5200 EVERGREEN WAY 2019-05-29 - Laserfiche WebLink

Former Brien Ford Property Everett, Washington Phase II Supplemental Site Investigation excavation. The petroleum hydrocarbons appear to have migrated vertically downward into the underlying advance outwash deposits, and east toward Evergreen Way. Geologic Cross-Sections B-B' and C-C' (Figures 4 and 5, respectively) are oriented in an approximate northeast-southwest direction (Figure 2). Cross-Section C-C' extends through the former UST excavation. Petroleum contaminants appear to have migrated laterally away from the UST excavation source along one or more permeable layers or lenses within the ice-contact and advance outwash deposits. Variations in sediment physical characteristics (grain size, permeability, etc.) have resulted in one or more preferential contaminant transport pathways via layers and lenses of permeable sediments. As shown on Figure 4, the petroleum- contaminated soil does not appear to extend downward to depths greater than about 16 to 18 feet bgs in the advance outwash deposits. The petroleum-contaminated soil appears to be the thickest under the historic dry cleaner and immediately east of the former UST excavation area. The petroleum-contaminated soil decreases in thickness at increasing distances from the former UST source area, and appears to be following more permeable lenses and layers of sediments northeast of the source area. Contamination appears to be wide-spread under the former dry cleaning building and stops prior to the east face of the commercial sales building except for a narrow lens moving east. Data obtained from boring GP-16 indicates that soil and ground water contamination extends into the upper portions of the underlying advance outwash deposits. The source of the GRPH and DRPH detected in the sample obtained from boring GP-27 at a depth interval of 11 to 12 feet bgs appears to be related to the former UST source based on depth, location, detected contaminants, and the lack of other known contaminant, sources. However, the location and orientation of one or more presumed contaminant transport pathways between the former UST excavation and boring GP-27 have not been identified. The extent of contaminants detected in boring GP-27 has not been defined. Several discontinuous water-bearing zones were encountered in four of the borings. The ground water sample obtained from boring GP-16 at a depth of about 8 feet was the only ground water sample collected with GRPH and DRPH concentrations exceeding MICA Method A cleanup levels. A continuous water-bearing zone or shallow aquifer has not been encountered at depths extending to about 20 feet bgs, the maximum depth of explorations completed to-date at the Property. CONCLUSIONS Based upon the results of this Phase II SSI, it appears that soil located in the vicinity of the former UST location and beneath the current commercial sales building up to depths of about 17 feet below existing grade contains GRPH at concentrations exceeding MICA Method A cleanup levels. Soil samples collected from borings GP-16, GP-18, GP-19, GP-21, GP-27, and GP-28 contained concentrations of GRPH above the MTCA Method A cleanup level. Soil samples -- March 31,2017 ASSOCIATED EARTH SCIENCES,INC. TWL/!d-20160594V002-2-Projectsk20160594\KV\WP Page 6