Microbiological control of the environment

dear all,

Today I do an annual review of the results of microbiological environmental monitoring, I noticed that my results are close to the action limits
(Air sample : Class C: 100 UFC/m3 , Class D: 200 UFC/m3 )

I would like to set warning limits, but I don’t know what statistical approach I should follow.

Best regards

Refer trend data. based upon that u can set the alert and action limits.