How many U.S. construction workers are exposed to hazardous noise on the worksite?

According to a study by the National Institute for Occupational Safety and Health (NIOSH), over 500,000 construction workers are exposed to hazardous noise.

source: 
Source: Suter, Alice. "Construction Noise: Exposures, Effects, and the Potential for Remediation; A Review and Analysis" http://www.cdc.gov/elcosh/docs/d0100/d000054/d000054.html