The fire began on Saturday, July 20, at Recology Grover Environmental Products, 3909 Gaffery Road in Vernalis.
Tracy Fire Division Chief Andrew Kellogg said the cause is unknown but noted that Saturday’s temperatures and high humidity could have led to a spontaneous combustion of the pile.
Kellogg described the pile as generic compost — tree trimmings, mulch and other vegetation. Recology Grover Environmental Products’ website describes the Vernalis facility as a 166-acre site that creates premium quality compost from primarily yard clippings and food scraps.
On Saturday, the Tracy Fire Department responded to the fire and found the one large pile — more than 500 feet long, 200 feet wide and 40 feet high — burning and several spot fires burning in adjacent compost piles, according to Kellogg.
Tracy fire crews joined those of Stanislaus County in fighting the fires.
The decision was made to put out the smaller fires, move compost material away from the large pile to isolate it and let it burn, according to Kellogg.
Tracy fire crews stayed at the scene for about five hours, he said.
On Sunday, July 21, Stanislaus County fire crews turned the scene over to the compost company to extinguish the fire.
Kellogg said the compost company has a fire suppression system and that they would continue to try and put the fire burning in the large pile themselves.
A few 911 calls of a grass fire were received over the weekend as smoke from the burning compost was mistaken for a new fire by Tracy area residents.
Kellogg said he had reports that smoke from the fire was drifting low over the valley almost to Merced.
Recology Grover Environmental Products could take more than five days to extinguish the fires in the compost piles, Kellogg said.
•Contact Glenn Moore at 830-4252 or firstname.lastname@example.org