Subsection 096-525-3-IV - Special considerations [see 40 CFR 133.103](a) Combined sewers. Treatment works subject to this Chapter may not be capable of meeting the percentage removal requirements established under Subsection III(a)(3) and Subsection III(b)(3), or Subsections VI(a)(3) and Subsection VI(b)(3) during wet weather where the treatment works receive flows from combined sewers (i.e., sewers which are designed to transport both storm water and sanitary sewage). For such treatment works, the decision must be made on a case-by-case basis as to whether any attainable percentage removal level can be defined, and if so, what the level should be.(b) Industrial wastes. For certain industrial categories, the discharge to navigable waters of BOD-5 and SS permitted under sections 301(b)(1)(A)(i), (b)(2)(E) or 306 of the Act may be less stringent than the values given in Subsection III(a)(1), Subsection III(a)(4)(i), Subsection III(b)(1), Subsection VI(a)(1), Subsection VI(b)(1) and Subsection VI(e)(1)(i). In cases when wastes would be introduced from such an industrial category into a publicly owned treatment works, the values for BOD-5 and SS in Subsection III(a)(1), Subsection III(a)(4)(i), Subsection III(b)(1), Subsection VI(a)(1), Subsection VI(b)(1), and Subsection VI(e)(1)(i) maybe adjusted upwards provided that: (1) The permitted discharge of such pollutants, attributable to the industrial category, would not be greater than that which would be permitted under sections 301(b)(1)(A)(i), 301(b)(2)(E) or 306 of the Act if such industrial category were to discharge directly into the navigable waters, and (2) the flow or loading of such pollutants introduced by the industrial category exceeds 10 percent of the design flow or loading of the publicly owned treatment works. When such an adjustment is made, the values for BOD-5 or SS in Subsection III(a)(2), Subsection III(a)(4)(ii), Subsection III(b)(2), Subsection VI(a)(2), Subsection VI(b)(2), and Subsection VI(e)(1)(ii) should be adjusted proportionately.(c) Waste stabilization ponds. The Department, subject to EPA approval, is authorized to adjust the minimum levels of effluent quality set forth in Subsections VI(b)(1), (b)(2), and (b)(3) for treatment works subject to this Chapter, to conform to the SS concentrations achievable with waste stabilization ponds, provided that: (1) Waste stabilization ponds are the principal process used for secondary treatment; and (2) operation and maintenance data indicate that the SS values specified in Subsections VI(b)(1),(b)(2), and (b)(3) cannot be achieved. The term ``SS concentrations achievable with waste stabilization ponds'' means a SS value, determined by the Department, subject to EPA approval, which is equal to the effluent concentration achieved 90 percent of the time within a State or appropriate contiguous geographical area by waste stabilization ponds that are achieving the levels of effluent quality for BOD-5 specified in Subsection VI(a)(1).(d) Less concentrated influent wastewater for separate sewers. The Department is authorized to substitute either a lower percent removal requirement or a mass loading limit for the percent removal requirements set forth in Subsection III(a)(3), Subsection III(a)(4)(iii), Subsection III(b)(3), Subsection VI(a)(3), Subsection VI(b)(3) and Subsection VI(e)(1)(iii) provided that the permittee satisfactorily demonstrates that: (1) The treatment works is consistently meeting, or will consistently meet, its permit effluent concentration limits but its percent removal requirements cannot be met due to less concentrated influent wastewater, (2) to meet the percent removal requirements, the treatment works would have to achieve significantly more stringent limitations than would otherwise be required by the concentration-based standards, and (3) the less concentrated influent wastewater is not the result of excessive I/I. The determination of whether the less concentrated wastewater is the result of excessive I/I will use the definition of excessive I/I in 40 CFR 35.2005(b)(16) plus the additional criterion that inflow is non excessive if the total flow to the POTW (i.e., wastewater plus inflow plus infiltration) is less than 275 gallons per capita per day.(e) Less concentrated influent wastewater for combined sewers during dry weather. The Department is authorized to substitute either a lower percent removal requirement or a mass loading limit for the percent removal requirements set forth in Subsection III(a)(3), Subsection III(a)(4)(iii), Subsection III(b)(3), Subsection VI(a)(3), Subsection VI(b)(3) and Subsection VI(e)(1)(iii) provided that the permittee satisfactorily demonstrates that: (1) The treatment works is consistently meeting, or will consistently meet, its permit effluent concentration limits, but the percent removal requirements cannot be met due to less concentrated influent wastewater; (2) to meet the percent removal requirements, the treatment works would have to achieve significantly more stringent effluent concentrations than would otherwise be required by the concentration-based standards; and (3) the less concentrated influent wastewater does not result from either excessive infiltration or clear water industrial discharges during dry weather periods. The determination of whether the less concentrated wastewater results from excessive infiltration is discussed in 40 CFR 35.2005(b)(28), plus the additional criterion that either 40 gallons pre capita per day (gpcd) or 1500 gallons per inch diameter per mile of sewer (gpdim) may be used as the threshold value for that portion of the dry weather base flow attributed to infiltration. If the less concentrated influent wastewater is the result of clear water industrial discharges, then the treatment works must control such discharges pursuant to Chapter 528. C.M.R. 06, 096, ch. 525, § 096-525-3, subsec. 096-525-3-IV