| ENERGY | GEOMICRODISTRICTS A Study Advocates for a Utility-scale Approach to Replace Existing Gas Lines with Ground-source Heat Pumps WRITTEN BY | RICHA YADAV I GeoMicroDistrict: Ground-source heat pump closed vertical systems could be installed in a single row along an existing utility corridor. Vertical boreholes and service connections could be located between existing infrastructure. n 2019, about 97 percent of U.S. natural gas pipelines were made of plastic or steel. Cast-and wrought-iron pipes were the remaining few and among the oldest gas lines in the country, according to the U.S. Department of Transportation’s Pipeline and Hazardous Safety Administration (read more at bit.ly/2UwHgdM). Nearly half of all iron pipes are concentrated in four states, includ-ing Massachusetts, New Jersey, New York and Pennsylvania. If cast-iron (and bare-steel pipelines) are left in the ground beyond their service life, utilities have to spend millions of dollars repairing leaks on old pipelines. When left unattended, leaking gas pipes release methane, which is a highly combustible gas that poses significant health, public safety and environmental risks. In September 2018, a natural-gas leak resulted in 131 fires and three explosions in three communities in Merrimack Valley, Mass. Thousands of people from the city of Lawrence and towns of Andover and North Andover were forced to evacuate their homes. About 25 people were injured and one person died in the incident. In the winter months that followed, more than 8,000 customers had no access to heat, hot water and gas. After a yearlong investigation, the National Safety Transportation Board determined there was inadequate planning and manage-ment by Columbia Gas of Massachusetts, PHOTOS: KING COUNTY which led to over pressurization in the valley’s aging cast-iron gas pipes. (Read a synopsis of NTSB’s report at bit.ly/3ajO59i.) Massachusetts Rethinks Gas Infrastructure Massachusetts has the second-oldest gas infrastructure system in the country with 6,000 miles of aging and leak-prone pipes, which make up 26 percent of the state’s gas system. In recent years, natural-gas com-panies have faced a great deal of backlash caused by pipeline failures and methane leaks from aging pipelines. Gas companies are therefore actively replacing aging pipe-lines with corrosion-resistant high-density polyethylene plastic pipelines. It is estimated that repairing and replacing the state’s leaking gas system can cost taxpayers more than $9 billion during the next 20 years. This 44 RETROFIT // May-June 2020