20030179 Ver 6_Staff Comments_20071102

comments on Dillsboro Dam biological monitoring
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Subject: comments on Dillsboro Dam biological monitoring
From: Larry Eaton <[e-mail]>
Date: Fri, 02 Nov 2007 13:24:45 -0400
To: John Dorney <[e-mail]>
Pre removal monitoring
/ Both benthos and fish are proposed for biennial monitoring before dam removal. It
J would be nice if a minimum of two collections could be taken before removal.
Before collections in the pool behind the dam would be problematic, since both
methods require the area be wadable and the bug sampling requires that there be flow
for the kick net to operate correctly. Even downstream, the DWQ fish method is
designed for low order (lst-3rd) streams and "the NCIBI is applicable only to streams
that are wadeable from one shoreline across to the other and for a distance of 600
feet." I don't think that is the case in many places in the Tuckaseegee R. I
believe that USGS has developed some fish sampling methods for deeper waters and
perhaps these methods need to be investigated.
Full Scale benthic macroinvertebrate collections (not EPT) should be used for
monitoring.
Post removal monitoring
I couldn't find specifically how long post removal monitoring would continue.
Biannual sampling would be fine if monitoring continued long enough to get at least 3
V samples in. Once again, benthic monitoring should be Full Scale (not EPT) and fish
sampling should either be in places where 600 feet of stream are wadable (bank to
bank - approx 4 1/2 feet max depth) or another fish sampling method should be
employed.
1 of 1 11 /7/2007 1:42 PM

John-
Here are the combined comments from Steve, Eric, and I after quick reviews of the Dillsboro
Dam removal monitoring plan.
n
Stored sediment characterization
A primary concern is that the sediment currently stored behind the dam has not been properly
characterized, in terms of particle size or chemistry. In reviewing the comments from the
geologists at WCU, we agree that the sampling that has been done already for characterization of
particle size was insufficient and not truly representative of the majority of the sediment deposit:
only surficial sediments were sampled, and the sediment deposits are described as being 5-11
feet in depth. Multiple deep cores should be taken and the analysis repeated, and DWQ should
specify appropriate criteria for determination of whether the sediments must be removed or can
be flushed; the process used to get rid of the sediment must prevent habitat smothering, increases
in riffle embeddedness, etc. downstream.
The other concern over the stored sediment is that no analyses for chemical contaminants have
been done. Though there may be only an estimated 1-2 years' worth of sediment stored behind
the dam, it has likely been deposited throughout the life of the dam. If there is a significant
amount of organic material in the sediments, these are more likely to have higher concentrations
of metals, organics (pesticides, herbicides, PCBs, etc.), and other contaminants adsorbed to them,
which may be a water quality issue if allowed to flush downstream. We could propose three
options:

v

~4~

Before leaving the subject of the sediment and its downstream effects, some sort of monitoring
should be performed to ensure that habitat smothering, riffle embeddedness, pool infill, etc. is
not occurring downstream in response to removal activities, including flushing of the sediment.
The appendices were not included in the copy of the document that we removed, so someone
should review the proposed habitat assessment method to ensure that these metrics are included.
Pebble counts are also recommended (pre-, during, and post-removal), and should be performed
bi-annually along with the biological community sampling.
S
~ ~" ~
Chemical/physical monitoring
As far as chemistry sampling is concerned, the parametric coverage seems adequate (dissolved
oxygen, temperature, pH, specific conductance, turbidity, and TSS). However, the number of
sampling events is wholly inadequate. Quarterly samples are nearly useless. A bare minimum
of monthly samples/measurements should be performed during the pre-removal phase, and taken
under a range of flow conditions to appropriately characterize concentrations under varying flow
regimes. Current flow status at the time of sampling should be recorded.
~;
Duke should perform these analyses to show that the risk to aquatic and human health
from re-suspending/re-distributing these types of toxic compounds in the water
column is minimal if allowed to flush downstream;
They should be able to give a compelling case as to why they believe that it is
unlikely that these types of compounds, are stored in these sediments (e.g., inventory
and characterization of all current and inactive discharges, land use, hazardous
material spills, etc. since the dam was built within the entire upstream watershed).
Or: They should agree to dredge/remove the sediments instead of flushing them.
During dredging and removal of the sediment, an even higher frequency may be warranted, and
the use of datasondes/dataloggers above and below the site (in addition to continued monthly

sampling) should be encouraged to record DO, temperature, pH, specific conductance, and
turbidity at regular intervals throughout the day. The data from the datasondes should be
reviewed at least weekly to ensure that the dredging and removal activities are not causing
prolonged exceedences of the instream WQ standard for turbidity downstream. If this is
occurring (without corresponding exceedences at the upstream site) dredging/removal activities
should be altered, or additional instream sediment trapping structures should be installed to
address this before work continues. If DWQ should receive copies of these data, specify
contacts for RO and CO.
Post-removal, chemistry sampling should continue monthly for at least the first 1-2 years. It's
expected that this site will continue changing fairly rapidly during this time period. If
measurements start to stabilize (i.e., less variability is documented), perhaps samples could be
taken less frequently, but that is something that should be assessed each year post-removal.
As the WCU geologists specified, flow will be needed for determination of total sediment
\ ~j loading. Though a USGS gage is shown just below the dam on the topo, in checking the USGS
~~,N~ website it appears that the gage is no longer active. Duke should be responsible for providing
discharge for the monthly samples.
Bedload sampling is not specified during the pre-removal period. This should be added in order
to provide a baseline.
It is unclear why monitoring for nickel is required just post-removal. I'm curious as to why only
that metal is of concern, why only post-removal,. and what will the results be compared to. The
rationale for this should be provided so we can determine if it would be appropriate to add V„~1
additional metals and/or include this sampling in the earlier phases of the project.
Benthos~and rsh monitoring
I know that Larry's already provided comments on this, so likely everything I'm saying has
already been said, so guess you just get to hear it again:
• DWQ methods are only applicable to wadeable streams. It appears that BAU has a
normal basinwide site on the Tuckasegee below the dam, so that area should be
wadeable. I don't know the site, granted, but I strongly doubt that the impounded area is
wadeable and will have a very different,ty~pe of community than downstream of the dam,
but believe they have proposed sampl'mg~"there.
• It's not clear how the fish and benthos data will be used. They refer to the IBI and BI and
bioclassifications, but it seems a more valuable tool here would be to see if over time the
upstream and downstream communities become more similar, i.e., the percent abundant
taxa in common increases. I would think that there would be obvious differences now
(especially for fish). (Maybe this is already stipulated, I don't know) If they will be
using the IBI, BI, and/or bioclassifications, how will they be used?
• Full scale collections should be performed at all locations (not EPT) to assess as many
habitats as possible.
• T-7 is specified as a control site. It's not clear where it is located, so can't determine
whether it is an appropriate control site or not.
.;;~:
:;. a . .