A $294\mathrm{.}2-$g sample of ground water is analyzed for calcium. The Ca$2+$ in the sample is first precipitated and filtered$-$off as NH$4$CaPO$47$H$2$O$.$ This precipitate is dried and heated, releasing water and ammonia to yield anhydrous calcium pyrophosphate $($Ca$2$P$2$O$7).$ The mass of Ca$2$P$2$O$7$ obtained is $0\mathrm{.}0768$ g$.$

Give the calcium content of the ground water in parts per million $($to three significant figures$).$

ppm