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Description
Data from thirty-six water wells around Descanso, California, were analyzed to evaluate relationships between the productivity of water wells in crystalline rock and the proximity of wells to lineaments, the classification of the lineament according to genesis for wells near a lineament, and the frequency distribution of lineaments near wells. Stereopairs of diverse images were interpreted using a mirror stereoscope to identify lineaments which were then plotted on the corresponding topographic maps. For the proximity analysis, one lineament was classified as a high-confidence lineament because of somewhat greater certainty that the lineament represented a true subsurface discontinuity and because of the proximity of several wells. Of the thirty-six wells, ten were classified as on-lineament wells, of which six were on the high-confidence lineament and one was on the intersection of two lineaments. Comparison of the yields of the ten wells on lineaments and the six wells on the high-confidence lineament with the yields of the twenty-six off-lineament wells showed that the on-lineament and high-confidence lineament wells were more likely to yield in excess of 100 gpm (6.3 lps) and had greater variances; when normalized with respect to well depth, however, wells off lineaments were more likely to have high normalized yields (equaling or exceeding 1 gpm/ft (0.21 lps/m)) than wells on lineaments or wells on the high-confidence lineament. The one well on the intersection of two lineaments was more productive than all but one (approximately 3%) of the thirty-five wells away from the intersection of two lineaments in terms of yield and all but five (approximately 14%) of the thirty-five wells away from the intersection of two lineaments in terms of normalized yield. Due to lack of data, analysis of the relationships between well productivity and lineament genesis was inconclusive. A 900-element grid was constructed on a copy of the 1:24,000 lineaments map of the approximately 20 square miles (52 square kilometers) study area to enable counting the lineaments per unit area to examine relationships between productivity and lineament frequency near wells. Any mapped lineament, even if dashed to indicate uncertainty of its presence or precise location, either partially or wholly within the boundaries of a grid element was tallied as a lineament occurrence. Kriging estimates of both the natural frequency distribution and a transformed (modified logarithmic) frequency distribution of lineaments per grid cell were generated. Linear regression analysis between the kriging estimates of both the natural and transformed frequency distributions of lineaments and yield, natural logarithm of the yield, normalized yield, and the natural logarithm of the normalized yield suggested very poor correlation. For both the natural and transformed distributions, 90% confidence intervals for yield and normalized yield calculated for low and high lineament-frequency groups indicated no apparent statistical difference between the low and high groups for three of the four comparisons of frequency and well productivity.
