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,
ft^3 , 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 m^3. 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 m^2 ) site contaminated with pe-
troleum hydrocarbons, gasoline, and sludge. Estimates show that some 100,000 yd^3
(76,500 m^3 ) 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.