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This report presents an extensive review of information on SFSs, including analytical results for metals and metalloids (including both totals and leach test results), PAHs, phenolics, dibenzodioxins and furans, and dioxin-like PCBs. It also includes deterministic risk screening model results for the inhalation exposure scenario and probabilistic screening and refined model results for the home gardener exposure scenario. Taken together, this information provides the scientific basis for decision makers to determine theappropriate soil-related applications for certain unencapsulated beneficial uses of SFS. The major findings and conclusions from this report as they pertain to silica-based SFSs produced by iron, steel, and aluminum foundries, and their use in manufactured soil, soil-less potting media, and road subbase, are summarized below.

7.1

Beneficial Use of SFS (Chapter 1)

 SFS is a valuable industrial byproduct, and therefore, there are economic and possibly environmental advantages to identifying which soil-related applications are appropriate SFS beneficial uses.

 State regulators need access to sound scientific data and analyses to support the decision- making process regarding the beneficial use of SFS.

7.2

Characterization of SFS (Chapter 2)

 SFS has a number of soil-like qualities that make it an attractive material for use in roadway subbase, soil-less media, and manufactured soils.

 The concentrations of organic constituents and trace elements (including metals and metalloids) are, on average, very low in silica-based SFS produced by iron, steel, or aluminum foundries.

 Published background concentrations of metals in soils provides additional information in evaluating the scientific basis for considering the implications of adding SFS as soil amendments.

 The current data on SFS show that the distributions of metal constituents in silica-based SFS from iron, steel, and aluminum foundries are very similar to the background

distributions of metals in native soils.

 The presence of manganese and iron and the neutral pH of SFS strongly suggest that soil- related applications will likely reduce the mobility, bioavailability, and toxicity of metal constituents in SFS and, possibly, metal constituents already in the soil.

 Although applications of SFS in strongly acidic soils (pH <5) could increase the mobility of metals, this increase would mirror the same increase in natural soil. The common agricultural practices of testing pH and liming to ensure good crop growth conditions are expected to preclude highly acidic conditions from occurring.

 Based strictly on a comparison between the SFS and background concentrations of metals, it is unlikely that the addition of silica-based SFS from iron, steel, and aluminum foundries would significantly alter the composition of soil.

7.3

Exposure Scenarios Examined (Chapter 3)

Risk Assessment of Spent Foundry Sands in Soil-Related Applications 7-2 in roadway construction, (2) use in soil-less potting media, and (3) blending in

manufactured soils.

7.4

Screening of Exposure Pathways (Chapter 4)

 The inhalation pathway screening indicates that even high-end concentrations of the constituents in SFS were well below screening values for all constituents for which inhalation benchmarks were available.

 The groundwater ingestion pathway screening indicates that even high-end

concentrations of metal constituents in SFS were below water quality screening criteria for all constituents for which such criteria were available, except antimony, arsenic, beryllium, cadmium, and lead.

 The soil ingestion pathway screening indicates that even high-end concentrations of metal constituents in SFS were below soil screening criteria for all constituents for which such criteria were available, except antimony, arsenic, chromium III, cobalt, copper, iron, manganese, and nickel.

7.5

Modeling of Exposures from Home Gardening (Chapter 5)

 Eight metals (antimony, arsenic, chromium III, cobalt, copper, iron, manganese, and nickel) were evaluated with probabilistic screening modeling and refined modeling. Arsenic, cobalt, and iron were evaluated for human exposures through the soil/produce ingestion pathway but, only arsenic was evaluated under the groundwater pathway. Although concentrations of manganese and nickel in SFS were below their respective human health screening criteria (described in Chapter 4), they were modeled in the home gardening scenario because of their high potential for phytotoxicity. Similarly,

concentrations of antimony, trivalent chromium, and copper were below their human health screening levels, but they were retained for further study due to the potential to impact small insectivorous mammals.

 One of the more conservative assumptions for the home gardener soil/produce pathway screening modeling was the addition of exposures across all five produce categories (e.g., exposed vegetables), which results in consumption rates for the home gardener that are well above expected values.

 Investigation of the influence of produce consumption rates suggests that adding across produce categories is likely more appropriate for the median consumption rates for the home gardener, and that the use of values at the tail of the exposure factor distributions is associated with higher levels of uncertainty.

 The refined groundwater modeling used the distribution of the home garden source model outputs (i.e., leachate fluxes and annual average leachate infiltration rates) as input to the groundwater model. Coupling the home garden source and groundwater modeling

captured variability in conditions within the SFS economic feasibility areas when

predicting SFS constituent fate and transport in the environment. The conservative nature of the assessment was maintained through the placement of the drinking water receptor well 1 m from the edge of the garden in the centerline of the plume.

 Because arsenic has the potential to exhibit nonlinear behavior during transport through the unsaturated zone as simulated by EPACMTP, it was necessary to ensure the

appropriateness of applying the unitized approach to the groundwater pathway. As a result, an analysis was performed which demonstrated that arsenic would behave linearly

concentrations found in SFS samples. (Appendix J and Chapter 5).

 An analysis was performed to evaluate anticipated arrival times of peak contaminant concentrations in the receptor drinking water well. Based on the analysis, it is unlikely that peak surface and peak groundwater exposures will occur within the same timeframe. For example, the earliest estimated timeframe for arrival of arsenic in the well spanned from 29 to 200 years following the application of the SFS-manufactured soil. Given this timeframe, it is likely that the peak well concentrations will not occur until well past the receptor’s timeframe of residency (i.e., exposure duration). Therefore, surface and subsurface ingestion exposures would not occur together during the same exposure period. (Appendix J and Chapter 5).

 The probabilistic modeling for the home gardener scenario demonstrated that, even using consumption rates at the upper end of the distribution, the estimated exposures were below health benchmarks.

7.6

Characterization of Risks Associated With SFS Beneficial Use (Chapter

6)

 The assumption of a 1:1 mix for manufactured soil in the home gardener scenario was a conservative assumption, because this would be cost prohibitive for even small home gardens. A more likely scenario would be a manufactured soil consisting of 5–10% SFS, rather than the 50% SFS modeled here. Therefore, this assumption likely overestimates soil concentrations.

 Evaluating the national-scale beneficial use of SFS in road subbase, soil-less potting media, and manufactured soil includes numerous sources of variability. However, the findings from the available multiple lines of inquiry—such as newly available analytical results for SFS, research on metals behavior in soil (including SFS-specific studies), and risk screening methods (including modeling), all within the context of well-established soil science—when used collectively provide a sound scientific basis for determining appropriate soil-related uses of SFS.

 Given the assumption of high-end concentrations of the metals and other constituents in SFS, and the application of highly conservative screening techniques, risk screening models and refined models, the preponderance of the evidence demonstrates that the evaluated uses of silica-based SFS produced by iron, steel, and aluminum foundries are unlikely to cause adverse effects to human health and ecological receptors.

Table 7-1 provides a useful data summary for regulatory decision makers and other stakeholders; the table presents the analytical and background information on metal constituents in SFS, as well as the HH-SSLs and Eco-SSLs. In addition, the table provides the SFS-specific modeled screening values for the specific home gardener scenario evaluated in this report, as well as modeled screening values based on median and high-end consumption by the general public.55 As shown in this table, the concentrations of metal constituents found in SFS are below the health-based and ecological screening levels for soil and are present at levels that are similar to those found in native soils.

Risk Assessment of Spent Foundry Sands in Soil-Related Applications 7-4

Table 7-1. Comparing SFS Concentrations to Various Screening Values (mg kg-1 _{unless otherwise noted)}

Elements

Silica-based Iron, Steel, and

Aluminum Sandsa _{Human Screening Values Eco Screening Values}

U.S. and Canadian