(a) In the application of effluent limitations, water quality standards, and other applicable requirements, pursuant to this Part, the department may specify daily average, monthly average, seven-day average, annual average, 12-month rolling average, peak hourly, annual maximum, instantaneous maximum and daily maximum quantitative limitations for the level of pollutants in the authorized discharge in terms of weight or, as in the case of flow, pH, temperature, and for any other pollutants not appropriately expressed by weight, in other appropriate terms. The department may, in addition to or in lieu of the specification of daily quantitative limitations by weight or by other terms, specify other limitations, such as average or maximum concentration limits, on the pollutants in the authorized discharge.

(b) Any point source, the construction of which is commenced after October 18, 1972, and which is so constructed or physically modified, provided the cost of such modification exceeds 50 percent of the initial capital costs of the facility or new source which meets the applicable promulgated new source performance standards before the commencement of the discharge, to meet all applicable standards of performance set forth in the point source SPDES permit and fact sheet shall not be subject to a more stringent technology based standard of performance (under section 301[b][2] of the act) requiring the construction of additional treatment facilities during a 10-year period beginning on the date of completion of such construction or during the period of depreciation or amortization of such facility for the purposes of section 167 or 169 (or both) of the Internal Revenue Code of 1986, whichever period ends first; provided, however, that if the operation of such source causes or contributes to any contravention of any State water quality standard the department shall require that abatement action be taken by the permittee and modify the permit pursuant to section 750-1.18 of this Subpart.

(c) Notwithstanding any other provision of this Part, when effluent limitations are established they must be at least as stringent as the effluent limitations previously required unless the department determines that an exception is warranted because the circumstances on which the previous permit was based have materially and substantially changed since the time the permit was issued and would constitute cause for permit modification. A permit may be modified to contain a less stringent effluent limitation applicable to a pollutant, if:

(d) In no event may a permit be modified in accordance with subdivision (c) of this section to contain an effluent limitation that is less stringent than required by effluent guidelines, including variances thereto, in effect at the time the permit is modified. In no event may such a permit to discharge into waters be modified in accordance with subdivision (c) of this section to contain a less stringent effluent limitation if the implementation of such limitation would result in a violation of a water quality standard or guidance value applicable to such waters as set forth in Parts 700-706, et seq. of this Title.