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 567-135.8 - Risk-based Corrective Action

Current through Register Vol. 47, No. 3, July 24, 2024
(1)
General.
The objective
				of risk-based corrective action is to effectively evaluate the risks posed by
				contamination to human health, safety and the environment using a progressively
				more site-specific, three-tiered approach to site assessment and data analysis.
				Based on the tiered assessment, a corrective action response is determined
				sufficient to remove or minimize risks to acceptable levels. Corrective action
				response includes a broad range of options including reduction of contaminant
				concentrations through active or passive methods, monitoring of contamination,
				use of technological controls or institutional controls.
a.
Tier 1.
The purpose of a
				Tier 1 assessment is to identify whether a site poses an unreasonable risk to
				public health and safety or the environment based on limited site data. The
				objective is to determine maximum concentrations of chemicals of concern at the
				source of a release(s) in soil and groundwater. The Tier 1 assessment assumes
				worst-case scenarios in which actual or potential receptors could be exposed to
				these chemicals at maximum concentrations through certain soil and groundwater
				pathways. The point of exposure is assumed to be the source showing maximum
				concentrations. Risk-based screening levels (Tier 1 levels) contained in the
				Tier 1 Look-Up Table have been derived from models which use conservative
				assumptions to predict exposure to actual and potential receptors. (These
				models and default assumptions are contained in Appendix A.) If Tier 1 levels
				are not exceeded for a pathway, that pathway may not require further
				assessment. If the maximum concentrations exceed a Tier 1 level, the options
				are to conduct a more extensive Tier 2 assessment, apply an institutional
				control, or in limited circumstances excavate contaminated soil to below Tier 1
				levels. If all pathways clear the Tier 1 levels, it is possible for the site to
				obtain a no action required classification.
b.
Tier 2.
The purpose of a
				Tier 2 assessment is to use site-specific data to assess the risk from
				chemicals of concern to existing receptors and potential receptors using fate
				and transport models in accordance with
				567-135.10 (455B). See
				135.10(2)
"a."
c.
Tier 3.
Where site conditions may not be adequately addressed
				by Tier 2 procedures, a Tier 3 assessment may provide more accurate risk
				assessment. The purpose of Tier 3 is to identify reasonable exposure levels of
				chemicals of concern and to assess the risk of exposure to existing and
				potential receptors based on additional site assessment information,
				probabilistic evaluations, or sophisticated chemical fate and transport models
				in accordance with 567-135.11 (455B).
d.
Notification.
Whenever
				the department requires a tiered site assessment and a public water supply well
				is within 2,500 feet of a leaking underground storage tank site, the department
				will notify the public water supply operator.
e.
Pathway reevaluation.
Prior to issuance of a no further action certificate in accordance with
				135.12(10) and Iowa Code section
				455B.474(1)
"h"
(3), if it is determined that the conditions for an
				individual pathway that has been classified as "no action required" no longer
				exist, or the site presents an unreasonable risk to a public water supply well
				and the model used to obtain the pathway clearance underpredicts the actual
				contaminant plume, the individual pathway shall be further assessed consistent
				with the risk-based corrective action provisions in rules 567-135.8 (455B)
				through 567-135.12
				(455B).