He is shown as being in the reserve corps:

"2nd Regiment, US Reserve Corps, Missouri Infantry

Overview: Reorganized at St. Louis August 23 to September 20, 1861. Attached to District of St. Louis to October, 1861. 4th Division, Army of the Southwest, to May, 1862. 2nd Division, Army of the Mississippi, to June, 1862. 5th Division, Army of the Mississippi, to August.

Service:Campaign in Missouri October, 1861, to February, 1862. Guard railroad beyond Rolla, Mo., till May, 1862. Ordered to Pittsburg Landing, Tenn., May 6. Siege of Corinth, Miss., May 22-30. Duty at Corinth, Miss., till August. Ordered to St. Louis, Mo., August 12, 1862. Mustered out September 3, 1862."

He is not listed in the rolls of the Missouri Engineers, which began life as Bissell's Engineers of the West. It could be that he was in the pioneer company that organized at the beginning of the war, and was part of Lyon's move to Boonville, prior to the formal organizing of the engineers.

"Miners and sappers" (an archaic term by the Civil War) were traditionally in charge of digging under an enemy's fortifications. In the Civil War, engineers rarely did that kind of thing. There were plenty of experienced miners in the infantry ranks for such duties, like at Vicksburg. Generally (there are exceptions) engineers built roads and bridges as well as other projects such as specialty fortifications.