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During the week prior to the subject runoff event, the region surrounding Colowyo experienced a <br />very wet, spring snowstorm which delivered in excess of 0.75 inch of precipitation. The <br />precipitation from this storm was in addition to an existing above average snowpack. In addition, <br />the existing snowpack was located on soils that had been saturated from near 100-year flood <br />events occurring during the fall of 1997. <br />During the week of March 23-26, 1998 due to high ambient temperatures and windy conditions, <br />we observed a very significant volume of snowmelt entering the Prospect pond. In fact by the <br />afternoon of March 23, the pond had quickly filled to where the 10 foot tall 12" diameter riser <br />pipe was overtopping and flowing at full pipe flow at the pond outlet. According to page 14 of the <br />SEDCAD model, the peak stage of the water discharge through the riser pipe was 1.3 cfs or 2.6 <br />ac/ft per day. This 2.6 ac/ft per day discharge is 464% greater than the design 10-year/24-hour <br />storm event volume. <br />The volume entering the pond was so great that the primary outlet was not keeping up with the <br />flow and the level in the pond was approaching the emergency spillway. With this concern in <br />mind, on March 24 Colowyo mobilized a Godwin HL5M diesel pump to aid in the pond <br />discharge. The pump was utilized to pump water from the surface of the pond with the hose <br />outlet located in the emergency spillway. The pump ran at approximately 1100 RPM for 24 <br />hours/day for 3 days. According to the pump performance information (See Exhibit 2 - "Godwin <br />Pump HL5M Performance Information") the volume of water being pumped at 1100 RPM is <br />approximately 800 g.p.m. or 1.78 cfs or 3.56 ac/ft per day. <br />Summary <br />~f~/~ ~Y° <br />V \1,,~ <br />~~~ <br />0" <br />~~" .~ <br />ka'~ <br />~/ <br />The combined total of pipe discharge plus pump discharge equaled 6.16 ac/ft per day. The 6.16 <br />ac/ft per day discharge from the Prospect pond was 1100% greater than the design 10-year/24- <br />hourstorm event volume of 0.56 ac/ft per day required of the pond. <br />2; A similar significant snowmelt event at a neighboring surface coal mine. the <br />Trapper Mine. occurred with similar results. <br />During the same week the Trapper mine, located 18 miles northeast of Colowyo, was also <br />experiencing an abnormally high snowmelt event. On March 25, 1998 an Inspector from the <br />Colorado Division of Minerals and Geology (CDMG) was on routine inspection at the Trapper <br />mine and noted similar flooding conditions as we were experiencing at Colowyo. Due to the <br />severe runoff, unfortunately, the Trapper mine had a sedimentation pond which overtopped. <br />Fortunately, little damage occurred as a result of the flooding. Subsequently the CDMG issued <br />an NOV for the event. <br />We have included as Exhibit 3 - "Trapper Mine Discussion Regarding March 1998 Floods" <br />correspondence from Mr. Forrest Luke, Environmental Manager describing the events <br />surrounding the same flooding conditions as we experienced at Colowyo. You will note that the <br />conditions at Trapper and Colowyo were nearly identical. <br />31 Craig. Colorado experienced a 500 Year flood event. <br />We have attached as, Exhibit 4, a copy of the March 26, 1998 Craig Daily Press describing the <br />similar flooding that occurred in Craig, Colorado. Craig is located 23 miles northeast of the <br />Colowyo minesite and experienced flooding not seen for decades. Fortification Creek, which <br />flows through the middle of Craig, ran out of the banks into the 500-year floodplain. <br />~?~-~""t x, 3z6 = ,ZGS <br />