PENDLETON — The number of documented COVID-19 cases in the Pendleton area began to climb in late June, but the city’s sewers anticipated a surge sooner than that.

The city of Pendleton has contracted with Biobot Analytics to test its wastewater for the coronavirus since early March, with city officials looking at it as a novel way to study the virus’ spread in the city.

Staff members began collecting 24-hour composite samples at the city’s wastewater treatment plant before sending the material to Biobot’s Massachusetts facility for analysis.

But besides a brief blip on April 5, the tests didn’t reveal any evidence of COVID-19 in human waste. The city was on the verge of scaling back its sewer testing from once per week to twice per month as the cost of Biobot’s tests began to rise when the samples started returning traces of the virus again.

In the June 7 sample, Biobot estimated that 4.2% of the sample included COVID-19, a percentage that the organization used to project 730 cases in the community. By July 5, Biobot was projecting 4,200.

In the most recent test, on July 19, Biobot estimated a more than 50% prevalency rate in the wastewater and estimated more than 8,800 COVID-12 cases.

While the statistics from local and state health officials don’t show any numbers that high, Oregon Health Authority data has shown a massive uptick. Over the past month, the total number of COVID-19 cases in the 97801 area code has grown 2,000%. The city of Pendleton’s sewer system covers most people in the ZIP code, not only within Pendleton city limits but also in Rieth and the Mission area of the Umatilla Indian Reservation.

Despite the big numbers, Pendleton has chosen not to publicize or widely share the data, citing the volatility of the data and the newness of the testing data.

Public Works Director Bob Patterson said the city is still using the tests as a way to track COVID-19 trends in the Pendleton area. Patterson said the data shows that the virus is a growing presence in the city and its surrounding communities.

Biobot advertises itself to public officials as a business that can give governments a way to analyze the spread of COVID-19 beyond the confines of medical testing. Given that many COVID-19 carriers can have the virus without feeling any symptoms, the tests are meant to give its customers a clearer picture of the pandemic.

Sewer testing is starting to become more popular outside of Biobot customers.

As a part of Oregon State University’s TRACE study, researchers did tests on the sewer systems for Hermiston and Boardman. In two communities that have combined for more than 1,200 documented cases, the researchers found that “viral signals” remained high over time and did not fall, according to an OSU press release.

“The levels recorded are significantly higher than any of TRACE’s previous wastewater samples,” lead researcher Tyler Radniecki said in a statement.

The city of Pendleton will continue to monitor its sewer system for COVID-19 in the coming months, having contracted with Biobot through the end of the year.