"Always graph your data."
Back in 2012 I took a class with Dr. Kirk Cameron who was the primary author of USEPA’s Unified Guidance - Statistical Analysis of Groundwater Monitoring Data at RCRA Facilities“ and one thing he drove home......"Always graph your data.” Graphing data allow us to see trends and identify patterns. Also, outliers are normally pronounced. The following are some methods that I have found very useful.
Time Series Plots