NOCA_Geotech_FOR_PRINT_0007.pdf

REPORT

Well Testing and Foundation Recommendations Stehekin Fire Fighting Facilities Development

Submitted to:

Otak, Inc.

11241 Willows Road NE, Suite 200

Redmond, WA 98052-1009

Submitted by:

Golder Associates Inc.

18300 NE Union Hill Road, Suite 200, Redmond, Washington, USA 98052

+1 425 883-0777

19135747

January 29, 2021

January 29, 2021 19135747 ii

Table of Contents

1.0 INTRODUCTION

1.1 Scope of Work

2.0 WELL TESTING AND INSPECTION

2.1 Existing Well Information

2.1.1 Company Creek Well

2.1.2 Maintenance Well

2.2 Well Inspection and Video Logging

2.2.1 Company Creek Well

2.2.1.1 Video Inspection

2.2.2 Maintenance Well

2.2.2.1 Video Inspection

2.3 Pumping Tests

2.3.1 Company Creek Well

2.3.1.1 Groundwater Level Response

2.3.1.2 Test Evaluation

2.3.2 Maintenance Well

2.3.2.1 Groundwater Level Response

2.3.2.2 Test Evaluation

2.4 Overall Evaluation of Wells

3.0 GEOTECHNICAL INVESTIGATION

3.1 Test Pits

3.1.1 Test Pit 1

3.1.2 Test Pit 2

3.1.3 Test Pit 3

3.1.4 Test Pit 4

3.1.5 Test Pit 5

3.1.6 Test Pit 6

iii

3.1.7 Test Pit 7

3.1.8 Test Pit 8

3.2 Laboratory Testing

3.3 Subsurface Conditions

3.3.1 Geologic Setting

3.3.2 Subsurface Soil Conditions

3.3.3 Groundwater

3.4 Engineering Recommendations

3.4.1 General

3.4.2 Seismic Design

3.4.2.1 Site Class

3.4.2.2 Ground Motion Parameters

3.4.2.3 Liquefaction Potential

3.4.3 Shallow Foundation Design Criteria

3.5 Foundation Construction Recommendations

3.5.1 Site Drainage

3.5.2 Site Preparation and Topsoil Removal

3.5.3 Use of onsite soils

3.5.4 Subgrade and Footing Preparation

3.5.5 Earthworks

3.5.5.1 Removal of Unsuitable Soil, Undocumented Fill, or Other Materials

3.5.5.2 Subgrades

3.5.5.3 Structural Fill Materials and Placement

4.0 USE OF REPORT

5.0 CLOSING

6.0 REFERENCES

iv

TABLES

Table 1: Field Groundwater Quality - Company Creek Well

Table 2: Maintenance Well Field Groundwater Quality

Table 3: Soil Testing Summary

Table 4: Design Ground Motion Parameters

FIGURES

Figure 1: Site Plan

Figure 2: Exploration Plan

Figure 3: Company Creek Well Testing Period Hydrograph

Figure 4: Company Creek Well Pumping Test Hydrograph

Figure 5: Company Creek Well Step Pumping Test 60-Minute and End of Test Specific Capacity

Figure 6: Company Creek Well Pumping Test Recovery Analysis

Figure 7: Maintenance Well Testing Period Hydrograph

Figure 8: Maintenance Well Pumping Test Hydrograph

Figure 9: Maintenance Well Step Pumping Test 60-Minute and End of Test Specific Capacity

Figure 10: Maintenance Well Pumping Test Recovery Analysis

No table of figures entries found.

APPENDICES

APPENDIX A

Well Inspection Photographs

APPENDIX B

Well Video Log Photographs

APPENDIX C

Well Video Logs (provided separately)

APPENDIX D

Test Pit Logs

APPENDIX E

Laboratory Testing

1.0 INTRODUCTION

Golder Associates Inc. (Golder) is pleased to present this report to Otak, Inc. (Otak) to provide well testing and foundation recommendations in support of the National Park Service (NPS) Stehekin Fire Fighting Facilities

Development Project, North Cascades National Park, Washington.

1.1 Scope of Work

The scope of work for the geotechnical investigation and well testing was presented to Otak via email in August

2020. Authorization to proceed was received September 2, 2020 via Task Order 140P2020F0273. The proposed scope of work consisted of the following tasks.

Well Inspection & Testing

Inspection of the existing well facilities.

Removal of the existing pumps, drop pipe, and wire.

Completion of downhole video logging of the wells.

Installation of a temporary pump and completion of step-rate pumping tests.

Removal of the temporary pump and disinfection and re-installation of the existing pumps and testing the wells to ensure proper operation.

Geotechnical Investigation

Coordination of work activities and site access with the NPS project team.

Notification of the public utility locate service (811) and Park Maintenance staff prior to the start of excavation.

Geotechnical logging and sampling of soils excavated by NPS staff.

Submitted representative samples for laboratory testing. Testing included 9 sieve analyses.

Preparation of a geotechnical report (this document) that includes:

▪ Exploration location map (Figure 2), test pit logs (Appendix D), and a description of site and geologic subsurface conditions (Section 3.3).

▪ General earthworks and construction recommendations (Section 3.5).

▪ Allowable soil bearing pressure and settlement estimates for spread footing and mat foundations, including minimum foundation embedment (Section 3.4.3).

Seismic design values based on the 2018 International Building Code (Section 3.4.2).

2.0 WELL TESTING AND INSPECTION

This section presents the results of the inspection of the Company Creek Well and Maintenance Wells at the

NOCA Stehekin Valley Fire Facility in Stehekin, Washington. The well locations are shown on Figure 1. The work was performed between October 8 and October 12, 2020.

2.1 Existing Well Information

This section summarizes the existing information on the Company Creek and Maintenance Wells. Well logs and a summary of the well completions are provided in HECO Engineers (HECO 2018).

2.1.1 Company Creek Well

The well log for the Company Creek Well and information in HECO (2018) indicates the well was drilled in 1977 to a depth of 34 feet below ground surface (feet bgs). The well log indicates the following well construction:

A cement and bentonite surface seal to a depth of 18 feet bgs.

6-inch diameter steel casing to 34 feet bgs.

36, 3-inch long by 3/16-inch perforations from 30 to 34 feet bgs.

The well log indicates the well is completed in 3 to 5-inch diameter gravels with a small amount of sand. The depth to water following well completion was 8.58 feet bgs. A short (2-hour) pumping test was completed after the well was drilled. The well was pumped at 25 gallons per minute (gpm) with 1.67 feet of drawdown measured at the end of the test.

Based on information in HECO (2018), the well is housed in a 5-foot by 5-foot well house and is equipped with a

2 horsepower (hp) pump capable of pumping about 10 gpm; no flowmeter is installed on the well. Although the well log reports the well is 34 feet deep, a photograph of notes on the pump control panel in HECO (2018) indicates the pump is set at a depth of 39 feet.

2.1.2 Maintenance Well

The well log for the Maintenance Well is mostly illegible; information in HECO (2018) indicates the well was drilled in 1973 to a depth of 42 feet bgs. The well is reportedly completed with 6-inch diameter steel casing and appears to be completed with a surface seal and a well screen, but the depths are uncertain. The well log suggests a pumping test was completed with 1.17 feet drawdown, but the pumping rate and duration are not legible. Based on the proximity to the Company Creek Well and similar depth, the Maintenance Well is likely completed in gravel and sand materials.

Based on information in HECO (2018), the Maintenance Well is housed in a 5-foot by 5-foot well house and is equipped with a 5 hp, 26-stage pump capable of pumping about 20 gpm (based on a spare pump stored onsite);

no flowmeter is installed on the well.

2.2 Well Inspection and Video Logging

This section describes the inspection of the wells, including verification of pump make, model, and set depth, and the downhole video logs completed in each well. Holt Services Inc. (Holt), a Golder subcontractor, removed and reinstalled the existing pumps and provided a temporary pump and generator for completion of pumping tests.

Holt disconnected and locked out the power to the pumps prior to pulling the pumps. The roofs on the well houses are designed to be removed to provide access for pulling the pumps and were partially removed to allow access to the wells. The existing pumps, drop pipe, and wire were pulled from the wells using a pump hoist, and stored adjacent to the wells on plastic sheeting. Appendix A includes photographs of the pump and drop pipe from each well.

The video logs were completed using an Allegheny Instruments Geovision Nano downhole video camera. In each well, a down-looking run was made followed by a run with both down- and side-looking images. In both wells, poor visibility below the water level resulting from disturbance of the water column after the pumps were pulled obscured a portion of the view of the well casings. The depth counter on the video logs is referenced to ground surface. The casing stickup on the Company Creek Well is about one foot above ground, and the casing stickup on the Maintenance Well is about 1.5 feet above ground. The well video logs (Appendix C) are included as a separate DVD attachment. Appendix B includes screen captures from the video logs in each well.

2.2.1 Company Creek Well

The Company Creek Well pump is set on 36 feet (3 x 10-foot pieces and 1 x 6-foot piece) of 1.5-inch diameter galvanized steel drop pipe. The pump is a Grundfos 40S20-7, 7-stage pump connected to a Franklin Electric 2 hp motor. After pulling the pump, the bottom of the well was tagged using a weighted tape at 41.7 feet below the top of the casing (btoc), or about 40.7 feet below the wellhouse floor. This about is 6.7 feet deeper than the reported depth of the well based on the well log and information in HECO (2018).

The threads on the pump column and couplers were in good condition and were disassembled and reassembled without difficulty. The well seal and above-ground portions of the discharge piping were noted to be in good condition. Iron oxide encrustation, scaling, and iron bacteria deposits were observed on the pump column starting at about 15 feet btoc, and became thicker below 20 feet btoc, and were also present on the pump and motor

(Appendix A).

2.2.1.1 Video Inspection

The video inspection of the Company Creek Well indicated the following:

The well casing is scaled and encrusted with iron oxide materials. Several welds were observed above the water level that appeared to be in good condition. The thickness of the scale materials increases with depth, with the thickest deposits observed below the water level (Photographs B-1 and B-2).

At a depth of about 36.7 feet bgs, the top of a stainless-steel, continuous Vee-wire wrap well screen was observed (Photograph B-3). Because of the heavy encrustation, no riser pipe was observed on the top of the well screen.

The well screen was clean and only had a few small pieces of scale wedged into the slots (Photograph B-4).

The screen slot size is unknown but appears to be relatively coarse.

The base of the well was observed at a depth of about 40.5 feet bgs (Photograph B-5). The base of the well has a small amount of fill material that appears to be fine scale and possibly formation materials (fine sand) that are small enough to pass through the well screen.

There are several discrepancies between the well inspection and video log and the well construction reported in

HECO (2018) based on a well log:

The well log indicated the well depth was 34 feet bgs. The pump was set on 36 feet of drop pipe and the pump and motor are about 3.4 feet long. After the pump was pulled, the well depth was measured at

41.7 feet btoc, or about 40.7 feet bgs. With a casing stickup of about one foot, this is similar to the depth measured in the video log.

The well log indicated the well was completed with perforated casing from 30 to 34 feet bgs. The well video log indicates the well is completed with stainless-steel, continuous Vee-wire wrapped well screen from about

36.7 feet bgs to at least 40.5 feet bgs.

Based on the well video log, the Company Creek Well casing, which is mild steel, is heavily encrusted and scaled with iron oxide materials that may in part be the result of iron bacterial activity in the well. The well screen, which is stainless steel, is clean and appears to be in good condition, although the base of the well screen is filled small amount of scale and possibly fine formation materials. The well log in HECO (2018) that is reported to be for

Company Creek Well appears to be for a different well based on the well video log unless the well was deepened and modified at some point after drilling and the work was not documented.

2.2.2 Maintenance Well

The Maintenance Well pump is set on 31.05 feet (1 x 21.6-foot piece and 1 x 9.45-foot piece) of 1.5-inch diameter galvanized steel drop pipe. The pump is a Jacuzzi 5S4D30S/A connected to a Franklin Electric 5 hp motor. The threads on the pump column and couplers were in good condition and were disassembled and reassembled without difficulty. The well seal and above-ground portions of the discharge piping were noted to be in good condition.

After pulling the pump, the bottom of the well was tagged using a weighted tape at 38.1 feet btoc. A 5-inch diameter bailer was run into the well to determine if the casing was restricted by encrustation or scale; the bailer was run to the bottom of the well and used to clean out loose, accumulated material. The well was cleaned out to a depth of about 43.4 feet btoc or about 41.9 feet bgs; the casing stickup is about 1.5 feet.

2.2.2.1 Video Inspection

The video inspection of the Maintenance Well indicated the following:

The well casing is scaled and encrusted with iron oxide materials. Several welds were observed above the water level that appeared to be in good condition. The thickness of the scale materials increases with depth, with the thickest deposits observed below the water level (Photographs B-6, B-7, and B-8).

At a depth of about 36.1 feet bgs, the top of a stainless-steel, continuous Vee-wire wrap well screen was observed (Photographs B-9 and B-10). The screen slot size cannot be determined from the video log. The top of the screen appears to be completed with a lead packer wedged against the casing.

The upper approximate one foot of the well screen was partially encrusted (Photograph B-11). The reason for this is uncertain, it is possible that the well casing overlaps the top of the well screen and no water is transmitted through the upper foot of the well screen. The remainder of the well screen is clean

(Photograph B-12) with no encrustation or scale.

The base of the well was observed at a depth of about 41.3 feet bgs (Photograph B-13). The base of the well has a small amount of fill that appears to be fine scale and possibly formation materials (fine sand) that is small enough to pass through the well screen.

The well inspection and well video log generally confirms the well construction details described in HECO (2018):

The well was reported to be drilled to 42 feet bgs; the well depth was measured at 41.9 feet bgs.

The HECO 2018 report indicated the well was completed with a well screen. The well video log confirmed the well is completed with stainless-steel, continuous Vee-wire wrapped well screen from about 36.1 feet bgs to at least 41.3 feet bgs.

Based on the well video log, the Maintenance Well casing (mild steel) is heavily encrusted and scaled with iron oxide materials that may in part be the result of iron bacterial activity in the well. The stainless-steel well screen is clean (except for the upper foot) and appears to be in good condition, although the base of the well screen is filled with a small amount of scale and possibly fine formation materials.

2.3 Pumping Tests

Step-rate pumping tests were completed in each well using a temporary submersible pump (Grundfos 230S100 with a 10 hp motor) installed by Holt following completion of the video logs. The temporary pump was disinfected prior to installation. Holt installed two, 1-inch inside diameter PVC sounding tubes in the wells to allow installation of a pressure transducer and datalogger in one sounding tube for automated groundwater level measurements. A manual water level tape was used in the second for groundwater level measurements. Pumping rates were measured using an instantaneous and totalizing flowmeter installed on the discharge line. The discharge from the wells was routed about 300 feet downgradient of each well to grass covered areas using a temporary pipeline and allowed to infiltrate. Plywood and plastic sheeting were used to prevent erosion at the discharge point.

The general testing procedure was to pump the wells for four, approximately one-hour steps of increasing pumping rate. At the end of the fourth step, pumping continued at the fourth step rate for an additional 5 to

6 hours. At the end of the extended fourth step, the pump was shut down and the groundwater level recovery measured overnight (about 12 hours) using the pressure transducer and datalogger. During pumping, field groundwater quality parameters (pH, temperature, turbidity, specific conductance, and dissolved oxygen) were periodically monitored.

At the end of the recovery period (i.e. the morning after the start of the pumping tests), the temporary pump and sounding tubes were removed from the wells. The encrustation was cleaned from permanent pumps, particularly around the intakes, and the permanent pumps, drop pipe, and drop wire were disinfected and re-installed in the well. Prior to reconnecting the wells to the water systems, the wells were pumped to waste to remove chlorinated water from the well. The water discharge during pumping was de-chlorinated and allowed to infiltrate. Once testing (completed with chlorine test strips) indicated the discharge did not contain chlorine, the wells were reconnected to the water systems and the pump and system operation tested.

Groundwater levels described in this section are referenced to the top of the well casings.

2.3.1 Company Creek Well

The temporary pump was installed in the Company Creek Well on October 8, 2020 with the intake at a depth of

32.3 feet btoc; the pump could not be lowered any deeper because of encrustation and scale on the inside of the casing preventing a deeper setting. The depth to water prior to pump installation was 18.68 feet bgs. A short

(about 2 hours duration) shake-down pumping test was conducted following the pump installation.

The pumping test was conducted on October 9. The depth to water at the start of the test was 18.70 feet bgs.

During the pumping test, groundwater levels were also measured using a pressure transducer in a private well

(Valenti/Gempko Well) located about 300 feet west-northwest from the Company Creek Well (Figure 1). The

Valenti/Gempko Well is 48 feet deep and competed as an open-bottom cased well in clean sand and gravel. The depth to water in the Valenti/Gempko Well was 7.31 feet bgs before the start of the test.

2.3.1.1 Groundwater Level Response

A groundwater level hydrograph for the shakedown test and pumping test is shown on Figure 3 and Figure 4 is a hydrograph for the pumping test completed on October 9, 2020. During the shakedown test, the pumping rate varied between about 5 and 60 gpm; the pumping rate was incrementally increased about every 10 to 15 minutes to evaluate the well response. The depth to water varied from about 18.7 feet bgs at the start of the test to about

19.7 feet btoc when pumping at maximum rate of about 60 gpm for 15 minutes. During the shake-down test, the pumping rate was difficult to maintain because scale from the well casing that was dislodged during pump installation and possibly during higher pumping rates and partially blocked the pump intakes and clogged the valve on the discharge line. At the end of the shake-down test (about 2.2 hours of pumping), the depth to water was 19.62 feet btoc; recovery was near-instantaneous (within several seconds) when the pump was shut off.

The October 9, 2020 pumping test hydrograph is shown on Figure 4. The depth to water was 18.70 feet bgs immediately before the test started. The Company Creek Well was pumped for four steps of increasing pumping rate (14.0 gpm, 24.6 gpm, 54.5 gpm, and 68.8 gpm). The duration for the first 3 steps ranged from about 68 to

83 minutes. The fourth step was extended for a duration of 352 minutes. The total pumping duration was

572 minutes (about 9.5 hours). During the pumping test, particularly at the highest pumping rate, the pumping rate varied and as a result, drawdown varied between about 1 and 1.3 feet. This is likely because the pump intake and/or valving on the discharge were periodically partially clogged with scale loosened during pumping or from when the pump was installed. An adjustment in the pumping rate was also made after about 100 minutes of pumping in step 4, resulting in an increase in pumping rate of about 10 gpm.

At the end of the test, the depth to water was about 19.95 feet bgs, or a drawdown of 1.25 feet. When the pump was shut down, the groundwater level recovered immediately and the depth to water was 18.75 feet bgs within one minute of the pump shutdown. At the end of the recovery period (about 13 hours after the pump was shut off), the depth to water was 18.72 feet btoc.

The groundwater level in the Valenti/Gempko Well gradually decreased over the pumping test (Figure 4); the groundwater level decrease was less than 0.05 foot.

2.3.1.2 Test Evaluation

Figure 5 shows the drawdown over the duration of the pumping test and the calculated specific capacity (pumping rate divided by drawdown, a measure of well performance). The specific capacity was calculated using the measured drawdown 60 minutes after the start of each pumping step and at the end of the test. The specific capacity ranged from about 92 gallons per minute per foot of drawdown (gpm/ft) at the end of the first step to about 59 gpm/ft 60 minutes after the fourth step started. At the end of the test, the specific capacity was

53 gpm/ft.

Figure 6 shows an analysis of the recovery data to estimate the aquifer transmissivity. The recovery data were analyzed using the Theis (1935) recovery method. The estimated aquifer transmissivity is 101,100 feet squared per day (ft2/d) indicating the aquifer is high permeability, consistent with the well log description of gravels and sand in the interval the well is completed in.

Field groundwater quality (pH, temperature, conductivity, turbidity, and dissolved oxygen) were periodically measured during the pumping test. The field groundwater quality measurements are summarized in Table 1.

Table 1: Field Groundwater Quality - Company Creek Well

Time pH (s.u.)

Conductivity

(S/cm) Temperature (oC)

Turbidity

(NTU)

Dissolved Oxygen (mg/L)

9:16 6.65 71.0 11.3 2.41 9.01

10:21 6.14 58.6 11.0 2.07 9.09

12:00 5.43 58.9 10.4 0.56 8.98

13:10 5.20 58.7 10.1 0.65 9.54

14:18 5.28 58.4 9.7 NM 8.93

14:41 5.94 59.0 12.9 1.06 8.53

15:27 5.18 58.7 9.7 0.64 9.20

16:45 5.50 63.2 10.5 0.34 8.99

17:19 5.27 58.9 9.7 0.62 8.87

17:55 5.58 59.0 9.8 1.31 9.07

Notes:

Measurements made on October 9, 2020 s.u. - standard units

S/cm - microSiemens per centimeter

NTU -Nephelometric Turbidity Units

°C - degrees Celsius mg/L - milligrams per liter

NM - Not Measured

The field groundwater quality data indicate:

The pH is slightly acidic at about 5.2 to 6.65 standard units (s.u.).

The conductivity is low (less than 71 microSiemens per centimeter [S/cm]) reflecting a low dissolved solids content in the groundwater.

The temperature ranged from about 9.7 to 11.3 degrees Celsius (°C).

The turbidity ranged from about 0.34 to 2.41 Nephelometric Turbidity Units (NTU) and generally decreased over the test, likely because turbid water resulting from pump removal and installation was removed from the well.

Dissolved oxygen ranged from about 9 to 9.5 milligrams per liter (mg/L).

A groundwater quality sample was not collected during the pumping test. Groundwater quality data provided in

HECO (2018) indicates groundwater quality meets drinking water criteria, with the exception of pH which was slightly below the secondary water quality criterion of 6.5 to 8.5 s.u.

2.3.2 Maintenance Well

The temporary pump was installed in the Maintenance Well on October 10, 2020 with the intake at a depth of

34 feet btoc. A short (about 2 hours duration) shake-down pumping test was conducted following the pump installation. The step-pumping test was completed on October 11.

2.3.2.1 Groundwater Level Response

A groundwater level hydrograph for the shakedown test and pumping test is shown on Figure 7 and Figure 8 is a hydrograph for the pumping test completed on October 11, 2020. The depth to water prior to the start of the shakedown test was 6.56 feet bgs. The well was pumped over a range of rates from about 6 to 68.5 gpm; the depth to water when pumping at 68.5 gpm after several minutes was 7.26 feet. At the end of the shake-down test

(about 1.3 hours of pumping), the depth to water was 6.65 feet btoc (Figure 7). Recovery was near-instantaneous when the pump was shut off.

The Maintenance Well pumping test was conducted on October 11. The depth to water at the start of the test was

6.50 feet bgs. A test hydrograph is shown on Figure 8. The Maintenance Well was pumped for four steps of increasing pumping rate (12.4 gpm, 27.2 gpm, 48 gpm, and 78 gpm). The duration for the first 3 steps ranged from about 63 to 76 minutes. The fourth step was extended for a duration of 305 minutes. The total pumping duration was 508 minutes (about 8.5 hours). At the end of the test, the depth to water was about 7.89 feet bgs, or a drawdown of 1.39 feet. When the pump was shut down, the groundwater level recovered immediately and was

6.52 feet bgs within one minute of the pump shutdown. About 13 hours after the pump was shut down, the groundwater level was about 0.2 feet higher than at the start of the of the test. The groundwater level rise above the pre-test level is likely because of infiltration of precipitation after the pump was shut off. About 0.9 inches of rain were measured at the Stehekin Airstrip during the recovery period.

2.3.2.2 Test Evaluation

Figure 9 shows the drawdown over the duration of the pumping test and the calculated specific capacity. The specific capacity was calculated using the measured drawdown 60 minutes after the start of each pumping step and at the end of the test. The specific capacity ranged from about 468 gpm/ft at the end of the first step to about

60.3 gpm/ft 60 minutes after the fourth step started. At the end of the test, the specific capacity was 56.6 gpm/ft.

Figure 10 shows an analysis of the recovery data to estimate the aquifer transmissivity. The recovery data were analyzed using the Theis (1935) recovery method. The estimated aquifer transmissivity is 87,500 ft2/d, similar to the transmissivity estimated from the Company Creek Well recovery analysis. The high transmissivity indicates the aquifer is high permeability, consistent with the well log descriptions of gravels and sand in nearby wells.

Field groundwater quality (pH, temperature, conductivity, turbidity, and dissolved oxygen) were periodically measured during the pumping test. The field groundwater quality measurements are summarized on Table 2.

Table 2: Maintenance Well Field Groundwater Quality

Time pH (s.u.)

Conductivity

(S/cm) Temperature (oC)

Turbidity

(NTU)

Dissolved Oxygen (mg/L)

9:07 6.33 60.8 8.4 3.91 9.20

9:45 6.19 55.7 8.5 2.31 9.60

10:32 6.61 56.3 8.3 1.24 9.45

11:16 6.52 55.3 8.1 2.16 9.34

11:54 6.49 55.6 8.0 0.89 9.58

12:12 6.47 54.9 8.0 4.11 9.60

Time pH (s.u.)

Conductivity

(S/cm) Temperature (oC)

Turbidity

(NTU)

Dissolved Oxygen (mg/L)

13:03 6.36 55.5 8.2 1.17 9.41

15:21 6.38 56.1 7.8 0.63 9.17

16:25 6.44 56.1 7.9 0.71 9.40

16:50 6.61 53.7 7.7 0.45 9.34

Notes:

Measurements made on October 11, 2020 s.u. - standard units

S/cm - microSiemens per centimeter

NTU -Nephelometric Turbidity Units

°C - degrees Celsius mg/L - milligrams per liter

The field groundwater quality data indicate:

The pH is slightly acidic at about 6.2 to 6.5 s.u.

The conductivity is low (less than 61 S/cm) reflecting a low dissolved solids content in the groundwater.

The temperature ranged from about 7.7 to 8.5 °C.

The turbidity ranged from about 4.11 to 0.89 NTU and was lower over the last 2 to 3 hours of the test, likely because turbid water resulting from pump removal and installation was removed from the well.

Dissolved oxygen ranged from about 9.2 to 9.6 mg/L.

A groundwater quality sample was not collected during the pumping test. Groundwater quality data provided in

HECO (2018) indicates groundwater quality meets drinking water criteria.

2.4 Overall Evaluation of Wells

The well inspections and well video logs indicated the following:

The galvanized steel drop pipes and mild steel well casings, particularly below the water level, were moderately to heavily scaled and encrusted with iron oxide and iron bacteria deposits. The threads on the drop pipe and couplers are in good condition.

The stainless-steel pumps and motors had some iron bacteria deposits but did not have scale or encrustation.

The Company Creek Well is deeper than reported in the HECO (2018) report and is completed with a stainless-steel well screen rather than a perforated casing. The well log included in HECO (2018) appears to be for a different well.

The stainless-steel well screens are in good condition. No scale or encrustation was observed on the screens except for the upper foot of the Maintenance Well screen.

Both wells have a small amount of scale and possibly formation sand that passed the well screens at the base of the screens.

The pumping tests indicated the following:

Both the Company Creek Well and the Maintenance Well are completed in permeable gravel and sand.

The Company Creek Well was pumped at up to about 67 gpm with 1.25 feet of drawdown after 9.5 hours of pumping. This is a greater specific capacity than reported on the well log of 25 gpm with 1.67 feet of drawdown after 2 hours of pumping, suggesting that along with the differences in well construction between the well log and well video, the well log may be for a different well. We understand that the Company Creek

Well will continue to be used to supply water for three residences and a shop with no changes in the desired pumping rate. The Company Creek Well can easily meet this water demand based on the pumping test and long-term operation of the well.

Drawdown of less than 0.1 foot was measured in the Valenti/Gempko Well during the Company Creek Well pumping test. There is likely little measurable drawdown in the Valenti/Gempko Well during operation of the

Company Creek Well with the currently installed pump capable of pumping at about 10 gpm.

The Maintenance Well was pumped at up to about 78 gpm with 1.38 feet of drawdown after 8.5 hours of pumping. We understand that the desired future short-term yield from Maintenance Well may be about

36 gpm, while the average pumping rate may be in the range of 2 to 5 gpm. Based on the step-pumping test, the 60-minute specific capacity of the Maintenance Well at a pumping rate of 36 gpm is estimated to be about 275 gpm/ft; this corresponds to a drawdown of about 0.13 feet after one hour of pumping. Based on the pumping test, the Maintenance Well can be equipped with a larger pump to meet the desired future short-term well yields.

If new pumps and motors are installed in either well, a new pump drop pipe should be installed with the new pumps because of the observed encrustation and scaling of the existing drop pipe.

3.0 GEOTECHNICAL INVESTIGATION

Golder participated in a meeting with Otak on September 2, 2020 to discuss the locations of the proposed test pits. At the time of the meeting, the location of the tanks were not known so the test pit locations were selected by

Otak based on the anticipated locations. The geotechnical investigation consisted of excavation of 8 test pits on

October 13, 2020 in the general vicinity of the proposed structures. Test pits exploration depths were from 4.5 to

9.0 feet bgs. The test pits were excavated using a CAT 420D backhoe operated by NPS personnel. Soils excavated were logged by Golder Geologist Daniel Bida from the Redmond, Washington Office. The locations of the test pits are shown in Figure 1 and the test pit logs are presented in Appendix D.

The subsurface soil conditions were examined and classified in general accordance with Golder technical guidance TP-1.2-6, as summarized in the Classification Legend in Appendix D. Test pit records include sample depth, stratigraphy, groundwater occurrence (if observed), and engineering characteristics. Stratigraphic contacts shown on the test pit log represent the approximate boundaries between soil units; actual transitions may be more gradual. The groundwater and subsurface conditions depicted are for the specific date and location reported and therefore, are not necessarily representative of conditions at other locations and times.

3.1 Test Pits

3.1.1 Test Pit 1

Test Pit 1 (GTP-1) encountered coarse alluvium consisting of well-graded gravel (GW) with 50% cobbles and boulders (by volume). The material was largely clast supported and test pit sidewalls caved during excavation.

The test pit was terminated at a depth of 4.5 feet due to difficulty excavating and dislodging boulders and cobbles.

3.1.2 Test Pit 2

Test Pit 2 (GTP-2) encountered stratified beds of fine-to-coarse alluvium consisting of poorly graded sand with gravel (SP) with up to 40% cobbles (by volume). The bedding coarsened with depth becoming clast supported and caving easily near the bottom of the excavation. The test pit was terminated at a depth of 6.5 feet due to excessive caving.

3.1.3 Test Pit 3

Test Pit 3 (GTP-3) encountered fine-to-coarse alluvium consisting of well-graded gravel with sand (GW) and

50% cobbles (by volume). The test pit was terminated at a depth of 7.5 feet due to excessive caving.

3.1.4 Test Pit 4

Test Pit 4 (GTP-4) encountered stratified beds of fine-to-coarse alluvium consisting of poorly graded gravel and sand (GP) and up to 25% cobbles (by volume) that coarsened with depth. The test pit was terminated at a depth of 7.0 feet due to excessive caving at the bottom of the excavation.

3.1.5 Test Pit 5

Test Pit 5 (GTP-5) encountered stratified beds of alluvium consisting of poorly graded gravel with sand (GP) overlying well-graded gravel with sand (GW) and 40% cobbles (by volume). The material at depth was largely clast supported and test pit sidewalls caved during excavation. The test pit was terminated at a depth of 7.5 feet due to excessive caving.

3.1.6 Test Pit 6

Test Pit 6 (GTP-6) encountered stratified alluvium consisting of fine to medium silty sand (SM) overlying poorly graded gravel with sand (GP) and 15% cobbles (by volume). The material at depth caved during excavation and the test pit was terminated at a depth of 9.0 feet.

3.1.7 Test Pit 7

Test Pit 7 (GTP-7) encountered stratified alluvium that coarsened with depth, consisting of beds of sand and gravel (SP-SM) and silty sand (SM), overlying and poorly graded gravel with sand (GP) and 20% cobbles (by volume). The material at depth caved during excavation and the test pit was terminated at a depth of 8.5 feet.

3.1.8 Test Pit 8

Test Pit 8 (GTP-8) encountered coarse fill material consisting of poorly graded gravel with silt and sand (GP-GM) with 30% cobbles and boulders, overlying well-graded gravel alluvium (GW) with 40% cobbles and boulders (by volume). The alluvium was largely clast supported and caved during excavation. The test pit was terminated at a depth of 4.5 feet due to difficulty excavating and dislodging boulders and cobbles.

3.2 Laboratory Testing

Representative samples were selected and submitted to a Redmond, Washington soil laboratory for index testing.

Samples were submitted to calibrate field classifications and characterize engineering and index properties of the site soils. In total 9 samples were submitted for sieve analysis. The tests were completed in general accordance with ASTM D6913 (Standard Test Methods for Particle-Size Distribution (Gradation) of Soils Using Sieve

Analysis). Table 3 summarizes the results of the analysis and the soil classification based on the Unified Soil

Classification System (USCS). Laboratory testing results are provided in Appendix E.

Table 3: Soil Testing Summary

Test Pit Sample Sample Depth (feet bgs)

MC% %

Gravel

Sand

Fines

USCS

GTP-1 S-1 3.5 4 62 33 5 Well graded GRAVEL with sand (GW)

GTP-2 S-1 1.5 2.4 39 60 1 Poorly graded SAND with gravel (SP)

GTP-3 S-2 5 3.3 66 33 1 Well graded GRAVEL with sand (GW)

GTP-4 S-1 6 2.2 77 19 4 Poorly graded GRAVEL with sand (GP)

GTP-5 S-1 5 2.2 74 25 1 Well graded GRAVEL with sand (GW)

GTP-6 S-1 2 5.2 0 65 35 Silty SAND (SM)

GTP-6 S-2 7 2.2 60 36 4 Poorly graded GRAVEL with sand (GP)

GTP-7 S-1 2 4.6 37 56 7 Poorly graded SAND with silt and gravel (SP-SM)

GTP-8 S-1 3.5 6 68 28 4 Well graded GRAVEL with sand (GW)

3.3 Subsurface Conditions

3.3.1 Geologic Setting

Stehekin sits at the north end of Lake Chelan which is a steep valley basin scoured out by recent glaciation events. The northern end of the lake has been fed by the Stehekin River throughout the Holocene, prograding some 4 kilometers in the last 9,000 years.

As mapped, the surficial geology in the vicinity of the Stehekin Fire Fighting Facilities Development Project is composed of Quaternary alluvial fans or older alluvium (WADGER 2016). Alluvial fans are created where tributary streams coming off steeper valleys joining the mainstream of the Stehekin River. The tributary stream loses the ability to transport coarser material and deposits the material creating alluvial fans.

3.3.2 Subsurface Soil Conditions

3.3.3 Groundwater

Groundwater was not encountered to the depths explored during the October 2020 test pit exploration program.

Water well installation records searched through the State of Washington Department of Ecology, Well

Construction and Licensing online search tool returned 5 wells in the area with static water levels at the time of installation between 9 and 14 feet bgs. The November 2018 Title 1 – Scoping Trip Report, PMIS 237297, contained a single test pit record that encountered groundwater at a depth of 12 feet bgs. An open standpipe monitoring well installed in the scoping visit test pit reported water levels of 11.2 feet bgs (June 2018), 12 feet bgs

(July 2018), and >12.25 ft bgs (August 2018).

We expect that groundwater was just beyond the limits of the excavation equipment at the time of our exploration program. From the well records and previous explorations, we assumed a depth to groundwater of 10 feet in our analysis.

3.4 Engineering Recommendations

3.4.1 General

3.4.2 Seismic Design

The 2018 International Building Code (IBC) seismic design section provides information to be used as the basis for seismic design of structures.

3.4.2.1 Site Class

Section 1613 of the 2018 IBC provides information on earthquake loads and site ground motion needed for liquefaction potential assessment. Based on the IBC design criteria, sites are classified according to the average soil profile properties in the first 100 feet bgs. The deepest test pit in the proposed Stehekin Fire Fighting

Facilities Development project site was excavated to a depth of 9.3 feet bgs and wells installation in the vicinity of the project show similar soil conditions to a depth of roughly 50 feet bgs. Based on our understanding of the site and historical geology we expect the properties below 50 feet bgs are expected to be similar or denser than the soils at the bottom depths of explorations. The site should be classified as Site Class D site based on our interpretation of the subsurface conditions and consistent with the requirements of Section 1613.2.2 of 2018 IBC.

3.4.2.2 Ground Motion Parameters

Ground motion parameters used for design per ASCE 7-16 include the site coefficient and mapped spectral accelerations, provided in the United States Geological Survey (USGS) Seismic Design Maps. The interpolated probabilistic ground motion values in percent gravity were obtained from the ASCE 7 online hazard tool based on the USGS US Seismic Design Maps (https://asce7hazardtool.online/). The results shown in Table 4 were obtained for latitude 48.347345 and longitude -120.720256 (a point located near the center of the site) assuming a

Risk Category of II and a default Site Class D (see Section 11.4.3 of ASCE 7-16).

Table 4: Design Ground Motion Parameters

Ground Motion Parameter Acceleration (g)

Peak Ground Acceleration (PGA) 0.242

Modified PGA (PGAM) 0.329

Short (0.2 second) Spectral Response (SS) 0.552

1.0 Second Spectral Response (S1) 0.213

Modified Short Spectral Response (SMS) 0.75

Ground Motion Parameter Acceleration (g)

Modified 1.0 Second Spectral Response (SM1) 0.463

Design Short Spectral Response (SDS) 0.5

Design 1.0 Second Spectral Response (SD1) 0.309

Note: Modified and design spectral response values provided for default Site Class D soil condition (see Section 11.4.4 of ASCE 7-16).

Structures on Site Class D soils with S1 greater than or equal to 0.2 require a site-specific ground motion hazard analysis, with exceptions described in ASCE 7-16 Section 11.4.8. The values in Table 2 assume the exceptions apply to the project.

3.4.2.3 Liquefaction Potential

Based upon the results of our subsurface exploration and general depth to groundwater, it is our opinion that the potential for liquefaction occurring at this site is relatively low.

3.4.3 Shallow Foundation Design Criteria

The foundations for the proposed project consist of spread footing and mat foundations. Based on our understanding of the Stehekin Fire Facility, the dormitory and Fire Cache will be constructed on strip footings and water tanks on mat foundations.

Based on the explorations in the area, the foundations are expected to be in alluvium consisting of compact sand and gravel. The assumed groundwater table is expected to be 10 feet bgs. Explorations took place in the fall when water levels are generally lowest and were not encountered to the depths explored.

The subgrade soil encountered should be over-excavated and replaced in accordance with recommendations contained in Section 3.5. If the foundations are placed on properly placed and compacted structural fill significant long-term settlement is not expected at the site.

Conventional shallow isolated or continuous foundations placed on compacted structural fill should be designed based on the following recommendations. Please refer to Section 3.5 for construction recommendations pertaining to spread footings. The foundation recommendations are based on our current understanding of the conceptual plans. If the configuration of the project changes, Golder should be notified to review the updated plans and revise the foundation recommendations accordingly.

Design isolated footings for a maximum allowable bearing pressure of 5 kips per square foot (ksf) assuming a minimum footing width of 3 feet and a maximum footing width of 8 feet.

Design mat foundation maximum allowable bearing capacity:

Dimension (feet) Allowable bearing capacity

(ksf)

Settlement (in)

32 x 32 1.3 1

35 x 35 1.2 1

40 x 40 1.0 1

Golder was provided updated drawings (Water Preferred Alternative) after the exploration program. The updated drawings show the locations of the water tanks are outside of the explorations areas previously identified during the September 2020 meeting. A qualified person must verify the recommendations presented in this report are appropriate and applicable for the ground conditions encountered during construction.

Design continuous footings using a maximum allowable bearing pressure of 5 ksf assuming a minimum footing width of 2 feet and maximum footing width of 4 feet.

The maximum allowable bearing pressures meet the required factor of safety according to IBC.

The recommended maximum allowable pressures are gross bearing pressures.

The recommended maximum allowable bearing pressures will result in less than 1 inch of total settlement.

The values presented may be increased by one-third for short-term wind and seismic loading.

Both isolated and continuous footings should be embedded a minimum of 2 feet below adjacent finished grade for frost protection.

The above recommendations are based on concentric pressures applied at the base of the footings. In the case of eccentric pressures (e.g., due to lateral stress), Golder may need to re-evaluate the recommended pressures.

The preceding recommendations are for locations in the general vicinity of the explorations conducted. Structures located outside of the limits of the explorations may have different subsurface conditions and therefore different bearing capacities.

3.5 Foundation Construction Recommendations

Exposed subgrades for footings, floor slabs, and other structures should be over-excavated and replaced with compacted structural fill, see Section 3.5.5. Any organic, soft, or pumping soils observed within a subgrade should be over-excavated and replaced with a suitable structural fill material. Unsuitable excavated materials should not be mixed with materials to be used as structural fill.

3.5.1 Site Drainage

Permanent control of surface water should be incorporated in the final grading design, and vegetative protection should be established. Areas around footings should be backfilled with free-draining material and the site graded to direct water away from structures. During construction, the contractor must implement necessary drainage measures to prevent degradation of the excavation areas and foundation subgrade.

3.5.2 Site Preparation and Topsoil Removal

The site earthwork will include preparation of the footing and building subgrades and installing new utilities.

Excavations should be sequenced to limit the amount of exposed subgrade.

The building and pavement areas and areas where structural fill is to be placed should be stripped and cleared of surface vegetation, organic matter, topsoil, and other deleterious material. Explorations in the area generally encounter a thin vegetative mat followed by topsoil unit up to 1 feet bgs. Based on site observations we estimate a stripping depth range of 0.5 to 1 foot, although localized areas of deeper stripping could be required.

3.5.3 Use of onsite soils

Based on our explorations we expect that excavation will encounter native alluvium deposits. The soil generated from excavations are expected to be suitable for potential use as structural fill under the following conditions:

Material is primarily sand and gravel.

Free of debris, organics, and other deleterious material.

Oversize material is removed.

Material is able to be placed and compacted at appropriate moisture content and relative density.

3.5.4 Subgrade and Footing Preparation

3.5.5 Earthworks

3.5.5.1 Removal of Unsuitable Soil, Undocumented Fill, or Other Materials

Undocumented fill should not be utilized as compacted fill or beneath planned structures. Depending on the nature of the undocumented fill, it may be reusable as compacted fill with appropriate processing to meet the specification for the intended use.

3.5.5.2 Subgrades

Exposed subgrades for any proposed structure should be compacted with a vibratory roller to a firm, unyielding state. Any localized zones of loose granular soils or soft fine-grained soils observed within a subgrade should be compacted to a density appropriate for planned structure; if this is not possible, the subgrade should be over excavated to a denser stratum fill.

3.5.5.3 Structural Fill Materials and Placement

Structural fill should be free of organic and inorganic debris, be near the optimum moisture content, and capable of being compacted to the required specifications for application.

Fill placed to support structures need to be specified as structural fill as described below:

Structural fill placed beneath foundations should meet the requirements of section 704.01 Foundation Fill, FP-14 (FHWA 2014).

If the onsite soils do not meet the above criteria, or cannot be reworked to a suitable condition, we recommend using imported granular fill consisting of imported, clean, well-graded sand and gravel. Other fill materials may be used with approval of the engineer.

If imported material is needed for filling during wet weather, the project specifications should include provisions for using imported, clean, well-graded sand and gravel, and the percent passing the US No. 200 sieve should be no greater than 5%.

Fill should be placed in accordance with Section 209 Structure Excavation and Backfill in the FP-14 (FHWA

2014), except compaction should be in accordance with AASHTO T 180 Method D instead of AASHTO T 99

Method C. Any structural fill placed beneath footings should extend laterally outside of the footing base at a

1H:1V slope projected down and away from the bottom footing edge.

We recommend that structural fill used for onsite applications be compacted to a minimum 95% compaction based on AASHTO T 180 Method D.

4.0 USE OF REPORT

This report has been prepared exclusively for the use of OTAK and their consultants and contractors for specific application for the planned construction of the NPS Stehekin Fire Fighting Facilities Development Project. We encourage review of this report by bidders and/or contractors as it relates to factual data only. The conclusions and recommendations presented in this report are based on the explorations and observations completed for this study, review of previous geotechnical work in the project area, and conversations with various authorities regarding the project and are not intended, nor should they be construed to represent, a warranty, but are forwarded to assist in the planning and design process.

The subsurface explorations were performed in general accordance with locally accepted geotechnical engineering practice, subject to the time limits and financial and physical constraints applicable to the services for this project, to provide information for the areas explored. Judgment has been applied in interpreting and presenting the results. Variations in subsurface conditions over small distances are common, and actual conditions encountered during construction may be different from those interpreted herein. When the project design is finalized, we recommend that we be given the opportunity to review the plans and specifications to verify that they are in accordance with the conditions and recommendations presented in this report.

5.0 CLOSING

If you have any questions, please call us at (425) 883-0777.

Golder Associates Inc.

Michael Klisch, LHG

Senior Project Hydrologist

Kyle Obermiller, LEG, PE Josh Hanson, PE

Senior Project Engineer Associate Engineer

MPK/KEO/JLH/ks

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