Diagrama de Flujo de Información

The information on the SFS characteristics and constituents presented in Chapter 2 was used to develop the conceptual models. The conceptual models describe the sources, exposure pathways, and receptors associated with SFS use in roadway construction, blending operations that produce manufactured soils and soil-less potting media, and use of manufactured soils in home gardens.

Figure 3-1 shows the conceptual model for SFS used as road subbase. Road subbase is a layer of material required in some roadway applications to change the physical characteristics of the land area on which the roadway is to be built so that the pavement is capable of withstanding the stress of vehicle traffic and seasonal changes (e.g., freeze/thaw cycles). The subbase is placed directly onto the subgrade and is covered by the base course, which is the layer in the roadway beneath the pavement. Subbase thickness varies depending on road type, site requirements, and material used, but sand subbase thickness typically ranges from 10–25 cm (i.e., 4-9 inches, U.S. ACE, 1984). Pre-use storage and processing would vary by proposed use, but would likely involve at least some storage in open areas. Rainfall on stored SFS piles or not yet covered subbase could potentially leach constituents that could migrate through the subsurface and contaminate an underlying groundwater aquifer. While possible, constituent releases into surface waterbodies are not likely to be significant because standard road construction practices include engineering controls to prevent significant runoff/erosion15. During loading and unloading

15 _{Runoff controls are a legal requirement under the National Pollutant Discharge Elimination System (NPDES) that}

is part of the Clean Water Act. Most states have been authorized to implement the NPDES storm water program (http://cfpub.epa.gov/npdes/stormwater/authorizationstatus.cfm ), although some areas (e.g., tribal lands) remain

Risk Assessment of Spent Foundry Sands in Soil-Related Applications 3-4 operations at roadway construction sites, nearby residents could be exposed via the inhalation of particulate emissions and/or the incidental ingestion of soil following particle deposition;

terrestrial receptors (e.g., small mammals, soil invertebrates) could be exposed to chemical constituents in SFS through direct and indirect exposure pathways.

SFS Source Exposure Pathways Receptors

Roadway Subbase Particulate/ Volatile Emissions Deposition Dispersion Runoff/ Erosion

Surface water Aquatic biota

Soil

Resident

Air Inhalation

Terrestrial Receptors

Leaching Groundwater Ingestion/

Dermal contact

Temporary storage pile

Ingestion/ Dermal contact

--> The scenario assumes that engineering controls would prevent significant runoff/erosion from releasing constituents into surface waters.

--> The scenario assumes that engineering controls would be used to significantly reduce the particulate and volatile emissions from the temporary storage pile.

Figure 3-1. Conceptual model: the use of SFS in roadway subbase.

Given their inherent properties and low cost, SFS could potentially be of value as feedstock for the blending of soil-less potting media and manufactured soil. Soil-less potting media are generally used by nurseries as temporary growth media while individual plants await sale, whereas manufactured soils more closely mimic native soils, and can be used on a much larger scale as a long-term replacement for degraded native soils. Soil-less potting media and manufactured soil could be mixed at the site of application (e.g., manufactured soil blended at a construction site to landscape degraded topsoil), or mixed at a nursery, landscaping company, or commercial soil-blending operation (hereafter referred to collectively as blending sites). SFS used in these horticultural or agricultural applications is not encapsulated, and piles of SFS feedstock may be uncovered for short periods of time. Figure 3-2 shows the conceptual model for residents near a blending site. This scenario assumes that SFS would be temporarily stored on site near other media components, along with piles of various blended soil and soil-less potting media.

If uncovered, rainfall on stored SFS and blended piles could potentially leach

constituents; if the piles are stored on a pervious surface, these constituents could potentially

under the direction of EPA. The NPDES regulations establish best management practices (BMPs) for any source of sediment, from sites or operations (e.g., construction, agricultural, or industrial), that might impact surface waters. Many of the BMPs applicable to the control of runoff are similarly used to control fugitive dust emissions as required under the Clean Air Act.

Complete pathway Incomplete pathway

migrate through the subsurface and contaminate an underlying aquifer. In addition, rainfall and windblown erosion could result in some portion of the SFS running off and possibly reaching nearby surface waters, assuming that the blending site did not include any sort of runoff collection system. Storage and blending processes at commercial soil-blending facilities could potentially be conducted on a much larger scale relative to storage and blending soil-less potting media, and cover a wide range of manufactured soil “recipes.” During storage, and particularly during the blending process, chemical constituents could volatilize or be released via particulate emissions. Nearby residents could be exposed through the groundwater pathways or the

inhalation of ambient air. Terrestrial receptors could be exposed to chemical constituents in SFS through direct and indirect exposure pathways.

Exposure Pathways Receptors

Deposition Dispersion

Runoff

Surface water Aquatic biota

Soil Resident Air Inhalation Leaching Groundwater SFS Source Temporary Storage Pile Particulate/ Volatile Emissions Mixing/ Blending Ingestion/ Dermal contact Ingestion/ Dermal contact Terrestrial Receptors

--> The scenario assumes that engineering controls would prevent significant runoff/erosion from releasing constituents into surface waters.

--> The scenario assumes that deposition would result in insignificant exposures for the soil pathways when compared to the home gardener scenario (Figure 3-3).

Figure 3-2. Conceptual model: the blending site.

Figure 3-3 shows the conceptual model for the use of SFS-manufactured soil (i.e., blended soils containing SFS) in home gardens. Although SFS-manufactured soil could be used in corporate and residential landscaping (e.g., resurfacing construction sites), the home gardener could potentially receive a much higher exposure to SFS constituents under the following assumptions

 The home gardener incorporates a significant amount of SFS-manufactured soil into the home garden

 The home gardener frequently works in the garden, thereby increasing the opportunities of dermal contact and incidental ingestion of the SFS-manufactured soil, and

 A significant portion of produce consumed by the home gardener would be taken from the garden consisting of SFS-manufactured soil.

Complete pathway Incomplete pathway

Risk Assessment of Spent Foundry Sands in Soil-Related Applications 3-6 Because the SFS-manufactured soil is unencapsulated, direct exposures (e.g., ingestion, dermal contact) could occur, and constituents could leach from the home garden following rainfall events and/or irrigation. Additionally, terrestrial receptors could be exposed to chemical constituents in SFS through direct and indirect exposure pathways.

SFS Source Exposure Pathways Receptors

Garden/field Particulate/ Volatile Emissions Deposition Dispersion Runoff/ Erosion

Surface water Aquatic biota

Soil

Resident

Air Inhalation

Terrestrial Receptors

Leaching Groundwater Ingestion/

Dermal contact Produce Temporary storage pile Ingestion Ingestion/ Dermal contact

--> The scenario assumes that the home gardener would impose controls to prevent significant runoff/erosion of manufactured soil from the garden.

--> The scenario assumes that manufactured soil is used soon after delivery, so constituent releases from the temporary storage pile are insignificant.

Figure 3-3. Conceptual model: the use of SFS-manufactured soils in home gardens.

The three conceptual models shown above were used in developing the Analytical Plan discussed in Section 3.3.