The effectiveness of borehole restoration techniques on recharge boreholes has been assessed by repetitive step-drawdown tests. The step-drawdown tests were run with up to 10 steps and repeated up to five times on a single borehole.

The borehole restorations after well-clogging by recharge show that the chemical methods of acidization and polyphosphate dispersion are more effective than physical methods such as surging by pumping.

The step-drawdown test analyses confirm that the squared relationship in the ‘well loss’ in the Jacob equation is valid in uniform aquifers where the total drawdown is a small proportion of the saturated thickness. They also show quite clearly that the so-called ‘aquifer loss’ in the Jacob equation can include large elements of ‘well loss’ indicating that the exact meaning of this equation needs re-examining.

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