Runtime Assertion Checking (RAC) for expressive specification languages is a non-trivial verification task, that becomes even more complex for memory-related properties of imperative languages with dynamic memory allocation. It is important to ensure the soundness of RAC verdicts, in particular when RAC reports the absence of failures for execution traces. This paper presents a formalization of a program transformation technique for RAC of memory properties for a representative language with pointers and memory operations, including dynamic allocation and deallocation. The generated program instrumentation relies on an axiomatized observation memory model, which is essential to record and monitor memory-related properties. We prove the soundness of RAC verdicts with regard to the semantics of this language.