AN APPLICATION OF GEOSTATISTICS TO DETERMINE REGIONAL GROUND-WATER FLOW IN THE SAN ANDRES FORMATION, TEXAS AND NEW MEXICO

The construction of a contour map of hydraulic head for groundwater in the San Andres Formation in west Texas and eastern New Mexico is problematic due to variability in quality and distribution of data. The direction of regional groundwater flow can be inferred from raw data only in the northern part of the study area where reliable drill-stem tests and water-level measurements make up most of the data. In the southern area, where unreliable and highly variable drill-stem tests comprise the bulk of the data, variogram analysis and kriging successfully remove the effects of high measurement error. This allows the regional trend to be seen. However, kriged block estimates cannot be computed for a critical region with sparse data in the northeastern part of the study area. The most complete potentiometric surface can be contoured from hybrid data: kriged block estimates from the southern region, and original head measurements in the northern region.