Reaching Back to Prior Monitoring Events

Normally, if a component has no inspection in the selected period, the protocol would assign the Average Emission Factor (sometimes referred to as the Default Factor for Unmonitored Components) for the entire time span. This can significantly inflate emissions because it assumes an “average” leak rate with no reference to that component’s actual behavior.

To avoid this, many LDAR programs allow a “reach back” or “look back” approach. Instead of defaulting to the Average Factor, the system can reach back to the most recent inspection reading prior to the calculation period and use that value as the starting point for emissions calculations.

For example:

• You are calculating emissions for 2024.
• A connector was last monitored in October 2023 with a reading of 5 ppm.
• The connector was not monitored at all during 2024.
• With “reach back” enabled, the system will carry forward that October 2023 result and treat it as the baseline for the 2024 calculation period.

This method provides a more realistic estimate because it is based on the component’s actual historical data rather than substituting in an “average” emissions factor. However, the prior inspection should be reasonably recent, and the approach should be applied consistently across all components to maintain defensibility.

How Chateau Implements Reach Back

Chateau makes this process flexible by letting you define how far back the system should search for a prior inspection result. When setting up your Emission Model, you’ll see the option:

“Reach Back to get earlier PPM event.”

• If selected, Chateau will look back a specified number of quarters to find the most recent monitoring event.
• You choose the number of quarters, anywhere from 1 to 99 (up to 25 years).
• If a qualifying reading is found within that window, Chateau uses that PPM value as the baseline for the emissions period.
• If no reading exists within the reach back range, the software defaults to the Average Emission Factor for that component class.

By default, the Reach Back feature applies to only components monitored during the emissions calculation period. To include all components in the reach back, ensure the “Reach Back for Unmonitored components as well?” option is selected.

Example:
If you are running calculations for 2024 and set the reach back to 4 quarters, Chateau will search 2023 for the most recent result. If one exists, it will apply that value to 2024. If not, the Average Factor will be used.

This flexibility allows facilities to tune the model:

• A shorter reach back period (e.g., 1–2 quarters) prevents older data from skewing results.
• A longer reach back period minimizes inflated emissions from components that are rarely monitored.

In short, Chateau’s reach back option helps balance accuracy and defensibility, ensuring your emissions estimates reflect real inspection data whenever possible.