Typically six or more mud pits of various sizes are located at the surface of most wells, but at any one time all mud pits are not necessarily “active”, i.e., contributing {TAIL ~ volume} to the closed loop system of {HEAD ~ the circulating mud} going into the wellbore WB and returning to the surface S 
Typically six or more mud pits of various sizes are located at the surface of most wells , but at any one time all mud pits are not necessarily “ active ” , i.e. , contributing { TAIL ~ volume } to the closed loop system of { HEAD ~ the circulating mud } going into the wellbore WB and returning to the surface S
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH