Interpreting fecal coliform lab results can be like trying to solve a mystery without all the clues. We can only learn so much from lab data; after that, we need local watershed knowledge, eyes on the ground, a little technical advice, and many inquiring minds. Care to join us as we examine our June results? Read the summary below, and let us know what you think! Comment on this post, or use the ‘Contact Us’ page here. (See a link for the full report at the end of this page.)
Background: our Tenmile Creek watershed has been meeting both water quality standards for more than 18 months now. We want to continue this!
Problem: our results for the last 12 months provide a warning that this record could be at risk, due to persistent high results at two particular sample sites.
Questions: what could be causing this pattern, and what can we do about it?
Here are the trends as-of June. Site T1, where the creek flows into the river, is what ultimately determines whether the watershed is meeting the standards. The upstream sites tell us how various stretches of the creek are doing. All sites are meeting the standard for Geometric Mean (or ‘average’); a red line indicates the standard.
But we have problems with the 90th Percentile, below; this measure is sensitive to occasional spikes in results (90% of samples must be less than 200) and thus is harder to meet. You can see we have 4 sites failing this standard. The black ‘dot’ in each bar indicates direction of the 12-month trend: T2 & T3 are gradually getting better. DC1 & TM15 are getting worse, and if this trend continues, these high values could ‘drag’ the value of T1 back into the red (as the T1 dot indicates), and our watershed would again be failing this standard.
So where are these sample site locations? These two maps give you an idea. It is important to also note the next site upstream, because if the upstream lab results are lower (and they are), then we assume something entering the stream in between the two sites is likely causing the problem. First, DC1 is on Deer Creek, west of Northwest Drive; second, TM15 is on Tenmile Creek at Northwest. Each site has a mix of land use upstream, both dense residential with septic systems and larger Ag parcels; there is also greenbelt habitat for wildlife, including beavers.
So what could be causing this troublesome trend? One idea is that wildly variable weather recently, with alternating periods of wet & dry, create more chances for rainfall ‘flushes’ of the landscape. Another speculates about wildlife concentrations & migrations. There is always suspicion of failing septic systems, but there is no inspection data to support this. What do you think?
If you like, you can download the most recent (June) report here, but this and all other available prior reports are also catalogued on our Meeting Notes page here, on the same line for each appropriate month.
Whatcom County’s Pollution, Identification & Correction (PIC) program publishes this monthly report of fecal coliform lab results specific to Tenmile, and uses the standard 3-page, pdf-format template like other PIC focus-areas.