Hi Crackcrack,  Inflow and infiltration(I&I) can disrupt an activated sludge system greatly.  Some variables are how poor the collection system is, how intense and duration of the storm and how saturated the soil is, and any flow equalization the facility has.  If the plant is running less than design that may help buffer it.  This is based on our facility.  Solids can be washed out(wasted) in the effluent.  This disrupts the bug population and depending on the facility permit limits may not be met.  We will cut back or quit wasting during a wet weather event depending on the duration and intensity of the event.  It can recover very quickly or slow.  I know that is vague but there are many variables.  The only thing I can suggest is to monitor the plant closely during a washout event. I hope this helps,  
David

Normal means of coping with potential washout during heavy rain events is to increase your return rate to the aeration system to help prevent solids washout in final clarifiers.  Another strategy to employ is to step feed your RAS and influent flows into the aeration sytem.  This allows you to handle more flow over short durations.  This second option can only be done if your plant has the physical means of being valved up for step feeding.  

Other option is to equalize the storm flow and feed it in at a lower rate over a longer time frame than the actual storm event.  We do this up until the storm flow exceeds our holding capacity in our EQ tank, then we are forced to begin bypassing some of the flow and chlorinating it before it exits the plant.

~Eric          A little bit of frost on the grass this morning!  But 80 degrees on Sunday!