A Perspective for Building on Landfills

by Christina Rain,PE, Senior Project Manager for Langan

Figure SEQ Figure \* ARABIC 1 Aerial view above West Contra Costa Sanitary Landfill in Richmond California

Each year, Americans throw away 300 million tons of trash – that’s nearly 2,000 pounds of trash for every person! There are approximately 3,000 active landfills and as many as 10,000 closed landfills in the US. Landfill regulations were first established in the US in the 1960s and 1970s. Prior to this time, waste was placed in dumps that were largely uncontrolled.

Environmental stewardship of landfill properties, especially those landfills closed prior to the enactment of environmental regulations, can be achieved by pursuing landfill development projects that are beneficial to communities and the environment. States, counties, and municipalities set forth requirements for implementing environmental protections as part of landfill “post-closure” approvals. These additional environmental protections are generally not possible without redevelopment.

Langan, an engineering and environmental consulting firm, provides engineering, planning, design, and construction services for landfill and other brownfield reuse projects. Examples of current projects Langan is supporting demonstrate the variety of reuse we see at landfills today and exemplify the new community benefits and environmental protections they afford:

• Phase3 Real Estate’s Genesis Marina at the Former Sierra Point Landfill in Brisbane, California, was recently completed in 2024 and now serves the Life Science sector. The development included installing an engineered landfill cover not previously in place, installing a vapor mitigation system to control landfill gas intrusion to indoor air, completing another segment of the San Francisco Bay trail, and achieved LEED Gold (Leadership in Energy and Environmental Design Gold-standard green building rating) for construction.

Figure SEQ Figure \* ARABIC 2 Aerial view of Sierra Point

Figure SEQ Figure \* ARABIC 3 Rendering of Genesis Marina

• River Trail Village is an on-campus student affordable housing development at Napa Valley College in Napa California. The site is on a former construction debris landfill and directly east of a former disposal site for incinerated waste (ash landfill). All the construction debris was removed prior to construction of the student housing development, and interim ash landfill closure measures were constructed, all under regulatory oversight. The housing units are scheduled to open this summer.

• Netflix’s planned film and television production studio at the former Fort Monmouth Army Base in New Jersey is expected to increase the State ’s film industry and stimulate economic growth in the region. Development planning is currently in progress and includes development over three separate landfill areas.

• Kilroy’s life sciences campus currently under construction at the Former Oyster Point landfill in South San Francisco, California, has included not only bringing the landfill cover up to current State standards, but also improving or adding to numerous amenities available to the community. These include new and updated segments of the San Francisco Bay trail, three new public restrooms along the trail, improvements to the public marina’s docks, a new sandy beach area with picnic tables, improved access for pedestrians, cyclists, and public transit to the existing ferry terminal, and a new sports field. All of these improvements comply with the Americans with Disabilities Act (ADA), ensuring accessibility to all.

Renewable energy uses, whether methane capture, solar farms, or battery storage, offer another great opportunity for beneficial reuse for landfill properties. The US Environmental Protection Agency’s Re-powering America’s Land initiative encourages and provides resources to those interested in this possibility.

Landfill development comes with engineering challenges. Detailed project planning, having an interdisciplinary environmental, geotechnical and civil engineering team member, like Langan, and in-depth coordination with regulators and other local authorities is imperative. Understanding the regulatory requirements and oversight framework early will help developers navigate the landfill development process successfully.

Not all sites are created equal. The type of wastes disposed of at a landfill, whether construction debris, municipal (household) waste, hazardous waste, or a mix of waste types, will affect requirements pertaining to environmental investigation, targeted cleanup or remediation, and the need for new or added leachate and landfill gas controls. These site-specific considerations will affect decisions on suitable reuse options. As with all brownfields sites, environmental controls and mitigation systems must be put in place to ensure reuse will be safe for future site users. Typically, these controls will include landfill capping and installation of a landfill gas (methane) mitigation system. In California, capping is no less than two feet of cover over refuse and consists of a foundation layer that may be refuse or another appropriate material that meets required engineering criteria to support the overlying layers, a one-foot low permeability layer like clay, and a one-foot erosion-resistant layer like vegetated soil. A landfill gas mitigation system typically includes active venting and a barrier membrane installed beneath a building, monitoring within the building, and other controls to minimize the build-up of methane gas within the building and alert occupants to methane gas concerns.

Other engineering design considerations include: land settlement (the lowering of the ground surface), corrosive environments (causing rust or otherwise degrading metals used in construction), and vulnerabilities to earthquakes. Land settlement at landfills can be significant – on the order of several feet. Settlement also may occur unevenly depending on underlying waste depth and type. Therefore, buildings, foundations, and utilities must be engineered to accommodate differential settlement, resist corrosivity, and remain safe during a seismic event. Long-term maintenance is needed to adapt the property to settlement and other future challenges as the landfill and the development structures age.

Environmental stewardship and protections, community benefits, and economic outcomes of landfill developments generally outweigh the potential challenges associated with their development. As shown through the above and many other project examples, landfill redevelopment is achievable today. The number of landfill redevelopments can be expected to grow and in doing so help to achieve a more sustainable future.