J.6-TREATMENT AREA DRAINAGE PLAN v.3.pdf

DIOXIN REMEDIATION AT BIEN HOA

AIRBASE AREA PROJECT

DRAFT TREATMENT AREA PRELIMINARY

DRAINAGE PLAN

JUNE 28, 2021

This publication was produced for review by the United States Agency for International Development

DISCLAIMER

THE VIEWS EXPRESSED IN THIS PUBLICATION DO NOT NECESSARILY REFLECT THE VIEWS OF THE UNITED STATES AGENCY

FOR INTERNATIONAL DEVELOPMENT OR THE UNITED STATES GOVERNMENT.

DIOXIN REMEDIATION AT BIEN HOA

AIRBASE AREA PROJECT

DRAFT TREATMENT AREA PRELIMINARY

DRAINAGE PLAN

US AGENCY FOR INTERNATIONAL DEVELOPMENT

CONTRACT NUMBER: AID-OAA-I-15-00053

ORDER NUMBER: 72044019F00001

JUNE 28, 2021

PREPARED BY

TRIGON ASSOCIATES, LLC

1515 POYDRAS ST. SUITE 2200

NEW ORLEANS, LA 70112

USA

CONTENTS

LIST OF ACRONYMS AND ABBREVIATIONS ................................................................................................. II

1 INTRODUCTION

1.1 LOCATION

1.2 SITE CHARACTERISTICS

2 DRAINAGE SYSTEM

2.1 SCOPE

2.2 ASSUMPTIONS AND CALCULATIONS

3 RECOMMENDATIONS

FIGURES

FIGURE 1. TREATMENT AREA EXISTING DRAINAGE SYSTEM

FIGURE 2. TREATMENT AREA PRELIMINARY SITE LAYOUT

FIGURE 3. MODELED RAINFALL DATA

FIGURE 4. TREATMENT SITE DRAINAGE MODEL

FIGURE 5. WEST DRAINAGE CHANNEL PROFILE

FIGURE 6. EAST DRAINAGE CHANNEL PROFILE

FIGURE 7. TREATMENT AREA DRAINAGE PLAN

APPENDICES

APPENDIX 1. Hydrometeorological Bureau Center Precipitation Data at Bien Hoa Station, Dong Nai Province (2020)

DIOXIN REMEDIATION AT BIEN HOA AIRBASE AREA PROJECT

DRAFT TREATMENT AREA PRELIMINARY DRAINAGE PLAN

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LIST OF ACRONYMS AND ABBREVIATIONS

A&E Contractor Architect & Engineering Contractor for Dioxin Remediation at Bien Hoa Airbase Area – Trigon Associates, LLC.

GVN Government of Vietnam mm millimeter m meter m2 square meter

MONRE Ministry of Natural Resources and Environment

PTSA Pre-treatment Storage Area

SWMM Stormwater Management Model

TCH Thermal Conductive Heating

TMSA Treated Material Storage Area

USEPA US Environmental Protection Agency’s

UXO Unexploded ordanance

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1 INTRODUCTION

This document was prepared by the A&E Contractor to describe the preliminary drainage plan for the treatment area. This area includes the activities of the Treatment – Phase 1 contract and the Civil Works

– Phase 1 contract. The Civil Works – Phase I Contractor will be responsible for hauling road improvements, the pre-treatment storage area (PTSA), associated detention ponds, and the treatment area drainage system. The Treatment – Phase 1 Contractor will be responsible for site preparation of the treatment plant and all associated components as well as the treated material storage area (TMSA). The Treatment – Phase 1 Contractor will also be responsible for conveying the treated water discharge and catchment from the TMSA to concrete lined channels installed by the Civil Works – Phase 1 Contractor.

1.1 LOCATION

The treatment area for the Dioxin Remediation at Bien Hoa Airbase Area Project is located in the ZT area of the Airbase. This area was a former taxiway for transportation of herbicide, aircraft loading/unloading, and for moving equipment during the war.

1.2 SITE CHARACTERISTICS

1.2.1 NATURAL CHARACTERISTICS

Bien Hoa Airbase area is located within an area of Asian monsoon tropical climate; influenced by the Northeast monsoon, Southwest monsoon, and the Pacific Ocean tropic atmosphere with two distinct wet and dry seasons. The wet season lasts approximately six (6) months, from May 1 through October 31.

April and November are transitional months with variable dry and rainy weather conditions.

Precipitation data was obtained for the Bien Hoa Station from the Government of Vietnam (GVN) Hydrometeorological General Bureau, Hydrometeorological Monitoring Center for the years 1994 through 2019 (Appendix I). Rainfall during the season accounts for approximately 84 percent (%) of the annual total rainfall. Annual and seasonal rainfall, monthly rainfall and rainy days per month are provided in this report.

1.2.2 SITE DESIGN

Most of the site identified as the treatment area is currently undeveloped. The site has existing drainage channels shown in the Figure I below. These channels will be either relocated/rerouted or enlarged to accommodate the proposed facilities.

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FIGURE 1. TREATMENT AREA EXISTING DRAINAGE SYSTEM

The designated treatment area shown in the preliminary site layout (Figure 2) is primarily open with concrete and asphalt paved surfaces and unpaved vegetated areas. The work area designated in the preliminary site layout for the PTSA and TMSA is primarily unpaved vegetated areas. The total area is approximately 15.28 ha.

The site will contain the PTSA with detention ponds, the TMSA, thermal conductive heating (TCH) treatment plant, wastewater/vapor treatment systems, electrical substation and water supply, site office, guard shacks, and site improvements to access facilities. The Treatment – Phase I Contractor and Civil Works – Phase 1 Contractor will each be responsible for grading their areas of work and ensuring positive drainage to the perimeter channels.

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FIGURE 2. TREATMENT AREA PRELIMINARY SITE LAYOUT

2 DRAINAGE SYSTEM

2.1 SCOPE

Type of construction: Treatment Area Drainage

To build the necessary infrastructure to drain water from the treatment area and remove it from the site.

The Civil Works – 1 Contractor will convey discharge from the PTSA drainage ponds to the concrete lined channel.

The Treatment-Phase 1 Contractor will coordinate the connection between the treated wastewater discharge and the adjacent lined channel. The Treatment – Phase 1 Contractor will confirm the maximum discharge flow from the wastewater treatment system and convey the discharge to the concrete lined channel. The Treatment – Phase 1 Contractor will convey catchment from the TMSA to the adjacent lined channel.

2.2 ASSUMPTIONS AND CALCULATIONS

The drainage system provides a means to collect and move water away from the treatment area. Runoff from the site will move over the surface via sheet flow, piped treated water discharge, piped PTSA detention pond discharge, and piped discharge from the TMSA to the perimeter channels. The perimeter channels will be concrete lined with culverts under access road crossings to enter/exit the site. Water will flow from north to south following the natural gradient of the site, with the channel ending at the Z1-9 Pond before flowing over the weir to merge with the city drainage system.

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The max day rainfall from 1994 to 2019 occurred on September 26, 2016 according to the data provided in Appendix I – Hydrometeorological Bureau Hydrometeorological Monitoring Center Precipitation Data at Bien Hoa Station, Dong Nai Province (2020). Rainfall by interval was also included in the data for this date. The rainfall interval data provided the data points in Figure 3 below, for time steps at 5, 10, 20, 30, 60 and 90 minutes, with a cumulative depth of 117,0 mm. According to the data, the total depth of rain on this date was 189,0 mm. Therefore, additional points were extrapolated for times 120, 150, 180, and 210 minutes following approximately the same trendline to reach the total depth of rainfall for this date.

FIGURE 3. MODELED RAINFALL DATA

Calculations

The US Environmental Protection Agency’s (USEPA) Stormwater Management Model (SWMM) was used to estimate treatment area runoff. According to the USEPA, SWMM “is used throughout the world for planning, analysis, and design related to stormwater runoff…and other drainage systems in urban areas.”

(https://www.epa.gov/waterdata/epas-stormwater-management-model-swmm) The model incorporated the design storm and the estimated surface cover types to determine the runoff from the treatment and surrounding areas. The model assumes that the runoff from within the site and upstream catchment to the north is captured in the drainage system. The catchments outside the treatment area perimeter to the east and west are assumed to drain in other directions. The modeling is generally conservative in order to ensure the drainage system will have capacity to accommodate possible changes as the treatment area activities move forward. Additional assumptions made for modeling purposes include:

The design frequency for the drainage work is P=4%, 1 day maximum rainfall

100% impervious PTSA and TMSA (due to use of waterproof membranes)

100% impervious treatment plant areas (worst case assumption since design is undefined at this time and site may be almost entirely paved)

0% impervious undisturbed natural areas

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Flow of 1500 m3/d from the secondary waste treatment plant (vapor treatment system and wastewater treatment system) which includes both the water entrained in the soil/sediment which is released during treatment and the water added to the treatment system for cooling

Free outfall

All runoff flows to Z1-9 pond south of the treatment area.

The flow from the wastewater treatment system will be confirmed/revised as design of the treatment processes advance. The preliminary drainage model assumes that flow from the PTSA passes through the detention ponds with no detention time, in order to model a worst-case scenario in which the ponds are full and water short-circuits through the ponds instead of receiving detention time.

Modeling Results

A map showing the drainage system, subcatchments and proposed channels/culverts is presented in Figure 4 below.

FIGURE 4. TREATMENT SITE DRAINAGE MODEL

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Flows in the primary perimeter channels from the northernmost point to the outfall at the maximum depth are shown in the profile figures below. Figure 5 is the west side channel, Figure 6 is the east side channel.

FIGURE 5. WEST DRAINAGE CHANNEL PROFILE

FIGURE 6. EAST DRAINAGE CHANNEL PROFILE

Limitations

The preliminary drainage plan follows current topography, flowing from north to south. This is based on data available at the time this report was written. Topo survey map with scale 1:2000 was conducted in 2009 by aerial image technology. VN2000 datum was used for surveying. An updated site survey has not yet been conducted; survey is awaiting UXO clearance. The drainage system design may require modification when survey results are available for the site.

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The model assumes a free outfall at the discharge point. This assumption is based on the pond being empty, likely during dry periods of the year. During the rainy season, it is possible that there will be standing water in the pond, preventing a free outfall from the drainage system. In this situation, the water will back up into the lined channel and may cause localized flooding into the adjacent fields. As the lands around the channels are vegetated this is unlikely to cause issues. However, when survey becomes available, the elevation of the buildings adjacent to the pond to the west and south should be reviewed to verify the buildings are at a higher elevation.

3 RECOMMENDATIONS

The recommended drainage system for the treatment area is a perimeter trapezoidal channel with round culverts installed at points of site entrance/egress. The channels will be routed along the east and west sides of the treatment area. South of the treatment area, the channels will follow the route of current drainage pathways and combine flows before continuing south to an existing Z1-9 pond. The proposed locations of the channels, culverts and outfall are shown in Figure 7. All existing culverts will be replaced as part of this project. The channels around the treatment area are concrete lined, and those channels between the treatment area and the outfall location are earthen, matching the existing channel material.

The treatment area will be graded to the perimeter channels to ensure sheet flow and eliminate the need for ditches across the area. This will approach will allow the free movement of heavy equipment as needed for operations.

FIGURE 7. TREATMENT AREA DRAINAGE PLAN

As the design of the treatment facilities develop, the wastewater treatment system effluent flow and connection must be coordinated. The Treatment – Phase 1 Contractor will confirm the requirements and work with the A&E Contractor and the Civil Works – Phase 1 Contractor to finalize the connection.

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APPENDIX 1. HYDROMETEOROLOGICAL BUREAU

HYDROMETEOROLOGICAL MONITORING CENTER

PRECIPITATION DATA AT BIEN HOA STATION,

DONG NAI PROVINCE (2020)