Page 365 - Materials Chemistry, Second Edition

CAT3525_C10.qxd 1/31/2005 12:00 PM Page 336
336 Waste Management Practices: Municipal, Hazardous, and Industrial
This equation can be used to calculate the maximum allowable pipe spacing based on the
maximum allowable design head, anticipated leachate impingement rate, slope of the liner, and
permeability of drainage materials. The equation suggests that, holding all other parameters con-
stant, the closer the pipes are placed, the lower the head will be. A reduced head on the liner results
in a lower hydraulic driving force through the liner, and the consequence of a puncture in the liner
is similarly reduced.

EXAMPLE 10.7

Determine the spacing between pipes in a leachate-collection system using granular drainage mate-
rial and the following properties. Assume that in the most conservative design all stormwater from
a 25-year, 24-h storm enters the leachate collection system.

Design storm (25 years, 24 hours ) 8.2 in. 0.00028 cm/s
Hydraulic conductivity 10 2 cm/sec
Drainage slope 1.5%

Maximum design depth on liner 14.2 cm
2Y max
P
2
q Ktan α Ktanα q 1/2
2
1 tan α
K q q K
2(14.2)
P 1105 cm
0.0028 0.01(0.15) 2 0.01(0.15) 0.0028 1/2
1 (0.015)
2
0.01 0.00028 0.00028 0.01

10.4.26 SUMPS
Sumps are situated in engineered low points in the composite liner system and are constructed
to collect leachate. Figure 10.25 shows a low-volume sump. The leachate removal standpipe must
be extended through the entire landfill from lowest liner to the cover, and then through the cover
itself. It also must be maintained for the entire postclosure care period of 30 years or longer.
Because of the difficulty in seam-testing sumps, sump areas often are designed with an additional
layer of geomembrane. Figure 10.26 shows a sump being installed in a landfill.

10.4.27 LEACHATE TREATMENT
The recovered leachate is either stored in a tank until it can be safely removed, diverted directly into
the sanitary sewer, or reapplied to the surface of the landfill. Leachate collection tanks should be
both corrosion-resistant and able to withstand climatic extremes.
Treatment of leachate must meet the water quality standards set by regulatory authorities. There
are six primary types of leachate treatment:

● Aerobic biological
● Anaerobic biological
● Land application
● Physicochemical
● Recycling leachate though the landfill
● Treatment with municipal wastewater