Environmental Problems, Their Causes, and Sustainability 1

Most hazardous waste in the United States is disposedof on land in deep underground wells, surfaceimpoundments such as ponds, pits, or lagoons, andstate-of-the-art landfills.In deep-well disposal, liquid hazardous wastes arepumped under pressure through a pipe into dry,porous geologic formations or zones of rock far beneathaquifers tapped for drinking and irrigation water.Theoretically, these liquids soak into the porousrock material and are isolated from overlying groundwaterby essentially impermeable layers of rock.Figure 24-21 lists the advantages and disadvantagesof deep-well disposal of liquid hazardous wastes.Take time to study this figure. Many scientists believecurrent regulations for deep-well disposal in theUnited States are inadequate and should be improved.xHOW WOULD YOU VOTE? Do the advantages of deepwelldisposal of hazardous waste outweigh their disadvantages?Cast your vote online at http://biology.brookscole.com/miller14.Surface impoundments are excavated depressionssuch as ponds, pits, or lagoons into which liquid hazardouswastes are drained and stored (Figure 22-9,p. 502). As water evaporates, the waste settles and becomesmore concentrated. Figure 24-22 lists the advantagesand advantages of this method. Study this figurecarefully. EPA studies found that 70% of these storagebasins in the United States have no liners and as manyas 90% may threaten groundwater. According to theAdvantagesSafe method ifsites are chosencarefullyWastes can beretrieved ifproblemsdevelopEasy to doLow costT rade-OffsDeep Underground WellsDisadvantagesLeaks or spills atsurfaceLeaks fromcorrosion of wellcasingExisting fracturesor earthquakescan allow wastesto escape intogroundwaterEncourageswaste productionFigure 24-21 Trade-offs: advantages and disadvantages ofinjecting liquid hazardous wastes into deep underground wells.Pick the single advantage and disadvantage that you think arethe most important.AdvantagesLow constructioncostsLow operatingcostsCan be builtquicklyWastes can beretrieved ifnecessaryCan store wastesindefinitely withsecure doublelinersT rade-OffsSurface ImpoundmentsDisadvantagesGroundwatercontaminationfrom leaking liners(or no lining)Air pollution fromvolatile organiccompoundsOverflow fromfloodingDisruption andleakage fromearthquakesPromotes wasteproductionFigure 24-22 Trade-offs: advantages and disadvantages ofstoring liquid hazardous wastes in surface impoundments. Pickthe single advantage and disadvantage that you think are themost important.EPA, eventually all liners are likely to leak and cancontaminate groundwater.Sometimes liquid and solid hazardous wastes areput into drums or other containers and buried in carefullydesigned and monitored secure hazardous wastelandfills (Figure 24-23, p. 554). Many large companieshave secure landfills to treat their own hazardouswaste but there are 23 commercial hazardous wastelandfills in the United States.Sweden goes further and buries its concentratedhazardous wastes in underground vaults made of reinforcedconcrete. By contrast, in the United Kingdommost hazardous wastes are mixed with householdgarbage and stored in hundreds of conventional landfillsthroughout the country.Hazardous wastes can also be stored in carefullydesigned aboveground buildings. This is especially usefulin areas where the water table is close to the surfaceor areas that are above aquifers used for drinking water.These structures are built to withstand storms andto prevent the release of toxic gases. Leaks are monitoredand any leakage is collected and treated.Each year there are more than 500,000 shipments ofhazardous chemicals in the United States. Most go bytrucks or trains to landfills and incinerators. Hazardousraw materials are also shipped to manufacturingplants. On average, these shipments result in about13,000 accidents per year in the United States, involvingabout 100 deaths, than 10,000 injuries, and evacuationshttp://biology.brookscole.com/miller14553