TEMPORARY DEWATERING FEASIBILITY STUDY Redmond Square

REPORT TEMPORARY DEWATERING FEASIBILITY STUDY Redmond Square

Submitted to: MGRM LLC 1111 3rd Ave. Suite 2850 Seattle, WA 98101

Submitted by: Golder Associates Inc. 18300 NE Union Hill Road, Suite 200, Redmond, Washington, USA 98052

+1 425 883-0777

1661044.900

November 2019

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Table of Contents

1.0 INTRODUCTION ...... 1

2.0 GEOTECHNICAL REQUIREMENTS ...... 1

2.1 Stratigraphy ...... 1

2.2 Primary Aquifer...... 2

2.3 Aquifer Transmissivity and Hydraulic Conductivity ...... 2

2.4 Groundwater Elevations ...... 2

2.4.1 Historic Record from Nearby Monitoring Wells ...... 2

2.4.2 Groundwater Levels in On-Site Monitoring Wells ...... 3

2.5 Potential Construction Dewatering Pumping Rates ...... 4

2.6 Aquifer Drawdown ...... 6

3.0 PROPOSED PROJECT DESCRIPTION ...... 6

3.1 Proposed Excavation ...... 6

3.2 Preliminary Dewatering Scheme ...... 7

3.3 Area of Groundwater Lowering ...... 7

3.4 Conveyance ...... 7

4.0 WATER QUALITY ...... 7

5.0 CLOSING ...... 8

6.0 REFERENCES ...... 9

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TABLES

Table 1: Predicted Pumping Rates, Drawdown, and Radius of Influence for Elevator Pit Dewatering

FIGURES

Figure 1: Vicinity Map Figure 2: Site Map and Proposed Excavation Boundaries

Figure 3: Monitoring Wells in Vicinity of Redmond Square Site

Figure 4: City of Redmond Monitoring Well Groundwater Elevations

Figure 5: Groundwater Drawdown Profile

Figure 6: Estimated Radius of Influence from Potential Elevator Pit Dewatering

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1.0 INTRODUCTION This report presents a feasibility study to meet the requirements for the City of Redmond’s Temporary Construction Dewatering Operating Policy (Attachment A; Redmond 2016) for the Redmond Square Site (Site), a proposed mixed-use development site by MGRM LLC in Redmond, Washington (Figure 1). The proposed project includes two buildings and will encompass approximately 3.5-acres, bounded by Redmond Way to the north, 164th Avenue NE to the west, 166th Avenue NE to the east, and Cleveland Street to the south (Tiscareno 2019).

The project will be constructed in two phases. The first phase entails the construction of Building B on the eastern portion of the Site and the second phase will be the construction of Building A on the western portion of the Site (Figure 2). The current project design includes one story of below-grade parking below both buildings. The underground parking structure below Building B will encompass approximately 1.5 acres (65,000 square feet [ft2]), while the structure below Building A will be slightly smaller (approximately 1.4 acres or 60,000 ft2). Each building will have two elevators. A concrete wall will separate the two foundations.

The finished floor slab elevation for the below-grade parking will be approximately 34 feet (all elevations in this report are referenced to NAVD88 datum), or approximately 10 feet below ground surface (bgs) assuming a ground elevation of 44 feet. Based on this slab elevation, the elevation of the bottom of the footings is estimated to be 32 feet. Groundwater elevations in the vicinity of the site typically range from 24 feet during the summer and early fall (dry season) to 32 feet during the winter and spring (wet season; Section 2.3). Based on these elevations and the timeline for construction (Section 3), temporary construction dewatering for the foundation will likely not be necessary.

The bottom of the elevator pits will extend to an elevation of 28 feet (bottom of slab elevation) and, depending on static water levels at the time of construction, some localized dewatering may be required around the elevator pits during the winter months. Static groundwater elevations will likely be below the bottom of the elevator pits during the summer months (approximately May to November), meaning no dewatering will be needed during the summer.

Groundwater elevations in the vicinity of the site have been artificially lowered from nearby construction dewatering projects for approximately the last 3 years (2017 through 2019). While there are currently no active construction dewatering projects (beginning in June 2019), groundwater elevations could remain lower than normal when project construction is planned to start (October 2020). This could reduce or eliminate the need for construction dewatering around the elevator pits during the winter season.

As detailed later in this report, the potential need for temporary dewatering and the necessary dewatering rates are dependent on antecedent groundwater levels and weather conditions during construction, subsurface geologic conditions, and potential impacts of other construction dewatering projects that may be occurring in the City at the time of construction. 2.0 GEOTECHNICAL REQUIREMENTS 2.1 Stratigraphy The Site is underlain by alluvial and recessional outwash sands and gravels. These materials were encountered to a depth of at least 27 feet bgs in fourteen borings completed on or adjacent to the Site as part of the Site geotechnical investigation (Golder 2019a). Nearby City monitoring wells (MW008 for example) indicate that alluvium extends to at least 30 feet bgs in the vicinity of the Site. Information in other reports (Golder 2003a,

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2003b; Parametrix 1997) indicates these materials extend to about 35 to 70 feet bgs in the downtown Redmond area. The alluvial and recessional outwash materials are underlain by fine sand and silt materials. 2.2 Primary Aquifer The alluvial and recessional outwash sands and gravels form the primary aquifer in the vicinity of the Site. These materials extend to a depth of about 35 to 70 feet bgs. The sands and gravels are underlain by fine sand and silt materials that do not form a productive aquifer in the downtown Redmond area. 2.3 Aquifer Transmissivity and Hydraulic Conductivity The transmissivity and hydraulic conductivity of the alluvial and recessional outwash aquifer is generally very high but there is wide variability in the estimated values in the vicinity of the Site. Testing of City Wells No. 1 and No. 2 in Anderson Park suggest a transmissivity of the about 22,000 to 47,000 ft2/day (Golder 2003a, 2003b). The City’s wellhead protection report cites transmissivities of approximately 5,300 to 134,000 ft2/day near the Site (Parametrix 1997). Based on these estimates and assuming an aquifer thickness of 50 feet1, the hydraulic conductivity ranges from about 200 feet per day (ft/day) to over 2,000 ft/day. A pumping test performed at a nearby development site (Bear Creek Mixed Use), located approximately 1,500 feet west of the project site, indicated aquifer transmissivities of 39,000 to 50,000 ft2/day or hydraulic conductivities of 800 to 1,000 ft/day based on an aquifer thickness of 50 feet (Bender 2018). The City’s groundwater flow model used hydraulic conductivity values of approximately 5,000 to 7,500 ft/day for the portion of the aquiver near the Site, as part of the model calibration process (GeoEngineers 2018).

The hydraulic conductivity of the alluvial and recessional outwash underlying the Site was also estimated from three samples collected from two borings during the geotechnical study of the Redmond Square. The samples were collected from depths ranging from 15 to 20 feet bgs. The hydraulic conductivities were estimated using an empirical equation developed from grain size analyses (Massmann et al. 2003), as described in the Western Washington Stormwater Manual (Ecology 2012). The estimated hydraulic conductivities of these samples ranged from 108 to 165 ft/day with an average of 138 ft/day (Golder 2019b). 2.4 Groundwater Elevations 2.4.1 Historic Record from Nearby Monitoring Wells Seasonal groundwater elevation data are available from City-owned monitoring wells located near the Site. The period of record for the City monitoring wells begins as early as 2008 and includes semi-annual manual water level measurements and, in some instances, near-continuous automated (i.e., pressure transducer) data. The available period of record for the automated data varies between wells. The nearby City-owned monitoring wells are shown on Figure 3 and include:  Monitoring Well MW008 is located approximately 250 feet north of the Project Site, on the northwest corner of NE 79th Street and 166th Avenue NE.  MW009 is located about 1,000 feet east of the Redmond Square, in Anderson Park near City production Wells No. 1 and 2.

1 Transmissivity is defined as the hydraulic conductivity times the aquifer thickness.

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 MW045 is located approximately 150 feet southwest of the Project Site near the corner of NE 76th Street and 164th Avenue NE.  MW341 is located approximately 200 feet southeast of the Project Site near the corner of NE 76th Street and 166th Avenue NE.

The groundwater elevations from the nearby City-owned monitoring wells are shown on Figure 4. MW009 has the longest period of record of pressure transducer data (January 2008 to present). Seasonal groundwater elevations at MW009 have typically ranged from approximately 24 to 26 feet during the summer (dry season) to 29 to 32 feet during the winter (wet season). In early 2009 and again in late 2010, groundwater elevations reached as high as 33 to 34 feet for short durations (for 2 weeks or less).

Groundwater elevations from 2017 to 2019 were slightly lower than in earlier years (Figure 4), and this is attributed to nearby temporary construction dewatering projects that were occurring in the general vicinity of the project site. During this period, groundwater elevations ranged from approximately 22 feet to 29 feet, or approximately 2 to 3 feet lower than measured during the earlier period (2008 to 2016).

The period of record prior to October 2016 shown on Figure 4 is more indicative of “natural” groundwater elevations in the vicinity of the Site, or in other words, unaffected by construction dewatering. During this period, the annual range in groundwater elevations was generally between 24 to 32 feet. The pressure transducer data at MW009 indicate the following:  Winter maximum groundwater elevations (daily average elevation) exceeded 32 feet in 6 of the 8 years of record between October 2008 and October 2016 but groundwater elevations remained above 32 feet for only short durations:

▪ During years when groundwater elevations were above 32 feet, they remained above 32 feet for an average of 9 days;

▪ The maximum duration that groundwater elevations were above 32 feet was 21 days in December 2012;

▪ During years when groundwater elevations were above 32 feet, the earliest occurrence of groundwater levels exceeding 32 feet (on a water year basis: October through September) was mid-December.  During most years, groundwater elevations were above 31 feet for only one month or less. The maximum and minimum groundwater elevation for a given year will be dependent on the amount and timing of precipitation, groundwater levels at the start of the Water Year, and potentially the influence of other temporary construction dewatering projects that might be ongoing at the time of construction. 2.4.2 Groundwater Levels in On-Site Monitoring Wells There are two monitoring wells on the Site (Figure 2) and the groundwater levels measured in these wells are consistent with the water levels in the nearby City monitoring wells, as follows:  Groundwater levels on the Site were approximately 17.9 and 18.1 feet bgs, respectively, in July 2016, or an elevation of approximately 26 feet2 using an estimated surface elevation of 44 feet. This is approximately

2 Elevations are approximate because the wells at the Redmond Square site have not been surveyed, an estimated ground surface of 44 feet was used for calculations.

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equivalent to the groundwater elevations measured in City wells MW008, MW009, and MW0341 in July 2016.  Groundwater levels at the Site were approximately 19.7 to 21.7 feet bgs between October and November 2018, or approximately 22 to 24 feet using an estimated surface elevation of 44 feet. This is approximately equivalent to the groundwater elevations measured in City wells MW008, MW009, and MW0341 in late summer 2018. 2.5 Potential Construction Dewatering Pumping Rates Dewatering of the full excavation (either project phase) will not be necessary because groundwater elevations generally do not rise above the proposed depth of the excavations (32 feet) for either phase (Section 2.4). In the unlikely event that groundwater elevations temporarily rise above 32 feet before the foundation slab is completed, it is assumed that the foundation excavation will be allowed to flood temporarily until groundwater elevations recede. The historic data suggest that if groundwater elevations rise about 32 feet, they will not remain above 32 feet for more than 10 days (Section 2.4). The current plans call for construction to being in October 2020, before peak groundwater elevations occur. Some localized dewatering, if needed, around the elevator pit will act to lower the groundwater elevations across the entire excavation, as described below.

Each building will have two elevator pits that will extend to 28 feet (elevation) or approximately 16 feet bgs. Seasonal dewatering may be required to lower groundwater levels around these structures. The historic groundwater elevation data (Figure 4) indicate that groundwater elevations at the Site are typically above 28 feet during the winter (from approximately November to April). Groundwater elevations are generally below 28 feet during the summer and fall (approximately May to October), meaning elevator pit dewatering will not be necessary during summer and fall.

As noted above, the foundation excavation will be allowed to flood temporarily if groundwater elevations rise above 32 feet. Therefore, dewatering the elevator pits will only be required when groundwater elevations are between 28 and 32 feet, and the maximum drawdown needed to dewater the elevator pits is 4 feet.

Steady-state dewatering pumping rates for the elevator pits were estimated using the Cooper-Jacob (1946) method from a hypothetical wellfield where interference drawdown is calculated from two dewatering wells (one well in the vicinity of each elevator pit). The dewatering estimates assume:  Dewatering will occur when groundwater elevations range between 28 and 32 feet and a maximum of 4 feet of drawdown will be required (see above).  Groundwater levels at the Site will not be affected by any other potential dewatering projects occurring simultaneously with the proposed project.  The aquifer thickness is 50 feet.  The aquifer storage coefficient ranges between 0.1 and 0.2 .  The hydraulic conductivity of the aquifer ranges from 500 to 1,000 feet per day (see below).  Each elevator pit will have a footprint of approximately 1,000 ft2 and there will be two elevator pits in each building.

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 The estimates were developed for the Phase 1 construction (Building B), similar estimates are anticipated for Phase 2 (Building A) given the similarity in the design.

The analytical method used to develop dewatering rate predictions is sensitive to the hydraulic conductivity estimates that are used. The hydraulic conductivity of the aquifer materials underlying the site is unknown and therefore predictions were developed for a range of values. Using the upper range of hydraulic conductivity values presented in Section 2.3 resulted in unrealistically high dewatering estimates. Previous dewatering projects in Redmond provide insight to the potential range of dewatering pumping rates needed to dewater the elevator pits at the Site:  The Redmond Triangle site is located adjacent to the north (across Redmond Way) from the Redmond Square site. The Redmond Triangle excavation was approximately 50,000 ft2 and the slab elevation was about 29 feet. Dewatering for Redmond Triangle occurred from October 2016 to July 2017 and the average monthly dewatering rates ranged from 2,500 to 3,100 gallons per minute (gpm) during the winter months and 1,000 to 2,000 gpm during the late spring and early summer. Dewatering at the Station House Lofts project, to the north of the Triangle site, occurred simultaneous to the Triangle Project and may have influenced water levels and pumping rates at the Triangle. The extent of this influence is unknown but a rough, conservative assumption is that an additional 1,000 gpm may have been required at the Triangle site if the Station House Lofts project was not dewatering at the same time.  The Bear Creek mixed-use site is located approximately 1,500 feet west of the Redmond Square site. The Bear Creek excavation was approximately 70,000 ft2. The drawdown requirements for construction of that site were 14 to 18 feet. Dewatering occurred from July 2018 to May 2019 and the average monthly dewatering rates ranged from approximately 6,000 to 6,400 gpm during the winter months and 4,000 to 5,000 gpm during the late spring and early summer. The Bear Creek site is located closer to the Sammamish River and the aquifer materials at this location may be slightly finer than expected at Redmond Square.

Both of the projects described above required dewatering for their full excavations, much larger than the elevator pit dewatering requirements. However, the dewatering information from these projects, particularly for the Triangle project because of its proximity to the Site, were used to calibrate our analytical model for selecting reasonable hydraulic conductivity estimates. This information suggests that a hydraulic conductivity of 750 ft/day is a reasonable estimate. To account for potential variability, a range of 500 to 1,000 ft/day was used.

The estimated steady-state dewatering rates developed from the analytical method described above are summarized on Table 1. These estimates represent the combined pumping requirements for two elevator pits during each phase of construction. Predictions were developed for a range of required drawdown of 1 to 4 feet. The predicted dewatering rates each drawdown requirement (1 to 4 feet) are as follows:  4 feet of drawdown: Range of 700 to 1300 gpm; average of 1,000 gpm.  3 feet of drawdown: Range of 500 to 1000 gpm; average of 750 gpm.  2 feet of drawdown: Range of 300 to 700 gpm; average of 500 gpm.  1 foot of drawdown: Range of 200 to 300 gpm; average of 250 gpm.

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The maximum drawdown (4 feet) is needed only at static groundwater elevations of 32 feet, which may occur for only short durations during the winter. The much more likely scenario is that 1 to 3 feet of drawdown may be needed, which will require pumping rates of approximately 250 to 750 gpm. 2.6 Aquifer Drawdown Groundwater level profiles were developed for four drawdown scenarios (1 to 4 feet of drawdown) using the predicted pumping rates and aquifer properties from the wellfield interference calculations. The results are shown on Figures 5A to 5D. The high transmissivity of the aquifer results in a relatively flat cone of depression, meaning the targeted drawdown at the elevator pits will extend outward and create a similar amount of drawdown across the entire excavation. For the 4 feet of drawdown scenario, for example, there will be approximately 2 to 3 feet of drawdown at the perimeter of the excavation (Figure 5A).

City Wells No. 1 and 2 are located approximately 1,000 feet east (and upgradient) of the proposed excavation. The predicted drawdown in the aquifer (i.e. lowering of the water table as a result of dewatering) at City Wells No. 1 and 2 is estimated to be about 0.4 to 1.8 feet (Table 1, Figure 5A to Figure 5D). These estimates are conservative and assume 100 days of continuous pumping and therefore represent the maximum drawdown at the City wells. They also do not consider the hydraulic gradient in the area, which will result in less drawdown at the City Wells No. 1 and 2 because they are upgradient of the project site, and seasonal recharge which could result in less drawdown. These estimates also assume that no other dewatering projects will be occurring simultaneously with the Redmond Square project.

The three other City production wells are located farther from the proposed project as follows: Well No. 3 is 6,900 feet away, Well No. 4 is 3,400 feet away, and Well No. 5 is 5,000 feet away. Significant drawdown impacts from site dewatering are not expected to occur at these wells. Based on the analysis described above, the maximum likely drawdown estimated to occur at these locations is less than 1 foot. These estimates are conservative because they do not consider the natural hydraulic gradient of the aquifer or recharge. 3.0 PROPOSED PROJECT DESCRIPTION 3.1 Proposed Excavation The current Project Site development plans include two proposed buildings, separated by a pedestrian walkway and Fire Lane. Building A will be situated on the western portion of the Site and Building B will be situated on the eastern side of the Site. Each building will have courtyards, one story of below-grade parking and two stories of above-grade parking; with six stories of residential units above one level of at-grade retail space (Tiscareno 2019). Each building will have two elevators, the bottom of the elevator pits will extend to an elevation of 28 feet (bottom of slab elevation). The project will be constructed in phases, with Building B completed during Phase 1 and Building A completed in Phase 2. The underground parking structure below Building B will encompass approximately 1.5 acres (65,000 ft2), while the structure below Building A will be slightly smaller (1.4 acres or 60,000 ft2). A concrete wall will separate the two foundations. The proposed project footprint is shown on Figure 2.

The finished floor of the below-grade parking level in both buildings is expected to be 34 feet elevation (all elevations in this report presented in NAVD88), or approximately 10 feet bgs (referenced 44 feet, the existing average grade of the site). This does not include the foundation system, vaults, sumps, elevator pit excavations, or tower crane foundation. Based on this design the approximate excavation elevations are estimated as follows:  Bottom of lower parking level slab: 34 feet

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 Bottom of footing: 32 feet  Bottom of elevator pit: 28 feet 3.2 Preliminary Dewatering Scheme Dewatering, if needed, will be accomplished using wells. The final dewatering system design will be prepared by the dewatering contractor. The preliminary dewatering design includes one dewatering well located in the near vicinity of each elevator pit (Figure 2). It may also be necessary to locate additional wells near the elevator pits, depending on well capacity and drawdown requirements. 3.3 Area of Groundwater Lowering The area of groundwater lowering (radius of influence) as a result of dewatering the proposed project was calculated using the analytical methods used to estimate the dewatering pumping rates. The predicted calculated radius of influence from the dewatering varies based on the dewatering rate and estimated hydraulic conductivity and storage coefficient of the aquifer. The predictions are very conservative and represent the maximum radius of influence after 100 days of pumping. The predictions range from approximately 5,000 feet to 10,000 feet and are provided in (Table 1 and Figure 6). 3.4 Conveyance It is our understanding that any pumped groundwater up to 1,470 gpm can be sent to the City’s stormwater conveyance system. The layout and conveyance calculations will be provided by the project civil engineer in a separate report. The predicted dewatering pumping rates shown in Table 1 for the elevator pits are all below the City’s stormwater conveyance system capacity. Therefore, no offsite conveyance system, for the purpose of disposing of dewatering water, is needed. 4.0 WATER QUALITY A summary of the previous environmental assessments performed on the Property was completed by Sound Earth Strategies (SoundEarth 2018). We understand that a MTCA-compliant cleanup action is proposed to occur concurrently with the redevelopment of the Property (SoundEarth 2018).

Tetrachloroethene (PCE) and other related chlorinated volatile organic compounds (VOCs) are known to be present in groundwater in several areas of downtown Redmond at low concentrations. A small contaminant plume is known to exist at the Bear Creek Village shopping center, which is located approximately 2,500 feet upgradient (east) of the Site and approximately 1,600 feet upgradient (east) of City Wells No. 1 and 2. PCE concentrations remain above detection limits in certain monitoring wells in Bear Creek Village but concentrations in all wells at the Bear Creek Village site have been below cleanup levels (5 µg/L) since 2013.

Per City requirements, pumped groundwater that is discharged from the Site will be monitored daily for pH and turbidity on a daily basis and PCE in the discharge will be monitored on a weekly basis. Additional monitoring for PCE may be conducted during dewatering in one or more City monitoring wells adjacent to the Site and Wells No. 1 and 2.

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5.0 CLOSING We trust that this report meets your needs. Please contact us if you have any questions or comments.

Golder Associates Inc.

Jay Pietraszek, LG James G. Johnson, LG, LEG Senior Hydrologist Principal

Michael Klisch, LHG Senior Project Hydrogeologist

JP/JGJ/MK/ks

Golder and the G logo are trademarks of Golder Associates Corporation

p:\projects\2016\1661044_legacy redmond square\2018-2019\dewatering\report\rev3\1661044-r-rev3-dewatering feasibility study-111319.docx

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6.0 REFERENCES Bender Consulting LLC. 2018. Revision 2- Dewatering Design Recommendations – Bear Creek Mixed-Use Project, Redmond, Washington. January 9.

Cooper, H.H. and C.E. Jacob. 1946. A Generalized Graphical Method for Evaluation of Formation Constants and Summarizing Wellfield History. Am. Geophys. Union Trans. Vol. 27, pp.526-534.

GeoEnginners. 2018. Groundwater Flow Model Development Report, City of Redmond Groundwater Model. March 30.

Golder Associates Inc. (Golder). 2003a. Final Well Completion Report, Anderson Well Field Replacement Well 1. July 1.

Golder. 2003b. Final Well Completion Report, Anderson Well Field Replacement Well 2. July 1.

Golder. 2015. Level 2 Hydrogeologic Assessment, Redmond Triangle. May 08.

Golder. 2016. Phase 2 Environmental Site Assessment, Redmond Square 16505 and 16541 Redmond Way, 16564, 16528, and 16421 Cleveland Street, Redmond Washington 98052. December 22.

Golder. 2019a. Geotechnical Report, Redmond Square 16505 and 16541 Redmond Way, 16564, 16528, and 16421 Cleveland Street, Redmond Washington 98052. November. Golder. 2019b. Level II Hydrologeologic Assessment, Redmond Square. November.

Marinelli, F., and W. L. Niccoli. 2000. Simple analytical equations for estimating ground water inflow to a mine pit. Ground Water 38, no. 2: 311-314.

Massmann, J.W., C. Butchart, and S. Stolar. 2003. Infiltration Characteristics, Performance, and Design of Stormwater Facilities, Final Research Report, Research Project T1803, Task 12, Washington State Department of Transportation, Olympia, Washington.

Parametrix, Inc. 1997. Wellhead Protection Report. October 30.

Redmond (City of). 2016. City of Redmond, Temporary Construction Dewatering Operating Policy. June 7.

SoundEarth Strategies Inc. (SoundEarth). 2018. Environmental Summary Letter – Redmond Square Property – 16505 Redmond Way, Redmond, Washington 98052. December 18, 2018. Prepared for MGRM LLC.

Tiscareno Associates. 2019. Redmond Square: Reduced Footprint Parking Study - Sections. Date 07/11/2019. Submitted to Golder via email on July 11, 2019.

Washington Department of Ecology. (Ecology). 2012. Western Washington Stormwater Manual.

Table

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Table 1: Predicted Pumping Rates, Drawdown, and Radius of Influence for Elevator Pit Dewatering

Predicted Pumping Rates (gpm) Scenario Parameters 4 ft of drawdown 3 ft of drawdown 2 ft of drawdown 1 ft of drawdown 1 K=1000, S=0.2 1300 1000 660 340 2 K=1000, S=0.1 1200 930 630 310 3 K=750, S=0.2 1000 780 520 260 4 K=750, S=0.1 970 720 480 240 5 K=500, S=0.2 730 540 360 180 6 K=500, S=0.1 670 500 340 170

Predicted Drawdown at City Wells 1 and 2 (feet) Scenario Parameters 4 ft of drawdown 3 ft of drawdown 2 ft of drawdown 1 ft of drawdown 1 K=1000, S=0.2 1.7 1.2 0.8 0.4 2 K=1000, S=0.1 1.8 1.3 0.9 0.4 3 K=750, S=0.2 1.6 1.2 0.8 0.4 4 K=750, S=0.1 1.8 1.3 0.9 0.4 5 K=500, S=0.2 1.5 1.1 0.7 0.4 6 K=500, S=0.1 1.7 1.2 0.8 0.4

Total Radius of Influence (feet) Scenario Parameters 4 ft of drawdown 3 ft of drawdown 2 ft of drawdown 1 ft of drawdown 1 K=1000, S=0.2 7300 7300 7200 7000 2 K=1000, S=0.1 10300 10300 10200 9900 3 K=750, S=0.2 6300 6300 6200 6100 4 K=750, S=0.1 8900 8900 8800 8600 5 K=500, S=0.2 5100 5100 5100 4900 6 K=500, S=0.1 7300 7300 7200 7000 Notes: 1. Dewatering estimates are the combined pumping rate for two elevator pits. K= Hydraulic Conductivity, ft/day; S=storage coefficient, dimensionless.

Figures

KEY MAP

PROJECT SITE

PROJECT SITE LOCATION

LEGEND CLIENT PROJECT SITE LOCATION MGRM LLC

PROJECT REDMOND SQUARE TEMPORARY DEWATERING FEASIBILITY STUDY REDMOND, WA TITLE VICINITY MAP

0 2,000 4,000 IF THIS IF MEASUREMENTDOES NOT IS WHAT MATCH SHOWN,THE SHEETSIZE HASBEEN MODIFIED FROM:A ANSI CONSULTANT YYYY-MM-DD 2018-12-06 1 IN = 2,000 FT FEET in1 DESIGNED BVJ REFERENCE(S) 1. GOLDER (PROJECT LOCATION) PREPARED BVJ 2. COORDINATE SYSTEM: NAD 1983 STATE PLANE WASHINGTON NORTH (FT) 3. SERVICE LAYER CREDITS: SOURCES: ESRI, HERE, DELORME, INTERMAP, INCREMENT P REVIEWED EA CORP., GEBCO, USGS, FAO, NPS, NRCAN, GEOBASE, IGN, KADASTER NL, ORDNANCE SURVEY, APPROVED SM ESRI JAPAN, METI, ESRI CHINA (HONG KONG), SWISSTOPO, MAPMYINDIA, © OPENSTREETMAP CONTRIBUTORS, AND THE GIS USER COMMUNITY PROJECT NO. PHASE REV. FIGURE 1661044 900 0

PATH: G:\Legacy\Redmond_Square\99_PROJECTS\1661044_PhaseII_ESA\900_Dewatering\Production\MXD\Rev0\1661044_900_001_F1_Rev0_VicinityMap.mxdPATH: PRINTED 12:24:53 ON: PM 2018-12-14AT: 1 0 KEY MAP LEGEND Aerial Extent of Excavation Phase 1 Phase 2 Elevator Location (approximate)

0 250

FEET 1 IN = 76 FT

REFERENCE(S) 1. GOLDER (PROJECT LOCATION, BORINGS) 2. COORDINATE SYSTEM: NAD 1983 STATE PLANE WASHINGTON NORTH (FT) 3. SERVICE LAYER CREDITS: SOURCE: ESRI, DIGITALGLOBE, GEOEYE, EARTHSTAR GEOGRAPHICS, CNES/AIRBUS DS, USDA, USGS, AEROGRID, IGN, AND THE GIS USER COMMUNITY

CLIENT MGRM LLC

PROJECT REDMOND SQUARE TEMPORARY DEWATERING FEASIBILITY STUDY REDMOND, WA TITLE SITE MAP AND PROPOSED EXCAVATION BOUNDARIES IF IF THISMEASUREMENT DOES NOT MATCH WHATIS SHOWN, THE SHEET SIZEHAS BEEN MODIFIED FROM:ANSI B CONSULTANT YYYY-MM-DD 2019-10-21 1 in1

DESIGNED JP/BVJ Note: Dewatering wells, if necessary, will be located inside the PREPARED BVJ excavation, near the elevator shafts. Boundaries and locations are REVIEWED JP

approximate. APPROVED SM PROJECT NO. PHASE REV. FIGURE 1661044 900 2 PATH: G:\Legacy\Redmond_Square\99_PROJECTS\1661044_PhaseII_ESA\900_Dewatering\Production\MXD\Rev2\1661044_900_003_F2_Rev2_DWLayout.mxdPATH: PRINTED ON: 2019-10-21 11:46:48AM AT:

2 0 KEY MAP LEGEND *# BORING LOCATION (GOLDER) ! MONITORING WELL A (SOUND EARTH STRATEGIES) ! PRODUCTION WELL A (CITY OF REDMOND) MW340 ! MONITORING WELL A! A (CITY OF REDMOND) PROPERTY BOUNDARY Aerial Extent of Excavation Phase 1 Phase 2

MW008 City Monitoring Well OCMW-3 A!

MW011 LRS-05DP *# A!! LRS-14DP LRS-01MW City Well No. 1 A *# LRS-06DP A! MW052 LRS-09DP A! ! LRS-13DP A! A MW392 *# *# City Well No. 2 *# *# A! *# A! LRS-04B *# LRS-03B MW012 LRS-07DP *# AA!! ! *# MW009 A LRS-08DP MW013 0 350 700 *# ! ! FEET A LRS-10DP A 1 IN = 206 FT MW045 *# REFERENCE(S) 1. GOLDER (PROJECT LOCATION, BORINGS) MW010 2. CITY OF REDMOND (MONITORING AND PRODUCTION WELLS) 3. SOUND EARTH STRATEGIES (MONITORING WELLS) LRS-12DP LRS-02MW 4. COORDINATE SYSTEM: NAD 1983 STATE PLANE WASHINGTON NORTH (FT) 5. SERVICE LAYER CREDITS: SOURCE: ESRI, DIGITALGLOBE, GEOEYE, EARTHSTAR GEOGRAPHICS, CNES/AIRBUS DS, USDA, USGS, AEROGRID, IGN, AND THE GIS USER LRS-11DP COMMUNITY ! A CLIENT MGRM LLC MW341 PROJECT REDMOND SQUARE TEMPORARY DEWATERING FEASIBILITY STUDY REDMOND, WA TITLE WELLS IN VICINITY OF REDMOND SQUARE SITE IF IF THISMEASUREMENT DOES NOT MATCH WHATIS SHOWN, THE SHEET SIZEHAS BEEN MODIFIED FROM:ANSI B CONSULTANT YYYY-MM-DD 2018-12-11 1 in1

DESIGNED JP/BVJ

PREPARED BVJ

REVIEWED EA ! APPROVED SM A PROJECT NO. PHASE REV. FIGURE 1661044 900 0 PATH: G:\Legacy\Redmond_Square\99_PROJECTS\1661044_PhaseII_ESA\900_Dewatering\Production\MXD\Rev0\1661044_900_002_F3_Rev0_WellMap.mxdPATH: PRINTED ON: 2019-10-2111:47:15 AM AT:

3 0 MW342 PATH: P:\PROJECTS\2016\1661044_Legacy Redmond Square\2018-2019\Dewatering\Calculations | FILE NAME: Groundwater Levels_V5.xlsx

CLIENT 35

YYYY-MM-DD 34 DESIGNED PREPARED REVIEWED 33 APPROVED PROJECT 32 TITLE 31 PROJECT NO. PHASE 30 REV. FIGURE CONSULTANT 29 ScaleMin ScaleMax ScaleStatement 28 PATH: | FILE NAME:

27 Path&File

25 GroundwaterElevation (feet NAVD88) LEGEND 24

20 Oct-07 Oct-08 Oct-09 Oct-10 Oct-11 Oct-12 Oct-13 Oct-14 Oct-15 Oct-16 Oct-17 Oct-18 Oct-19 Elevations in NAVD 88 Date LEGEND MW341 (transducer) CLIENT PROJECT MW341 (manual data) MGRM LLC REDMOND SQUARE MW008 (transducer) TEMPORARY DEWATERING FEASIBILITY STUDY MW008 (manual data) REDMOND, WA MW009 (transducer data) CONSULTANT TITLE MW009 (manual data) CITY OF REDMOND MONITORING WELL MW045 (manual data) GROUNDWATER ELEVATIONS Elevation of Base of Parking (~34 feet)

Proposed Excvation Depth (bottom of footings) PROJECT NO. PHASE REV. FIGURE Proposed Bottom of Elevator Pit 1661044 900 1 4 PATH: P:\PROJECTS\2016\1661044_Legacy Redmond Square\2018-2019\Dewatering\Calculations\Revised Dewatering Predictions\Version 3 | FILE NAME: Interference_v6_phased_Oct-19Design.xlsx

CLIENT 0.0

YYYY-MM-DD DESIGNED PREPARED REVIEWED 0.5 APPROVED PROJECT

TITLE 1.0 PROJECT NO. PHASE REV. FIGURE CONSULTANT 1.5 ScaleMin ScaleMax ScaleStatement PATH: | FILE NAME: 2.0 Path&File

Predicted Drawdown Predicted Drawdown (ft) 2.5

LEGEND

3.0

Note: The figure shows groundwater drawdown after 100 days of pumping through a transect starts 1000 feet outside of 3.5 excavation boundary, passes near (within 20 feet) of a hypothetical dewatering well location and continues outside of transect to the point of zero drawdown.

4.0 -1000 1000 3000 5000 7000 9000 11000 Distance (feet)

LEGEND CLIENT PROJECT Scenario 1A, K=1000ft/d S=0.2 Q=1300gpm MGRM LLC REDMOND SQUARE TEMPORARY DEWATERING FEASIBILITY STUDY Scenario 2A, K=1000ft/d S=0.1 Q=1200gpm REDMOND, WA Scenario 4A, K=750ft/d S=0.2 Q=1000gpm CONSULTANT TITLE Scenario 5A, K=750ft/d S=0.1 Q=1000gpm GROUNDWATER DRAWDOWN PROFILE - 4 FT OF DRAWDOWN Scenario 5A, K=500ft/d S=0.2 Q=700gpm

Scenario 6A, K=500ft/d S=0.1 Q=700gpm PROJECT NO. PHASE REV. FIGURE 1661044 900 1 5A PATH: P:\PROJECTS\2016\1661044_Legacy Redmond Square\2018-2019\Dewatering\Calculations\Revised Dewatering Predictions\Version 3 | FILE NAME: Interference_v6_phased_Oct-19Design.xlsx

CLIENT 0.0

YYYY-MM-DD DESIGNED PREPARED REVIEWED APPROVED PROJECT 0.5

TITLE

PROJECT NO. PHASE REV. 1.0 FIGURE CONSULTANT ScaleMin ScaleMax ScaleStatement PATH: | FILE NAME: 1.5 Path&File Predicted Drawdown Predicted Drawdown (ft)

2.0 LEGEND

Note: The figure shows groundwater drawdown after 100 days 2.5 of pumping through a transect starts 1000 feet outside of excavation boundary, passes near (within 20 feet) of a hypothetical dewatering well location and continues outside of transect to the point of zero drawdown.

3.0 -1000 1000 3000 5000 7000 9000 11000 Distance (feet)

LEGEND CLIENT PROJECT Scenario 1B, K=1000ft/d S=0.2 Q=1000gpm MGRM LLC REDMOND SQUARE TEMPORARY DEWATERING FEASIBILITY STUDY Scenario 2B, K=1000ft/d S=0.1 Q=900gpm REDMOND, WA Scenario 3B, K=750ft/d S=0.2 Q=800gpm CONSULTANT TITLE Scenario 4B, K=750ft/d S=0.1 Q=700gpm GROUNDWATER DRAWDOWN PROFILE - 3 FT OF DRAWDOWN Scenario 5B, K=500ft/d S=0.2 Q=500gpm

Scenario 6B, K=500ft/d S=0.1 Q=500gpm PROJECT NO. PHASE REV. FIGURE 1661044 900 1 5B PATH: P:\PROJECTS\2016\1661044_Legacy Redmond Square\2018-2019\Dewatering\Calculations\Revised Dewatering Predictions\Version 3 | FILE NAME: Interference_v6_phased_Oct-19Design.xlsx

CLIENT 0.0

YYYY-MM-DD DESIGNED PREPARED 0.2 REVIEWED APPROVED PROJECT

0.4 TITLE

PROJECT NO. 0.6 PHASE REV. FIGURE CONSULTANT ScaleMin 0.8 ScaleMax ScaleStatement PATH: | FILE NAME: 1.0 Path&File

1.2 Predicted Drawdown Predicted Drawdown (ft)

LEGEND 1.4

1.6 Note: The figure shows groundwater drawdown after 100 days of pumping through a transect starts 1000 feet outside of excavation boundary, passes near (within 20 feet) of a 1.8 hypothetical dewatering well location and continues outside of transect to the point of zero drawdown.

2.0 -1000 1000 3000 5000 7000 9000 11000 Distance (feet)

LEGEND CLIENT PROJECT Scenario 1C, K=1000ft/d S=0.2 Q=700gpm MGRM LLC REDMOND SQUARE TEMPORARY DEWATERING FEASIBILITY STUDY Scenario 2C, K=1000ft/d S=0.1 Q=600gpm REDMOND, WA Scenario 3C, K=750ft/d S=0.2 Q=500gpm CONSULTANT TITLE Scenario 4C, K=750ft/d S=0.1 Q=500gpm GROUNDWATER DRAWDOWN PROFILE - 2 FT OF DRAWDOWN Scenario 5C, K=500ft/d S=0.2 Q=400gpm

Scenario 6C, K=500ft/d S=0.1 Q=300gpm PROJECT NO. PHASE REV. FIGURE 1661044 900 1 5C PATH: P:\PROJECTS\2016\1661044_Legacy Redmond Square\2018-2019\Dewatering\Calculations\Revised Dewatering Predictions\Version 3 | FILE NAME: Interference_v6_phased_Oct-19Design.xlsx

CLIENT 0.0

YYYY-MM-DD DESIGNED PREPARED 0.1 REVIEWED APPROVED PROJECT

0.2 TITLE

PROJECT NO. 0.3 PHASE REV. FIGURE CONSULTANT ScaleMin 0.4 ScaleMax ScaleStatement PATH: | FILE NAME: 0.5 Path&File

0.6 Predicted Drawdown Predicted Drawdown (ft)

LEGEND 0.7

0.8 Note: The figure shows groundwater drawdown after 100 days of pumping through a transect starts 1000 feet outside of excavation boundary, passes near (within 20 feet) of a hypothetical dewatering 0.9 well location and continues outside of transect to the point of zero drawdown.

1.0 -1000 1000 3000 5000 7000 9000 11000 Distance (feet)

LEGEND CLIENT PROJECT Scenario 1D, K=1000ft/d S=0.2 Q=300gpm MGRM LLC REDMOND SQUARE TEMPORARY DEWATERING FEASIBILITY STUDY Scenario 2D, K=1000ft/d S=0.1 Q=300gpm REDMOND, WA Scenario 3D, K=750ft/d S=0.2 Q=300gpm CONSULTANT TITLE Scenario 4D, K=750ft/d S=0.1 Q=200gpm GROUNDWATER DRAWDOWN PROFILE - 1 FT OF DRAWDOWN Scenario 5D, K=500ft/d S=0.2 Q=200gpm

Scenario 6D, K=500ft/d S=0.1 Q=200gpm PROJECT NO. PHASE REV. FIGURE 1661044 900 1 5D 1320000 KEY MAP

LEGEND Site Location Radius of Influence Low-End Estimate (r=4,900 feet) High-End Estimate (r-10,300 feet)

0 5,000

FEET 1 IN = 2,180 FT

CLIENT MGRM LLC

PROJECT REDMOND SQUARE TEMPORARY DEWATERING FEASIBILITY STUDY 240000 240000 REDMOND, WA TITLE ESTIMATED RADIUS OF INFLUENCE FROM POTENTIAL ELEVATOR PIT DEWATERING IF IF THISMEASUREMENT DOES NOT MATCH WHATIS SHOWN, THE SHEET SIZEHAS BEEN MODIFIED FROM:ANSI B CONSULTANT YYYY-MM-DD 2019-10-21 1 in1

DESIGNED JP/BVJ

PREPARED BVJ

REVIEWED JP

APPROVED SM PROJECT NO. PHASE REV. FIGURE

1320000 1661044 900 2 PATH: G:\Legacy\Redmond_Square\99_PROJECTS\1661044_PhaseII_ESA\900_Dewatering\Production\MXD\Rev0\1661044_900_003_F5_Rev0_RadiusOfInfluence.mxdPATH: PRINTED ON:2019-10-21 12:24:11PMAT: 6 0

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