So far this year, the number of sewage spills in Honolulu has decreased, the director of the city's Environmental Services Department said in a statement released Friday.

Eric Takamura said the 22 spills recorded in the first quarter of 2008 represent a drop of more than 26 percent over the 30 spills that occurred during the same three months last year.

Takamura said the department's Collection System Maintenance Branch has been effective in analyzing and correcting problem areas as it's making an increased effort to maintain the city's sewage infrastructure.

The month of March — during which only one spill was recorded — is particularly notable, Takamura said. That's the lowest monthly total number of spills on record in Honolulu, he said.

Among a number of high-impact projects the city is ready to begin is a 30-month job that encompasses Kalihi and Nu'uanu, he said.

Grease and tree roots have been the main cause of sewage spills during the past two years, Takamura said, while damaged pipes and wet weather spills also have been a primary reason.

Since taking office in January 2005, Mayor Mufi Hannemann said the task of improved sewage system maintenance has been one of the city's top priorities. So far, the mayor has appropriated more than $1 billion to refurbish the city's sewer infrastructure, and he expects to appropriate $1.5 billion more for the work in the next six years, the statement said.