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:COLORADO DEPARTMENT OF PUBLIC HEALTH AND ENVIRONMENT, Water Quality Control Division <br />Rationale -Page 5, Permit No. CO-0045161 <br />Also, the permittee wants the option to discharge vehicle wash water that can be controlled and then discharged if <br />necessary. This wash water has the pateruial to contain coal dust, ail and other petroleum products. The water <br />flows to the Washbay Pond, a normally nondischarging pond. If the Washbay Pond fills, it Wray be necessary to <br />transfer the water to the Work Area Pond, from which discharge may occur to Taylor Creek (see the permit, Figure <br />3). This would happen infrequently. To accommodate this, the outfall from the Washbay Pond will 6e designated as <br />ourfall 0026 and the outfall from the Work Area Pond to Taylor Creek will be designated as outfa(1 002a. <br />The permittee recently reevaluated all ponds, using the Colorado Division of Minerals and Geology-approved <br />SEDCAD hydrology model, for conversion to the "treatment" mode, wherein discharge occurs automatically when <br />the volume reaches a certain level. Primary discharge structures consist of perforated riser pipes; secondary/ <br />emergency spillways consist of open channels near the top of the ponds. Al! ponds can maintain a permanent pool" <br />of water that remains below the level of the perforated riser pipe unless the lower gate is manually opened to release <br />it. <br />As flow comes into the pond it displaces the water in the permanent pool. Typically, a primary spillway will <br />adequately discharge mast flows; secondary spillways serve to discharge larger flows due to rainfall or snowmelt <br />equivalent to the 25-year, 24-hour event or greater. When the incoming flows are within the range treatable by the <br />ponds, the effluent quality should be within the discharge standards, providing the ponds are properly mairaained <br />and operated. Colowyo worked with the Colorado Division of Minerals and Geology to receive approval to make <br />this change. All ponds are expected to be modified to operate in this mode, weather permitting, by spring 1999. <br />Ponds associated with outfalls OOla and 008a were modeled with base flows of 0.15 cfs and 0.03 cfs respectively. <br />This was done to account far the following: <br />I) Outfa[1 OOla - receives a steady inflow from the Streeter Fill underdrain and groundwater associated with the <br />Good Spring drainage. - <br />2) Outfa11008a -natural spring water, potential future under drain water. <br />All changes to pond design or factors affecting the pond inflow or outflow are reviewed acrd approved by the CDMG <br />prior to implementation. <br />Table !V-2, following, shows data related to all outfalLs (including the internal outfalLs) authorized under this permit. <br />Table IV 2-Treatment and Out(aU Data <br /> <br />:~: ~ OatPall~ ~:: ~ :. <br /> <br />:..~Nfnsiber:: •.. <br />W.astewatrt Soarm~ .: ~. <br /> <br />.. .:. .~. ... ~::.:. ~.. :: <br />. 30 Day. Avg .. ~ ~:: <br /> <br />~F7ow,~MGD~:•~.`: <br />: ~ Daffp~ Mac Ftow,: ~ <br />,. <br /> <br />MGD!':::'.:::.: <br />~~ Io-Yr,24~-.Hr ::::..: <br /> <br />.. ~. <br />Capaaty,.MG~ <br />~~ Pond .: ~.::~ ~ ~..: . <br /> <br />. <br />Volome,MGs <br />001 a r ace ntna inurmittent 0.59 4.46 2.92 <br />002a ace sotto intcrmincnt 0.31 1.69 3.57 <br /> <br />0026 <br />vchic4 wash water to <br />002a r J <br />N/A r <br />003a s ace now intermittent 0.17 0.69 0.81 <br />004a ace intermittent 1.41 1.75 0.94 <br /> <br />0046 <br />it a e ro 004a J r <br />N/A r <br />OOSa su ace sotto intermittent 0.63 0.019 0.93 <br />006a ace rtuto intermittent 0 0.163 0.14 <br />007a surface runoff intermittent 0.90 1.40 1.24 <br /> <br />0076 <br />it tun aXe to C07a f S <br />,V/A J <br />008a s ace sotto ' intermittent 0.52 1.73 2. T <br /> <br />0086 <br />pit pumpage to 008a J f <br />N/A J <br />009a surface runoff intermittent 0.98 1.~3 1.35 <br />