As counterbalance to our last blog post showing our concerning results for November, the County has provided their November report (see here) that summarizes data for the metrics actually used for comparison to water quality standards – this is the ultimate measure for a long term look as well as trends. By this test, we are still meeting both standards! This is continuing good news, which also includes a cautionary reminder.

The Geometric Mean is the easier standard to meet as it is a long term average. As the chart makes clear, all of our sample stations not only meet the standard, but are improving – exactly what we want to see!
The 90th Percentile is the second, tougher standard because it counts peak results; so if a site frequently ‘spikes‘ high, it can easily exceed the standard. In this case, site T1 at the mouth shows the creek is [barely] meeting the standard (which is really what counts) but multiple individual sites are struggling – and these are the same ones we saw spiking-high during recent rain events, as shown in our special samples (see last blog post.) So the lesson is clear: even brief events that create exceedances can hurt our long term progress. Vigilance is always needed!