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Samish Basin Water Quality Monitoring

Samish basin water quality monitoring grew out of the Skagit County Water Quality Monitoring Program (SCMP), which is a larger effort aimed at determining status and trends of water quality at 40 sites throughout the County.

Sampling from SCMP, along with Ecology and local volunteers, shows that the Samish Basin has a continual problem with high fecal coliform counts at many sampling stations. High fecal coliform counts have led to repeated closures of the commercial and recreational shellfish beds in Samish Bay. Previous work by Ecology and the County has shown that while fecal coliform pollution is widespread in the basin, the Samish River is the biggest source of bacteria to the bay.

riverAs a response to this problem, Skagit County has embarked on a Pollution Identification and Correction (PIC) program designed to determine pollution sources in the basin. One of the first steps in this process is to increase both sampling frequency and number of sample locations. The SCMP had 11 sampling sites in the Samish Basin; with the PIC program, the County has increased this number to 20 sites, with the option of adding more sites as needed. In addition to the regular biweekly sampling, the County will attempt to sample all rain events and sample selected locations on a weekly basis. By increasing the number of sites and the frequency of sampling, the County will be able to determine more precisely the pollution source locations that are adding large amounts of fecal coliform bacteria to the river. Skagit County can then target and correct polluted stretches of the river through education, outreach activities, and voluntary property inspections.

Skagit County applied, and was selected, for a grant from EPA to support the PIC program in the Samish. Skagit County is currently in the process of negotiating a final agreement for this funding. In the meantime, support for the Samish PIC program comes from the County's Clean Water Fund.

Fecal Coliform Basics
Fecal coliform bacteria are bacteria from the intestinal tracts of warm-blooded animals, which when shed into the environment through feces, can be associated with certain diseases in humans. Fecal coliform are measured in "colony-forming units" per 100 mL of sample, commonly abbreviated as "cfu". The higher the number, the more bacteria and the greater the health threat to in-stream users like swimmers and fishermen, as well as consumers of raw shellfish from the bay.

The state water quality standard for most freshwaters, including the Samish River and its tributaries, is a geometric mean of no greater than 100 cfu, with no more than 10% of the samples exceeding 200 cfu. The standards are designed to protect human health from bacterial infection during contact recreation (swimming, boating, and fishing) and downstream beneficial uses such as shellfish culture.

A geometric mean is an alternative method of calculating an average that is less influenced over time by the occasional very high sample. It is used to prevent occasional high samples from causing a stream to be out of compliance with the state standards if most other samples are within the standard.

Calculating the Geometric Mean

The geometric mean is calculated by taking the "nth" root of the product of all the samples. For example, for three samples reading 3 cfu, 4, cfu, and 10 cfu, the product is 3 x 4 x 10 = 120. The geometric mean is the cube (3rd) root of that product, which, in this case, is 4.9 cfu. For comparison, the more common arithmetic mean would be 17/3 = 5.7. If the three fecal coliform counts were 3 cfu, 4 cfu, and 1000 cfu, the geometric mean would be 23 compared to an arithmetic mean of 336.

For more information contact Kevin Jackman, 360-416-1443,

Water Quality Reports







Storm Sampling