You can get soil salinity meters. Not sure such a small amount of salt would cause a problem. If concerned & bed has good drainage, should be able to leach salt out with 2-3 heavy waterings.
I don't know about beans specifically. In general folks water stuff too little, too often. 15min/day seems like that. built in drip emitters are usually 1 gal/hr. I'll have clients run drip for an hour to get water deeper. then wait 3 days or more to water again.