Problems/Comments

Contamination was encountered by an equipment operator during a gravel mining operation in Cell 9 of the Anchorage Regional Landfill (ARL). It is not known how the contamination came to be at this location. The gravel mined is used as daily cover for the ARL. On October 13, 2016 an operator was excavating soil in Cell 9 of the ARL when he encountered a stained area of soil that exhibited petroleum odor. The Municipality of Anchorage hired a consultant to evaluate the site and sample the soil. The contaminated area was approximately 12 feet in radius and was comprised of grey sandy gravel and exhibited a strong petroleum odor. Two samples were collected and analyzed for gasoline range organics, diesel range organics (DRO), residual range organics, volatile organic compounds, and select metals. DRO results exceed ADEC migration to groundwater levels at 3,920 mg/kg and 1,410 mg/kg respectively. One sample exceeds ADEC migration to groundwater for naphthalene at 3.83 mg/kg. The total amount of contaminated soil is estimated to be approximately 5 cubic yards. The federal land disposal restriction under 40 CFR 268.40 lists the maximum allowable concentration of naphthalene at 5.6 mg/L by toxicity characteristic leaching procedure. There is no federal land disposal limit in 40 CFR 268.40 for DRO. The soil is proposed to be disposed of by using it for its original purpose as daily cover for the landfill. Sampling occurred on October 11, 2020 at the site. Approximately 40 to 60 feet of removed overburden between the petroleum contaminated soils, identified in 2016 and the final excavation floor. Ten field screening samples, including five at each of the two 2016 sample locations were taken; one at each 2016 sample location, one field screening sample at the original sample location, one in each of the four cardinal directions, and each 5 feet from the original location samples were collected. Each field screening sample was collected at a depth of 6 to 12 inches below the fresh surface of the excavation. PID readings ranged from 0.5 to 6.7 parts per million. Three soil samples were collected, two primary and one duplicate sample, at locations associated with the two highest field screening results. Samples are identified ARL-SO-03, ARL-SO-04, ARL-SO-05(Duplicate). Samples were analyzed for DRO, RRO, Polynuclear Nuclear Hydrocarbon (PAHs), and as well for geotechnical parameters (including soil bulk density, soil porosity, total organic carbon, and percent solids) to support calculation of alternative cleanup levels, if necessary. No staining, petroleum odor, or other visual or olfactory evidence of contamination was observed below the location of the 2016 samples. All analytical results were below ADEC Method Two cleanup levels, demonstrating that the small volume of contaminated soil identified in 2016, was fully excavated over the course of constructing Cell 9. As described above, the soil was used as daily cover on the face of the active landfill with the approval of ADEC.

Action Information

Contaminant Information

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Requirements