Flood Mitigation and Prevention

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Do not remove this notice

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Flood Mitigation and Prevention

Draft Study

GSA FEDERAL TRIANGLE BUILDINGS

WASHINGTON, DC

INTERNAL REVENUE SERVICE

DEPARTMENT

OF

JUSTICE

DEPARTMENT OF COMMERCE

OLD POST OFFICE ANNEX

January 23, 2007

General Services Administration

National Capital Region

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PROPERTY OF THE UNITED STATES GOVERNMENT

COPYING, DISSEMINATION, OR DISTRIBUTION OF THIS REPORT

TO UNAUTHORIZED USERS IS PROHIBITED

DO NOT REMOVE THIS NOTICE

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Draft Study

January 23, 2007

FLOOD MITIGATION AND PREVENTION

INTERNAL REVENUE SERVICE

DEPARTMENT OF JUSTICE

DEPARTMENT OF COMMERCE

OLD POST OFFICE ANNEX

GSA FEDERAL TRIANGLE BUILDINGS

WASHINGTON, DC

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1.3 Recommendations

2. Introduction... 5

3. June 2006 – The Flood Event ... 7

3.1 Peak Rainfall

3.2 Peak Stage / High Water Marks

3.3 Historical Flooding Events

4. Causes and Extent of Flooding ... 13

4.1 Constitution Avenue: Street Flooding Evaluation

4.2 Street Level

4.3 Internal Revenue Service Building

4.4 Department of Justice Building

4.5 Department of Commerce Building

4.6 Old Post Office Annex

5. D.C. Water and Sewer Authority ... 33

5.1 WASA Organizational Structure

5.2 WASA System Overview

5.3 Combined Sewer Overflows (CSO)

5.4 June 2006 Event

5.5 Possible Scenarios to Rapid Rise and Fall of Flooding on Constitution Avenue

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6. Government Communications Protocols ... 44

6.1 Department of Homeland Security

6.6 D.C. Water and Sewer Authority Communications

6.7 D.C. Emergency Management Agency

6.8 Protocol Recommendations

7. Flood Mitigation Alternatives... 48

7.1 Introduction

7.2 Site and Exterior Modifications

Appendices: (Separate report)

Appendix A: WASA System, Existing Conditions and DC-EMA Maps

Appendix B: Government Correspondence/Meeting Minutes

Appendix C: Photographs – Internal Revenue Service Building

Appendix D: Photographs – Department of Justice Building

Appendix E: Photographs – Department of Commerce Building

Appendix F: Photographs – Old Post Office Annex

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Headquarters, Old Post Office (OPO) Annex, and the Department of Commerce (DOC) at Ariel Rios and its surroundings within the Federal Triangle were evaluated within the context of mitigating future flood damage. Mitigation alternatives focused the following elements:

• Enhancing protocols between the Federal Government and the District of Columbia Water and Sewer Authority (WASA)

• Creating physical barriers around the buildings to block floodwaters • Relocating critical building systems to points above the flood level

• Providing a better means to physically extract flood waters infiltrating the buildings • Utilizing a pumping station and storm drain upgrades to reduce flood depths on

Constitution Avenue, NW

Each of these measures may be considered in whole or in part, and each of them have varying degrees of physical impact to the use, occupancy, operations, and historic fabric of each building. The impact to the existing and possible future spatial configurations will require consultation and coordination with each building’s facilities group. The integration of these measures should also be evaluated within the context of future building modernization plans (not presently within the scope of this work). In addition, there are significant cost implications associated with each measure considered. The restoration measures taken to date at the IRS and DOJ buildings have only brought the buildings back to pre-flood conditions.

The Federal Triangle is located in Northwest Washington, DC, within the Pennsylvania Avenue National Historic District. The buildings included in this study are prominent and historically significant structures within the Historic District. As a result, any and all proposed measures to mitigate future flood damage which impact the site, surroundings, façades, and historic fabric will require coordination with GSA’s Historic Preservation Officer, a Section 106 Review, and approvals by the Advisory Council on Historic Preservation, State Historic Preservation Office, National Capital Planning Commission, and the Commission of Fine Arts. Individual building measures will be reviewed within the context of the overall planning guidelines established by these agencies for the monumental corridor. In addition, these measures would also interface with the National Capital Urban Design and Security Plan.

1.2 Results and Findings

The most intense 24-hour portion of the June 2006 storm event dropped 7.01 inches of rain. The historic rainfall data indicates at least three other 24-hour rainfall totals on record that were approximately 7 inches. By comparison to standard design storm events for engineering studies, a storm event in the DC area that is believed to have a recurrence interval of 50 years (a.k.a. the 50-Year Event) would result in approximately 7.04 inches of rainfall over a 24-hour period. By comparison, the DC WASA system for street drainage is reported to try and achieve a 15-year,

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24-hour performance standard (approximately 5.5 inches of rainfall). It is important to note that the flooding began on Constitution Avenue at 10:30 p.m. after only approximately 2.25 inches of rain had fallen in a 3-hour period. If the rain had stopped at the time of the power failure, the 2.25 inches of rain would have been considered much less than the 15-year event that the WASA sewer system should be designed to handle. According to the NOAA Precipitation Frequency Data Chart in Figure 1-1, the June 2006 event came very close to a 3-hour rainfall for only a 5-year event.

The preliminary results of the analysis seem to indicate that each building was capable of handling the storm water until such time that the infrastructure in the adjacent roadways failed to accommodate the flow of storm water and overflows started to occur. This failure resulted in an extreme and rapid rise in floodwaters on Constitution Avenue, resulting in the backup of storm water into the buildings and subsequent disruption of electrical service to support pumping causing additional rise in floodwaters and further failure of interior building systems.

Estimates of water infiltration volumes suggest that the Internal Revenue Service Building flooded with approximately 6 million gallons and the Department of Justice Building flooded with approximately 3.5 million gallons. This is compared to an estimated 38 million gallons of storm water in Constitution Avenue at peak stage.

According to information obtained through interviews, the main flooding of the Department of Justice Building occurred between 10:00 p.m. and 1:00 a.m. An IRS building security guard report stated that the power failed at 10:32 p.m. and power resumed at 10:42 p.m., when the emergency generator started. The lights began flickering at 10:45 p.m. and at approximately 10:55 p.m. the emergency generator was overwhelmed by the flooding and failed. Video surveillance tapes provided by the Department of Justice Building show that the water level on Constitution Avenue rose most substantially between 10:00 p.m. and 10:30 p.m. It is important to note that both the Department of Justice Building and the Internal Revenue Service Building flooded, but in very different manners.

The Internal Revenue Service Building had water penetration at the perimeter moats along 10th Street, Constitution Avenue, and 12th Street. Excessive hydrostatic pressure built up and caused a number of window assemblies to fail. Alternately, the Department of Justice had a 15-inch storm water sewer main fail in the basement, causing severe flooding near an adjacent electrical room. Water did not penetrate the Department of Justice Building through the moats. Both buildings had secondary flooding through electrical service duct banks, abandoned duct banks, and miscellaneous pipe penetrations.

When water started entering both buildings, the electrical rooms located on the lower levels, as well as emergency power equipment, were flooded and failed. After primary power and emergency power failure, the storm water pumps could no longer operate and the buildings quickly filled with water due to the street flooding and also from the building storm water system.

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NOAA, National Weather Service, Silver Spring, Maryland, 2004, Extracted: Thu Sep 28 2006 G.M. Bonnin, D. Martin, B. Lin, T. Parzybok, M.Yekta, and D. Riley

from "Precipitation-Frequency Atlas of the United States" NOAA Atlas 14, Volume 2, Version 3

WASHINGTON REAGAN AP, VIRGINIA (44-8906) 38.865 N 77.0342 W 22 feet

NOTE - Worst-Case Rainfalls in June 2006 was 3.73” (3hr), 5.91” (6hr), 7.01” (24hr), 9.41” (48hr) and 12.11 (7 day)

Source

-ARI* 5 10 15 30 60 120 3 6 12 24 48 4 7 10 20 30 45 60

(years) min min min min min min hr hr hr hr hr day day day day day day day

1 0.36 0.57 0.71 0.97 1.21 1.41 1.50 1.84 2.22 2.57 2.99 3.33 3.85 4.41 5.95 7.32 9.19 10.94 2 0.43 0.68 0.86 1.18 1.49 1.71 1.83 2.23 2.67 3.11 3.62 4.02 4.64 5.29 7.07 8.66 10.84 12.86 5 0.51 0.81 1.03 1.46 1.87 2.17 2.32 2.81 3.40 4.00 4.64 5.14 5.86 6.61 8.55 10.30 12.67 14.86 10 0.57 0.91 1.15 1.66 2.16 2.52 2.71 3.29 4.02 4.78 5.51 6.10 6.91 7.71 9.74 11.62 14.08 16.37 25 0.64 1.02 1.30 1.92 2.56 3.02 3.26 4.00 4.97 5.98 6.83 7.55 8.48 9.31 11.41 13.43 15.93 18.32 50 0.70 1.11 1.41 2.12 2.87 3.43 3.72 4.61 5.80 7.04 7.98 8.80 9.83 10.65 12.76 14.88 17.35 19.77 100 0.75 1.20 1.51 2.31 3.19 3.85 4.21 5.26 6.72 8.24 9.25 10.20 11.32 12.11 14.16 16.36 18.73 21.16 200 0.81 1.28 1.61 2.51 3.52 4.30 4.72 5.97 7.75 9.61 10.68 11.75 12.96 13.67 15.61 17.88 20.09 22.48 500 0.87 1.38 1.74 2.77 3.97 4.93 5.45 7.01 9.32 11.71 12.83 14.08 15.42 15.98 17.63 19.94 21.84 24.16 1000 0.93 1.46 1.83 2.97 4.33 5.44 6.06 7.89 10.67 13.55 14.68 16.08 17.51 17.89 19.22 21.55 23.14 25.37

Precipitation Frequency Estimates (inches)

this common wall location. It should also be noted that the penetrations through this wall may pose security and fire integrity issues as well.

Figure 1-1: NOAA Precipitation Frequency Data Server

1.3 Recommendations

The recommendations for the IRS and Department of Justice buildings are numerous, starting with a single level and proceeding to a multi-level effort. Consideration will be given to the reliability of each proposed alternative, including consequences of a failure of the proposed method to adequately control floodwaters entering the buildings. Since the Department of Commerce Building and the Old Post Office Annex flooded in clearly defined ways, there are more defined alternatives available to prevent future water intrusion. The Internal Revenue Service and Department of Justice buildings by comparison have multiple alternatives which need consideration as viable to move forward. A feasibility study should be pursued to clearly assess the best available alternative.

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MATRIX OF FLOOD MITIGATION ALTERNATIVES

AREA DESCRIPTIONS LEVEL OF PROTECTION COMMENTS COST RANGE

Protocols A. HIGH LEVEL DIRECT COMMUNICATION HIGH Direct communications between WASA, DCEMA, and GSA Minor

BETWEEN GOVERNMENT AGENCIES

B. EMERGENCY ACTION PLAN FOR EACH BUILDING HIGH Minor

Site and Exterior A. UPGRADE WASA STORM WATER CAPACITY FOR A 50-YEAR EVENT HIGH WASA system designed for a 15-year event currently – Large capital improvement costs TBD

B. PUMPING STATION & CONVEYANCE SYSTEM MED Viable alternative requiring interagency cooperation $5 M - $10 M

C. CATCH BASIN MAINTENANCE IMPROVEMENTS LOW Controlling litter may avoid system blockages $10 M

D. SIDEWALK LEVEE SYSTEM HIGH Significant impact to surroundings $9 M - $15M

IRS Building A. SEAL ABANDONED FEEDERS HIGH Recommended, easy to implement $20k - $50k

B. WATER TIGHT FIRE PUMP ROOM HIGH Life safety equipment must remain operational $100k - $150k

C. FLOOD GATES/REMOVABLE BARRIERS MED Minimizes water infiltration $200k - $500k

D. GROUND WATER PUMPING STATIONS MED Extensive modifications to building infrastructure $1 M - $2 M

E. RELOCATE EMERGENCY POWER EQUIPMENT HIGH Recommended $2 - $4 M

F. IMPROVED STORM/BLAST WINDOWS MED Minimizes water infiltration $3 M - $5 M

G. WINDOW WELL WATER-TIGHT COVERS MED Deployment difficulties $3 M - $5 M

H. EARTHEN BERMS LOW Impractical $4M - $6M

I. MOAT WALL EXTENSIONS MED Minimizes water infiltration $7 M - $10 M

J. RELOCATE MAJOR MECHANICAL AND ELECTRICAL SYSTEMS HIGH Extensive modifications to building infrastructure $40 M - $50M

DOJ Building A. STORM WATER PIPING MODIFICATIONS HIGH Recommended, easy to implement $25k

B. SEAL UTILITY PENETRATIONS HIGH Recommended, easy to implement $20k - $50k

C. ISOLATE ELECTRICAL ROOM HIGH Recommended, easy to implement $100k - $150k

D. ISOLATE FIRE PUMP ROOM HIGH Life safety equipment must remain operational $100k - $150k

E. FLOOD GATES MED Minimizes water infiltration $800k - $1.2M

F. RELOCATE EMERGENCY POWER HIGH Recommended $1.5M - 2.5M

G. RAISE RETAINING WALLS ON CONSTITUTION AV ENUE LOW Existing moats provided protection during event $2 M - $3 M

H. RELOCATE MAJOR MECHANICAL AND ELECTRICAL HIGH Extensive modifications to building infrastructure $30M - $40M

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The General Services Administration has contracted Setty & Associates, Ltd. to investigate the heavy rainfall that occurred in June 2006 for its impact on limited buildings in the Federal Triangle area. The focus of this study is limited to four prominent buildings, including the Department of Justice (DOJ), Internal Revenue Service (IRS) Headquarters, Old Post Office Annex (OPO), and the Department of Commerce (DOC) at Ariel Rios. The study area is bounded by Constitution Avenue, NW; Pennsylvania Avenue, NW; 13th Street, NW; and 9th Street, NW.

The study includes a description of the June 2006 flood, analysis of flood severity in comparison to historical events, causes and extent of flooding within the study area, an investigation of emergency event protocols for various parties involved, and concepts for mitigating or reducing the likelihood of future flooding problems within the buildings included in the study. The study will not serve as a guideline to protect the entire Federal Triangle area from future flooding, but only as an investigation as to protecting the aforementioned buildings.

Proposed modifications to the site, surroundings, façades, and interior historic fabric resulting from the recommendations contained in this report will require further research, design details, and close coordination with the GSA’s Historic Preservation Officer, a Section 106 Reviews, and approvals by the State Historic Preservation Office, the National Capital Planning Commission, the Commission of Fine Arts, and the Advisory Council on Historic Preservation.

The Scope of Work for this study is as follows:

A. Review the operations of the District of Columbia’s storm and sanitary sewer system, WASA, and its Blue Plains treatment plant to ascertain what, if any, relationship these have to the flooding conditions occurring in the foreseeable future.

1. Make any recommendations for appropriate communication protocols between GSA and the District in future events of comparable rainfall.

2. Review reports of rapid water reductions on the Constitution Avenue corridor at approximately 4:30 a.m., Monday, June 26, 2006.

3. Review the current maximum capacity/throughput of WASA’s Blue Plains treatment plant to handle combined stormwater and sanitary sewage and WASA’s future plans. B. Provide study services including cost estimates for each building listed below:

1. IRS Building

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b. Provide analysis and recommend actions the government can take to prevent similar flooding. Compile data including, but not limited to, photographs. Interview GSA building managers and agency personnel. Indicate priority of work. The A/E shall explore all alternatives including but not limited to:

1)

Multi-stage ground water pumping systems with emergency power.

2)

Berms / Barriers.

3)

Window well watertight coverings.

4)

Improved storm/blast windows.

5)

Recommendations to move all the HVAC/electrical equipment to other areas

utilizing the Flood Damage Report.

c. All recommendations need to comply with relevant codes and governing authorities’ requirements; National Capital Planning Commission, Commission of Fine Arts, National Historic Preservation Guidelines, DC Department of Public Works Streetscape requirements, etc.

d. Utilize information contained in the following reports:

1)

Flood Damage Assessment Report for the IRS Building dated July 5, 2006, by

Jacobs Facilities Inc.

2)

Flood Damage Phasing Construction Assessments; draft dated August 2, 2006.

2. Department of Justice Building

a. Study the existing garage doors at basement level to act as floodgates in similar flood events. Provide recommendations to modify garage doors to behave as such.

b. Study and make recommendations to make utility penetrations at the basement and foundation walls watertight, such as PEPCO electric feeders.

c. Evaluate the feasibility of raising retaining walls on Constitution Avenue, raising equipment bases/footings and relocating HVAC and electric equipment from basement/sub-basement to the roof and other areas.

3. Department of Commerce Building

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including the 3-hour total (3.73 inches) and the 6-hour total (5.91 inches) for June 2006.

Figure 3-1: Hourly Rainfall for the Worst Case 24-Hour Period, June 25 – June 26, 2006

Chief meteorologist, Jim Lee, from the National Weather Service in Sterling, Virginia, stated that the cause of the heavy rainfall was a “tropical connection” that funneled an extremely wet air mass up the East Coast. The moist air was up against a stationary front that had hung over the Mid-Atlantic region for that past week. The following figure outlines some of the problems caused by the heavy rain in the District of Columbia Metropolitan Area.

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Figure 3-2: Chaos created in the DC Metropolitan Area by the June 2006 Inundation

3.2 Peak Stage / High Water Marks

Peak stage for the June 2006 event was not as historically significant as the extreme rainfall that is noted above in this study. The U.S. Army Corps of Engineers has indicated that the Potomac River peak stage was measured at 9.5 feet at the Little Falls Gauging Station in their letter to the U.S. Attorney General dated July 14, 2006, included in Appendix B. This peak stage is a little higher than the peak stage indicated on the United States Geological Service (USGS) website of 7.94 feet (76,800 cubic feet per second) on June 29, 2006. Either 9.5 feet or 7.94 feet is a low peak stage when compared to historical records for the Little Falls Stream Gauge (USGS

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Date Flow, cfs Stage, ft Date Flow, cfs Stage, ft

April 3, 1931 37,900 6.90 March 27, 1969 30,600 5.75 May 14, 1932 168,000 15.25 April 3, 1970 95,600 9.34 April 22, 1933 127,000 12.80 February 24, 1971 91,200 9.15

March 15, 1900 53,500 7.80 June 24, 1972 359,000 22.03 (Hurricane Agnes) December 2, 1934 139,000 13.50 October 8, 1972 90,800 9.08 March 19, 1936 484,000 28.10 December 28, 1973 120,000 10.36 April 28, 1937 347,000 23.30 September 27, 1975 195,000 13.39 October 30, 1937 181,000 15.62 January 3, 1976 103,000 9.59 February 5, 1939 129,000 12.60 October 11, 1976 208,000 13.18 April 22, 1940 107,000 11.29 March 16, 1978 153,000 10.83 April 7, 1941 73,300 9.07 February 26, 1979 206,000 13.12 May 24, 1942 139,000 13.17 October 12, 1979 81,700 8.15 October 17, 1942 447,000 26.88 April 15, 1981 55,000 6.95 May 9, 1944 77,800 9.43 June 15, 1982 102,000 8.91 September 20, 1945 138,000 13.88 April 26, 1983 128,000 9.81 June 4, 1946 69,000 9.47 February 16, 1984 222,000 13.73 March 17, 1947 43,900 7.53 February 14, 1985 106,000 9.08 April 16, 1948 97,300 10.69 November 7, 1985 317,000 17.99 June 20, 1949 135,000 13.00 April 19, 1987 167,000 11.41 February 3, 1950 77,200 10.01 May 20, 1988 129,000 9.83 December 6, 1950 140,000 13.85 May 18, 1989 107,000 9.10 April 29, 1952 148,000 14.17 May 31, 1990 61,000 7.24 November 23, 1952 140,000 13.76 October 25, 1990 102,000 8.94 March 3, 1954 116,000 12.47 April 24, 1992 106,000 9.07 August 20, 1955 216,000 17.60 March 6, 1993 189,000 12.35 July 21, 1956 72,500 10.75 March 30, 1994 142,000 10.37 April 7, 1957 78,600 11.40 January 17, 1995 101,000 8.90 May 7, 1958 82,100 12.02 January 21, 1996 347,000 19.29 June 4, 1959 61,400 9.61 December 3, 1996 105,000 9.02 May 10, 1960 124,000 13.66 March 22, 1998 152,000 10.79 February 21, 1961 116,000 13.15 March 20, 1999 46,400 6.51 March 23, 1962 120,000 13.43 February 21, 2000 63,500 7.36 March 21, 1963 128,000 13.91 March 23, 2001 75,200 7.88 March 6, 1964 94,800 11.85 April 24, 2002 55,400 6.97

March 7, 1965 111,000 9.98 September 21, 2003 167,000 11.44 (Hurricane Isabel) February 15, 1966 88,700 9.04 December 12, 2003 154,000 10.87

March 9, 1967 147,000 11.48 March 30, 2005 140,000 10.28 March 18, 1968 81,400 8.71 June 29, 2006 76,800 7.94

Maximum Flow = 484,000 cfs

Peak Stage = 28.10 ft

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Photo 3-1: 1881 High Water Mark on Constitution Avenue

This study included data collection in the field, but there were no apparent June 2006 high water marks (i.e., stains, debris, etc.) visible. Reports varied as to the depth of the flooding since it occurred in the middle of the night, however, the videotape seemed to indicate floodwaters near the top of the concrete planters along Constitution Avenue, which is approximately an elevation of 11.0 feet (3-foot depth of flooding on sidewalks).

The high watermark at the intersection of Constitution Avenue and 15th Street NW was also considered. This watermark is believed to indicate a “worst case” flooding near the Federal Triangle of approximately 38 inches above the sidewalk elevation (11.2 feet) on February 12, 1881. The actual flood depth and condition on Constitution Avenue was obtained from the watermark as shown in Photo 3-1.

3.3 Historical Flooding Events

There are many historic storm events resulting from either a peak stage in the Potomac River or flooding in city streets due to excessive local rainfall. Some of these are described below for further comparison to the June 2006 event.

The old pump house at the intersection of Constitution

Avenue and 15th StreetNWis marked 38 inches above

the sidewalk elevation (approximately 8.0 feet) and is labeled “February 12, 1881”. History documents that during the flood of 1881, raw sewage, which had inundated the swamp at Potomac Flats, mixed with the floodwaters and reached to within three blocks of the White House in this area. The 1881 flood prompted Congress to fund the dredging of Potomac Flats, creating what is now known as Potomac Park.

On June 2, 1889, a 2-day rainfall of 4.4 inches caused a peak stage in the Potomac River of 19.5 feet, which is a crest elevation 12.5 feet above flood stage. This is still the unofficial record and the photograph below shows where flooding along Pennsylvania Avenue between 9th and 10th Streets was between 1 and 4 feet in depth.

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Photo 3-3: 1942 Floodwaters around the Jefferson Memorial (NOAA Library)

Hurricane Camille passed nearest the District of Columbia area in August 20, 1969, however the worst flooding occurred just prior to the hurricane on July 22, 1969. This peak rainfall event dropped 3.29 inches of rainfall in one hour (4.38 inches total rainfall), causing localized flash flooding throughout the District of Columbia. The June 2006 event is reported in this study to have dropped 3.16 inches in approximately one hour, which is very similar over a short duration of time.

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The remnants of Hurricane Agnes passed through three years later on June 21, 1972, when Agnes dropped a total of 7.19 inches in a 24-hour period. On November 27, 1993, flash flooding occurred when 6 inches of nearly continuous rainfall fell across the city in a 12-hour period. Floods from January 20 to 23, 1996, were a result of a combination of up to 2 inches of snowmelt and up to 3 inches of rain. The river crested at 13.88-feet near Wisconsin Avenue. At Great Falls, 15 miles upstream, the Potomac River raised a reported 8.5 feet in 48 hours.

Photos 3-5 & 3-6: Rapid Rise of Floodwaters in January 1996 at Great Falls (National Park Service)

More recently, the eye of Hurricane Floyd passed just southeast of the District of Columbia late in the evening on September 16, 1999. Up to 6 inches of rain fell across the District of Columbia, with 4.57 inches measured at Reagan National Airport. Two years later, flash flooding on August 11, 2001, dropped an estimated 7 inches of rain in one day in Northwest DC, but only 2 inches in Southeast DC. The 2001 cloudburst caused a reported $6 million in damage to 50 governmental buildings and more than 3,000 homes in the Metropolitan Area as storm drain systems were overwhelmed. In some parts of the District of Columbia, between 5 and 7 inches of rain fell in less than three hours, following heavy rainfall from the preceding day.

On September 23, 2003, heavy rain fell on ground previously saturated by Hurricane Isabel, which had struck a few days before on September 18, 2003. Numerous roads began flooding during rush hour, including Constitution Avenue, and rainfall totals were approximately 3 inches for the event. The June 2006 event has similarities to many of

these historic events and will be considered in future years as another flash flooding event resulting from heavy rainfall in short durations. The resulting flooding and overwhelmed storm drainage systems can be expected to continue in

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NOTE - Worst-Case Rainfalls in June 2006 was 3.73” (3hr), 5.91” (6hr), 7.01” (24hr), 9.41” (48hr) and 12.11 (7 day)

Source

-ARI* 5 10 15 30 60 120 3 6 12 24 48 4 7 10 20 30 45 60

(years) min min min min min min hr hr hr hr hr day day day day day day day

1 0.36 0.57 0.71 0.97 1.21 1.41 1.50 1.84 2.22 2.57 2.99 3.33 3.85 4.41 5.95 7.32 9.19 10.94 2 0.43 0.68 0.86 1.18 1.49 1.71 1.83 2.23 2.67 3.11 3.62 4.02 4.64 5.29 7.07 8.66 10.84 12.86 5 0.51 0.81 1.03 1.46 1.87 2.17 2.32 2.81 3.40 4.00 4.64 5.14 5.86 6.61 8.55 10.30 12.67 14.86 10 0.57 0.91 1.15 1.66 2.16 2.52 2.71 3.29 4.02 4.78 5.51 6.10 6.91 7.71 9.74 11.62 14.08 16.37 25 0.64 1.02 1.30 1.92 2.56 3.02 3.26 4.00 4.97 5.98 6.83 7.55 8.48 9.31 11.41 13.43 15.93 18.32 50 0.70 1.11 1.41 2.12 2.87 3.43 3.72 4.61 5.80 7.04 7.98 8.80 9.83 10.65 12.76 14.88 17.35 19.77 100 0.75 1.20 1.51 2.31 3.19 3.85 4.21 5.26 6.72 8.24 9.25 10.20 11.32 12.11 14.16 16.36 18.73 21.16 200 0.81 1.28 1.61 2.51 3.52 4.30 4.72 5.97 7.75 9.61 10.68 11.75 12.96 13.67 15.61 17.88 20.09 22.48 500 0.87 1.38 1.74 2.77 3.97 4.93 5.45 7.01 9.32 11.71 12.83 14.08 15.42 15.98 17.63 19.94 21.84 24.16 1000 0.93 1.46 1.83 2.97 4.33 5.44 6.06 7.89 10.67 13.55 14.68 16.08 17.51 17.89 19.22 21.55 23.14 25.37

Precipitation Frequency Estimates (inches)

The National Atmospheric and Oceanic Administration (NOAA) National Weather Service (NWS) Precipitation Frequency Data Server was utilized in comparing the June 2006 rainfall totals with reported design rainfall events. This data represents the latest statistical analysis of rainfall at the Reagan National Airport, last updated in September 2004. Highlighted in red are rainfall depths that most closely resemble the measured June 2006 rainfall over 3-hour, 6-hour, 24-hour, 48-hour, and 7-day lengths of time. Highlighted in yellow is the range of recurrence intervals associated with the June 2006 event, which was determined in this study to fall between a 50-Year and 200-Year Event depending on the duration of time evaluated. In comparison, the DC WASA system for street drainage is reported to achieve an estimated 15-Year, 24-Hour performance standard (approximately 5.5 inches of rainfall). For the purposes of this study, alternatives for the June 2006 actual event are described instead of applying design events reported in the table below. This is because the June 2006 event falls within the range of design events that are considered reasonable and appropriate to evaluating flood protection alternatives in the Federal Triangle area.

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Peak Stage

For the purposes of this study, the estimated high water mark of 11.2 feet from February 12, 1881, is used since it is very similar to the 11.0 feet indicated in the videotapes for June 2006. Other historic events indicate that a flood stage of 11.0 feet has occurred along Pennsylvania Avenue and Constitution Avenue on other occasions. The use of 11.2 feet provides a baseline in this study for the June 2006 event instead of applying design peak stages in the Potomac River (such as the FEMA 100-Year Flood Stage of 13.2 feet). The use of a lower flood stage for this study is reasonable because:

• High water events in the Potomac River typically provide a few days of lead time and the Corps of Engineers will continue to use sandbags to protect against inflows through Potomac Park in this area; and

• The Corps of Engineers has plans described in the letter they provided to develop a more permanent flood protection system in Potomac Park to protect against high flood stages in the Potomac River of 13.2 feet.

This approach to using the 11.2 foot flood stage is considered reasonable and appropriate to evaluating flood protection alternatives in the Federal Triangle area.

Peak Volume / City Topography

City topographic mapping of Washington, DC, at 1-foot contour intervals was also used for the study. The mapping shows a low section of Constitution Avenue in front of the IRS and DOJ buildings at elevation 8.0 feet street centerline. This creates a “bowl” in the city street system which will fill up with water during a flood event, unless the underlying storm drain and combined sewer systems have enough capacity to keep up with the rainfall.

Other low lying areas indicated on the topographic mapping reviewed include the Tidal Basin (Potomac Park) and 3rd Street in front of the U.S Capital. It appears from the topographic mapping that storm water can break out from Constitution Avenue onto 3rd Street at an approximate elevation of 12.0 feet and onto 17th Street NW at an approximate elevation of 14.0 feet. City topographic mapping was also used to determine the total water accumulation volume on Constitution Avenue. For the “worst case” flooding which occurred in February 1881 and appears to have in some ways reoccurred in the June 2006 event, both accumulated approximately 38 million gallons of water in the streets (at elevation 11.0 feet) as shown in Photos 4-1 and 4-2.

TABLE 4-1: WATER ACCUMULATION ON CONSTITUTION AVENUE

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Photos 4-1 & 4-2: Street Flooding at Federal Triangle, June 26, 2006

4.3 Internal Revenue Service Building

The IRS Building is located between Pennsylvania Avenue and Constitution Avenue, and 10th and 12th Streets and is listed in the National Register of Historic Places as part of the Pennsylvania Avenue National Historic Site. The site slopes from a high point of El.16.0’+/- at Pennsylvania Avenue and 12th Street and of El.12.0’+/- at Pennsylvania Avenue and 10th Street to a low point of El.8.0’+/- at Constitution Avenue. The existing first floor is at El.11.63’, the basement is at El.(-)1.37’ and the sub-basement is El.(-)10.37’. The building consists of four quadrants and Courtyards A through D, and the Old Post Office Annex. The service entrance, loading dock, and parking garage ramp are located in Courtyard A and are accessible from 12th Street. Courtyards B, C and D are interior. The childcare playground is located in Courtyard C. The annex and quadrant C adjoin the Old Post Office Pavilion. Moats are located around the perimeter of the building as well as the interior courts.

The primary cause of flooding at the IRS Building resulted from water infiltration at the building perimeter moats along 10th Street, Constitution Avenue and 12th Street. The total amount of water accumulation attributable to rainfall on the building and site represented only 8 percent of the total water volume that flooded the structure, clearly indicating that flooding from the exterior was the major contribution to the problem. (Refer to Table 4-2 for total water accumulations in the basement and sub-basement of the IRS Building and Table 4-3 for a tabulation of all water that fell on the roof of the building from the point when flooding began).

Storm water overflowed the moat gratings approximately 1-foot above grade level, overwhelmed the drainage system, and filled the moats. Excessive hydrostatic pressure was placed on the original double hung steel frame windows and the recently installed operable interior blast window assemblies. A number of the window assemblies failed under the excessive pressure, allowing water to flow into the basement and sub-basement levels. The existing steel frame windows were not air/water tight and the blast window systems were not designed to be waterproof assemblies. The windows were designed only to mitigate flying glass shards following an explosive event. The damage assessment of these windows indicates that the laminated cases absorbed the hydrostatic load placed on them, the glass fractured within the frame, and the load was transferred to the frame with the resultant deformation of the assembly. This level of damage is consistent with the performance criteria for GSA’s Level C criteria, however, the deformation and damage of the assembly obviously allowed for the infiltration of

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water. Figure 4-3 designates the locations of the window wells where water entered the building, with the darker blue arrows indicating heavier water infiltration. As documented in the July 2006 Flood Damage Assessment Report, prepared by Jacobs Facilities Inc., the majority of the window damage was observed along the 10th Street perimeter, some damage was observed along Constitution Avenue, and no damage was observed at the southwest façade at 12th Street. Figure 4-2 illustrates how the water infiltrated through the window wells of the IRS Building.

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The conditions at the interior courtyard moats were quite different than the exterior moats. No window damage or significant water infiltration was observed at the interior locations. This supports the conclusion that the building storm water drainage system and specifically the moat drains were handling the rainfall until such time that the power and pumps failed. Two conditions in service Courtyard A present points of potential water infiltration into the building during an extreme flooding event. The first condition is the parking garage ramp to the basement and the second condition is the entrance at stairwell No. 1103. The high point of the ramp is at El.9.13’ and the low point at basement El.(-)1.37’. The entrance at stairwell No. 1103 is at mid-landing and El.9.8’+/-. Water infiltration at the exterior doors at this point would flow down the stairwell and flood the basement level and potentially the sub-basement.

A secondary contribution to flooding originated from water infiltration at an electrical service duct bank along 12th Street. The duct bank was abandoned and the concrete plugs on the interior of the building appeared to have failed. Evidence at adjacent buildings suggests that the PEPCO street vaults were flooded and resulted in water infiltration through the duct banks.

The total water accumulation within the IRS Building as a result of the flooding was an estimated 6.1 million gallons, indicated by Table 4-2. The sub-basement level was completely inundated under 13 feet of water and the basement was flooded to an average depth of 4 to 5 feet (see Figure 4-4).

TABLE 4-2

Amount of Water accumulated in IRS building

Area (sq ft) Water Depth (ft) Water Accumulation (cu. ft.) Water Accumulation (GAL) SUB BASEMENT 7,298 13 94,874 709,657 BASEMENT 181,827 4 727,308 5,440,264 Total 6,149,921

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Figure 4-4: Flood Level in Basement and Sub-basement of IRS Building

For comparison, Table 4-3 shows the total amount rainfall that fell on the projected roof and courtyard area of the building between the hours of approximately 10:30 p.m. and 6:00 a.m. on June 26. Calculations show that the roof and courtyard areas, which feed into the storm drainage system, accumulated only 492 thousand gallons of water. This represents only about 8 percent of the more than 6 million gallons which flooded the basement and sub-basement areas.

TABLE 4-3

Actual rainfall on IRS building projected area (Roof and Courts)

Area (sq ft) Water Depth (in) Water Accumulation (ft^3) Water Accumulation (GAL) Court A 11,528 4.07 3,910 29,246 Court B 11,528 4.07 3,910 29,246 Court C 11,528 4.07 3,910 29,246 Court D 11,528 4.07 3,910 29,246 Roof 147,959 4.07 50,183 375,367 Total Projected Area 194,071 Total 492,352

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4.4 Department of Justice Building

The Department of Justice Building is located between Pennsylvania Avenue, Constitution Avenue, 9th and 10th Streets. The Building is listed in the National Register of Historic Places as part of the Pennsylvania Avenue National Historic Site. The site slopes from a high point of El.12.0’+/- at Pennsylvania Avenue and 10th Street and of El.10.0’+/- at Pennsylvania and 9th Street to a low point of El.8.0’+/- at Constitution Avenue. The existing first floor is at El.12.0’, the basement is at El.(-)1.0’ and the sub-basement is El.(-)15.5’. The building consists of four quadrants and courtyards A through E. The service entrance and parking garage ramps are located in Courtyard A and are accessible from both 9th and 10th Streets. The Attorney General’s entrance ramp is located under Courtyard E off of 10th Street and the Solicitor General’s entrance ramp is located under Courtyard D off of 9th Street. The moats and basement windows along each of the building’s façades are protected by 42-inch high walls from the sidewalk level.

Figure 4-5: Final Water Levels in the Department of Justice Building

Based on interviews and surveys, it appears as though the DOJ building pumps were initially able to handle the storm run-off into the building. Eyewitness accounts put the water level of Constitution Avenue at approximately 36 inches high at its deepest. This height reached near the

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Photo 4-3: High Water Mark - Planters Photo 4-4: High Water Mark – Moat Wall

The buildup of water on Constitution Avenue was eventually compounded by the water cascading down 9th and 10th Streets. At approximately 10:30 p.m., the water pressure in the main storm discharge line built up, causing the service weight gasket to blow on the main U tube fitting on the line (see Photo 4-5 and Figure 4-6). This fitting is not designed to take larger pressures and it is likely that 5-10 psi of pressure would have dislodged this seal. The seal is designed to relieve the pressure in the pipe so that water does not back up the pipe and flood other floor drains.

Photo 4-5: Storm Water Main which Failed Photo 4-6: Flooded Switchgear Room

Once the pipe had been compromised, the room flooded quickly. Adjacent to this room through an open passageway is the electrical switchgear room. The water quickly entered both spaces and shorted out the electricity. The water level reached 51 inches in the electrical room (see Photo 4-6). The damage was not as severe due to the fact that the equipment was already on a 36-inch platform, which afforded some protection. When the power shorted out, the pumps stopped working initially until the emergency power started. However, the emergency power is supplied by generators which are all located on the basement level. These generators were soon overwhelmed by the floodwaters and ceased operation. Reports stated that the emergency power ran the four sets of building sump pumps for approximately 15 minutes before the generators were inundated and became inoperable. After emergency power was lost, the rain continued for almost three hours with no means of pumping the water out of the building. At this point, water was entering in the building from the Attorney General’s and Solicitor General’s ramps, overwhelming the trench drains.

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Figure 4-6: Primary Means of Basement Flooding, Department of Justice Building

A secondary cause of flooding resulted from water infiltration at an Attorney General’s Ramp at 10th Street and the Solicitor General’s Ramp at 9th Street (see photos 4-7 and 4-8). Additional water flowed into the parking level from the ramps at Courtyard A, overwhelming the trench drains at the base of the ramps (see photos 4-9 and 4-10 on next page). It was also noted that the existing gratings do not span the entire width of the ramps and heavy rainfall tends to flow to the side curbs, overshooting the gratings.

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Photo 4-9: Flooded Courtyard and Tunnel Photo 4-10: Garage Trench Drains

Water was also entering the basement through the PEPCO feeders in the electrical room, which was also the case at the IRS Building (see photo 4-11). As the water level rose on Constitution Avenue, this duct bank started to channel the water into the electrical room. The rate of water entry is not known but eyewitness accounts said that water was flowing through the duct bank.

Photo 4-11: PEPCO Feeders Photo 4-12: IRS Moats and PEPCO Feeders

Water entered the sub-basement mainly through a trap door which is used for moving equipment in and out of the sub-basement. The trap door is located in the loading dock, where the water reached nearly 30 inches in depth at its peak (see photos 4-13 and 4-14).

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Department of Justice Building security staff provided video from security cameras to the project team for the 30 minute period between 10:00 p.m. and 10:30 p.m. on the night of the event. The video tracked rising water to extreme levels along Constitution Avenue, 9th and 10th Streets. Within a very short 15 minute period, water rose to the planter rims and the top main entrance steps. The exterior and interior doors to the Attorney General’s and Solicitor General’s ramps were breached shortly thereafter.

Figure 4-7 offers a perspective of how much rain fell between 10:00 p.m. and 10:30 p.m., when primary power was lost, and how much rain fell after the power was lost. The most significant periods of precipitation occurred between the hours of 9:00 p.m. and 11:00 p.m. and 1:00 a.m. and 2:00 a.m., when over an inch of rain per hour was falling. The heaviest rainfall occurred between the hours of 10:00 p.m. and 11:00 p.m., when two inches of rain accumulated within the hour. It was also during this period of the heaviest rainfall that initial water infiltration into the buildings occurred and continued once the initial barriers were breached.

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the final water depths recorded within the basement and sub-basement areas.

TABLE 4-4

Amount of Water accumulated in DOJ Building

Location Area (sq. ft) Water Depth (ft.) Water Accumulation (cu. ft.) Water Accumulation (GAL.) Sub-Basement 13177 14.5 191067 1429177 Area # 1 10342 2.75 28441 212735 Area # 2 4799 14.5 69586 520500 Area #3 44231 1.5 66347 496272 Area #4 30943 1.5 46415 347180 Area #5 37968 .17 6328 47333 Area #6 4298 3.17 13610 101805 Area #7 8778 4.25 37307 279053 Total 3,434,056

Table 4-5 shows the total amount of water that fell on the Department of Justice Building between the hours of approximately 10:30 p.m. on June 25 and 6:00 a.m. on June 26. Calculations show that the roof and courtyard areas, which feed storm water into the drainage system, accumulated roughly 838,000 gallons of rain water. This represents about 25 percent of the nearly 3.5 million gallons which flooded the basement area. Thus, the Department of Justice Building was flooded by a larger percentage of water that hit the building projected area than the IRS Building. The logical explanation for this discrepancy is the fact that the window wells were penetrated at the IRS Building but were not at the DOJ Building. Also, floodwaters at the DOJ Building entered primarily through a pipe which collects storm water from the roof and courtyards and expels it to the sewer system.

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Court E 10,102 4.07 3,426 25,628

Roof 257,292 4.07 87,265 652,741

Total Projected

Area 330,453 Total 838,348

Figure 4-9: Final Water Depths, Department of Justice

Because Courtyard A also flooded during the June 2006 event (see Photos 4-15 and 4-16), an investigation was performed on the building storm drainage system to check the capacity. It was found that Courtyard A is served by two main rainwater drain pipes which run below the courtyard and serve to prevent rainwater from backing up in the area and causing a flood. The sizes of these drain pipes are 10 inches each. According to the 2003 International Plumbing

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Code, the maximum capacity for storm drains of this size, assuming a 1 percent slope, is 20,700 square feet of coverage each. However, the area of each half of Courtyard A is approximately 21,930 square feet. Therefore, using the design criteria of a 100-year rain event that yields 4 inches of rain per hour, these drains are undersized by approximately 6 percent, indicating that flooding of the courtyard area could occur in a future, more severe event. Yet, the rainfall which occurred on June 25 and June 26 did not meet the 100-year design criteria since the maximum one-hour rainfall amount was only 2 inches. Thus, for this event, the storm drain system for Courtyard A should have been sufficient to handle the load. Again, the building was compromised by the storm water pumps failing.

Photo 4-15: Flooded Courtyard Photo 4-16: Courtyard High Water Mark

The total capacity for all eight Department of Justice Building rainwater drains combined, the locations and sizes of which are indicated by Figure 4-10 and Table 4-6, is 319,800 square feet of rainwater collection space according to the 2003 International Plumbing Code. The total rainwater collection area for the Department of Justice Building, including the roof and all courtyard areas, is 330,453 square feet. In the event of a rainfall which yields 4 inches of rain in one hour, the storm drainage system for the building would need to operate at about 3 percent beyond current capacity, indicating that the system is slightly undersized for a 100-year event. However, the event which occurred on June 25 and June 26 yielded only 2 inches of rain in one hour, putting the system under a load of only about 50 percent of capacity. Therefore, the drainage system was capable of handling this particular load. It was not, however, designed to accommodate the impacts from adjacent street flooding and the backup of storm drain systems.

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Figure 4-10: Rainwater Drain Pipe Locations

TABLE 4-6: Total Capacity for all DOJ Building Rainwater Drains

Building RW Drains Drain Size (in.) Max Storm Drain Capacity (sq. ft)

A 15 59500 B 10 20700 C 15 59500 D 15 59500 E 12 33300 F 12 33300 G 12 33300 H 10 20700 Building Capacity 319,800

Actual Building Area 330,453

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4.5 Department of Commerce Building

The Commerce Building is located between 14th and 15th Streets NW with Pennsylvania Avenue to its north and Constitution Avenue to the south.

Photo 4-17: Commerce Building, 1401 Constitution Ave NW, Washington, DC 20230

The existing structure of the Commerce Building dates from the 1930’s with several renovations and maintenance projects having taken place since then. The original foundation of pile clusters, thick concrete slab, and retaining walls is in good condition and does not show any serious signs of cracking or water infiltration. Where ground water seeps through the floor in the sub-basement level, it is collected into a deep sump and then pumped up to the basement ejector sump pumps.

Another constant source of water inflow into the building is the steam condensate return which is prevented from returning into the central system. The condensate return flows into the storm sump in the Basement Main Compressor Room and is ejected by the existing pumps. These two sources of continuous water flow into the building are manageable by the present ejector pumping system but remain a constant maintenance responsibility.

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Photo 4-18: Commerce Building, 1401 Constitution Ave NW, Washington, DC 20230

As reported, the recent flooding incident was caused by floodwater bursting through the steam tunnel doors. It was also reported that there was no floodwater inflow from the 15th Street drive ramps/loading docks into the basement and no inflow from Constitution Avenue, 14th Street or from Pennsylvania Avenue or E Street to the north. In addition, there was no flooding reported coming in from the courtyards.

The flooding that occurred in June 2006 originated only from the steam tunnels to the east and west sides of the building. The steam tunnels had filled with storm water completely and the pressure forced the tunnel doors open. The water entered the basement level (where the tunnel doors opened) and flooded the area to a depth of at least 3 feet. The water then ran down through various openings and flooded the sub-basement.

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4.6 Old Post Office Annex

The existing structure of the Old Post Office Annex was constructed after the construction of the IRS Building. It is believed that structural support of the Annex utilizes the IRS exterior wall only to a minor extent, having its own steel column, concrete footing, and steel deck concrete floor slab systems. The columns running parallel with construction which are run at the exterior of the rear of the IRS Building shows angle bracing for a portion of the structural system to be cantilevered. Existing IRS footings were unburied along the wall of the Annex and supplemental footing was added above the floor level of the Annex. The existing and new footing extend approximately 4 feet into the Annex’s lowest level floor. The sub-basement of the IRS does not share any of the common wall between the Annex and the IRS basement and it does not appear that water penetrated the footing system as a point of entry.

The lowest floor level of the Annex is not at grade but approximately 10’-0” feet below grade with a floor to floor height of approximately 20’-0” to the first floor level. This lower level has natural light due to the open court floor plan of the first floor and does not feel like a basement. The floor level is approximately 1’-6” below the IRS basement finished floors and had a floor water level of some five to six feet above the finished floor. A sloped and depressed former theater area was filled with water to an additional depth of approximately 8’-0”.

The main lower level floor area had floor drains in the Men’s, Women’s and Handicapped toilets but not in the Theatre area or any other locations. In the toilet rooms, the water level was above the water closets and sinks. No determination could be made as to whether these fixtures had a direct effect on the flooding due to back-ups.

The theater depression (at its lowest level) showed some reaction to the unusually high ground water pressure as the construction point at the retaining wall/floor slab showed some back wash and opening. The Theater area “held” water much longer than the main and lower level. It was not clear whether the water was eventually pumped out, evaporated or swept out through this construction point since no floor drains are located in this area.

As noted, the IRS building was in existence prior to the design and construction of the Old Post Office Annex. The shared wall between the buildings is constructed of several different materials including brick and concrete masonry unit, poured-in-place construction concrete, limestone, and concrete block. The wall also has approximately 25 metal frame single pane windows with a rough opening of 32.5 square feet each. Most windows on the Annex side are hidden behind drywall partitions. Due to the demolition and reconstruction of the IRS basement, most windows are currently viewable from the IRS side of the wall. Evidence of floodwater lines still exist on many of these windows. Some window panes are broken out, allowing floodwater to freely interchange between the two building entries.

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Engineering and Technical Services to discuss the June 2006 event, WASA’s Blue Plains operations, and WASA’s future capital improvements. These representatives of WASA are highly placed within the WASA organizational structure (see Figure 5-1). The minutes of this meeting are in Appendix B. Additionally, the intent of the meeting was to gain a better understanding of WASA operations and protocols to enhance inter-governmental communications in times of emergency. Many topics were discussed with WASA but two important pieces of information were brought to light.

Firstly, WASA indicated that they try and achieve a 15-year storm event performance in the combined sewer and drainage systems, but very few parts of the system that they have taken over maintenance for in DC meet this design guideline. In other words, the WASA storm water system in the vicinity of the Federal Triangle is probably not capable of handling a 15-year storm event. Upgrading the storm water system to handle a 50-year event would help to mitigate certain storm events and may have helped during the June 2006 event. Upgrading the system would take several years and be very costly. There are currently no WASA plans to upgrade their infrastructure to handle a 50-year event.

Secondly, WASA has two main pump stations, one near the Anacostia River and one near the Potomac River. Neither pump station has backup power, but WASA only confirmed a power outage at the 12th Street Tunnel pump station, which they indicated drains away from the Federal Triangle to the south. The locations of both main pumping stations are indicated on the WASA System Map in Appendix A. According to WASA, if there is a power outage at their main pump stations the system automatically allows the storm water to be dumped into either the Potomac or Anacostia Rivers directly without treatment. There may be a small backup in the system depending on the river height but the system is designed for overflow into the rivers

5.1 WASA Organizational Structure

WASA is a semi-autonomous regional entity created by the U.S. Government and the District of Columbia government in 1996, which serves several counties and cities in Virginia, Maryland, and Washington, DC, primarily as a public water and wastewater utility provider. They have close ties with the DC Department of Public Works for a large portion of their system, but are also separate with federal funding approved directly by the U.S. Congress.

WASA operations are led by a General Manager who reports to an 11-member Board of Directors. The board includes six members representing the District of Columbia, two members representing Prince George’s County, two members representing Montgomery County, and one member representing Fairfax County. Additional staff and their organizational structure are shown in Figure 5-1. Coordination for this study included significant efforts to attain information

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from the WASA Chief Engineer (Deputy General Manager), John T. Dunn, and his staff for use in this study.

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facility of its type in the United States with a permitted average daily capacity of 370 million gallons per day (MGD) and a peak wet weather capacity of 847 million gallons per day. The Blue Plains facility treats all storm and sewer water from Washington, DC, conveyed through the combined sewer system. Also, much of the wastewater from municipalities in Maryland and Virginia, who choose to purchase treatment services from WASA, is funneled to Blue Plains. The MS-4 permit is held by the District of Columbia and WASA operates the Blue Plains plant only.

WASA indicated that the combined sewer main in Constitution Avenue drains in both directions. There is a 460 MGD pump station to the west near the Potomac River. There is also a 200 MGD pump station (with plans to increase capacity to 240 MGD) near the Anacostia River. There is also a separated storm drain system in Constitution Avenue which drains directly to the Tidal Basin. Two maps showing the overall WASA system to the Blue Plains Wastewater Treatment Plant and some details of the pipe sizes for the separated storm drain along Constitution Avenue are included in Appendix A (map pockets).

The Tiber Creek Sewer Interceptor handles all combined sewage flows along Constitution Avenue, and is sized on average as 12’x12’ cross section. It drains east along Constitution Avenue and then southeast towards the WASA main pumping station, which pushes sewage flows under the Anacostia River through 60-inch siphons and has a 200 MGD capacity. The sewer main then drains south to the Blue Plains Wastewater Treatment Plant along the Anacostia River. The Tiber Creek Sewer Interceptor also loops back to the west, where it connects to a 460 MGD pump station on the banks of the Potomac River, which then drains south to the Blue Plains Wastewater Treatment Plant.

The Constitution Avenue storm drain was created when a bulkhead was installed near the intersection of 9th Street NW to separate flows from the combined sewer system. Street drainage systems are connected to the storm drain, and then drain west through a culvert that increases in size from a 5’-0” span (rise unknown) to a 9’-0” x 6’-9” culvert in front of the White House. The storm drain then runs south to the Tidal Basin in Potomac Park, where the size decreases to a 6’-0”x 4’-9” before discharging to a submerged outlet pipe. A new tide gate was installed in 2003 (Tideflex by Red Valve) to prevent backflow into the pipe system from the Potomac River. From a maintenance standpoint, WASA inspects and cleans catch basins and pump stations on an annual schedule with additional cleaning in response to customer requests on their 24-hour emergency hotline, (202) 612-3400. However, WASA indicated that piping systems underneath the street network in Washington, DC are rarely inspected or cleaned.

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5.3 Combined Sewer Overflows (CSO)

Combined Sewer Overflow (CSO) is a significant policy issue for WASA in managing the system in the Metropolitan DC Area and demands some discussion in this report. During storm events when the capacity of the combined sewer system is unable to convey the mixture of wastewater and storm water to the treatment plant, CSO will occur. WASA has 53 CSO outfalls listed in their National Pollutant Discharge Elimination System (NPDES) storm water permit that was issued by the EPA to WASA. These CSO outfalls discharge a mixture of storm and sewage flows that can create a significant environmental and health concern related to heavy flooding events in Washington, DC.

In December 2004, WASA reached an agreement in a suit filed by the federal government to implement a very extensive program of CSO Abatement that will dramatically reduce the overflows from the District’s combined sewer system to help protect the Anacostia, Potomac, and Rock Creek/Piney Branch waterways. The agreement calls for WASA to implement a plan over a 20-year period for a variety of capital improvements throughout the District.

The CSO Abatement Program over the past decade has made an effort to reduce CSO discharges and maximize in-pipe storage of sewer overflows. To date, overflows are down an estimated 24 percent due mostly to the replacement of tide gates to reduce backflow, installation of 12 inflatable dams that hold back sewer overflows, construction of separated storm drain systems, plant/pumping stations upgrades, and the construction of a sewer monitoring and control system. WASA is now completing $140 million in additional projects that are projected to further reduce overflows by an additional 40 percent, mostly through the construction of tunnels along the banks of the Potomac and Anacostia Rivers to store CSO until the downstream system to the plant can receive the flow; however, this will not improve the capacity of the storm water system.

It should be noted that the WASA capital improvement plan (CIP) shows very little funding for the construction of improvements to the separated storm drainage systems in Washington, DC, which is the only way to avoid treating storm water runoff at the plant by improving the capacity of the separated storm drainage system. WASA has modeled only 5 percent of the DC sewer infrastructure at a cost of nearly $15 million. A complete model of the system will most likely need to be completed in order for the system upgrades to be implemented and funded. WASA’s intent to complete the modeling of the remaining 95 percent of the system is still under consideration. Various portions of WASA’s capital improvement plan are included in Appendix G.

5.4 June 2006 Event

There was a very sudden rise and rapid reduction of the floodwaters on Constitution Avenue over a 30-minute period as reported by Government personnel. Our rough calculations using the high watermarks and the DC topographical maps indicate approximately 38 million of gallons of water

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the Little Falls Gauging Station. The USGS website stated the peak stage three days later was 7.94 feet (equal to at least 3.26 feet of head pressure in the system).

It should also be noted that the combined sewer system is separate from the storm drainage system in Constitution Avenue and would likely have contributed to the flooding although there is no clear way to determine which pipe caused the backups.

5.5 Possible Scenarios to Rapid Rise and Fall of Flood Waters on Constitution Avenue

Although the exact cause of the flooding of Constitution Avenue is not known, several possible scenarios or combinations thereof could have contributed to it. These scenarios were discussed with WASA during the meeting but no definitive causes were supported. In rare situations such as the recent flooding of the Shockoe Creek Watershed in Richmond, Virginia, from Hurricane Gaston in 2004, a sudden rise of this magnitude can occur mostly due to overtaxed piping systems. In the case of Constitution Avenue in June 2006, the exact cause of the sudden rise and fall of storm water remains unknown.

Scenario One – WASA Main Pumping Station

The main pumping stations could have stopped operating causing the water to backup rapidly in the storm water system and then into the streets. The pumping stations could have lost power; there were PEPCO outages across the city that night. It was determined there was no standby power for these pump stations. The rapid decline in the water off of Constitution Avenue also lends itself to pumps re-energizing and thereby draining the area rapidly.

During discussions with WASA, it was discovered that the main pumping stations were operational continuously on June 25 and June 26, 2006. The 12th Street tunnel pump station did lose power and was not pumping during the event peak as it does not have standby power. Furthermore, if the main pumping stations did not operate, combined storm and sewer flow would reportedly discharge directly into the Potomac and Anacostia Rivers at the WASA pumping stations due to overtopping.

Scenario Two – WASA System Blockage

On June 24 and 25, 2006, the National Barbeque Battle took place on Pennsylvania Avenue. This is an annual event occurring between 9th and 14th streets on Pennsylvania Avenue. The large volume of litter created by the event, if not removed properly, could have contributed to diminished capacity in the storm system. This event was discussed with WASA and they said that cleaning of catch basins is the responsibility of WASA and is done regularly but the impact on the storm water system is likely to be minimal. Generally, there are excessive amounts of litter in the WASA system from all parts of DC. The introduction of litter into the system is extremely difficult to assess as to overall impact.

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The rapid rise could have been a blockage and the rapid fall could have been a release of the blockage in the system. Also, portions of the storm water may have been able to make it through the blockage. WASA reported no large system blockages during the event, but has not provided any inspection reports to date.

Scenario Three – Tide Gates

WASA installed new tide gates in 2003, including the tidal basin storm line (Tideflex by Red Valve). These valves will open and close automatically with no human intervention and function based on the pressure in the storm line. These particular gates also do not allow any backflow of the Potomac River into the storm water system under Constitution Avenue. It is possible that the gates did not open due to excessive back pressure from the Potomac water level or inadequate pressure from the storm sewer.

Based on rough estimates of head losses for the WASA pipe system and tide flex valve as well as the water level difference between the high water level and the Tidal Basin, it is estimated that approximately 4 feet of head would have had to have been overcome to force the floodwater through the system and into the basin. The graph in Figure 5-2 shows the head loss ratings for various sizes of Tideflex Valves, the same model installed in the discharge line a few hundred feet before the pipe terminates at the Tidal Basin. Figure 5-3 illustrates the storm water discharge system that collects storm water from the area around Constitution Avenue and passes it through approximately 5,000 feet of pipe before dumping it into the Tidal Basin. Using this information, an estimated head loss for the valve was obtained. Finally, Table 5-1 indicates where the assumed losses are in the system and identifies how a total required head of 4 feet was derived as an initial estimate. It is recommended that a detailed study and flow model should be used to attain the actual hydraulic gradients and head loss in the system.

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Figure 5-3: WASA Storm Drain System

TABLE 5-1

Anticipated System Losses for June 2006 Peak Stage

Component Head Loss (ft) Comments

Tide Flex Valve 0.55 Assumed 9,000 gpm flow through a 48” tide gate WASA Structure Losses 2.0 Due to junction/minor losses in WASA structures WASA Pipe Losses 1.45 Due to friction and various losses in 5000 feet of pipe

Total 4.0

5.6 WASA Related Questions and Answers

5.6.1 Original WASA Email

GSA to WASA, 4-December-2006

GSA commissioned a study by Setty & Associates, an independent consultant, to review all aspects of the flooding of the Federal Triangle on June 25, 2006. The scope of this study included all buildings in the Federal Triangle affected by the floodwaters so that a comprehensive plan can be developed to mitigate/prevent future occurrences. The scope included:

1. Investigating and documenting the modes and sequencing of flooding at each building; including 1111 Constitution Avenue.