George Waltham is recorded in the Returns of the Colony as sub-inspector of roads between February 1835 and 1841. For one year only, 1837, is he specifically stated as working in Berrima. His salary was £82/2/- plus forage for one horse.
The only other record of a George Waltham found on ancestry.com is to a convict who arrived on the Admiral Gambier and Friends in 1811. Given the profession of Berrima’s George Waltham they are unlikely to be the same person.