturbance Waste Location Waste Characteristics Gas Emissions Surface Water Management Groundwater Quality

10 WHAT ARE THE CONCERNS IN DEVELOPING OVER OLD LANDFILLS WASTE DISTURBANCE: Typically old waste, who knows what is buried? SUBSURFACE: How do you mitigate for heterogeneous waste in the subsurface / foundation? GAS EMISSIONS: How do you protect human health and the environment? SURFACE WATER MANAGEMENT: How do you prevent surface water from percolating through the waste and spreading contamination? GROUNDWATER QUALITY: How do you prevent impacts to groundwater quality?

11 SUBSURFACE CONCERNS o Waste Limitations (how far does it extend laterally and vertically) o Waste Grades (what does it look like on the surface) o Waste Characteristics (chemical / physical properties) o Waste voids (how do you compact) o Differential settlement (how do you limit)

12 TOOLS TO ADDRESS CONCERNS: Subsurface o Waste Limitations: Test Pits with a backhoe and / or borings o Waste Grades: Survey o Waste Characteristics: Laboratory Analysis o Waste voids: Subsurface Improvements o Differential settlement: determine tolerance

13 TOOLS TO ADDRESS CONCERNS: EXTENT OF WASTE Borings can be used to determine the vertical limits of the waste The borings should be logged in the field

14 TOOLS TO ADDRESS CONCERNS: SUBSURFACE SETTLEMENT o Dynamic Compaction: Waste voids can be compacted with dynamic compaction o Piles: Buildings can be supported on piles o Static Load: Waste can be loaded with a static load, allow for compaction over time

15 GAS EMISSIONS o Waste still generating methane o Build up below buildings TOOLS TO ADDRESS CONCERNS o Barrier Layer o Passive Gas Venting System o Active Gas Collection System o Monitoring for explosive gases

16 SURFACE WATER MANAGEMENT o Infiltration through underlying waste o Spread contamination TOOLS TO ADDRESS CONCERNS o Barrier Layer to prevent surface water infiltration o Venting system to prevent uplift of barrier layer

17 GROUNDWATER QUALITY o o Concern: Developing over waste may cause a squeezing of liquids trapped in void spaces in waste to groundwater To Address Concern: Modeling of groundwater, monitoring

18 PROJECT DEVELOPMENT: Miami-Dade County, Florida Design Issues / Solutions Develop a new landfill over an existing one: determine suitability of subsurface materials Manage leachate: creative grading Groundwater Monitoring: convince regulators that monitoring wells should be located outside of waste boundary Site included more than 350 acres of landfilled construction and demolition debris material, none that was closed.

19 LANDFILL DEVELOPMENT: Broward County, Florida Design Issues / Solutions Building over waste: pile foundation to support Landfill gas detected in waste below the building: vapor barrier and passive gas venting system Landfill gas detected in waste below the surface water pond: liner to prevent surface water infiltration, passive venting system to prevent uplift of the liner Utility connections transitioning between waste and native soils: use flexible piping that can allow for movement between the two conditions

20 PROJECT DEVELOPMENT: Broward County, Florida Design Issues / Solutions PROJECT DESCRIPTION: Developed a warehouse structure over an old closed dump without addressing the environmental issues (gas, surface water, groundwater) PROJECT CHALLENGES: Systems installed following construction Surface Water Management designed with infiltration had to be redesigned without, and liner was installed Gas Management was not included under the building so a vertical active system was designed and installed around the perimeter of the building

21 LANDFILL DEVELOPMENT: Broward County, Florida Design Issues / Solutions Construction and demolition debris / lake fill material detected below the building footprint to depths of 25 ft: dynamically compact the building footprint Confirm desired subsurface improvements: Standard penetration test borings performed to confirm improvements from dynamic compaction

22 LANDFILL DEVELOPMENT: Broward County, Florida Design Issues / Solutions Excavation of solid waste for site grading: waste relocated to site green areas and berms to minimize construction costs Solid waste detected at depths up to 35 ft below the building footprint: developed a dynamic compaction program to compact the waste Landfill gas detected in waste below the building: installed a geomembrane vapor barrier with a permeable layer below to allow venting of the gas Solid waste in the surface water management area: liner to prevent surface water infiltration, passive venting system to prevent uplift of the liner

23 LANDFILL DEVELOPMENT Broward County, Florida Design Issues / Solutions Municipal solid waste detected below the building footprint to depths of 25 ft: dynamically compact the building footprint Landfill gas detected: Vapor barrier installed with passive gas system below the liner

24 LANDFILL DEVELOPMENT EXPERIENCE PROJECT GOAL: Develop a landfill over the existing waste PROBLEM: Modifications to a facility with an existing gas venting layer. Site included more than 350 acres of landfilled construction SOLUTION: and Spray demolition on barrier debris layer material. PROJECT CHALLENGES: Stability of underlying materials Surface Water Management

25 BISCAYNE LANDING DEVELOPMENT OPPORTUNITY 193 Acres of Generally Vacant Land in North Miami, FL Centrally Located Between Miami / Ft. Lauderdale in Commercial Corridor (Biscayne Blvd/US-1) Adjacent to State-Owned Mangroves Preserve Coastal Proximity and High Site Elevations Bay/Ocean Views from 4th Story and Above Former Munisport Landfill C&D Debris, Yard Waste, MSW

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27 PLANNED MIXED USE DEVELOPMENT 4000 Residential Units 750,000 SF Retail/Commercial 150 Room Hotel Auto dealer(s) Assisted Living/Office Community Center Active/Passive Parks

28 CONCEPTUAL MASTER PLAN

29 CHALLENGES Historical Use as an Unpermitted/Unlined Landfill Landfill Material (MSW, C&D, Yard Waste) up to 30 feet Below Surface Presence of Landfill Gas Groundwater Contamination (Ammonia) Existing Old Borrow Pits Excavated to 25 ft below Groundwater Table Various Layers of Jurisdictional Agencies (FDEP, SFWMD, Miami-Dade County, City of North Miami

30 DESIGN ISSUES / SOLUTIONS Site Grading o Waste Relocation Plan o Hazardous Waste Contingency Plan Gas Management o Buildings Vapor Barriers/Venting Gas Sensors (24/7/365) o Utilities Sealoffs and Venting Boxes Permeable Trenches Groundwater Remediation/Monitoring

31 DESIGN ISSUES / SOLUTIONS Differential Settlement o Roadway Deep Dynamic Compaction o Buildings Piles or Subsurface Improvement (DDC/Surcharge) o Utilities Forcemains; HDPE piping; Expansion Joints Stormwater Management o Perimeter Retention Areas (Partially Lined) o Drainage Wells

32 IMPACTS TO A DEVELOPER Costs o Soft Costs Design Consultants, Compliance Monitoring, Environmental Attorneys, etc. o Hard Costs Land Development, Structural o Grants and Other Subsidies Can Offset Time o Additional Permitting and Public Notice Requirements o Extended Construction Schedule Public Relations Stigma Impacting Sales o Toxic Dump o Hazardous Waste Reduced Flexibility to Make Modifications Long Term Responsible Entity

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