CONCORD -- A task force of local and state law enforcement officers launched a pre-dawn sweep of about 20 homeless encampments in Contra Costa County Tuesday, informing the residents of those camps that they have to leave within 48 hours or face arrest.

Concord and East Bay Regional Park officers, California Highway Patrol officers and agents from the state Fish and Game Department conducted the sweep.

Lt. Jon King, of the East Bay Park Police, said the sweep was sparked by concerns over health and pollution problems intensified by the upcoming rainy winter weather season.

"It (the sweep) is important because we have identified a lot of safety issues in the homeless camps," King said. "A lot of them are in the flood control canals so when we get a good rain and have a lot of water flowing down there we have people at risk."

"There is also a lot of pollution. In these homeless encampments, we have car batteries, petroleum products, human waste, needles and syringes and all that stuff. If we don't get that cleaned out -- when those rains come -- it will flow right out into the Bay and cause a lot of pollution."

King said campers would be informed of a variety county services that were available to them. But he added that in some preliminary contact with the homeless, most said they would not seek help.

"Out of 100 people we have contacted there were only about 35 who wanted county services," King said. "Our winter shelters are about to open in the next couple weeks, hopefully some will be able to take advantage of that and the county just received in excess of $1 million grant fund from HUD to house some of these people."

"So there are a lot of things coming into the play right now. With the weather and everything we had to make our move right now."

But some encampment residents said they would not go to shelters.

"I'm not homeless by choice," said Tom Gardner. "I won't give up my dog to go into a shelter. I owe more to him than that. I owe more to myself than to go into a shelter. There are more drugs in the shelters than there is on the streets."

On Tuesday, the encampments were tagged for removal, occupants identified and conditions of the encampment documented. The homeless outreach teams were with the officers and told the campers about the services available.

On Thursday, the teams will be back and take appropriate enforcement action if occupants are located. The District Attorney's office has been contacted and is prepared to prosecute those who are cited or arrested.

Crews from Caltrans, Contra Costa County, East Bay Regional Parks and City of Concord will follow and begin the cleanup of the camps.

"There are some who many not want to leave and then unfortunately they will come under the purview of the criminal justice system," King said.

Concern among local property owners and police agencies about the homeless encampments has been growing for months.

Caltrans has estimated that $150,000 has been spent for cleanup of homeless encampments in the I-680/Hwy 242 areas while the Contra Costa Flood Control District has spent an equivalent amount cleaning encampments in the flood control channels in the same area.

Police agencies also have seen an increase in criminal activities around and associated with large homeless encampments.