DRAFT

Phase I Remedial Action Plan Centennial Mills – Tanner Creek Sewer 1362 NW Naito Parkway Portland, Oregon ECSI No. 5136

Prepared for Prosper Portland

October 28, 2019 150-012-003

DRAFT Phase I Remedial Action Plan Centennial Mills – Tanner Creek Sewer 1362 NW Naito Parkway Portland, Oregon ECSI No. 5136

Prepared for Prosper Portland

October 28, 2019 150-012-003

Prepared by Hart Crowser, Inc.

DRAFT DRAFT

Christopher W. Martin, PE Richard D. Ernst, RG Environmental Engineer Principal Geologist

6420 SW Macadam Avenue, Suite 100 Portland, OR 97239 503.620.7284

Contents

ACRONYMS II

1.0 INTRODUCTION 1 1.1 Purpose 1 1.2 Scope of Work 1 1.3 Limitations 2

2.0 BACKGROUND 2 2.1 Centennial Mills Site 2 2.2 Tanner Creek Sewer 4 2.3 Remedial Action Objectives 9

3.0 TANNER CREEK SEWER MITIGATION PLAN 10 3.1 Installation of Phase I – LPH Removal 10 3.2 Ongoing Operation of Phase I – LPH Removal 16 3.3 Future Phase II – Grout Barrier Installation 18

4.0 REPORTING 18

5.0 REFERENCES 19

FIGURES 1 Vicinity Map 2 Site Plan and Previous Explorations

APPENDIX A Specification Drawings

APPENDIX B Loading/Unloading Procedures Checklist

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ACRONYMS ATCS abandoned Tanner Creek Sewer bgs below the ground surface BMP best management practice BNSF Burlington Northern Santa Fe CDF controlled density fill COPD City of Portland datum DEQ Oregon Department of Environmental Quality DOT U.S. Department of Transportation ECSI Environmental Cleanup Site Information ESCP Erosion and Sediment Control Plan FFS Focused Feasibility Study HHRA Human Health Risk Assessment IDW investigation-derived waste JSCS Joint Source Control Strategy LPH liquid phase hydrocarbons mg/kg milligrams per kilogram MGP manufactured gas plant MPU Mounted Patrol Unit PAHs polycyclic aromatic hydrocarbons PCBs polychlorinated biphenyls PHSS Portland Harbor Superfund Site PPE personal protective equipment psi pounds per square inch RA remedial action ROA remedial action objectives RAP Remedial Action Plan RBC risk-based concentration ROD Record of Decision SCE Source Control Evaluation TCS Tanner Creek Sewer TPH total petroleum hydrocarbons UST underground storage tank VOCs volatile organic compounds

150-012-003 DRAFT October 28, 2019

Phase I Remedial Action Plan Centennial Mills – Tanner Creek Sewer 1362 NW Naito Parkway Portland, Oregon

1.0 INTRODUCTION This Remedial Action Plan (RAP) presents the scope and design for the first phase of a Remedial Action (RA) to mitigate groundwater contamination migrating through backfill around the Tanner Creek Sewer (TCS) beneath the Centennial Mills site (the “site”) at 1362 NW Naito Parkway in Portland, Oregon (Figure 1). The backfill represents a preferential pathway for petroleum contamination to migrate from upland sources to the Willamette River and, as a result, pose a potential risk to ecological receptors around the TCS outfall. This RAP describes the first phase of a two phase RA to address this pathway. Phase I includes installing two groundwater extraction wells within the TCS backfill to remove liquid-phase hydrocarbons (LPH) from the groundwater. Phase I will be completed in fall of 2019. The second phase of the RA involves installing a grout collar along both sides of the TCS in the fall of 2020.

1.1 Purpose Previous environmental investigations at the Centennial Mills site have identified total petroleum hydrocarbons (TPH) as diesel and oil, polycyclic aromatic hydrocarbons (PAHs), and lead in soil and groundwater. A Source Control Evaluation (SCE) for the site determined that this contamination does not pose an unacceptable risk to the river, except for contamination likely migrating through backfill around the TCS (Hart Crowser 2013a). Petroleum contamination, including LPH, was found in soil and groundwater in backfill around the TCS and in monitoring well MW-2 (Figure 2). While environmental activities have removed on-site sources such as underground storage tanks (USTs) and associated soil contamination, the presence of residual contamination and a preferential pathway on the site necessitate a concerted but measured and sequential source control effort. The purpose of this RAP is to present the scope and design of the first phase of the remedial activities to address this challenge.

1.2 Scope of Work This RAP presents the scope of work for implementing the first phase of an RA to mitigate petroleum contamination that is likely migrating through backfill of the TCS beneath the Centennial Mills site. Phase I of the RAP involves depressing the water table within the TCS backfill to contain and collect contaminated groundwater and LPH. To achieve this, Phase I consists of installing two groundwater extraction wells, one on each side of the TCS. Extracted liquids will be conveyed to a water storage tank via a double diaphragm pump. Collected groundwater and LPH will be transferred to an oil recycling facility for treatment.

The above activities are more fully described in this RAP. Detailed plans and specifications have been prepared for the on-site remedy (Appendix A). While these documents represent the current Phase I design, changes may be necessary to incorporate the means and methods of the construction contractor, and address conditions, either unforeseen or contingent, encountered during implementation.

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1.3 Limitations This RAP has been prepared for Prosper Portland to implement an RA, as requested by the Oregon Department of Environmental Quality (DEQ). Prosper Portland is voluntarily proposing this RA to address a preferential contaminant pathway to the Willamette River. Prosper Portland’s authority to implement an RA over certain cost levels or undertake long-term liabilities may require the approval of Prosper Portland Board of Commissioners. Prosper Portland purchased the Centennial Mills site for the purpose of improving the economic condition and viability of the area. Prosper Portland denies any responsibility for the original release of contamination but is willing to aid the DEQ in this source control effort. Work described in this RAP will be performed in accordance with generally accepted professional practices relating to the nature of work completed at the same or similar localities. This RAP is intended for the exclusive use of Prosper Portland for specific application to the site. No other warranty, express or implied, is made.

2.0 BACKGROUND This section provides a summary about the Centennial Mills site and specific information regarding the TCS, including nature and extent of contamination, identified risks, and potential sources. The remedial action objectives (RAOs) for the proposed remedy for the on-site TCS backfill are also presented. More detailed information about the site and the TCS is provided in our SCE, Human Health Risk Assessment (HHRA), and Focused Feasibility Study (FFS) (Hart Crowser 2013a,b, 2014). References are provided in Section 5.

2.1 Centennial Mills Site The project site, Centennial Mills, started as a flour mill in 1910 along the southwest bank of the Willamette River. Originally just a couple buildings, the mill expanded to the 12 joined buildings by 1940. Operations continued until 2000, when Prosper Portland purchased the mill property. Information about the mill and its environmental condition is presented below.

2.1.1 Location and Description The Centennial Mills site is located at 1362 NW Naito Parkway, just north of its intersection with NW 9th Avenue in Portland, Oregon (Figures 1 and 2). The site is located along the southwest bank of the Willamette River at approximately river mile 11.4, adjacent to the Portland Harbor Superfund Site (PHSS). The property is located within the River District Urban Renewal District and is zoned Central Employment (City of Portland 2016). Surrounding properties include a commercial building to the northwest; the Waterfront Pearl condominiums to the southeast; and across Naito Parkway, by The Fields Neighborhood Park, condominiums, Oregon State University Food Innovation Center, and Union Station.

Figure 2 shows recent site features in the general vicinity of the TCS. Overall, the site property covers a rectangular area of approximately 4.75 acres, of which 3.5 acres are upland property. The mill occupied the northern two-thirds of the property. After purchasing the mill, Prosper Portland renovated a portion of the mill in 2001 for the City of Portland Mounted Patrol Unit (MPU) and constructed a paddock on the former mill parking lot on the southern third of the property. The MPU improvements also included

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installing landscaping along NW Naito Parkway, around the paddock, and along the top of the bank. Former Centennial Mills buildings were demolished in 2015 through 2017, leaving only the former flour mill building and Warehouse E. The TCS, currently a stormwater-only sewer, is present just south of the Warehouse E building.

The elevation of the property at NW Naito Parkway is approximately 31 feet City of Portland datum (COPD). In the southeastern third of the property, the grade slopes down to approximately 23 feet at the top of the riverbank at the parking area (approximately the same elevation as the mill’s basement). The bank then steeply drops to the river. The riverbank has been armored with riprap and has occasional debris, such as concrete and brick. Blackberry brambles have invaded the riprap. The Ordinary Low Water elevation is 3.22 feet and the Ordinary High Water elevation is 17.9 feet.

2.1.2 Historical and Current Use In 1910, Crown Mills was constructed on the site, consisting of a flour mill, a grain elevator, and two warehouses. Between 1916 and 1940, the mill was expanded to the 12 joined buildings that covered the northern two-thirds of the property. Riverfront warehouses were built on piles over the water, while other structures were built on the original bank or on fill placed on the property. In the 1930s, the property to the southeast was acquired, expanding the mill property essentially to its current extent. Buildings and a ferry landing in this area were removed, leaving an embayment to the river. This area was filled by 1950 for use as the mill parking lot.

In 1948, Centennial Flouring Mills Company purchased the mill, but continued operating it as Crown Mills until 1955 when it was renamed Centennial Mills. The mill underwent several changes in ownership during the ensuing decades. In 1981, ADM Milling purchased the property and continued flouring operations under the Centennial Mills name until 2000, when Prosper Portland purchased the property. In 2001, Prosper Portland remodeled a portion of the mill for the MPU and the mill parking lot was removed, and the MPU paddock, driveway, and new parking area were constructed (Figure 2).

Due to continued deterioration of the mill buildings, the MPU vacated the site in 2015. To address concerns of potential building collapse and to aid in redevelopment efforts for the site, Prosper Portland demolished select buildings between 2015 and 2017, in three phases. Phase I consisted of demolishing Warehouses A, B, C, D, and F and Elevators A, B, and C; Phase II consisted of removing the concrete wharf deck over the Willamette River; and Phase III consisted of demolishing the Feed Mill Building (Prosper Portland 2019). After removal of building foundations, the demolition contractor placed a temporary cap on the exposed soil, consisting of approximately 1.5 to 2 feet of crushed concrete covered with 1 foot of imported top soil, which was then hydroseeded.

Future property redevelopment will likely include new building construction, remodeling or demolition of remaining site buildings, and a greenway setback from the top of bank. It is anticipated that redevelopment will likely be commercial or mixed commercial/urban residential (i.e., ground floor retail shops, upper floor residences, and subgrade parking).

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2.1.3 Previous Environmental Activities Numerous environmental activities have been completed at the site, starting with a Phase II assessment in late 1999 (Hart Crowser 2000). Subsequent soil and groundwater sampling occurred during paddock construction; for UST removals, a remedial excavation of a former UST nest, data gap investigations, an SCE, and risk assessment data; and after mill building demolition (Hart Crowser 2002, 2009, 2013a,b, 2017a,b). In 2006, surface sediment samples were also obtained along the northeast side of the property (Maul Foster & Alongi, Inc. 2006).

Chemical results from these investigations primarily detected TPH as diesel and oil, PAHs, and lead in soil and groundwater. Volatile organic compounds (VOCs), polychlorinated biphenyls (PCBs), and elevated concentrations of cadmium, chromium, copper, mercury, and zinc were infrequently detected. The majority of the contamination was detected within the southeastern third of the site and along the northwest portion (former Elevators B and C). Relatively high concentrations of TPH and PAHs were also detected in material within the abandoned Tanner Creek Sewer (ATCS) beneath the site; however, this sewer has been sealed off at several points, including at its outfall. Explorations adjacent to the current TCS found petroleum contamination, including LPH, in backfill around the sewer on and off the site (Hart Crowser 2013a, 2017a). LPH was also measured in on-site monitoring well MW-2, near the TCS (Figure 2).

In 2013, an SCE was completed to evaluate whether potential or existing upland sources of chemical contamination at the site posed an environmental concern to the river (Hart Crowser 2013a). The SCE determined that the site did not pose unacceptable risks to the river, except for contamination potentially migrating through backfill around the TCS. Because off-site sources were suspected, the TCS was subsequently excluded from the site so that a Source Control Decision could be obtained from the DEQ for the remainder of the Centennial Mills site (DEQ 2014a). An HHRA for the site identified unacceptable risks from contaminants (primarily carcinogenic PAHs) in soil only. To address these risks, an FFS was conducted that recommended excavating two hot spots and placing an engineered cap on all areas of the site not covered by mill buildings. The DEQ agreed with this remedy in its Record of Decision (ROD; DEQ 2014b).

2.2 Tanner Creek Sewer The TCS was constructed through the Centennial Mills site in 1917. On the site, it is a cast-in-place, reinforced concrete structure approximately 6.5 feet wide and 10 feet high, with an arched top. The top of the sewer is approximately 17 feet deep beneath NW Naito Parkway and approximately 6 feet deep beneath the top of the bank. Environmental investigations have found petroleum contamination in the backfill around the TCS and in monitoring well MW-2, near the TCS. Historical and current occurrences of contamination associated with the TCS and potential upland sources are summarized below.

2.2.1 Findings of Previous Environmental Activities Contamination issues have been associated with the TCS beginning in approximately 1970 when oil sheens were observed emanating from the outfall due to up-pipe sources. On- and off-site investigations have been conducted to determine the origin, nature, magnitude, and extent of contamination. This section summarizes the findings of these investigations. Further details are available in the SCE and Upgradient

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Data Gap Investigation Report (Hart Crowser 2013a, 2017a). Figures 2 and 3 show explorations along the TCS.

Contamination in Stormwater Discharges. After sheens were observed discharging from the TCS outfall, investigations found that petroleum was entering through breaks in a 27-inch-diameter sewer beneath 9th Avenue, adjacent to the Hoyt Street Railyard. Contaminated soil and groundwater, with an extensive pool of LPH, were delineated in the area west of NW 9th Avenue between NW Northup and NW Overton Streets, corresponding to the Burlington Northern Santa Fe’s (BNSF’s) Second Fueling Area that was in this location from approximately 1943 until 1997 (this area was located two blocks up-pipe from the Centennial Mills property). Because of the depth and condition of the sewers in the area, shallow groundwater (and LPH) had infiltrated into the sewers and caused the groundwater table to be depressed along the sewers.

To address sheens at the outfall, BNSF maintained oil absorbent booms at the outfall from the 1970s until 2008. Extensive on-site remediation of the Second Fueling Area was also conducted (RETEC 2002, 2004). Starting in 1975, a contaminant and LPH recovery system was installed that included wells along the west side of NW 9th Avenue to depress the groundwater table to prevent LPH from seeping into the sewers. The system operated periodically until 1995, when it operated full-time until 2001. Between April 1992 and September 2001, the system recovered 6,662 gallons of LPH. In 2001, remedial excavation removed 18,800 tons of petroleum-contaminated soil. The excavation, however, only extended to the east property line and was sloped, leaving approximately 20 to 40 feet of potentially contaminated soil between the 27-inch sewer beneath NW 9th Avenue and the excavation. LPH was still observed seeping from pockets and lenses along the east sidewall of the excavation. After remediation, the property was redeveloped in 2004 for the Pinnacle Condos.

Videos of the TCS and the 27-inch sewer beneath NW 9th Avenue in 2002 noted black staining at several lateral connections to the TCS and between NW Northrup and Overton Streets along the 27-inch sewer; although this appeared to be related to past seepage of oils into the sewer. Stormwater sampling has been conducted from manholes along both sewers in 2002 and from 2008 through 2010, with results detecting metals and PAHs, sometimes exceeding water quality criteria. These detections and exceedances, however, cannot be attributed to the Hoyt Street Railyard site, as higher concentrations were detected upstream of the former railyard.

TCS Backfill Assessments. To assess whether backfill is acting as a preferential pathway for groundwater contamination, BNSF had their consultant complete push probes in 2002 on both sides of the TCS sewer, at two locations on the mill site and an upgradient location on the southwest side of Naito Parkway (RASB- series on Figure 2). Petroleum contamination, including LPH, was present in soil and groundwater in backfill around the sewer, particularly on the mill property. Because anthracene (a PAH) in a groundwater sample showed a slight potential risk to aquatic receptors, two monitoring wells (CMW-1 and CMW-2 on Figure 2) were installed in 2005 within the TCS backfill at the upgradient location. Four quarters of groundwater monitoring were performed, with PAH concentrations being below threshold reference values for aquatic receptors. Based on these data, BNSF concluded, and the DEQ agreed, that the Hoyt Street Railyard did not appear to be contributing significant levels of contaminants to the Willamette River that would pose a risk to human or ecological receptors.

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In 2011, further investigation along the TCS was conducted due to the presence of PAHs and LPH in well MW-2 and 6,100 milligrams per kilogram (mg/kg) TPH in the sidewall closest to the sewer in the former UST nest excavation (Figure 2). Test pit “TC” was excavated from this sidewall toward the sewer. Petroleum-contaminated soil was encountered above and adjacent to the TCS, and wood cribbing was present adjacent to the sewer at 7 feet below the ground surface (bgs). Groundwater started entering the excavation at 9 to 10 feet bgs. When cribbing was pulled back from the sewer, water with LPH flowed in from the upgradient side of the test pit, filling the test pit to approximately 8 feet bgs. After sampling, the excavation was backfilled with controlled density fill (CDF). Push probes were then performed on both sides of the TCS at three locations (GP-series on Figure 2), including on the upgradient property line. Petroleum contamination, including LPH, was present in all probes, primarily at a depth equivalent to the side of the sewer. A probe approximately 1 foot away from the sewer did not encounter backfill material or LPH; only a moderate sheen and slight petroleum odor were noted.

In 2016, an upgradient data gaps investigation was performed southwest of NW Naito Parkway to assess for upgradient sources of contamination to the Centennial Mills site, including through backfill along the TCS (Hart Crowser 2017a; Figure 3). Probes GP-42 and GP-48 encountered gravel backfill on both sides of the TCS between 15 and 25 feet bgs, with petroleum contamination observed between 20 and 25 feet bgs (i.e., heavy sheen, petroleum globules). TPH was detected at up to 2,193 mg/kg in soil and at 31,570 micrograms/liter in groundwater. Other probes completed near these probes did not encounter gravel or field evidence of contamination.

Nature of Contamination. Petroleum contamination, including LPH, has been detected in backfill along the TCS and in monitoring well MW-2 on the site. Contamination is generally limited to the sides of the sewer. Vertically, contamination extends from just below the top of the sewer to a few feet below its base. It does not extend laterally away from the sewer, as explorations further away had no or less indications of contamination.

TPH analyses from samples collected on the site indicate predominately diesel-range hydrocarbons with a small oil-range component. Diesel-range hydrocarbons represent 71 to 88 percent of the TPH in soil and 76 to 93 percent of the TPH in groundwater. TPH concentrations appear higher near the river, but this is more likely due to these samples being fine-grained and thus able to hold more LPH. In the upgradient probes across NW Naito Parkway, a similar percentage of diesel-range hydrocarbons were encountered, with 65 to 88 percent in soil and 79 to 89 percent in groundwater. Two soil samples from probes RASB-13NW and RASB-13SEA had more oil contamination in soil, but these samples were obtained at 16 feet (above the sewer) and not of the gravel backfill.

Chemical analyses for semivolatile organic compounds and PAHs indicate that primarily PAHs are detected in soil and groundwater. Overall, PAHs comprise less than 0.25 percent by weight of the TPH (diesel and oil). Diesel-range PAHs (non-carcinogenic PAHs and naphthalene – benzo[g,h,i]perylene) comprise over 75 percent by weight of the PAHs on the site. Gasoline-associated VOCs and several chlorinated VOCs were detected at low concentrations in soil on the site, primarily in on-site upgradient probes GP-13 and GP-14. Other detections in soil on the site either migrated downgradient or were associated with downgradient releases, such as in the former UST nest. VOCs were less frequently detected in groundwater on the site. VOCs were not detected in soil or groundwater across NW Naito Parkway.

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Geology and Hydrogeology. At the Centennial Mills site, the subsurface geology consists of up to 20 feet of fill (primarily silt, silty sand, and sandy silt, with occasional gravel and debris) placed on native alluvium (sandy silt, silty sand, and sand). Explorations along the TCS encountered a mixture of sands and silts, with discontinuous pockets and layers of gravel. Upgradient and mid-property probes encountered backfill material consisting of gravel and sand (with LPH) adjacent to the sewer. At the river, sand and gravel fill was present over sandy silt and sand. LPH was present within this lower finer unit. Wood cribbing was occasionally encountered and is likely the form used to build for sewer, which was reportedly left in place.

Groundwater levels vary seasonally with higher levels in the winter and spring due to rainfall infiltration and higher river levels. Along the top of the bank, groundwater levels are generally equivalent to river levels. Shallow groundwater on the site has been encountered ranging from 5 to 24 feet bgs, equating to elevations from 17 to 6 feet COPD. In monitoring wells CMW-1 and CMW-2, across Naito Parkway, shallow groundwater fluctuated between approximately 17 and 10 feet COPD during 2005 and 2006 (RETEC 2007). Further inland, along the east side of NW 9th Avenue, across from the former Hoyt Street Railyard site, groundwater fluctuated between approximately 20 and 15 feet COPD (i.e., 11 to 15 feet bgs in wells MW-4 and MW-5; RETEC 1996).

Shallow groundwater flow is expected to be toward the river, although groundwater infiltration in deeper sewers in the area has been known to have a localized effect on adjacent groundwater gradients (RETEC 1996). During the upgradient data gaps investigation, groundwater levels were 2.7 feet lower in probe GP-42 on the northwest side of the TCS than in nearby probes GP-35 and GP-43 (Figure 3). The calculated groundwater elevation of GP-42 is 8.35 feet COPD, a couple feet higher than the bottom of the TCS.

Risk Evaluation. Contaminants in the TCS backfill can reach the river through groundwater migration and emerge as surface water and by infiltration into the TCS with discharge to the river. Sewer videos do not indicate that the latter pathway is complete, with no observable groundwater seepage into the sewer (there’s occasional cracks but no apparent seepage). In the SCE, screening of groundwater data from backfill samples against Joint Source Control Strategy (JSCS) screening levels (DEQ/EPA 2007) indicated exceedances by PAHs. For probe samples, this is likely due to sample turbidity elevating PAH concentrations as PAHs tend to adsorb to soil particles.

Evaluation of groundwater data from well MW-2 showed that several PAHs, lead, and zinc detections exceed JSCS ecological screening level values and, with the presence of LPH, could pose a risk to the benthic environment. Because petroleum is limited to backfill around the TCS, the extent of possible impact at the river is probably localized to the area within 10 feet of either side of the sewer, considering some lateral spreading in the finer-grained soils along the riverbank and perhaps due to the absence of TCS backfill and construction cribbing near the outfall. Risks to human health through fish consumption and river water ingestion would be non-existent considering the localized nature of potential water quality impacts and the significant dilution by the river.

The HHRA for the Centennial Mills site excluded the TCS backfill because contamination could be from an off-site source and did not represent environmental conditions of the rest of the site. The HHRA, however, screened VOC data for the backfill to assess for potential vapor intrusion risks. No unacceptable risks were

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identified. Because the contaminated backfill is fairly deep (greater than 5 feet), it might be contacted by construction or excavation workers resulting in a health risk. A review of the soil data in the SCE against DEQ risk-based concentrations (RBCs) did not indicate an unacceptable risk from soil, but groundwater concentrations show some RBC exceedances for carcinogenic PAHs (likely due to the presence of LPH). The presence of LPH in backfill and recent observations of sheens at the TCS outfall suggest that the LPH may constitute a “hot spot” as its highly concentrated, highly mobile, and not reliably containable (DEQ 1998).

2.2.2 Potential Sources Environmental investigations have identified petroleum contamination, particularly LPH, within the TCS backfill. The presence of LPH at the upgradient (Naito Parkway) edge of the site suggests that off-site source(s) of contamination are likely present. However, releases from former USTs on the mill site may have contributed to contamination. These sources are discussed below. Further information can be found in Hart Crowser’s SCE and technical review (Hart Crowser 2013a, 2015).

Former UST Nest. In 1989, two diesel USTs were decommissioned by removal from the site. Based on the presence of two vent pipes, these USTs were likely located at the top of the riverbank. No release was reported, but a probe in this area found petroleum contamination. In 2009, approximately 200 tons of petroleum-contaminated soil were excavated (see Former UST Nest Excavation on Figure 2). A buried concrete pad at 9 feet bgs for anchoring the USTs and a wall on the riverside of the UST nest restricted petroleum migration downward and eastward. Beyond this pad, excavation proceeded to 14 feet bgs. Residual TPH concentrations ranged from non-detect to 500 mg/kg, except on the bottom (1,023 mg/kg) and northwest sidewall closest to the TCS (6,100 mg/kg). At the time, further excavation was not conducted to the northwest due to the proximity of the TCS. In 2011, test pit “TC” was completed in this area, which encountered LPH in the TCS cribbing/backfill. A determination of the degree that the former UST nest as a contributor to contamination in the backfill and/or nearby well MW-2 cannot be made.

Former Gasoline UST. A gasoline UST was present in the middle of the mill site near the TCS. Because diesel is the predominant hydrocarbon release, this UST is not the source of backfill contamination.

Former Heating Oil UST. A 12,000-gallon heating oil UST was once located over the TCS in the area currently between the mill building and paddock (Figure 2). It was installed in 1948, lined in 1970, used until 1988, decommissioned in-place in 1990, and removed in 2001. When removed, petroleum- contaminated soil was encountered on the top and around the northeast side of the middle portion of the UST. Contaminated soil was removed, and samples were collected from beneath the ends of the UST, from gray-stained soil in excavation sidewalls, and above and below the gray-stained soil. The only substantial TPH detection was 2,135 mg/kg (mostly oil-range) at 12 feet bgs on the northwest end of the UST. PAH analysis did not detect several PAHs that are present in nearby backfill probes, such as acenaphthene, anthracene, and fluorene. While a release did occur, it does not appear to be extensive and result in the significant contamination present in probes GP-13 and GP-14, located approximately 54 feet upgradient.

Hoyt Street Railyard. Environmental investigations at the Hoyt Street Railyard delineated petroleum- contaminated soil and groundwater, including a pool of LPH, at the location of the Second Fueling Area west of NW 9th Avenue between NW Northup and NW Overton Streets. As discussed in Section 2.2.1,

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contamination extended into 9th Avenue and had seeped into the 27-inch 9th Avenue stormwater sewer. Groundwater pumping recovered at least 6,662 gallons of LPH, and excavation removed 18,800 tons of contaminated soil. Contamination, however, still remains beneath 9th Avenue.

In June 2016, Hart Crowser performed an upgradient data gap investigation southwest of NW Naito Parkway to further investigate the former Hoyt Street Railyard as a potential source for site contamination (Hart Crowser 2017a). As described in Section 2.2.1, the investigation found significant petroleum contamination in gravel backfill on both sides of the TCS. The TCS backfill, therefore, represents a likely ongoing preferential pathway for the petroleum as LPH and/or dissolved-phase petroleum constituents, such as PAHs, to migrate with groundwater to the Centennial Mills site. Because relatively substantial petroleum contamination is present, it could reduce the long-term effectiveness of the proposed remedy at the Centennial Mills site.

ATCS and Up-Pipe Manufactured Gas Plant. Before the TCS was installed, an earlier municipal sewer had been in place for stormwater and sanitary water from approximately 1887 to when it was abandoned in 1917 by filling with sand. The ATCS, as it is known, could also act as a potential preferential pathway. It has been breached on several occasions and found to contain petroleum-contaminated materials and fill. In 2002, excavation work near NW Marshall Street breached the ATCS and oily water and oily sands were observed. In 2009, the ATCS was also accessed by a test pit at the Centennial Mills site – it was partially filled with petroleum-contaminated material, but no water was present. In 2016, the upgradient data gap investigation targeted the ATCS with two probes (GP-35 and GP-36; Figure 3) intercepting the ATCS. It was filled with sand and had a basal gravel with LPH and/or a heavy sheen. No contamination has been found outside of the ATCS.

The source of the contamination within the ATCS is likely from a manufactured gas plant (MGP) located at the intersection of NW 9th Avenue and NW Lovejoy Street, approximately 1,300 feet south of the Centennial Mills site (Hart Crowser 2015). The MGP operated from approximately 1893 until 1934, producing compressed gas from crude oil for the lighting of railroad cars. MGPs utilize water during the gas manufacturing process, and sewer records show a potential connection of the plant to a new sewer that replaced the ATCS in this area in approximately 1917. While an earlier connection to the ATCS is highly suspected, no plans are present for the ATCS that show lateral connections.

Currently, the ATCS is not a current ongoing preferential pathway. CDF was used to fill the breach at NW Marshall Street and the test pit at Centennial Mills. The ATCS outfall has also been plugged. Additionally, the ATCS was intersected by the construction of the TCS in 1917 and likely again by a 30-inch sewer in 1998 (Figure 3). Probes 49 through 52 in the area of this latter intersection failed to find the ATCS and significant contamination, suggesting that LPH is not currently migrating northward into the area. The data, however, support that historical petroleum discharges did occur through the ATCS; after it was intersected by the TCS, residual product could have historically migrated to the backfill around the TCS.

2.3 Remedial Action Objectives Petroleum contamination, including LPH, is present in backfill around the TCS and in monitoring well MW-2 (Figure 2). The presence of this contamination, a preferential contaminant migration pathway, and

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a potential risk to benthic receptors in the Willamette River, necessitate a source control measure to prevent contaminants from migrating to the river. Additionally, groundwater contamination might pose an unacceptable risk to excavation workers. RAOs that have been identified to address this migration pathway and its potential risks are presented below.

 Remove mobile LPH to the extent practicable near the Willamette River through groundwater extraction wells installed within the TCS backfill (Phase I).

 Mitigate the contaminant migration pathway within the TCS backfill so that contaminants and LPH can no longer migrate to the river. The on-site remedy (and source control measure) will consist of replacing backfill along both sides of the TCS beneath the site with a grout barrier, thus removing the preferential backfill pathway and preventing riverward migration of contamination (Phase II).

 Reduce risks from backfill contamination to excavation workers. During implementation of the remedy, appropriate health and safety protocols will be used. To address future risks and per the FFS and ROD (Hart Crowser 2014, DEQ 2014b), a cap will be placed over the TCS and an Easement and Equitable Servitude will be recorded for the Centennial Mills site, notifying others of the underlying contamination. Capping will likely be completed during future development of the Centennial Mills property.

3.0 TANNER CREEK SEWER MITIGATION PLAN Previous investigations of backfill around the TCS on the Centennial Mills site have found petroleum contamination, including LPH, in soil and groundwater. The presence of this contamination and a preferential pathway necessitate a source control measure to prevent contaminants from migrating to the river. Phase I of the mitigation plan consists of installing two groundwater extraction wells and associated extraction equipment to recover mobile LPH from the subsurface. Phase I will be completed in fall 2019. This system will be operated intermittently for approximately 1 year. Phase II consists of installing a grout barrier at the lower end of the TCS on the site to seal and isolate the TCS backfill beneath the site and prevent further groundwater migration through the backfill. Phase II is scheduled for completion in fall 2020.

Phase I is described in detail below. Phase II is briefly described in this RAP. A subsequent RAP for Phase II will be prepared once subsurface conditions are directly observed while completing Phase I.

3.1 Installation of Phase I – LPH Removal The first phase of the RA will involve installing two extraction wells along the TCS in the proposed area of remedial excavation. The purpose of the wells will be to recover mobile LPH, to the extent practicable, along the TCS over the course of 6 months to 1 year during both high and low seasonal groundwater levels. The objectives of extraction are: (1) to remove heavily contaminated groundwater and/or mobile LPH not only within the Phase II remedial excavation area, but to draw it from upgradient and downgradient areas along the TCS; and (2) reduce the potential for contamination to migrate toward the river. Running the pumps intermittently will allow for LPH to migrate and/or accumulate on the water table and to target the various depth intervals as the water table raises and falls. The extraction pump will be run for a few days up to a week at a time, until diminishing contamination is observed. Appendix A includes plans and specifications of the Phase I system.

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3.1.1 Preparatory Activities In preparing for Phase I of the remedial activities, certain preparatory activities will be completed that include the following.

Subcontractor Procurement. Hart Crowser will conduct a solicitation to procure a well driller and remedial contractor to install the extraction wells, conveyance piping, pump, and electrical connections in accordance with the plans and specifications in Appendix A. Although this section and Appendix A represent the current understanding of site conditions, changes may be necessary to address conditions encountered during the remedial activities.

Permitting and Plan Preparation. The selected subcontractor will be required to obtain all required permits prior to beginning work. This includes Well Start Cards from the Oregon Water Resource Department for the extraction wells, electrical permits for any modifications required to the electrical supply, and a permit from the City of Portland to drill next to the TCS and within their utility easement on the property. Other permits may be required and will be the responsibility of the remedial contractor to identify and obtain. Additionally, the contractor will prepare an Erosion and Sediment Control Plan (ESCP) and install erosion and sediment control measures prior to any ground disturbing activities. Hart Crowser’s on-site representative will possess a Certified Erosion and Sediment Control Lead certification and will review the ESCP prior to the start of work. Hart Crowser’s on-site representative will also inspect that best management practices (BMPs) identified in the ESCP are installed properly and are working as intended during site work. The ESCP will be modified as needed if BMPs are not working properly. The contractor and Hart Crowser will each prepare a site-specific Health and Safety Plan in general accordance with Occupational Safety and Health Association and Oregon Administrative Rules for their own use during the remedial activities.

Underground Utility Location. Prior to the remedial activities, the selected subcontractor will arrange to have underground utilities located and marked by contacting the Oregon Utility Notification Center, who will in turn notify the various utilities in the area to mark any underground installations in the vicinity of the site. The contractor will also have a private utility locate conducted and/or assess for buried utilities.

3.1.2 Extraction Well Installation and Vacuum Truck Exploration An Oregon-licensed well driller will install two extraction wells, one on each side of the TCS where remedial excavation is proposed. These wells will be located approximately 15 feet from the downgradient end of the proposed extent of excavation. A pump will be installed at the surface with suction end pipes installed in each well and used to pull water and product from within the footprint of the proposed excavation. The depression in the groundwater table caused by extraction could also possibly pull back LPH in the riverbank area and may also mobilize potential LPH upgradient of the remedial excavation that poses a long-term concern. These wells will be removed by excavation during the Phase II remedial excavation. Extracted groundwater will be conveyed to a water storage tank staged on the site.

Initially, a vacuum truck will be used to locate both sides of the TCS. Approximately 3 to 5 feet parallel to the sewer edge will be exposed to observe the remaining formwork (i.e., wood cribbing) used when constructing the TCS. These observations will inform the design of the Phase II excavation. Historical photographs indicate that the wood cribbing was installed continuously along the TCS during construction,

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but the degree to which it remains, and its construction, are unknown except for what was briefly observed during test pitting in 2011. Once the edge of the TCS is observed, the removed soil will be returned to the excavation. There will not be any compaction requirements for the backfill, but this will need to be confirmed with the City of Portland. The vacuum truck will then excavate a second vertical void along each edge of the TCS to assist in accurately placing the extraction well without damaging the TCS. Potholing is schematically shown on Sheet 3 in Appendix A.

A hollow-stem auger drill rig will be used to install 4-inch-diameter extraction wells immediately adjacent to the sides of the sewer wall. The hollow-stem auger will provide approximately 8.25 inches of annular space. Wells will be installed to a depth of 22 feet bgs, or to a depth of approximately 4 feet below the base of the sewer (the bottom of the TCS is approximately 18 feet bgs). The wells will be screened from 22 to 7 feet bgs. The sand filter pack will be installed within the annular space of the boring from the bottom of the boring to approximately 5 feet bgs (2 feet above the screened interval). Bentonite chips (3/8-inch hole plug) will be installed from the top of the sand filter pack to approximately 1.5 feet bgs to seal the screened well casing from the ground surface. Bentonite chips will be placed dry and subsequently hydrated. Centralizers will be used to center the well casing within the borehole. Extraction wells will be finished at the surface within flush mounted vaults, as described below. Well details are provided on Sheet 3 in Appendix A. Investigation-derived waste (IDW) management is described in Section 3.1.5.

3.1.3 Groundwater Conveyance Groundwater conveyance will carry groundwater from the extraction wells to the groundwater storage tank. The conveyance layout is shown on Sheet 2 in Appendix A, while details of the groundwater conveyance components are shown on Sheet 4 in Appendix A.

3.1.3.1 Conveyance Design Wells will be completed within flush-mounted and lockable steel vaults. Vaults will provide a secure subsurface area for wellhead and conveyance line connections. Each vault will be open-bottomed and approximately 24 inches by 24 inches by 18 inches deep (manufactured by Emco Wheaton or similar).

Because contaminated groundwater is being pumped near the Willamette River, extracted water will be conveyed underground through double-walled piping to preclude potential breakage of above-ground piping due to vandalism or freezing. The outer pipe will provide secondary containment if the inner pipe is breached. Double-walled piping will consist of an inner 1-inch-diameter Schedule 80 PVC pipe installed within a 2-inch-diameter Schedule 80 PVC pipe. Secondary containment will be installed between the two extraction well vaults and from the northern extraction vault (Extraction Vault #2 in Sheet 4) to the water storage tank.

A series of fittings and valves will be installed to transition extracted groundwater and LPH from the riser pipe to the conveyance piping. Well vault details are provided on Sheet 4 in Appendix A. A pitless adapter will be installed at the top of each riser pipe to allow easy removal and replacement of the riser pipe. This offers a convenient way to change the length of the riser pipe without disruption to horizontal conveyance. The two riser pipes will be installed at approximately 1 foot below the lowest presumed groundwater elevation for the upcoming week. A few pre-cut lengths of riser pipe will be kept on-site for

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each well head to be installed depending on the desired depth. A compression coupling will be installed below the pitless adapter to allow riser pipes to be changed. The pitless adapter will also be fitted with a small “tee” handle to aid in removing the riser pipe.

Once outside the well casing, conveyance pipe will be fitted with a gate valve to adjust or isolate flowrates and a check valve to prevent extracted groundwater/LPH from flowing back down the well. Groundwater will be combined in the vault nearest the water storage tank. Gravel bedding will be used to support pipes and pipe fittings within the vaults. PVC couplings will be slip type and glued together following manufacturers recommendations. Right angle “elbow” and “tee” fittings will be avoided. Where 90-degree angles are required, they will be achieved using two 45 degree “elbow” fittings or a long sweep 90-degree “elbow”. This will reduce turbulence and increase pumping efficiency.

At the downstream (pump) end of the conveyance pipe, a third vault will be installed to house the extraction pump and transition conveyance pipe from below ground to the water storage tank. This vault will be 30 inches by 30 inches by 30 inches deep and will be closed bottom. The top of this vault will be installed slightly above the surrounding grade to prevent surface water inflow; it will be secured with a lockable steel cover.

Conveyance piping will be 1-inch-diameter Schedule 80 PVC into the pump and will transition to reinforced 1-inch-diameter PVC tubing from the pump discharge to the water storage tank. The pump discharge line will need to be flexible to be removable from the water tank. This tube will be contained within a secondary containment pipe to the top of the tank. Secondary containment above ground will be 4-inch-diameter Schedule 80 PVC pipe. Joints in the above-ground conveyance will be joined using rubber Fernco-type fittings so conveyance can be moved and adjusted while the water storage tank is being removed or replaced. This flexibility will allow connections to a variety of tank types if a new water storage tank is needed. Secondary containment will also house the air supply hose from the air compressor to the extraction pump.

Conveyance from the pump discharge will pass horizontally through the vault wall and transition to above ground near the water storage tank. It is not anticipated that freeze protection will be required for the above-ground conveyance pipe. The precise connection of the containment hose to the water tank will be determined when the water tank arrives on the site as tanks can have a variety of connections available. Conveyance discharge will be securely connected to the tank as suggested by the manufacturer. Secondary containment will be terminated in a manner that will prevent rain from entering the pipe.

3.1.3.2 Installation Vault Installation. The three vaults will be placed approximately 1 inch above surrounding grade to prevent surface water flow from infiltrating the vault. The vault boxes will be secured using concrete collars. Formwork will be installed to assure concrete is uniformly placed around the perimeter of each vault. Concrete collars will be at least 4 inches wide and 4 inches deep. Concrete will be shaped to uniformly slope concrete from the vault boxes to the surrounding grade. Concrete formwork will be removed once concrete cures. Any depressions remaining from removing the formwork will be filled using clean, imported ¾-inch minus gravel.

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Pavement. The area of the extraction wells and conveyance pipe is paved with asphalt-concrete. A concrete cutter will be used to cut asphalt pavement from the footprint of the conveyance path and from the footprint of the extraction well vaults. A single rectangular cut can be made to encompass both extraction well vaults and the area between the two. Asphalt pavement removed during installation will be recycled off site. Phase I will not require asphalt pavement to be replaced at the completion of work.

Trenching. Conveyance piping will be installed a minimum of 12 inches underground. The trench will be approximately 12 inches wide, or as wide as needed, to install conveyance pipe. It is not anticipated that the trench bottom will require pipe bedding; however, this determination will be issued after the subsurface conditions can be inspected by the project engineer. Before installing conveyance pipe, the trench bottom will be mechanically compacted using a vibratory plate compactor. A percent compaction will not be specified but should be sufficient to minimize the likelihood of settling. Sufficient compaction will be determined by the project engineer or geologist. Soil removed for trenching will be replaced to the trench. Clean, imported ¾-inch minus gravel will be placed over the trench backfill, as needed, to bring the surface back to grade.

Utility Tracer Wire. A solid 12-gauge tracer will be attached to the conveyance pipe prior to burying the pipe. Underground connections will be minimized by using a single continuous tracer wire for conveyance pipe where possible. When necessary, buried tracer wire segments will be connected using a moisture- proof and gel-filled splice to prevent corrosion (3M Direct Bury Splice Kit, or similar).

3.1.3.3 Conveyance Pipe Pressure Test Complete runs of underground conveyance pipe and fittings will be tested for leaks using a hydrostatic pressure test. Pipes will be filled with water and pressurized to 150 pounds per square inch (psi). Pipe should be able to hold pressure for 30 minutes with a pressure loss of 5 psi or less to be considered passing. Hart Crowser will be present to observe and document all pressure tests.

A hydrostatic test pump designed for this purpose will be used to complete the test(s). The length of underground conveyance pipes from the pump vault to the nearest groundwater extraction well vault will be tested. Pipe and fittings within the vaults will not be tested using a hydrostatic pressure test, neither will the segment of conveyance pipe between the two extraction well vaults. These fittings and segments of pipe will instead be observed for leaks. The conveyance pipe between the two vaults will likely be one segment of pipe with no joints or fittings.

To complete the pressure test, an exposed end of the conveyance pipe will be fitted with a glued PVC slip coupling, then reduced to hold a galvanized tee fitting with a pressure gauge. A ball valve will be fitted to the opposite end of the tee where the hydrostatic pump hose will be secured. At the opposite end of the conveyance pipe, a glued PVC slip coupling will be installed and fitted to hold a second ball valve. The ball valve will be open to the atmosphere to begin the testing procedure.

The testing procedure is generally as follows:

 The conveyance pipe will be slowly filled with water from the hydrostatic test pump.

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 Once water is observed flowing steadily from the opposite end of the conveyance pipe, the ball valve at the opposite end will be shut and the pressure allowed to build within the pipe as recorded on the gauge.

 When pressure builds up to 150 psi, the second ball valve will be closed.

 The gauge will be monitored for pressure loss.

 The conveyance pipe will remain undisturbed for 30 minutes and the pressure loss recorded.

Pressure testing should be completed before backfilling the trench so that if any leaks are encountered, they can be addressed without having to re-excavate the trench.

3.1.4 Groundwater Extraction System The goal of groundwater extraction is to pull groundwater and LPH from near the top of the water column. To achieve this goal, a double diaphragm pump will be used to pull fluids from both extraction wells and direct it to the water tank for storage. Sheet 2 in Appendix A shows the location of the water storage tank, pump vault, and compressor used to power the pump. A diaphragm pump will be installed in the pump vault just below the ground surface. This type of pump allows groundwater, LPH, and air to be pulled from the well casings without damage to the pump or requiring a prime if water levels in the wells drop below the riser pipes. The pump will be powered using compressed air. The extraction pump and air compressor will be installed near the water storage tank as shown on Sheet 2 in Appendix A.

A benefit of using a vault-housed pump is that the pump and compressor can be installed near the electrical power source at Warehouse E, so trenching and installing electrical power to the extraction wells will not be required. Additionally, by not having a down-well pump, staff will be able to pull the riser pipe and adjust the extraction height easily as seasonal groundwater levels change. The pump will initially be operated intermittently alternating from 1 week of operation and 1 week of shut down to allow re- accumulation of LPH. A timed shut-off valve may be installed on the air supply line to the pump to automatically shut off the pump. This device will reduce the number of site visits to operate the system. The duration of operation will be adjusted based on recovery observations.

Schedule 80 PVC conveyance pipe will be directly threaded into the pump inlet and outlet. Conveyance pipe from the pump to the storage tank will depend on the fittings on the actual tank supplied on the site. Conveyance piping will remain double-walled until conveyance is within a secured location on, or adjacent to, the water storage tank. Site security is described below.

Compressor. The air compressor will be a “quiet” type capable of operating continuously at 10 cubic feet per minute at a pressure of 90 psi and at 60 decibels, or less, at the property line in accordance with City of Portland Code (Chapter 18.10). The compressor will be contained within a secured enclosure (i.e., cabinet) designed to house a compressor without causing overheating.

Power Supply. Power to the air compressor will be provided by tapping into power identified at Warehouse E. Wire to the pump will be contained within electrical conduit. Wire connection and conduit

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installation will likely require a permit and will need to be installed by a licensed electrician. The specifications of the air compressor will likely require 120 volts power.

Extracted groundwater will be stored in a bulk storage tank staged on the site near Warehouse E. The tank will be enclosed and secured to prevent access to the contaminated groundwater and any LPH. The tank will either be equipped with built in secondary containment, or external secondary containment will be provided around the tank to contain a minimum of 110 percent of the storage capacity of the tank.

Fence. The storage tank, pump, air compressor, and electrical supply will be secured within a fenced area. Fencing will be constructed using a series of temporary-style fence panels approximately 6 feet in height. Footings at the fence panel joints will be anchored to the ground surface to prevent unauthorized removal of fence panels. Additionally, panels will be bolted together using standard hardware and chained and locked together. The exception will be an access gate that will be constructed of the same panels, however, the panels will not be anchored to the ground.

Initial System Startup. Once complete, the system will be started up to make sure all components are operating as intended. Any deficient components will be addressed before the contractor demobilizes from the site.

3.1.5 Investigation-Derived Waste IDW will consist of soil and decontamination water generated during well installation, soil generated from trenching and vault installation, and personal protective equipment (PPE). PPE will be disposed of as solid waste. Soil removed by the vacuum truck and excess soil from trenching and vault installation will be returned to the hole from which it was removed. Any excess soil, unless obviously contaminated, will be staged under the covered horse paddock until Phase II excavation activities are completed. This soil will be placed on, and covered with, plastic sheeting and secured to prevent wind and rain erosion. Water generated during well installation will be stored in drums and later added to the water storage tank. Transfer and disposal of liquids from the storage tank are described in Section 3.2.

3.2 Ongoing Operation of Phase I – LPH Removal The extraction system will be operated to recover mobile LPH and remove heavily contaminated groundwater along the TCS for up to 1 year during both high and low seasonal groundwater levels. Running the pumps intermittently will allow for LPH to migrate and/or accumulate on the water table and to target the various depth intervals as the water table raises and falls. The extraction pump will be run for a few days up to 1 week at a time, until diminishing contamination is observed. Hart Crowser will operate the extraction system and monitor extraction rates and the recovery of mobile LPH.

3.2.1 Site Visits Hart Crowser will initially conduct site visits daily following startup to monitor treatment system operation and extraction rates. Once operations are standardized, site visits will be reduced; it is anticipated that visits will be conducted weekly but will be adjusted based on observed operations.

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During each site visit, Hart Crowser will have field forms prepared to record pump rates, estimated extraction volume, water level in the storage tank, weather conditions, river elevation, extraction depth, and other pertinent observations.

Riser Adjustment. The extraction depth will be adjusted during each site visit, as needed, to remove groundwater from the top of the water column. To adjust the extraction depth, multiple pre-cut PVC pipe lengths will be available on the site. As the riser pipe is removed, staff will wear protective gloves and use an oil-absorbent pad to clean the riser pipe. The riser pipe will be stored within the fenced area near the storage tank and stored on, and covered with, plastic sheeting. Field PPE and waste material will be disposed of as solid waste.

Sheen Inspections. During each site visit the area of the TCS outfall will be inspected for sheens on river water. If present, the nature and the extent of sheen will be described. If droplets of LPH are observed on water, we will notify Prosper Portland. Observations will be recorded in standardized field forms and will include photographs where appropriate. These inspection reports will be transmitted to Prosper Portland for their use and records.

LPH Measurement/Removal from MW-2. On approximately a monthly basis, monitoring well MW-2 will be assessed for LPH using a water level meter capable of detecting petroleum/water interfaces. The groundwater level and thickness of LPH, if present, will be recorded. If LPH is present, it will be skimmed off the water table using a peristaltic pump or bailer until recovery diminishes to a sheen or miniscule droplets. Field observations of purging and LPH recovery will also be recorded in field notes. Purged water and LPH will be placed in the water storage tank. Waste materials will be disposed of as solid waste.

3.2.2 Groundwater/LPH Disposal Ongoing operation of the Phase I extraction system will produce extracted groundwater and LPH. Water and LPH stored in the on-site storage tank may be tested but will not likely require treatment before being delivered to an oil recycling facility. The water tank will be directly loaded and transferred to an oil recycling facility. Treatment and disposal will require discussions with, and pre-approval from, the recycling facility.

Tank unloading procedures will meet the locally-accepted standards and the U.S. Department of Transportation (DOT) requirements. We have included a check list for loading/unloading procedures prepared for fuel transport vehicles in Appendix B. This form, or similar and equivalent form, will be used during each water transfer event. Applicable DOT requirements include:

 Only trained personnel, who are knowledgeable with applicable regulations, shall perform transfer procedures.

 Transfer operations must be completed during daylight hours or with adequate lighting.

 The transport truck driver must have assistance while backing up to prevent hitting the obstructions.

 Set truck brakes and block wheels. A trained operator must remain with the vehicle and observe the transfer during the entire loading and unloading period.

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 Place caution signs in the vicinity of the transfer truck to warn approaching personnel. Leave signs up until operation is complete and transfer truck is disconnected.

 Smoking and producing open flames within 50 feet of a point where petroleum-contaminated water is being transferred shall be prohibited. Only spark-proof tools are to be used.

 Make sure the tank being loaded is vented before connecting the loading line.

 Read the level indicator and visually inspect the receiving tank to be sure sufficient space is available to receive material being transferred.

3.3 Future Phase II – Grout Barrier Installation Phase II of the RA includes installing a low-permeable barrier along the TCS to prevent the further migration of petroleum-contaminated groundwater through the backfill to the Willamette River. The low- permeable barrier will be approximately 50 feet long and installed using two excavations along both sides of the TCS.

Phase II is anticipated to be completed in September/October 2020 during seasonally low water levels. Subcontractors procured as part of Phase I will not necessarily be retained to implement Phase II; however, Phase I system components will be decommissioned in conjunction with Phase II activities by Hart Crowser and the Phase II contractor.

We will prepare a detailed Phase II RAP following our observation of the TCS cribbing during Phase I. From historical photographs and previous environmental activities, it is anticipated that TCS cribbing is continuous; this assumption will be partially confirmed during Phase I and shoring is directly observed using the vacuum truck. Trench excavation will be completed to approximately 22 feet bgs (an estimated 4 feet below the bottom of the TCS). Although not anticipated, this depth may be deepened if significant contamination is observed.

Trenches will be a minimum of 2 feet in width to remove cribbing and backfill material immediately adjacent to the TCS. Previous environmental activities have shown that contamination is localized to within 2 feet of the sewer walls. These trenches will be backfilled with low-density grout and CDF to provide a seal around the TCS.

4.0 REPORTING RAs will be completed on the Centennial Mills site to mitigate the preferential pathway for groundwater contamination and LPH to migrate in backfill around the TCS. Phase I will consist of installing two groundwater extraction wells within the TCS backfill to recover LPH, to the extent practicable, and to control contaminant migration. In 2020, a grout barrier is planned to be placed at the downgradient portion of the TCS to remove the preferential TCS backfill pathway and create a seal for groundwater migration along the TCS beneath the site. Reporting for Phase I is described below.

Phase I Mitigation Installation Report. After completing the TCS mitigation activities, we will prepare a Phase I Mitigation Installation Report that documents implementation of the mitigation activities,

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including the means and methods used by the remedial contractor, our observations as recorded in our field notes, deviations from this RAP, and the analytical results of any sampling performed. Representative photographs of the activities, disposal documentation, and laboratory reports will be included in appendices.

Quarterly Reporting. On a quarterly basis, a letter report will be submitted to the DEQ discussing Phase I extraction system operation and describing the observations from the sheen inspections and MW-2 monitoring over the prior quarter. Copies of field notes, representative photographs, and water/LPH disposal documentation will be attached. The letter will evaluate the apparent effectiveness of the remedial activities and whether changes to the inspection program are needed.

5.0 REFERENCES City of Portland 2016. Portland Maps website for publicly available information. Accessed April 2016 at: http://www.portlandmaps.com/.

DEQ 1998. Guidance for Identification of Hot Spots. April 23, 1998.

DEQ 2014a. Source Control Decision, Centennial Mills, ECSI #5136. March 7, 2014.

DEQ 2014b. Selected Remedial Action, Record of Decision for the Centennial Mills Site, Portland, Oregon. December 2014.

DEQ/EPA 2007. Portland Harbor Joint Source Control Strategy. December 2005. Table 3-1 of Screening Level Values updated on July 16, 2007.

Hart Crowser 2000. Phase I and II Environmental Site Assessment, Centennial Mill, 1362 NW Naito Parkway, Portland, Oregon. February 2, 2000.

Hart Crowser 2002. Soil Closure Report, Centennial Mill/Mounted Police Unit Site, 1362 NW Naito Parkway, Portland, Oregon. May 3, 2002.

Hart Crowser 2009. Data Gap Investigation Report, Centennial Mill Redevelopment, 1362 NW Naito Parkway, Portland, Oregon. December 29, 2009.

Hart Crowser 2013a. Final Upland Source Control Evaluation, Centennial Mills, 1362 NW Naito Parkway, Portland, Oregon. March 21, 2013.

Hart Crowser 2013b. Final Human Health Risk Assessment, Centennial Mills, 1362 NW Naito Parkway, Portland, Oregon. November 14, 2013.

Hart Crowser 2014. Focused Feasibility Study, Centennial Mills, 1362 NW Naito Parkway, Portland, Oregon. April 16, 2014.

Hart Crowser 2015. Technical Review of Investigation Summary Report, Abandoned Tanner Creek Sewer and 9th and Lovejoy Street, Portland, Oregon. May 15, 2015.

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Hart Crowser 2017a. Upgradient Data Gap Investigation, Centennial Mills – Tanner Creek Sewer, 1362 NW Naito Parkway, Portland, Oregon. May 26, 2017.

Hart Crowser 2017b. Phase II Environmental Site Assessment, Centennial Mills Post-Demolition Sampling, 1362 NW Naito Parkway, Portland, Oregon. July 10, 2017.

Maul Foster & Alongi, Inc. 2006. Sediment Characterization Report, Waterside Impact Evaluation, Portland Development Commission, Centennial Mills Site, Portland, Oregon. July 27, 2006.

Prosper Portland 2019. Prosper Portland Website. Centennial Mills Project Details. Accessed August 2019 at https://prosperportland.us/portfolio-items/centennial-mills-project/.

RETEC 1996. Remedial Investigation Report for the Burlington Northern Hoyt Street Site. October 1996.

RETEC 2002. 2001 Annual Progress Report, Hoyt Street Property Containment and Recovery System and LNAPL Excavation Completion Report. April 4, 2002.

RETEC 2004. Tanner Creek Sewer Investigation and Evaluation, Former Hoyt Street Railyard, Portland, Oregon. February 2, 2004.

RETEC 2007. Annual Groundwater Monitoring Report: Former Hoyt Street Railyard - Portland, Oregon. March 28, 2007.

150-012-003 DRAFT October 28, 2019 Document Path: F:\Notebooks\1582501_PDC Phase II Demo Env Oversight\GIS\1582501_VMap.mxd Date: 4/4/2017 User Name: melissaschweitzer California Washington Portland OREGON 0 1,000 Nevada ,0 4,000 2,000 Idaho Feet N MapmyIndia, © OpenStreetMap contributors, and the GIS User Community User GIS the and contributors, © OpenStreetMap MapmyIndia, (Thailand), Esri Kong), (Hong China Esri METI, Japan, Esri NRCAN, Sources:Esri, HERE, DeLorme,USGS, Intermap, increment P Corp., Project Location Project 15825-01 Portland, Oregon Centennial Mills Centennial Vicinity Map Vicinity Figure 1 4/17 Abandoned Tanner Creek Sewer (1887-1917)

Tanner Centennial Creek Sewer Mills (1917)

MW-2

Former Diesel UST Nest Excavation

Sewer Easement

Former Gasoline UST Excavation

Former Heating Oil UST Author: melissaschweitzer Front Avenue (1924, 1985) Excavation

Upgradient Investigation Area (See Figure 3) MPU Paddock Front Avenue (1985)

Front Avenue (Abandoned)

Pettygrove Sewer (1890-1917?)

9th Avenue 8" Sewer 30" Sewer 27" Sewer (1923) (1961) (1998)

LEGEND Centennial Mills Push Probe (2011) Railyard Monitoring Portland, Oregon Well (2005) Test Pit (2011) Exploration (2002) Site Plan and Sewer Existing Monitoring Previous Explorations MW-2 Well N Abandoned Sewer 15825-01 4/17 Tax Lot 0 60 120 Figure Scale in Feet Note: Feature locations are approximate. File: F:\Notebooks\1582501_PDC Phase II Demo Env Oversight\CAD\1582501_(ExpPlan).dwg Layout:Previous Date: 04-04-2017 2 02040 Scale in Feet

N Abandoned Tanner Creek Sewer (1887-1917)

Front Avenue (1924, 1985)

Tanner Creek Sewer (1917)

GP-43

GP-42 GP-39 GP-40 GP-41 GP-38

Author: melissaschweitzer GP-48 GP-37 Front GP-35 Avenue GP-34 (1985) GP-36 GP-44

GP-45 GP-51 GP-52 GP-46 Front Avenue GP-50 (Abandoned) GP-49 GP-47

30" Sewer (1998) 8" Sewer (1923) Pettygrove Sewer (1890-1917?)

9th Avenue 27" Sewer (1961)

LEGEND Centennial Mills 2016 Push Probe Tax Lot Portland, Oregon 2016 Push Probe with Utilities Temporary Well COP Exploration Locations and Groundwater Groundwater Elevation Underground Utility Elevations - June 2016 (Surface at GP-35 = 31 feet) 15825-01 4/17 Sewer WCDM Figure Abandoned Sewer PPL Note: Feature locations are approximate. File: F:\Notebooks\1582501_PDC Phase II Demo Env Oversight\CAD\1582501_(ExpPlan).dwg Layout:SP2_GWEL Date: 04-04-2017 3

APPENDIX A Specification Drawings

DRAFT 150-012-003 October 28, 2019 CENTENNIAL MILLS Appr. Date TANNER CREEK MITIGATION Description PORTLAND, OREGON Mark OCTOBER 2019 Appr. Date ENGINEERING DRAWINGS Description Mark

SITE AERIAL PHOTOGRAPH SITE LOCATION MAP Rev. 0

DRAWING INDEX:

W I L L A M E T T E R I V E R Job Number: 150-012-003 : : File name: Plot scale: SEE DRAWING 150012003_(EngineeringSet).dwg Date: 10/19 1. COVER PAGE

WAREHOUSE D

2. TANNER CREEK SEWER MITIGATION PLAN Ckd by: ??

3. EXTRACTION WELL DETAILS WAREHOUSE B Designed by: CM Dwn by: MAS Reviewed by: ?? Submitted by: HART CROWSER, INC. ELEVATORGRAIN B RIVER DOCK 4. EXTRACTION WELL FITTING DETAILS ELEVATORGRAIN A

BLENDING BINS PROJECT AREA

ELEVATORGRAIN C PROJECT AREA WAREHOUSE C FEED MILL

FLOUR MILL

WAREHOUSE F

Warehouse A

RAMP UP

LOADING WAREHOUSE E DOCK AREA

NW NAITO PARKWAY

RIVER BANK

HORSE PADDOCK OREGON 0 2,000 4,000 Portland COVER PAGE N APPROXIMATE SCALE IN FEET

OREGON SEWER MITIGATION, PORTLAND, CENTENNIAL MILLS, TANNER CREEK

0 80 160 Sheet N APPROXIMATE SCALE IN FEET Reference Number: 1 Sheet 1 of 4 F:\Notebooks\150012003_PP_Centennial_Mill_TCS_Mitigation\CAD\150012003_(EngineeringSet).dwg W I L L A M E T T E R I V E R

N 0 15 30

APPROXIMATE SCALE IN FEET Appr. Date FENCE

A D

4 4 Description FORMER TANNER CREEK SEWER TANNER CREEK SEWER BULKHEAD Mark VAULT Appr. Date

WATER STORAGE TANK Description

AIR COMPRESSOR WAREHOUSE E POWER SUPPLY Mark (TO BE MODIFIED)

0 5 10 RIVER BANK Rev. 0 APPROXIMATE SCALE IN FEET A B B 3 3 4 Job Number: 150-012-003 : : File name: Plot scale: SEE DRAWING 150012003_(EngineeringSet).dwg Date: 10/19

A D A B C Ckd by: ?? 4 4 3 3 4 Designed by: CM Dwn by: MAS Reviewed by: ?? Submitted by: HART CROWSER, INC.

EXTENT OF PHASE II REMEDIAL EXCAVATIONS WATER AND PRODUCT STORAGE CONTAINER

OVERBURDEN SOIL STOCKPILE AREA

WAREHOUSE E OREGON FLOUR MILL HORSE PADDOCK MITIGATION PLAN TANNER CREEK SEWER LEGEND SEWER MITIGATION, PORTLAND,

PIPING UNDERGROUND CENTENNIAL MILLS, TANNER CREEK OR BENEATH MILL

ABANDONED PIPING Sheet Reference SECURITY FENCING NOTES: Number: 1. NOT ALL LATERALS AND STUBS SHOWN. EXTRACTION WELL & VAULT 2. FEATURE LOCATIONS ARE APPROXIMATE. 3. UNDERGROUND PIPE FROM HISTORICAL BUILDING PLANS. 2 4. THIS PLAN SHOULD NOT BE USED FOR CONSTRUCTION PURPOSES. Sheet 2 of 4 SOURCES: HISTORICAL BUILDING PLANS, PLUMBING PERMITS, SEWER VIDEOS, AND SITE RECONNAISSANCE. VAULT F:\Notebooks\150012003_PP_Centennial_Mill_TCS_Mitigation\CAD\150012003_(EngineeringSet).dwg CONCRETE COLLAR Appr. POTHOLE PRIOR GROUND

TO INSTALL SURFACE Date GROUND SURFACE Description STEEL VAULT TOP OF CASING (~1' BGS)

~6' TOP OF BENTONITE PLUG (1.5' BGS) Mark

8" BOREHOLE Appr.

3/8" BENTONITE CHIPS HOLE PLUG Date

1" SCH 40 PVC RISER PIPE FOR SUBMERSIBLE PUMP

(LENGTH VARIES) Description

TOP OF FILTER PACK (5' BGS) Mark 4" SCH 40 PVC WELL CASING Rev. 0 FILTER PACK, 8-12 MESH SIZE SAND TOP OF WELL SCREEN (7' BGS) Job Number: 150-012-003 : : File name: Plot scale: SEE DRAWING 150012003_(EngineeringSet).dwg Date: 10/19 ~12' Ckd by: ?? Designed by: CM Dwn by: MAS Reviewed by: ?? Submitted by: HART CROWSER, INC.

4" SCH 40 PVC, 0.040" MACHINE-SLOTTED WELL SCREEN

~4'

TOP OF SUMP SUMP WITH END CAP

BOTTOM OF WELL (22' BGS) OREGON

WELL INSTALLATION CROSS SECTION A WELL DETAIL B NOT TO SCALE 3 NOT TO SCALE 3 SEWER MITIGATION, PORTLAND, EXTRACTION WELL DETAILS CENTENNIAL MILLS, TANNER CREEK

Sheet Reference Number: 3 Sheet 3 of 4 F:\Notebooks\150012003_PP_Centennial_Mill_TCS_Mitigation\CAD\150012003_(EngineeringSet).dwg CONCRETE CONCRETE 24" 24" COLLAR COLLAR

4" Ø EXTRACTION 1" Ø SCH40 PVC WELL RISER PIPE Appr. Date PITLESS ADAPTER

STEEL VAULT STEEL VAULT GATE VALVE 4" Ø SCH 80 CONTAINMENT PIPE Description WATER DISCHARGE HOSE 1" Ø SCH 80 PVC TO STORAGE TANK

CHECK VALVE Mark 30" 24" 24" Appr.

GATE VALVE Date

AIR SUPPLY 2" Ø SCH 80 PVC LINE CONTAINMENT PIPE 1" Ø SCH80 PVC 2" Ø SCH80 PVC 1" Ø SCH80 45° ELBOW CONTAINMENT PIPE 4" Ø PVC WYE 1" Ø SCH80 GATE VALVE 1" Ø SCH80 EXTRACTION PVC PVC WELL Description CONCRETE COLLAR DOUBLE DIAPHRAGM PUMP

PITLESS ADAPTER 2" Ø SCH 80 PVC CHECK VALVE Mark CONTAINMENT PIPE 1" Ø SCH40 PVC RISER PIPE Rev. 0

EXTRACTION WELL #2 VAULT & FITTINGS EXTRACTION WELL #1 VAULT & FITTINGS PLAN VIEW B PLAN VIEW C 30" Job Number: 150-012-003 : : File name: Plot scale: SEE DRAWING 150012003_(EngineeringSet).dwg NOT TO SCALE 4 NOT TO SCALE 4 Date: 10/19

EXTRACTION PUMP VAULT PLAN VIEW A Ckd by: ?? NOT TO SCALE 4 Designed by: CM Dwn by: MAS Reviewed by: ?? Submitted by: HART CROWSER, INC.

TO WATER STORAGE TANK

CONCRETE COLLAR

GROUND SURFACE TEE HANDLE

WATER DISCHARGE HOSE

TO WATER STORAGE TANK 1" Ø PITLESS ADAPTER AIR SUPPLY LINE 4" Ø SCH 80 CONTAINMENT PIPE

1" Ø SCH40 PVC OREGON

EXTRACTION DETAILS WELL CASING 1" Ø SCH 80 PVC

1" Ø COMPRESSION COUPLING EXTRACTION WELL FITTING SEWER MITIGATION, PORTLAND, CENTENNIAL MILLS, TANNER CREEK

Sheet 1" Ø SCH40 PVC RISER PIPE Reference Number: EXTRACTION PUMP VAULT RISER PIPE FITTINGS DETAIL PROFILE VIEW D PROFILE VIEW E 4 NOT TO SCALE 4 NOT TO SCALE 4 Sheet 4 of 4 F:\Notebooks\150012003_PP_Centennial_Mill_TCS_Mitigation\CAD\150012003_(EngineeringSet).dwg

APPENDIX B Loading/Unloading Procedures Checklist

DRAFT 150-012-003 October 28, 2019 Fuel Loading/Unloading Procedures Tanner Creek Sewer Remedial Action

3.14.2 Loading/Unloading Procedures – 40 CFR 112.7(h)(2) & (3) All suppliers must meet the minimum requirements and regulations for tank truck loading/unloading established by the U.S. Department of Transportation. Procedures will be established so that the vendor(s) understands the site layout, knows the protocol for entering the Site and unloading product, and has the necessary equipment to respond to a discharge from the vehicle or fuel delivery hose.

The departmental manager or his/her designee supervises oil deliveries for all new suppliers, and periodically observes deliveries for existing, approved suppliers. Vehicle/equipment filling operations are performed by operating personnel trained in proper discharge prevention procedures. The driver or equipment operating personnel will remain with the vehicle/equipment at all times while fuel is being transferred. Transfer operations are performed according to the minimum procedures outlined in the table below.

Task Description Procedures Prior to loading/unloading Visually check all hoses for leaks and wet spots. Verify that sufficient volume is available in the storage tank or truck. Secure the tank vehicle with wheel chocks and interlocks. Verify that the vehicle’s parking brakes are set. Verify proper alignment of valves and proper functioning of the pumping system. Establish adequate bonding/grounding prior to connecting to the fuel transfer point. Turn off cell phone.

During loading/unloading Driver must stay with the vehicle at all times during loading/unloading activities. Facility manager or designee should observe the delivery driver during loading/unloading. Periodically inspect all systems, hoses and connections. When loading, keep internal and external valves on the receiving tank open along with the pressure relief valves. When making a connection, shut off the vehicle engine. When transferring Class 3 materials, shut

off the vehicle engine unless it is used to operate a pump. Maintain communication with the pumping and receiving stations. Monitor the liquid level in the receiving tank to prevent overflow. Monitor flow meters to determine rate of flow. When topping off the tank, reduce flow rate to prevent overflow. After loading/unloading Make sure the transfer operation is completed. Close all tank and loading valves before disconnecting. Securely close all vehicle internal, external, and dome cover valves before disconnecting. Secure all hatches. Disconnect grounding/bonding wires. Make sure the hoses are drained to remove the remaining oil before moving them away from the connection. Use a drip pan. Cap the end of the hose and other connecting devices before moving them to prevent uncontrolled leakage. Remove wheel chocks and interlocks. Inspect the lowermost drain and all outlets on tank truck prior to departure. If necessary, tighten, adjust, or replace caps, valves, or other equipment to prevent oil leaking while in transit.