There are tests for sulphates in soil, so it should be possible to test sulphate in concrete. If the concrete is having a sulphate attack, it would no doubt have come from the soil, so you could test the soil in the vicinity of the problem. Type 5 Sulphate resisting cement should have been used if the sulphate content in the soil is high. It is not expensive.
When sulphate attack is present, it is usually possible to see a white colored salt on the concrete members near the soil. If you have that evidence, you could take a sample of the powder to a lab for testing.
BA