At least 13 toxic waste sites in Texas were flooded or damaged by Hurricane Harvey, adding to the challenges as the area begins clean-up efforts following the deadly storm.

The Environmental Protection Agency announced Saturday that it had assessed 41 Superfund sites using aerial images, and determined the ones badly affected by the storm. The impact of flooding on the sites is unknown.

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The EPA said its workers have not been able to "safely access the sites" but are ready to do so as soon as the floodwaters recede.

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