Testing the water in Lodi — literally Storm Drain Detectives add E. coli tests to their water monitoring duties
Working side by side, Lodi High School science teachers Jud Atwater and Melissa Turner carefully insert Petri dishes under their respective microscopes. With gloved hands, they slowly move the dishes, freshly out of an incubator, to look for the distinctive purple spot that would indicate the presence of E. coli.
The samples were collected from the same site at Lodi Lake that has been nicknamed the “Armpit” — due to its position at the bend of the lake, and also because it “sweats” neighborhood nuisance water, or “urban drool,” into the lake.
“I see one,” Turner said, referring to a purple spot.
Atwater also sees one on his dish.
It’s the third day of a multi-day process of testing Lodi Lake and
Mokelumne River water for E. coli — the newest addition to the Storm Drain Detectives’ testing protocol — and it’s too soon yet to say what the final results will be.
E. coli requires a 48-hour incubation period. Once fully incubated, its presence will be marked by purple or dark blue colonies, with or without a pink or teal halo. Other bacteria can also be present, and show up as pink or teal colonies; these are are not counted.
E. coli is a specific subgroup of fecal coliform bacteria, which is found in the environment and in the gut of all warm-blooded animals. While most E. coli bacteria are relatively harmless, several strains can cause severe illness in humans.
The testing process started on Tuesday, with the Storm Drain Detectives — now reduced to just the teachers due to the ongoing COVID-19 pandemic — joining
lab technician Justin Santiago from the White Slough Water Pollution Control Facility to collect water samples at the lake. Santiago oversees the process and guides the teachers on proper procedure.
Santiago provided Kathy Grant, the city’s watershed program coordinator, and the teachers and students with a Standard Operating Procedure, an in-depth guide on how to sample, plate and report test results at a college and professional level.
“I feel like the SOP will give the kids a taste for what it is like to work in laboratory,” Santiago said.
It’s a rigorous, detailed procedure with quality assurance protocols that must be followed to avoid introducing contaminants. Samples must also be stored at a proper temperature after collection and be handled in a precise manner to be ready for plating in the classroom.
Once plated, the samples have to be incubated at a certain temperature to ensure proper growth of the E. coli. Control samples, or blank samples, also have to be gathered. They are used to identify errors in sample collection and analysis.
The work of the Storm Drain Detectives — which also includes monitoring precipitation, temperature, dissolved oxygen, turbidity, pH levels, electrical conductivity and nitrates in local waterways — now includes an opportunity for students to learn hands-on how to handle and measure bacteria such as E. coli.
Santiago said Grant approached him and asked if there is a way to measure coliform or E. coli in the river and lake water.
The White Slough staff uses Environmental Laboratory Accreditation Program-certified methods and equipment to conduct testing, and is overseen by the Environmental Protection Agency. But there is a more affordable testing method for E. coli that can be used by the local high schoolers under the guidance of Santiago.
“We found out that using this pour-plate method is a really cheap way and really a great way of engaging students. And I believe this so far is going great,” Santiago said. “They are able to count out the colonies and see how microbiology is all around us, especially with COVID-19 going on. This shows that these little particles can actually grow, and potentially harm you, if not in check.”
Last month, Santiago, using EPA and ELAP certified methods, conducted a side-by-side comparison with Atwater’s samples and found that they were pretty close.
“We sampled 270 (colony forming units) and his was 310,” Grant said. “He was comfortable that sample was within reason.”
Grant described the collection process used by Storm Drain Detectives, as taught to them by Santiago and outlined in the SOP.
It starts at the gathering site, where samples are gathered at mid-depth in mid-stream — but not before double rinsing the equipment prior to use.
The next step is to pour the sample into the bottle, being careful not to touch anything, Grant said.
“Then you cap it and close it, while leaving a bit of head room. Then it’s time to identify the sample. You write down the time, who you are, the date and site. After that it gets put on ice, because it has to stay chilled until you take it back to lab,” she explained. Before being plated, samples can be stored for 24 hours at a temperature of 6 degrees Celsius.
Keeping track of the chain of custody — who collected it, who transported it, who got it — is also important, Grant noted.
After 24 hours, it’s time for the next step: plating. The samples have to be removed from the freezer two to three hours before plating to ensure they have reached room temperature.
Turner explained the process. They use the Method Coliscan Easy Gel to test for E. coli and general coliform bacteria.
“We recorded our date, the site, our initials and the time the plate is going to be made. And to keep a sterile technique going, we want to make sure that our caps stay pointed down, and that we only expose the liquid for a very short period of time. And that’s using a sterile pipette and that we always keep that tip very sterile,” Turner said.
They then add the sample to the pectin-gel mix in the bottle before screwing the cap back on and inverting it slowly to mix it. After that, they pour it into the Petri dish, again keeping the cap facing down.
Then they do a short figure 8 pattern to mix it into the Petri dish.
“And then these have to sit until they solidify before we move them and put them in the incubator, approximately 30 minutes. But I usually put them in after an hour; that way they are good and solidified,” Turner said.
After the Petri dishes have solidified and sealed with parafilm, they are placed right-side up in the incubator, where a steady incubation temperature of 35 degrees Celsius is maintained.
After the first count at 24 hours, they are returned to the incubator, and after 48 hours a complete count can be conducted.
“Then you count your colonies,” Grant said, noting that between 60 to 200 colonies in a sample is what a river would have.
In previous tests, E. coli has been found at all the sites tested at Lodi Lake and in the Mokelumne River, Grant said, but the numbers fluctuate. The numbers tend to be higher where humans, animals and geese are present. But it can also enter the water through the city’s storm drains.
“The reason we’re doing this is that when it rains, when the streets drain storm water into the river, (the numbers go) way high, and within 24 to 48 hours, it’s gone,” she said.
Turner said learning about the E. coli presence in the water can provide a good learning opportunity to study the environment.
Grant is excited about the new way students can learn about bacteria through E. coli testing.
“This gives kids an opportunity to learn about bacteria. How does E. coli get into our watershed?” she said.
The testing will help students think locally about clean water, and it will teach them how to conduct lab work, she added.
“And maybe even they start to think about who is doing all this work every day. You take a drink out of the faucet — how did it get there? There is a lot of people who work on it. We salute firefighters and police, but I don’t think enough people salute all the inspectors, mechanics, the slew of people who make sure you have clean water. It’s not magic,” Grant said.