Opinion ID: 6498785
Heading Depth: 3
Heading Rank: 2

Heading: The Hazard Ranking System

Text: CERCLA required the EPA to develop “criteria for determining priorities among releases or threatened releases [of hazardous substances] throughout the United States for the purpose of taking remedial action.” 42 U.S.C. § 9605(a)(8)(A). Pursuant to that mandate, the EPA promulgated the HRS regulation to screen the sites that make the NPL. See 40 C.F.R. § 300.425(c)(1); see also HRS § 1.0 (“The [HRS] is the principal mechanism the [EPA] uses to place sites on the [NPL].”). The HRS lays out a “comprehensive methodology and mathematical model” that “quantif[ies] the environmental risks a site poses.” Carus Chem., 395 F.3d at 437 (quoting in second quotation Tex Tin Corp. v. EPA, 992 F.2d 353, 353 (D.C. Cir. 1993)). Because the HRS scoring procedures are central to the petitioners’ claims, it is necessary to march through important 6 aspects of the HRS analysis regarding a groundwater® contamination site. The first is the relevance of classifying the site as a groundwater plume with no identified source.
According to the HRS, a “[s]ite” is an “[a]rea[] where a hazardous substance has been deposited, stored, disposed, or placed, or has otherwise come to be located. Such areas may include multiple sources and may include the area between sources.” HRS § 1.1. The scope of the site may expand or contract after listing if additional study reveals more (or less) expansive contamination, see Wash. State Dep’t of Transp., 917 F.2d at 1310 n.1, and as the EPA explained in the listing at issue, “[t]he NPL does not describe releases in precise geographical terms. . . . Indeed, the precise nature and extent of the site are typically not known at the time of listing.” Site Listing Rule, 85 Fed. Reg. at 54,932. For each site, the HRS allows the EPA to assess a site’s “relative degree of risk to human health and the environment,” 42 U.S.C. § 9605(c)(1), by examining possible migration pathways of hazardous substances, see HRS § 2.1 (listing air, soil, surface water and groundwater as pathways). The EPA calculates a numerical score for each potentially affected pathway based on three factors: the (1) “likelihood of release,” meaning the risk that a hazardous substance “has been or will be released,” id. § 2.3; (2) “waste characteristics,” including 3 “Ground water’ and ‘groundwater’ are synonymous; the spelling is...due to “ground water’ being codified as part of the HRS, while ‘groundwater’ is the modern spelling.” HRS Revised Documentation Record, Highway 100 and County Road 3 Groundwater Plume, at 1 n.1 (Sept. 2020) (Revised Documentation Record), reprinted in J.A. 296-356. 7 the substance’s mobility and toxicity, id. § 2.4; and (3) “targets” (e.g., humans or environments) of the contamination associated with that pathway, id. § 2.5. Based on the evidence for each pathway, the EPA then “plug[s] the resulting individual pathway scores into a formula to obtain the site score.” US Magnesium, LLC v. EPA, 630 F.3d 188, 189-90 (D.C. Cir. 2011). The site score ranges from 0 to 100, HRS § 2.1.1, and a site is eligible for NPL listing if the score is over 28.50, National Priorities List, Final Rule No. 53, 77 Fed. Reg. 15,276, 15,278 (Mar. 15, 2012). When analyzing a groundwater pathway, the EPA assesses various factors for each aquifer. See HRS § 3.0 (Table 3-1). The likelihood of release factor for an individual aquifer” “is assigned the maximum value... whenever the criteria for an observed release are met.” Id. § 2.3 (emphasis added). The EPA assigns an observed release to an aquifer “by demonstrating that the site has released a hazardous substance to the aquifer,” based on either “[d]irect observation” or “Tc]hemical analysis.” /d. § 3.1.1. The EPA shows an observed release through chemical analysis by comparing groundwater samples. If a sample has a hazardous substance concentration that is “significantly above” that of a background sample, the EPA has established an observed release. See id. Similar to a “site,” a “[s]ource” is “[a]ny area where a hazardous substance has been deposited, stored, disposed, or placed, plus those soils that have become contaminated from migration of a hazardous substance.” /d. § 1.1. With one exception, a source does not “include those volumes 4 An aquifer is a layer “of rock or sediment that is saturated and sufficiently permeable to yield economically significant quantities of water to wells or springs.” EPA, HRS Guidance Manual 116 (1992) (ARS Manual), reprinted in J.A. 546-92. 8 of... ground water...that have become contaminated by migration.” /d. The exception is crucial to this case: “In the case of ...a ground water plume with no identified source . . . , the plume ...may be considered a source.” Jd. According to longstanding EPA guidance, “a contaminated ground water plume can only be evaluated as a source for HRS scoring purposes when the original source of hazardous substances contributing to the plume cannot be reasonably identified.” EPA, Publication 9320.8-O1FS, Evaluating Ground Water Plumes Under the Hazard Ranking System 1 (1998). Connecting a “source” to an observed release that was established using chemical analysis, the EPA typically must show attribution—that the “significant increase” of contaminants comes from the site—to establish an observed release through chemical analysis. HRS § 3.1.1. But “when the source itself consists of a ground water plume with no identified source, no separate attribution is required.” /d. Accordingly, if the EPA cannot reasonably identify an original source of contamination, the observed releases—not a specific source or boundaries—define the site. b, Aquifer Interconnections The second relevant aspect of the HRS analysis is aquifer interconnections. Jd. § 3.0.1.2.1. An individual aquifer is ordinarily scored by treating it as separate from surrounding aquifers. See id. The EPA may, however, “[c]ombine multiple aquifers into a single hydrologic unit for scoring purposes if aquifer interconnections can be established for these aquifers.” Id. § 3.0.1.2. To assess interconnection, the HRS directs as follows: Evaluate whether aquifer interconnections occur within 2 miles of the sources at the site. If they occur within this 2-mile distance, combine 9 the aquifers having interconnections in scoring the site. In addition, if observed ground water contamination attributable to the sources at the site extends beyond 2 miles from the sources, use any locations within the limits of this observed ground water contamination in evaluating aquifer interconnections. Id. § 3.0.1.2.1. The EPA’s guidance manual for HRS scoring provides examples of evidence that usually establish interconnectivity. See generally EPA, HRS Guidance Manual (1992) (HRS Manual), reprinted in J.A. 546-92. Relevant examples include: well logs> showing there is “no continuous, significantly lower hydraulic conductivity layer” separating the aquifers; pump tests showing that withdrawing water from one aquifer affects water levels in another; and observed contamination across an aquifer boundary separating the aquifers within the two-mile radius. Jd. at 127. Importantly, for the last example, “the mechanism of vertical migration does not have to be defined, and the [contaminants] do not have to be attributable to the site being evaluated.” Hazard Ranking System, 55 Fed. Reg. 51,532, 51,553 (Dec. 14, 1990). After the EPA has adequate evidence of aquifer interconnections, it then must consider whether there are aquifer discontinuities. “An aquifer discontinuity occurs for scoring purposes only when a geologic, topographic, or other structure or feature entirely transects an aquifer within the > A well log is a “record of geologic materials with depth based on data obtained beneath a point on the land surface and representative of types, depths, and thicknesses of materials beneath that point. The data may represent visual observations, physical/chemical characterizations, and/or geophysical properties.” ARS Manual, supra, at 117. 10 4-mile target distance limit, thereby creating a continuous boundary to ground water flow within this limit.” HRS § 3.0.1.2.2 (emphasis added). A boundary preventing the migration of groundwater is also known as an “aquitard” or “confining layer.” And the “target distance limit” for a groundwater plume with no identified source is measured from the center of the plume. Jd. § 3.0.1.1. The HRS directs, however, that “if hazardous substances have migrated across an apparent discontinuity within the 4-mile target distance limit, do not consider this to be a discontinuity in scoring the site.” Id. § 3.0.1.2.2. In sum, “[a]quifer interconnections cannot be assumed, but must be supported by evidence.” HRS Manual, supra, at 135. And if the EPA shows observed releases of hazardous substances on both sides of an apparent aquifer boundary, sufficient evidence for aquifer interconnection exists notwithstanding the boundary is an “apparent discontinuity,” HRS § 3.0.1.2.2, or the lack of an established migration mechanism between the aquifers, Hazard Ranking System, 55 Fed. Reg. at 51,553.