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Dames & Moore, 1999 - USDA Forest Service

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4.4.3.5 Groundwater Uses<br />

Groundwater is not used as a potable source at Holden Village. The well at the Lucerne Bar USFS guard<br />

station provides that facility with domestic water; the well is installed in alluvium near the mouth of<br />

Railroad Creek, and is assumed to include a mixture of Railroad Creek and Lake Chelan water.<br />

4.4.4 Site Specific Water Balance<br />

4.4.4.1 Approach and Background<br />

Objectives and Approach<br />

A general basin-wide, climatic water balance or budget was developed for the entire Railroad Creek<br />

watershed for use in analyzing flow characteristics and predicting minimum riprap sizing to protect the<br />

lowermost portions of the tailings piles from erosion by Railroad Creek. The results of the basin-wide<br />

water budget were discussed previously in Section 4.3.5. The results of the analyses to predict minimum<br />

riprap sizing utilizing HEC-I modeling are presented in Section 4.3.6.2.<br />

This section describes the site-specific water balance that was developed to assess the seasonal flow<br />

characteristics of water source inputs to Railroad Creek in the vicinity of the Site only. The potential<br />

sources of water analyzed on the Site include precipitation runoff, tributary inflow, and groundwater<br />

inflow. Groundwater inflow may include flow through the alluvial aquifer associated with Railroad<br />

Creek, flow through the tailings piles, and groundwater inflow from the bedrock and mine workings.<br />

The site-specific water balance approach is to reference all of the water balance components to gain or<br />

loss of water in Railroad Creek. Flow measurements recorded in Railroad Creek provide the most<br />

representative, complete, and accurate measure of the flow of water entering and leaving the Site.<br />

Railroad Creek, adjacent to the Site, was subdivided into two reaches: Reach 1 from station RC-1 to RC-<br />

4, and Reach 2 from station RC-4 to RC-2. These reaches represent unique hydrologic environments.<br />

Reach 1 transitions from background conditions to the affected portions of the Site, including the inputs<br />

from the Portal Drainage. Reach 2 represents conditions potentially affected by the tailings piles.<br />

The water balance analysis was completed for the period of May 151June 15, 1997, and September 1997<br />

using flow data obtained during the respective sampling periods. Data collected in 1997 is reflective of a<br />

greater than normal snowpack for this area. The relatively high snowpack resulted in higher than normal<br />

spring and summer melt flows. These two sampling periods represent the range of seasonal conditions<br />

observed during 1997. The component source inflows were quantified within the accuracy of the<br />

available data, and compared with baseflow gain in Railroad Creek for the MayIJune 1997 and September<br />

1997 timefrarnes. Average flow conditions were used or estimated for the source inflows and baseflow<br />

gain in Railroad Creek, and storage effects were not directly quantified.<br />

Flow data was also collected in October 1998; however, only select stations were measured. The October<br />

1998 flow data was used to refine the water balance analysis.<br />

G:\WPDATA\OOJ\REPORTSWOLDEN-ZW\4-0.DOC<br />

17693-005-019Uuly 19, <strong>1999</strong>;4:51 PM;DRAFT FMAL RI REPORT<br />

DAMES & MOORE

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