Hurricane Sandy dumped about 11bn gallons of raw and untreated sewage into waterways from Washington DC to Connecticut, the science journalism group Climate Central said on Tuesday. That's or enough human waste to cover New York's Central Park in 41ft of sewage, or fill 17,000 Olympic-sized swimming pools, scientists told a conference call with reporters.

The group, which drew on data from the Environmental Protection Agency, state protection agencies and water treatment plants, said most of the outflow during the storm, which hit the eastern US in October last year, was caused by storm surges, which overwhelmed sewage treatment plants. But power shutdowns – and heavy rain in Washington DC – also played a part. A third of the sewage was untreated.

The scientists said the report exposed yet another risk factor to America's crumbling infrastructure, due to climate change.

New York City authorities have been working for years to reinforce the city's subway system, which is vulnerable to flooding, and to shore up power stations, which are located along the coast. The scientists said that in the wake of Sandy, when storm surges raised waters more than 9ft above the high tide mark, it was time to look at waste-treatment plants.

"Our sewage infrastructure isn't built to withstand such surges and we are putting our property, safety and lives at risk if we don't adequately plan for these challenges," said Alyson Kenward, a senior scientist and research manager for Climate Central, adding that almost all of the sewage had ended up in New Jersey and New York. It was unclear, however, what the effects were on human health.

The estimated cost of repairs to New York and New Jersey's sewage treatment plants could reach $4.7bn. "In the long run, sea-level rise is going to force us to rework our infrastructure physically if we are going to keep it intact," she said.