Subject: Sediment Cleanup, was: Lead shot
Date: Jul 21 09:07:00 1995
From: "Michelsen, Teresa" - TEMI461 at ecy.wa.gov




Jon asks:

>If lead (or heavy metals or whatever) are NOT relatively stable when
>buried by silts/clays/organic materials (relative to Exposed toxins) then
>we are all in jeopardy every time we get splashed with water waiting for
>a Ferry in Elliott Bay or Commencement Bay.... The fishes should be
>turning belly-up and the birds kicking their little feets into the air...

>I'd be interested in hearing from an Ecology Dept or EPA person
>in-the-know on the merits of disturbing or leaving alone buried lead.

Sorry it took so long to reply, my tardy e-mail system just delivered this
message to me today (3 days later).
I do sediment/aquatic cleanup for a living, so may have something to add to
this. A lot of the stability of metals in sediments depends on other
chemical factors that are present. The presence or absence of oxygen, the
degree of biological and human disturbance of the sediments, the pH,
salinity, and the presence of sulfides and other cations such as Fe that
serve as coprecipitators have a lot to do with what happens to metals when
they end up in sediments. It's fairly tricky and site-specific to predict
what will happen. Not only that, each metal behaves very differently,
confounding the efforts of national experts to develop sediment cleanup
criteria. For example, certain metals, like selenium, arsenic, mercury, and
organotins behave strangely in the aquatic environment because they have
metabolic pathways that convert them to organometallic compounds.

Acidic, well-oxygenated systems will tend to leach metals, such as the peat
bog under discussion. However, peat bogs are relatively unusual, and most
sediments in Puget Sound are not like that. Often because of organic
contamination sediments in our urban bays may be anaerobic. This
contributes to the stability of metals in the sediments. I should note that
one reason we don't like to pick up contaminated sediments, dewater them,
and place them in landfills, is that this tends to increase the pH and
degree of oxygenation, releasing metals from the sediments that would
otherwise have stayed put. Instead, we tend to cap them or contain them in
the aquatic environment, where they are relatively unavailable (assuming
they are capped or otherwise protected from bioturbation, aquatic
construction, and prop wash).

Funny you should mention Elliott and Commencement Bays. In fact, you are in
danger if you eat seafood from these areas, although the dangers are more
related to bioaccumulative contaminants like PCBs than to metals. Fish from
these areas contain high levels of these contaminants and we are concerned
with what it's doing to aquatic birds and their ability to reproduce. NOAA
recently published a report on salmon in these urban bays, showing damage to
enzymatic and immune systems from these chemicals (one can only wonder if
the birds are also affected, though not studied). There are fishing
adviseries in these bays, though widely ignored. One woman I know was
unable to nurse her child as a result of the PCBs that had accumulated in
her system from eating seafood caught one summer in Elliott Bay.

I am currently working on cleaning up the worst of these areas in Elliott
Bay, near Harbor Island, where bioaccumulative contaminants are the main
concern. Though fish and birds are not kicking their little feet up in the
air, exactly, I have seen streams where all the fish were one intermediate
gender (and unable to reproduce) due to PCBs. In both Elliott Bay and
Commencement Bay, it is certainly true that there are large areas where
there are few benthic organisms for fish and birds to eat, due to
contamination, and those that there are are likely to pass contaminants up
the food chain. The trick is, how do you clean up an entire contaminated
mouth of an estuary without doing an equivalent amount of physical damage to
the ecosystem.

Finally, on the influence of ferries and other large vessels, I have just
completed a major study of sediment transport in Elliott Bay, along the
Seattle waterfront. And it turns out that ship traffic is an important
mechanism for resuspension of contaminated sediments. Prop wash is one of
the biggest logistical problem when trying to design a cap or other in-water
containment facility in active working waterfronts. Commencement Bay will be
especially difficult, due to its heavy shipping traffic and relatively
shallow waterways. As noted above, this type of cleanup solution
(basically isolation and protection from disturbance) is generally
considered preferable to dredging it and taking the stuff upland, because of
the release of contaminants that occurs when you dredge, the sheer volume of
material that has to be handled, dewatered, trucked and disposed of (in the
case of Elliott Bay, 1-2 million cubic yards of sediment), and the
environmental changes that occur in landfills. So vessel traffic IS a major
problem, both in Elliott and Commencement Bays, and keeps the sediments
resuspended and exposed.

In wetlands, we try to consider the specific wildlife uses that are present
before designing a cleanup (or deciding that it's best to leave well enough
alone). For example, we recently completed a cleanup action plan for a
couple of old sewage treatment lagoons that were filled with PCB and
metals-laden sediment. However, they had also managed to turn themselves
into wetlands over the last 30 years, creating all kinds of logistical and
permitting difficulties for the cleanup. In designing a capping
alternative, we first conducted a habitat and wildlife inventory, and did a
food web analysis to determine which species were most at risk. Then we
considered such things as how deep a bird's beak might penetrate into the
sediments, how deep aquatic plants were rooted that might be pulled up by
ducks, and how deep a frog or turtle might burrow into the sediments. In
the end, we decided that it was best to pull all the PCBs out, since the
wetlands were in really poor shape and created an "attractive nuisance"
attracting wildlife to the contaminants. We then restored the wetlands to
more natural contours and replanted with a greater diversity of wetlands
plants. Other wetlands I've worked on we've decided it's best left alone,
particularly if the contamination is likely to degrade (e.g., petroleum
compounds) and the wetland is high quality.

Hope this wasn't too much of a digression!! I've gotten interested lately
in how important habitat considerations are when designing aquatic cleanups,
and hope to make use of your collective expertise more in the future.

Teresa Michelsen
temi461 at ecy.wa.gov