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

Heading: interconnectivity challenges

Text: Largely renewing arguments included in their comments, the petitioners argue that the aquifer interconnections in the HRS analysis were not supported by substantial evidence and that the EPA acted arbitrarily and capriciously by concluding that the aquifers were interconnected. Pet’rs Br. 17-48. Their arguments founder because the EPA properly established To support their multi-aquifer-well pathway argument, the petitioners point to radioisotope studies showing “that the groundwater in the contaminated portion of the Prairie du ChienJordan Aquifer is ‘newer’ than the contaminated groundwater in the St. Peter Aquifer above it,” Pet’rs Br. 46, and to evidence that the St. Peter Aquifer is “cleane[r]” than the Prairie du Chien-Jordan Aquifer, id. at 43-44. They claim that these data suggest a contaminated groundwater is migrating not through descending aquifers but through multi-aquifer wells. fd. at 44, 46-47. But the EPA reasonably established interconnectivity without relying on any specific migration mechanism. See Hazard Ranking System, 55 Fed. Reg. at 51,553. Moreover, the EPA recognizes that multi-aquifer wells may be contributing to contaminant migration, see Revised Documentation Record at 14, 31; Support Document at 52, and that subsequent investigations may reveal more information regarding specific contaminant sources, see Support Document at 41. 22 aquifer interconnectivity by showing observed contaminant migration through observed releases in each of the aquifers. See Support Document at 48; HRS Manual, supra, at 127. As already described, the HRS regulations and accompanying guidance provide the structure for establishing aquifer interconnections. See supra, at 8-10. And one method to establish interconnectivity is by observed contamination across aquifers. See Hazard Ranking System, 55 Fed. Reg. at 51,553; HRS Manual, supra, at 127, 131. Here, the EPA provided copious documentation of observed releases across all four aquifers through chemical analysis. See Revised Documentation Record at 33-53. Relying on the HRS procedures and the observed releases within two miles of the Site, the EPA reasonably concluded that “contamination has migrated through the aquifer layers into the Prairie du Chien [A]quifer.” Support Document at 48. The EPA then considered whether there were any qualifying aquifer discontinuities and concluded that although confining layers existed in portions of the Platteville-Glenwood formation and the St. Peter formation, these layers were “documented to either not be present at locations in the [target distance limit] or are documented to allow contamination to migrate through” the formations. /d. at 49 (emphasis added). Because the “apparent discontinuit[ies]” allowed hazardous substances to migrate, the EPA properly found that there were no _ qualifying discontinuities, HRS § 3.0.1.2.2, and reasonably concluded that the aquifers were interconnected based on observed contamination, see id. § 3.0.1.2.1. Challenging the EPA’s use of the observed-contamination method of proving interconnectivity, the petitioners argue that the EPA did not adequately establish observed releases. Pet’rs Br. 35-39. In particular, they contend that the EPA’s chemical analysis was flawed. 7d. at 35-36. Recall that showing an 23 observed release by chemical analysis requires comparing a sample from a background well to a sample from a release well and determining whether the concentration in the release well is “significantly above the background concentration.” See HRS § 3.1.1. The petitioners first argue that the EPA improperly listed five Prairie du Chien-Jordan wells as “release wells” because they failed to exceed the requisite threshold of one contaminant, TCE, to qualify as an observed release relative to the background concentration. Pet’rs Br. 36. They then briefly argue that EPA “cherry-picked” well data and background wells, specifically asserting that the EPA should have picked more wells farther north and west to better capture its theory of contamination migration. /d. at 38. None of these arguments is persuasive. First, the EPA did not improperly list five wells as “release wells.” The petitioners misread the chart listing the wells and the hazardous substances exceeding the release threshold. See Revised Documentation Record at 39. The EPA lists six wells that qualified as “release wells” based on releases of different hazardous substances but, as the petitioners point out, only one exceeded the threshold limit for TCE. See id. The EPA accordingly did not include TCE in the list of qualifying releases for all six release wells and instead listed five of the wells as release wells for other CVOCs detected in the aquifers. Jd. Second, the EPA did not arbitrarily select well data. “The HRS does not identify requirements or define conditions for establishing background levels,” nor for selecting background wells. Support Document at 62. Here, the EPA provided adequate evidence of observed releases across numerous wells and over four years, see Revised Documentation Record at 33-53, and sufficiently responded to comments about the selection of well data, see Support Document at 11—12, 66-68. In any listing decision, the EPA balances “the need for certainty before action with the need for inexpensive, expeditious procedures to identify 24 potentially hazardous sites.” Eagle-Picher I, 759 F.2d at 921. Its reliance on previously compiled well data that comprehensively demonstrated observed releases was anything but arbitrary and capricious. The petitioners next challenge the EPA’s purported “natural migration pathway” theory of interconnectivity.' Pet’rs Br. 17, 43. They first argue that the EPA’s conclusion on the lack of continuous confining layers was not supported by substantial evidence. /d. at 18-32. In particular, they point to errors in one figure that the EPA used to illustrate that the St. Peter confining layer was not continuous. See id. at 23. In this figure, the EPA allegedly inaccurately depicted the continuity of the St. Peter confining layer at certain wells. See id. The petitioners reproduced maps and geological figures from the U.S. Geological Survey (USGS) to show the presence of the same confining layer. Jd. at 26-27. Although one of the figures shows that the confining layer is absent east of the Site—as shown in well log data for well HS-1, see Support Document at 45— they contend that absence is “almost two miles outside of EPA’s alleged plume area” and that “interconnectedness at HS-1 has no bearing on [the] EPA’s allegation that a ‘plume’ is migrating from the Drift Aquifer Area to the Prairie du Chien-Jordan Aquifer.” Pet’rs Br. 40. For its part, the EPA indeed maintained that the St. Peter confining layer is “locally absent due to erosion,” relying on the same USGS study. See Revised Documentation Record at 27. It also noted that well HS-1 is located about 1.55 miles east of municipal well SLP4, an observed-release well. Jd. Citing '3 The petitioners also challenge the use of pump test data to establish interconnectivity. Pet’rs Br. 33-34. That challenge is meritless because the EPA disclaimed reliance on the pump tests to establish interconnectivity. See Support Document at 51. 25 the HRS regulation that identifies “well logs indicating that a... confining layer separating the aquifers is not continuous through the two-mile radius” as one “of the types of information useful in identifying aquifer interconnections,” Hazard Ranking System, 55 Fed. Reg. at 51,553, the EPA concluded that in addition to the observed-contamination method of proving interconnectivity, the lack of a continuous confining layer also supported interconnectivity. Support Document at 48. We need not resolve this conflict because the petitioners’ migration-pathway argument is not responsive to the observedrelease method of establishing interconnectivity. See Hazard Ranking System, 55 Fed. Reg. at 51,553 (“For [the observedcontamination method], the mechanism of vertical migration does not have to be defined.”); accord Genuine Parts, 890 F.3d at 316 (noting irrelevance of groundwater flow to HRS analysis when assessing targets). Further, the EPA correctly noted that “at this stage of the listing, groundwater modeling, 3D or otherwise, to predict migration pathways [is] not required as part of an HRS evaluation.” Revised Documentation Record at 40. Accordingly, even if they are correct about the continuity of the St. Peter confining layer, the EPA’s error was harmless because it established interconnectivity via observed releases across the aquifers and did not rely on a specific migration pathway. See Jicarilla Apache Nation v. U.S. Dep’t of Interior, 613 F.3d 1112, 1121 (D.C. Cir. 2010) (harmless error applies to agency action because “if the agency’s mistake did not affect the outcome, if it did not prejudice the petitioner, it would be senseless to vacate and remand for reconsideration.” (alteration omitted) (quoting PDK Laby’s., Inc. v. DEA, 362 F.3d 786, 799 (D.C. Cir. 2004)).!4 ' Tex Tin and Genuine Parts do not help the petitioners. Pet’rs Br. 30-31 (citing Genuine Parts, 890 F.3d at 307, 310-11, 315), 48 26