Large Volume Leak Study

In 2016, a law was passed in Mass. that “environmentally significant” natural gas leaks must be repaired. Recent research had shown that just 7% of the leaks emit 50% of all the emissions. Natural gas is over 90% methane, a powerful greenhouse gas. Fixing these few big leaks would cut the emissions in half for the least cost and disruption.

The problem is there are over 16,000 gas leaks across the state. No one has ever tried to come up with a fast, inexpensive and reliable method of identifying the large volume leaks in a population that big.

Using the best available knowledge, the Dept. of Public Utilities suggested the utilities use the barhole method for finding these large volume leaks.

With the barhole method, a hole is made in the ground and the nozzle of a combustible gas indicator inserted into the hole to read the percent gas in the soil. If the percent is over 50% for two years in a row, that leak would be considered a large volume leak.

Goal

‘The goal of the study was to learn if the barhole method would reliably identify large volume leaks. If it didn’t, the goal would be to find some other method that would.

Columbia Gas, Eversource and National Grid participated in the study. They selected 69 leaks to be part of the study using the barhole method.

The researchers studied these leaks, first by performing a leak survey on each of the leaks
The research team also used a Picarro (a high precision GPS-enabled natural gas analyzer) to find the large volume leaks. The team selected 14 additional leaks for the study using the Picarro.

Comparing Leak Rates

The research team used the chamber method to measure the emissions of each of the leaks in the study.

The chamber method is a scientifically verified, peer-reviewed technique for comparing the rate of emissions, but it’s very laborious. The team compared the chamber method’s results with the results of other methods. The team wanted to find out which method:

  1. Was most reliable as a proxy method at finding the large volume leaks
  2. Could verify that the proxy method selected large volume leaks for repair, while providing feedback for continued improvement
One of the methods tested was the MultiSensor Scientific camera. It is a new technology currently being developed. It can find leaks and compare the leak rates through infrared spectroscopy.
Another method tested was the FLUXbar. The FLUXbar was created by the coalition of HEET, Mothers Out Front, Millibar, Columbia Gas and Eversource. It is a fast and reliable way of performing an apples-to-apples comparison between leaks in order to prioritize the leaks emitting the most.

Results

The leak footprint was found to be the fastest and most reliable proxy method of identifying the large volume leaks.

The FLUXbar was found to be the best method of verifying large leaks were selected, while providing feedback to the utilities so they can continue to improve.

Action Plan

The three utilities, HEET, Mothers Out Front and the researchers have agreed on a shared action plan based on the results of the study. The plan includes leak footprint, the FLUXbar, as well as data transparency, annual reassessment and independent verification.

The result can reduce, within just two years, the equivalent of 2 to 6% of Massachusetts’ greenhouse gas emission inventory (depending on the timeframe and assumptions).

The results can help gas companies across the country change how they prioritize gas leaks for repair.

A Full Explanation

If you want more than the cliff notes, but a more full report, here’s a presentation that summarizes the methods and results of the Large Volume Leak study.

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