arlington high school preferred schematic report 48...arlington high school preferred schematic...

Arlington High School Preferred Schematic Report 48

June 27, 2018

GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERS2269 Massachusetts AvenueCambridge, Massachusetts 02140(617) 868-1420

HMFH Architects130 Bishop Allen DriveCambridge, MA 02139

Attention: Ms. Lori Cowles

Reference: Arlington High School; Arlington, MassachusettsPreliminary Foundation Engineering Report

Ladies and Gentlemen:

This report documents the results of our subsurface exploration program and preliminary foundation design study to be included as part of a feasibility study to assess the renovation/additions and/or construction of a new school building at the site of the Arlington High School located at 869 Massachusetts Avenue in Arlington, Massachusetts. Refer to the Project Location Plan (Figure 1) for the general site location.

This report was prepared in accordance with our proposal dated March 2, 2018, and the subsequent authorization of HMFH Architects (HMFH). These services are subject to the limitations contained in Appendix A.

Purpose and Scope

The purpose of our preliminary design study was to obtain initial subsurface information across the proposed building sites and to identify preliminary foundation design considerations associated with the feasibility study assessing options for the proposed project.

Available Information

Information available to McPhail Associates, LLC (McPhail) for use in the preparation of this report included the following:

• 30-scale site survey entitled “Limited Existing Conditions Plan of Land” prepared by Samiotes Consultants, Inc. dated May 18, 2018;

• Several drawings dated May 18, 2018 prepared by HMFH indicating preliminary floor plans for four (4) options for the renovations/additions and/or construction of a new school;

• A report entitled "Phase I Environmental Site Assessment Report; Arlington High School; Arlington, Massachusetts” dated April 20, 2018 and prepared by McPhail; and

Arlington High School Preferred Schematic Report49

HMFH ArchitectsJune 27, 2018

• Multiple sets of structural and architectural drawings from original construction of the existing buildings prepared by others, ranging in dates from 1930 to 1963, provided by HMFH.

Elevations referenced herein are in feet and are referenced to the North American Vertical Datum of 1988 (NAVD 88).

Existing Conditions and Site History

Fronting onto Massachusetts Avenue to the south, the approximately 22-acre Arlington High School campus is bounded to the west, north and east by residential and commercial properties. The existing school complex is located near the center of the campus and is surrounded by athletic fields, asphalt paved parking lots and landscaped areas. The remaining exterior portions of the site are occupied by a grassed area located along Massachusetts Avenue, a playground and basketball courts located adjacent to thenortheast of the school complex as well as parking lots and driveways that connect to Millbook Drive and Massachusetts Avenue.

Existing ground surface to the south of the existing school complex generally slopes downward from south to north from about Elevation +77 to Elevation +68. Within the northern portion of the campus, a majority of which is occupied by athletic fields, the existing grade gradually slopes from west to east from approximately Elevation +54 to about Elevation +45.

The existing ground surface immediately surrounding the existing building is generally level at about Elevation +68 to Elevation +73 on the south side, slopes downward from south to north from about Elevation +73 to Elevation +49 on the west side, and slopes downward from west to east from about Elevation +49 to Elevation +45 on the north and east sides.

The school complex consists of six (6) interconnected buildings that were constructed and/or renovated in various phases from about 1914 through 1981. The six (6) buildings which comprise the school complex are referred to herein as Fusco, Collomb House, Auditorium, Blue Gym, Red Gym and Downs House. The center of the complex consists of an open-air courtyard, a majority of which is covered by concrete and pavement. Two smaller courtyards containing landscaping, gardens and/or grass areas are located at the eastern and western wings of the school complex.

The northern portion of the subject site was formerly occupied by Cutter’s Mill Pond. In 1908, the pond had been drained of water and a sluice-way was constructed through the center of Pond. Subsequently, water fed from Mill Brook was rerouted through a large culvert that traverses beneath portions of the current athletic fields. By 1930, the area of the Pond was backfilled and converted into a playground and playing field.



Historical records indicate that the subject site was initially developed in 1914 with the construction of the 6-story Fusco Building (southwestern portion of the current school complex). Subsequently, in 1938 the 4-story T-shaped Collomb House was constructed to the east of the Fusco Building. In 1961 and 1964, additional portions of the current school complex were constructed which included the 3-level Blue Gym, the 3.5-story Auditorium Building and the 4-story Downs House. By 1981, the most recent phase of construction was completed with the Red Gym and links additions at the northwestern portion of the school complex.

The southern portion of the school complex, which generally contains the Fusco, Collomb House and Auditorium buildings, contain partial below grade levels with lowest level slabs at approximately Elevation +62.2, Elevation +49.5, and Elevation +46.5, respectively. The northern portion of the school complex, which contains the Blue Gym, Red Gym, and Downs House, are understood to have lowest level slabs varying from approximately Elevation +52.5 to Elevation +49.3. Portions of the lowest level slabs are underlain by crawl spaces.

As indicated above, McPhail prepared a Phase I Environmental Site Assessment for the subject site. In summary, the historical usage of the surrounding properties has affected soil and groundwater at the Arlington High School campus. In addition, some of the contamination is volatizing from groundwater and affecting indoor air within portions of the existing school complex. Currently, the northern portion of the campus is covered by engineered barriers or direct exposure barriers to prevent human exposure to the contamination that is present in soil and groundwater. Although mitigation measures have not yet been implemented, contamination is also present in groundwater at the southern portion of the campus. Additionally, the historical presence of underground storage tanks have been documented beneath and adjacent to the existing school building. While some of these underground storage tanks have been removed off-site, others remain in-place of which the impacts to soil and groundwater are currently unknown.

Proposed Development

It is understood that a feasibility study is being conducted to assess several alternatives for renovation/addition to the existing school and/or construction of a new school building. The project may include the renovation of the Fusco and/or Collomb buildings, demolition of the remaining structures, and construction of new additions. New additions would be constructed south and/or north of the existing buildings to remain. Alternatively, a new freestanding school building may be constructed within the general footprint of the existing school complex or to the south of the existing school. It is understood that the proposed additions or new buildings would contain up to six (6) levels. Depending on the location of the additions or new building on the site and the proposed finished grades, it is anticipated that the proposed structures may be benched into the site such that portions of the proposed buildings contain below-grade space. The site grade will likely be raised by approximately 4 feet with imported fill to minimize excavation and removal of existing site soils and to create a general working pad for construction.



Subsurface Exploration Program

A subsurface exploration program consisting of eleven (11) borings was conducted at the site on May 12, 30 and 31, and June 16, 2018 by Carr-Dee Corp. of Medford, Massachusetts under contract to McPhail. Boring logs prepared by Carr-Dee Corp. are contained in Appendix B and approximate plan locations of the borings are as indicated on the enclosed Subsurface Exploration Plan, Figure 2.

Borings M-1 and M-2 were performed utilizing track-mounted drilling equipment and the remaining borings were performed utilizing truck-mounted drilling equipment. Each boring was advanced using 2.25-inch inner diameter hollow stem augers and/or 3-inch inner diameter casing utilizing wet rotary drilling methods. Standard 2-inch O.D. split-spoon samples and standard penetration tests (SPT) were generally obtained at 5-foot intervals of depth in accordance with the standard procedures in ASTM D1586. The borings were terminated at depths ranging from 11.5 to 52 feet below the existing ground surface.

The explorations were observed by a representative of McPhail who performed field layout, prepared field logs, obtained and visually classified soil samples, monitored groundwater conditions in the borings, and made minor adjustments to the exploration locations and determined the required exploration depths based upon the actual subsurface conditions encountered.

Field locations of the borings were determined by taping from existing site features indicated on the available plan. The existing ground surface elevation at each boring location was typically determined by a level survey performed by our field staff utilizing vertical control information indicated on the plan.

Laboratory Testing

At the completion of the subsurface exploration program, soil samples were returned to our laboratory for more detailed classification, analysis, and testing. The laboratory testing consisted of sieve analyses to determine the grain size distribution and confirm the visual classifications of the fill and glacial outwash deposits. Laboratory test procedures were in general accordance with applicable ASTM Standards. Results of the gradation testing appear on Figure 3 and Figure 4 following the text of this report.

Previous Subsurface Exploration Programs

Several phases of subsurface explorations were previously completed in the general site area for environmental purposes by others. The results of the previous subsurface explorations provided to McPhail were reviewed as part of our preliminary foundation design study. Locations of previous explorations which are considered to contain relevant



geotechnical information are indicated on the Subsurface Exploration Plan, Figure 2. The logs of these previous explorations are contained in Appendix C.

Subsurface Conditions

A detailed description of the subsurface conditions encountered within the borings is documented on the recent and previous boring logs contained in Appendix B and Appendix C, respectively. Based on these explorations, the following is a description of the generalized subsurface conditions encountered across the site from ground surface downward.

Underlying the existing surface treatments which consisted of a 2-foot thickness of topsoil, 6 inches of concrete, or a 3- to 4-inch thickness of bituminous concrete, the borings encountered fill soil which extends to depths of about 2 to 25 feet below ground surface. Within borings M-1 through M-6, which were performed around the northern portion of the existing building, the fill was observed to vary from 9 to 15 feet in thickness. The fill thickness in the remaining borings performed to the south of the existing building was highly variable and was 2 and 3.5 feet thick at borings M-10 and M-7, 14 feet thick at boring M-12, and 21 and 25 feet thick in borings M-8 and M-9, respectively. The fill generally consists of a very loose to very dense, black-brown to yellow-brown sand and gravel with trace to some silt varying to a silty, gravelly sand. Grain size distributions of samples of the fill are shown on Figure 3. The fill also contains varying amounts of wood, ash, cinders, cobbles, glass and asphalt.

An organic deposit was encountered underlying the fill within boring M-5. The organic deposit was encountered at an approximate depth of 9 feet below the existing ground surface, extending to the glacial outwash deposit at a depth of approximately 11 feet. The organic deposit was generally observed to consist of a soft, dark brown fibrous peat.

Underlying the fill and/or organics, a natural glacial outwash deposit was encountered within the borings. In borings M-1 to M-6 the surface of the glacial outwash was observed to vary from depths of 9 to 15 feet below grade, specifically ranging from Elevation +42.5 at boring M-3 to about Elevation +33 at boring M-2. In the remaining borings, the surface of the glacial outwash was observed to vary from Elevation +71.6 at boring M-10 to Elevation +44.6 at boring M-9, at depths of about 2 to 25 feet below ground surface. The glacial outwash deposit was observed to generally consist of a compact to very dense, brown to gray sand and gravel with trace to some silt. Grain size distributions of samples of the glacial outwash deposit are shown on Figure 4.

Borings M-1 through M-5, M-9, M-10 and M-12 were terminated in the glacial outwashdeposit at depths of 17 to 52 feet below ground surface. Borings M-6, M-7 and M-8 wereterminated upon auger or split spoon refusal, which is generally assumed to be indicative of cobbles or boulders within the glacial outwash deposit or the underlying bedrock surface, at approximate depths varying from 11.5 to 25.1 feet below ground surface.



Groundwater was observed in borings M-1 through M-6 and M-9 upon completion of drilling at approximate depths ranging from about 5 to 28 feet below ground surface, corresponding to levels ranging from about Elevation +46.5 to about Elevation +40.3. It is anticipated that future groundwater levels across the site may vary from those reported herein due to factors such as normal seasonal changes, periods of heavy precipitation and alterations of existing drainage patterns.

Existing Foundation Conditions

Based upon our review of foundation plans included in the above-referenced existing sets of plans prepared by others, the foundations of the existing school complex are understood to generally consist of conventional footings, concrete shafts, and pressure-injected footings (PIFs). Conventional footings, anticipated to be supporting the Fusco building and Collomb House, are anticipated to bear on the natural glacial outwash deposit. Furthermore, based on the existing subsurface conditions and our knowledge of the surrounding area, the concrete shafts and PIFs are anticipated to bear in the glacial outwash deposit.

The following table presents the summary of our review.

Table 1 – Existing Foundation Summary

BuildingYear of

ConstructionPlans

AvailableAnticipated Foundation

Fusco 1914 None Available Conventional Footings

Collomb House 1938No Structural

AvailableConventional Footings

or PilesBlue Gym, Auditorium, 1-story wings 1960/1961

Structural and Architectural

120-ton PIFs andConventional Footings

Downs House 1964Structural and Architectural Concrete Shafts

Red Gym, Links, Corridors, Elevators, Misc. Renovations 1981

Structural Available 120-ton PIFs

Preliminary Foundation Design Recommendations

Based on our current understanding of the proposed development and the subsurface soil and groundwater conditions as characterized above, it is recommended that foundation support of the proposed structures transfer the structural load to the natural, inorganic glacial outwash deposit that underlies the project site. The specific foundation system used to support the proposed structures will depend upon the magnitude of the final structural loadings and the depth to the glacial outwash bearing strata relative to the elevation of the lowest level slabs. In the vicinity of borings M-7 and M-10, foundation support consisting of



spread footing foundations may be possible in consideration of the relatively shallow depth to the surface of the natural, inorganic glacial outwash deposit. However, elsewhere on the site piles or ground improvement will likely be required.

Therefore, for preliminary design purposes, there are currently two (2) foundation support options that we would recommend for this project: footings bearing directly on the glacial outwash deposit or on soil improved with ground improvement methods, and pressure-injected footings (PIFs) (aka enlarged base piles). In conjunction with the footing support option the lowest level slabs could be designed as conventional soil-supported slabs-on-grade that are supported on soil improved with ground improvement methods. Conversely, lowest level slabs in pile supported areas should be designed as structurally supported or framed slabs. All foundations should be designed in accordance with the Code.

Preliminary foundation design recommendations are provided below along with general foundation design recommendations.

Footing Foundations and Slabs-on-Grade

The footings should bear directly on the undisturbed natural glacial outwash deposit or on fill soil that is improved by ground improvement methods. For preliminary design purposes, it is recommended that the footings be proportioned utilizing a maximum design bearing pressure of three (3) tons per square-foot (tsf). Recommended minimum footing widths for continuous and isolated spread footings are 24 and 36 inches, respectively.

The bottoms of all footings should be located such that they are below a theoretical line drawn upward and outward at 2 to 1 (horizontal to vertical) from the bottom exterior edge of adjacent foundations of the existing building and proposed footings. Where the new foundations are located immediately adjacent to existing foundations, the bottom of the new foundations should extend to the same elevation as the existing foundations.

Depending on the location of the proposed building, the elevation of the lowest level slab, design footing depth, and depth to the natural glacial outwash deposit, it is anticipated that footings in limited areas around the site may bear directly on the glacial outwash deposit. For instance, the natural glacial outwash deposit was observed at depths of 3.5 and 2 feet below grade in borings M-7 and M-10. Elsewhere across the site, the depth to the natural glacial outwash deposit in the borings varied from about 9 to 25 feet below existing grade. Therefore, in these areas, it is recommended that the spread footing foundations bear on fill soil that is improved with ground improvement methods.

Aggregate piers (APs) and rigid inclusions (RIs) are two (2) common ground improvement methods installed to improve the density and stiffness of existing soils. Either method would be considered acceptable for this project site. Ground improvement methods would densify the existing fill and increase the lateral stress in the soil matrix beneath the proposed building foundations. Thus, the uncontrolled existing fill soils would be improved



to a stiffer composite soil matrix allowing the use of footing foundations by keeping minimizing settlement to within acceptable limits.

The lowest level slabs in areas where footing support is utilized should be designed as conventional soil-supported slabs bearing on the aggregate pier-improved fill.

In general, for APs an aggregate pier cavity is created by driving a specially designed 12- to 16-inch diameter mandrel and tamper foot using a large static force augmented by dynamic vertical impact energy. A sacrificial plate is placed at the bottom of the tamper foot to prevent soil from entering the mandrel during installation. This method of advancement minimizes drill spoils as penetrated soils are displaced laterally. After installation to the design depth, coarse aggregate is placed inside the mandrel and the mandrel is lifted, leaving the sacrificial plate at the bottom of the cavity. Typically, the tamper foot is lifted approximately four feet and then driven and vibrated back down three feet, forming a one-foot thick compacted lift of approximately 20 inches in diameter. This process is repeated to the top of the cavity, forming the completed aggregate pier.

RIs are constructed by advancing a hollow mandrel to the design depth, densifying the surrounding soils by displacement. Once reaching the design depth, concrete is pumped through the mandrel, which opens as it is raised. If required, the mandrel can be raised and lowered several times, vertically ramming lifts of concrete to create an expanded base. The RI elements are typically installed in a grid pattern and are used in conjunction with an engineered granular pad to produce an intermediate foundation system for support of foundation loads. The type and thickness of the engineered pad is dependent on the design bearing pressure and is designed by the RI design-build consultant.

Since ground improvement techniques are provided by a design-build consultant, detailed design calculations should be submitted to the Architect and design team for review prior to the beginning of construction. A detailed explanation of the design parameters for capacity and settlement calculations should be included in the design submittal. The design submittal should also include a testing program to demonstrate the capacity of the elements. All calculations and drawings should be prepared and sealed by a Professional Engineer who is licensed in the Commonwealth of Massachusetts, and is retained by the Contractor who is to perform the work.

The following general criteria should be utilized in the design of the aggregate piers:

1. Aggregate piers should extend at least to the surface of the natural glacial outwash deposit;

2. Estimated long-term settlement for footings and slabs should be less than 1-inch;

3. Estimated long-term differential settlement of adjacent footings should be less than 1/2-inch; and



4. Modulus load tests should be performed on a selective AP and/or RI to a minimum of 150 percent of the maximum design stress.

Pressure-Injected Footings (PIFs) and Structural Slabs

While it is anticipated that ground improvement methods could be utilized across the majority of the site, it may be more economical to utilize PIFs to provide foundation support for the gymnasiums, auditoriums, and other long-span building spaces if there are high structural loads. Based upon the anticipated building column loads, it is recommended that the PIFs be designed for a maximum design capacity of up to 120 tons per unit in compression for support of column loads. Based on discussions with the project Structural Engineer, it is understood that PIFs with a design compressive capacity of 100 tons per unit may be an efficient match given the anticipated column loads. The PIFs should be installed utilizing cased shafts. Based on the requirements of the Massachusetts State Building Code, a pile load test is not required for a PIF with an allowable load carrying capacity of 120 tons or less.

The 120-ton PIF is a relatively short pile driven through the fill and organic deposits and then "based up" in the upper portion of the underlying glacial outwash deposit. Typically, the PIF base should be a minimum of 4 feet below the underside of the pile cap to allow for proper construction of the PIF shaft. Therefore, PIFs may not be feasible in portions of the southern area of the site due to the relatively shallow depth to the surface of the natural, inorganic glacial outwash soil. If that is the case, foundation support should be provided by conventional footing foundations.

The base consists of zero slump concrete having a 28-day compressive strength of at least 4,000 pounds per square-inch (psi) driven and compacted in 5 cubic-foot batches by a drop hammer delivering not less than 140,000 foot-pounds of energy per blow. The number of blows of the compaction hammer per 5 cubic-foot batch has been empirically correlated with pile capacity.

After completion of the base, the pile shaft is formed by pouring concrete into a corrugated metal shell having an outside diameter of about 16 inches which has been attached to the enlarged base. The piles should be provided with seismic reinforcement, as required based on the applicable Seismic Design Category, in accordance with Section 1810.3.9.4 of the Code. The minimum center-to-center pile spacing shall be not less than 4 feet for the 120-ton design capacity PIFs in accordance with Section 1810.3.14 of the Code.

If significant lateral loads are generated along the perimeter foundation walls in long-span areas, in order to resist the lateral loads, battered PIFs could be installed using uncased shafts and a maximum batter of 1 horizontal to 6 vertical (1H:6V). Thus, utilizing the maximum 1H:6V batter, the design horizontal capacity of the PIF would be 20 tons.

The proposed lowest level floor slabs in areas where pile support is utilized should be designed as structurally-supported or framed slabs.



Vapor Mitigation System

As indicated above, some of the contamination at the subject site is volatizing from groundwater and affecting indoor air within portions of the existing school complex. In consideration of this, the installation of a vapor mitigation system beneath any new buildings that may constructed and/or existing buildings that may be renovated is recommended as part of the planned scope of development at the subject site.

Specifically, it is recommended that the lowest level slabs be provided with the following:

• A 30 to 40 mil thick HDPE vapor barrier or a waterproofing membrane such as PrePrufe 300R as manufactured by CFP Applied Technologies.

• A 12-inch minimum thickness of ¾-inch crushed stone underlain by a thickness of filter fabric.

• A grid of 4-inch diameter perforated PVC pipes laid out at a maximum spacing of 30 feet on center. The pipes would be surrounded on all sides by a 6-inch minimum thickness of ¾-inch crushed stone.

• A minimum of one (1) 4-inch diameter vertical riser pipe for every approximate 4,000 square-feet of building footprint.

• Provisions to allow the future conversion of the passive system to an active system; including alarms and remote telemetry connected to the Massachusetts Department of Environmental Protection (DEP).

In addition to the above, installation of a vapor membrane on the negative side of below-grade foundation walls, in particular south facing walls, may be required. Although a few products may be suitable for this application, Retro-Coat by Land Science is documented to be effective for VOC vapor mitigation.

Additional information regarding the soil and groundwater contamination is contained in the above-referenced Phase I Environmental Site Assessment report prepared by McPhail.

General Foundation Design Recommendations

If portions of the proposed lowest level slabs will be below-grade, surface water runoff that infiltrates into the ground could potentially infiltrate into the occupied below-grade space. Therefore, foundation walls and slabs in below-grade areas are recommended to be waterproofed. All localized depressions in the lowest level slab (such as elevator pits, etc.)should be provided with properly tied continuous waterstops in all construction joints and membrane waterproofing to protect against groundwater intrusion.

Perimeter footings and pile caps should be provided with a minimum 4-foot thickness of soil cover as frost protection. Interior footings and pile caps should be located such that the top of the foundation concrete is a minimum of 6 inches below the underside of the lowest level slab.



Below-grade foundation walls receiving lateral support at the top and bottom (i.e. restrained walls) should be designed for a lateral earth pressure corresponding to an equivalent fluid density of 60 pounds per cubic-foot. Similarly, drained cantilevered retaining walls, (i.e. receiving no lateral support at the top) should be designed for a lateral earth pressure corresponding to an equivalent fluid density of 40 pounds per cubic-foot. To these values must be added the pressures attributable to earthquake forces per Section 1610.2 of the Code.

Lateral forces can be considered to be transmitted from the structure to the soil by passive pressure against the foundation walls, footings and/or pile caps utilizing an equivalent fluid density of 120 pounds per cubic-foot providing that the walls are designed to resist these pressures. Lateral force can also be considered to be transmitted from the structure to the soil by friction on the base of footings using a coefficient of 0.4, to which a safety factor of 1.5 should be applied.

Seismic Design Considerations

For the purposes of determining parameters for structural seismic design, for preliminary design purposes, the site is considered to be classified as a Site Class D as defined in Section 1613.5.2 of the Code. Further, the bearing stratum on the proposed site is not considered to be subject to liquefaction during an earthquake based on the criterion of Section 1806.4 of the Code.

Preliminary Geotechnical Construction Considerations

Preliminary geotechnical construction considerations addressed herein include the following: environmental considerations due to the documented soil and groundwater contamination at the subject site; the removal of existing foundation remains where required; placement of ordinary fill; temporary excavation support; vibrations generated during ground improvement and pile installation; construction dewatering; and, off-site removal of excavated soil.

With respect to the documented soil and groundwater contamination, the construction at the subject site will require the following:

• The implementation of health and safety provisions to prevent exposures to workers and surrounding public. While an elevated level of personal protection equipment may be required for workers working within areas of elevated contamination, hazardous waste training will also be necessary. Specifically, 40 hours of personnel protection and safety training for hazardous waste site activities pursuant to OSHA 29 CFR 1910, and 8 hours of refresher training, as required, will be required for personnel directly working with contaminated soils.



• Preparation of a clean building pad and utility corridors prior to the construction of building foundations and above-grade structures. As indicated above, the site grade will likely be raised by approximately 4 feet with imported fill at the start of construction to minimize excavation and removal of existing site soils and to create a general working pad for construction;

• Bulk excavation of contaminated soil or excavation activities which expose large areas of contaminated soil is not recommended during the school year. Appropriate dust suppression and management methods will be necessary during excavation of contaminated soil;

• Based on our observations during the subsurface exploration program, groundwater is not anticipated to be encountered within the building areas during general excavation. It is anticipated that dewatering, if required, by means of strategically located sumps and trenches should suffice during foundation construction operations. In addition, trapped surface water may accumulate within localized depressions in the ground surface across the site after periods of heavy precipitation and will most likely necessitate localized sumping. Due to the presence of contaminants in the groundwater at the site, on-site recharge of groundwater is not recommended. Temporary off-site discharge of groundwater during construction activities to a storm drain or combined sewer will require on-site treatment and the submittal of an application for a temporary construction dewatering permit to either the US Environmental Protection Agency (EPA) or the Massachusetts Water Resource Authority (MWRA). Treatment of pumped groundwater will be necessary prior to off-site discharge;

• The engineered barriers and direct exposure barriers located on the northern portion of the site will need to be repaired and/or locally replaced if impacted by the construction; and

• A Release Abatement Measure (RAM) Plan will be prepared and submitted to the Massachusetts Department of Environmental Protection to manage the excavation and off-site removal of site soils.

All existing foundations remains such as foundations from previous structures and utilities should be removed where they interfere with new construction. Foundation remains may remain in place where they do not conflict with proposed footing, ground improvement installation, or pile locations, and outside of the proposed building footprint provided that they are removed to 24 inches beneath the proposed finished grade or slab elevation.

Obstructions to ground improvement or pile installation activities encountered in the fill should be removed by the earthwork contractor. Obstructions encountered during ground improvement or pile installations that prevent continued installation at a particular location should be evaluated on a case-by-case basis to determine the necessity to remove the obstruction or to design the footing to span over the obstruction.



A substantial amount of imported fill is anticipated to be required to raise the existing site grade. With the use of AP supported slabs-on-grade or structural slabs, ordinary fill can be used in lieu of structural fill to raise the grade within the building footprint. Ordinary fill generally costs less than structural fill to import and since the compaction requirements for ordinary fill are less, it can generally be placed more quickly. As such, ordinary fill should be placed to raise the grade within the proposed building footprint up to the underside of the 12-inch thickness of ¾” crushed stone below the lowest level slabs. Ordinary fill should be placed in maximum 12-inch thick loose lifts and compacted to a minimum of 92 percent of its maximum modified Proctor dry density. APs would then be installed from the crushed stone subgrade.

It is currently anticipated that excavated soil will not be able to be re-used on-site. As such, should excess excavated soil generated from the proposed construction require off-site disposal, current Department of Environmental Protection (DEP) policies and regulations for off-site reuse of excess excavated soil require environmental characterization of the excavated soil prior to its off-site removal.

Depending on the location of the building, depth of excavation, contractor phasing and available laydown area, a temporary excavation support system may be required to retain adjacent soils and protect adjacent structures and utilities. If required, the temporary excavation support system could consist of a steel soldier pile and timber lagging wall or a soil nail wall. The temporary excavation support systems should be designed by a professional engineer registered in the Commonwealth of Massachusetts who is employed by the Contractor.

Ground vibrations are produced as a result of the PIF and/or ground improvement installation procedures. Based on our experience, impacts from these vibrations are not anticipated to result in structural damage to existing, adjacent structures, however, the magnitude of vibrations may be of sufficient magnitude to cause cosmetic cracking of adjacent structures and annoyance of occupants. It is not anticipated that ground vibrations caused by construction will cause damage to nearby structures. However, due to the proximity of the adjacent buildings to the site, it is recommended that preconstructionsurveys of adjacent buildings be completed before the start of construction and that vibration monitoring be performed during the ground improvement and/or pile installation activities.

Final Comments

The subsurface information obtained from the recent borings is considered sufficient for preliminary foundation design purposes. However, an additional subsurface exploration consisting of borings is recommended to be performed to obtain further subsurface information in the area of the proposed structures. Additionally, test pit explorations may be required to determine the depth and existing foundation configurations where the new



additions will be adjacent to the existing building or to determine the configuration of existing foundations which will be demolished.

It is recommended that McPhail be retained to perform the additional subsurface exploration and to prepare a final foundation engineering report which provides final foundation recommendations based on the specific project design. The final foundation engineering report would contain additional geotechnical design recommendations for foundation support and will also contain foundation construction considerations. Furthermore, after the submission of the final foundation engineering report, it is recommended that McPhail be retained to provide final design phase geotechnical engineering services, including providing design assistance to the Architect and Structural Engineer during the final design phase of this project.

We trust that the above is sufficient for your present requirements. Should you have any questions concerning the recommendations presented herein, please do not hesitate to call us.

Very truly yours,

McPHAIL ASSOCIATES, LLC

Christopher P. Miller

Jonathan W. Patch, P.E.

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APPENDIX A:

LIMITATIONS


LIMITATIONS

This preliminary report has been prepared on behalf of and for the exclusive use of HMFH Architects for specific application to the proposed renovations/additions to the Arlington High School located at 869 Massachusetts Avenue in Arlington, Massachusetts in accordance with generally accepted soil and geotechnical engineering practices. No other warranty, expressed or implied, is made.

The recommendations contained in this report are for preliminary pricing and design purposes only. Final subsurface exploration program and foundation engineering analyses will be required for the design and construction of the proposed project. In the event that any changes in nature, design, or location of the proposed construction are planned, the conclusions and recommendations contained in this report should not be considered valid unless the changes are reviewed and conclusions of this report modified or verified in writing by McPhail Associates.

The preliminary analyses and recommendations presented in this report are based upon the data obtained from the preliminary subsurface explorations performed at the approximate locations indicated to McPhail. If variations in the nature and extent of subsurface conditions between the widely spaced explorations become evident during thecourse of construction, it will be necessary for a re-evaluation of the recommendations of this report to be made after performing on-site observations during the construction period and noting the characteristics of any variations.


APPENDIX B:

RECENT BORING LOGS M-1 THROUGH M-10 AND M-12PREPARED BY CARR-DEE CORP.


6"

14'

18'

GROUNDSURFACE+48+/-

WATER LEVEL 5'DRILLER: G. SMITH, INSPECTOR: J. MILLERDATE STARTED & COMPLETED: 5-12-2018

CONCRETE

SAND, GRAVEL, SILT (FILL)

VERY DENSE FINE TO MEDIUMSAND & GRAVEL, SOME SILT

S#1, 6" to 2' (11-14-11) RECOVERED 10 in. S#2, 2' to 4' (7-4-1-1) RECOVERED 1 in. S#3, 4' to 6' (2-1-2-3) RECOVERED 12 in.

S#4, 6' to 8' (1/12"-3-2) RECOVERED 12 in.

S#5, 8' to 10' (1-1-1-2) RECOVERED 10 in.

S#6, 10' to 12' (2-1-2-4) RECOVERED 10 in.

S#7, 12' to 14' (20-37-41-23) RECOVERED 0 in.

S#8, 14' to 16' (16-30-26-30) RECOVERED 12 in.

S#9, 16' to 18' (85-31-21-21) RECOVERED 1 in.

CARR-DEE CORP.37 LINDEN STREET MEDFORD, MA 02155-0001 Telephone (781) 391-4500To: MCPHAIL ASSOC., LLC, 2269 MASS. AVE., CAMBRIDGE, MA Date: 6-18-2018 Job No.: 2018-85

Location: ARLINGTON HIGH SCHOOL, 869 MASS. AVE., ARLINGTON, MA Scale: 1 in.= 5 ft.

BORING M-1

All samples have been visually classified by . Unless otherwise specified, water levels noted were observed at completionof borings, and do not necessarily represent permanent ground water levels. Figures in parenthesis indicate the number of blowsrequired to drive Two-inch Split Sampler 6 inches using 140 lb. weight falling 30 inches(). Figures in column to left(if noted) indicate number of blows to drive casing one foot, using 300 lb. weight falling 24 inches ().

Sheet 1 of 1


6"

13'

21'

GROUNDSURFACE+46+/-

CONCRETE

SILT, SAND, GRAVEL, WITHCINDERS, ASH (FILL)

COMPACT FINE TO MEDIUM SAND& GRAVEL, SOME SILT

COMPACT FINE TO MEDIUM SAND& GRAVEL, TRACE SILT

S#1, 6" to 2' (7-9-5) RECOVERED 4 in. S#2, 2' to 4' (5-5-5-3) RECOVERED 4 in. S#3, 4' to 6' (8-2-3-2) RECOVERED 5 in.

S#4, 6' to 8' (14-11-4-2) RECOVERED 6 in.

S#5, 8' to 10' (2-3-2-1) RECOVERED 6 in.

S#6, 10' to 12' (4-2-4-18) RECOVERED 2 in.

S#7, 12' to 13' (15-11) RECOVERED 2 in. S#7A, 13' to 14' (8-10) RECOVERED 2 in. S#8, 15' to 17' (14-13-16-18) RECOVERED 8 in.

S#9, 20' to 21' (4-5) RECOVERED 3 in. S#9A, 21' to 22' (11-8) RECOVERED 3 in.

S#10, 25' to 27' (12-7-8-13) RECOVERED 2 in.

S#11, 30' to 32' (15-12-11-13) RECOVERED 2 in.

S#12, 35' to 37' (34-12-11-7) RECOVERED 6 in.

S#13, 40' to 42'



BORING M-2


Sheet 1 of 2


52'

WATER LEVEL 5'SIZE OF CASING: NW, LENGTH: 50'0"DRILLER: G. SMITH, INSPECTOR: J. MILLERDATE STARTED & COMPLETED: 5-12-2018

(18-39-15-8) RECOVERED 2 in.

S#14, 45' to 47' (25-11-15-8) RECOVERED 2 in.

S#15, 50' to 52' (15-9-11-13) RECOVERED 1 in.



BORING M-2


Sheet 2 of 2


3"

15'

22'

GROUNDSURFACE+57.5

WATER LEVEL 11'SIZE OF AUGERS: 2-1/4" I.D., LENGTH: 20'0"DRILLER: G. SMITH, INSPECTOR: T. CORMICANDATE STARTED & COMPLETED: 5-31-2018

ASPAHLT

SILT, SAND, GRAVEL, WITHCOBBLES (FILL)


S#1, 6" to 2' (7-11-11) RECOVERED 12 in. S#2, 2' to 4' (14-9-11-10) RECOVERED 12 in.

S#3, 5' to 7' (12-8-4-4) RECOVERED 10 in.

S#4, 7' to 9' (7-20-27-21) RECOVERED 2 in.

S#5, 10' to 12' (18-74-29-37) RECOVERED 10 in.

S#6, 15' to 17' (10-15-19-22) RECOVERED 12 in.

S#7, 20' to 22' (24-11-12-27) RECOVERED 24 in.



BORING M-3


Sheet 1 of 1


4"

10'

17'

GROUNDSURFACE+48.4

WATER LEVEL 5'SIZE OF CASING: NW, LENGTH: 10'0"DRILLER: G. SMITH, INSPECTOR: C. FOLEYDATE STARTED & COMPLETED: 6-16-2018

ASPHALT

SILTY SAND, GRAVEL, LOAM(FILL)


S#1, 6" to 2'6" (11-8-7-10) RECOVERED 5 in.

S#2, 5' to 7' (4-3-1-5) RECOVERED 10 in.

S#3, 10' to 12' (8-13-22-23) RECOVERED 8 in.

S#4, 15' to 17' (22-19-17-18) RECOVERED 14 in.



BORING M-4


Sheet 1 of 1


3"

9'

11'

17'

GROUNDSURFACE+45.8

WATER LEVEL 5'6"SIZE OF CASING: NW, LENGTH: 15'0"DRILLER: G. SMITH, INSPECTOR: C. FOLEYDATE STARTED & COMPLETED: 6-16-2018

ASPHALT

SILTY SAND, SOME GRAVEL,TRACE, WOOD & ASPHALT(FILL)

PEAT

DENSE TO COMPACT FINE TOMEDIUM SAND & GRAVEL, TRACESILT

S#1, 6" to 2'6" (12-10-11-9) RECOVERED 16 in.

S#2, 5' to 7' (6-5-5-3) RECOVERED 5 in.


S#4, 15' to 17' (15-16-14-14) RECOVERED 6 in.



BORING M-5


Sheet 1 of 1


3"

10'

20'6"

24'2"

GROUNDSURFACE+45.6

- R E F U S A L -(NO PENETRATION WITH ROLLER BIT)

WATER LEVEL 5'SIZE OF CASING: NW, LENGTH: 20'0"DRILLER: G. SMITH, INSPECTOR: C. FOLEYDATE STARTED & COMPLETED: 6-16-2018

ASPHALT

SILTY SAND, TRACE GRAVEL,WITH ASPHALT & GLASS (FILL)


DENSE FINE SILTY SAND,TRACE GRAVEL

S#1, 6" to 2'6" (9-7-7-5) RECOVERED 12 in.

S#2, 5' to 7' (3-7-8-12) RECOVERED 11 in.

S#3, 10' to 12' (12-11-12-12) RECOVERED 4 in.

S#4, 15' to 17' (8-9-8-9) RECOVERED 8 in.

S#5, 20' to 20'6" (13) RECOVERED 3 in. S#5A, 20'6" to 22' (16-17-26) RECOVERED 6 in.

S#6, 24' to 24'2" (100/2") RECOVERED 0 in.



BORING M-6


Sheet 1 of 1


3"

3'6"

11'6"

GROUNDSURFACE+76.3

- R E F U S A L -(NO PENETRATION WITH AUGERS)NO WATER ENCOUNTEREDSIZE OF AUGERS: 2-1/4" I.D., LENGTH: 11'0"DRILLER: G. SMITH, INSPECTOR: T. CORMICANDATE STARTED & COMPLETED: 5-31-2018

ASPHALT

SILTY SAND, & GRAVEL (FILL)

DENSE TO VERY DENSE FINE TOMEDIUM SAND & GRAVEL, TRACESILT, WITH COBBLES

S#1, 6" to 2' (9-8-3) RECOVERED 12 in. S#2, 2' to 3'6" (10-7-7) RECOVERED 12 in. S#2A, 3'6" to 4' (24) RECOVERED 5 in. S#3, 5' to 7' (10-14-18-69) RECOVERED 14 in.

S#4, 10' to 11'6" (35-41-102) RECOVERED 12 in.



BORING M-7


Sheet 1 of 1


2"

21'

25'1"

GROUNDSURFACE+70.0

NO WATER ENCOUNTEREDSIZE OF AUGERS: 3-3/4" I.D., LENGTH: 25'0"DRILLER: G. SMITH, INSPECTOR: T. CORMICANDATE STARTED & COMPLETED: 5-30-2018

ASPHALT

SAND, GRAVEL, SILT (FILL)

VERY DENSE FINE TO MEDIUMSAND & GRAVEL, SOME SILT

S#1, 6" to 2' (10-12-24) RECOVERED 14 in.

S#2, 5' to 7' (2-2-5-5) RECOVERED 10 in.

S#3, 7' to 9' (7-3-2-2) RECOVERED 8 in.

S#4, 10' to 12' (5-2-2-7) RECOVERED 10 in.

S#5, 12' to 14' (6-5-6-4) RECOVERED 4 in.

S#6, 15' to 17' (3-4-3-1) RECOVERED 6 in.

S#7, 17' to 19' (3-2-9-9) RECOVERED 10 in.

S#8, 20' to 21' (14-19) RECOVERED 8 in. S#8A, 21' to 22' (45-45) RECOVERED 6 in. S#9, 22' to 24' (24-20-20-30) RECOVERED 12 in. S#10, 25' to 25'1" (100/1") RECOVERED 0 in.



BORING M-8


Sheet 1 of 1


3"

25'

31'

GROUNDSURFACE+69.6

WATER LEVEL 28'SIZE OF AUGERS: 2-1/4" I.D., LENGTH: 25'0"DRILLER: G. SMITH, INSPECTOR: T. CORMICANDATE STARTED & COMPLETED: 5-31-2018

ASPHALT

SILT, SAND, GRAVEL, WITHWOOD, ASH, CINDERS &COBBLES (FILL)

COMPACT FINE TO MEDIUMSAND, SOME GRAVEL, TRACESILT


S#3, 5' to 7' (7-5-8-13) RECOVERED 14 in.

S#4, 10' to 12' (12-12-9-24) RECOVERED 14 in.

S#5, 12' to 13'6" (47-25-20) RECOVERED 12 in.

S#6, 15' to 17' (6-5-4-6) RECOVERED 10 in.

S#7, 20' to 22' (4-3-4-3) RECOVERED 2 in.

S#8, 22' to 24' (4-3-6-13) RECOVERED 24 in.

S#9, 25' to 27' (11-15-15-17) RECOVERED 10 in.

S#10, 27' to 29' (15-9-11-13) RECOVERED 10 in.

S#11, 29' to 31' (8-8-8-8) RECOVERED 12 in.



BORING M-9


Sheet 1 of 1


3"

2'

17'

GROUNDSURFACE+73.6


ASPHALT

SILTY SAND, GRAVEL (FILL)

DENSE TO VERY DENSE FINE TOMEDIUM SAND & GRAVEL, SOMESILT


S#3, 5' to 7' (20-26-19-25) RECOVERED 16 in.

S#4, 10' to 12' (26-26-31-36) RECOVERED 14 in.

S#5, 15' to 17' (23-27-32-29) RECOVERED 18 in.



BORING M-10


Sheet 1 of 1


2'

14'

17'

18'

GROUNDSURFACE+78.0


SILT & FINE SAND, SOMEORGANICS, TRACE GRAVEL(TOPSOIL)

SAND, GRAVEL, SOME SILT,WITH CINDERS, ASH (FILL)

COMPACT FINE TO MEDIUMSAND, TRACE GRAVEL

VERY DENSE FINE SAND &GRAVEL, TRACE SILT

S#1, 0' to 2' (1-2-3-3) RECOVERED 18 in. S#2, 2' to 4' (4-5-4-1) RECOVERED 18 in.

S#3, 5' to 7' (1-1-1-1) RECOVERED 18 in.

S#4, 10' to 12' (2-2-1-2) RECOVERED 18 in.

S#5, 12' to 14' (6-8-11-9) RECOVERED 18 in.

S#6, 14' to 16' (6-6-5-6) RECOVERED 18 in.




BORING M-12


Sheet 1 of 1


APPENDIX C:

PREVIOUS BORING LOGS