Spatial Sampling Strategies for Mapping a Volcanic Ground Water Plume in Sierra Valey, California
Accurately mapping a region’s ground water quality depends upon the spatial sampling strategies employed, including where and how often field data are collected. This study compares the relative values of three field sampling strategies for mapping a known migrating plume of volcanic ground water in Sierra Valley, California. The first strategy sampled wells once each year during 1957, 1972, and 1980 (n=63, 45, and 57, respectively) and portrayed spatial–temporal changes in ground water quality more clearly on maps than did two alternative sampling strategies. One of these alternatives, Strategy 2, sampled one well per township per year during 1957, 1972, and 1980 (n=11) and did not detect the migrating plume, despite being a recommended strategy. The other alternative, Strategy 3, frequently sampled in time a small, fixed group of indicator wells (n=13) every four years for the same period, again producing maps with little correlation to the original pattern detected by Strategy 1.