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The Thiem equation gives steady confined-aquifer well yield as Q = 2 pi T s / ln(R/rw). With transmissivity 250 m2/day, 6 m of drawdown, a 0.15 m well and a 300 m radius of influence, the yield is about 1240 m3/day or 14.4 L/s. Because the well radius enters logarithmically, doubling the borehole diameter adds only a few percent.
Thiem equation
Q = 2 pi T s / ln(R / rw)
Specific capacity
capacity = Q / drawdown
Because the radius appears inside a logarithm. Yield is set by aquifer transmissivity, not hole size.
The distance at which drawdown becomes negligible. It grows with pumping time and is often estimated rather than measured.