Geology topics
J. M. Neil
Publications and source records attributed to J. M. Neil.
Test holes for monitoring surface-water/ground-water relations in the Cottonwood Creek area, Shasta and Tehama Counties, California, 1984-85
Ten test holes were drilled to obtain hydrogeologic information for an investigation of stream-aquifer interaction near proposed damsites on Cottonwood Creek and South Fork Cottonwood Creek, California. At each site, one deep well was completed below the first confining clay encountered in the upper Tehama Formation to determine hydraulic gradients between water-bearing deposits in the Tehama Formation and overlying channel deposits. At three sites along Cottonwood Creek, two shallow wells were drilled at each site on a line perpendicular to the stream channel to determine if groundwater in channel deposits is moving toward or away from the stream channel and to monitor water levels. Geophysical logs were correlated with lithologic logs compiled from analyses of drill cuttings to determine depths for setting well screens. After pumping to confirm hydraulic connection between each well and the Tehama Formation, water levels were monitored monthly from June 1984 to June 1985; at two sites, water levels were above the altitude of the stream channel bottom during all streamflow conditions. Tritium dating indicates two wells have water more than 100 years old; one well has either a mixture of old and new water or an intermediate-aged water. (USGS)
Data for selected pesticides and volatile organic compounds for wells in the western San Joaquin Valley, California, February to July 1985
During February to July 1985, water samples were collected from 55 wells in the western San Joaquin Valley, California, for chemical analysis to determine if 20 selected pesticides and 26 volatile organic compounds were present. Twenty-six of the sampled wells are completed in the shallow unconfined regional aquifer and 29 wells are completed in the deep confined regional aquifer. Water from six of the sampled wells, four of which are completed in the shallow unconfined aquifer, contained detectable levels of the pesticides or volatile organic compounds. Four samples contained a single pesticide, one sample contained two pesticides, and one sample contained 5.9 microgm/liter of toluene, a volatile organic compound. Five of the six pesticides detected were triazine herbicides; the maximum concentration was 0.2 microgm/liter. Four samples with detectable concentrations of triazine herbicides are from wells used for domestic water supply; however, drinking-water standards have not been established for triazine herbicides. (USGS)
Map of California showing distribution of selenium concentrations in wells sampled by the U.S. Geological Survey, 1975-85
Samples from 230 wells in California were analyzed for dissolved selenium during 1975-85. Most of the sample wells are concentrated in eight areas of the State. Selenium was detected in all eight areas; however, only 6 of the 230 wells had concentrations greater than 10 micrograms per liter. Selenium was detected most frequently in wells of the Davis-Woodland area of the Sacramento Valley and in wells in Santa Barbara County.