  Knowledge of the mass composition of ultra-high-energy cosmic rays is
understood to be a salient component in answering the open questions in the
field. The AugerPrime upgrade of the Pierre Auger Observatory aims to enhance
its surface detector with the hardware necessary to reconstruct primary mass
for individual events. This involves placing a scintillation-based detector
with an active area of $3.8 \,\mathrm{m}^2$ on top of each existing
water-Cherenkov detector in its surface detector array. Here, we present the
methods for simulating this Scintillator Surface Detector. These simulations
have and will continue to aid in the interpretation of measurements with
AugerPrime as well as the development and improvement of event reconstruction
algorithms including primary mass.
