California – Composting Rules

California’s regulations are written to encourage the production of high quality compost. The state promotes the use of compost for the agricultural sector of its economy, seeking to bolster production from rangeland and horticulture while reducing greenhouse gas emissions. The promotion of compost use has now also become part of California’s Healthy Soils Program, started in 2015. CalRecycle’s page on “Compost Use in Agriculture” offers scientific case studies quantifying the benefits of using compost as a soil amendment for the state’s agricultural land.


California Composting Rules

Most Californian composting operations are required to apply for a permit; however, there are many exemptions, some of which are listed below. For example, facilities that have less than 500 cubic yards of compost on-site (of which less than 10 percent is food scraps) are exempt from the requirement to obtain a permit. In addition, in-vessel composting of up to 50 cubic yards is allowed without a permit.

Composting operations that are deemed a greater risk are required to either notify the enforcement agency or apply for a full permit. Facilities applying for a permit must adhere to specific site requirements. These include rules on the location and design of the facility, as well as the development of a plan to minimize odors and limit pathogen production.

According to 14 CCR § 17855, on-farm, small-scale food scrap composting operations that are exempt from the requirement to obtain a solid waste permit include the following:

  • Composting agricultural material derived on-site and of which no more than 1,000 cubic yards are sold or given away annually
  • Vermicomposting is exempt; however, handling of compostable material prior to or after vermicomposting composting is subject to regulation
  • Mushroom farming
  • “Handling of green material, feedstock, additives, amendments, compost, or chipped and ground material is an excluded activity if 500 cubic yards or less is on-site at any one time, the compostable materials are generated on-site and if no more than 1,000 cubic yards of materials are either sold or given away annually. The compostable material may also include up to 10% food material by volume”
  • Non-commercial composting of less than one cubic yard of food material produced and used on-site
  • In-vessel composting in vessels with a capacity less than 50 cubic yards


Requirements for Permits, Siting, and Performance Standards

There are many site requirements a compost facility must fulfill in order to receive a permit. Other requirements, such as testing for pathogens and preventing run-off of pollutants, are ongoing. In addition, compost facility operators must consent to inspection by the state enforcement agency (EA).

A few of the major site requirements stated in California Regulations, Title 14, Division 7, Ch. 3.1, Article 6 include:

  • “All handling activities shall be conducted in a manner that minimizes vectors, odor impacts, litter, hazards, nuisances, and noise impacts; and minimizes human contact with, inhalation, ingestion, and transportation of dust, particulates, and pathogenic organisms.”
  • Random checks for contaminants in the load contents of feedstocks, additives, and amendments will be conducted
  • “Contamination of compostable materials that has undergone pathogen reduction […] with feedstocks, compost, or wastes that have not undergone pathogen reduction […] or additives shall be prevented.”
  • Prevention to unauthorized human or animal access to the facility
  • “The operator shall provide fire prevention, protection and control measures, including, but not limited to, temperature monitoring of windrows and piles, adequate water supply for fire suppression, and the isolation of potential ignition sources from combustible materials. Firelanes shall be provided to allow fire control equipment access to all operation areas.”
  • “Physical contaminants and refuse removed from feedstock, compost, or chipped and ground material shall be removed from the site within seven days and transported to an appropriate facility.”
  • If the operation is open to the public, an attendant must be on duty during business hours
  • “Operators shall ensure that all personnel assigned to the operation shall be trained in subjects pertinent to operations and maintenance […] with emphasis on odor impact management and emergency procedures.”


central valley california organic farming compost
Table from Chapter 31, Article 2, Section 17854


Agricultural Material Composting

There are additional requirements for composters who sell finished compost, which are found in Title 14, Division 7, Ch. 3.1, Article 2. According to Section 17856 of this article, if an operation’s feedstock is solely agricultural material, then they may handle an unlimited quantity of agricultural materials, as well as sell or give away the compost they produce. Such an operation will be inspected once a year “at a time when compostable material on the site is active compost.”

An operation processing a mix of agricultural and green materials may be subject to quantity restrictions, depending on the zoning of the location in which it operates. Specifically, if the mixed feedstock operation is located on land zoned for agricultural use and sells/gives away less than 1,000 cubic yards of compost per year, then it may handle an unlimited quantity of material. An enforcement agency could, however, limit the amount of feedstock on-site at any one time to no more than 12,500 cubic yards, provided that the agency submits written findings of excess materials posing public health or environmental hazards.

Operations producing compost from a mix of agricultural and green material feedstocks that sell/give away more than 1,000 cubic yards of compost per year, but are located on non-agricultural land, are also allowed to handle an unlimited amount of agricultural material. They may not, however, stockpile more than 12,500 cubic yards of green material feedstock on-site at any one time. A noted difference for operations on non-agricultural land is that they must be inspected every three months. The number of inspections per year may never drop below one per year, but the frequency of inspections may be reduced if both the enforcement agency and the Department agree that the individual operation does not pose public health or environmental hazards.


Green Material Operations 

Section 17857.1 of Ch 3.1, Article 2 states that green material composting operations may not store more than 12,500 cubic yards of “feedstock, chipped and ground material, amendments, additives, active compost, and stabilized compost on-site at any one time.” Regardless, to allow operators to mange the seasonal variation in compost demand by compost users, operators may request in writing that finished compost products (i.e. those in a stabilized state) be excluded from the materials counted towards the 12,500 cubic yards maximum.

This is termed “seasonal storage adjustment” for stabilized compost, and “may be extended to the storage time and storage volume specified in the land use entitlement for the site, if the EA finds, on the basis of substantial evidence, that the adjustment does not increase the potential harm to public health and safety, and the environment.” When submitting a request for seasonal storage adjustment in a given year, the operator must also send a storage plan to the enforcement agency that includes detailed capacity calculations for storage and management plans for odor minimization and fire prevention.


More Information

Original post from July 30, 2012
Updated July 23, 2021