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Silver Creek - Division of Water Quality - Utah.gov

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<strong>Silver</strong> <strong>Creek</strong> <strong>Water</strong>shed TMDL Final Report<br />

IV. Significant Sources<br />

(See Section 6.0 for details)<br />

Historical evidence indicates the source <strong>of</strong> metals <strong>of</strong> concern in this watershed are from historical<br />

mining activities in the Park City area. Most <strong>of</strong> the mining activity occurred within the upper<br />

watershed, primarily within Empire Canyon. Tailings from these mines were stored onsite or<br />

removed to another location, typically downstream. Significant source areas for zinc and<br />

cadmium are identified on Figure 22 and summarized in the following table:<br />

Description<br />

Upper <strong>Water</strong>shed Sources<br />

Prospector Square<br />

<strong>Silver</strong> Maple Claims<br />

Flood Plain Tails<br />

Richardson Flats<br />

Meadow Area<br />

Owner<br />

United Park City Mines<br />

Park City Municipal Corporation<br />

BLM<br />

United Park City Mines<br />

United Park City Mines<br />

Various Private Land Owners<br />

V. Technical Analysis<br />

(See Section 7.0 for details)<br />

Data are presented in Section 4.0 showing average concentrations and flows for bi-monthly<br />

periods at each “key” sampling location. Table 7 presents a summary <strong>of</strong> flows, concentrations<br />

and loads at key stations for each <strong>of</strong> these bi-monthly periods. Sections 9.0 and 10.0 provide the<br />

Best Management Practices (BMPs) that can be used to remedy the widespread nonpoint sources<br />

<strong>of</strong> metals in the <strong>Silver</strong> <strong>Creek</strong> <strong>Water</strong>shed. Literature values for the effectiveness <strong>of</strong> each BMP are<br />

provided in Table 14. Utilizing the removal efficiencies for each BMP, reductions in zinc and<br />

cadmium loading values are calculated along with anticipated stream concentrations after BMP<br />

implementation. Completion <strong>of</strong> scheduled BMPs is expected to achieve and maintain the TMDL<br />

endpoints for <strong>Silver</strong> <strong>Creek</strong>.<br />

VI. Margin <strong>of</strong> Safety & Seasonality<br />

(See Sections 4.0 & 5.0)<br />

There is significant variability in the existing flow and chemical data set for this TMDL which<br />

lends uncertainty to the loading analysis. Additionally, there is uncertainty in the actual degree<br />

<strong>of</strong> success that implementation <strong>of</strong> the BMPs identified to address nonpoint sources will achieve.<br />

Accordingly, the Margin <strong>of</strong> Safety to address these sources <strong>of</strong> uncertainty for this TMDL will<br />

include the following components:<br />

• An explicit margin <strong>of</strong> safety <strong>of</strong> 25% is utilized in the allocation calculations for the<br />

<strong>Silver</strong> <strong>Creek</strong> TMDL<br />

• Ongoing Monitoring Program will be implemented<br />

• Use <strong>of</strong> the maximum hardness <strong>of</strong> 400 mg/l in calculating the hardness adjusted <strong>Water</strong><br />

<strong>Quality</strong> Standards that are used as the endpoint for this TMDL (use <strong>of</strong> actual hardness<br />

would have resulted in higher values for the <strong>Water</strong> <strong>Quality</strong> Standards)<br />

Page 4

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