Staff: material on site is mulch; spontaneous combustion risk tied to composting, not typical mulch piles

Cochise County staff told the Board of Supervisors that the material stockpiled on the property near Ocotillo Road appears to be chipped mulch rather than active composting and that, while spontaneous combustion can occur in compost piles, typical dry mulch used for land restoration carries a lower risk.

Jackie Watkins and other staff described the material as chipped green waste and tree prunings. A staff presenter noted that “mulch is used to restore property” and that typical restoration rates cited by county and federal guidance are in the range of 4–10 tons per acre depending on the work. The presenter said Sierra Vista’s municipal program mixes green waste and wastewater solids to produce class A compost and that leftover screened material becomes mulch; by contrast, the material observed on the Ocotillo Road site appeared to be wood chips and shredded branches.

Supervisors asked whether the pile had recently burned at a prior location and whether the pile posed a fire hazard on the Cochise County site. Staff said spontaneous combustion events are associated with composting processes that involve microbial heat and moisture and that dry chipped mulch is less prone to spontaneous combustion. “You have to have moisture in the compost to get it to combust,” a staff speaker said. The property owner told staff he intends to spread the mulch around his site for erosion control and restoration.

Staff also said Development Services has no permit for mulch at this site and that spreading mulch for land restoration would be an allowed use on private property. County staff said they observed the material during a site visit and that drones and photos were used to document the stockpile.

Ending: No enforcement action was taken during the work session; staff will follow up with the property owner and neighbors and include the matter in additional outreach and another public meeting if needed.