2018-11-05_PERMIT FILE - C1981044 (12)

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COLORADO DEPAR'1't3EN'i OF HEALTH • Water Quality Control Division Nationale - Page 4 Permit No. CO -0034142 Outfall 023 (Continued) A septic tauK-leaching field system of wastewater disposal was utilized prior to construction of this facility. With the exception of the septic tank -leaching field serving the warehouse/office, all the other existing onsite disposal systems were abandoned at time of start-up. Within 3 to 5 years after start-up, it is projected that wastewater flow will increase from 8800 gpd to 12,000 gpd and within 5 to 10 years an increase to 22,000 gpd is expected. Flows should not increase beyond 22,000 gpd, for this represents the flow from the work force maximum limit of 900 employees. It is realized that these projections are tied to coal production which is in turn sensitive to the market demand. Therefore, the proposed time table may not be realized. It should be noted, however, that the permittee is required to initiate engineering and financial planning for expansion of the treatment works whenever throughput and treatment reaches 80 percent of design capacity. At 95 percent of design capacity the permittee shall commence construction of the necessary treatment expansion. (See page lc of the permit). • The hydraulic design capacity, 0.012 MGD, and the organic loading capacity, 25 lb BOD5/day, were obtained from tine Engineering Report for the facility wnich was prepared by Engineering Science, consulting engineers (Dec., 1981). APPLICABLE RULES AND REGULATIONS: Outfalls 004, 006, 007, 009, 011 - 021 Federal RPT (Best Practicable Control Technology) and BAT (Best Available Technology Currently Achievable) recently promulgated specify the following effluent limitations for reclamation areas: TABLE 1 Parameter BPT BAT PH (s.u.) 6.0 to 9.0 N/A Settleable solids (ml/1)* 0.5 0.5 *This parameter does not apply to discharges caused by precipitation greater than the 10 -year, 24 hour event (or equivalent snowmelt volume). State Effluent Standards (SES) dictate the imposition of an Oil and Grease . limitation of 10.0 mg/l for all discharges not otherwise limited. Additionally, State Water Quality Standards (WQS) dictate a pH limitation of 6.5 to 9.0 s.u. This supersedes the BPT limitation for pH shown in Table 1. Because discharge will be intermittent and will normally occur only during precipitation events (periods when receiving water flows will be high) no water quality standard -based effluent limitations are appropriate other than pH.