Iowa Administrative Code › Agency 567 - Environmental Protection Commission › Title IX - Spills and Hazardous Conditions › Chapter 135 - Technical Standards and Corrective Action Requirements for Owners and Operators of Underground Storage Tanks › Rule 567-135.12 - Tier 2 and 3 Site Classification and Corrective Action Response

Current through Register Vol. 47, No. 3, July 24, 2024
(1)
General.
1995 Iowa Code section
				455B.474(1)
"d"
(2) provides that sites shall be classified as
				high risk, low risk and no action required. Risk classification is accomplished
				by comparing actual contaminate concentrations to the concentrations that are
				predicted by the use of models. Concentrations must be compared to the
				simulation model which uses the maximum concentrations at a source and predicts
				at what levels actual or potential receptors could be impacted in the future.
				Concentrations must also be compared to the site-specific target level line
				which assumes a target level concentration at the point of exposure and is used
				to predict the reduction in concentration that must be achieved at the source
				in order to meet the applicable target level at the point of exposure. These
				models not only predict concentrations at points of exposure or a point of
				compliance at a source but also predict a distribution of concentrations
				between the source and the point of exposure which may also be points of
				compliance. The comparison of contaminate concentrations with these
				distribution curves primarily is considered for purposes of judging whether the
				modeled data is reasonably predictive and what measures such as monitoring are
				prudent to determine the reliability of modeled data and actual contaminate
				concentrations.
For the soil vapor to enclosed space and soil to water line
				  pathways, there are no horizontal transport models to use for predicting future
				  impacts. Therefore, for these pathways, sites are classified as high risk, low
				  risk or no action required based on specified criteria below and in rule
				  567-135.10
				  (455B).
(2)
High
				risk classification.
Except as provided below, sites shall be
				classified as high risk if, for any pathway, any actual contaminate
				concentrations exceed the site-specific target level line at any point for an
				actual receptor.
a. For the soil vapor to
				enclosed space and soil to water line pathways, sites shall be classified as
				high risk if the target levels for actual receptors are exceeded as provided in
				135.10(7) and 135.10(9).
b. For the
				soil vapor or groundwater vapor to enclosed space pathways, sites shall be
				classified as high risk if the explosivity levels at applicable points of
				compliance are exceeded as provided in 135.10(6) and 135.10(7).
c. Generally, sites are classified as low
				risk if only potential receptor points of compliance are exceeded. The
				following is an exception. For the soil leaching to groundwater ingestion
				pathway for potential receptor conditions, the site shall be classified as high
				risk if the groundwater concentration(s) exceeds the groundwater Tier 1 level
				for potential receptor and the soil concentration exceeds the soil leaching
				site-specific target level at the source.