West Virginia's Senate has followed the House and passed legislation to let industrial plants discharge more pollution into West Virginia waterways.
The bill that passed 20-13 would authorize the Department of Environmental Protection to calculate water pollution limits for cancer-causing and other chemicals using an average-flow figure called the "harmonic mean."
That would replace low-flow waterway volume now used to calculate dilution and determine allowable discharge amounts.
That would allow larger discharges from individual sites.
Backers say overall water quality standards would remain the same.
The change has long been sought by the West Virginia Manufacturers Association, which says it will help redevelopment of vacant industrial properties.
The West Virginia Rivers Coalition opposes the change and another in the bill to allow overlapping "mixing zones" of discharges from multiple sites.