Dames & Moore, 1999 - USDA Forest Service

arely,,(2) occasionally, and (3) frequently associated with adverse effects. These categories are based upon
the results of a number of different studies with varying endpoints. Each has its own strenfis and
weaknesses. For this reason, the USEPA (1992) has mommended that a range of chemical concentratichs @
should be used rather than a single value. Nevertheless, the Long et al. (1995) guidelines only present single
'values for ER-M and ER-L.
Concentrations below the ER-L (between the above-mentioned "rarely" and "occasionally" categories)
represent a "minimal effects" range, while concentrations between the ER-L and the ER-M represent a
"possible effects" range where adverse effects were occasionally observed. According to Long et al. (1995).
concentrations above the ER-M represent a "probable effects" range within which adverse effects are more
likely to occur. Nevertheless, Long et al. (1995) recommended that these sediment quality guidelines
should be used as "informal screening tools," and NOAA (O'Co~or et al., 1998) has recently reported that
fewer than 40 percent of the samples that exceeded the ER-M in an extensive sediment quality assessment
program, were actually toxic in bioassays. It is important to note, therefore, that because sediment toxicity is
not well understood, neither these guidelines, nor any other sediment quality guidelines (see below), have
been promulgated into law (i.e., criteria).
The lowest effect level (LEL) of the Ontario Minisby of the Environment (Persaud et al., 1993) indicates a
level of sediment contamination that has no effect on the majority of benthic organisms and is calculated as
the 5th percentile using the screening level concentration (SLC) method. The severe effect level (SEL)
indicates the concentration of a compound that would likely be detrimental to most benthic species and is
calculated as the 95th percentile using the SLC method (Persaud et a]., 1993). The LEL and SEL values
therefore are generally comparable to those of Long et al. (1995), even though the LEL may be somewhat
more conservative and the SEL may be more liberal.
Because sediments account for such a small portion of Railroad Creek and because there is little sediment
toxicity data for burrowing freshwater invertebrates, no site-specific TRVs were developed for benthic
invertebrates exposed to sediments and default sediment guidance values were used. Because reports have
shown that metals may interact either synergistically or antagonistically, depending upon the study selected,
it was assumed that all metals act independently of each other.
Comparison of the UCL site data from Table 7.2.2-1C with the ER-L screening pidance values presented
in Table 7.2.3-2A shows that several metals in sediments and flocculent fall below the screening values.
The sediment sample data collected h m Lucerne Bar during the RI (see Section 5.0) was not addressed in
the ERA as additional sampling is pending. Elements were eliminated if they did not exceed the screening
value (ER-L or LEL) or if there was no toxicity benchmark by which to judge potential toxicity. Screening
values are not available for aluminum, barium, beryllium, or selenium and potential toxicity cannot,
therefore be assessed. In summary, there was no need to further evaluate:
Invertebrate Bioassavs
Sediment - aluminum, barium, beryllium, lead, mercury, and selenium
Flocculent - aluminum, barium, beryllium, lead; manganese; nickel and selenium
Sediment bioassays are very difficult to interpret because of the complex matrix interferences with organic
carbon and sulfides, and because it is the pore-water of sediments, not the bulk sediment metals
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17693-005-019Wuly 27.1999;5:16 PWRAFT FINAL RI REPORT