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[`iati~uu lc l'a "c i ~l. a i~ ..... d,: r.... i Post Mining As with active mining, pli and oil and grease limitations apply co all discharges regardless of precipitation conditions. Buc, for post-mining dischatiges, Che settleable solids limitation applies unless exempted as described above. Exemption is onl}' available wl+c+i discharge is caused by precipitation greater than the 10-near, 24-bolo' event (or equivalent snowmelt volume). Example 2: The post-mining area served by pond and outfall 004 receives snowmelt volume during ono 2-;-hour period las measured by continuous influent recorder) grzatar ;:ban thr LO-ye:u, 24•hour equivalent voluue. The pcrmitcee collects samples wliil~: inflow is occurring to the pond. 1'he permictee submits the results along ~:it:h flu+o totalizer data and requests an exemption Erow the settleable solids l.imitacion. .Upon acceptance of the proof, the division still de [ermine cowpliance with Ure pH and oil and grease limitations only. snowmelt Freacer than 10-sear 24-hour event Section 40 CFR 434.G3(d)(2) states that the exemption From '1'SS, co cal iron and settleable solids limitations is :,vailal~le oi+1y Eor discharges "caused by precipitation within any 24-hour period greater tl+an Che 10-year 24-hour precipitation event (or snowir.zlt of equivalent volume)." Thus Eor snowmelt, pond inflow volume must be grcateL' than tl~u 10-yzar, 24-hour even[ equivalent volume (regardless of effluent volume). Thus, [he permitcee must be able to submit documentation showing that tk~e total volume over a 24-hour period into a pond is greater than the 10-year. 24-hour even[ equivalent volwne. Continuous inflow volume monitoring is typically reyuirc:d Eor this demonstration. The division allows this exemption for an addition:,) 4B hours co allow the pond [o stabilize. Ocher WOS-Based Parameters Surface runoff discharges From coal mining Facilities are intermittent and normally occur during periods whin receiving waters are well above lots flow. The Colorado Mined Land Rzclamation Division and the State Engineers Office typically require ponds to be dzwacered wicl+in 24 [0 3G hours after a storm event. For these reasons no tdQS-based Liniite+tions ocher chair p11 are deemed necessary ac this dine to protect inscreain beneficial uses. Total Suspended Solids The State Effluent Limitation Regulations dictate that cohere Federal EEFluenc Guidelines exist they shall take precedence over SES. 1'l~is is the reason Eor selection of BPT-based TSS limitations.