There could be thousands of old oil wells across Colorado that are low producing or not producing at all, but havent been cleaned up by their operators.These sites are referred to as zombie wells or orphaned wells. A zombiewell is a non-producing or low-producing well that is still under the operator. An orphaned well, on the other hand, has been turned over to the state for cleanup.Denver7s Angelika Albaladejo visited more than a dozen of these sites to investigate what dangers they posed to their surrounding communities. It was part of a joint investigation with ABC News.Hear about her work in the field across Colorado in the video player below. Denver7 investigates, ABC News partnered to examine orphaned oil wells in Colorado. Here's what we found.We had some devices that can actually pick up combustible gasses, for example, like climate-warming methane, that come off of these wells, Albaladejo said. What we found was the orphaned wells that are already under state care didn't seem to have any issues, but when we went to some of these lower producing wells, that's where we found some problems.Those problems include spills and leaks from broken-down equipment, which pose risks to health and to the environment. To make matters worse, Many of the old wells are close to homes, schools and places of business.One operator, K.P. Kauffman, has been fined repeatedly by the state for a series of violations tied to leaks and emissions releases.The problem is that there are thousands of wells across Colorado, and the state just can't inspect all of them at the same time, Albaladejo said. So even though they say they're trying to go about every one-and-a-half years to every well, in this case, they hadn't been there for about four years.Read Angelikas two-part investigation here and here.