Question about EPA filters and Gross Beta

Just asking this question may show that there's a whole bunch of stuff that I don't understand about this process, but here is my question.

https://cdxnode64.epa.gov/radnet-public/query.do

When I go to the query site to look at some data, I've noticed that the sampling volume in the data can vary quite a bit. Over several days, the volume will increase, and then drop. The period of time (in days) over which this occurs appears to be variable, and the max value of sampling volume also does not appear to be consistent.

When the sample volume drops significantly, is this when the filter is changed? If not, what's happening there?

Also, should the beta count drop when this happens?

It does seem to be that when the beta count gets pretty high, when this drop in volume occurs, it seems to be a way to also decrease the beta. It certainly isn't try that the beta count is cumulative.

I may not have explained things well. Can anyone explain more about what the sampling volume is actually measuring and its relationship, if any, to the gross beta count?