Neighborhood Wastewater Data

How to read regional wastewater graphs

After collection, wastewater samples are analyzed in a UC Davis lab to determine the concentration of virus copies present. Concentration data are normalized (to adjust for things like rainfall and other factors that could affect the sample dilution) and plotted against the City’s Wastewater Treatment Plant numbers (the city-wide average).

By comparing site-specific data (in blue) to the city-wide average (in yellow), we can see how trends compare: whether the detectable amount of virus in a sampling zone is going up, going down, or staying about the same. These plots are updated every Saturday.

Technical notes:

• Virus copy concentration represents an average of the detected concentrations of the N1 and N2 regions of the SARS-CoV-2 genome.
• To visualize the data, we truncate outliers at the [1,99] percentile levels, calculate a two-week moving average, and apply a smoothed linear fit on the moving average to achieve a trendline.
• In early March 2020, the sample-processing method was changed from ultrafiltration-based concentration and column-based manual extraction to automated concentration and extraction using magnetic particles.
• In early September 2020, the sample-analysis method was changed from quantitative polymerase chain reaction (qPCR) to digital droplet polymerase chain reaction (ddPCR). Technical challenges associated with the methods switch resulted in lost data from early September to early October.