Economics of Cleanup Methods in Soil Mechanics

Four procedures pre-sented here give the economics and techniques currently used to clean contaminated soil sites.. Determine the profit potential of the wastes considered Profit potenti

Calculation Procedure:

1 Describe how/ dummy piles may be used

A pile made of reinforced concrete and built integrally with the pier is restrained against

rotation relative to the pier As shown in Fig 19c, the fixed supports of pile AB may be re-placed with hinges provided that dummy piles AC and DE are added, the latter being con-nected to the pier by means of a rigid arm through D.

2 Compute the lengths of the dummy piles

IfD is placed at the lower third point as indicated, the lengths to be assigned to the

dum-my piles are

L' = — and L" = — (39)

Replace the given group of piles with its equivalent group, and follow the method of solu-tion in the previous calculasolu-tion procedure

Economics of Cleanup Methods in Soil Mechanics

Many tasks in soil mechanics are hindered by polluted soil which must be cleaned before foundations, tunnels, sluiceways, or other structures can be built Four procedures pre-sented here give the economics and techniques currently used to clean contaminated soil sites While there are numerous rules and regulations governing soil cleaning, these pro-cedures will help the civil engineer understand the approaches being used today With the information presented in these procedures the civil engineer should be able to make an in-telligent choice of a feasible cleanup method And the first procedure gives the economics

of not polluting the soil—i.e., recycling polluting materials for profit Such an approach may be the ultimate answer to soil redmediation—preventing polution before it starts, us-ing the profit potential as the motivatus-ing force for a "clean" planet

RECYCLE PROFIT POTENTIALS

IN MUNICIPAL WASTES

Analyze the profit potential in typical municipal wastes listed in Table 2 Use data on price increases of suitable municipal waste to compute the profit potential for a typical city, town, or state

Calculation Procedure:

1 Compute the percentage price increase for the waste shown

Municipal waste may be classed in several categories: (1) newspapers, magazines, and other newsprint; (2) corrugated cardboard; (3) plastic jugs and bottles—clear or colored; (4) copper wire and pipe Other wastes, such as steel pipe, discarded internal combus-tion engines, electric motors, refrigerators, air condicombus-tioners, etc., require specialized han-dling and are not generated in quantities as large as the four numbered categories For

TABLE 2 Examples of Price Changes in Municipal

Wastes*

Price per ton, $ Last year Current year Newspapers 60 150

Corrugated cardboard 18 150

Plastic jugs, bottles 125 600

Copper wire and pipe 9060 1200

*Based on typical city wastes.

this reason, they are not normally included in estimates of municipal wastes for a given locality

For the four categories of wastes listed above, the percentage price increases in one year for an Eastern city in the United States were as follows: Category 1—newspaper: Percentage price increase = 100(current price, $ - last year's price, $)/last year's price, $

Or 100(150 60)760 = 150 percent Category 2: Percentage price increase = 100(150 -18)718 = 733 percent Category 3: Percentage price increase = 100(600 - 125)7125 = 380 percent Category 4: Percentage price increase = 100(1200 - 960)7960 = 25 percent

2 Determine the profit potential of the wastes considered

Profit potential is a function of collection costs and landfill savings When collection of several wastes can be combined to use a single truck or other transport means, the profit potential can be much higher than when more than one collection method must be used Let's assume that a city can collect Category 1, newspapers, and Category 3, plastic, in

one vehicle The profit potential, P, will be: P = (sales price of the materials to be

recy-cled, $ per ton - cost per ton to collect the materials for recycling, $) With a cost of $80

per ton for collection, the profit for collecting 75 tons of Category 1 wastes would be P =

75($150 - $80) = $5250 For collecting 90 tons of Category 3 wastes, the profit would be

P = 90($600-80) = $46,800

Where landfill space is saved by recycling waste, the dollar saving can be added to the profit Thus, assume that landfill space and handling costs are valued at $30 per ton The profit on Category 1 waste would rise by 75($3O) = $2250, while the profit on Category 3 wastes would rise by 90($30) = $2700 When collection is included in the price paid for municipal wastes, the savings can be larger because the city or town does not have to use its equipment or personnel to collect the wastes Hence, if collection can be included in a waste recycling contract the profits to the municipality can be significant However, even when the municipality performs the collection chore, the profit from selling waste for re-cycling can still be high In some cities the price of used newspapers is so high that gangs steal the bundles of papers from sidewalks before they are collected by the city trucks

Related Calculations Recyclers are working on ways to reuse almost all the

ordinary waste generated by residents of urban areas Thus, telephone books, magazines, color-printed advertisements, waxed milk jars, etc are now being recycled and converted into useful products The environmental impact of these activities is positive throughout Thus, landfill space is saved because the recycled products do not enter landfill; instead they are remanufactured into other useful products Indeed, in many cases, the energy re-quired to reuse waste is less than the energy needed to produce another product for use in place of the waste

Some products are better recycled in other ways Thus, the United States discards,

ac-cording to industry records, over 12 million computers a year These computers, weighing

an estimated 600 million pounds (272 million kg) contribute toxic waste to landfills Bet-ter that these compuBet-ters be contributed to schools, colleges, and universities where they can be put to use in student training Such computers may be slower and less modern than today's models, but their value in training programs has little to do with their speed or software Instead, they will enable students to learn, at minimal cost to the school, the fundamentals of computer use in their personal and business lives

Recycling waste products has further benefits for municipalities The U.S Clean Air Act's Title V consolidates all existing air pollution regulations into one massive operating permit program Landfills that burn, pollute the atmosphere And most of the waste we're considering in this procedure burns when deposited in a landfill By recycling this waste the hazardous air pollutants they may have produced while burning in a landfill are elimi-nated from the atmosphere This results in one less worry and problem for the municipal-ity and its officials In a recent year, the U.S Environmental Protection Agency took 2247 enforcement actions and levied some $165-million in civil penalties and criminal fines against violators

Any recycling situation can be reduced to numbers because you basically have the cost of collection balanced against the revenue generated by sale of the waste Beyond this are nonfinancial considerations related to landfill availability and expected life-span

If waste has to be carted to another location for disposal, the cost of carting can be fac-tored into the economic study of recycling

Municipalities using waste collection programs state that their streets and sidewalks are cleaner They attribute the increased cleanliness to the organization of people's think-ing by the waste collection program While stiff fines may have to be imposed on non-complying individuals, most cities report a high level of compliance from the first day of the program The concept of the "green city" is catching on and people are willing to sep-arate their trash and insert it in specific containers to comply with the law

"Green products, i.e., those that produce less pollution, are also strongly favored by the general population of the United States today Manufacturing companies are finding a greater sales acceptance for their "green" products Even automobile manufacturers are stating the percentage of each which is recyclable, appealing to the "green" thinking per-meating the population

Recent studies show that every ton of paper not landfilled saves 3 yd3 (2.3 m3) of land-fill space Further, it takes 95 percent less energy to manufacture new products from recy-cled materials Both these findings are strong motivators for recycling of waste materials

by all municipalities and industrial firms

Decorative holiday trees are being recycled by many communities The trees are chipped into mulch which are given to residents and used by the community in parks, recreation areas, hiking trails, and landfill cover Seaside communities sometimes plant discarded holiday trees on beaches to protect sand dunes from being carried away by the sea

CHOICE OF CLEANUP TECHNOLOGY

FOR CONTAMINATED WASTE SITES

A contaminated waste site contains polluted water, solid wastes, dangerous metals, and organic contaminants Evaluate the various treatment technologies available for such a site and the relative cost of each Estimate the landfill volume required if the rate of solid-waste generation for the site is 1,500,000 Ib (681,818 kg) per year What land area will be

required for this waste generation rate if the landfill is designed for the minimum recom-mended depth of fill? Determine the engineer's role in site cleanup and in the economic studies needed for evaluation of available alternatives

Calculation Procedure:

1 Analyze the available treatment technologies for cleaning contaminated waste sites

Table 3 lists 13 available treatment technologies for cleaning contaminated waste sites, along with the type of contamination for which each is applicable, and the relative cost of the technology This tabulation gives a bird's eye view of technologies the engineer can consider for any waste site cleanup

When approaching any cleanup task, the first step is to make a health-risk assessment

to determine if any organisms are exposed to compounds on, or migrating from, a site If there is such an exposure, determine whether the organisms could suffer any adverse health effects The results of a health-risk assessment can be used to determine whether there is sufficient risk at a site to require remediation

This same assessment of risks to human health and the environment can also be used

to determine a target for the remediation effort that reduces health and environmental risks to acceptable levels It is often possible to negotiate with regulatory agencies a re-mediation level for a site based on the risk of exposure to both a maximum concentration

of materials and a weighted average The data in Table 2 are useful for starting a site cleanup having the overall goals of protecting human health and the environment

2 Make a health-risk assessment of the site to determine

cleanup goals1

Divide the health-risk assessment into these four steps: (1) Hazard Identification—Asks

"Does the facility or site pose sufficient risk to require further investigation?" If the

an-swer is Yes, then: (a) Select compounds to include in the assessment; (b) Identify exposed populations; (c) Identify exposure pathways.

(2) Exposure Assessment—Asks "To how much of a compound are people and the en-vironment exposed?" For exposure to occur, four events must happen: (a) release; (b) contact; (c) transport; (d) absorption Taken together, these four events form an exposure

pathway There are many possible exposure pathways for a facility or site

(3) Toxicity Assessment—Asks "What adverse health effects in humans are potentially

caused by the compounds in question?" This assessment reviews the threshold and non-threshold effects potentially caused by the compounds at the environmental concentration levels

(4) Risk Characterization—Asks "At the exposures estimated in the Exposure

Assess-ment, is there potential for adverse health effects to occur; if so, what kind and to what ex-tent?" The Risk Characterization develops a hazard index for threshold effects and esti-mates the excess lifetime cancer-risk for carcinogens

3 Select suitable treatment methods and estimate the

relative costs

The site contains polluted water, solid wastes, dangerous metals, and organic contami-nants Of these four components, the polluted water is the simplest to treat Hence, we will look at the other contaminants to see how they might best be treated As Table 3

Copper, David R., "Cleaning Up Contaminated Waste Sites," Chemical Engineering, Aug.,

1989.

TABLE 3 Various Treatment Technologies Available to Clean Up a Contaminated Waste Site*

Relative cost Low

Low

Medium

Medium to high

High Medium to high

Low

Applicable contamination Volatile and some semivolatile organics

Organic wastes and certain (soluble) inorganic wastes Applies primarily to metals; mixed results when used to treat organics

Volatile and semivolatile organics;

volatile metals such as elemental mercury

Organic wastes; metals do not burn, but concentrate in ash

Organic wastes

Metals

Description Air flow is induced through the soil

by pulling a vacuum on holes drilled into the soil, and carries out volatilized contaminants Excavated soil is flushed with water

or other solvent to leach out contaminants

Waste is mixed with agents that physically immobilize or chemically precipitate constituents Solid waste is heated to 200-80O 0 F

to drive off volatile contaminants, which are separated from the waste and further treated

Waste is burned at very high temperatures to destroy organics Heat volatilizes contaminants into

an oxygen-starved air system at temperatures sufficient to pyrolzye the organic contaminants Frequently, the heat is delivered by infrared radiation

Solubilized metals are separated from water by precipitating them

as insoluble salts

Technology

Soil vapor extraction

Soil washing or soil flushing

Stabilization and solidification

Thermal desorption

Incineration

Thermal pyrolysis

Chemical precipitation

Low

Low to medium when regeneration is possible

Low Low but rising fast

Medium

Mostly volatile organics

Mostly volatile organics

Most organics, though normally restricted to those with sufficien volatility to allow carbon regeneration

Organic wastes Solid, nonhazardous wastes

Inorganic wastes, possibly organic wastes; not applicable to very large volumes

Contaminated water is pumped through a column where it is contacted with a countercurrent air flow, which strips out certain pollutants

Similar to air stripping except steam is used as the stripping fluid

Organic contaminants are removed from a water or air stream by passing the stream through a bed

of activated carbon that absorbs the organics

Bacterial degradation of organic compounds is enhanced Covering solid wastes with soil in a facility designed to minimize leachate formation Electric current is passed through soil or waste, which increases the temperature and melts the waste

or soil The mass fuses upon cooling

Aeration or air stripping

Steam stripping

Carbon adsorption

Bioremediation

Landfilling

In situ vitrification

* Chemical Engineering.

shows, thermal desorption treats volatile and semivolatile organics and volatile metals; cost is medium to high Alternatively, incineration handles organic wastes and metals with an ash residue; cost is high Nonhazardous solid wastes can be landfilled at low cost But the future cost may be much higher because landfill costs are rising as available land becomes scarcer

Polluted water can be treated with chemicals, aeration, or air stripping—all at low cost None of these methods can be combined with the earlier tentative choices Hence, the polluted water will have to be treated separately

4 Determine the landfill dimensions and other parameters

Annual landfill space requirements can be determined from V A = Wl 1100, where V A

-landfill volume required, per year, yd3 (m3); W= annual weight, Ib (kg) of waste

generat-ed for the landfill; 1100 lb/yd3 (650 kg/m3) = solid waste compaction per yd3 or m3

Sub-stituting for this site, V A = 1,500,000/1100 = 1363.6 yd3 (1043.2 m3)

The minimum recommended depth for landfills is 20 ft (6 m); minimum

recommend-ed life is 10 years If this landfill were designrecommend-ed for the minimum depth of 20 ft (6 m), it would have an annual required area of 1363.6 x 27 fVVyd3 •= 36,817.2 ft3/20 ft high -1840.8 ft2 (171.0 m2), or 1840.9 ft2/43,560 ft2/acre = 0.042 acre (169.9 m2 0.017 ha) per year With a 10-year life the landfill area required to handle solid wastes generated for this site would be 10 x 0.042 = 0.42 acre (1699.7 m2, 0.17 ha); with a 20-year life the area required would be 20 x 0.042 = 0.84 acre (3399.3 m2; 0.34 ha)

As these calculations show, the area required for this landfill is relatively modest— less than an acre with a 20-year life However, in heavily populated areas the waste gen-eration could be significantly larger Thus, when planning a sanitary landfill, the usual as-sumption is that each person generates 5 Ib (2.26 kg) per day of solid waste This number

is based on an assumption of half the waste (2.5 Ib; 1.13 kg) being from residential sources and the other half being from commercial and industrial sources Hence, in a city having a population of !-million people, the annual solid-waste generation would be 1,000,000 people x 5 lb/day per person x 355 days per year = 1,825,000,000 Ib (828,550,000 kg)

Following the same method of calculation as above, the annual landfill space

require-ment would be V A = 1,825,000,000/1100 = 1,659,091 yd3 (1,269,205 m3) With a 20-ft (6-m) height for the landfill, the annual area required would be 1,659,091 x 27/20 x

43,560 = 51.4 acres (208,002 m2; 20.8 ha) Increasing the landfill height to 40 ft (12 m) would reduce the required area to 25.7 acres (104,037 m2; 10.4 ha) A 60-ft high landfill would reduce the required area to 17.1 acres (69,334 m2; 6.9 ha) In densely populated ar-eas, landfills sometimes reach heights of 100 ft (30.5 m) to conserve horizontal space This example graphically shows why landfills are becoming so much more expensive Further, with the possibility of air and stream pollution from a landfill, there is greater regulation of landfills every year This example also shows why incineration of solid waste to reduce its volume while generating useful heat is so attractive to communities and industries Further advantages of incineration include reduction of the possibility of groundwater pollution from the landfill and the chance to recover valuable minerals which can be sold or reused Residue from incineration can be used in road and highway construction or for fill in areas needing it

Related Calculations Use this general procedure for tentative choices of

treat-ment technologies for cleaning up contaminated waste sites The greatest risks faced by industry are where human life is at stake Penalties are severe where human health is en-dangered by contaminated wastes Hence, any expenditures for treatment equipment can usually be justified by the savings obtained by eliminating lawsuits, judgments, and years

of protracted legal wrangling A good example is the asbestos lawsuits which have been

in the courts for years

To show what industry has done to reduce harmful wastes, here are results published

in the Wall Street Journal for the years 1974 and 1993: Lead emissions declined from

223,686 tons in 1973 to 4885 tons in 1993 or to 2.2 percent of the original emissions; car-bon monoxide emissions for the same period fell from 124.8 million tons to 97.2 million tons, or 77.9 percent of the original; rivers with fecal coliform above the federal standard were 31 percent in 1974 and 26 percent in 1994; municipal waste recovered for recycling was 7.9 percent in 1974 and 22.0 percent in 1994

The simplest way to dispose of solid wastes is to put them in landfills This practice was followed for years, but recent studies show that rain falling on landfilled wastes seeps through and into the wastes, and can become contaminated if the wastes are harmful Eventually, unless geological conditions are ideal, the contaminated rainwater seeps into the groundwater under the landfill Once in the groundwater, the contaminants must be treated before the water can be used for drinking or other household purposes

Most landfills will have a leachate seepage area, Fig 21 There may also be a contam-inant plume, as shown, which reaches, and pollutes, the groundwater This is why more and more communities are restricting, or prohibiting, landfills Engineers are therefore more pressed than ever to find better, and safer, ways to dispose of contaminated wastes And with greater environmental oversight by both Federal and State governments, the pressure on engineers to find safe, economical treatment methods is growing The sug-gested treatments in Table 2 are a good starting point for choosing suitable and safe ways

to handle contaminated wastes of all types

Landfills must be covered daily A 6-in (15-cm) thick cover of the compacted refuse is required by most regulatory agencies and local authorities The volume of landfill cover,

ft3, required each day can be computed from: (Landfill working face length, ft)(landfill working width, ft)(0.5) Multiply by 0.0283 to convert to m3 Since the daily cover,

usual-ly soil, must be moved by machinery operated by humans, the cost can be significant when the landfill becomes high-more than 30 ft (9.1 m) The greater the height of a land-fill, the more optimal, in general, is the site and its utilization For this reason, landfills have grown in height in recent years in many urban areas

Table 3 is the work of David R Hopper, Chemical Process Engineering Program Manager, ENSR Consulting and Engineering, as reported in Chemical Engineering maga-zine

CLEANING UPA CONTAMINATED WASTE

SITE VIA BIOREMEDIATION

Evaluate the economics of cleaning up a 40-acre (161,872 m2) site contaminated with pe-troleum hydrocarbons, gasoline, and sludge Estimates show that some 100,000 yd3 (76,500 m3) must be remediated to meet federal and local environmental requirements The site has three impoundments containing weathered crude oils, tars, and drilling muds ranging in concentration from 3800 to 40,000 ppm, as measured by the Environmental Protection Agency (EPA) Method 8015M While hydrocarbon concentrations in the soil are high, tests for flash point, pH, 96-h fish bioassay, show that the soil could be classified

as nonhazardous Total petroleum hydrocarbons are less than 500 ppm Speed of treat-ment is not needed by the owner of the project Show how to compute the net present

val-ue for the investment in alternative treatment methods for which the parameters are given

in step 4 of this procedure

FIGURE 21 Leachate seepage in landfill (McGraw-Hill).

Calculation Procedure:

1 Compare the treatment technologies available

A number of treatment technologies are available to remediate such a site Where total pe-troleum hydrocarbons are less than 500 ppm, as at this site, biological land treatment is usually sufficient to meet regulatory and human safety needs Further, hazardous and nonhazardous waste cleanup via bioremediation is gaining popularity One reason is the

TABLE 4 Comparison of Biological Treatment Technologies*

Type/cost ($/yd 3 )

Land treatment

$30-$90

Bioventing

$50-$120

Bioreactor

$150-$250

Advantages

• Can be used for in situ or ex situ treatment depending upon contaminant and soil type

• Little or no residual waste streams generated

• Long history of effective treatment for many petroleum compounds (gasoline, diesel)

• Can be used as polishing treatment following soil washing or bioslurry treatment

• Excellent removal of volatile compounds from soil matrix

• Depending upon vapor treatment method, little or no residual waste streams to dispose

• Moderate treatment time

• Can be used for in situ or ex situ treatment depending upon contaminant and soil type

• Enhanced separation of many contaminants from soil

• Excellent destruction efficiency

of contaminants

• Fast treatment time

Disadvantages

• Moderate destruction efficiency depending upon contaminants

• Long treatment time relative to other methods

• In situ treatment only practical when contamination is within two feet of the surface

• Requires relatively large, dedicated area for treatment cell

• Treatment of vapor using activated carbon can be expensive at high concentrations of contaminants

• System typically requires an air permit for operation

• High mobilization and demobilization costs for small projects

• Materials handling requirements increase costs

• Treated solids must be dewatered

• Fullscale application has only become common in recent years

* Chemical Engineering magazine.

high degree of public acceptance of bioremediation vs alternatives such as incineration The Resource Conservation and Recovery Act (RCRA) defines hazardous waste as specifically listed wastes or as wastes that are characteristically toxic, corrosive, flamma-ble, or reactive Wastes at this site fit certain of these categories

Table 4 compares three biological treatment technologies currently in use The type of treatment, and approximate cost, $/ft3 ($/m3), are also given Since petroleum hydrocar-bons are less than 500 ppm at this site, biological land treatment will be chosen as the treatment method

Looking at the range of costs in Table 4 shows a minimum of $30/yd3 ($39/m3) for land treatment and a maximum of $250/yd3 ($327/m3) for bioreactor treatment This is a ratio of $250/$30 = 8.3:1 Thus, where acceptable results will be obtained, the lowest cost treatment technology would probably be the most suitable choice