Free Online Pumping Test Analysis Tool: Cooper-Jacob Transmissivity
Paste one reading per line: time, drawdown in meters. Commas, semicolons, or tabs all work.
What this tool does
A constant rate pumping test produces the least glamorous dataset in hydrogeology: a column of times and a column of drawdowns. Buried in it are the two numbers that describe the aquifer, transmissivity and storativity. This analyzer fits the Cooper Jacob straight line to your data by least squares, reads T from the slope and S from the zero drawdown intercept, and draws the whole thing on a proper log time plot so you can see exactly what the fit believes.
The early time problem, handled
The Cooper Jacob approximation only becomes valid once pumping has gone on long enough that the well function collapses to a logarithm, conventionally when u falls below about 0.05. Early readings sit above the straight line and drag a naive fit toward flatter slopes and inflated storativity. This tool fits, computes the validity time from its own first answer, excludes the readings that fail the test, and refits. Excluded points stay on the plot, circled in red, so nothing is hidden: you see what was used and what was set aside.
Reading the results
Transmissivity comes out in square meters per day, and dividing by the aquifer thickness gives hydraulic conductivity if you provide b. Storativity is dimensionless: expect ten to the minus four or smaller for confined aquifers, and values in the hundredths for unconfined water table response. The drawdown per log cycle is the number old school hydrogeologists read straight off semilog paper, and the RMS error tells you how straight your line really is. A poor fit is information too: curvature late in the test hints at boundaries, leakage, or a well that never reached the ideal regime.
Try it against known ground
The demo button loads the pumping test from our Demo Valley worked project, generated from an aquifer with T of 350 and S of 0.0002 plus a little measurement noise. The fitter recovers both within a percent or two, excluding the three earliest readings on its own. Feed the same aquifer into the groundwater flow simulator and you can watch the cone of depression those numbers imply.
Pumping Test Analysis Report (Cooper-Jacob)
| Pumping rate | " + $('ptaQ').value + " m3/day |
| Observation distance | " + $('ptaR').value + " m |
| Points fitted | " + F.nFit + " beyond " + F.tfit + " min |
| Slope per log cycle | " + F.slope.toFixed(4) + " m |
| Transmissivity T | " + F.T.toFixed(1) + " m2/day |
| Storativity S | " + F.S.toExponential(3) + " |
| Zero-drawdown intercept t0 | " + F.t0.toFixed(2) + " min |
Generated by calculatgeek.com Free Online Pumping Test Analysis Tool
"; $('ptaPrintArea').innerHTML = html; document.body.appendChild($('ptaPrintArea')); window.print(); }); })();Pumping test analysis in your browser
A pumping test is hydrogeology reduced to its essentials: pump one well at a constant rate, watch the water level fall in another, and the shape of that decline reveals the aquifer. The tool above performs the Cooper-Jacob straight-line analysis, the workhorse method used in nearly every consulting report: paste time and drawdown from your observation well, set the pumping rate and well spacing, and it fits the semilog line and reports transmissivity, storativity, and the slope per log cycle, with the early invalid data excluded and the u criterion checked explicitly. The demo loads a textbook confined aquifer test whose known answers the fit recovers.
This opens the Hydrogeology and Water Suite, linked in the bar above, which gathers the groundwater tools on calculatgeek into one connected family. As always, your test data never leaves the browser.
What T and S actually mean
Transmissivity is the aquifer conveyance: how many cubic meters per day flow through a strip of aquifer one meter wide under a unit gradient. It sets how productive wells can be and how far drawdown reaches. Storativity is the release: how much water a unit area yields per meter of head decline. Confined aquifers release only elastic storage and show storativities in the 0.00001 to 0.001 range; unconfined aquifers actually drain their pores and land near 0.05 to 0.3, which is why the tool suggests an aquifer type from the fitted value. Together they parameterize every prediction that follows: interference between wells, capture zones, and sustainable yield.
Related Calculators and Reference
- Hazen Permeability Calculator for the grain-size estimate of K to compare against the test.
- Water Tank Sizing Calculator for the supply side the aquifer feeds.
- Consolidation Settlement Calculator for what excessive drawdown does to the ground.
- Free Online Well Test Analysis Tool, the petroleum cousin of this exact method.
- External reference: the USGS Water Resources Mission Area, publisher of the standard aquifer test methods.
Common Questions
What is the Cooper and Jacob method?
A simplification of the Theis solution for pumping tests: at late time, drawdown plots as a straight line against the logarithm of time, and the slope gives transmissivity while the intercept gives storativity.
What is transmissivity?
The rate at which water moves through the full saturated thickness of an aquifer under a unit gradient, equal to hydraulic conductivity times aquifer thickness. It is the single most useful number a pumping test produces.
How long should a pumping test run?
Long enough for the straight line to develop and for boundaries to show if they are near, commonly several hours to several days. Short tests risk fitting the early data the method explicitly excludes.