As large tracts of geographically desirable vacant land become scarcer, residential and commercial property developers are increasingly turning to old landfills or former dumps. However, such redevelopment is complex and rife with uncertainties. When compared to greenfield development, the land acquisition costs are lower. Still, any savings are typically offset by greater environmental and infrastructure costs associated with the foundation, landfill gas management, stormwater management, groundwater impacts, meeting closure requirements, and multiple regulatory agency coordination. Therefore, it is important to maximize the developable area while providing engineering solutions to make the project economically feasible. In this blog, we identify some options to reuse challenging sites and lessons learned to contribute to successful redevelopment projects.
Deep Dynamic Compaction
Old landfills or dumps present some unique soil stability challenges. Deep dynamic compaction (DDC) is a ground stabilization technique that has gained popularity in recent years to improve subsurface soil conditions. DDC involves dropping 6 to 30-ton weights from a height between 30 and 75 feet to achieve the desired soil compaction. DDC can effectively apply to a range of subsurface materials, including former C&D debris or municipal solid waste dumps.
DDC provides a stable foundation for future development, minimizes differential settlement while leaving the landfill waste in place, and eliminates the costs associated with removing, transporting, and disposing of buried waste, costing millions of dollars. For simplicity’s sake, let’s consider a 1-acre old landfill or a dumpsite with an average of 15 feet of waste. If excavating the waste and replacing it with clean fill, the disposal fee costs for the excavated waste alone could exceed $400,000. Alternatively, DDC costs range from $1.50 to $2.00 per square foot or $65,000 to $87,120 per acre, excluding mobilization, which costs around $30,000.
Gas Mitigation Systems
Constructing buildings on top of dynamically compacted areas generally requires a combustible gas barrier layer below the building foundation to manage subsurface combustible gases (typically methane). The barrier is required because the waste remains in place. In its simplified form, gas mitigation systems include:
These gas mitigation systems can be either a passive or an active system with a blower. The cost of such systems varies depending on the size of the building, location, and type of liner system used. Typical capital costs for passive systems are in the range of $7 to $9 per square foot for the spray-applied liner and $3 to $4 per square foot for the HDPE liner. For an active system using blowers, add $3 to $4 per square foot. The designer configures a system from these options to address the client’s risk preference and considering future tenant preferences.
Using innovative approaches, impaired lands are increasingly attractive to developers. Beyond the cost-saving benefits to developers realized through DDC and an appropriate gas mitigation system, such projects also create local jobs, increase the tax base, and protect public health and the environment.
About the Authors:
Somshekhar Kundral – Mr. Kundralis, PE, is a Senior Project Manager with over 12 years of broad and diverse environmental engineering experience that includes projects in landfill redevelopment, landfill gas management system design, site assessment, groundwater remediation system design, stormwater management, and injection well system construction. Som is experienced with site permitting, compliance reporting and construction administration services, and remediation systems’ operation and management.
Manuel J. Hernandez – Mr. Hernandez, PE, BCEE, is a Project Director with 21 years of experience in the environmental field. Manny focuses on solid waste management, and he is an expert in local and federal environmental regulations. His experience includes comprehensive project development, including planning, evaluation, contract negotiations, permitting, design, construction administration, and public outreach. He is known for his leadership, mentoring and team-building skills within multicultural teams.
Both engineer’s environmental works include public and private clients. SCS Engineers is a member of the U.S. Green Building Council and the Center for Creative Land Recycling.
SCS Engineers’ SCSeTools® platform and applications help facilities and companies operate more efficiently by continually gauging operational health and identify trends critical to operations and the environment.
SCS Technology Services®, the technology development practice within SCS Engineers, announces a new application for tracking and analyzing environmental data. The application expands the firm’s SCSeTools® platform, demonstrating its commitment to developing the most advanced data-driven technology in the environmental services industry.
Groundwater monitoring and compliance services are long-term and expensive responsibilities that generate enormous amounts of monitoring and laboratory data. SCS Groundwater™ is a tool to monitor and manage the data associated with operations and reporting requirements for various sites. Sites include active or closed landfills, plants, and impact sites such as former dry cleaners or industrial facilities.
The application also monitors and manages data effectively for clean groundwater applications such as groundwater basin management projects consistent with standard protocol under state and federal environmental compliance rules. SCS Groundwater™ collects and efficiently organizes groundwater monitoring and maintenance data providing those responsible for environmental compliance with a reliable, consistent, and cost-effective way to manage the large volume of information.
The application’s primary value is enabling users to set up a detailed monitoring plan for any number of events, including the sampling points to include and what analyses to perform at each point. Once the information upload is finished, the application checks incoming data against the plan to confirm all work is complete.
SCS Groundwater™ generates reporting components such as data tables, charts, graphs, and maps for compliance, reporting, and finding trends. For example, on a brownfield site, the compliance manager could upload historical monitoring data results, view the data trends over time, and then produce report tables and figures. Operators can also use the data in other applications for additional analysis or visualization.
SCS Engineers’ environmental solutions and technology directly result from our experience and dedication to industries responsible for safeguarding the environment as they deliver services and products. For information about SCS, visit the SCS eTools pages or enjoy our 50th Anniversary video to see the technology in action.
The SCSeTools® platform and applications help facilities operate more efficiently by continually gauging operational health and spot trends that help determine when and how to invest in infrastructure. Field staff, environmental compliance experts, brownfields, developers, and clients in the waste industry guide the technology designs. For additional information and demonstrations of these productivity-enhancing tools, please contact .