American Linen Supply Co Dexter Ave: Remedial Investigation
January 29, 2026
Tena Seeds
Washington State Department of Ecology
15700 Dayton Avenue N
Shoreline, WA 98133
Dear Tena Seeds,
Vulcan Real Estate (VRE) appreciates the opportunity to review the Public Review Draft Remedial Investigation (RI) Report for the ...↓American Linen Supply Co Dexter Ave Site (Site) and 700 Dexter Ave N Property (Property) in Seattle, WA. VRE has prepared the following key comments for your consideration prior to the finalization of the Draft RI Report.
Comment 1. Inclusion of data collected after Q2 2021
The analytical and hydrogeologic data evaluated in the RI Report includes data collected through the second quarter of 2021. Groundwater data is available, however, through at least the fourth quarter of 2024, which covers a more than three-year period where no dewatering has occurred within or adjacent to the Site. Statements throughout the RI Report regarding chlorinated volatile organic compounds (CVOC) trends over time in response to dewatering events should be withdrawn until groundwater monitoring data collected post-June 2021 is included in the CVOC Time-Trend Plots (Appendix L) and current conditions have been evaluated. At a minimum, we recommend that any discussion regarding groundwater quality and plume dynamics be more clearly and expressly qualified in each instance to state that such trends represent conditions existing more than four years ago and may not reflect recent trends or current conditions.
We recommend data collected after the second quarter of 2021, including any natural attenuation parameters, should be thoroughly evaluated and the conceptual site model should be updated and documented in an addendum to the RI prior to commencing preparation of the Feasibility Study.
Comment 2. Historical extent of CVOC Plume
Section 6.2.2.2, page 115 of the RI Report, states the “extent of the Intermediate B Zone and Deep Zone CVOC plume at the southeast corner of the Site (near the intersection of Westlake Avenue North and Mercer Street) has been extended to the southeast by dewatering in properties in the vicinity, with the current extent to near the northwest corner of Block 38 West (Figures 43 and 44).” (Emphasis added.) A similar statement is made in Section 8.4.2 (page 144 of the RI text). VRE assumes that “current extent” refers to 2021 and not to recent groundwater conditions, as evidenced by data collected after 2021. (As noted in Comment 1, this statement should be withdrawn or qualified as it is likely to confuse public reviewers of the Final RI Report.) For the reasons set forth below, the RI Report should acknowledge that the CVOC plume was present in this area prior to dewatering at Block 43 and Block 37 but was pulled back northward during dewatering at these properties.
Due to the lack of deep monitoring wells in the South Lake Union neighborhood prior to construction dewatering at Blocks 43 and 44, the boundaries of the pre-2013 CVOC plume were not defined. The dewatering events at Block 43 in 2013-2014 and Block 37 in 2017 captured the CVOC plume south of Mercer Street and pulled it northward to near the southern borders of these blocks. It is more likely than not that the historical extent of the CVOC plume extended east of Westlake Avenue North (but not as far as Terry Avenue North) and south of Mercer Street.
Residual concentrations of cis-1,2-DCE were present at wells FMW-137, FMW-130, and FMW-138 across Block 38 West prior to dewatering at Block 38 West in 2020-2021. Dewatering at Block 38 West just returned the southern extent of the post-2017 CVOC plume footprint exceeding PCULs south of the intersection of Westlake Avenue North and Mercer Avenue to within the historical footprint of the pre-dewatering era CVOC plume. Thus, the statement that the CVOC plume has been “extended” to Block 38 West is inaccurate and should be revised.
Comment 3. Extents of CVOC plume south and east of the Property
Section 7.2.2.2, page 134 of the RI Report, states that the CVOC plume extent was “modified by past construction dewatering at properties to the south…”. Further details are provided in Section 8.3.3.2, page 141 of the RI Report, which states “The presence of CVOC concentrations multiple orders of magnitude above the PCULs to the south and southeast of the Property are reflective of past construction dewatering at properties to the south (e.g. Block 50, 55, and 56, see Figure 10).”
Insufficient evidence is presented in the RI Report to support the conclusion that dewatering events at Blocks 50, 55, and 56 influenced the 2021 CVOC plume footprint shown on Figures 43 and 44. The only information presented is the timing and volumes of water extracted at each location. This is insufficient to support conclusions on the short-term or long-term influences of dewatering on the south and southeast footprint of the CVOC plume.
As but one example, the dewatering event at Block 55 was limited to the southern portion of that block and was small in magnitude. Over the period of dewatering, the extraction rate averaged approximately 20 gallons per minute for the entire southern portion of the block. This equates to a mere 5 gallons per minute generated by the north dewatering wells over the 7-month period of active dewatering. It is unlikely that this modest extraction rate and short duration dewatering event would have any measurable influence on the CVOC plume footprint in the Shallow Water-Bearing Zone, and even less likely to influence the footprint in the Intermediate or Deep water-bearing zones.
The RI Report should include in Section 3.5.2 (page 19), Table 2, and Figure 10 references to dewatering that occurred around 2004 in association with the Seattle DOT Mercer Parcels southeast of the Property for the Denny Way/Lake Union Combined Sewer Overflow (CSO) project construction. This event occurred prior to construction at Blocks 50, 55, and 56. During the CSO construction, the approximately 70-foot-deep vertical shaft of the East Tunnel Portal Drop Structure was used for dewatering. General information regarding the CSO is provided in Section 2.1 of the Remedial Investigation, Seattle DOT Mercer Parcels prepared by Hart Crowser dated February 2, 2022 (Hart Crowser 2022). In addition, groundwater may be captured by the Mercer Tunnel and Lake Union Tunnel located in the Intermediate Water-Bearing Zone.[1] The CVOC plume maps presented in the RI Report (Figures 41 to 44) all show a southern CVOC plume footprint in the area of these features, and with respect to the Intermediate Water-Bearing Zone B map, a southwestern CVOC plume footprint (see feature locations on Figures 2-1 and 3-1 and various cross-sections in Hart Crowser 2022). These features are discussed in Section 2.2.2.2 but dewatering impacts during their installation are not included. More likely than not, the distribution of the CVOC plume on the SDOT Mercer property has been influenced by the co-located features (East Portal Drop Structure, Mercer Tunnel and Lake Union Tunnel) at that property.
Comment 4. Analysis of anaerobic biodegradation
Section 7.2.2.2, page 134 of the RI Report, states “Generally decreasing CVOC concentration trends and geochemical parameter concentrations supportive of anaerobic biodegradation indicate a stable to slowly shrinking plume, except where significantly influenced by the recent operation of construction-related dewatering systems.” A very similar statement is made in Section 8.3.3.2, page 141 of the RI Report.
The RI Report does not present any evidence that dewatering has altered geochemical parameters in a manner that limits biodegradation. In fact, as more fully discussed below, available data supports the opposite conclusion – i.e., that dewatering may be supportive of anaerobic biodegradation or has no apparent impact. It is thus likely that natural conditions across portions of the Site are not conducive to biodegradation, most notably the degradation of cis-1,2-DCE and vinyl chloride.
Review of natural attenuation screening scores listed in Table 17 of the RI Report for many wells screened in the Deep Zone and located in areas influenced by dewatering indicates conditions supportive of anaerobic biodegradation exist and are not exceptions as stated in Sections 7.2.2.2 and 8.3.3.2. Examples in the vicinity of Block 37 (north to south) include:
- Well MW128 where there is adequate to strong evidence of conditions supportive of anaerobic degradation during the entire sampling period;
- Well GEI-2 where there is adequate to strong evidence of conditions supportive of anaerobic degradation from 2017 through 2020; and
- FMW-131 where trends went from limited evidence of conditions supportive of anaerobic degradation prior to April 2020, to adequate and strong evidence thereafter.
In addition, there are several instances where operation of construction-related dewatering systems have reduced concentrations (i.e., CVOC mass dissolved in groundwater). For example, well MW128 at the southeast corner of the intersection of Valley Street and Westlake Avenue North is in an area that NV5 identifies as having been influenced by multiple construction-related dewatering events. The January 2014 sampling event conducted shortly after dewatering commenced at Block 43 documented concentrations of cis-1,2-DCE of 960 ug/l and vinyl chloride at 290 ug/l at this well. These elevated concentrations indicate that the CVOC plume had historically migrated east of Westlake Avenue North prior to many of the construction dewatering events documented in the RI Report.[2] Recent sampling at well MW128 (November 2024) indicates that PCE, TCE and cis-1,2-DCE were either non-detect or were detected less than the PCUL and vinyl chloride was 0.764 ug/l. Similarly, CVOC concentrations at formerly impacted deep monitoring wells FMW-131 and GEI-2 were either non-detect or were detected less than the PCUL during the November 2024 monitoring event. These results indicate that dewatering resulted in significant dissolved-phase CVOC mass removal at the areas in the vicinity of these wells and a decrease in the CVOC plume footprint east of Westlake Avenue North.[3]
Finally, there is a notable lack of MNA screening results for the portion of the Site east of 9th Avenue North to assess whether there is evidence of anaerobic biodegradation in the eastern portion of the historical or current footprint of the CVOC plume (see Figure 45). Including MNA screening results in the Final RI or RI addendum will provide a more substantive data set to evaluate remedial alternatives in the Feasibility Study.
Comment 5. Other releases impacting CVOC plume extent
Section 7.2.2.2, page 134 of the RI Report states “… the areas of concern in these [four water-bearing] zones are consistent with… potentially other CVOC sources in the South Lake Union Area.” Also, Section 8.3.3.2, page 141 of the RI Report, states that “… other CVOC sources in the South Lake Union Area may have also contributed CVOCs to the plume and may be significant sources in the more dilute, distal parts of the plume to the south and east.” Section 8.4.1 page 142 of the RI Report states that other properties “that could have sourced CVOCs include” Block 79E, Block 55, and the Seattle Roy Aloha Shops. There is no evidence to support the statement that Block 79E or Block 55 is a source of CVOCs to groundwater and in fact, there is ample evidence to the contrary.
Data collected during the recent remedial investigation under Ecology oversight at Block 79E did not identify a source of CVOCs impacting groundwater at this property.
As reported in Section 4.5.14, page 54 of the RI Report, PCE was detected in soil at Block 55 North, but was not detected in groundwater at concentrations exceeding the MTCA Method A cleanup level. Moreover, Block 55 North is not within the footprint of the CVOC plume (see RI Report Figures 43 and 44). Therefore, the release of PCE to soil at Block 55 North has not been shown to contribute to the CVOC plume.
The specific locations of these other alleged sources in the South Lake Union area, together with evidence to support such sources, should be presented in the RI Report. In addition, the magnitude of contribution from these alleged sources to the CVOC plume to the south and east should be demonstrated. If no such evidence exists, then these speculative statements should be withdrawn.
Comment 6. Vertical delineation of CVOC plume in deep zone
Sections 8.3.3.1 and 8.3.3.2, pages 140 and 141 of the RI text, do not present information on the vertical extent of CVOCs in the Deep Zone. Review of cross-sections B-B’ through H-H’ (Figures 33 through 39) indicates that the vertical extent of CVOCs has not been defined within the majority, if not all, of the Deep Zone CVOC plume footprint across the Site. For example, as shown on cross-section B-B’ (Figure 33) which is oriented in approximately the direction of groundwater flow, there is no location where the base of contamination was defined.
It is recommended that this data gap is resolved to define the vertical extent of the CVOC plume in the Deep Zone.
Comment 7. Benzene impacts in groundwater
We support the inclusion of a cleanup level for benzene in groundwater in this RI Report and the future Feasibility Study for the American Linen Supply Co Dexter Ave Site. Benzene in groundwater presents a vapor intrusion concern at downgradient properties including for current and future buildings that may be constructed within the plume boundaries.
An RI addendum and Feasibility Study report should more thoroughly depict the extents of benzene in soil and groundwater on- and off-property to better inform the site conceptual model and remedial alternatives for this contamination.
Thank you again for the opportunity to provide comments on the Draft RI Report.
Sincerely,
Corey Wilson, PE
Project Executive and Sr. Environmental Manager
[1] It is possible that additional shallow dewatering occurred associated with the Broad Street 1958-2012 alignment underpass beneath Dexter Avenue North and Mercer Street. This underpass was at least 20 feet below grade (Hart Crowser 2022).
[2] There are no known dewatering events to the east or northeast of well MW-128 prior to 2014; therefore, the presence of CVOCs at this location is the result of historical plume migration under natural flow conditions.
[3] These data points further reinforce the importance of evaluating data collected after 2021 in order to accurately portray existing conditions.
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January 29, 2026
Tena Seeds, PE
Washington State Department of Ecology
Toxics Cleanup Program
PO Box 330316
Shoreline, Washington 98133
SUBJECT: RESPONSE TO PUBLIC REVIEW DRAFT REMEDIAL INVESTIGATION REPORT
American Linen Supply Co Dexter Ave Site 700 Dexte...↓
Dear Ms. Seeds:
At the request of Seattle City Light (SCL), SoundEarth Strategies, Inc. (SoundEarth) has prepared this letter to provide comments on the Public Review Draft Remedial Investigation Report (RI Report) prepared for the American Linen Supply Co Dexter Ave Site (American Linen Site), prepared by NV5 Environmental Inc., dated October 3, 2025. The RI Report was issued for public comment on December 1, 2025, with a comment period end date of January 29, 2026.
The RI Report was prepared noting that the evaluation of site and environmental conditions were performed using data collected through the second quarter of 2021 and preliminary cleanup levels (PCULs) issued by the Washington State Department of Ecology (Ecology) in 2021. It appears that data collected after the second quarter of 2021 and changes to the PCULs or soil gas screening levels will be incorporated in a future RI data addendum (if prepared) or in the future Feasibility Study (FS) Report. Although the RI Report states it has met the substantive requirement of the Model Toxic Control Act, including addressing any outstanding data gaps to complete the evaluation of the nature and extent of contamination at the Site, it is uncertain as to the reasoning for withholding approximately 4 years of data presentation.
Based on review of the RI Report, SoundEarth disagrees with the following general statements and other similar statements made in the RI Report:
−SoundEarth disagrees with this statement based on reasons described below.
−SoundEarth disagrees with this statement based on reasons described below.
−Although the remedial investigation is not yet complete, there are no known sources ofchlorinated volatile organic compounds (CVOCs) on the Seattle Roy Aloha Shops property(Property). Sampling that has been conducted at that Site to date does not suggest thepresence of an on-property CVOC source.
For context, in December 2024, SoundEarth prepared a letter report in response to Ecology’s Preliminary Determination of Liability for Release of Hazardous Substances at the American Linen Site (Potentially Liable Party [PLP] Letter) on behalf of SCL. In the PLP Letter, Ecology proposed to find SCL liable for a release of benzene originating from the Property, which Ecology suggested may have comingled with CVOCs originating from the nearby American Linen Site. Primarily, Ecology suggested that the distribution of benzene in groundwater beneath and in the vicinity of the Property and the American Linen Site is consistent with a source of benzene originating at the Property, based on an easterly groundwater flow direction and general downward vertical hydraulic gradient.
SoundEarth does not dispute that a release of benzene originating on the Property has occurred and has resulted in current or former impacts to groundwater in the shallow water-bearing zone and potentially in the Intermediate A zone beneath and immediately downgradient (east) of the Property. However, SoundEarth refutes that a benzene release originating on the Property is the source of benzene impacts observed in the Intermediate B or deep water-bearing zones. SoundEarth is also of the opinion that the petroleum plume at the Property does not comingle with the American Linen Site CVOC plume. Overall, SoundEarth disagreed with Ecology’s proposed findings of liability as substantiated by findings presented in the December 2024 letter report to Ecology on behalf of SCL. In a letter dated January 21, 2025, Ecology deferred final determination of SCL’s liability as a PLP for the American Linen Site based on the currently available data.
Respectfully,
SoundEarth Strategies, Inc.
Clare Tochilin
Senior Geologist
Levi Fernandes, PE
Senior Engineer