Evaluating Water Sources
Newaygo Conservation District Produce Safety Technician
The FSMA Subpart E Agricultural Water requirements are two years away – but it’s not too early to get a handle on your water system and start evaluating irrigation wells and surface water sources.
Now is a good time to find a microbiological testing lab that is capable of doing one of the approved test methods for the Produce Safety Rule. For a lot of growers, their local District Health Department lab that they use for drinking water tests does not provide a test equivalent to the approved EPA Method 1603, making it important to find a private lab to partner with. A key consideration to ask a water testing lab is whether they can provide a numeric sample for a Microbial Water Quality Profile, which is used to average your test samples to calculate a Generic Mean (GM) and Statistical Threshold Value (STV).
In addition to knowing where to take these tests, it’s important to have a farm owner or employee trained on taking an aseptic sample. Conservation District Produce Safety Technicians are available to take the first couple of samples with produce growers and show farm operators the sampling techniques they’ve been trained on. Technicians are also able to work with the farm to develop an agricultural water system inspection plan, which can determine whether irrigation well backflow systems and any air gaps are working properly and if they’re using surface water sources, when those waters are likely to see an E. coli spike.
I had the opportunity to help sample for a watershed-wide E. Coli study in Southwest Michigan with EGLE stream biologists in 2018 and 2019; at the end of sampling, it was observed that E. coli levels were highest 1-2 days following rainfall events, as well as when streams and rivers are at their lowest from late-July to mid-September. For sampling locations within streams, areas where filamentous algae grew harbored higher E. coli loads than the centers of ponds or streams or areas with fast moving water.
From preliminary results of the [an EGLE E. coli in Michigan watersheds] study, most water bodies in Michigan within areas surrounded by septic tank-using households or heavy influence of animal agriculture are impacted by E. coli runoff and will likely have a seasonally-influenced E. coli increase. Because these spikes occur during the growing season, in the next two to four years leading up to the reinstatement of Supart F -depending on farm’s coverage implementation year- it will be extremely important for growers using surface water sources to actively seek out high E. coli samples in their water testing program. Using this time and location-based information, they can better understand the conditions that cause high test values. This will help growers avoid any high outliers, with the goal being the Generic Mean and Statistical Threshold Value calculations being a good estimate of the typical irrigation event on the farm, and not a result of low-outlier or high-outlier influenced sample collection.
Next in this water quality series, we’ll discuss checking backflow prevention systems spring-pressured valves for corrosion and inoperability and water system decontamination and surface water treatment.