Silver Creek - Division of Water Quality - Utah.gov

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Silver Creek Watershed TMDL Final Report conducted from July 2001 through June 2002 by UDWQ to augment the data set prior to completion of the TMDL. The Margin of Safety utilized in the TMDL is an additional mechanism that is aimed directly at issues of uncertainty. UDWQ believes that the 25% explicit Margin of Safety utilized is appropriate to compensate for any uncertainty in the data set. Additional sampling will continue by UDWQ in accordance with the monitoring program outlined section 11.0 and should further bolster the data set for Silver Creek. In regard to selection of the best BMPs to be utilized for implementing the TMDL, the selection of BMPs should proceed following completion of the TMDL during the implementation phase. UDWQ is quite open to supplemental monitoring that may be appropriate in order to select the best BMP for a given site should that need be apparent. UDWQ will work closely with sponsoring parties on each implementation project to assure that appropriate BMPs are supported. 6. One commenter wanted to make sure that the metals loading estimate provided for the Judge and Spiro tunnels in section 6.0 of the draft TMDL accurately reflected the actual flow and seasonality of flows from these two tunnels. Response - UDWQ used actual flow and metals data provided by Park City Municipal Corp. in calculating the loads contributed by the Judge and Spiro tunnels. The flows from the Spiro tunnel that enter the Silver Creek drainage were obtained from Mount Aire East Flume data provided by Joel Congor, Park City Municipal Water Dept. on 12-3-03. 7. Two comments expressed concern with the water quality standard for cadmium that is used in the TMDL to establish the stream water quality endpoint or target of 0.00076 mg/l. One commenter questioned why the stream endpoint for the Silver Creek TMDL could be more stringent than the Primary Drinking Water Standard of 0.005 mg/l. Both commenters raised concern that the TMDL endpoint for cadmium was below current laboratory detection limits. One commenter noted that the drinking water best available treatment technology (BAT) can only treat drinking water to a .005 mg/l level. . Response – TMDL allocations must result in meeting water quality standards. The cadmium endpoint selected for the Silver Creek TMDL is the Utah Water Quality Standard from R317- 2-14 adjusted for hardness for class 3A beneficial uses (cold water species of game fish). This value is the same as the cadmium value provided in the EPA National Recommended Water Quality Criteria: 2002 (EPA 822-R-02-047 Nov. 2002). Many of the metal water quality standards for aquatic beneficial uses are stricter than drinking water standards based on the fact that aquatic biota often have a greater sensitivity to metals than humans. The issue of the standard for cadmium being below the laboratory detection limit is a legitimate concern. The laboratory capability to analyze metals is improving. By the time 91
Silver Creek Watershed TMDL Final Report clean up activities are well under way in 5 years or more, detection limits may be below the water quality standard. If this is not the case then the generally accepted laboratory detection limit will have to be used as the measure of success for cadmium in this TMDL. If after clean up actions are completed with all of the known source areas and water quality levels for cadmium in Silver Creek still do not achieve the respective water quality standards, it would be appropriate to undertake a formal Use Attainability Study to ascertain what the stream standard should be. In regard to UPDES permit limits imposed as a result of the TMDL, the current approach used for water quality standards that are below laboratory detection limits is to set the permit limit at the detection limit. The details of this would be worked out with the permitee at the time the permit limits are developed. 8. One comment indicated that naturally occurring zinc concentrations as high as 74 ppm had been observed in soils in the Silver Creek drainage. The commenter wanted to know how the TMDL and the water quality standard for zinc have taken into account naturally occurring levels of zinc? Response – Given that the Park City area supported metal mining activities for around a century, it is not surprising to find naturally occurring zinc values as high as 74 ppm have been observed in area soils. What impact these naturally occurring values would have on background water quality is, at this point in time, virtually impossible to estimate in light of the fact that 74 ppm pales in significance to some of the metals values of mining impacted areas in the watershed. As an example, in the meadow area between US-248 and I-80, the Innovative Assessment Analytical Results Report on Lower Silver Creek (DERR 2002) observed zinc concentrations in the 20,000 to 60,000 ppm level. Accordingly, if clean up actions are completed with all of the known source areas and water quality levels for zinc and cadmium in Silver Creek still do not achieve the respective water quality standards, it would be appropriate to undertake a Use Attainability Study to ascertain what the stream standard should be. 9. One comment indicated that a more complete discussion of zinc and cadmium geochemistry should be included in the TMDL to include pH and hardness controls on the solubility of these two metals. The commenter requested that complete chemical analysis should be presented in the document for available samples. Response – A full explanation of the geochemistry of zinc and cadmium relative to pH and hardness is beyond the scope of the TMDL. A brief addition to the text has been included in Section 4.5 to address this need in part. The complete data set is available to any party that requests it but will not be added to the TMDL document. 10. One comment expressed concern that the introduction to section 10 of the Draft TMDL indicated that actual clean up and remediation of the source areas for metals in Silver Creek would best be handled in the Superfund arena. The commenter indicated that this would be 92
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Silver Creek Total Maximum Daily Lo
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4.0 DATA ANALYSIS RESULTS 4.1 Zinc
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Silver Creek - Division of Water Quality - Utah.gov

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