The name "Alum" comes from Native American sources.
Nipmuc Place Names of New England includes it in the discussion of Massachusetts place names:|
"Alum Pond, Sturbridge; and Little Alum Pond, Holland, Worcester County - "a dog". Sources of the Quinebaug River: the "Alum ponds," 1715. See Allum (RI)."
The Rhode Island section has: "Allum (or Wallum) Pond, Providence County - "a dog". On the n. line of Burrillville, RI, near the n.e. corner of CT. So called from a sachem of the Quinebaug band
of Nipmucs whose name (meaning 'The Fox') was variously written Allums, Allumps3, Hyems, Hyemps, Iams, etc. Col. Rec., iv. 272, 333, 351. See Alum (MA). "
One interesting thing here is to note that whereas the modern seems to agree on "Alum" with one "l", the original varied between one and two. Assuming that Orlin's source for the mention of "Attom Pond" chose to use the version with two l's, and given the idiosyncracies of handwriting, it is very easy to see how Orlin could have read "Attom" in place of "Allum."
That this is indeed the correct identification is confirmed by two other maps, one an 1870 version of the area that actually identifies "Fay Cove," and one a surveyor's map.