Dames & Moore, 1999 - USDA Forest Service

The erodibility of the bed and bank material and extent of ferricrete development was assessed in
Railroad Creek adjacent to the tailings piles. A backhoe was used to break through the ferricrete material
on the south bank and in the streambed at three locations adjacent to the tailings piles. The test pits were
logged to document the nature of the bank materials and visually assess ferricrete and groundwater
conditions on the streambank. The extent of the ferricrete was mapped based on field observations in the
upstream and downstream direction as well as across the channel. The results of the ferricrete assessment
are presented in Section 4.3.9.
3.3 TASK 3 - HYDROGEOLOGIC INVESTIGATION
,3.3.1 Groundwater Quality and Water Level Data Collection and Analytical
The following sections summarize methods and equipment used in collecting groundwater-level and
groundwater-quality data during the RI activities.
3.3.1.1 Tailings Pile
Referring to Figures 3.3-1 and 3.3-2 and Tables 3.0-1 (under "Groundwater Monitoring Wells") and 3.2-
2 through 3.2-5, an initial assessment of groundwater monitoring wells at the Site was conducted in mid-
May 1997 to evaluate the suitability of the wells for use for water-level and water-quality sampling. The
assessment was completed by checking surface completions for well integrity and measuring total depths
in wells for concurrence with depths noted during well construction. Well PZ-2A was concluded to be
damaged below the surface and well TP2-5A was substituted for water quality sampling.
Water levels were collected from 48 wells at the Site during four sampling rounds in mid-May, mid-June,
mid-July, and mid-September of 1997. Water levels were collected from wells located apparently
upgradient and downgradient of tailings piles 1, 2, and 3, downgradient of the mill building complex, and
on the north side of Railroad Creek; the inferred groundwater flow direction is generally to the north to
northeast. Water levels were collected from piezometer clusters installed previously within the tailings
piles in order to assess groundwater flow directions within the piles. The results of water level
measurements are discussed in Section 4.4.3.
Water quality samples were collected from 24 wells at the Site during the May sampling round and 21
wells in September. Two wells scheduled for sampling in May-June (PZ-3C and CC-BKG) were not
sampled as they were dry. Three additional wells (PZ-IA, TP2-5A, and TP3-4) were not sampled in
September as they were also dry. Samples were collected following the removal of a minimum of three
casing volumes and when water parameters were stabilized. Prior to ihe first.sampling round, wells that
had not, previously been developed were developed (the removal of water from a well in order to remove
sediment produced during well construction and to encourage flow) using either decontaminated
downhole pumps, dedicated disposable bailers, or decontaminated PVC bailers.
Purging of groundwater wells was accomplished using either decontaminated downhole pumps or
decontaminated PVC bailers. Samples were collected using decontaminated PVC bailers during the May
sampling event, and decontaminated dedicated PVC bailers during the September sampling round.
Groundwater samples were tested in the field for pH, specific conductance, temperature, ferrous iron, and
oxidationlreduction potential as outlined in the associated SAPS. Samples were submitted to the
laboratory for dissolved metal analyses (aluminum, arsenic, barium, beryllium, cadmium, calcium,
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