Arsenic is not tied up by calcium. Calcium arsenate was a common pesticide used in the days before DDT, and was made by mixing lime with arsenic oxide. It is fairly water soluble, so since it went out of favor in the 1950s, most of it has probably been leached out of the soil since then. Unless you are in an area where mining activity would have concentrated it (silver, gold or lead mining operations), or there is a naturally high background, arsenic is probably not a cause for concern.
Here is a link to an
EPA report on Arsenic Bioavailability in soils.