Alum and stormwater treatment
joew
Tue, 28 Jan 1997 10:06:26 -0800
Water quality is vital all over the world and the more we can network the
better off we all will be.
I have a question that you may be able give some input to
concerning Alum as a surface / storm water treatment process. In Florida
the St. John's River Water Management District has approved Alum
treatment for stormwater ponds, provided the water quality is poor to bad
based upon the tropic state index (TSI) and where an urban retrofit is
the needed for stormwater treatment. It is being implemented in several
lakes and some stormwater pond treatment systems as a single treatment.
I know that Alum removes sediment including metals and nutrients attached
to the sediment and reduces BOD, Turbidity, & coliforms. However, given
an urban retro-fit area space is limited thereby removing the settling
tank yielding Alum accumulation discharge of the system. Also with the
alum in the system, aluminum is released into the water (uasually not in
great quantities). If the pH is not maintained in the range of 6 - 7 the
Alum becomes increasingly soluble and released. The natural alkalinity
of the system can only do so much then the procedure is to add a NaOH
buffer.
My question is that assuming the Alum is injected at say 15 mg/L
and NaOH at 10 mg/L what other impacts to the system can I expect in
terms of dissolved oxygen, bottom vegitation, etc. Alum is great in
surface water treatment of DRINKING Water; How is the natural surface
water system affected with reqards to fish, swimming, health of the
system. Once you start Alum treatment are you forever forced down that
treatment path. Is there a water quality parameter that Alum removes,
Too Well, that would have an adverse affect on the natural system?
I would be eager to hear what you have to say?
Thanks
--
-----------------------------------------------------
Joe Walter, BSEEnv EIT
"Water water everywhere..."
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NW Floods- Worst Yet to Come
dosewallip@aol.com (Dosewallip)
29 Jan 1997 06:42:46 GMT
Here Come The Floods---What You Need To Know
This isn't the snow and rain we are used to. Its snow and rain reminiscent
of our past, typical of the eras in our region when we expected snow each
year rather were surprised by it. Indeed the storms of last November and
the holidays have left lingering memories and damage as well as several
questions: is there something peculiar with the weather? What can we do to
prevent damage when these storms return? You could be putting your answers
to the test this winter.
According to the National Weather Service, the Cascades have 110-175%
their
normal snow pack for this date (January 28). However, the average snow
water
content ranges from a whopping 150-200% normal. That's 150-200% of water
available for run-off for the end of January. This snow is a wish come
true
for irrigators, skiers, boaters and municipal water suppliers. But, it's a
ticking time bomb for surface water managers and floodplain residents.
Right
now are one "Pineapple Express" away from "The Big One".
The Bad News
If you think it's been particularly wet here in recent years, call
yourself
observant. Indeed, some climatologists feel we are moving into a new
phase
of our climate cycle, into the wet side, although its too early to tell.
Annual precipitation totals vary greatly from year to year, but tends to
vary cyclically from wet periods to dry period over the course of decades.
What is considered "normal" is usually a 30 year average, so what's normal
can fluctuate over the years. Not much of a standard.
Still, scientists can calculate fairly accurately what the climate was
like
here over the last several hundred thousand years from clues like pollen,
tree rings and even lake sediments. Since about the early 1970's until
1994,
the Pacific Northwest has been in a drier than normal phase. Our climate
cycles vary from about 15 to 25 years, so we may be due for a change. This
is good and bad news, as is always the case with weather. The bad news
is
you can count on unprecedented flooding events.
There are many reasons why we can expect serious flooding. Increased
precipitation isn't necessarily one of them. A deep snow pack that melts
slowly can distribute runoff all summer and never reach flood stage. But
the
potential for a devastating flood remains higher with a large snow pack
than
without it, especially if the Pineapple Express rolls into town.
Them Darn Dams Did It
You may have noticed that there are frequent flood watches and warnings on
certain Washington rivers. Generally, the first river to receive such a
notice is the Skokomish River. Many rivers affected by dams such as the
Skokomish River are shallower or have aggraded with sediment over time far
downstream from a dam. Its ironic that a dammed river could suffer from so
many flood-related problems. But consider that sediment is trapped
downstream from the dam because restricted flows (the North Fork of the
Skokomish is often completely diverted) have prevented the river from do
its
job---flushing sediment downstream. This sediment raises the river bed
along
reaches and exacerbates flooding. Now smaller peak flows and storms cause
more damage than before because the channel can handle less water before
cresting. So if we increase precipitation and runoff in the equation, one
of two things will happen: more regular flooding and occasional
catastrophic
flooding.
Other engineered features such as dikes and levees which constrict flows
and
generate water velocity, often make floods more destructive downstream.
Engineered solutions can solve site-specific problems, but always (yes,
that's a defensible "always") create new ones downstream. At the reservoir
management scale, solutions to these problems are different per year and
per
flood event. If the magnitudes of flood events increase in the coming
years,
look for more frequent dam failures.
Vegetation is one of our greatest allies protecting us from the ravages of
flooding. Trees and plants literally pipe moisture away from the earth
and
liberate it as water vapor through evapotranspiration. They prevent
erosion
by binding hillslopes and river banks with their roots. Mature forests
moderate temperature, and prevent rapid melting of snow. Unfortunately,
many
of our mature forests are gone and a huge percentage of land is incapable
of
providing these beneficial effects. Our current vegetative-cover has yet
to
experience the "wet years" of our cycle. Many harvested and re-planted
clear-cuts are less than 30 years old, including clear-cuts and "reprods"
from the era of our largest timber harvests --- the 1980's. A potential
increase in peak run-off, landslides, siltation of salmon streams, blown
out
culverts and road washouts, and potentially catastrophic rain-on-snow
events
are likely in our future.
Much of the ground in Western Washington has been effectively saturated
since November of '95, a because of it we are very susceptible to mass
wasting such as mudflows and landslides. Freezing and thawing has also
been
a conspirator. Freezing causes water-filled pores in sediments to expand
and
stay expanded after thawing. When water fills these expanded pores, the
water adds mass, and the soil looses cohesion and strength. Things can and
do get moving as mudslides or debris flows, which is different from a
landslide. Seattle and Puget Sound is especially prone to landslides .
Bluffs capped by till, a mix of rock to clay sized particles left by the
glaciers and is slow to absorb water, but retains it well. Beneath the
tills
are sands left by glacier meltwaters which readily store and transmit
water
to a bottom layer of clay. When the weight of saturated materials above it
is too great, the slope fails along the "greasy" clay surface causing a
landslide. Cracks in the clay bed from freezing and thawing can weaken the
clay bed and initiate a slide. Since these slopes are everywhere from the
foothills to tidewater, preventative measures need to be taken to minimize
the potential for damage. A long sustained drying period is needed of to
reverse this vulnerable trend we are current in.
In our foothills and urban areas we need to redouble our efforts to
replant
clear-cuts, decommission logging roads, fix culverts and restore more
streams and hydrologically-significant wetlands. Wetlands are an often
ignored asset to flood protection which distribute water and dissipate
flood
energy. The filling of wetlands re-distributes flood waters often to areas
where flooding usually doesn't occur. Expect major flooding in both urban
and rural areas where the connectivity between wetlands has been lost.
Expect Urban Flooding, Plan For It
Rural areas below heavily deforested watersheds will be hit hard, but
urban
areas maybe hit the hardest. Like our current forest cover, our level of
urban development and impermeable surface area has yet to experience the
wrath of wet years. Urbanization often begets storm water flooding.
People
need to be prepared. The best advice is be mindful of where you live.
Live
on a hill, ridge, or even a slight rise where there is little or nothing
draining towards you. Avoid living above, below or near steep banks,
particularly those underlined by clay. Stay out of ravines, narrow
valleys,
large basins or the 100 year floodplain when building or buying a house.
Whether you live in the county or the city, learn about your drainage
basin,
and where water flows immediately above and below the hillside of your
house. During a big event, check your storm drains around your house,
clear
them if it's safe to do so.
Uncle Sam Insurance Man
Other things you can do for yourself whether in the city or the country is
consider purchasing federal flood insurance. A county needs a federally
approved flood management plan to be eligible for flood insurance. If you
do not have flood insurance, and suffer flood damage, you will not be
eligible for federal assistance unless the President declares your region
a
disaster area. Without a declaration and or no insurance, you could lose
everything. Even if a disaster is declared, grants are usually less than
$2,500.
A future sustained wet period here in Washington is a natural and
inevitable
expectation rather than an anomaly, so we need to plan for it. Even if we
consider Greenhouse models, the Pacific Northwest is still headed for
wilder, wetter winters. Ultimately, it will get wetter whether we like it
or
not. Think of it, there ought to be some serious whitewater in the coming
years. Hopefully, the waters will stay in our rivers and out of our living
rooms.
