The federal regulation
restricts leachate head to 30 cm. The drainage length, drainage slope, permeability
of the drainage materials, and the leachate impingement rate control the head
on the liner.

The HELP model calculates the maximum heads over liner using McEnroe's equation. Due to the complexities involved in the calculations, an easier equation can be used to predict maximum saturated depth over the liner for granular drainage material.

_{}

*H*max = maximum saturated depth over the
liner, L

*L* = distance between collection pipes
(drainage length), L

*q* = infiltration from a 25 year 24 hour
storm, LT^{-1}

*k* = hydraulic conductivity of the drainage
layer, LT ^{-1}

*a*
= slope of the liner, dimensionless

When a drainage net
(material texture 34) is used the spacing between collection pipes in a LCS
using a geonet between the liner and gravel is given by

_{}

* *

*q** *_{req}
= transmissivity of geonet, L^{2}T ^{-1}

**Calculator for the value of maximum head on liner for
granular material**

In simulation 3, the peak
infiltration on to drainage layer-2, was 83.97 mm / d. For the data below,
using the calculator the maximum head on top of layer 3 was calculated.

L = 60 ft.

*q* = 83.97mm/d or 9.718E-05 cm/s

*k* = 0.58E-02 cm/s

*a* =
0.030 (3 %)

*H* max = 125 mm,

**Class Exercise**: Use the liner
calculator to develop plots of head on the liner s a function of liner slope,
distance between pipes, and hydraulic conductivity of the drainage layer.
Discuss the relationship between head on the liner and these variables.