Urbanization and the Geoenvironment - Sustainable Practices in Geoenvironmental Engineering - page 253

that assesses the capability of the engineered clay barrier material to attenuate the con-
taminants in the leachate plume. This will be discussed in Section 7.5.2.
The EngNA as a direct link from NA is also used as the foundation base for the double-
liner barrier system for landill containment of hazardous waste. There are several options
for the foundation base seen in the diagram. Since a fully compacted foundation base is a
standard requirement—to provide support for the material contained above—one has the
option of working with the native material if it has the proper assimilative potential, or
with imported ill material. Again, the purpose of the foundation base is to provide attenu-
ation of contaminants should leakage of contaminants through the double-liner system
occur. This in essence constitutes a third line of defence against contaminant transport
into the subsurface soils.
One of the signiicant beneits in applying the protocols for evidence of EngNA capability
is the determination of the required thickness of the contaminant attenuating layer and
the engineered clay barrier shown in Figure 7.16. This speciication can be obtained from
the calculations from fate and transport models using the results of supporting laboratory
research on partitioning and other attenuating phenomena. Since the dimensions for the
engineered clay barriers specify “greater than or equal to” designations, application of the
protocols for evidence of EngNA capability will likely provide dimensions that should satisfy
regulatory requirements.

Determine if
engineered clay barrier
material meets
k criterion

Hydraulic conductivity
tests with leachates
as permeants

No Apply procedures for

soil improvement

Yes

Supporting
laboratory research

Determine if
results satisfy requirements
of attenuation

Apply procedures for
development of ENA

No

Modeling
and predictions

Yes

Approve for use as engineered
clay barrier or foundation base

Yes

Modify specifications
for engineered clay
barrier or foundation
base preparation

Determine if
core samples meet
requirements

Coring and samples
from prepared clay
barrier or foundation

No

Yes

Determine if
engineered clay barrier or
foundation base meets regulatory
requirements

Positive evidence
of EngNA
capability

Yes No

FIGURE 7.16
Protocol for determination of positive evidence of EngNA capability as required for use of engineered clay barriers
or as foundation base material for double-liner systems. (Adapted from Yong, R.N. and Mulligan, C.N., Natural
Attenuation of Contaminants in Soils , CRC Press, Boca Raton, FL, 310 pp., 2004.)