On 5/4/10 EE alleges he hurt lower back when assigned to remove 3 & 4"" pipe from one section of the stockpile & install air vents. On 5/7/10 EE reported his lower back was sore to sup. The EE did not want medical treatment. On 5/10/10 EE spoke with his supervisor at start of shift reported his back was still sore and now wanted to be checked out. Still under investigation.