NHIS: Non-Hazardous Hydrocarbon Impacted Soil Program
soil on liner

Two feet of clean soil being placed over the liner as protection, prior to NHIS placement. The two feet of clean cover will ensure the liner is not damaged when incoming trucks of NHIS dump their loads. Only those soils that meet the State-approved NHIS acceptance criteria are used at the landfill.


The landfill cap includes an impervious clay liner (as shown in this diagram), complete with an engineered drainage system. This is covered by a layer of clean soil and plants, which is sloped to prevent rainwater and surface water from infiltrating the NHIS and buried trash.

The landfill cap consists of four layers, listed here from bottom to top: 1) the NHIS final grade, 2) a geosynthethic clay liner, 3) a drainage layer, and 4) three feet of soil with low-rooting vegetation planted on the surface of the Closed Active Area. This diagram shows the cross-section view of the encapsulated NHIS materials between the impermeable liner and landfill cap.

NHIS is encapsulated at the landfill in the following manner. It is separated from the buried trash with a layer of clean soil and industry-standard flexible plastic liner. This plastic liner adds an impermeable barrier between the NHIS and groundwater. The closure cap adds a second permanent barrier over the NHIS, to ensure that surface water does not leak into the NHIS. The bottom liner and the final cap completely encase the NHIS material.

What is allowed into the landfill is highly regulated. The landfill design has been approved by State and local regulatory agencies and follows Federal Environmental Protection Agency standards. As a fully-permitted, licensed and audited government waste disposal site, the project has a comprehensive waste screening and data management program, complete with an environmental monitoring system. State and Federal laws mandate that landfills be monitored for at least 30 years after landfill closure. This ensures that any problems will be discovered and remediated in a timely manner.

double-lined disposal cell

Construction of the double-lined disposal cell in the “Active Area”

Landfill History »
Monitoring Program »