area of 15,000 m
2 . Furthermore, the leachate collection system is installed above
the seepage control layer to ensure no leachate infiltrates underground. The system
includes a 30 cm thick drainage layer comprised of river pebbles (with a diameter
of 5–10 cm). About 500 m long drainage pipes, made of DX160 HDPE, can drain
the leachate to the 150 m
3 leachate sump for collection. The water is naturally
evaporated, while the residues are landfilled. In addition, the excess supernatants
can be used for spraying the land surface of the landfill to suppress dust. With an
effective capacity of 150 m
3 , the leachate sump can store the leachate produced on
the maximum precipitation day. Mechanical spray for recharge and atmospheric
evaporation are adopted for leachate treatment, considering local great evaporation.
(b) Layout of groundwater monitoring wells
In order to timely grasp the results of seepage control and monitor groundwater and
soil pollution associated with leachate, five monitoring wells are deployed for the
landfill:
• A well is deployed, 30–50 m upstream of the landfill (according to groundwater
flow direction), to monitor the environmental background;
• Two wells are deployed, 30–50 m on the two sides of the landfill each, to
monitor pollution diffusion;
• Two wells are deployed, 30 and 50 m downstream of the landfill respectively, to
monitor pollution status.
The above-mentioned wells for monitoring pollution diffusion and pollution
status were not used in this survey. Instead, appropriate downstream pumping wells
and household wells are selected to monitor the groundwater pollution. The
background values are derived from the data of background monitoring wells.
At the time of the survey, there was no vegetation distributed in the vicinity of
the landfill. A 120.5 m deep pumping well about 4 km downstream of the landfill is
identified as the No. 1 monitoring well, where the depth to water table is 35.35 m.
The well was created at the end of 2011. The water quality data for the year 2011
and the observational data for the year 2015 have been collected. According to the
actual investigation, another nine downstream pumping wells and household wells
were selected, making a total of ten monitoring wells.
The background values are monitored when the landfill is put into use, and
thereafter, monitoring is conducted every year, once during the dry, wet and normal
seasons each, until the landfill runs stably.
(c) Sampling and detection
• Sampling
In order to further ascertain the groundwater quality of the landfill, groundwater
samples are taken at the ten monitoring wells for analysis.
5.2 Northwest China
171
2 . Furthermore, the leachate collection system is installed above
the seepage control layer to ensure no leachate infiltrates underground. The system
includes a 30 cm thick drainage layer comprised of river pebbles (with a diameter
of 5–10 cm). About 500 m long drainage pipes, made of DX160 HDPE, can drain
the leachate to the 150 m
3 leachate sump for collection. The water is naturally
evaporated, while the residues are landfilled. In addition, the excess supernatants
can be used for spraying the land surface of the landfill to suppress dust. With an
effective capacity of 150 m
3 , the leachate sump can store the leachate produced on
the maximum precipitation day. Mechanical spray for recharge and atmospheric
evaporation are adopted for leachate treatment, considering local great evaporation.
(b) Layout of groundwater monitoring wells
In order to timely grasp the results of seepage control and monitor groundwater and
soil pollution associated with leachate, five monitoring wells are deployed for the
landfill:
• A well is deployed, 30–50 m upstream of the landfill (according to groundwater
flow direction), to monitor the environmental background;
• Two wells are deployed, 30–50 m on the two sides of the landfill each, to
monitor pollution diffusion;
• Two wells are deployed, 30 and 50 m downstream of the landfill respectively, to
monitor pollution status.
The above-mentioned wells for monitoring pollution diffusion and pollution
status were not used in this survey. Instead, appropriate downstream pumping wells
and household wells are selected to monitor the groundwater pollution. The
background values are derived from the data of background monitoring wells.
At the time of the survey, there was no vegetation distributed in the vicinity of
the landfill. A 120.5 m deep pumping well about 4 km downstream of the landfill is
identified as the No. 1 monitoring well, where the depth to water table is 35.35 m.
The well was created at the end of 2011. The water quality data for the year 2011
and the observational data for the year 2015 have been collected. According to the
actual investigation, another nine downstream pumping wells and household wells
were selected, making a total of ten monitoring wells.
The background values are monitored when the landfill is put into use, and
thereafter, monitoring is conducted every year, once during the dry, wet and normal
seasons each, until the landfill runs stably.
(c) Sampling and detection
• Sampling
In order to further ascertain the groundwater quality of the landfill, groundwater
samples are taken at the ten monitoring wells for analysis.
5.2 Northwest China
171