Introduction

A remedial investigation/feasibility study (RI/FS) was conducted at a former wood-treating and storage facility in Virginia that is currently included on EPA's National Priority List (NPL) of Superfund sites. A final RI report, which characterized the nature and extent of contamination of surface and subsurface soils at the site as well as groundwater in the shallow, unconfined Columbia Aquifer and the deep Yorktown Aquifer beneath the site, was submitted to the EPA and VDWM and was subsequently approved. Analytical groundwater data acquired for the shallow, unconfined aquifer during the RI revealed that detectable concentrations of polycyclic aromatic hydrocarbons (PAHs) were present in the groundwater. Analytical data acquired during the RI also revealed the presence of the same PAHs in the unsaturated zone soils above the

Figure 4 Total hazard index vs. total PAHs—on-site workers.

Total PAHs (mg/Kg)

Figure 4 Total hazard index vs. total PAHs—on-site workers.

Figure 5 Total hazard index vs. total PAHs—construction workers.

Total PAHs (mg/Kg)

Figure 5 Total hazard index vs. total PAHs—construction workers.

Table 14 Summary of Polycyclic Aromatic Hydrocarbons (PAHs) Detected in Soil and Groundwater Samples During Remedial Investigation

Potentially carcinogenic PAHs

Noncarcinogenic PAHs

Benzo[a]anthracene

Acenaphthene

Benzo[a]pyrene

Acenaphthylene

Benzo[6]fluoranthene

Anthracene

Benzo[&]fluoranthene

Benzo[g,/i,(]perylene

Chrysene

Fluoranthene

Dibenzo[a,/i]anthracene

Fluorene

Indeno[l ,2,3-a/]pyrene

Naphthalene

Phenanthrene

Pyrene

shallow aquifer. Both potentially carcinogenic and noncarcinogenic PAHs (cPAHs and nPAHs, respectively) that are commonly associated with wood-treating and storage activities were identified as contaminants in a public health and environmental assessment (PHEA) that was performed as part of the final RI for the site (Table 14).

Two areas, areas A and B, were delineated as potential source areas on the western and eastern portions of the site, respectively (Figure 6). The presence of PAHs in the soil and groundwater samples collected from these areas implies the possibility of downward vertical movement of organic leachate from the unsaturated zone to the groundwater of the Columbia Aquifer. Once in the groundwater, the potential exists for the transport of PAHs from beneath source areas A and B to a receptor domestic well and an adjacent estuarine river, respectively. Although the aquifer is not currently being used as a potable water supply, it could be used as such in the future. Hypothetical off-site domestic wells in areas west of the site are therefore considered to be potential receptors in a future scenario. The adjacent river is considered to be a potential environmental receptor for those PAHs that have leached from the soil into the shallow aquifer at the site.

For the purpose of conducting a focused feasibility study, it became necessary to develop soil cleanup goals for PAHs that were protective of (1) humans consuming groundwater at a receptor well location impacted by area A, (2) organisms inhabiting the river, and (3) humans consuming organisms from the river impacted by area B. It was suggested by EPA that this task be performed by applying EPA's Multimedia Exposure Assessment Model (Multimed) to designated source area(s) at the site [8]. The monitoring well designated MW-102 (Figure 6), installed in the Columbia Aquifer in the southwestern portion of the site, was selected as the receptor well location for PAHs migrating from area A, since it is situated downgradient of source area A and PAHs were detected in groundwater samples collected from this location. In addition, property west of the site is more likely to undergo residential development than property at any other on-site or offsite location. The adjacent river, as stated previously, was determined to be the potential environmental receptor for constituents migrating from source area B.

The purpose of Multimed in the development of soil cleanup goals was the derivation of dilution-attenuation factors (DAFs) that are used as multipliers for selected applicable and appropriate performance standards at the receptor location of interest. This will be explained in greater detail in a later discussion.

AREA B FORMER PROCESS AREA EASTERN SOURCE AREA MODELED BY MULTI-MED (10. 000 m2)

AREA A

FORMER WOOD STORAGE AREA WESTERN SOURCE AREA MODELED BY MULTI-MED (B. 260 m2)

AREA B FORMER PROCESS AREA EASTERN SOURCE AREA MODELED BY MULTI-MED (10. 000 m2)

AREA A

FORMER WOOD STORAGE AREA WESTERN SOURCE AREA MODELED BY MULTI-MED (B. 260 m2)

LEGEND

- MONITORING WELL LOCATION

Xp - LONGITUDINAL DISTANCE TO

DOWNGRADIENT RECEPTOR LOCATION

SCALE (FEET) 0 100 200 300

Figure 6 Source areas modeled by EPA Exposure Assessment Multimedia Model.

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