Revision: 1 – 1/3/14 Turk Pond Treatment System Description Page 1 of 64 Revision: 1 – 1/3/14 Turk Pond Treatment System Description Page 2 of 64 Figure 1 - Pond Treatment System Basic Flow Reference Diagram Revision: 1 – 1/3/14 Turk Pond Treatment System Description Page 3 of 64 Turk Pond Water Treatment System Description NOTE: Figure 1 can be referenced to provide an elementary flow path for the Pond Water Treatment System. Additionally the following flow diagrams can be referenced for specific information: Flow Diagram Description 1-51WW001 COAL PILE RUNOFF POND 1-51WW002 PROCESS WATER POND 1-51PW004 POTABLE WATER 1-51SW011 SERVICE WATER 1-51QW010 LAMELLA SETTLERS 1-51QW011 THICKENER, FILTER PRESS 1-51QW012 EFFLUENT TANK, PUMPS 1-51QW013 BACKWASH, RINSE WATER TANK 1-51QW014 BACKWASH AND RINSE PIPING 1-51QW015 MULTI MEDIA FILTERS 1-51QW016 MULTI MEDIA FILTERS 1-51QW017 MULTI MEDIA FILTERS 1-51QW019 FLOCCULENT PUMPS 1. Introduction 1.1. Purpose The coal pile run-off pond (CPRP) and process water pond (PWP) discharge water treatment system is intended to reduce total suspended solids (TSS) to the levels required for discharging to internal outfalls 201 and 101 respectively. This is accomplished through supplemental treatment to achieve the required TSS reductions and simultaneously manage water inventory. The CPRP discharge treatment system consists of coagulation, flocculation, settling through a Lamella clarifier, and finally filtration. The PWP discharge treatment system consists of filtration only. Typical operation of the CPRP is to provide storage (surge) capacity during rain events, such that the treatment system is not overburdened. Routine management of CPRP water levels are to ensure that free storage volume is readily available to hold run-off water from major rain events. Thus CPRP levels must be maintained at as low a level as possible (ideally empty) at all times (when practical) by discharging to the PWP, or when necessary to outfall 201. Therefore utilization of the treatment system at the start of all significant / measurable rain events, providing the required TSS reduction, must be implemented to ensure that the CPRP provides Revision: 1 – 1/3/14 Turk Pond Treatment System Description Page 4 of 64 ample retention for subsequent major rain events and prevents the need for any potential discharge to outfall 002 or exceedences of outfall 201’s TSS limits. Typical operation of the PWP is to supply and store water to and from plant process water users / contributors as needed. The PWP also provides surge capacity, though it is intended to operate as a net consumer of water, without the need for surplus discharge to control pond levels. However should excess PWP influent(s) ultimately require discharge to outfall 101 to manage pond levels; this flow is treated with multi-media filtration (MMF) for TSS removal to prevent exceedences of outfall 101’s TSS limits. The treatment system for both internal outfalls (101 and 201) is combined and share common multi-media filtration equipment that can only be used for treatment of one pond waters at a time. The options to manage CPRP and/or PWP discharge within the treatment system are determined / selected based on several operational factors and provide the functionality to support the three following scenarios: 1) Treatment of CPRP discharge only 2) Treatment of PWP discharge only 3) Simultaneous treatment of both CPRP and PWP discharge Additionally, within these three treatment scenarios, subsequent options exist for the treated effluent location of the pond(s) discharge and/or processing steps. These include the following: Treatment of CPRP discharge only A) For routine management of CPRP levels, CPRP discharge is sent through the Lamella clarifiers followed by multi-media filtration, with the final treated effluent directed into the PWP. This provides a high quality effluent for supplemental PWP make-up while managing CPRP levels. This option is available provided the PWP levels are low enough to accept this effluent. Based upon the overall system design (subsequently described) this treatment option is suggested for CPRP discharge flow rates ranging from 100 to 400 gpm. B) For CPRP discharge treatment rates greater than 400 gpm that are used to supply supplemental make-up water to the PWP; the option available is to send the Lamella effluent directly to the PWP. This is accomplished by a controlled overflow of the Lamella effluent storage tank, which is directed into the PWP. This also provides a relatively high quality make-up water to the PWP, though it may be slightly higher in TSS than a filtered effluent. C) If the level in the PWP becomes/is too high to accept treated CPRP discharge or if a decision is made to select this effluent destination, the treated water can be directed into the make-up water pond (MWP) through outfall 201 to control CPRP levels. With this option the CPRP discharge is treated through the Lamella clarifiers, then the following options are available to send the Lamella effluent to the MWP: a. Further treatment with multi-media filtration, provided the filters are not treating PWP discharge and are available, sending the filtered effluent to outfall 201. This is the recommended treatment for flow rates up to 550 gpm. b. Directing the Lamella effluent storage tank into outfall 201. This option is available if the multi-media filters are unavailable and/or when flow rates exceed 550 gpm. Revision: 1 – 1/3/14 Turk Pond Treatment System Description Page 5 of 64 c. Any flow rate combinations of the two previously described options (a. and/or b.), depending on equipment availability (filters) and/or the total CPRP discharge flow rates required to manage CPRP levels. The two treated effluents are combined prior to the 201 outfall and sent to the MWP. Treatment of PWP discharge only Treatment of surplus PWP discharge is accomplished by multi-media filtration only. A portion of the PWP sump pump discharge is directed through the multi-media filters at a nominal designed flow rate of 300 gpm. Filtered effluent is combined with cooling tower blowdown through outfall 101 and ultimately sent into the waste water pond (WWP). Simultaneous treatment of both CPRP and PWP discharge With simultaneous treatment of both pond discharges; the multi-media filters can only treat discharge from the PWP. Therefore, PWP treatment proceeds as previously summarized, through the multi-media filters into internal outfall 101. Discharge from the CPRP is treated thought the Lamella clarifiers and is pumped from the Lamella effluent storage tank to the MWP through internal outfall 201. The pond treatment system is sized based on historic rain event data to provide an adequate treatment rate, storage volume for routine rain events, and historically frequent major rain events. However, atypical high frequency major rain events may exceed the design flow of the treatment system. These rare instances are outside of the design basis and in order to quickly regain the surge capacity of the CPRP and prevent a discharge to external outfall 002, the CPRP is pumped directly to the MWP, thought internal outfall 201, via the (treatment system) bypass line. If bypassing the CPRP discharge treatment system is necessary, the TSS could be in excess of outfall 201’s permit limits, though a discharge to outfall 002 would be avoided. 2. Design Basis 2.1. CPRP Design Basis and Operation The CPRP is sized to provide storage of rain water run-off from a 25 year rain event, approximately 9 million gallons of water. In order to maintain and restore the pond’s storage capacity from routine rain events, two sets of pumps are employed. Normal operation is with two 100% low-flow pumps each rated at approximately 200 gpm, pumping to the treatment system and into the PWP. For management of extreme rain events or emergency circumstances, two 50% high-flow pumps each rated at 3,350 gpm discharges into the plant’s MWP via a dedicated 20-inch line. To protect the integrity of the pond walls, the pond also employs an overflow weir that discharges to Bridge Creek (waters of the State), through external outfall 002. NOTE: Any operation of the high flow pumps, bypassing the treatment system and discharging to the MWP, and/or weir overflows to outfall 002 are only employed to manage extreme and/or emergency situations. These are not anticipated to occur and are not considered standard operation. Revision: 1 – 1/3/14 Turk Pond Treatment System Description Page 6 of 64 2.2. TSS Management – PWP and CPRP The objective of the pond treatment system is to reduce the TSS levels in the CPRP and PWP discharge water to less than 30 mg/L. This level of TSS ensures that the permit limit for both internal outfalls, which is 30 mg/L monthly average, and 50 mg/L daily maximum, are met. Empirical testing has demonstrated that the required TSS reduction of the CPRP discharge is achieved by a combination Lamella clarifier followed by a multi-media filter (MMF) system. Similarly, multi-media filtration alone has demonstrated the required TSS reduction for treatment of PWP discharge. 2.3. Water Treatment System Capacity Evaluations of historical rainfall data for the region assessed the likely outcomes of varying capacities of CPRP discharge treatment systems. The analysis assumed that at the onset of a significant / measureable / typical rainfall event, defined as a rain event with rainfall totals below the 25 year rain event, plant personnel would initiate operation of the CPRP water treatment system, discharging to the PWP or when necessary to outfall 201. This is to ensure adequate pond inventory for storage of major rain event(s) run-off water, defined as a rain event with rainfall totals up to the 25 year rain event.