2024-10-15_PERMIT FILE - M2024053 (4)

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Table G-1. Surface Water Discharge Monitoring Requirements in NPDES Discharge Permit Parameter Monitoring Frequency Sample Type Flow Instantaneous, Monthly In-situ pH 2x/month Grab Total Suspended 2x/month Grab Solids Oil and Grease Visual 2x/month Visual Oil and Grease Contingent on visibility Grab of oil and grease Total Flow Instantaneous, Monthly Calculated Selenium,Potentially 2x/month Grab Dissolved Total Dissolved Solids Quarterly Grab Note:these are the anticipated analytes based on operator experience at similar sites.CDPHE may issue different sampling requirements with the permit. 3. Floodplain The site has not been mapped for flood potential by the Federal Emergency Management Agency. Based on upstream data, the areas surrounding the drainage are likely within the 100- year floodplain of the Big Sandy Creek, but not within the floodway. 4. Wetlands The National Wetlands Inventory aerial-based mapping indicates the presence of wetlands within the permit area. These wetlands are mostly in the existing drainage and will not be disturbed, aside from wetlands crossings for access. A USACE Wetlands Permit will be obtained prior to any wetlands disturbances. Exhibit C and F maps show the NWI mapped wetlands. 5. Aquifers The Big Sandy Creek aquifer is the only identified aquifer located at the site. It has an approximate depth of 10 feet in the upland areas of the site. It is approximately 35 feet below the surface of the terraces further from the creek. 6. Surface Water The mining operation will impact surface water in the area through the stormwater runoff that enters the site. Map G-1 shows the drainage patterns and how they are affected throughout the life of the mine. The maps include information on the drainage basins currently, during mining, Limon Sand& Gravel Pit Lewicki&Associates August 2024