Dames & Moore, 1999 - USDA Forest Service

Wolman pebble counts), occurrence and extent of iron flocculent and precipitate. sediment transport. and
sediment sources. The field findings are summarized in Sections 4.3.3.3 and 4.6.1.2.
Sampling and analysis of streambed sediment at the Site was not feasible because the dominant streambed
material was cobble and small boulder throughout the affected reach of Railroad Creek.
3.4.3.1 Railroad Creek Ferricrete Assessment
The main objective of the ferricrete assessment was to describe the extent, thickness and character of the
ferricrete along Railroad Creek, and develop a conceptual model of ferricrete formation and its effect on
the hydrologic/hydrogeologic regime. To achieve these objectives. field reconnaissance along the south
and north banks of Railroad Creek (in the vicinity of the tailings) was conducted during late September
and early October 1997. The channel and banks were inspected for conditions characteristic of ferricrete.
In addition, test pits were excavated into areas of observed ferricrete formation to assess the vertical and
lateral character of the deposits. Due to limited accessibility of the channel with mechanized excavation
equipment, two areas were chosen to excavate test pits: immediately east of tailings pile 1 and
immediately east of tailings pile 3.
During September 1997, four test pits were excavated by Cragg's Excavating under subcontract to Dames
& Moore (Figure 3.1-2 and Table 3.0-1 under "Subsurface/Surface Soil"). Three of the test pits
(DMTP3E-I, 2 and 3) were located in the high water channel or wetland floodplain of Railroad Creek,
just east of tailings pile 3. One test pit (DMTPIE-I) was located in the high water channel of Railroad
Creek about midway between the confluence of Copper Creek and the east end of tailings pile I. Each
test pit was photo-documented and described according to Unified Soil Classification System (USCS)
methods and with additional comments related to the observed hydrogeologic conditions. In addition,
partially cemented to cemented material was also encountered in trench DMTP3-4, which was excavated
into the side and base of tailings pile 3, in the same general area of the three other test pits. The field
findings are presented in Section 4.3.9.
3.5 TASK 5 - MILL BUILDING ASSESSMENT
Referring to Figures 3.1-2 and 3.1-3, and Table 3.0-1 (under "Feature/Arean), the mill site was assessed as
part of the RI.
3.5.1 USGS Assessment of Mill Building-Related Salts and Unprocessed Ore
Samples of the mill-related salts and unprocessed ore have been sampled by others in the recent past
(USGS, 1996 and 1997); seven samples were collected in 1995 and two samples were collected in 1996.
The results of the studies were agreed upon by the Holden Mine RIRS Technical Group to be sufficient
and of adequate data quality for use in RI characterization. Additional sampling of the salts and
unprocessed ore was not conducted during the RI. The data were evaluated in order to characterize the
environmental conditions in the mill building. The laboratory test results are presented in Section 5.4.3.2
under "Mill Building Drip Water."
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17693-005-019Wuly 19. 1999:2:07 PM;DRAFT FINAL RI REPORT