The massive sewage spill on the Tijuana River in Mexico that fouled South County beaches may have been significantly larger than first estimated, although it’s unclear how regulators arrived at the new figure.

Standing next to the river valley for a news conference Monday, Rep. Scott Peters said the U.S. Environmental Protection Agency now suspects that discharges may have totaled 230 million gallons, up from an initial figure of 143 million gallons. The original volume already ranked as one of the biggest single sewage spills in the region’s history.

The new number has yet to be confirmed. The EPA said it received the data for its assessment from Baja California’s State Public Service Commission, which on Monday denied giving out that information and said it hasn’t released any data about the size of the spill.

It and other Mexican offices have been criticized by their U.S. counterparts for not providing prompt notice of the spill, which may have begun right after the new year and lasted until at least late February.

“Something went wrong on the other side of the border, and so I’m trying to track that down,” said Peters, D-San Diego, whose 52nd congressional district includes Coronado. Effluent from the spill has spread along the coastline from Baja California to Coronado.

U.S. and Mexican leaders of the International Boundary and Water Commission said Thursday that a binational group will investigate the spill and report back within 30 days. The international commission oversees water treaties between the two countries, among other things.

On Feb. 24, it announced that sewage had spewed into the Tijuana River for weeks. The discharge happened during repairs to a major sewer infrastructure near the confluence of Mexico’s Alamar and Tijuana rivers, according to officials in Mexico and the U.S.

At Monday’s press event, Imperial Beach Councilman Mark West voiced concerns about what he saw as a continuing lack of transparency. “To this date, the city of Imperial Beach and the city of Coronado and our South County representatives have not been given a definitive answer about what happened,” he said.