Tiered Development of Human Health PCLs Page: 22
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Tiered Development of Human Health PCLs under TRRP
use, the Texas-specific median background concentration is the critical PCL.
See TCEQ guidance document Critical PCLs (RG-366/TRRP-25) for more
detailed guidance on determining the critical PCL and Determining
Representative Concentrations (RG-366/TRRP-15) for further discussion of
comparing critical PCLs to representative COC concentrations from the
affected property.
Table 8. Comparison of Site Lead Data with Tiered PCLs
PCL Tier 1 Tier 2 Maximum Concentration
TotSOjlComb (Com/Ind) 1,600 mg/kg 982 mg/kg
TotSOilComb (Residential) 500 mg/kg 982 mg/kg
GWSOilng 3 mg/kg 1051 mg/kg 982 mg/kg
Texas-specific median background 15 mg/kg 982 mg/kg
Consider Progressing to Tier 2
Since soil lead concentrations exceed the residential critical PCL, the person
may decide to either apply the Tier 1 PCL as a remedy objective, or develop a
Tier 2 PCL based on site-specific data. In this case study, the following site-
specific data were collected during the affected property assessment and
installation of monitor wells for use in Tier 2.
The results of pH and textural analysis of soils revealed a site-specific soil pH
of 7.4 to 7.6 for loamy soils. Soils contain concentrations exceeding the Texas-
specific median background concentration of lead to a depth of 2 feet bgs. The
depth to groundwater is 30 feet. The person can choose to use these data as
site-specific affected property parameters to calculate a Tier 2 GWSoilIng PCL.
Therefore, since some of the data pertinent to Tier 2 PCL development were
collected during the affected property assessment, a Tier 2 PCL can now be
developed with minimal additional cost to the person performing the response
action.
Tier 2 calculations for Residential TotSoilcomb. Per 350.76(c) that is specific for
lead, the Tier 1 residential TotSoilcomb PCL for lead is 500 mg/kg. However, the
data needs for Tier 2 are extensive so the tiered process does not provide
flexibility for lead for this exposure pathway.
Tier 2 calculations for GWSoilIng. Since the POE for potential groundwater
ingestion is located below the affected soil, the Tier 2 GWSoilIng PCL is calculated
using the following equation:
GW GW RBELng . LDF L2
Soilin =
""Ksw 4
Per 350.74(f)(2), the GWRBELIng for lead in Class 1 and 2 groundwater is the
most currently available federal action level for drinking water (i.e., 0.015Revised April 2013
TCEQ publication RG-366/TRRP-22
22
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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/m1/22/: accessed July 16, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu; crediting UNT Libraries Government Documents Department.