_GENERAL DOCUMENTS - C1981017 ‎(289)‎

• Permit No: C1981017
• IBM Index Class Name: GENERAL DOCUMENTS
• Doc Name: Bid Documents ‎(IMP)‎
• Media Type: D
• Archive: No

streams carried only suspended clay sediment whereas the fast-
flowing streams carried both sand, silt and clay. The sediment
retention ponds probably allowed fine clays to pass through the
system, whereas prior to their installation, all of the sediment
passed through. Another contributing factor may be that waters
during the high-flow season are purer than those of the low flow
season, but this is probably only a minor component, and probably
not dicipherable from the data.
4b. TSS versus time. TSS were highest during the first two years
of the data set and decreased, progressively through the end of
1984. After 1984, TSS achieved very low values, and remained low
through 1992 .
It appears that mining had a positive impact on the sediment load;
site management practices, particularly the installation of
sediment retention ponds, caused the sediment load to diminish.
Sample collection practices may have had some control over TSS
concentrations. Unless the sampling events were pre-ordained, it
is likely that samples were collected during good weather, i.e.
locally low flow, and that sample collection did not routinely take
place during or immediately following storms . Samples collected
during the early years of the data set were collected at closely
spaced intervals, and thus are likely to have picked up more of the
results of storms. Sampling in later years, which occurred only
twice yearly, probably took place during good weather, which would
have been during low flow when sediment loads consisted only of
clays.
4c. TSS versus flow. TSS shows a slight positive exponential
relationship with flow. However, virtually all of the high TSS
measurements were taken during lower flow.
5a. Evaluation of outliers . Data for Conductivity, TDS, and TSS
were plotted relative to flow and curves were fit to the data. A
one standard deviation range was established in order to highlight
the samples above (or below) one standard deviation from the mean
for any given rate of flow. The choice of one standard deviation
was selected arbitrarily. There is no reason to believe that this
method is any more valid than other, more or less empirical methods
for evaluating the data. Rather, the test was to see whether the
positive outliers bear any relationship to time of sampling.
5b. Conductivity and TDS Outliers. Table 1 shows the data and the
variation of the data relative to the standard deviation of the
population at station #20 . This evaluation of variance relative to
the mean and standard dev\iation is different from that shown on
the graphs . The graphs highlight the outliers at any specific
value of flow whereas Table 1 highlights the outliers relative to
the entire population, regardless of the rate of flow.
TDS outliers normalized to flow shows outliers that range from
about 430 to 1312 ; conductivity outliers normalized to flow range
from 600 to 1900 . However, TDS outliers relative to the mean of