Good conduct allowances shall be based upon a four-level classification system. Such system shall be established as follows:
1. Class I at a rate of thirty days credit for each thirty days served. Class I shall be reserved for persons whose initiative, conduct and performance in their assignments are exemplary. Consideration for Class I credit shall be given to persons who perform in assignments requiring a high degree of trust, extra long hours or specialized skills.
2. Class II at a rate of twenty days credit for each thirty days served. Class II shall be reserved for persons whose initiative, conduct and performance in their assignments are satisfactory. Consideration for Class II credit shall be given to persons who require moderate supervision in their assignments and whose assignments require responsibility in the care and maintenance of property.
3. Class III at a rate of ten days credit for each thirty days served. Class III shall be reserved for persons whose conduct and performance in their assignments are marginal. Persons requiring intensive supervision in their assignments and exhibiting minor disciplinary problems may be assigned to Class III.
4. Class IV at a rate of no credit for each thirty days served. Class IV shall be reserved for persons who are in isolation or segregation status for disciplinary or security reasons and persons whose conduct and performance in their assignments are so unsatisfactory as to eliminate consideration for good conduct allowance. Persons may be reclassified for an increase or decrease in class according to rules and regulations established pursuant to § 53.1-200.