Dames & Moore, 1999 - USDA Forest Service

Since none of the UCL concentrations exceeded the acute or chronic benchmarks calculated in Table 7.1.3-
2B, there is no need to conduct a further analysis of risk to benthic invertebrates in South Bank or
mainstream of Railroad Creek from these metals.
Benthic Invertebrates- Sediments
In addition to the benthic macroinvertebrates that are attached to hard substrates, there may be benthic
invertebrates that burrow in the sediments of Railroad Creek. Sediment samples were collected by USGS
(1994) and analyzed in by a non-standard method that provided worst possible conditions for comparison
with sediment quality benchmarks. Because there is relatively little sediment in Railroad Creek. the samples
were collected from behind boulders, and from sandban. The samples were sieved, air dried. and then
pulverized to a fine flow prior to extraction and analysis by ICP-AES. Pulverizing the sediments would
have increased the amount of metal in contact with the strong acid and resulted in an apparent higher
concentration than normal extraction procedures. USBM (1995) and Ecology (1997) collected sediment in
Railroad Creek. With the exception of silver, the USGS data were the highest sediment values available.
In Table 7.2.4-2C, the results of this analysis are compared against the sediment quality guideline values.
The most conservative guidelines (ER-L) were used for screening purposes, although it must be noted that
none of the samples exceeded the Ecology (1991) guidelines for freshwater sediments. Exceedances of the
ER-Ls for cadmium, copper, iron, manganese and zinc are shown on Table 7.24-2C.
Since risk was found for the UCLs of sediments, the median sediment concentrations were evaluated. There
were insufficient data points to calculate median concentrations in upstream sediments.
Exceedance of the ER-L means that sediments may "occasionally" be toxic (Long et al., 1995). Therefore,
it is not appropriate to use these exceedances as evidence of adverse effects to the benthic communities at
the sites where data was collected or for Railroad Creek in general. Because of the uncertainty associated
with interpretation of sediment quality guidelines, it may be more appropriate to assess the potential toxicity
of Railroad Creek sediments by exceedance of the ER-M, those concenb-ation "frequently" associated with
toxicity. When this is done, exceedances are only found for manganese downstream from the mining site,
and HQ is only slightly greater than 1.0.
Washington State (Ecology, 1997) has recently developed freshwater sediment quality values (FSQVs).
The FSQVs (freshwater sediment quality values) are probable apparent effects thresholds (PAETs). PAETs
are the 95th percentile concentrations of compounds of concern from field collected studies above the
highest concentration where no significant biological effects were found. The PAET is the concentration in
freshwater sediments below which biological effects are unlikely to occur. When the concentrations are
compared to FSQVs, only manganese and silver present risk to benthic invertebrates (Table 7.2.4-2C). In
support of this usage of sediment quality guidelines, it is noteworthy that Ecology (1997) found sediments
from the mine site area were non-toxic to the sensitive bioassay animal (Hyalelle asreca). Toxicity test data
are generally believed to be a more reliable indicator of potential toxicity than comparison to sediment
toxicity "guidance" values due to site-specific variations in conditions.
Harper Owes (1989) sampled sediments 170 m offshore of the mouth of Railroad Creek in Lake Chelan.
These sediments exceeded sediment quality guidelines for arsenic, iron, and zinc. However, it is important
to note that Ecology (1997) found that sediments collected from the delta at the mouth of Railroad Creek
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