Langan Storm Sewer Report.pdf

Technical Memorandum

1300 Wilson Boulevard, Suite 450, Arlington, VA 22209 T: 571-366-6800 F: 571-366-6801

To: Christa J. Gaffigan

From: Juan C. Osorio

Info: Anne Weber

Date: 19 March 2018

Re: Storm Sewer – Pipe Cleaning and Condition Assessment

Meridian Hill Park

2330 15th Street, Washington, DC 20009

Langan Project No.: 270060901

Langan Engineering and Environmental Services prepared this memorandum to summarize the conditions of the existing storm sewer pipe network at the lower plaza and upper terrace of the

Meridian Hill Park. The following findings are based on our field observations conducted by Langan personnel and our review of the inspection videos performed by Master Locators Inc., the contractor, on November 21st and 27th, and December 5th, 2017.

Investigation Approach and Pipe Condition Classifications

The contractor manually removed plant material, roots, soils and debris from all the accessible storm system structures, including trench drains, inlets, gutters and catch basins. Where possible, the pipes were hydro-blasted, cleaned and flushed to the next downstream structure, but the high state of disrepair of the system severely limited the amount of investigation that could be accomplished within the allotted timeframe and budget.

In an effort to maximize the results from our storm pipe investigation, and based on the results from our geotechnical investigation, which recommended that the upper plaza be over excavated and backfilled, we focused the hydroblast and video inspection on the Lower Plaza area. Visual observations of all inlets and storm pipes on the Upper Plaza were conducted using traditional survey methods. Figure 1 shows the pipes that were hydroblasted (green), not accessible (yellow) and not found (red).

Based on our site observations and the review of the inspection videos of the accessible pipes, we categorized each pipe based on the following criteria:

Failed Condition (Red) - This classification was assigned to pipes that have completely failed, have significant joint displacement, large fractures, or have large tree root infiltration. Approximately 50-

LF of 8-inch and 10-inch diameter pipes were identified in this category. It is our recommendation that these pipes be replaced as part of the Meridian Hill Park upgrade project to ensure adequate drainage is provided.

TECHNICAL

MEMO

Storm Sewer – Pipe Cleaning and Condition Assessment

Meridian Hill Park

Washington, DC 20009

Langan Project No.: 270060901

19 March 2018- Page 2 of 2

Critical Condition (Green) - This classification was assigned to pipes that show signs of disrepair, have cracks, small offset joints, and small root infiltration. A total of approximately 450-LF of pipes ranging from 6-inch to 10-inch in diameter were identified in this category. It is our recommendation that these pipes be cleaned, repaired and monitored to avoid a potential failure.

Fair Condition (Blue) - This classification was assigned to pipes that show minor signs of disrepair, pipes that have small cracks, or pipes that have small offset joints but are adequately conveying storm flows. A total of 450-LF of pipes ranging from 6-inch to 12-inch in diameter were identified in this category. It is our recommendation that these pipes be included in a regular monitoring and maintenance program to ensure adequate performance in the future.

Inaccessible (Orange) - This classification was assigned to pipes that were not accessible due to the high density of debris and tree roots intrusion. Based on our observations during the assessment process, these pipes provide inadequate drainage. It is safe to assume that these pipes are in critical condition since they do not convey flow as intended. In the case of the Upper Terrace, it is safe to assume that due to the confirmed settlement most of the existing pipes are either cracked or disconnected from the inlet structure. It is our recommendation that these pipes be treated the same as pipes classified as critical. Approximately 1,550-LF of pipes ranging between 4-inch and 12-inch in diameter were identified in this category.

In addition to the pipes we made general observations of the storm inlet structures, and classified them using the same rating system. Figure 2 and 3 identify the condition of the existing pipes and structures within the Lower Plaza and the Upper Terrace using the above classification. Screenshots of the video assessment and field photographs illustrating the above categories are included in

Attachment A.

Lower Plaza Recommendations

In general the existing stormwater conveyance system on the Lower Plaza has failed and is in critical condition. Based on field observations, runoff sheet flow toward W Street is causing overland causing soil erosion and potential icing issues. It is our recommendation that the conveyance system be cleaned, repaired, and replaced per the criteria above.

Initial observation of the existing storm conveyance structures shows that they are in good condition, but further investigation should be completed to assess their structural stability. In many places the existing inlet and trench drain grates are missing or completely broken, and must be replaced.

Upper Terrace Recommendations

Per our geotechnical findings, the majority of the upper plaza paving will need to be excavated and re-compacted to address the existing settlement. It is our recommendation that the entire upper plaza drainage system be completely removed and replaced with new infrastructure. Additional investigation must be conducted to assess the structural condition of the existing inlets and determine if they can be re-used in the future. New grate inlets with more flow capacity are recommended to enhance the performance of the conveyance system. Field photographs of the upper plaza can be seen as Attachment B.

Filename: \\langan.com\data\ARL\data9\270060901\Project Data\CAD\01\SheetFiles\Storm Documentation Location Plan.dwg Date: 12/18/2017 Time: 17:29 User: cchekan Style Table: Langan.stb Layout: ANSIB-BL

1300 Wilson Boulevard, Suite 450

Arlington, VA 22209

T: 571.366.6800 F: 571.366.6801 www.langan.com

L a n g a n

Filename: \\langan.com\data\ARL\data9\270060901\Project Data\CAD\01\SheetFiles\Strom Assessment Plan.dwg Date: 12/18/2017 Time: 21:13 User: jcanchan Style Table: Langan.stb Layout: ANSIB-BL

Arlington, VA 22209

T: 571.366.6800 F: 571.366.6801 www.langan.com

L a n g a

Arlington, VA 22209

T: 571.366.6800 F: 571.366.6801 www.langan.com

L a n g a

Filename: \\langan.com\data\ARL\data9\270060901\Project Data\CAD\01\SheetFiles\Figure 3 - Upper Terrace.dwg Date: 1/4/2018 Time: 15:07 User: jcanchan Style Table: Langan.stb Layout: Upper Terrace

ATTACHMENT A

LOWER PLAZA VIDEO

SCREENSHOTS AND FIELD

PHOTOGRAPHS

Representative Photos

Failed

Failed: Turf-like Sediment and Tree Root Intrusions

Failed: Joint Fractured, Soil is Visible.

Critical

Critical: Offset Joint Turf-like System of Roots Compromising Pipe Capacity.

Critical: Root infiltration.

Fair Condition

Fair Condition: Small cracks in top of pipe.

Fair Condition: Minor Offset joints.

Inaccessible

Inaccessible: Debris and Dense Tree Roots Clogging the Pipes

Inaccessible: Catch Basin Buried Under Soil (Left); Drain Inlet Welded and Filled with Debris (Right)

Typical Catch Basin Grate and Slit Drain Condition

Catch Basin Grate Corroded

Wide Cracks and Exposed Soil at the Bottom of the Slit Drain.

ATTACHMENT B

UPPER TERRACE

PHOTOGRAPHS

Trench Drain Channel Filled with Tree Roots and Soil

Trench Drain Bottom Outlet Filled with Soil and Debris

Trench Drain Channel Filled with Soil

Trench Drain Channel Filled with Debris and Trash

Drainage Inlet Filled with Soil and Vegetation Roots

Trench Drain Channel Filled with Soil and Debris

BENCHMARKS

NO ELEV DESCRIPTION

872 HV 95003 198.66 BRASS DISK

BM-63 141.14 PK-NAIL

872 HV 95005 138.79

BRASS DISK (NF)

BENCHMARKS

NO ELEV DESCRIPTION

872 HV 95003 198.66 BRASS DISK

BM-63 141.14 PK-NAIL

872 HV 95005 138.79

BRASS DISK (NF)