Water softener brine tank discharges directly into the storm sewer pipe

The plumbing for the sump pump discharge goes up to an elbow. From the elbow the 2 inch pipe slopes down to a 4 inch pipe. The water softener drain is connected at the top of the 2 inch sloped pipe.
Is this acceptable?
I know you can’t have any direct connection to a sewer line but not sure about storm sewer.

Where does a “storm sewer” drain to?

To the river.

You need an air gap and/or indirect drain connection to prevent back siphonage or cross contamination.

A storm sewer contains contaminated, polluted or harmful water, that shouldn’t mix with potable water.