Knowledge of supervisory and administrative principles, practices, and techniques; Advanced knowledge of trade-related methods, techniques and practices and of the properties, characteristics and uses of related equipment, materials and tools; Knowledge of national, state, and local trades and safety codes; Knowledge of inspection requirements; Knowledge of trade-related hazards and necessary safety precautions; Ability to carry out a maintenance activity within established policy, plans, and requirements and to coordinate work with other shops and departments; Ability to read and interpret work orders, diagrams, sketches, blueprints and manufacturers manuals; Ability to perform complex trade-related work; Ability to instruct, motivate and train subordinates in all phases of the work and assist them with work problems; Ability to establish and maintain effective working relationships with customers, partners, contractors, peers, subordinates, and superiors; Ability to enforce safety and other regulations; Ability to estimate trade-related costs and scheduling parameters; Ability to communicate effectively, both orally and in writing; Ability to prepare and deliver accurate reports and to keep accurate records; Ability to use personal computers and software programs. DPWES provides award-winning solid waste collection services for approximately 45,000 homes, operates a transfer station and landfill, regulates solid waste services, and leads sustainability initiatives to promote zero waste goals for Fairfax County.