  DEAP-3600 is a single-phase liquid argon detector aiming to directly detect
Weakly Interacting Massive Particles (WIMPs), located at SNOLAB (Sudbury,
Canada). After analyzing data taken during the first year of operation, a null
result was used to place an upper bound on the WIMP-nucleon spin-independent,
isoscalar cross section. This study reinterprets this result within a
Non-Relativistic Effective Field Theory framework, and further examines how
various possible substructures in the local dark matter halo may affect these
constraints. Such substructures are hinted at by kinematic structures in the
local stellar distribution observed by the Gaia satellite and other recent
astronomical surveys. These include the Gaia Sausage (or Enceladus), as well as
a number of distinct streams identified in recent studies. Limits are presented
for the coupling strength of the effective contact interaction operators
$\mathcal{O}_1$, $\mathcal{O}_3$, $\mathcal{O}_5$, $\mathcal{O}_8$, and
$\mathcal{O}_{11}$, considering isoscalar, isovector, and xenonphobic
scenarios, as well as the specific operators corresponding to millicharge,
magnetic dipole, electric dipole, and anapole interactions. The effects of halo
substructures on each of these operators are explored as well, showing that the
$\mathcal{O}_5$ and $\mathcal{O}_8$ operators are particularly sensitive to the
velocity distribution, even at dark matter masses above 100 GeV/$c^2$.
