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/






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:

  1. Dunnivant, F. Enviroland 3.0 -- available at http://edusolns.com/enviroland/ -- produced in conjunction with Hartwick College, 1997.
  2.  http://www.coe.ttu.edu/ce/TRM/en09002.htm  -- last visited 12/1/00.
  3.  http://k12science.stevens-tech.edu/curriculum/waterproj/bod.html -- last visited 12/1/00.
  4. http://courses.ncsu.edu:8020/classes/wps460001/lec298/sld001.htm -- last visited 12/1/00.
  5. http://stream.rsl.psw.fs.fed.us:80/streamnt/jan98/jan98a4t.html -- last visited 12/1/00.