THE GATEWAY ENGINEERS, INC.

100 MCMORRIS ROAD.

PITTSBURGH, PA 15205

412-921-4030 PHONE

412-921-9960 FAX

www.gatewayengineers.com

February 8, 2024

C-46493

Klavon Design Associates, Inc.

48 S 15th Street

Pittsburgh, PA 15203

ATTN: Dina Cole Klavon, RLA, ASLA

Subject: Geohazard Mitigation Review

Proposed Sheraden Park Improvements

Surban Street, 20th Ward

City of Pittsburgh, Allegheny County, Pennsylvania

Dear Dina:

As requested, we have completed our review of potential geohazards at the subject site. This report describes the findings of the review, and presents grading, drainage, and subgrade preparation considerations for the design and construction of the proposed park improvements.

SITE LOCATION AND CONDITIONS

The subject site consists of Tax Parcel 42-F-10, situated along Surban Street, in the 20th Ward of the City of Pittsburgh, Allegheny County, Pennsylvania. The ground surface in the project area falls from the northeast and southwest down to a filled valley, at elevations ranging from 885 ft to 765 ft on grades ranging from about twelve percent (12 ft vertical fall in 100 ft horizontal distance) to 50 percent, as illustrated on proposed Grading Plan Sheets L115 through L119, authored by your project team and dated

January 25, 2024. Those elevations are based on the ground surface elevations indicated on the project plans authored by Klavon Design. Those elevations reference the North American Vertical Datum of

1988 (NAVD88).

GEOLOGIC RECONNAISSANCE

Geologically, the site is located south of the southern terminus of the south-dipping Kellersburg Anticline

(a ridge-like fold in the bedrock strata) about 2.5 mile from its axis. Surficial bedrock at the site dip, and groundwater in the bedrock migrates, south on a grade of about 1.5 percent.

Consultations with the USGS Open-File Report 78-1057, Landslides and Related Features, Ohio, West

Virginia, and Pennsylvania, dated 1978, indicate that soil and bedrock susceptible to movement exists within the natural slopes at the project site. The attached Figure 1 illustrates the soil and bedrock in the area are susceptible to sliding where excavations break continuity of the slope, or the slope is overloaded by fill, or the slope experiences elevated levels of groundwater.

A review of the Pennsylvania Department of Environmental Resources, Mineral Resource Report 89, Coal Resources of Allegheny County, Pennsylvania, Part 1, dated 1986, indicates that the Pittsburgh Coal seam horizon - a significant marker bed in this locale - lies at about elev 1140, based on the USGS datum.

That implies the coal seam is at least 250 ft upslope of the surface elevations at the proposed park improvements. That reference does not indicate commercial mining of any lower coal seams below the site. Thus, mine subsidence nor strip mine spoil hazards are not a concern for the proposed project.

Surficial bedrock at the site represents the Casselman Formation, Conemaugh Group, Pennsylvanian

System, consisting of cyclic sequences of sandstone, shale, thin limestone, claystone, and coal seams.

A field walk to observe geohazard features was performed on May 21, 2023. The walk consisted of reviewing existing natural and man-made features, observations for surface erosion, creep-movement of surfaces, or structural distresses. Based on our review, there were no indications of excessive slope movement in the vicinity of the existing and proposed park features. However, there is evidence of long-term slope creep along the outer slopes of the access road and adjacent walking trail, as well as, erosion and deposition of soils in a natural channel south and upslope of the parking lot adjacent to the ball field.

DISCUSSION AND RECOMMENDATIONS

Based on our understanding, the project consists of replacing existing deteriorated pavement and walking trail surfaces, installation of new vegetation and playground equipment, the construction of new ADA compliant parking stalls and associated retaining walls, construction new fill slopes and roadways, and replacing of existing or construction of new stormwater control devices.

From our review of LiDAR data of the project area between 2017 and 2020 hosted by PASDA, the landslide feature map of the Pittsburgh West Quadrangle, City of Pittsburgh Geodetic Survey maps from

1928, the project drawings authored by Klavon Design, and our site visits to observe the existing conditions, we believe that the subject property is generally stable. However, erosion and elevated soil moisture conditions are present and will impact the long-term performance of the proposed park features.

As countermeasures to the geohazards described above, the following should be considered.

1. Vegetation that is conducive for poorly draining soils that persistent saturated conditions should be considered,

2. Subsurface drains, as illustrated on the attached Figure 2, should be installed along impervious hardscape features, such as, roadways, walking trails, or slabs-on-grade. Outside slopes of existing hardscape evidence distresses due to long-term saturated soils that induce long-term slope creep. The subsurface drains can reduce the frequency and duration of saturation in the subgrade soils and mitigate deterioration of hardscape surfaces over time

3. Keyway and bench drains should be installed underneath all proposed fill slope areas, as illustrated on Figure 3. The underdrains will control soil moisture conditions within the proposed fill slope and the underlying natural soils to ensure the slopes maintain satisfactory stability over time;

4. Bearing subgrades for fill slopes and site retaining walls should be proofrolled as described below;

5. Aggregate walking surfaces should be thoroughly wetted above the optimum moisture value of the material as determined by ASTM International D698, Standard Test Methods for Laboratory

Compaction Characteristics of Soil Using Standard Effort, prior to installation and compaction to reduce trapped air voids and increase the resiliency of the material to erosion.

FILL/BACKFILL CONSIDERATIONS

For grading around the basketball parking lot and the new ADA accessible parking stalls, all topsoil, vegetation, and other deleterious materials should be removed. The exposed subgrades should then be proof-rolled with a minimum of ten passes with a walk-behind (static weight) vibratory roller compactor.

Soft or loose zones delineated by the proof-rolling should be undercut an additional foot below the final respective subgrade level. Should the undercut subgrade remain unsuitable, it should be stabilized by

"punching" suitable, inert (non-carbonaceous, non-pyritiferous, non-expansive, and non-slag) crushed stone meeting the size and grading requirements of American Association of State Highway and

Transportation Officials (AASHTO) No. 1 into it to create a "working surface" deemed adequate by our field personnel. The vacated volumes should then be raised to their respective final subgrade level with suitable, inert, properly compacted, on- or off-site borrow. It is recommended that excavated material to be used as backfill be either placed and compacted in the work area as soon as possible to limit its exposure to rainfall events, or protected with plastic tarps if installation requires multiple days.

Cohesive fill should be compacted to a minimum of 95 percent of the maximum standard proctor dry density as determined by ASTM Test Designation: D698, at water contents within three percent (±3%) of the optimum water content established by that test. Granular fill should be compacted to at least 70 percent relative density as determined by ASTM Test Designations: D4253- and 4254-16.

QUALITY VERIFICATION CONSIDERATIONS

This report has been prepared using field and laboratory procedures and analysis methods conforming to commonly accepted local geotechnical engineering practices. All recommendations and/or conclusions herein pertain only to this specific project and should not be used or interpreted by others for modifica-tions to this project, unless reviewed and approved by us, or for other projects or sites. Even within the project context, subsurface conditions depicted herein are representative only at the time of our site review; actual conditions may vary. Due in part to such variability in subsurface conditions, the implementation of the recommended measures must be inspected by our personnel to confirm that the subsurface conditions encountered during construction are consistent with observations and our engineering analysis, and to verify that the subgrades, backfills, and all other geomaterials used are behaving as anticipated. Some conditions or material/subgrade behavior and/or performance may require modifications to our recommendations, which can typically only be determined "on-the-spot" during full-time inspections by one of our soil technicians, under the direct supervision of our professional (licensed) geotechnical engineers.

Not only could the interpretation and field inspection of our recommendations by others result in a structure or pavement that does not perform as intended, but inspection by individuals not qualified and/or not under the direct supervision of a professional geotechnical engineer could result in structure or pavement failures. We therefore will not be responsible nor professionally liable for the performance and/or suitability of any structures or pavements affected by geotechnical elements of the project inspected by others. The selected inspection agency must take full responsibility for proper implementation and performance of the project geotechnical recommendations for this site.

We sincerely appreciate the opportunity to be of service to you on this project. Should you have any questions regarding our findings or recommendations, please do not hesitate to contact us.

Respectfully submitted, THE GATEWAY ENGINEERS, INC.

BY:____________________________

Nathaniel S. Hayes, P.E.

Geotechnical Engineer

NSH

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REVISION RECORDNoDate No

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Full-Service Civil Engineering & Surveying gatewayengineers.com Pittsburgh, PA

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The Gateway Engineers, Inc.-

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1 IN = 2000 FT

LANDSLIDE

FEATURES MAP

48 S 15th Street Pittsburgh, PA 15203

Sheraden Park Surban Street, 20th Ward, City of Pittsburgh, Allegheny County, PA

GEOHAZARD REVIEW

KLAVON DESIGN ASSOCIATES

C-46493

FEB 2024

PREPARED FOR:

Project Number:

Drawing Scale:

Date Issued:

Index Number:

Drawn By:

Checked By:

Project Manager:

Path & Filename=G:\Projects\41000\41634 413 Edith Street Geotech\Dwg\Edith Street Geotech Figures.dwg Plot Date=2/25/2022 11:08 AM John P. Malizia, P.G. Save Date=2/24/2022 3:39 PM ##

Full-Service Civil Engineering & Surveying gatewayengineers.com Pittsburgh, PA

G at ew ay E ng in ee rs

In c.

A ll

R ig ht s

R es er ve d

855-634-9284

The Gateway Engineers, Inc.-

JPM

NSH

NSH

FIGURE

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48 S 15th Street Pittsburgh, PA 15203

Sheraden Park Surban Street, 20th Ward, City of Pittsburgh, Allegheny County, PA

GEOHAZARD REVIEW

KLAVON DESIGN ASSOCIATES

C-46493

FEB 2024

TYPICAL UNDERDRAIN

DETAIL

GEOTEXTILE

FILTER FABRIC

ROUNDED

AGGREGATE

(AASHTO #57)

4" PERFORATED

PLASTIC PIPE

18" MIN

COMPACTED

ON-SITE SOIL 12

MIN

1. INSTALL WITH POSITIVE DRAINAGE.

2. INSTALL UNDER EXISTING

TO MAINTAIN POSITIVE DRAINAGE, IF

NECESSARY.

3. INSTALL OUTLET TO DISCHARGE

GROUNDWATER AT LIMITS OF

DISTURBANCE.

SCALE: N.T.S.

UNDERDRAIN DETAIL

PAVEMENTS

3FT

PREPARED FOR:

Project Number:

Drawing Scale:

Date Issued:

Index Number:

Drawn By:

Checked By:

Project Manager:

Path & Filename=G:\Projects\41000\41634 413 Edith Street Geotech\Dwg\Edith Street Geotech Figures.dwg Plot Date=2/25/2022 11:08 AM John P. Malizia, P.G. Save Date=2/24/2022 3:39 PM ##

Full-Service Civil Engineering & Surveying gatewayengineers.com Pittsburgh, PA

G at ew ay E ng in ee rs

In c.

A ll

R ig ht s

R es er ve d

855-634-9284

The Gateway Engineers, Inc.

N.T.S.

JPM

NSH

NSH

FIGURE

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Pittsburgh, PA 15203

Sheraden Park Surban Street, 20th Ward, City of Pittsburgh, Allegheny County, PA

GEOHAZARD REVIEW

KLAVON DESIGN ASSOCIATES

C-46493

FEB 2024

TYPICAL KEYWAY

AND BENCH

DETAIL

LIMIT OF REMOVAL

TEMPORARY FILL

BENCH OR STOCKPILE

EXISTING CROSS-SLOPING

GROUND SURFACE

STIFF OR STIFFER COLLUVIAL

OR RESIDUAL SOIL

COLLECTOR DRAIN

(SEE DETAIL "B")

PROPOSED

TOE OF SLOPE

BELOW TOE

OF RESTORED

RIGHT OF WAY

KEYWAY OR BENCH FIELD

DRAIN (SEE DETAIL "A")

OUTLET DRAIN

(SEE DETAIL "B")

TY

P)

15' MIN. WIDTH

15' MIN. WIDTH

(MAX SLOPE)

KEYWAY

BENCH

NOTE:

LOCATION AND EXTENT OF

COLLECTOR / OUTLET DRAINS TO

BE DETERMINED IN THE FIELD

4" PERFORATED

PLASTIC PIPE

GEOTEXTILE

FILTER FABRIC

COARSE AGGREGATE

(AASHTO #57)

12" MIN

" M

IN

FIELD DRAIN

4" PERFORATED

PLASTIC PIPE

GEOTEXTILE

FILTER FABRIC

COARSE AGGREGATE

(AASHTO #57)

12" MIN

" M

IN

" M

IN

NEED FOR, AND EXTENT OF,

GRAVEL BLANKET TO BE

DETERMINED IN THE FIELD

FIELD DRAIN WITH OPTIONAL

GRAVEL BLANKET

6" SOLID

PLASTIC PIPE

GEOTEXTILE

FILTER FABRIC

COARSE AGGREGATE

(AASHTO #57)

COMPACTED

BACKFILL

GROUND

SURFACE

18" MIN

VA

R

IE

S

" M

IN

COLLECTOR / OUTLET DRAIN

DETAIL "A" DETAIL "B"

PROPOSED FILL

SLOPE