The AZ Dept. of Environmental Quality (ADEQ) has designated the stretch of the Verde River from Sycamore Creek to the confluence with Oak Creek as an “Impaired Waterway.” This declaration was necessitated by high readings of E. coli on a few occasions and low dissolved oxygen (D.O.) on a few. The sources of these data were ADEQ’s own tests, some from USGS and several from the Sierra Club’s Water Sentinels.
An impaired waterway declaration doesn’t by itself affect recreational use – even swimming is OK, until the exceedances get too high. The Verde is not there yet, so we have time to work. When a stretch gets this designation, it triggers more resources from ADEQ (ultimately EPA) to find the cause of the impairment and create a TMDL (Total Manageable Daily Load) plan. That plan would spell out how the exceedances are addressed, and trigger funding for the mitigation or remediation of the problems.
But the number and spacing of the tests that showed exceedances is just too sparse, both in spatial and temporal resolution. We need many more tests and they need to be located where they will give the fastest and most accurate picture of what’s happening and why, if we are to address the problems quickly and accurately. When the data upon which the declaration was made are examined, including where it was gathered and when, it becomes clear that the tests are being done not where they are most needed, but more where they are most convenient. Only 4 test locations were used in those 20 miles of river to substantiate the declaration.
The Verde River Institute began to look for a way to increase the spatial and temporal resolution of water tests that would allow us to determine the problem areas more quickly and more economically. We contacted the Arizona Department of Water Resources (ADEQ) to see how we could help, and we proposed a new method of gathering samples using an Unmanned Aerial Vehicle (UAV, or drone). We have been working on the project since March of 2017, and we have arrived at a solution that will give valid results faster and less expensively than traditional sampling protocols. We can now sample water from the river in more than 30 different locations over the 33-mile stretch, in just 5-6 hours. We can also get to parts of the river that are otherwise difficult to access because of topography, accessibility, or ownership considerations, and can gather samples from Box Canyon and other areas that would previously take hours just to access, and can do it in 5 minutes!
We’ve developed a drone-borne sampling rig that collects two 100 ml samples on each flight – one is a sterile E. coli bottle, the other will be an identical, but non-sterile bottle, which will be used to test for parameters like dissolved oxygen (D.O.), pH, turbidity, and total dissolved solids (TDS), as well as temperature. A white paper about the sampling rig and how it’s used can be downloaded here. We have now tested this system and its progenitors approximately 650 times, taking the water temperature each time, and have begun testing for D.O., pH, turbidity, E. coli, and TDS. ADEQ is enthusiastic about the potential of this new method, since it allows sampling from so many places easily and economically.
We are in the process of developing a defensible, duplicable and valid testing protocol that includes the sample gathering and methodology for this stretch. You can download a Google Earth file of the full protocol site map is at: http://www.verderiverinstitute.org/WaterSampling/Water%20Sampling1.kmz, and a new, truncated site Google Earth file is at: http://www.verderiverinstitute.org/WaterSampling/Water Sampling - truncated1.kmz. These locations were chosen to allow testing above and below the most likely sources of contaminants, so we should have a very accurate idea where the E. coli is coming from and when.
Read about our progress on this project here.