A reservoir modeling study was performed to simulate a pilot sequestration site located in the San Juan coal basin of northern New Mexico. Several unknown reservoir properties at the field site were estimated by modeling the coal seam as a dual porosity formation and by history matching the methane production and CO2 injection. In addition to reservoir modeling of methane production and CO2 injection, tracer injection was modeled. Tracers serve as a surrogate for determining potential leakage of CO2. The tracer was modeled as a non-reactive gas and was injected into the reservoir as a mixture along with CO2. Geologic and geometric details of the field site, numerical modeling details of methane production, CO2 injection, and tracer injection are presented in this paper. Moreover, the numerical predictions of the tracer arrival times were compared with the measured field data. Results show that tracer modeling is useful in investigating movement of injected CO2 into the coal seam at the field site. Also, such new modeling techniques can be utilized to determine potential leakage pathways, and to investigate reservoir anisotropy and heterogeneity.