Ontario Ph.D. Student Researches the Impact of Urban Runoff on Lake Ontario with Help from GNSS

“Saline-ient” Findings Could Help Municipalities Better Manage Road-Salt Usage

Along a 100-km (about 60-mile) stretch of Canadian shoreline between Ajax and Burlington, Ontario, a salty research project is underway.

Western University Ph.D. Student Junwei Zhu is one year into a several-year project with the school’s Research for Subsurface Transport and Remediation (RESTORE) group. His focus? To understand salt loading dynamics — in other words, how salts accumulate, move, and change concentration over time — in the Lake Ontario Basin due to direct groundwater discharge from urban runoff.

Many urban activities, especially winter road salting, generate pollutants that are picked up by rainwater or snowmelt. This is called urban runoff, and it can impact the level of pollution in nearby lakes. Road salt enters freshwater systems like Lake Ontario through multiple interconnected pathways, including surface runoff and stormwater drainage.

Existing studies on groundwater salinization have concentrated primarily on groundwater discharge into streams and tributaries (indirect pathways to the Great Lakes Basin). But significant research gaps remain regarding the direct discharge of groundwater into the Great Lakes Basin along the shorelines. This is what Zhu is studying.

“Not many people look into direct discharge,” Zhu said. “But if you count only indirect discharge and ignore the groundwater, you have a missing puzzle piece.”

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A Clever Approach to Studying Groundwater

To measure the salinity of groundwater where it meets Lake Ontario, Zhu set his project at several sites along the lake’s northwest shoreline, outside Toronto. So far, he has surveyed 12 complete sites.

At each site, Zhu performs two types of field work: Electromagnetic Imaging (EMI) measurements to determine Electrical Conductivity (EC) variation, and groundwater sampling to verify if the EM readings come from salinity rather than other causes.

First, Zhu walks the shoreline with a variety of geophysical instruments to measure changes in the groundwater. EMI instruments send waves through the ground and measure EC readings. Salinity is one of several factors that can cause changes in the EM readings, allowing Zhu to potentially identify salinity changes in the groundwater.

Western University Ph.D. student Junwei Zhu gets help from a colleague while setting up the CMD Explorer conductivity meter.

The primary instrument he uses for this is the CMD Explorer conductivity meter from GF Instruments. This four-meter orange rod has a transmitter at one end and a receiver at the other. It charts variations in groundwater conductivity at six depth levels — without contacting the soil. As Zhu walks the shoreline with the rod, its controller logs the conductivity readings at a rate of twice per second.

Zhu walks the Lake Ontario shoreline while operating a CMD Explorer electromagnetic (EM) instrument. The EM conductivity meter takes readings at six different depths, without having to contact the ground.

But as Zhu says, “You need to geo-reference the graph, or it means nothing.”

The CMD Explorer rod included a built-in GPS receiver, but its accuracy was only five meters. Zhu needed submeter accuracy so he could geo-reference the EM spikes to specific places along the path he walked.

“That’s how we know the specific locations of the areas of interest during our surveys,” Zhu said.

A Finer-Grain GPS

Zhu paired the CMD Explorer to an Arrow 100® GNSS receiver so it could geo-reference the EM readings with submeter accuracy along the path he walked.

After researching a variety of global navigation satellite system (GNSS) receivers, Zhu tried the Arrow 100® GNSS receiver from Eos Positioning Systems® (Eos).

“CDM Explorer’s built-in GPS was not accurate enough for the project. But with the Arrow 100, the line was representative of my location.”

— Junwei Zhu, Ph.D. Student, Western University

The Arrow 100 is a submeter GNSS receiver capable of keeping up with the controller’s half-second output rate, and it also fits Zhu’s research budget. When he tested it in the field, it met his accuracy needs.

“CDM Explorer’s built-in GPS was not accurate enough for the project,” Zhu said. “But with the Arrow 100, the line was representative of my location.”

It didn’t hurt that the Arrow 100 was also lightweight. “At the end of the day, my whole body is sore from all the geophysical equipment, which is huge and heavy,” he said. “The small size of the GNSS receiver helped.”

Zhu connected the Arrow 100 to the CMD Explorer’s controller via Bluetooth, allowing the controller to collect both location data and EM logs.

Back in the office, Zhu exported the data from CMD Explorer to Excel, which he then uploaded to ArcGIS® for the second phase of his field work — revisiting sites where the EM readings had spiked.

“We can see a trend of how the electromagnetic field changes over the path we walked on the shoreline, so I can find any areas of interest and see what’s really going on with the readings,” he said.

The above charts are based on the EM readings from the two sites Zhu has so far surveyed. The lines represent electroconductivity readings as Zhu walked the beach, in meters traveled. Each line color represents a different depth at which the CMD Explorer rod measured EM readings. Spikes represent areas of high conductivity, indicating these locations for further analysis.

“Peppering” the Path with Drive Points

A number of factors, including soil moisture and buried metal, may cause an EM reading spike. To verify whether his EM spikes stemmed from salinity or other causes, Zhu navigated back to points of interest to collect groundwater samples.

“We want to make sure what we’re seeing in the EM charts is driven by chloride concentration variation in groundwater,” Zhu said.

In ArcGIS, Zhu identified points of interest where EM readings had spiked. These sites he would later revisit to take water samples, helping to confirm if EM spikes were caused by salinity changes. The colors (blue, maroon) represent to which survey site the point of interest belonged.

At points of interest, Zhu took drive points. A drive point is a spot where a researcher uses a long, hollow shaft to puncture the ground and pump out a water sample. The water is collected and sent to a lab for analysis. At the two sites Zhu has surveyed so far, he took dozens of water samples. Results from the lab will help validate if the EM spikes at these locations were caused by high salinity.

Western University undergraduate student Mario Sanabria, who helped Zhu during the 2025 summer, uses a specialized instrument to pump out groundwater samples at points of interest along his survey sites. These samples, once analyzed in a lab, will help Zhu determine whether the EM spikes he recorded stemmed from high salinity.

Zhu used ArcGIS Field Maps on an iPhone to navigate back to points of interest. Within Field Maps, he could see both the path he’d walked based on the Arrow 100 coordinates and the EM spikes along these paths.

“We pick a point right on that line and then compare the geophysical data with the drive points,” Zhu said.

This blue line represents a complete surveyed path at one of Zhu’s survey sites.

Zhu navigated back to points of interest by using ArcGIS Field Maps, where he had loaded his shoreline paths. To navigate to precise locations of EM spikes with high accuracy, he paired his iPhone® with a Skadi 100 GNSS receiver.

For accurate navigation to these locations, Zhu used a Skadi 100™ submeter GNSS receiver, also from Eos. The Skadi 100 functions similarly to the Arrow 100, but its handheld formfactor made it easier to carry during navigation to drive points, when Zhu didn’t have to carry the heavy conductivity meter.

Zhu and Sanabria used a handheld Skadi 100 to navigate back to points of interest, where he collected groundwater samples using a specialized instrument.

A Pinch of Insight from a Salty Project

In ArcGIS, Zhu then color-codes his drive points based on high or low salinity findings. While he still relies on CMD Explorer software to derive insights into the groundwater constitution, ArcGIS is his primary software for spatially presenting his findings.

Zhu’s project could take up to two more years to complete, and he hopes to publish one to two papers about his findings. Ultimately, he hopes the results will provide municipalities with insights they could use to better manage road-salt usage to hopefully reduce the pollution of Lake Ontario.

While Zhu’s project focuses on Lake Ontario, his findings will be generalized, so other municipalities may benefit.