Dames & Moore, 1999 - USDA Forest Service

Department of Ecology samples collected June 1996 and September 1996 were also
considered.
Sample station locations are shown on Figures 5.3-1 through 5.3-4.
Calculation methods to determine background concentrations are outlined in WAC 173-340-708(1l) and
in Ecology's statistical guidance (1992). The statistical guidance and Ecology's MTCAStat statistical
program were used to perform the analyses. Statistical analysis was performed for total and dissolved
concentrations for aluminum, arsenic, barium; beryllium, cadmium, calcium, chromium, copper, iron,
lead, magnesium, manganese, mercury, molybdenum, nickel, potassium, selenium, silver, sodium,
thallium, uranium, and zinc. The data were compiled into a total data set that included all data points
listed above without regard to season or time collected. The number of and specific data points included
in the analysis are shown in Table 5.3-1.
For a select list of dissolved metals including: aluminum, arsenic, beryllium, cadmium, chromium,
copper, iron, lead, magnesium, manganese, selenium, silver, and zinc, the total data set was subdivided
into two seasonal data sets, spring and fall. These metals represent the broad suite of PCOCs and other
metals of interest related to the Holden Mine. The number of data points for each seasonal data set is
shown below. Specific data points used are shown in Tables 5.3-2 to 5.3-14.
Eight data points were considered a minimum data set for performing statistical calculations, with one
exception (seven points for the arsenic fall data set).
Metal Seasonal Set - Spring # Data Points Seasonal Set-Fall
# Data Points
Aluminum 19 13
Arsenic 10 7
Beryllium 19 I I
Cadmium 20 12
Chromium 17 12
Copper 17 12
Iron 19 I I
Lead 18 12
Magnesium 18 I I
Manganese
Selenium
17 I I
Silver
-
Zinc
19
20
11
13
Insufficient data points available for statistical analysis
Two other data sets, Sets 1A and lB, were evaluated to assess the comparability of Railroad Creek
background stations with Railroad Creek tributaries and other reference stations and to verify that pooling
of the data are appropriate. As with the seasonal data sets, only dissolved aluminum, arsenic, beryllium,
cadmium, chromium, copper, iron, lead, magnesium, manganese, selenium, silver, and zinc were included
in the analysis. The stations included in each set are as follows:
Set IA: Select historical and RI stations RC-1, RC-6, and RC-1 I were pooled.
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17693-005-019Uuly 28, 1999;11:09 AMDRAFT FINAL RI REPORT