A Chemical Study of
Mill Creek: Biological Oxygen Demand, Septic Tanks, and Forest Fires.
By: Elliot
Anders
Summary
only, click to read the entire thesis http://www.edusolns.com/thesisWebSite/
Introduction:
The
summer of 2000 was said to be “undoubtedly one of the most challenging on
record. . . . As early as September, more than 6.5 million acres . . . ha[d]
burned” (Managing, 2000) in the United States, and “As early as October,
more than 6.8 million acres of public and private lands had burned” (Laverty
and Williams, 2000). The City of
Walla Walla was very lucky during this last fire season.
One of our most precious local resources, the watershed that supplies
Walla Walla its drinking water, managed to escape completely unscathed into the
wetter portion of the year.
Contamination,
fire, and mismanagement are a constant threat in watersheds.
The Walla Walla Municipal Watershed has been well protected, both from
contamination and fire. The
watershed itself is completely closed to entry without permit (USDA, 1918) and
well watched during the fire season by the Table Rock fire lookout.
The most threatening problem the Walla Walla watershed faces is not a
natural or accidental disaster, but a managerial miscalculation. The Walla Walla
Ranger District of the US Forest Service has been extinguishing all flame in the
watershed since the adoption of an ordinance in 1918.
Now, 83 years later, the management approach is up for re-evaluation, and
initial suggestions will require drastic management changes.
The changes in management could take many forms,
but at the forefront of suggestions at this time is a proposal written by a fire
expert of the Walla Walla District (USFS), Jim Beekman.
The main point of his proposal is to begin the incorporation of managed
fire in the Walla Walla watershed. The
Forest Service realizes that a “catastrophic fire may occur in the watershed
in the next few years if management to prevent such an event does not begin
soon. In addition, the watershed
had an extremely dry year in 2000, but through luck suffered no fire damage.
Because fire was absent in the past year, it is unlikely that Mill Creek, fed by
the watershed, saw much change in chemistry due to changes in the watershed
caused by fire, and therefore it was a good year to create a baseline that
attempts to show the water quality when unaffected by fire.
Another
factor is the increase in human population living close to the banks of Mill
Creek below the watershed boundary. The
population of the Kooskooskie area is visibly encroaching on the creek, leaving
little room for domestic liquid waste disposal between house and creek.
The research for this thesis provides a background data set that could
link the water quality of runoff from the Walla Walla Municipal Watershed with
the occurrence of forest fires, and in-stream nutrient levels with leaking
wastewater systems (cesspools, septic tanks, and drain fields).
The
Research:
A year-long study of the water chemistry of Mill
Creek was conducted to generate baseline data on the creek for future use. Study
parameters included: pH, turbidity, temperature, conductivity, dissolved oxygen,
limiting nutrient, and biological oxygen demand.
It was found that all measured parameters were within acceptable ranges
set out by the Watershed Professionals Network (1999) for fish habitat.
The pH hovered between 5.8 and 8.5 (6.5 – 8.5 acceptable), the
turbidity reached a high of just under 6 NTU (maximum 50 NTU acceptable), the
conductivity varied over a large range from around 50 to just over 200 µS/cm
(no accepted value given), dissolved oxygen was always over the minimum accepted
value of 8.0 mg/L and was as high as 9 to 14 mg/L.
The limiting nutrient was determined to be phosphorous, which is the
limiting nutrient in most freshwater around the world.
BOD varied greatly between sites, but was low at all sites, never
exceeding 2.5 mg/L over a BOD5 measurement and ranging down to 0.25
mg/L.
Five sites were chosen along Mill Creek to create
the baseline. The sites were spaced
from the base of the watershed to a site just below the Walla Walla wastewater
treatment plant. The five sites
were located: (1) just above the confluence of Mill Creek and Tiger Canyon
roughly 1/4 mile from the base of the watershed, (2) just above the bridge in
Kooskooskie roughly four miles downstream from the watershed, (3) on the
downstream side of the Five-Mile Road bridge roughly 13 miles downstream from
the watershed, (4) at the Yellowhawk Creek branch from Mill Creek at the Army
Corps office roughly 17 miles downstream from the watershed, and (5) on the
upstream side of the bridge just downstream from the Walla Walla wastewater
treatment plant roughly 21 miles downstream from the watershed (Figure 3). The
sites at Yellowhawk Creek (Army Corps) and at the Five-Mile Road bridge were
chosen because of USGS monitoring stations located at those sites that collect
daily stream flow data. This data
will become significant when future studies of the creek chemistry are done for
comparison of baseline data.
Figure
3 – Locations of the five sampling sites.
Literature Cited:
1.
Laverty, L. and Williams, J. Protecting People and Sustaining
Resources in Fire-Adapted Ecosystems, A Cohesive Strategy, 2000, available
online at http://www.fs.fed.us/pub/fam/Cohesive-Strategy-00oct13.pdf.
2.
Managing
the Impact of Wildfires on Communities and the Environment,
A Report to the President In Response to the Wildfires of 2000 September 8,
2000, available online at http://www.whitehouse.gov/CEQ/firereport.html.
3.
Watershed Professionals Network, 1999 Oregon Watershed Assessment
Manual, June 1999, Prepared for the Governor’s Watershed Endangerment
Board Salem, Oregon.
Websites and
useful computer programs: