When the legislative body determines that an enterprise is necessary and convenient for the preservation of public health, it may adopt a general specification for the enterprise setting forth:
(a)
Definite criteria of capacity and general location of the enterprise.
(b)
General structural requirements.
(c)
Degree of purification and manner of disposal of effluent and sludge.
(d)
The duration of operation under the control, supervision, and responsibility of the contractor after the required performance has been demonstrated.