By DIRK LAMMERSSIOUX FALLS, S.D. (AP) â¿¿ Federal mine safety officials have not been excessive in their enforcement of regulations in South Dakota, the Inspector General's Office of the U.S. Department of Labor said Friday. U.S. Sen. John Thune, R-S.D., requested an investigation in 2011 in response to complaints from South Dakota gravel pit operators that they were being regulated as if they were running deep coal mines. Assistant inspector general Elliot Lewis said in the report that Mine Safety and Health Administration enforcement numbers were higher in South Dakota than the national average, but that was largely due to two mine operators whose penalties were resolved on appeal. One of the operator's penalties was upheld, and the other received some reductions in penalties. "We found some variations in the data in some years; however, most of the variations could be traced to two mine operators, who significantly skewed the results for their group," Lewis wrote. Lewis said enforcement by the MSHA increased across the board in the 2009 fiscal year due to passage of the Mine Improvement and New Emergency Response Act of 2006. Congress also provided funding for MSHA to hire 170 new inspectors that year, he said. Thune said he appreciates the office's investigation and its explanation on complaint volume but it didn't address one of his major concerns, that investigators were using "overzealous, inconsistent, and aggressive tactics and didn't treat our small business owners with respect." "I have expressed this concern to MSHA leadership over the past 18 months, and I hope MSHA addresses this concern in their ongoing training of inspectors," he said Friday in a statement. Toby Crow, executive vice president for the South Dakota Associated General Contractors, said he hadn't yet seen the report and could not comment on the findings. Group officials have complained that MSHA inspectors were applying rules inconsistently and seemed to be seeing how many citations they could issue.