Little work has been published that compares actual yields from sand and gravel excavations with reserve calculations based on drilling. To do so sites must meet criteria of clear identification; in-house site investigation; full drilling; and properly recorded production. There are several potential sources of difference between calculated and actual figures.

Twenty-six sites were investigated, yielding from 63.64% to 152.400f calculated reserves. The mean of the results is 104.37%, the median 104.31% and the mode group 107.0–109%. This analysis confirms that, in a majority of cases, the measurement of reserves using conventional techniques is accurately carried out. A variance of ± 5 0s suggested as the geologist's target.

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