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• Vegetation, Soil, and Infiltration. A key consideration in the hydrologic model of this basin is the volume of water lost to interception and infiltration.The (Sabot, 2008)guidelines recommend the Green/Ampt Loss Rate (G/A) method for storms having ARI equal to or less than 100 years. This method accounts for ponding at the soil surface and for infiltrated water. Mine Permit Amendment 06 (AM-06) Figure AM-06-J-01 provided vegetation coverage information for the Secondary Containment Basin (Habitat, 2010). Adjustments were made to the coverage percentages using aerial photos and field observations. Minor adjustments were also made to the unit delineation to increase the accuracy to the scale of the basin. The "Holy Cross Soil Survey: Copper Mountain and Climax Quadrangles" (USDA, 2003) and associated report provided soil unit information over the basin.The USDA data includes soil texture information recorded at multiple depths.The (Sabot, 2008) provides saturated hydraulic conductivity values based on the most restrictive soil texture in each soil map unit (SMU).The soil data were supplemented with knowledge of impervious asphalt/concrete pads in the basin. Minor adjustments were made to the SMU delineations to increase the accuracy to the scale of the basin and to add the containment pool. The saturated hydraulic conductivities for each unit were used to compute an areal-weighted average of"bare soil surface" saturated hydraulic conductivity. In lieu of an estimated hydraulic conductivity for the "Made Lands" soil unit, it was assumed impervious conditions over the unit due to the lack of information over the soil texture.This assumption would account for any unknown buried asphalt or concrete within the unit. Other G/A loss parameters were estimated from satellite imagery and knowledge of the basin.The parameters were adjusted for effective slope,vegetal cover, and antecedent moisture condition following the recommendations in the (Sabot, 2008) document.The spoil piles captured in the 2016 Climax mapping were not included in any slope calculations. • Baseflow. The baseflow in the Secondary Containment basin is difficult to estimate due to the lack of a measurement gage or a comparable gaged basin in the region.When a basin lacks a gaged measurement point, it is typical to make a comparison to a similar basin and scale the baseflow based on certain basin characteristics.The typical approach is not applicable in this case due to the very small size, relatively shallow slope and mostly unvegetated lands. Most comparable gaged basins in the area are large, with significant vegetation cover, and steep slopes. Additionally,this basin experiences significant upstream regulation in the form of snow removal/relocation over the mine roadway that passes through the center. Using field estimations and site knowledge, it was conservatively estimated the peak baseflow to be 50 gpm (16.2 cfs/mi2).This baseflow is comparable to the previously estimated 10-year ARI peak day annual baseflow of 17.5 cfs/mil, as obtained from the 2019 Clinton & Mayflower Canal Flood Assessment Report (Wheeler, 2019). • Modeling storm and containment/pump sizes.Two models were constructed using the inputs and assumptions described above.These models evaluate basin hydrology, a governing storm event, and multiple design components for the Secondary Containment civil design. The first model was to determine the governing storm in the Secondary Containment Basin.The required size of conduit was also evaluated with the first model to route flows into the wet well. The governing storm is the storm which results in a higher peak water surface elevation (WSEL).