Fire Down Below (1997) on Netflix

EPA agent Jack Taggart is Stunned to hear from his boss Phil Pratt that his best friend and fellow agent Frank Elkins has been found dead in Kentucky after Frank's truck plunged into a river. The Kentucky State Police believes that it was an accident, but the EPA believes it was no accident. It all began with an anonymous letter from the small town of Jackson, Kentucky. Frank was sent to Jackson to investigate what the letter described as some kind of pollution that is causing fish to die and causing people to get sick enough to die. Frank sent back water and soil samples that all tested off the charts for toxic substances. After Frank discovered that the Hanner Coal Company, owned by Orin Hanner Sr., is being paid to dump toxic waste into an abandoned coal mine shaft, Frank ended up dead. Jack is assigned to go to Jackson, where his contact will be Reverend Bob Goodall, who runs a church in Jackson. After arriving in Jackson, Jack finds out that he'll be staying in a room in the church's basement, and as Jack's contact, of course Bob knows that Jack will be going undercover as a carpenter. Jack begins by repairing the roof at a house where he meets Henry Carr, his wife, and his kids Edie, Alberta, Christine, and Walter. Walter is sick because of the pollution. That night, Hanner's son Orin Hanner Jr., also known as Junior, spies on the church along with corrupt Sheriff Lloyd, who is on Hanner's payroll. On the next day, when Jack goes into downtown Jackson, he meets Betsy Hamill and her twin sister Patsy Hamill. Jack then walks down the street and introduces himself to Cotton Harry. Then Jack takes some water samples. At church on Sunday, Bob introduces Jack to everyone, and tells everyone that Jack is a carpenter. During lunchtime at the church, Jack introduces himself to Sarah Kellogg, a local outcast who is a beekeeper. Sarah has a brother named Earl. Jack goes to Sarah's house and offers to repair the steps on her front porch. Over time, Jack comes to believe that something is bothering Sarah, and it's something dark. Jack wants to save her from whatever it is, while trying to bring Hanner and his crew down.