NHIS: Non-Hazardous Hydrocarbon Impacted Soil Program
non-hazardous soil

NHIS soil contains more soil than oil and is not considered hazardous material.


The Santa Maria Regional Landfill is one of the most highly regulated sites in the area. In 1996, the City of Santa Maria was faced with the need to close its existing landfill, because undesirable substances were reaching the groundwater from liquids passing through decomposing trash. In order to close the landfill, City engineers had to meet all government regulatory requirements, while ensuring public safety and maintaining fiscal responsibility to City residents. City staff had to ensure that the landfill closure would comply with all environmental rules and regulations.

With approval from the Central Coast Regional Water Quality Control Board (CCRWQCB), and other regulatory agencies that oversee landfill issues, the City found a solution that enabled it to meet the timeline for closure, while ensuring public safety and producing positive fiscal impact for community rate payers.

Landfill Closure

As each section of the Santa Maria Regional Landfill reaches capacity, it will be closed by the building of a landfill cap over it. Soil mined from the Santa Maria Riverbed supplies some of what is used for the cap. However, State regulatory agencies limit the amount that can be mined from this source. Engineers determined that, without alternate sources, it would be financially and logistically impossible for the City to close all of the unlined landfill.

The Solution

Various areas in California have an abundance of soils that are considered non-hazardous but that contain varying amounts of oil. The Santa Maria Regional Landfill submitted sophisticated engineering studies to the CCRWQCB to determine what levels of oily soils would be acceptable for capping landfills. The City defines the soils that meet these approved levels as “non-hazardous hydrocarbon impacted soils,” (NHIS). NHIS result from a century of oil production in many areas of the State, contain more soil than oil, and are not considered hazardous.

The closure regulations in 27 California Code of Regulations (CCR) 21090(a)(1) allows the use of contaminated soil as final cover foundation layer. In addition, 27 CCR 20686 considers alternate materials for final cover foundation layer as a “beneficial reuse.” Thus, NHIS materials as a final cover foundation layer constitute a “beneficial reuse” that the relevant regulatory agencies recognize and accept. Central Coast Remedial Resources, Inc. will issue a Beneficial Reuse Certificate to each generator of NHIS, when requested.

The use of NHIS as part of the landfill cap allows the City meet the closure goal. An additional benefit is the bringing of financial resources to the City in the form of payment from the oil companies for the disposal of the soil. Funds that are received not only cover the cost of the closure, but provide for upgrading and enhancing staff and equipment in other City Departments, including Police and Fire. This program has been a large factor in the City’s ability to freeze solid waste service rate increases for the past seven years.

Photo of Guadalupe Dunes courtesy of Chevron Corporation

The Guadalupe Dunes project provides environmental benefits to that sensitive ecological area, while meeting all regulatory requirements for the City of Santa Maria’s landfill closure.