The state Department of Ecology, concerned about the number of pets that fall into abandoned wells, is encouraging property owners to locate and ensure old wells on their property are properly decommissioned.

The state also said property owners should report to state officials any old wells they find on their land and seek advice about how to decommission them. Landowners can face legal liability for injuries or groundwater contamination caused by abandoned wells that are not properly filled in and capped.

The Ecology Department has created a new web page — “Decommissioning of Abandoned Wells” — that provides information about how to locate and fill in old wells.

“Many abandoned wells date back to the post-World War II housing boom and were dug to serve single-family homes. Many of these wells have been covered over by brush or forest,” Bill Lum, the Ecology Department’s well construction and licensing coordinator, said in a news release. “Ecology has no way to track these wells unless they are reported.”

The number of abandoned wells in the state could be anywhere from 10,000 to 100,000, according to the release. Lum said he believes they’re “pretty widely distributed through the state.”

Every year, farm animals or pets are injured or die in Washington state after falling into abandoned water wells that have not been properly filled in and capped.

Among the reports received this year by the Department of Ecology was an 1,800-pound horse that fell into an abandoned well in Centralia in August after a concrete lid covering the top of the well collapsed under the horse’s weight. The horse died during a rescue attempt by local firefighters. In July, a 13-year-old pet draft horse fell through a covering on an abandoned well near Shelton but was pulled from the well by fire department rescuers. In April 2011, two Labrador retrievers that ran away from their Maury Island home were found drowned in an old well less than a half-mile away.

There have been no reports of people falling into abandoned wells in Washington in recent years, but the wells are of particular danger to children and can be found anywhere, state officials say. In August, a woman digging in her garden in Seattle reported to the state what was determined to be an abandoned cistern. It had created a hole 13 feet deep with an opening of one to two feet wide. The woman had the hole filled in with concrete.

State law requires a licensed well driller to fill an abandoned well with concrete, bentonite clay or grout. Once sealing materials are in place, landowners are allowed to put up to three feet of soil on top of that.

The Ecology Department works with property owners on how to locate and properly decommission abandoned wells.

“We do have the authority to fine property owners for noncompliance with these laws, but we’ve never used it,” Lum said. “Our priority is to help property owners do the right thing for public safety and to ensure these wells are properly filled in and represent no danger to children and animals.”

Counties that have the most success in having property owners properly cap abandoned wells are those with strong drinking water programs in their health departments, requiring old wells on a property to be identified and decommissioned before a building permit can be issued, Lum said. Kitsap, Clark, Pierce and Thurston counties are the most successful counties in term of well decommissioning work. King County doesn’t require identification and decommissioning of wells before issuing a building permit, he said.