A growing number of home foundations in central and northeastern Connecticut are failing because of the presence of pyrrhotite, a mineral that naturally reacts with oxygen and water. Over decades, that reaction can cause the concrete to crack and crumble, making some homes unsellable and unlivable.

The problem, which first came to light in the mid-1990s, has been traced to a Willington quarry that provided material to a concrete maker whose product was used in thousands of houses. The Connecticut attorney general has not pursued legal action against the company, saying it can’t prove violations of consumer protection laws.

Willington is one of 36 communities identified as potentially having homes with pyrrhotite problems. Possibly 30,000 or more homes and condominiums built throughout the region from the mid-1980s to 2016 could be affected, said Steven Webner, manager of the neighboring town of Tolland and co-chairman of a regional committee examining the problem.

A small but growing number have sought some relief from their town halls, appealing the local tax assessment of their houses. An Associated Press survey of the 36 communities found more than $1.2 million has so far been relinquished after roughly 500 residential properties were reassessed. Those reassessments vary depending on the level of deterioration.