Upon the voluntary retirement of a Borough employee with 20 years or more of service to the Borough, accrued sick days will be paid at the rate of 60% of final salary, not to exceed $15,000. "Voluntary retirement" means meeting all eligibility requirements and a pending application for retirement with the Public Employee Retirement System or Police and Firemen's Retirement System. Voluntary retirement does not include a retirement tendered during a pending criminal or administrative investigation, or pending criminal or disciplinary charges which carry a penalty of removal if sustained against the employee. Sick days will be prorated based on the date of retirement.