Case Study:

Sampson Disposal, LLC Landfill


The Sampson County Disposal, LLC landfill is a privately owned and operated landfill. During investigations for landfill expansion, we determined that existing groundwater elevations limited site optimization for tonnage and soil balance. Smith Gardner, Inc. sought to permanently lower the groundwater beneath the site with a gravity system, allowing for greater excavation and use of on-site soils, as well as to maximize the tonnage per acre site’s capacity.


The solutions for this property included:

  • Aquifer pump testing to accurately determine aquifer flow properties
  • Aquifer modeling to determine if permanent groundwater elevation reduction was possible
  • Design of a Gravity Groundwater Intercept System (GGI) to permanently lower groundwater through discharge to a nearby creek
  • Installation and monitoring of a GGI system in one landfill cell to prove the modeling
  • Long-term GGI monitoring

The solution used a phased approach to investigate whether this creative solution was viable for the site. This allowed us to gather incremental data and minimize the client’s financial risk on the solution. Each step of the way, our original theories were double-checked and modified to reflect the data received. Groundwater at the site has been lowered by approximately 15 to 20 feet below original levels.


The Sampson County Disposal LLC Landfill has constructed three 5-year cells that use the GGI system. The GGI system saved the client millions of dollars, the need for off-site soil and maximizing landfill airspace. Additionally, this design has created a more stable landfill configuration for the future.