Dames & Moore, 1999 - USDA Forest Service

Observations During Aquatic snorkel Survey
A snorkel survey was completed for portions of Railroad Creek as part of the Site aquatic biota
characterization (see Section 4.6). The survey included sampling stations adjacent to tailings pile 1 (RC-9)
and tailings pile 2 (RC-7) (see Figure4.6-I). The segments of Railroad Creek evaluated were
approximately 100 meters long fo; each sample station. Two snorkelers participated in the survey.
Both individuals visually assessed the qualitative conditions of the Railroad Creek substrate and submerged
sections of the streambank. The snorkelers reported that the substrate of Railroad Creek was loose and not
cemented at these locations. However, isolated portions of the south streambank near the northeast comer
of tailings pile 1 (RC-9) appeared to be cemented (Figure 4.3-3d).
4.4 HYDROGEOLOGY
4.4.1 Regional Hydrogeology
The groundwater in the region is normally found in both the bedrock and overlying material. The bedrock
groundwater is present within fractures, joints, and faults. The rate of movement of groundwater within the
bedrock is variable but is normally relatively slow, commonly requiring days to years to migrate the same
distance which required only minutes to days in soil. Groundwater is also commonly "perched" withiri
overlying weathered rock, alluvium, colluvium, and glacial materials (Patmont, 1989).
4.4.2 Overview of Railroad Creek Watershed Hydrogeology
The existing Railroad Creek valley was formed by glacial action and hence has steep sides cut into bedrock
and a fairly broad, flat bottom. The surface of the valley bottom slopes to the east toward Lake Chelan
(Figure 4.3-3). The valley bottom is covered throughout its length with a shallow and variable depth of
glacial, colluvial, and alluvial deposits. These deposits thin where bedrock comes closer to ground surface
(USGS, 1967a and 1967b).
Groundwater is recharged by snowmelt in the spring and early summer. Due to the relatively large amount
of snowfall in the region, groundwater recharge is large during this period. Once snowmelt is complete,
groundwater recharge is from rainfall and potentially from surface water loss from Railroad Creek. As
discussed in Section 4.3.3, highest average precipitation recorded at Holden Village is in November through
January and the lowest is during May through August. Therefore, groundwater recharge varies in both
amount (large in spring, small in summer) and source (snowmelt in spring, rainfall in summer).
As noted for the remainder of the Lake Chelan Basin (Patmont, 1989), source water for Railroad Creek is
supplied from glacial melting, snowmelt, and rainfall. Water is transported to the creek as groundwater,
seep flow, or tributary surface water input. With the beginning of snowmelt in the spring, water is supplied
to Railroad Creek from the adjacent valley sides as both overland flow and groundwater flow. Once
snowmelt is complete, Railroad Creek is supported by up-valley glacial melt, local groundwater flow, and
rainfall runoff from summer storms. Flow directions are generally to the north and south off the valley
sides, to Railroad Creek, which flows in an easterly direction.
G:\WPDATA\OO5\REPORTSWOLDEN-2UULid.DOC
17693-005-019Uuly 19. 1999:4:51 PM:DRAFI' FINAL RI REPORT