S.D. Codified Laws § 62-9-10
An employer is liable for the entire occupational hearing loss to which his employment has contributed; but, if previous deafness is established by a hearing test or other competent evidence, whether or not the employee was exposed to excessive noise within six months preceding such test, the employer is not liable for previous loss so established, nor is he liable for any loss for which compensation has previously been paid or awarded. The employer is liable only for the difference between the percentage of occupational hearing loss determined as of the date of disability, and the percentage of loss established by pre-employment and audiometric examinations excluding, in any event, hearing losses arising from nonoccupational causes. Hearing loss established by hearing tests or other competent evidence to have occurred prior to July 1, 1974, is not compensable.
SDCL 62-9-10