Keros Cartwright

Impact of urban development on the chemical composition of ground water in a fen-wetland complex

A 15-month-long hydrogeologic investigation of a fen-wetland complex in northeastern Illinois, USA indicated the encroachment of ground-water-borne anthropogenic contaminants into two of three high quality fens. Ground-water flow directions and chemical evidence indicated that plumes of ground water with anomalously large concentrations of Na− and Cl− originated from a private septic system and from rock salt spread on an adjacent road. The contamination, in turn, had an adverse effect on fen vegetation; within the plumes, diverse vegetation was replaced by the more salt-tolerant narrow-leaf cattail (Typha angustifolia). Ground water of the third fen contained large concentrations of SO42− as high as 516 mg/L. The SO42− anomaly was observed on a transient and/or seasonal basis in the fen ground water and in an adjacent marsh and pond. Isotopically light δ34S values in these waters indicated that the addition of SO42− resulted from the oxidation of pyrite within underlying peat and/or pyritic gravel. However, the large SO42− concentrations had no discernible effect on fen vegetation. The results of this investigation indicate how easily construction of houses with private septic systems and deicing agents from roadway maintenance can contaminate fen ground water with relatively large concentrations of Na+ and Cl−, resulting in a significant loss of biodiversity in fens.

Hydraulic potential in Lake Michigan bottom sediments

Abstract Cartwright, K., Hunt, C.S., Hughes, G.M. and Brower, R.D., 1979. Hydraulic potential in Lake Michigan bottom sediments. In: W. Back and D.A. Stephenson (Guest-Editors), Contemporary Hydrogeology — The George Burke Maxey Memorial Volume. J. Hydrol., 43: 67-78. The magnitude and direction of ground-water flux in the bottom sediments of Lake Michigan were deduced from measurements made during three shipboard cruises between 1973 and 1975. These factors affect the geochemical environment of the sediments and therefore the distribution of trace elements reported to be present. The near-shore, sandybottom and fine-grained, soft, deep-lake sediments were investigated; areas of hard till or bedrock were not included in the study. Thirty-three piezometers were placed in near-shore sands in waters 5-15 m deep. The piezometers were placed an average of 3 m into the bottom sediment. Water levels from the piezometers averaged 0.6 cm above the lake level, equivalent to an upward hydraulic gradient of about 0.002 cm/cm. Water samples taken from the piezometers have a distinctly different chemical composition from that of the lake water. The total dissolved mineral content and hardness of the ground-water are about twice those of the lake water. Twenty-two hydraulic gradient measurements were made in the fine-grained soft deep-lake sediments in waters 48-140 m deep by using a differential-pressure transducer dropped into the sediments. These measurements show an upward gradient averaging 0.2 cm/cm. No chemical data were obtained for the groundwater in the deep-lake sediments. The results of this study indicate that the groundwater flux is upward through the bottom sediments into Lake Michigan and that there is a chemical change in the water near the water—sediment contact.

Geological considerations in hazardouswaste disposal

Abstract Present regulations assume that long-term isolation of hazardous wastes — including toxic chemical, biological, radioactive, flammable and explosive wastes — may be effected by disposal in landfills that have liners of very low hydraulic conductivity. In reality, total isolation of wastes in humid areas is not possible; some migration of leachate from wastes buried in the gound will always occur. Regulations should provide performance standards applicable on a site-by-site basis rather than rigid criteria for site selection and design. The performance standards should take into account several factors: (1) the categories, segregation, degradation and toxicity of the wastes; (2) the site hydrogeology, which governs the direction and rate of contaminant transport; (3) the attenuation of contaminants by geochemical interactions with geologic materials; and (4) the release rate of unattenuated pollutants to surface or groundwater. An adequate monitoring system is essential. The system should both test the extent to which the operation of the site meets performance standards and provide sufficient warning of pollution problems to allow implementation of remedial measures. In recent years there has been a trend away from numerous, small disposal sites toward fewer and larger sites. The size of a disposal site should be based on the attenuation capacity of the geologic material, which has a finite, though generally not well-defined, limit. For slowly degradable wastes, engineered sites with leachate-collection systems appear to be only a temporary solution since the leachate collected will also require final disposal.

Water movement through an experimental soil liner

A field-scale soil liner was constructed to test whether compacted soil barriers in cover and liner systems could be built to meet the U.S. EPA saturated hydraulic conductivity requirement (≤ 1 × 10-7 cm s-1). The 8 × 15 × 0.9 m liner was constructed in 15 cm compacted lifts using a 20,037 kg pad-foot compactor and standard engineering practices. Water infiltration into the liner has been monitored for one year. Monitoring will continue until water break through at the base of the liner occurs. Estimated saturated hydraulic conductivities were 2.5 × 10-9, 4.0 × 10-8, and 5.0 × 10-8 cm s-1 based on measurements of water infiltration into the liner by large-and small-ring infiltrometers and a water balance analysis, respectively. Also investigated in this research was the variability of the liners hydraulic properties and estimates of the transit times for water and tracers. Small variances exhibited by small-ring flux data suggested that the liner was homogeneous with respect to infiltration fluxes. The predictions of water and tracer breakthrough at the base of the liner ranged from 2.4-12.6 y, depending on the method of calculation and assumptions made. The liner appeared to be saturated to a depth between 18 and 33 cm at the end of the first year of monitoring. Transit time calculations cannot be verified yet, since breakthrough has not occurred. The work conducted so far indicates that compacted soil barriers can be constructed to meet the saturated hydraulic conductivity requirement established by the U.S. EPA.

Predicted Impact of a New Highway on a Spring-Fed Wetland, Cook County, Illinois

The proposed route for a new interstate highway traverses the recharge area of a spring-fed wetland. An investigation was conducted to determine whether the potential loss of recharge would significantly decrease groundwater discharge to the wetland. The local ground-water flow system consists of: a) downward saturated flow through a fine-grained, low-permeability unit, b) downward, unsaturated flow through the upper portion of an underlying coarse-grained, high-permeability unit, c) horizontal saturated flow through the base of the high-permeability unit, and d) discharge to the spring-fed wetland and a nearby creek, both of which are incised into the high-permeability unit. The spring occurs where the water table intersects the land surface. A loss of recharge water may result in a lower water table elevation, which could cause a reduction in overall discharge at the spring. Modeling of ground-water flow suggests that spring discharge may be reduced by 8 to 35 percent after the highway is constructed. The reduction is dependent upon highway alignment and drainage options. The most likely scenarios cause an 8 to 13 percent decrease in discharge.