2015.08.13_Geotech_RPT_SAHO_WWTP_8.13.15.pdf

GEOTECHNICAL REPORT

Sandy Hook Wastewater Treatment Plant Resiliency Measures

Gateway National Recreation Area

Sandy Hook Unit, New Jersey

Yeh Project No.: 215-111

August 13, 2015

Prepared for:

Anderson Hallas Architects, P.C.

715 Fourteenth St Golden, CO 80401

Attn: Mr. David Anderson, AIA

Prepared by:

Yeh and Associates, Inc.

391 Front Street, Suite D

Grover Beach, California 93433

Phone: 805-481-9590

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August 13, 2015 Project No. 215-111

Anderson Hallas Architects, P.C.

715 Fourteenth St Golden, CO 80401

Attn: Mr. David Anderson, AIA

Subject: Geotechnical Report, Jim May Park Biofilter and Pump Stations Design, 809 Stanford Drive, Santa Maria, California

Dear Mr. Anderson:

Yeh and Associates, Inc. is pleased to submit this geotechnical report for the design of resiliency measures to the Sandy Hook Wastewater Treatment Plant in the Sandy Hook District of the Gateway National Recreation Area. This report was prepared in accordance with our subconsulting services agreement with Anderson Hallas Architects. This report provides grading and foundation design recommendations for the design of the treatment plant improvements.

The geotechnical evaluation consisted of a program of field exploration, laboratory testing, and analysis. Field and laboratory data collected for this study are attached to the report. Graphics showing the locations of the field explorations, an interpreted subsurface profile, and recommendations for the design of earthwork, seismic data, subexcavation, foundations, and pipe trenches and backfill are provided. The main geotechnical considerations that we have discussed in the report are:

• The soils encountered within the anticipated depths of excavation are generally sand associated with existing fill, dune sand, and alluvium. The excavated soils should be suitable for reuse as compacted fill.

• Groundwater was encountered and should be anticipated for excavations extending below about 4 feet.

• The design of temporary slopes and shoring systems should consider and provide a means to properly support adjacent structures, pipelines or other existing improvements that will need to remain in operation while the improvements are being constructed.

Geotechnical Report Yeh Project No. 215-111 Sandy Hook Wastewater Treatment Plant August 13, 2015

• Structures can be supported on shallow foundations supported on compacted fill materials as recommended in the report. Recommended bearing pressures, lateral load resistance and earth pressures are presented in this report.

We appreciate the opportunity to be of service. Please contact Jon Blanchard at 805-878-7784 or jblanchard@yeh-eng.com if you have questions or require additional information.

Sincerely, YEH AND ASSOCIATES, INC.

Jonathan D. Blanchard, P.E. (CA GE2312) John D. Duffy Principal Geotechnical Engineer Sr. Engineering Geologist mailto:jblanchard@yeh-eng.com i

Table of Contents

1. PURPOSE AND SCOPE OF STUDY

2. PROJECT UNDERSTANDING

3. FIELD EXPLORATION AND TESTING

3.1 DRILLING

3.2 LABORATORY TESTING

4. SITE CONDITIONS

4.1 GEOLOGIC SETTING

4.2 SUBSURFACE CONDITIONS

5. CONCLUSIONS AND RECOMMENDATIONS

5.1 GEOTECHNICAL CONSIDERATIONS FOR DESIGN AND CONSTRUCTION

5.1.1 COMPACTION

5.1.2 LOOSE SAND

5.1.3 REUSE OF EXCAVATED ONSITE SOIL

5.1.4 GROUNDWATER

5.1.5 ADJACENT STRUCTURES

5.2 SEISMIC DATA

5.3 EARTHWORK DESIGN

5.3.1 COMPACTION

5.3.2 CLEARING AND GRUBBING

5.3.3 FILL PLACEMENT

5.3.4 GRADED SLOPES

5.3.5 SURFACE DRAINAGE

5.4 SUBEXCAVATION FOR FOUNDATION AREAS

5.5 FOUNDATION DESIGN

5.5.1 LATERAL LOAD RESISTANCE OF SHALLOW FOUNDATIONS

5.6 RETAINING WALL DESIGN

5.7 TRENCH DESIGN

ii

5.7.1 FOUNDATION BEDDING

5.7.2 PIPE ZONE MATERIAL

5.7.3 TRENCH BACKFILL

5.8 SLAB-ON-GRADE

5.9 PAVEMENT DESIGN

5.10 CORROSION DATA

6. NOTES REGARDING CONSTRUCTION

6.1 SUBGRADE EVALUATION

6.2 GRADING OBSERVATION

7. LIMITATIONS

8. REFERENCES

List of Figures

FIGURE 1: PROJECT LOCATION MAP (FROM USGS 2014 SANDY HOOK EAST AND WEST QUADRANGLES)

FIGURE 2 – SITE PLAN (AHA 2015)

FIGURE 3: REGIONAL GEOLOGIC MAP

FIGURE 4 - TYPICAL TRENCH DETAIL

List of Tables

TABLE 1 – SUMMARY OF SELECTED GEOTECHNICAL PROPERTIES

TABLE 2 - RECOMMENDED RELATIVE COMPACTION

TABLE 3: RECOMMENDED SUBEXCAVATION AND STRUCTURAL FILL

TABLE 4: SHALLOW FOUNDATION DESIGN PARAMETERS

TABLE 5: LATERAL EARTH PRESSURES FOR RETAINING WALL DESIGN

List of Plates

Field Exploration Plan Subsurface Profile, A-A’ and B-B’ iii

List of Appendices

Page/No.

Appendix A – Boring Logs Legend for Symbols used on Borehole Logs ............................................................................................ A-1 Borehole Logs for 15E-01 ....................................................................................................................... A-2 Appendix B – Results of Laboratory Testing Moisture and Density Measurements .................................................................................................... B-1 Percent Passing No. 200 Sieve ................................................................................................................ B-2 Mechanical Sieve Analysis ............................................................................................................. B-3 to 10 pH and Resistivity ................................................................................................................................ B-11 Proctor Compaction ............................................................................................................................. B-12 CBR Test Results .................................................................................................................................. B-13 Direct Shear Test Results............................................................................................................. B-14 to 15

Appendix C –Logs of CPT Soundings CPT Data Report ........................................................................................................................... C-1 to 11 CPT Standard Log Plots for C-1 through C-5 .................................................................................. C-12 to18 CPT Normalized Log Plots for C-2, C-3 and C-4 ............................................................................. C-19 to 22 CPT Porepressure Dissipation Plots ............................................................................................. C-23 to 26 Appendix D –Logs from Previous Studies Site Plan ................................................................................................................................................ D-1 Logs of B-1 to B-3, B-5 to B-8 (B-4 and B-9 not drilled) .................................................................. C-12 to18

1. PURPOSE AND SCOPE OF

STUDY

Yeh and Associates was retained by Anderson Hallas Architects

(AHA) to provide geotechnical recommendations for the design of resiliency measures to the

Sandy Hook Wastewater

Treatment Plant in New Jersey.

The site is located on Atlantic

Avenue near Gunnison Beach.

The location of the site is shown on Figure 1.

The geotechnical evaluation consisted of a program of project coordination, preparing a health and safety plan for our work, marking drill hole locations and contacting Underground Services

Alert, reviewing existing data, clearing exploration locations for potential unexploded ordinates, field exploration, laboratory testing, and engineering analyses as a basis for providing the recommendations in this report.

2. PROJECT UNDERSTANDING

The site was impacted by coastal flooding associated with Hurricane Sandy in 2012. The project generally consists of the design of major improvement to the treatment plant to add resiliency to the plant in response to future flood or storm events.

Figure 1: Project Location Map (from USGS 2014 Sandy Hook East and West Quadrangles)

Site Description. The Sandy Hook Wastewater Treatment Plant is located on the west side of

Atlantic Drive near Gunnison Beach. The site is bordered by sand dunes to the south and east and by a one of the historic outposts for Fort Hancock to the north. Atlantic Drive runs generally north –south along the west side of the plant.

The plant appears to be within a graded area that was essentially cut into the dunes forming a terraced site, with the lower westerly half of the site near elevation (el.) 6 feet and the upper easterly half of the site near el. 17 feet. The site occupies a fenced area about 1 acre in size, and about 200-foot square. Retaining walls separate the upper and lower portions of the existing plant. The existing plant is mainly occupied by the existing facility, clarifiers, digesters, and operations buildings on the lower half of the site, and by existing trickling filters and clarifiers on the upper half of the site.

Proposed Design. The layout of the proposed improvements are shown on plans provided by AHA

(2015), and shown on Figure 2.

The main improvements will consist of relocating the main components of the facility to the upper portion of the site. The new plant will essentially be a package plant with new flow control, grit removal, aeration/anoxic tanks, clarifiers and chlorine contact basins. Sludge will be pumped off site by a sludge pump. The new structures will mostly be located on the upper half of the site, and founded at depths of approximately 6 to 12 feet below existing grade, generally above

el. 6 feet. The sludge pump will be located within an Figure 2 – Site Plan (AHA 2015) approximately 17-foot deep vault type structure founded near el. 0 feet. Various yard piping and force mains will be located within both the upper and lower portions of the site.

3. FIELD EXPLORATION AND TESTING

3.1 DRILLING

The drilling subcontractor for this project was Jersey Boring & Drilling Company of Fairfield, New Jersey. The boring locations and selected sampling depths were cleared by Oneida Total

Integrated Enterprises (OTIE) of Boston, Massachusetts under contract with AHA. Jersey used a CME-55 track-mounted drill rig equipped for mud-rotary drilling to advance a boring to approximately 50 feet below the ground surface on July 8, 2015. A log of the boring is presented in Appendix A. The boring location is shown on Plate-1, Field Exploration Plan.

The holes were sampled by driving a 2-inch outside diameter Standard Penetration Test (SPT) split spoon samplers into the soils encountered, typically at 5-foot intervals within each boring.

The samplers were driven into the ground at the bottom of the hole using a 140-pound automatic trip hammer in general accordance with ASTM 1586 (the Standard Penetration Test

(SPT). Bulk samples were collected from hand excavations adjacent to the drill holes. Yeh collected the drive samples in jars for subsequent laboratory testing, recorded blow counts (N-values) for the driven samples, and prepared a log of subsurface conditions encountered. The hole was backfilled with approved native fill after drilling.

3.2 LABORATORY TESTING

Laboratory tests for classification and selected geotechnical properties were performed on samples recovered from the field exploration program in our lab in Grover Beach, California

Additional direct shear tests were performed by the GEO-E lab at the Cal Poly Civil Engineering

Department in San Luis Obispo, California. Jersey Essay Laboratories of Fairfield, New Jersey performed a Proctor test for compaction and a test for California Bearing Ratio (CBR). Tests for moisture content, unit weight, percent passing the #200 sieve (fines content), particle size distribution by mechanical sieve analyses, pH and resistivity, maximum unit weight versus moisture content relation by the modified Proctor compaction test, and CBR were performed as part of this program. The results of laboratory tests are presented in Appendix B. The testing was performed in general accordance with applicable procedures of ASTM.

4. SITE CONDITIONS

4.1 GEOLOGIC SETTING

The site is located on the

Jersey Shore and along the Atlantic Ocean. The surface geology in the site vicinity is mapped as

Holocene-aged unconsolidated beach sand and related dune sand, estuarine deposits and alluvium that overlie

Tertiary sand and greensand sand deposits at the site. Deposition of these sediments are influenced by the dynamic coastal environment and processes associated with littoral drift along shore line and beach, onshore wind from the ocean that has blown beach sand, and sediment transported by rivers into the bay and ocean. The Sandy Hook

Wastewater Treatment

Plant appears to be on a graded pad excavated into coastal dunes along the leeward side of Gunnison Beach.

Disturbance to the site in association with its development, now conceal the dune with artificial fill derived from those sediments, paving, and the existing plant improvements.

Figure 3: Regional Geologic Map

4.2 SUBSURFACE CONDITIONS

The soils encountered at the site generally consisted of artificial fill, dune sand deposits and alluvium. The approximate locations of the drill holes are shown on Figure A-1 - Boring

Location Plan. A description of the units encountered is summarized below.

Artificial Fill (af). Artificial fill was encountered to approximately 5 feet below the ground surface in boring 15E-01, and in various hand dug excavations performed in association with the clearances for unexploded ordinates. The upper 5 feet generally consisted of loose sand with varying amounts of gravel and construction debris (bolts, nails, steel bars, plastic, wood).

There are also various existing utilities, pavements, retaining walls and buried structures at the site that have been backfilled with fill materials.

Dune Sand (Qds). Dune sand deposits were encountered to depths of approximately 18 feet below the ground surface within the higher easterly portion of the site, and to about 3 to 6 feet below the ground surface in C-5 and the previous borings (drilled in January 1994 by French &

Parrello (1994)) advanced within the lower portion of the site. The bottom elevation of the dune sand ranged from about el. -2 to 3 feet (generally near sea level). The dune sand consisted of predominantly medium dense, poorly graded sand (SP) with trace amounts of silt. The dune sand commonly had thin layering of dark colors, particularly near the base of those deposits that could be associated with cycles of deposition. The dune sand was underlain by alluvium in each the explorations.

Alluvium (Qa). Alluvium was encountered below the dune sand in each of the explorations, and to the maximum depths explored (about 75 feet (el. -57 feet) below the ground surface in C-3).

The alluvium generally consisted of dense poorly sorted sand and sand with silt, with varying amounts and interbedded lenses of coarse sand, fine gravel, and well graded sand. The alluvium was always encountered below the groundwater table.

Groundwater. Groundwater was encountered in each of the explorations, and in previous borings drilled in January 1994 by French & Parrello (1994). Groundwater was generally encountered at various depths in explorations, but corresponds to between elevation and 2 to 4 feet above sea level. Groundwater levels and soil moisture conditions will vary seasonally, and as a result of local groundwater pumping, irrigation, and rainfall.

Soil Properties. A summary of selected geotechnical properties for the soil samples tested this evaluation is presented below:

Table 1 – Summary of Selected Geotechnical Properties

Unit

Encountered in Boring Numbers:

Typical Depths/Elev.

Encountered

Moisture Content

% passing #200 sieve/ (%Gravel) Shear Strength

Artificial Fill

(af) 15E-01 Upper

~ 5 ft. of site 4-5 2

(0-2) φ = 35 degrees1

(remold 90% relative compaction)

Dune Sand (Qds) Each Above

~el. -2 to 3 ft.

4-5 above GWS

19-26 below GWS

(0-2) φ = 32 degrees1

(remold to 50% relative density) Alluvium

(Qa) Each Below ~el. 2 to 3 ft.

13-26 2 – 11 (5-23) --1

GWS = groundwater surface φ = friction angle (angle of repose) of soil

1. Peak friction angle measured from direct shear test

2. Peak friction angle estimated from empirical correlations to CPT data

5. CONCLUSIONS AND RECOMMENDATIONS

5.1 GEOTECHNICAL CONSIDERATIONS FOR DESIGN AND CONSTRUCTION

Geotechnical engineering related conditions that could affect design and construction include compaction, construction operation within loose sandy alluvium, groundwater, reuse of excavated onsite soil as fill or backfill, and excavation adjacent to existing structures. These general considerations are discussed below. Recommendations for the design earthwork, piping and the clay liners are provided in the following sections of this report.

5.1.1 COMPACTION

The soils encountered predominantly consist of poorly graded sand with a predominantly low fines content. Compaction of the subgrade should be performed using suitable equipment for the sandy soil conditions, such as smooth drummed rollers and/or vibratory compaction.

Although moisture conditions vary seasonally, water will likely need to be added to the soil to provide a moisture content suitable for compaction. Control of compaction layer thickness, moisture content, and providing an adequate amount of compactive effort will be necessary to achieve the minimum specified compaction.

5.1.2 LOOSE SAND

The Sandy Hook Wastewater Treatment Plant is within a coastal dune environment. The soils encountered within the anticipated depths of excavation generally consist of loose to medium dense sand with low fines content. The sand will likely be vulnerable to disturbance, may be easily eroded or moved when not confined and therefore may not provide adequate support for construction traffic, especially in areas where traffic may be on slopes or with tight turning movements, and may not support construction vehicles that may attempt to traffic over the uncompacted sand. Haul roads and access routes should be stabilized with gravel, base material or by watering depending on the types of traffic and support needed for the equipment being used.

5.1.3 REUSE OF EXCAVATED ONSITE SOIL

The soils encountered within the anticipated depths of excavation generally consisted of poorly sorted sand with low fines content and trace amounts of gravel. These soils, cleaned of organics, topsoil, debris, and oversized materials should be suitable for reuse as compacted fill.

The soils should be suitable for reuse as pipe bedding, pipe zone, structure backfill, and trench backfill material; however, additional processing of the material to remove gravel and segregate the sand from interbedded silty soils will be necessary to make the material suitable for placement as pipe bedding or pipe zone material. Oversized materials, such as gravel or debris

(bolts, steel bars, nails, or wood, such as was encountered within the existing fill materials) within the existing fill, may damage or cause abrasion to pipes and coatings during placement and compaction of the fill or due to pipe movements following construction and should be removed prior to placing the material as backfill around pipes.

5.1.4 GROUNDWATER

Groundwater was encountered at various depths in the current and previous explorations.

Generally, groundwater should be anticipated for excavations extending below el. 4 feet.

Potholing should be used at the time of construction to check for groundwater prior to beginning excavations. Dewatering should be provided in advance of beginning excavation such that the groundwater level is lowered at least 1 foot below the depth of the excavation, unless methods and a work plan for wet construction are submitted by the contractor and approved for use on the project in advance of beginning an excavation. Dewatering system should be designed by a qualified registered engineer or hdyrogeologist. Sumps, well screens, and dewatering pits should be properly filtered such that fines and the surrounding soils are not removed or disturbed by dewatering. Shoring systems extending below the groundwater table should consist of tight shoring systems (such as steel sheetpile) that are driven below the bottom of the excavation and will cut off the flow of water into the excavation. Slide rail shoring systems should not be considered suitable for support or dewatering of excavations extending below the groundwater table.

5.1.5 ADJACENT STRUCTURES

The existing plant has various building, piping, retaining walls, and buried structures. The design of temporary and permanent slopes should both consider the presence and location of those structures and existing buried pipes. Excavations should generally not extend within a 1:1 line projected downward and out from the edge of structures, unless special considerations for the design or shoring of excavated slopes are made with specific considerations for maintaining proper foundation support for those structures.

The soils encountered are predominantly considered to be Type C sandy soils based on Cal

OSHA guidelines for the design of temporary slopes and shoring systems. Per OSHA guidelines, Type C soils should be excavated no steeper than 1.5:1 (horizontal to vertical).

However, we have recommended that the biofilter slopes be designed at 2:1 or flatter. Slopes excavated steeper than 1.5:1 in sandy soils should not be considered stable. Steep or vertical slopes that may stand temporarily should be considered unstable and vulnerable to sudden collapse.

Shoring systems such as trench shields or slide rail shoring systems that do not provide positive support for excavated slopes should be considered suitable to underpinning or supporting adjacent structures, utilities, or other improvement that may be supported by the ground behind the shoring.

5.2 SEISMIC DATA

Structures should be designed to resist lateral forces generated by earthquake shaking in accordance with the current building code and design practice. Seismic data were estimated for use with the 2012 International Building Code (IBC). The site coordinates and USGS interactive web site were used to estimate ground motions and design map parameters for the site. The data were developed for Seismic Risk Categories I, II or III. Preliminary seismic data are presented in the following table.

Seismic Parameter Value

Latitude, degrees 40.45912

Longitude, degrees -73.99452

Site Class D, stiff soil

Earthquake Magnitude 5.7

Peak ground acceleration 2% in 50 year 0.15

Ss, Seismic Factor for Site Class B at 0.2 seconds 0.251

Seismic Parameter Value

S1, Seismic Factor for Site Class B at 1 second 0.067

Fa, Site Specific Site Coefficient 1.0

Fv, Site Specific Site Coefficient 1.5

SMS, Site Specific Response Parameter at 0.2 seconds 0.401

SM1, Site Specific Response Parameter at 1 seconds 0.161

SDS = 2/3 SMS 0.267

SD1 = 2/3 SM1 0.108

The design earthquake is estimated from a probabilistic analysis of the USGS database and proximity of the site to those faults. Most seismicity in the New Jersey area is related to northeast-southwest trending faults and folds mapped within a zone of about 7 to 50 miles west of the site, such as the Ramapo fault. Though relatively infrequent and small, historical earthquakes within New Jersey are mostly mapped within the Highland and Piedmont areas that represent the easterly boundary of the Appalachian Mountains. Although the New Jersey

Geologic Survey reports an earthquake of unknown magnitude that occurred in 1927 along the

Jersey Shore, which collapsed chimneys between Asbury Park and Long Branch.

5.3 EARTHWORK DESIGN

The recommendations of this report can be used in association with FHWA Standard

Specifications FP-14. Compliance with those specifications is needed for the recommendations in this report to remain applicable. Site grading should conform to the applicable sections of the

City standards unless specifically modified by the recommendations of this report.

5.3.1 COMPACTION

Fill placement should be observed and tested for compaction by a qualified geotechnical engineer and independent of the contractor performing the earthwork. Fill materials should be compacted to at least 90 percent relative compaction, unless a higher degree of compaction is otherwise recommended. Relative compaction should be assessed according to the latest approved edition of ASTM Standard Test Method D1557.

Table 2 - Recommended Relative Compaction

Location of Fill Placement Recommend Minimum Relative Compaction

General 90% U.O.N.

Utility trench bedding, pipe zone or backfill 90% U.O.N.

Retaining wall or pump station backfill 90% U.O.N.

Location of Fill Placement Recommend Minimum Relative Compaction

Fill or backfill placed within 3 feet of finished grade in pavement areas including below multi-use paths 95%

Fill placed below building or foundation areas 95%

Asphalt concrete, aggregate base, or subbase 95%

U.O.N. = unless otherwise noted

Gravel, crushed rock, and drainage materials that cannot be tested per those standards should be compacted with at least 4 passes using a vibratory plate or by track walking with construction equipment for each 1 foot of material that is placed. Fill should be compacted to the following minimum levels recommended for the location where the material is placed. Jetting or ponding should not be permitted for placement or compaction of fill materials, unless the contractor can demonstrate that the methods used can achieve the minimum recommended compaction, and that excess water can be properly controlled and drained from the trench or excavation.

5.3.2 CLEARING AND GRUBBING

Clearing and grubbing should be performed to remove existing vegetation and objectionable material from areas that will graded, receive fill, or serve as borrow sources. Grubbing should include removing stumps, roots, and buried vegetation. Care should be taken not to injure trees, plants or existing improvements outside of the clearing limits. Soil containing pavement, debris, organics, loose or disturbed materials, or other unsuitable materials, should be excavated and removed prior to commencing fill placement. Demolition areas should be cleared of existing fill, pavement, abandoned utilities or pipelines, and soil disturbed during the clearing and grubbing process. Depressions left from the removal and demolition of materials should be replaced with compacted fill.

5.3.3 FILL PLACEMENT

Fill material should be suitable for the area where the material is being placed and comply with the specified material for that area. Control of compaction layer thickness and moisture content is necessary to achieve compaction throughout the material being placed. Fill material should be spread in lifts that are suitable for compaction with the equipment being used, and should not exceed a loose lift thickness of 8 inches before compaction. Each layer should be spread evenly, moisture conditioned by adding water or drying the material to a moisture content that is suitable for compaction. The fill should be thoroughly mixed during the spreading to provide relative uniformity of material within each layer. The moisture content of the material should be such that the specified compaction can be achieved in a firm and stable condition. Soft or yielding materials should be removed and replaced with properly compacted material prior to placing the next layer of fill.

The fill should not contain rocks, cobble or other solid particles larger than 3 inches in the greatest dimension. Deleterious materials, such as soft rock particles, concrete or pavement rubble, metal, glass or sharp objects should not be placed within the fill material being placed.

Recycled or reused materials should only be used and placed within the fill when specifically permitted by the project specifications. Rocks should not be nested, and voids should be filled with compacted material.

5.3.4 GRADED SLOPES

Cut and fill slopes should be designed to a finished grade of 2:1 or flatter. Fill for graded slopes should be placed such that the fill is compacted beyond the finish grade of the slope, and then be cut back to reveal compacted fill material on the slope face. Fill material derived from onsite soil will likely be composed of sandy material that is vulnerable to disturbance and erosion.

Slopes should be seeded or landscaped with appropriate vegetation to reduce the potential for surface erosion. Slope maintenance and irrigation may be needed to help establish vegetation, and to repair areas where gullies or erosion to the slope occurs while vegetation is being established.

5.3.5 SURFACE DRAINAGE

Drainage should be provided to reduce the potential for water to pond on pavements, adjacent to foundations or flatwork, or for concentrated flows of runoff to run over the tops of slopes.

Downspouts should be provided to collect roof drainage and direct the water to drainage pipes or an area away from the building. Roadways should be designed with a cross slope to shed water directly to the edge of the pavement. Gravelly material (aggregate base or shoulder backing material) can be placed along the edge of pavement to help reduce the potential for erosion as water flows off the pavement. Down drains, solid pipes, or lined ditches should be provided to carry water to the base of slopes where needed.

5.4 SUBEXCAVATION FOR FOUNDATION AREAS

The proposed structures can be supported on shallow foundations bearing in compacted fill as recommended in this report. The depth of the structure below existing site grades and bearing elevations ere estimated from the Hydraulic Profile sheet provided by Anderson Hallas

Architects on June 1, 2015. As shown on the Subsurface Profiles (Plate 3), below grade structures are planned to extend to approximately 6 to 17 feet below the existing ground surface. Subexcavation and a mat of compacted fill is recommended to provide uniform support for the structures and to provide a working mat for construction. Loose to medium dense sand was encountered within the anticipated depths of excavation. Groundwater should be anticipated for excavations extending below about el. 4 feet. A summary of our recommended subexcavation and structural fill for the various structures is presented in the following table.

Table 3: Recommended Subexcavation and Structural Fill

Structure

Estimated Depth of

Structure (feet)

Estimated Bearing

Elevation Recommendation

Screen, grit system, splitter box, etc. Near surface el. 15 ft.

• Removed existing soil and fill to 5 feet below existing ground surface

• Extend excavation horizontally to at least 5 feet beyond the structure foot print/foundation

• Scarify subgrade to depth of 9 inches, moisture condition and compact to at least 95% relative compaction

• Place compacted fill to finished grades and compact to at least 95% relative compaction

Aeration-Anoxic Tank 12 ft. el. 6 ft. • Removed existing soil and fill to 1 foot below the bottom of the structure

• Scarify subgrade to depth of 9 inches, moisture condition and compact to at least 95% relative compaction

• Place at least 1-foot of drainage material and compact to at least 95 percent relative compaction to provide bearing surface for base of structure

Clarifier 7 to 9 ft. > el. 9 ft.

Chlorine Contract Tank 6 ft. el. 11 ft.

Sludge Pumping Station 17 ft. el. 0 ft.

• Provide dewatering and shoring to provide stable condition for excavation and construction.

• Remove existing soil to at least 2 feet below the bottom of the structure and provide undisturbed subgrade

• Place filter fabric and 2 feet of 1.5-inch crushed stone or place a slurry seal (minimum 2 feet thick) of suitable thickness to resist groundwater conditions encountered.

The geotechnical professional should review the bottom of excavation prior to placing fill materials to evaluate whether or not additional soil should be removed and if the exposed subgrade is suitable for placing compacted fill. The project specifications should provide for review of the excavation by the geotechnical engineer, and for increasing the depth of the excavation to remove additional loose soil, soft silts, or other unsuitable materials, if needed. Fill and backfill above the top of the subexcavation should be placed according to the recommendations of this report.

5.5 FOUNDATION DESIGN

The proposed structures can be supported on shallow foundations bearing in compacted fill prepared according to the recommendations of this report. It is assumed that shallow foundations for site walls or other minor structures will be founded above el. 6 feet. The sludge pumping station and other major structures that may be founded below el. 6 feet and into groundwater will have larger mat type foundations (greater than 4 feet wide) and can be designed to the allowable bearing pressures presented below. If footings less than 2 feet wide will be founded below el. 6 feet, Yeh should be contacted to review the foundation conditions and provide additional recommendation, if needed. The following parameters can be used for the design of spread footing foundations:

Table 4: Shallow Foundation Design Parameters

Parameter Value Conditions/Limitations Minimum width of pad footing, B 2 feet --

Minimum width of strip footing, B 1 foot Maybe to equivalent width of the reinforced edge of the bottom slab below buried tank walls.

Minimum footing embedment, D 2 feet Below lowest adjacent grade and at least

Minimum footing embedment adjacent to descending slopes, D as needed

10 feet horizontally between the bottom of the footing and the finished grade of the adjacent slope

Maximum allowable bearing capacity, qa 3,500 psf Increase by 1/3 when considering transient (wind or seismic) loads.

Retaining Wall Footings. The toe bearing pressure acting on the retaining wall footing can exceed the recommended maximum allowable bearing pressures by 1/3, provided the resultant force acts within the middle third of the footing.

Reinforcing. The structural engineer should design reinforcing for footings based on the expected foundation loading conditions. The soils encountered are generally sand that is considered non-expansive. Therefore no special recommendations for additional foundation reinforcement need to be considered for design.

Settlement Considerations. Foundation settlement could result from immediate settlement of the sandy foundation support soil encountered at the site, and as a result of ongoing compression of the compacted fill. Footings bearing in compacted fill should be designed to tolerate at least 1 inch of total settlement, and approximately ¾ inch of differential settlement in

30 feet or between similarly loaded foundation elements. The soils at the site are relatively dense and therefore not considered vulnerable to liquefaction or seismic settlement considering the design earthquake for the site.

5.5.1 LATERAL LOAD RESISTANCE OF SHALLOW FOUNDATIONS

Resistance to lateral loads can be provided by the soil passive resistance acting on the sides of foundations embedded in compacted fill, and by frictional resistance acting along the base of the foundations and slabs. A passive resistance of 400 pounds per cubic foot, equivalent fluid weight, can be used to estimate the lateral load resistance of foundations bearing in compacted fill. The passive resistance should be reduced by one half when considering submerged conditions. The recommended passive resistance does not account for descending slopes adjacent to footings. A friction coefficient of 0.4 can be used to estimate the sliding resistance along the bottoms of footings or slabs bearing in compacted fill. The recommended frictional and passive resistances can be increased by 1/3 when considering seismic or other transient loading conditions.

5.6 RETAINING WALL DESIGN

Retaining walls and buried structures should be designed to resist lateral earth pressures.

Retaining wall foundations should be designed to resist lateral and vertical loads using the foundations design recommendations provided in the previous section of this report. Retaining wall backfill material should be compacted to at least 90 percent relative compaction, unless 95 percent relative compaction is otherwise recommended below pavement or foundation areas.

The following table provides equivalent fluid weights that can be used to estimate the lateral earth pressure acting on retaining walls. The values presented are for level backslope conditions with either imported or onsite sand backfill. Active earth pressure conditions can be assumed where the top of the wall is free to rotate away from the backfill. If the wall is braced or non-yielding, the wall should be designed to resist at-rest conditions. The tabulated values presented below are based on a soil unit weight of 120 pounds per cubic foot (pcf).

Table 5: Lateral Earth Pressures for Retaining Wall Design

Condition Level Backslope

Active with level backfill and drainage 33 pcf

At-rest with level backfill and drainage 55 pcf

Submerged conditions. When considering submerged backfill conditions, the equivalent fluid weight can be reduced to one half of the value in the table, and the unit weight of water (62.4 pcf) should be added to the fluid weight.

Surcharges. The recommended equivalent fluid weights do not account for surcharge loads acting on the backfill. Traffic surcharges can be estimated as an additional 2 feet of soil cover, equal to a uniform pressure of 72 pounds per square foot, applied to the upper 5 feet of the wall.

The traffic surcharge can be neglected if the backside of the wall is outside the limits of a 0.5:1 line projected downward from the edge of the pavement.

Wall Drainage. Drainage should be provided behind the wall to reduce the potential for water to accumulate within the backfill. The wall should be backfilled with free draining on-site or imported sand having less than 5 percent material passing the number 200 sieve. A drain with a collector pipe should be placed near the bottom of the backfill and connected to an outlet point downstream of the wall.

Dynamic earth pressures. Dynamic earth pressures were estimated based on current seismic loading criteria using a reduction factor of 0.5 and the estimated peak horizontal ground acceleration of 0.1g. The seismic increment of active earth pressure can be approximated as a uniform pressure of 4H (lateral pressure in pounds per square foot and the wall height (H) in feet).

5.7 TRENCH DESIGN

5.7.1 FOUNDATION BEDDING

A typical trench detail for the design of pipe trenches is presented in Figure 5.

The foundation soils for piping within the anticipated depths of excavation should consist of sand with varying amounts of gravel that is considered suitable for bedding the pipe. Bedding the pipe can consist of either scarifying the trench subgrade to a depth of 9 inches, removing any coarse gravel or

Figure 4 - Typical Trench Detail cobbles from the subgrade that could potentially damage the pipe, and compacting those soils to at least 90 percent relatively compaction; or providing at least 4 inches of approved import sand. The pipe should be placed on the bedding such that the middle third of the pipe (Do/3) is in contact with the bedding prior to placing initial backfill within the pipe zone. The bedding maybe loosened along the invert of the pipe if necessary to help form the cradle.

Areas where the pipe trench will extend about el. 4 feet will likely encountered groundwater or wet subgrade conditions. Gravel bedding material should be provided in the event thetrench bottom is composed or is in wet or soft ground. It should be assumed that all trenches extending below el. 4 feet will require at least 12 inches of subtrench excavation and placement of at least 12 inches of gravel bedding refill. The gravel should be fully encased in geotextile to provide separation between the gravel and the in-situ soils and subsequent backfill.

Prior to placing bedding material, the foundation support soil exposed at the trench subgrade should be reviewed to allow for proper bedding and stabilization of the subgrade below the trench if needed. We recommend that a quantity be estimated to include gravel bedding below the pipe, and to allow for the quantity to be increased, decreased or deleted based on review of the trench subgrade conditions encountered during construction.

5.7.2 PIPE ZONE MATERIAL

Place Pipe Zone Material from the top of the bedding material to at least 12 inches above the crown of the pipe and compact it to at least 90 percent relative compaction. Pipe zone material should consist of approved on-site sand classified as SP, or import sand with no more than 5 percent material passing the No. 200 sieve. Pipe zone material should be placed such that there is an equal distribution of compaction and material on both sides of the pipe. Backfill should not be placed above springline until the fill below springline has been placed and compacted to properly support the haunches. Compaction within the pipe zone should be performed such that the pipe is fully supported during compaction and such that excessive deformation or damage to the pipe does not occur. Trench backfill should not be placed until compaction and testing of the pipe zone material is complete.

5.7.3 TRENCH BACKFILL

Trench backfill is material is to be placed in the trench from the top of the pipe zone to finished grade, and includes the pavement structural section. Excavated on-site soil, free of organics and deleterious materials, can be reused as Trench Backfill. Trench backfill placed below pavements or concrete flatwork should be compacted to at least 95 percent relative compaction.

Trench backfill placed outside of pavement areas should be compacted to at least 90 percent relative compaction unless a higher degree of compaction is otherwise recommended. In non-pavement areas the upper 2 feet of the backfill should consist of on-site native topsoil or approved landscape soils to help reduce the potential for surface water to infiltrate the trench.

5.8 SLAB-ON-GRADE

Concrete slab-on-grade is generally expected to consist of walk ways and equipment pads that will not be subject to vehicular traffic. The subgrade soils encountered generally consist of sand and is considered non-expansive. The upper 12 inches of the subgrade should be compacted to at least 90 percent relative compaction in areas where slab-on-grade will be placed. Slab thickness and reinforcement should be designed by a structural engineer to resist structural loading and to satisfy pertinent code, temperature, and shrinkage requirements. On the basis of the soil conditions encountered, we recommend that concrete slabs and flat work without vehicular traffic be at least 4 inches thick and be reinforced with at least No. 3 reinforcing placed at not more than 18 inches on center both ways. Reinforcement should be placed at mid-thickness of the slab and be supported such that the reinforcement will remain in place during construction and concrete placement. Expansion and control joints should be provided in accordance with the Portland Cement Associations guidelines or other applicable design guidelines.

5.9 PAVEMENT DESIGN

Thickness Design. Structural sections for asphalt concrete pavements were estimated based on methods presented in the AASHTO (1993) design manual and guidelines for federal lands

(FHWA 2008). A CBR-value of 20 was selected for the subgrade sandy soils encountered and the laboratory test result. Specific traffic loading information was not provided for the site.

Traffic was assumed to be about 20 vehicles per day with 80 percent autos or pickup trucks and10 percent 3- and 6-axle trucks. A minimum structural section of at least 3 inches of hot mix asphalt concrete pavement (HACP) over 4 inches of aggregate base (AB) can be used for the assumed traffic loading conditions. Pavement materials should conform to the FHWA Standard Specifications, FP-14.

Subgrade Preparation. The near surface soils encountered at the site are relatively loose. The existing soil should be removed to a depth of at least 2 feet below the existing ground surface or to the bottom of the proposed structural section, whichever is deeper. The bottom of the excavation should then be scarified to a depth of at least 9 inches, moisture-conditioned, and compacted in-place to at least 95 percent relative compaction. Fill materials can then be placed to the base of the structural section according to the recommendations of this report. Fill materials placed within 3 feet of finished grade in pavement areas should be compacted to at least 95 percent relative compaction. The project specifications should provide for review of the subgrade by the geotechnical engineer, and for increasing the depth of the excavation to remove wet subgrade or other unsuitable materials, if needed.

Maintenance. The pavement condition should be periodically evaluated to help plan and scope the need for maintenance and rehabilitation following the initial construction of the pavement.

Maintenance of asphalt concrete pavements should typically include periodic fog, chip or slurry seals to reduce the potential for weathering, or overlaying with additional HACP when needed to strengthen and further the life of the pavement. Sealing cracks periodically (every 1 to 2 years) and maintaining positive drainage from the pavements surface should help to extend the life of the pavement.

5.10 CORROSION DATA

Tests for pH and soil resistivity were performed on a soil sample obtained from the site. The test results suggest that the soil is not considered corrosive towards concrete. Considerations for the design of a project that is within a coastal environmental should also be considered.

6. NOTES REGARDING CONSTRUCTION

The geotechnical professional should continue to evaluate the subsurface conditions at site through construction, and observe that the work being performed and subsurface conditions encountered are consistent with the recommendations of this report. The following provides key items that should be evaluated or observed during construction.

6.1 SUBGRADE EVALUATION

The geotechnical professional should observe the base of excavations, the bottoms of trenches and the subgrade for the biofilter excavation to evaluate whether or not the exposed subgrade is suitable for fill placement. The project specifications should provide for review of the subgrade by the geotechnical professional, and for variations in the depth of excavation, if needed, to remove additional loose soil, undocumented fill, or unsuitable material.

6.2 GRADING OBSERVATION

The geotechnical professional should observe grading operations during construction on behalf of the owner to have reasonable certainty that fill placement and compaction is being performed according to the recommendations of this report. Field density testing should be performed to help evaluate the compaction and moisture content of the materials being placed. Fill and aggregates delivered to the site, and excavated onsite soil that will be reused as fill or backfill, should be sampled and tested for conformance with gradation and quality requirements for the project. The frequency and locations of the tests should be at the discretion of the geotechnical professional. The project specifications should include provisions for the contractor to allow for testing and to provide any shoring, ingress-egress, or traffic control needed to safely perform the testing at the locations and depths needed.

7. LIMITATIONS

This study has been conducted in general accordance with currently accepted geotechnical practices in this area for use by the client for design purposes. The conclusions and recommendations submitted in this report are based upon the data obtained from field reconnaissance, drilling and sampling, and our understanding of the proposed project and type of construction described in this report. If there are any changes in the project or site conditions, Yeh should review those changes and provide additional recommendations, if needed. Any modifications to the recommendations of this report or approval of changes made to the project should not be considered valid unless they are made in writing. The report and drawings contained in this report are intended for design-input; and are not intended to act as construction drawings or specifications.

Site conditions will vary between points of observation or sampling, seasonally, and with time.

The nature and extent of subsurface variations across the site may not become evident until excavation is performed. If during construction, fill, soil, or water conditions appear to be different from those described herein, Yeh should be advised and provided the opportunity to evaluate those conditions and provide additional recommendations, if necessary. The geotechnical professional should observe portions of the construction and site conditions, such as excavations, exposed subgrades and earthwork, to evaluate whether or not the conditions encountered are consistent with those assumed for design, and to provide additional recommendations during construction, if needed.

8. REFERENCES

American Association of State Highway and Transportation Officials (AASHTO), AASHTO

Guide for Design of Pavement Structures, Washington D.C., copyright 1993.

Anderson Hallas Architects, Plan Sheets C1.0 and C3.0: Hydraulic Profile and Site Plan, Sandy

Hook WWTP Resiliency Measures, received via email June 1, 2015.

French & Parrello Associates, Report of Subsurface Exploration and Geotechnical Engineering

Evaluation, Gateway National Recreation Areas, Wastewater Treatment Plant Modifications, Sand Hook, Monmouth County, New Jersey, consultant report prepared for Martin/Martin

Consulting Engineers, Archive D-264, dated January 28, 1994.

Louis Berger & Associates, Inc.,…