Indian Land, S.C. ? Residents in a subdivision of two-story brick homes near the North Carolina state line say they were promised roads and ball fields and tennis courts. But the developer has vanished and the neighbors never came so, when the rains do, the ground crumbles.

The potholes at Edenmoor are big enough to swallow car tires these days. With every deluge, miniature Grand Canyons carve through the red clay of the abandoned home sites, clogging a nearby stream with dirt and adding to a growing environmental problem.

The housing bust that has pockmarked the nation’s landscape with half-built construction projects has done more than crash home values. Federal officials and environmentalists says abandoned developments are polluting nearby waterways with sediment, endangering fish and plant life and flooding areas where the silt has built up.

A large chasm is shown at the Edenmoor development in Indian Land, S.C., in this April 9 photo. Environmentalists say the housing and construction bust that has pockmarked the nation’s landscape with half-built projects is filling rivers and streams with one of the most expensive forms of water pollution: sediment.

“We have some that are still not being taken over by anybody or they’re in limbo or they’re in litigation and they’re just sitting there, bleeding sediment into the state’s waters,” said Mell Nevils, director of the Division of Land Resources in North Carolina. He estimates that 40 halted and abandoned projects are polluting waterways in the state.

In April, the Environmental Protection Agency settled with one of the nation’s largest homebuilders for sediment runoff at almost 600 sites in 18 states and the District of Columbia. Hovnanian Enterprises agreed to pay $1 million and take steps to prevent runoff. The EPA, which monitors runoff as part of its enforcement of the Clean Water Act, said the agreement is expected to prevent the runoff of 366 million pounds of sediment nationwide.

Erosion experts say a construction site will lose about 200 tons of sediment per acre per year compared with just five to seven tons per acre per year for a farm.

The EPA considers sediment the leading — and most costly to fix — cause of water pollution. Projects abandoned by their owners, also known as orphan sites, are tougher to penalize because nobody takes responsibility.

“Storm water is one of those chronic, almost invisible problems throughout the nation, throughout the developed world in general, because no one really thinks about rain as being a source of pollution,” said Janelle Robbins, staff scientist with the Waterkeeper Alliance, an international coalition of waterway advocates. “I have seen some horrific construction storm water sites from active sites … the housing bubble bursting has just exacerbated an already really bad situation.”

North Carolina-based Muddy Water Watch estimates that sediment pollution causes $16 billion in environmental damage in the U.S. every year, with about 70 percent of the dirt pollution coming from human activities, such as land clearing for construction, logging and farming.