2021-08-30_REVISION - M1990057 - Laserfiche WebLink

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MEMO District Board,Leadville Sanitation District i� Union Milling Permit M1990-057(Version 4) Job No.:1119.2e August 24,2021 Page 3 of 4 mercury to the WWTF and implement strategies to control sources so that compliance with the total mercury effluent limitation could be attained. Low level mercury is present throughout Leadville in the soil,water and air due to historic mining operations.The potential for increased infiltration into the sewer collection system as previously stated from the new crushing facility could increase mercury concentrations to the WWTF resulting in effluent compliance issues for low level mercury. The District's WWTF consists of a headworks for screening and grit removal,two aeration basins,two covered clarifiers,a polishing pond,and a chlorine contact chamber for disinfection. Nearby seismic activity from the proposed Mill could have detrimental effects to the existing WWTF structures that are required for wastewater treatment and permit compliance. The WWTF operates under the Colorado Discharge Permit System Permit Number CO0021164.The District's permit establishes effluent limits for potentially dissolved copper and cadmium ranging from 1.1 to 1.6 ug/L depending on time of year.The permit limit for total mercury is 0.077 ug/L.The permit also establishes limits for potentially dissolved zinc ranging from 2658 to 480 ug/L depending on time of year. The permit also requires the District to report effluent limits for an extensive list of pollutants including arsenic, chromium,copper,cyanide, iron, lead, manganese, molybdenum, nickel,selenium,silver, uranium,sulfide, nonylphenol,cesium, radium,strontium,thorium, BTEX and benzene.The permit requires only reporting for the previously listed metals so that the Division can review the data and develop potential discharge limits on future discharge permit renewals. Since the Mill is located directly adjacent to the District's WWTF,the wind transport of metals from trucks entering and leaving the facility as well as ore,topsoil and overburden stockpiles and dust from the crushing facility could have detrimental effects and possibly contaminate the open air basins at the WWTF. Effects could be seen immediately or could occur over a period of time since the District has extremely low level metals limits in ug/L and is required to monitor metals on a frequent basis in the wastewater effluent and report this information to CDPHE. Also,it's important to note that the tailings detection limits per Table 5-2 below are in mg/L for the metals listed while the District's permit limits are in ug/L. If the Mill is only required to test the tailings to mg/L,they could be reporting non detectable values because of the test methods utilized are not capable of measure to low level ug/L limits.It's recommending the testing and reporting of all metals for the Mill be changed to ug/L.