(A) (1) Effluent limitation promulgated by the Federal Act shall apply in any instance where they are more stringent than those in this chapter. Under section 307(b) of the Act, Federal Pretreatment Standards are designed to achieve two purposes:
(a) To protect the operation of publicly-owned treatment works; and
(b) To prevent the discharge of pollutants which pass through such works inadequately treated.
(2) Users in Industrial Categories subject to effluent guidelines issued under Section 304(b) of the Act, which are discharging incompatible pollutants to publicly-owned treatment works, are required to adopt best practicable control technology currently available, as defined by the Administrator pursuant to section 304(b) of the Act. Where the town treatment works was designed to and does achieve substantial removal of pollutants other than the four pollutants listed in the definition for compatible pollutants in § 51.001, suspended solids, pH, and fecal coliform bacteria, it is not appropriate to require the industrial user to achieve best practicable control technology currently available, since this would lead to an uneconomical duplication of treatment facilities. While the “substantial removal” is not subject to precise definition, it generally contemplates removals in the order of 80% or greater. Minor incidental removals in the order of 10% to 30% are not considered “substantial.” For some industrial categories it may be necessary to define pretreatment guidelines for problems that may arise as a result of the discharge into publicly owned treatment works. However, any adjustments required for particular industrial categories should be considered in connection with the town's requirements rather than in the national pretreatment standard. Limitations on wastewater strength in § 51.042 may be supplemented with more stringent limitations pursuant to § 51.046(D).
('80 Code, § 13.36.026)