Geology topics
E. A. Lynch
Publications and source records attributed to E. A. Lynch.
Geohydrology and simulations of ground-water flow at Verona well field, Battle Creek, Michigan, 1988
Public water supply for the city of Battle Creek, Mich. is withdrawn from the Marshall Sandstone through wells at the Verona well field. Analysis of borehole acoustic televiewer, gamma, and single-point-resistance logs from wells in Bailey Park, near the well field, indicates 12 fracture zones in the Marshall Sandstone. Further interpretation of flow-meter and temperature logs from the same wells indicates that the fracture zones are locally interconnected but appear to remain isolated over a lateral distance of 3,000 feet. Organic chemicals were detected in water samples collected from water-supply wells in the Verona well field in 1981. In 1985, six water-supply wells were converted to purge wells to intercept organic chemicals and divert them from the remaining water-supply wells. Removal of these wells from service resulted in a water-supply shortage. A proposal in which an alternative purge system could be installed so that wells that are out of service may be reactivated was examined. A ground-water-flow model developed for this study indicates that, under the current purge configuration, most water from contaminant-source areas either is captured by purge wells or flows to the Battle Creek River. Some water, however, is captured by three water-supply wells. Model simulations indicate that with the addition of eight purge wells, the well field would be protected from contamination, most water from the contaminant-source areas would be captured by the purge system, and only a small portion would flow to the Battle Creek River. In an effort to augment the city's water supply, the potential for expansion of the Verona well field to the northeast also was investigated. Because of the addition of three municipal wells northeast of the well field, some water from the site of a gasoline spill may be captured by two water-supply wells. Ground water in the area northeast of Verona well field contains significantly lower concentrations of iron, manganese, and calcium carbonate than does water in the existing well field area. However, the Marshall Sandstone in this area has significantly lower transmissivities than those within Verona well field.
Geohydrology and contamination at the Michigan Department of Transportation maintenance garage area, Kalamazoo County, Michigan
A leaking underground storage tank was removed from the Michigan Department of Transportation maintenance garage area in Kalamazoo County., Mich., in 1985. The tank had been leaking unleaded gasoline. Although a remediation system was operational at the site for several years after the tank was removed, ground-water samples collected from monitoring wells in the area consistently showed high concentrations of benzene, toluene. ethylbenzene, and xylenes--indicators of the presence of gasoline. The U.S. Geological Survey did a study in cooperation with the Michigan Department of Transportation, to define the geology, hydrology, and occurrence of gasoline contamination in the maintenance garage area. The aquifer affected by gasoline contamination is an unconfined glaci'a.l sand and gravel aquifer. The average depth to water in the study area is about 74.7 feet. Water-level fluctuations are small; maximum fluctuation was slightly more than 1 foot during August 1993-August 1994. Hydraulic conductivities based on aquifer-test data collected for the study and estimated by use of the Cooper-Jacob method of solution ranged from 130 to 144 feet per day. Ground water is moving in an east-southeasterly direction at a rate of about I foot per day. Leakage from perforated pipes leading from the underground storage tanks to the pump station was identified as a second source of gasoline contamination to saturated and unsaturated zones. The existence of this previously unknown second source is part of the reason that previous remediation efforts were ineffective. Residual contaminants in the unsaturated zone are expected to continue to move to the water table with recharge, except in a small area covered by asphalt at the land surface. The gasoline plume from the perforated pipe source has merged with that from the leaking underground storage tank, and the combined plume in the saturated zone is estimated to cover an area of 30,000 square feet. The combined plume is in the upper 20 feet of the saturated zone. The relative distribution of benzene, toluene, ethylbenzene, and xylenes indicate that factors such as sorption, solubility, and susceptibility to microbial degradation are affecting the movement of the combined plume. Given these factors, the plume is expected to move at a rate of less than 1 foot per day.