NCD003162542_Badin Business Park_Corrective Action_20230427

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ALCOA/BADIN LANDFILL BASELINE ECOLOGICAL RISK ASSESSMENT WORK PLAN
BADIN BUSINESS PARK BADIN, NORTH CAROLINA NCD 003 162 542 GENERAL COMMENTS

Landfill leachate is a primary source contaminant of potential environmental concern entering the groundwater and surface water on and near the Alcoa/Badin Landfill. The landfill was used as both an industrial landfill to accept Alcoa–Badin Works waste streams and municipal solid waste (MSW) streams. This dual purpose expands the potential contaminants of interest based
on the wide variety of wastes generally associated with a MSW stream. This leachate impact to
groundwater is notable in sampling results collected at groundwater monitoring well ABL–MW005; however, the sampling effort does not consider volatile organic compounds (VOCs) or emerging contaminants such as 1,4–dioxane, perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA) and other per- and polyfluoroalkyl substances (PFAS). These
contaminants are typically associated with MSW and are likely to be in the leachate not being
captured in infiltrating downward from the unlined landfill to groundwater. Therefore, the contaminants should be assessed as part of the ecological risk assessment. Please include in the sampling suite for the groundwater monitoring wells (MW–1, MW–2, MW–3, MW–4, MW–5, and MW–6) at the Alcoa/Badin Landfill (and leachate monitoring from the leachate sump or
POTW discharge point) annual sampling for VOCs, PFOA, PFOS, and other PFAS–related
compounds, and update the ecological risk assessment as necessary to consider these MSW contaminants of interest. Alcoa must include a workplan to collect the groundwater samples including the sampling methodology and procedures, for the groundwater monitoring wells at the Alcoa/Badin Landfill.

The cover of the Alcoa/Badin Landfill is an item directly influencing the Alcoa/Badin Landfill
Baseline Ecological Risk Assessment Work Plan as it is a contributor to human health and environmental risk. The landfill cap is described as consisting of a non–typical cover comprised of a 12–inch soil layer of compacted silty clay with a 6–inch vegetative layer. Soil only landfill
caps are generally constructed in accordance with guidance for evapotranspiration covers which,
depending on soil type, typically have a minimum of 2.5 feet of soil along with a vegetative layer. The Plan discusses heavy leachate generation and flow after heavy precipitation events. This leachate generation scenario provides evidence that supports the likelihood that infiltration is occurring through this thin landfill cover. It is recommended that a more traditional landfill
cap design that includes modeling of infiltration potential using the free EPA Hydrologic
Evaluation of Landfill Performance (HELP) model. This information should be used to assess further enhancing the landfill cap design to promote a reduction of meteoric water infiltration and leachate generation to better protect human health and the environment from contaminants of concern generated by the industrial and municipal solid wastes contained by the landfill. A
more robust cap will reduce leachate generation to more manageable volumes and prevent
excessive leachate generation. Developing a landfill cap more typical of industry practice, in conjunction with existing leachate control practices, will result in fewer, or no, impacts to the environment from landfill leachate.
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SPECIFIC COMMENTS
Section 3.1.5.1 – Direct Contact, page 35.
The fifth sentence of the first paragraph states that dermal contact exposure routes to birds and mammals are not considered significant exposure routes due to feathers, fur, and scales on reptiles that mitigate direct dermal exposure in accordance with the EPA Guidance for
Developing Ecological Soil Screening Levels. Attachment 1–3 of the EPA guidance document
entitled Guidance for Developing Ecological Soil Screening Levels (Eco–SSLs) states in Section 1.1 (Dermal Contact with Contaminated Soils) that the data necessary to estimate dermal exposures for wildlife is generally not available and while feathers, fur, and scales are “believed” to reduce dermal exposure studies assessing the toxicity of dermal exposures for wildlife species
is limited. Please update this sentence in Section 3.1.5.1 to represent the guidance language
more accurately (i.e., that is the data necessary to estimate dermal exposures is not available). Section 2.3.2.2 – Site Hydrogeological Units, Figure 2–5 (ABL Cross–Section), page 15.

Figure 2–5 provides a cross–section (A to A’) but does not include a map view of the cross–section. Please provide a map–view showing the cross-sectional line A to A’.
Section 3.2.1.1.1 – Surface Water, page 46.
The seventh sentence of paragraph three references a surface water collection location as “downgradient” of Highway 740. We recommend the use of the term “downstream” for surface waters as opposed to the term downgradient which is typically used for groundwater
consideration.
Section 4.2 – Conceptual BERA Investigation Approach, Table 4–1 (Supplemental BERA Investigation Sampling Program Summary), page 68.

The groundwater sampling objectives consider source characterization using groundwater samples but does not address leachate sampling to further characterize source. Samples should be collected from the leachate sump for comparison to groundwater samples. Include in the conceptual BERA an investigative approach to assess leachate directly to provide a record of
constituents of concern that may be mobilized in the groundwater or impact surficial receptors.
Typically, leachate sampling of a landfill is conducted at least once annually. Section 4.2.3 – Background Characterization, page 75.

This section addresses collection of background data to support robust statistical evaluation to assess constituents of potential ecological concern from surface water, pore water, and sediments. The Plan does not discuss groundwater monitoring background data or provide any evidence of
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collecting background groundwater information from the upgradient background study area. The development of a baseline that represents the quality of groundwater entering the evaluation area
is necessary to ensure remedial efforts do not overlap with any potential contaminant inflow
from non-Site sources or does not attempt to remediate beyond natural background concentrations. Include in Section 4.2.3 installation of at least one representative background groundwater monitoring well that includes a regular sampling schedule of at least on sample annually to further assess the groundwater pathway and any associated plume that could impact a
receptor.