Central well. When organizing experimental pumping, the dynamic water levels in the central well are usually left out of observations, as the water-lifting pipe is filled with emulsion masking the position of the dynamic level. To observe dynamic levels, a special observation well of small diameter (piezometer) in the immediate vicinity of the central well is installed, and it is called a downhole observation well. At deep occurrence of the dynamic level in the aquifer, the sinking and anchoring of the downhole well becomes difficult. It is very convenient to replace such a well with a piezometric tube lowered into the central well next to the air pipe. If the lower edge of the piezometric tube is immersed 5-10 m below the mixer, the water in it is completely free from the impact of air supplied to the central well and set at a level corresponding to the dynamic level in the central well and aquifer. It remains only to periodically measure the position of this level with a level gauge. B.P. Ostroumov's level gauge is convenient.