San Juan County residents are concerned about a dangerous by-product that can surface from some of the natural gas wells in the area.

Many natural gas wells that test positive for hydrogen sulfide, or H2S, are in close proximity to homes and schools.

According to oil and gas company BP, hydrogen sulfide is a naturally occurring gas. In high doses it can be lethal.

Shirley McNall lives near one of the wells that has H2S and said she has gotten sick before. “I noticed that my throat was really getting sore and my head was pounding and before I could get back to my house my knees were wobbly…I was shaking all over,” said McNall.

Officials at BP said any wells found producing H2S are immediately treated.

Hydrogen sulfide is a flammable colorless gas. One of the biggest warning signs is the smell of rotten eggs.