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Dames & Moore, 1999 - USDA Forest Service

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5.4.2 Site Groundwater Quality<br />

The distribution and concentrations of metals and other chemical constituents From samples collected<br />

during the RI From Site monitoring wells, lysimeters, and seeps is described in the following sections.<br />

Topics discussed include distribution of concentrations and seasonal variability of results. As described in<br />

Section 4.4, two groundwater systems occur at the Site, one within the tailings, and the other in the<br />

alluvial/reworked till unit.<br />

Groundwater monitoring wells are identified based on geologic unit in which the wells were screened<br />

during installation. "A" series wells monitor groundwater from the alluviaUreworked till unit (TPl-1 A,<br />

TPl-2A, TPl-3A, TPI -4A, TPl-5A, TP1-6A, PZ-1 A, PZ3A, TP2-4A, TP2-5A, TP2-8A, TP2- I I A, PZ-<br />

6A, TP3-6A, TP3-IOA) and "B" and "C" series wells are screened within the tailings (PZ-IB). Additional<br />

wells without a series designation (HV-3, HBKG-I, HBKG-2, TP3-4, TP3-8, TP3-9, DS-I, DS-2) monitor<br />

the alluviaVreworked till unit or other native materials.<br />

Lysimeter results are reflective of tailings groundwater chemistry in the unsaturated portion of the tailings<br />

piles. Samples collected from lysimeters are identified with an "L" suffix (TPI -2L, TPI -3L. TPl-4L, TPI -<br />

6L, TP3-4L, TP3-6L, TP3-IOL). Seep discharge from the tailings piles is assumed to represent tailings<br />

groundwater discharge along either fractures in cemented tailings or water perched on a lower permeability<br />

layer at the base of the tailings. Seep discharge from the waste rock piles or the banks of Railroad Creek<br />

other than the tailings piles is assumed to be indicative of water percolating through the piles or<br />

alluviaVreworked till. Seeps are identified by a "SP" prefix. Samples were numbered based on sequencing<br />

in the field. The relationship of surface water and groundwater interaction with respect to seeps was<br />

previously described in Sections 4.3 and 4.4.<br />

5.4.2.1 Historical Groundwater and Seep Data<br />

Groundwater<br />

Groundwater samples were collected from groundwater monitoring wells during three previous sampling<br />

events completed by others at the Site. In June and August 1991, the USBM collected samples from<br />

selected wells on tailings piles 2 and 3. In 1995, the USBM collected samples from wells and lysimeters<br />

on tailings pile 2, and from wells HBKG-I and HBKG-2. The results are summarized on Table 5.4-3. In<br />

general, aluminum, copper, lead, and zinc concentrati.ons in samples collected in 1991 and 1995 are<br />

higher,than were found in samples from the RI sampling at the same locations.<br />

The USBM groundwater data were found to have limited use in the RI due to: (1) the limited list of<br />

metals analyzed when compared to those metals analyzed for the RI; (2) relatively high detection limits;<br />

(3) the limited number of wells sampled by USBM when compared to the RI; (4) analytical data that were<br />

suspect due to concentrations being significantly higher than those analyzed during the R-I (i.e., copper<br />

and zinc); and (5) the absence of quality assurancelquality control documentation for the USBM data.<br />

Therefore, the USBM data are not included in the RI groundwater discussion presented hereafter.<br />

Seeps<br />

Seep samples were collected by the USGS in July 1994 (Kilburn, et al., 1994), July 1995 (Kilburn and<br />

Sutley, 1996), May 1996 (Kilburn and Sutley, 1997), and September 1996 (Kilburn and Sutley,<br />

\WM-SEAI\VOLI\COMMOMWP\WDATA\OO5WPORTSWOLDEN-2UU 5-4 1<br />

17693-005-019Uuly 28, <strong>1999</strong>;11:09 AM;DRAFT FINAL RI REPORT

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