Data Quality Control (QC) is an important component of Ocean Observation Systems. Data quality control ensures that good and valid information is passed to researchers, educators, and the public for planning and decision making. Range checking is the second step in Data Quality Control. It checks the data, and flags it for further investigation if necessary. This paper explains the planning, programming and implementation of range checks of environmental monitoring data at Dauphin Island Sea Lab and Louisiana Universities Marine Consortium (LUMCON).