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 567-135.9 - Tier 1 Site Assessment Policy and Procedure

Current through Register Vol. 47, No. 3, July 24, 2024
(1)
General.
The main
				objective of a Tier 1 site assessment is to reasonably determine the highest
				concentrations of chemicals of concern which would be associated with any
				suspected or confirmed release and an accurate identification of applicable
				receptors. The potential source of a release, nature of the substance released,
				site stratigraphy, depth to groundwater, and other appropriate factors must be
				considered when selecting the sample types, sample locations, and measurements
				methods. The placement and depth of borings and the construction of monitoring
				wells must be sufficient to determine the sources of all releases, the vertical
				extent of contamination, an accurate description of site stratigraphy, and a
				reliable determination of groundwater flow direction.
a.
Pathway assessment.
The
				pathways to be evaluated at Tier 1 are the groundwater ingestion pathway, soil
				leaching to groundwater pathway, groundwater vapor to enclosed space pathway,
				soil vapor to enclosed space pathway, soil to water line pathway, groundwater
				to water line pathway and the surface water pathway. Assessment requires a
				determination of whether a pathway is complete, an evaluation of actual and
				potential receptors, and a determination of whether conditions are satisfied
				for obtaining no further action clearance for individual pathways or for
				obtaining a complete site classification of "no action required." A pathway is
				considered complete if a chemical of concern has a route which could be
				followed to reach an actual or potential receptor.
b.
Pathway clearance.
If
				contaminant concentrations for an individual pathway do not exceed the
				applicable Tier 1 levels or if a pathway is incomplete, no further action is
				required to evaluate the pathway unless otherwise specified in these rules. If
				the contaminant concentrations for a pathway exceed the applicable Tier 1
				level(s) in the "Iowa Tier 1 Look-up Table," the response is to conduct further
				assessment under Tier 2 or Tier 3 unless an effective institutional control is
				approved. In limited circumstances excavation of contaminated soils may be used
				as an option to obtain pathway clearance. If further site assessment indicates
				site data exceeds an applicable Tier 1 level(s) for a previously cleared
				pathway or the conditions justifying a determination of pathway incompleteness
				change, that pathway must be reevaluated as part of a Tier 2 or Tier 3
				assessment.
c.
Chemical
				group clearance.
If concentrations for all chemicals of concern within
				a designated group of chemicals are below the Tier 1 levels, no further action
				is required as to the group of chemicals unless otherwise specified in these
				rules. Group one consists of benzene, ethylbenzene, toluene, and xylenes
				(BTEX). Group two consists of naphthalene, benzo(a)pyrene, benz(a)anthracene
				and chrysene; TEH default values are incorporated into the Iowa Tier 1 Look-Up
				Table and Appendix A for group two chemicals.
d.
Site classification.
A
				site can be classified as no action required only after all pathways have met
				the conditions for pathway clearance as provided in this rule.
e.
Groundwater sampling
				procedure.
Groundwater sampling and field screening must be conducted
				in accordance with department Tier 1 guidance. A minimum of three properly
				constructed groundwater monitoring wells must be installed, subject to the
				limitations on maximum drilling depths, for the purpose of identifying maximum
				concentrations of groundwater contamination, suspected sources of releases, and
				groundwater flow direction.
(1) Field
				screening must be used to locate suspected releases and to determine locations
				with the greatest concentrations of contamination. Field screening is required
				as per department guidance at each former and current tank basin, each former
				and current pump island, along the piping, and at any other areas of actual or
				suspected releases. In placing monitoring wells, the following must be
				considered: field screening data, available current and historical information
				regarding the releases, tank and piping layout, site conditions, and drilling
				data available from sites in the vicinity. At least one well must be placed at
				each suspected source of release which shall include at a minimum: the pump
				island with the greatest field screening level, each current and former
				underground storage tank basin, and if field screening shows greater levels
				than at the pump islands or tank basins, at other suspected sources of
				releases. As a general rule, wells should be installed outside of the tank
				basin through native soils but as close to the tank basin as feasible. A well
				must be installed in a presumed downgradient direction and within 30 feet of
				the sample with the greatest field screening level. Three of the wells must be
				placed in a triangular arrangement to determine groundwater flow
				direction.
(2) Where the
				circumstances which prompt a Tier 1 assessment identify a discrete source and
				cause of a release, and the groundwater professional is able to rule out other
				suspected sources or contributing sources such as pump islands, piping runs and
				tank basins, the application of field screening and groundwater well placement
				may be limited to the known source.
f.
Soil sampling procedure.
The objective of soil sampling is to identify the maximum concentrations of
				soil contamination in the vadose and saturated zones and to identify sources of
				releases. The same principles stated above apply to soil sampling. Soil samples
				must be taken from borings with the greatest field screening levels even if the
				boring will not be converted to a monitoring well. At a minimum, soil and
				groundwater samples must be collected for analysis from all borings which are
				converted to monitoring wells.
Iowa Tier 1 Look-Up Table
Media
Exposure Pathway
Receptor
Group 1
Group 2: TEH
Benzene
Toluene
Ethylbenzene
Xylenes
Diesel*
Waste Oil
Groundwater (µg/L)
Groundwater Ingestion
Actual
5
1,000
700
10,000
1,200
400
Potential
290
7,300
3,700
73,000
75,000
40,000
Groundwater Vapor to Enclosed Space
All
1,540
20,190
46,000
NA
2,200,000
NA
Groundwater to Water Line
PVC or Gasketed Mains
7,500
6,250
40,000
48,000
75,000
40,000
PVC or Gasketed Service Lines
3,750
3,120
20,000
24,000
75,000
40,000
PE/PB/AC Mains or Service Lines
200
3,120
3,400
19,000
75,000
40,000
Surface Water
All
290
1,000
3,700
73,000
75,000
40,000
Soil (mg/kg)
Soil Leaching to Groundwater
All
0.54
42
15
NA
3,800
NA
Soil Vapor to Enclosed Space
All
1.16
48
79
NA
47,500
NA
Soil to Water Line
All
2.0
3.2
45
52
10,500
NA
NA: Not applicable. There are no limits for the chemical for
				  the pathway, because for groundwater pathways the concentration for the
				  designated risk would be greater than the solubility of the pure chemical in
				  water, and for soil pathways the concentration for the designated risk would be
				  greater than the soil concentration if pure chemical were present in the
				  soil.
TEH: Total Extractable Hydrocarbons. The TEH value is based
				  on risks from naphthalene, benzo(a)pyrene, benz(a)anthracene, and chrysene.
				  Refer to Appendix B for further details.
Diesel*: Standards in the Diesel column apply to all low
				  volatile petroleum hydrocarbons except waste oil.