Geotechnical News September 2011
31
WASTE GEOTECHNICS
volumes of MSW that was distributed
among several locations in each city.
For example, there were over 1,000
MSW dumping locations distributed in
the city of Beijing. Most of the simple
dumps have been closed, but controlled
closure measures have not always been
followed.
First-generation Controlled
Landfills
After the first
Technical Standard for
Sanitary Landfill of MSW
was issued
and put into action in 1988, landfill
technology and practice in China shifted
from simple dumping to controlled
landfilling. In the 1990s, so-called first-
generation controlled landfills were built
in many cities around China. During this
period, there were over 800 landfills,
about 45% of which were designed as
controlled landfills. The first-generation
of controlled landfills made use of
vertical barriers and toe drains for
leachate control. Most landfills were
located in a valley or canyon. The
low permeability bedrock generally
formed the shape of a “dustpan” with an
opening downstream from the landfill.
Vertical barriers, extending to the
underlying fresh bedrock, were installed
at the downstream opening. The vertical
barriers and the bedrock were expected
to form a closed barrier system against
the leachate transport to the surrounding
environment. The vertical barriers
commonly used in China consisted
of a plastic concrete cutoff wall in
the soil deposit and/or grout curtain
in the weathered rock. There is still
uncertainty and debate regarding the
long-term performance of this type of
vertical barrier. There are variations
in the geology and barrier design that
need to be taken into consideration.
Toe drains have been used for leachate
drainage at the first-generation
controlled landfills. The toe drains
were usually installed at the retaining
dam downstream of the landfill. Field
observations have shown that there can
be serious clogging problems for the toe
drains after the landfills have been in
operation for a while. The clogging of
toe drains combined with poor surface
water management has resulted in the
continual accumulation of leachate, and
hence, a high leachate mound within the
landfill. Figure 3 shows the distribution
of a leachate mound within the Suzhou
landfill. The plot of the leachate mound
was deduced from field measurements
of pore pressures and unsaturated-
saturated seepage modeling (Chen and
Zhan, 2007). The maximum height
of the leachate mound in the landfill
bottom is 15 m. A substantial perched
leachate mound was also observed on
the intermediate soil cover.
Control of landfill gas emission
was not widely implemented at first-
generation controlled landfills. Few
of the landfills were equipped to gen-
erate energy or recover landfill gas.
Additionally, many landfills had poor
management practices: landfill opera-
tions generally involved poor planning
of waste placement, poor compaction
of waste piles, use of soils for daily
and temporary covers, and poor man-
agement of surface water. As a result,
the daily leachate production at the
first-generation controlled landfills was
commonly more than 30% of the daily
dumping mass of wastes, which was
much greater than expected. The high
leachate production tended to over-
whelm the leachate storage pond and
treatment system. Stated another way,
the first-generation controlled landfills
operated at a low level. There is a lack
of detailed data, but it is quite clear that
some landfills have had an adverse en-
vironmental impact.
Second-generation Controlled
Landfills
In the 2000s, many of the first-
generation landfills had reached their
service design capacity. New and
expanded landfills are being built in
many cities in accordance with the
revised regulation and standards,
including the
Technical Standard for
Sanitary Landfill of MSW
(CJJ17-
2001, CJJ17-2004) and
Pollution
Control Standard for MSW Landfills
(GB 16889-1997, GB 16889-1997-
2008). The new landfills are called
second-generation controlled landfills.
The functionality of this generation
of landfills is quite similar to that of
modern landfills in North America.
A composite liner system, consisting
of a basal sealing liner and a leachate
drainage and collection system
(LDCS), is commonly used for leachate
control. China’s landfill technology and
capacity has increased significantly to
meet the service demand associated
with
rapidly
increasing
waste
generation. The daily filling capacity
for landfills in large cities is commonly
over 3,000 ton/day with a designed
service period of at least 20 years. For
example, the Laogang landfill site in
Shanghai has a daily capacity of 5,000
tons with an estimated service period of
45 years. With an increase in capacity,
the
number of controlled landfills in
China decreased significantly from 571
to 366 from 2001 to 2007.
Many second-generation controlled
landfills have taken measures to re-
duce landfill gas emission. Landfill
gas drainage and/or its collection have
been implemented at most controlled
landfills. Over 20 landfills are equipped
with gas recovery facilities, and the total
generation of electric power is about 50
MW. Several landfills have succeeded
in the application of projects adhering
to the Clean Development Mechanism
(CDM) under the United Nation Frame-
work Convention on Climate Change.
Landfill management practices have
also significantly improved. Many land-
fill operators devote considerable ef-
fort to develop waste phasing schemes
and surface water control measures to
separate precipitation from leachate. Al-
Figure 3. Pore pressures measured in the field and distribution of a leachate mound
predicted by numerical simulation.
