I believe this sandpiper is actually Curlew Sandpiper (Calidris ferruginea). Here's why....
The black legs - Purples have greenish-yellow legs and base of bill.
The rufous colouration of the mantle/coverts. Purples only have rufous/red fringes to the coverts during summer plumage. These birds show pale grey mantle/coverts with some rufous colouration being moulted in (this photo was taken in June which is perfect moulting time for this colouration).
The grey colouration of the base feathers - Purples have much darker colouration in all plumages.
Strong rufous colouration of lower belly - Purples never show such strong rufous on the breast/lower belly/flanks.
The bill is long and decurved - Purples bill is much shorter, usually is long as its head, and not so decurved.
