Dames & Moore, 1999 - USDA Forest Service

apparent lack of aquatic toxicity at RC-5a suggests that this reduction is more attributed tot he physical
presence of flocculent.
Fish survey results indicate reduced numbers at RC-5a (20 troutha)) compared to the reference densities
of 59 and 384 troutlha. However, trout density at RC-10 (92 troutha) was greater than the density
estimated for South Fork Agnes Creek (59 troutha). Additionally, four O+ year class trout (typically the
life stage most sensitive to metals toxicity) were collected at RC-I0 which may reflect the lack of water
quality criteria exceedances. Habitat evaluation scores were slightly higher at the reference stations.
Reference stations BC-I and SFAC-I scored the highest of all aquatic sampling stations at 120 and 113,
respectively. The onsite stations RC-5a and RC-10 scored slightly higher than the median score for all
stations at 1 10 and 108, respectively.
Comoanv Creek as a Reference for RC-3
The RC-3 station at the mouth of Railroad Creek was also discovered to be unique relative to the Railroad
Creek upstream reference stations (RC-6 and RC-I), primarily with respect to gradient (channel slope),
watershed area size, elevation, and its proximity to Lake Chelan (inhabited by a naturally reproducing
population of kokanee salmon). The only site, within the pool of candidate reference sites, remotely
similar to RC-3 was a site on lower Company Creek. This lower Company Creek site was initially
eliminated from the pool of reference sites because only five of the ten parameters were considered
comparable to the RC-3 site. However, because no other site was considered more comparable to RC-3 it
was subsequently decided that aquatic data would be collected at the lower Company Creek site and
analyzed for possible use.
The Company Creek station was situated immediately downstream of the Chelan County PUD hydroelectric
plant, and immediately upstream of the confluence of the Stehekin River, which is a spawning ground for
Kokanee salmon. The average total number of benthic macroinvertebrates collected in the eight replicate
samples was 1266 per square meter. The actual values in the replicate samples ranged from 670 per square
meter to 2950 per square meter. The total calculated number of fish caught at the Bridge Creek site was 571
per hectare, predominantly rainbow trout. The fish length ranged From approximately 10 to 250 millimeters.
Kokanee salmon were observed but not caught due to the sampling taking place during the spawning period.
Based on the comparison with only one reference station, RC-3 appears to have reduced benthic
macroinvertebrate densities. However, the Company Creek reference station was selected primarily to
reflect conditions of a stream that was or could be frequented by spawning kokanee. As such,
comparisons with the combined reference stations (non-Railroad Creek) provide a better indication of the
benthic macroinvertebrate community conditions expected in lower Railroad Creek. Comparing the
benthic macroinvertebrate results from RC-3 with the average densities of CC- I, BC- 1, and SFAC-I
indicates a reduction of approximately 34%. Water quality criteria were exceeded during April and May,
leaving relatively suitable conditions during the summer and fall months for colonization of benthic
macroinvertebrates.
Fish survey results at RC-3 indicated reduced trout density compared to the reference station (CC-I).
RC-3 densities were approximately 25% lower than those estimated for CC- 1. The habitat evaluation
score at RC-3 was 93, the second lowest score of all aquatic sampling stations, compared to a score of
108 for CC- 1 indicating possibly less desirable habitat than CC- 1. Surface water samples collected at RC-
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17693-005-OI9Uuly 28, 1999;10:24 AM;DRAFT FINAL RJ REPORT
DAMES & MOORE