(Excerpts from: U.S. Environmental Protection Agency, The Prevalence
of Subsurface Migration of Hazardous Chemical Substances at Selected
Industrial Waste Land Disposal Sites, U.S. Environmental Protection
Agency, EPA/530/SW-634, October, 1977, 528 p..)
(Study produced under contract by Geraghty & Miller)
Monitoring wells were sampled at 50 land disposal sites that had received large volumes of industrial wastes. The facilities include landfills, lagoons, and combinations of the two, both active and abandoned. They are located in 11 States in the humid region, east of the Mississippi River. The purpose of the investigation was to determine the prevalence of subsurface migration of hazardous chemical constituents.
The sites selected are representative of typical industrial land disposal facilities, and are situated in a wide variety of geologic environments. No previous contamination of groundwater with hazardous substances had been reported before sampling and waste disposal had been in progress for a minimum of three years. To meet the project site selection criteria, 727 facilities were inventoried in 41 States, and regulatory agency files were examined in 23 States. From this data base, 122 sites were selected for field inspection, the purpose of which was to determine geologic and hydrologic conditions, facility design and operation, and availability of monitoring wells. About 50 percent of the inspected facilities already contained monitoring wells, and nine percent are equipped with some type of engineered-ground-water protection system such as a liner. Based on the inspections, the final 50 sites to be sampled were chosen.
Ground water was considered contaminated with hazardous substances if one or more of the following constituents was detected: (1) heavy metals other than iron and manganese, (2) cyanide, arsenic, and selenium, (3) organic substances as determined by gas chromatography. One hundred seventy samples were collected for analysis from waste disposal sources, soil cores, springs, and wells, including 59 wells drilled at 19 sites specifically for this project.
Industrial land disposal sites are surrounded by other sources which also have the potential to add contaminants to ground water, e.g. septic tanks, leaky storage tanks and sewer lines, spills, agricultural lands receiving fertilizers and pesticides, and highway runoff. Thus, ground water free of some type of degradation is seldom present in urban, industrial, and agricultural areas. Therefore, four very strict criteria were used to evaluate whether migration of hazardous substances could be confirmed at a particular site and to determine which specific inorganic and/or organic chemicals had migrated at that site. First, one or more hazardous constituents must be detected beyond the boundary of the waste deposition area. Second, the concentration of a hazardous substance must exceed the concentration of the same substance in water from a background well or other background ground-water source. Third, all wells used to evaluate a site must tap the same aquifer. Finally, based on an interpretation of geohydrology and overall ground-water chemistry, the data must identify the landfill or lagoon under study as the source of the inorganic or organic substance.
At 43 of 50 sites, migration of one or more hazardous constituents was confirmed according to project criteria. At four other sites, although background wells had been chosen, the areal extent of ground water containing hazardous substances was greater than expected, or ground-water movement was not in the direction assumed during the field inspection prior to drilling and/or sampling. However, contamination by heavy metals and/or organic chemicals was detected at these four sites. At three sites, background data were not available because of the inability to obtain water from wells that had previously been chosen for background. Again, contamination with hazardous constituents was found in the monitoring wells sampled at the three sites.
Organic contaminants were detected at 40 of the 50 sites. Because most analyses were made by gas chromatography alone, individual organic compounds were not always identified. At 27 sites, migration of organic chemicals was confirmed according to the strict project criteria. At 13 sites, although organic compounds were detected in ground water, the landfill or lagoon under study could not be clearly identified as the source of organic contamination. Where this occurred, the site was ruled out as one at which organic substances had migrated. Using similar criteria, heavy metals, excluding iron and manganese, were found to be present at 49 sites and were confirmed to have migrated at 40 sites. Selenium, arsenic, and/or cyanide were found to be present at 37 sites, and were confirmed to have migrated at 30 sites.
In all, 86 wells and springs yielded water containing one or more hazardous substances with concentrations above background. The distance of the wells from the disposal area ranged from 3 m (10 ft) to more than 300 m (1,000 ft) . Depths ranged from about 2 m (6 ft) to 49 m (160 ft).
Twelve hazardous inorganic constituents were detected above background concentrations. The five most frequently occurring were selenium, barium, cyanide, copper, and nickel in that order. Organic substances that were identified in water from monitoring wells included PCB's, chlorinated phenols, benzene and derivatives, and organic solvents.
At 26 sites, hazardous inorganic constituents in water from one or more monitoring wells exceeded the EPA drinking water limits. Of the hazardous substances, selenium most frequently exceeded drinking water limits, followed by arsenic, chromium, and lead.. Halogenated pesticides, presently included in EPA drinking water standards, were analyzed for but not found.
- Ground-water contamination at industrial waste land disposal sites is a common occurrence.
- Hazardous substances from industrial waste land disposal sites are capable of migrating into and with ground water.
- Few hydrogeologic environments are suitable for land disposal of hazardous waste without some risk of groundwater contamination.
- Continued development of programs for monitoring industrial waste land disposal sites is necessary to protect ground-water quality.
- Most old industrial waste disposal sites, both active and abandoned, are located in geologic environments where ground water is particularly susceptible to contamination.
- Many waste disposal sites are located where the underlying aquifer system can act as a pipeline for discharge of hazardous substances to a surface-water body.
- At sites presently monitored, the use of wells as an aid in evaluating ground-water conditions is generally poor, due to inadequacies with respect to one or more of the following parameters:
- number of wells
- distance of wells from potential contamination source
- positioning of wells in relation to groundwater flow
- selection of screened intervals
- use of proper well construction materials
- sealing against surface-water contamination, or inter-aquifer water exchange
- completion methods, such as development, maintenance, and protection against vandalism
At sites presently monitored, the sampling program is generally poor due to inadequacies with respect to one or more of the following parameters:
- obtaining a sample representative of aquifer water
- sample preparation
- frequency of sampling
- availability of background water quality data
- selection of constituents to be analyzed
- availability of laboratories
- maintaining records in usable form
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