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HYDRO31322
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HYDRO31322
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Entry Properties
Last modified
8/24/2016 8:55:04 PM
Creation date
11/21/2007 1:32:18 AM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
C1980001
IBM Index Class Name
Hydrology
Doc Date
6/6/2007
Doc Name
Authorization to Discharge Under the Colo Discharge Permit System
From
Department of Health Department
To
DRMS
Permit Index Doc Type
NPDES
Media Type
D
Archive
No
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COLORADO DEPARTMENT OF PUBLIC HEALTH AND ENV/RONMENT, Water Quality Conrro/ Division <br />Rationale -Page 9, Permit No. CO-0032638 <br />Since the permitted ratio of the design flow to the chronic [ow flow is greater than 2:1 at both outfal[s, the permittee <br />is eligible for an exclusion jrom further analysis under the regulation. <br />g. .Salinity Regulations: !n complimrce with the Colorado River Salinity Standards and the Colorado Discha~re <br />Permit System Regulations the permittee shall monitor for total dissolved solids on a auarte~ basis. Samples shall <br />be taken at Outfalls 004A and 007A. <br />An evaluation of the iota/discharge of total dissolved solids indicates that the Edna Mine facility exceeds the <br />threshold of 1 ton/day or 365 tons/year of salinity. To determine TDS loading from this facility, the average <br />reported TDS values were multiplied by the average flow, then by 8.34 for each reporting period for Outfalls 004A <br />and 007A, then the sums of each outfall were added together. The average was determined to be in excess of I D <br />tons/day. The permittee submitted information in L996 stating that it was economically infeasible to prevent the <br />drscharge of all salt. Further, the site is in final reclamation and bond release is expected in the near future, at <br />which time this permit mny be terminated. <br />h. Whole Effluent Toxicity (WET) Testing: For Outfalls 004A and 007A, chronic WET testing is required (See Part <br />/.A of [he permit.) <br />i. Purpose of WET Testing: The Water Quality Control Division has established the use of WET testing as a <br />method for identifying and controlling toxic discharges from wastewater treatment facilities. WET testing rs <br />being utilised as a means to ensure that there are no discharges of pollutants "in amounts, concentrations or <br />combinations which are harmful to [he beneficial uses or toxic to humans, animals, plants, or aquatic life" as <br />required by Section 31. I t (I) of the Basic Standards and Methodolo¢ies for Surface Waters. <br />ii. In-Stream Waste Concentration (IWC): Where monitoring or limitations for WET are deemed appropriate by <br />the Division, chronic in-srream dilution as represented by the chronic /WC is critical in determining whether <br />acute or chronic conditions shall apply. According to the Colorado Water Quality Control Division <br />Btomonitariny Guidance Document, dated July 1, 1993, for those discharges where the chronic 1WC is greater <br />than 9. I % and the receiving stream has a Class I Aquatic Life use or Class 2 Aquatic Life use with all of the <br />appropriate aquatic life numeric standards, chronic condifions apply. Where the chronic !WC is less than or <br />equal to 9.7, or the stream is not classed as described above, acute conditions apply. The chronic IWC is <br />determined using the following equation: <br />/WC = [Facility Flow (FF)/(Stream Chronic Low Flow (annual) + FF)] X 100% <br />The flows and corresponding IWC for the appropriate discharge points are: <br />Outfall Chronic Low Flows, Facility Design Flows, IWC, (%) <br />30E$ (cfs) (cfs) <br />004A 0 1.9 100 % <br />007A 0.25 4.0 94% <br />The IWC for Outfa11004A is 100% which represents a wastewater concentration of 100% effluent. The IWC for <br />OutfaQ 007A is 94% which represents 94% effluent to 6% receiving stream. <br />iii. Chronic WET Limits: This facility has had WET exceedances in the past, of which the casue was determined to <br />be TDS. On this basis, the Division believes there is reasonable potential for the discharge to interfere with <br />attainment of applicable water quality classifications or standards and therefore, a chronic toxicity limit has <br />been incorporated into the permit. Previously, a chronic WET limit was a part of the permit and compliance <br />has been achieved for at [east [he two pas[ years, and thus the chronic WET limit is imposed effective <br />immediately. However, the frequency for WET tesh'ng has been reduced due to repeated compliance. <br />The permittee will be required to conduct two types of statistical derivations on the data, one looking for any <br />statistically sagntfican[ difference in toxicity between the control and the effluent concentrations and the second <br />identifying the /C25, should one exist. Both sets of calculations will look at the full range of toxicity (lethality, <br />growth and reproduction). If a level of chronic toxicity occurs, such that there is a statistically significant <br />difference in the lethality (at the 95% confidence Ieve1) between the control and any effluent concentration less <br />than or equal to the 1n-stream Waste Concentration (IWC) and if the lethality IC25 < the IWC, the permittee <br />will be required to follow the automatic compliance schedule identified in Par[ LA.4 ofthe permit, ifthe <br />
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