2016-08-29_PERMIT FILE - C1981035A (3)

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COLORADO DEPARTMENT OFPUBLIC HEALThiAiYD MNWROIVMENT, Water Quality Control Division Rw(Mak Page 6, 0004500000 Sond mid Gravel General Permit exempted from an antidegradation review. Based on the information and data to the application, the permit writer will make an assessment of the low flow dilution ratio of the discharge to determine if anddegradadon applies. Under this general permit an antidegradation (AD) limit will be calculated as 1 S% of the Water Quality Standard T h pen. .re would then have the choice of this AD limit, or of a non - impact limitation (AM). Me NIL is either the limitation contained as of September 2000, or may be deterndned by the use of an implicit limitation #a previous limit did not exist. The implicit limit is determined as the maximum effluent concentration in the years prior to September 2000 (later data may be substituted on a case bj case basis if data a unavailable from this time period). Alternately, if data does not exist, a compliance schedule may be added to the permit to obtain such data, to determine the implicit limitation and the final antidegradadon -based effluent limit. An individual permit will be required where the permittee requests consideration of dilution and ambient water quality. In addition, the pa mittee may elect to perform an alternatives analysis. As this may be subject to public notice requirements, an individual permit will be required. See Regulation 31.8(3)(4) and the Division's Antidegradation Guidance document for more information regarding an alternatives analysis. g. Whole Effluent ToxiM (W 7) — The Water Quality Control Division has established the use of WET testing as a method for identifying and controlling toxic discharges from wastewater treatment facilities. WET testing is being utilized as a means to ensure that there are no discharges ofpoilwants "in amounts, concentrations or combinations which are harmful to the beneficial uses or toxic to humans, animals, plants, or aquatic life" as required by Section 31.11(1) of the Basic Standards and Methodologies for Surface Waters. Some discharges covered under this general permit may exhibit whole effluent toxicity based on the potential pollutant concentrations in the discharge. Aus, WET testing maybe incorporated into the permit on a case -by -case basis. If it is determined that WET testing is required, Chronic WET testing will normally be incorporated into the permit. However, Acute testing may be applied where the receiving stream has a zero low flow in all months 04 the discharge is intermittent, or when deemed appropriate for any other saaVecific reason. h. wed and EnAawa- The US Fish and Wildlife Service and the Division have entered into a Memorandum of Agreement (MOA) regarding discharges to federal MBE waters. In this MOA, a permittee that discharges to a ME water r have additional constraints placed upon the discharge. These constraints may include accepting end-of -pipe limitations (& dilution), moving the discharge point to a different location, or using a diffuser to obtain instantaneous mixing of the effluent and the receiving water. This last option may allow for a portion of the available assimilative capacity (dilution) to be incorporated hm thepermit. However, as this is a generalpermit, all limitations are imposed as end-of -pipe limits, and therefore, the first option is met: Generally, it will be assumed that the end -of -pipe limitations will satisfy the MOA, and no further consideration is needed. Ot a case -by -case basis, additional constraints may need to be evaluated h. Mi4a Zones — Under this generalpermit mixing zone regulations do not apply, as the water quality standards are applied as the effluent limits(Le, no dilution is allowed). Dish tomes to 3030 Listed Waters — Where the receiving water is included on the state's 303(d) list, total maximum daily loads (TMDLs) are being developed in accordance with the Division's schedule for TMDL completion. Once a TMDL has been established, if it is necessary to incorporate limitations for a facility certified under this general permit, based upon the outcomes of the TMDL or the results of the data analysis, a modification to the certification to discharge, or an individual permit may be required to regulate discharges from a facility. Ae facility would continue to be covered under this general permit certification until the individual permit is issued For example, the industrial process of sand and gravel operations typically involves discharging alluvial water. When the alluvium is dewatered in an area of shale deposits (e.g. Mancos), selenium is likely to be present in elevated concentrations in the discharge and is automatically considered a pollutant of concern. Preliminary monitoring data indicates that operations it areas ofshale are likely contributing to exceedances ofstream standards for selenium, and therefore, monitoring requirements will be included for data collection for a future reasonable potential analysis. New discharges to these segments will be required to meet the water quality limitations for selenium upon commencement of discharge. The basic standards for selenium are found in Table III of The Basic Standards and Methodologies1gr Surface Water (S CCR 1002.31). There are currently ongoing national discussions between the USEPA and the USFWS on appropriate aquatic life standards for selenium. Should the USEPA adopt new water quality standards for selenium, the division's standards unit will beg incorporating federal standards into Colorado's water quality standards during basin triennial reviews. In the future, treatment of effluent to remove selenium may be required to attain water quality standards.