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;. <br />Cazla Lenkey <br />September 8, 1998 <br />Page 2 of 2 Pages <br />The pond was again inspected by the Division on April 1, 1998. The inspection record indicates <br />that at that time the discharge from Prospect Pond (NPDES 007) was estimated at 5 gallons per <br />1 1 seconds, that maximum water levels had been over the primary riser, that a pump had been <br />used to lower water levels in the pond, that sediment had filled the pond to the invert of the gate <br />valve, and that there was surface inflow into the pond. <br />The SEDCAD demonstration of reference b) indicates that the peak inflow from a 10-year, 24- <br />hour precipitation event is 6.68 cfs, the total flow is 0.56 acre feet, and the storage capacity of the <br />pond is 7.08 acre feet. The peak dischazge from the pond from a 10-yeaz, 24-hour precipitation <br />event is predicted to be 1.30 cubic feet per second (cfs) when the water level was at the top of the <br />primary spillway riser at the start of the event. <br />The Dischazge Monitoring Report (DMR) for Prospect Pond, Dischazge Number 007), submitted <br />under the letter of Apri120, 1998, reference a), indicates that the maximum dischazge was 0.265 <br />million gallons per day (MGD). 0.265 MGD = 0.41 cfs. <br />The predicted ] 0-yeaz, 24-hour peak discharge of 1.30 cfs was not exceeded at the time of the <br />grab sample (0.41 cfs). The SEDCAD demonstration indicates that there should be no settleable <br />solids in a discharge of 1.30 cfs over the primary riser. However, the physical conditions and the <br />method of operation of the Prospect Pond on Mazch 23, 1998, aze not described in CDMG <br />records, nor in the information provided by the Colowyo Coal Company. The high concentration <br />of settleable solids (0.8) could be a result of a number of causes. <br />Please call me if you have any additional questions. <br />Yours truly, <br />~ Z./~ <br />By~o~alker <br />Environmental Protection Specialist <br />C:\W PDOCS\DMRV.019 <br />