The City of Long Beach Building Department has established a Methane Mitigation Process that can be reviewed by referencing the Information Bulletin on Methane Gas Mitigation provided by the city and Chapter 18.79 of the Long Beach Municipal Code (LBMC).

If a new construction project is planned within the Long Beach building jurisdiction, a methane mitigation consultant shall review the Long Beach Methane Zone Map to determine whether the property is located within the City of Long Beach’s Methane Zone. The Long Beach Building Department methane zone map is available online for review. 

The scope of Methane Mitigation will be determined based on the property’s location and the size and type of project. If it is determined that a project is located within the Methane Zone, a Qualified Professional should be hired as a Long Beach Methane Mitigation Consultant. If a Methane Test is conducted on the property and determined that methane gas is not present, methane gas mitigation may not be necessary. It should be noted on the methane mitigation plan for the Long Beach Building Department’s Plan Check review.

Long Beach Plan Check approval for projects within the Methane Gas Zone

New Construction Projects located within the City of Long Beach Methane Zone will require a Methane Mitigation Qualified Professional to establish the Methane Mitigation requirements based on the City of Long Beach’s Methane Mitigation Code. A Methane Test may be completed in accordance with the Long Beach Testing procedures, which require the results to be presented on a Certificate of Compliance for Methane Test Data. The Methane Test Certificate of Compliance must be outlined on the methane mitigation plan prepared by the Methane Mitigation Designer.

The Methane Mitigation Design must be submitted according to the prescribed standards of the city for Methane Mitigation Plan Checking. The Methane Mitigation Design will outline the required Methane Mitigation components based on the Long Beach Methane Mitigation Building code and the corresponding Long Beach Methane Test. 

During the City of Long Beach Methane Plan Check, the project will be issued a project number that will correspond to a Building Permit. The methane mitigation consultant might also be required to receive a permit from the Long Beach fire department if the Methane Soil Gas Concentrations are high. 

The City of Long Inspection team will participate in a pre-construction meeting to discuss the scope of work for the project. The Methane Mitigation Scope might include the installation of the methane mitigation membrane, smoke testing, and inspection for the other active or inactive methane systems present in the design. If an active methane system is used, the Fire Department staff should inspect the project after the approval of the alarm plans.   

Some projects may require a code modification, which can affect the integrating sensors, methane systems, and alarm systems within the Methane Mitigation Design. The proposed modifications will be reviewed by the Building Official and Fire Marshal, and if approved, a building permit will be issued, and the proposed modifications can be executed. If a code modification is implemented within a Methane Mitigation Design, it should be noted in the methane plan sent to the Building Official.

Methane Testing & Methane Mitigation Design in Long Beach

Projects within the Long Beach building jurisdiction require initial shallow soil testing. Two or more tests are done in each site or one in every 10,000 sqft of site area. The probes to be used in the methane test are installed according to the California Department of Toxic Substances Control (DTSC) advisory on Active Soil Gas Investigations. They are installed 4 ft or more below ground surface and above the groundwater level where it is less than 4 ft bgs. 

Three soil gas probe tests are installed at the borehole with the highest concentration of soil gas at 5, 10, and 20 feet depths below the lowest building slab. Forty-eight hours after installation, the probes are sampled once or more depending on the methods of installation utilized. The methane concentrations and pressure in each of the sample locations will then be recorded.

The results of these tests are recorded in the methane mitigation plan. A site plan is also required to outline the shallow and soil gas tests’ locations and document the dimension and location of the proposed structure. Upon reviewing and approval of the plans, the design will be signed and stamped by a methane mitigation consultant

The City of Long Beach Building and Safety Bureau and the City of Long Beach Health Department established the requirements for the methane mitigation design based on the investigation on the soil gas test results. If the methane test results showed methane gas concentrations of less than 1,000 parts per million by volume (ppmv) and pressure less than or equal to zero, it would require no action. The property will be categorized as a Level I if the methane gas concentration is less than 50,000 ppmv with pressure less than 2 in of water column (WC). A Level II property has methane gas concentrations of up to 50,000 ppmv and pressure greater than 2 WC or methane gas concentrations between 50,000 ppmv or 300,000 ppmv at all pressures. The property will be categorized as Level III if it is located near abandoned oil wells or the methane gas concentration is found to be greater than 300,000 ppmv. 

Methane Mitigation Construction Components for Long Beach Building Department

The Long Beach Building Department requires the design of the methane mitigation system used for the project. The methane mitigation consultant also conducts a special inspection on the methane mitigation measures during the construction. The city of Long Beach will inspect the methane mitigation components according to Section 18.79.090 of the LBMC.  

The methane gas membrane barrier must be a continuous layer beneath the building, except under the grade beams and footings. A protection layer is installed above and below the barrier and includes either a 2-in minimum sand layer, 2-in minimum mud slab, or a 16 oz geotextile fabric. Any gas membrane barrier penetrations should be sealed according to the methane barrier manufacturer.

The sub-slab venting layer should be placed between the gas membrane barrier protection layer and subgrade. The Methane SubSlab Vent system will consist of a gravel blanket and perforate pipe wrapped amongst a geo-composite.

The SubSlab vent piping is installed within a trench in which no part of the foundation is more than 25 feet from the perforated vent pipe. This installation should be connected to the vertical vent risers, which should always have a diameter equal to or larger than the horizontal pipes. If the diameter of the vent piping is 3 inches, it should not be spaced greater than 50 ft apart on center. If the diameter is 4 inches, the piping should not be spaced greater than 100 feet apart on center. As for the horizontal piping, its total length should not exceed 100 feet and maintain a minimum of 1 % positive slope towards the vent riser.

To ensure the effectiveness and efficiency of the methane mitigation measures, the project should meet the requirements set by the Long Beach Building Department. Hiring a methane mitigation consultant is highly recommended to make sure all processes are executed correctly and within the city of Long Beach’s Methane Code. A Methane Testing and Methane Mitigation may not always be required, even if the property is located with the City of Long Beach’s Methane Zone.