COKRIGING LIMITED TRANSMISSIVITY DATA USING WIDELY SAMPLED SPECIFIC CAPACITY FROM PUMP TESTS IN AN ALLUVIAL AQUIFER

Use of the specific capacity of a pumping well to predict aquifer tran smissivity is desirable due to the cost of pumping tests and the avail ability of specific capacity measurements. The geostatistical techniqu e of cokriging is a method of incorporating the spatial variability of a correlated variable (e.g., specific capacity) in estimating: or rel ated undersampled variable (e.g., transmissivity). This study examines the reliability of cokriging transmissivity estimates using a data se t of 215 pairs Of transmissivity and specific capacity. Subsets of pai rs of transmissivity and specific capacity were selected and cokriged to estimate transmissivity at the remaining well locations. The estima tes of transmissivity were then compared to actual measurements of tra nsmissivity. The same subsets of pairs were used to estimate transmiss ivity with loglinear regression of transmissivity on specific capacity and ordinary kriging of transmissivity done. Comparison of these thre e methods indicates the number of wells with both transmissivity and s pecific capacity data necessary to obtain improvement in transmissivit y estimates with cokriging over the simpler regression and kriging met hods. The results show that significant improvement in the transmissiv ity estimate is obtained by cokriging with 50 or more pairs of transmi ssivity and specific capacity, and that loglinear regression is superi or when less than 30 pairs are available. With between 30 and 50 pairs of available data measurements, cokriging does not reliably improve t he estimate over loglinear regression.