A series of four suspicious fires — including three in one day — at an abandoned house just a block away from the Union Road fire station underscores a growing problem in Manteca: Arson.Arson fires are nothing new for Manteca. But until recent years they were confined primarily to dumpsters and vegetation fires.Although fires of suspicious origins rarely account for more than 10 percent of all fires in a given year they are responsible for a much larger chunk of losses. Arson fires have caused more than $1.6 million of the $5.5 million in losses during the past two years.A rundown of some of the suspicious fires during the past two years include:• In March playground equipment at McFall School on Hoyt Lane north of Northgate Park was torched by an arsonist.