An ion exchange resin, $$\text{RH}_2$$, can replace $$\text{Ca}^{2+}$$ in hard water as $$\text{RH}_2 + \text{Ca}^{2+} \to \text{RCa}^{2+} + 2\text{H}^+$$. When a 1.0 L hard water sample was passed through the resin, all $$\text{H}^+$$ ions were replaced by $$\text{Ca}^{2+}$$ ions and the pH of eluted water was found to be 2.0. The hardness of water (as ppm of $$\text{Ca}^{2+}$$) in the sample of water treated is