Tiered Development of Human Health PCLs Page: 6
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Tiered Development of Human Health PCLs under TRRP
In deciding which tier(s) to apply for a given situation, evaluate the data
needed to support PCL development at a higher tier, and the likelihood that
developing PCLs under a higher tier will modify the PCL such that reduced
remedial costs or remedial timeframes will yield savings that exceed the cost
of establishing PCLs at the higher tier. Situations such as a small volume of
shallow soil affected with low mobility COCs may be quickly and effectively
addressed under Tier 1 while a large contamination problem involving
multiple COCs and affected environmental media may be more effectively
addressed under a higher tier.
There is no need to calculate Tier 1 PCLs. TCEQ has already calculated and
published Tier 1 PCLs for over 675 COCs. Download Tier 1 PCL Tables from
the TRRP Web page listed at the beginning of this document. See guidance
document Tier 1 PCL Tables (RG-366/TRRP-23) for instructions on using the
tables and an explanation of the information that can be obtained from those
tables. In the event a Tier 1 PCL is not available, a Tier 1 PCL can be requested
from TCEQ. Additionally, the Tier 1 PCLs are updated each year. For more
information on requesting Tier 1 PCLs and the annual update, see TCEQ
guidance document Toxicity Factors and Chemical/Physical Parameters (RG-
366/TRRP-19).
Flexibility of the Tiered Human Health PCL Development
Process
A PCL is a numeric value that is either calculated from a mathematical
equation or based on a policy, such as a federal maximum contaminant level
(MCL). The PCL equations have two parts: RBEL and natural attenuation
factor (NAF). The relationship between the two is shown in Table 2. The
RBEL is the exposure medium COC concentration which is protective of human
health at the point of exposure. See Figure: 30 TAC 350.74(a) in the TRRP
rule for the RBEL equations. The NAF is based on fate and transport modeling
of the COC. See Figure: 30 TAC 350.75(b)(1) in the TRRP rule for the Tier 1
NAF equations.
Table 2 lists the potential modifications under Tier 2 and 3 for each exposure
pathway. Where tiered modifications are allowed for a given exposure
pathway, the modifications may be to the RBEL, NAF, or both. However, there
is minimal flexibility to modify residential RBELs. More flexibility is provided
for modification of commercial/industrial RBELs, but adjustments are strictly
controlled by the requirements of 350.74(j)(2). The greatest flexibility is the
ability to modify site-specific information in the calculation of NAFs.Revised April 2013
TCEQ publication RG-366/TRRP-22
6
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Texas Commission on Environmental Quality. Remediation Division. Tiered Development of Human Health PCLs, pamphlet, April 2013; Austin, Texas. (https://texashistory.unt.edu/ark:/67531/metapth624526/m1/6/: accessed July 16, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu.; crediting UNT Libraries Government Documents Department.