Water softener discharge contains magnesium and calcium salts that were removed by the resin exchange media, and also some waste sodium salts from the regeneration. It is not unusual for softeners to discharge to the ground, and many people who use softeners also use wells and have septic tanks. Discharges to the septic tank increase the salt-load, but rarely cause significant problems.

So, the answer to your question is, it is probably not a problem. If you are in a municipality, then your building department can tell you the requirement for softener discharge. As a practical matter, these best management practices are probably adequate for you in most parts of the country: http://www.dem.ri.gov/programs/benviron/water/permits/privwell/pdfs/backwash.pdf .

Water softener discharges are becoming an environmental issue in arid western states, where the increased salts can lead to ambient water quality problems, because they are not efficiently removed during biological wastewater treatment. As a result, some states are considering regulating new installations.