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MTF 1 to Asia 16-068

~T~~t~ I VIETNAM MEMORANDUM TO THE FILE

Date:

From:

Through:

To:

Subject:

Purpose

May 17, 2017

,p>f Maura Patterson, Contracting Officer's Representative (COR).Jt

Khuong Tran Chinh, Mission Environmental Officer (ME Andrei Barannik, Regional Environmental Adviser/Cen al an South Asia and Office of Afghanistan and Pakistan Affairs (REA/SCA & OAPA

Will Gibson, Asia Bureau Environmental Officer (BEO/~ i

Management of Lower Concentration Excess Volum or t Environmental Remediation of Dioxin Contamination at Danang Airport oject

The purpose of this Memorandum to the File (MTF) is to document the government-to-government solution for management of excess volume discovered during implementation of the Environmental Remediation of Dioxin Contamination at Danang Airport Project (the "Project"). This MTF is in accordance with requirements in Initial Environmental Examination (IEE) Amendment No. 3 (Asia 16-068), namely: "Changes in project activities .. . will necessitate amending the IEE or issuing a Memorandum to the File."

Overview In 2009, USAID launched the Project with the initiation of an Environmental Assessment (EA),

required by USAID pursuant to 22 CFR 216, for the Danang Airbase. Concluded in June 2010, the EA

identified a number of remediation strategies and found that the thermal treatment alternative had

the highest treatment effectiveness, the highest feasibility, the lowest potential environmental

impact, and a cost in roughly the same range as the other alternatives for the Danang cleanup. The

Government of Vietnam (GVN) conducted an Environmental Impact Assessment of the thermal

treatment alternative, which led to formal project approval by the Prime Minister of Vietnam in

2011. The "Project" was fully contracted in late 2012 at an estimated cost of about $84 million.

Those contracts and estimates were based on soil/sediment sampling at the site in prior years, which

had led to the technical conclusion that approximately 72,900 cubic meters (m3) of contaminated

so il and sediment required remediation to reach the different standards applicable to soil (1,000

parts per trillion or ppt) and sediment (150 ppt) . The remediation structure was designed to fit site

parameters (e.g., limited appropriate space) and accommodate extra soil/sediment over two phases

of treatment, which with complementary measures such as compaction provides for a total capacity

of about 90,000 m3.

Through implementation of the Project, approximately 163,000 m3 of contaminated soil and

sediment was discovered and excavated and about 95,000 m3 of the highest concentration material

(i.e., all contaminated soil and sediment greater than 1,000 ppt) has been thermally treated in two

phases. The first of two treatment phases was successfully completed in 2015; the second phase is

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undergoing confirmatory sampling at present. USAID and MND agreed that the remaining approximately 68,000 m3 of sediment excavated from the Project site with dioxin concentrations less than 1,000 ppt (and that could not fit within the second and final thermal treatment phase) do not require treatment. That material will instead be transported and stockpiled in a commercial/industrial area located in the southwest corner of the Danang Airbase property near the Pacer Ivy Storage Area per the Excess Volume Stockpile Area (EVSA) design recommended by the Project’s Construction Management Contractor (CMC) and approved by the GVN in February 2017. The EVSA construction is an in‐scope activity under the Dig & Haul mechanism and is within that award’s fully funded cost ceiling, as documented in USAID/Vietnam’s latest Activity Approval Design (AAD) Amendment No. 5 for the Project (approved by the Mission in December 2016) and in the Determination & Findings and Justification & Approval for Other Than Full and Open Competition package for the Project (approved by the Agency Administrator in March 2016). Finally, the scope of work and increased level of funding for the EVSA construction are included in IEE Amendment No. 3 for the Project (No: Asia 16‐068) and supporting Final Environmental Mitigation & Monitoring Plan–Phase 2 and Site Restoration (EMMP).

The IEE Amendment No. 3 (Asia 16‐068, dated May 31, 2016) evolved from the original Asia Bureau Environmental Officer (BEO/Asia)‐approved IEE and subsequent Amendments as follows:

Original IEE, May 26, 2009: Asia 09‐61 Record of Environmental Decision, January 28, 2011: Asia 11‐44 IEE Amendment No. 1, April 13, 2012: Asia 12‐77 IEE Amendment No. 2, March 28, 2013: Asia 13‐47

The original Project EMMP was approved by the BEO/Asia on April 20, 2012. The Final/Phase 2 EMMP for the Project (included in IEE Amendment No. 3) reflects a full review of Phase 1 of the Project and applies lessons learned to Phase 2 thermal operations, as well as all mitigation and monitoring needs anticipated to project completion (inclusive of the now‐named EVSA). Specifically, the Final/Phase 2 EMMP captures mitigation and monitoring of activities relevant to the EVSA such as material stockpiling, vehicle decontamination and refueling, erosion and runoff during storm events, and dust and ambient air monitoring during all earth moving, among others.

The IEE Amendment No. 3 further “reconfirm[s] that the scope and nature of all key activities remain the same…with duly approved fine‐tuning…in view inter alia of…on‐going discussions with the GVN authorities” and “reconfirm[s] the approach to the approved EMMP as a flexible process and a “living” document.” The excess volume excavations and EVSA construction are all in‐scope activities within the $112 million cost ceiling of the latest approved IEE, captured in the Final/Phase 2 EMMP. Through discussions between the GVN and USAID since 2014, the two governments have reached agreement on the specific EVSA design, and USAID has approval from the GVN to proceed.

Chronological Background of Excess Volume Issue The implementation plan for the “Project” estimated 72,900 cubic meters (m3) of contaminated soil and sediment for excavation and treatment to be completed in two phases. Excavations were to be completed in the 2013 and 2015 dry seasons with thermal treatment largely occurring in the 2014 and 2016 dry seasons. The first phase was estimated to treat approximately 34,800 m3 of largely

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soils from the topographically higher, southern portion of the site (Phase 1 area); the second phase was estimated to treat approximately 38,100 m3 of largely sediments from the lower lying, northern portion of the site, which consists of largely Sen Lake and the surrounding vegetated lowlands (Phase 2 area). The GVN national cleanup standards for dioxin of 1,000 ppt TEQ in soil and 150 ppt TEQ in sediment were applied at the Project per agreement with the GVN. Starting in late 2012, the Dig & Haul contractor constructed the In‐Pile Thermal Desorption (IPTD) treatment structure (105m x 70m x 6m internal dimensions) to be utilized for both phases and began preparations for the Phase 1 area excavations. The IPTD structure and thermal treatment system were designed to accommodate a 20% volume contingency in the case of excess volume, given that excess volumes are typical for soil/sediment remediation projects in the United States. A fifteen percent contingency was included in the Dig & Haul award as an anticipated risk mitigation measure so funding was readily available as needed during the excavation seasons. During the Phase 1 area excavations in the 2013 dry season, an excess volume of dioxin‐contaminated material was identified through confirmatory sampling of the design volume excavations identified in the implementation plan. All excavations were completed by the Project’s Dig & Haul contractor (TetraTech); all confirmatory samples were collected by the Project Construction Management Contractor or CMC (CDM Smith). The Vietnam Ministry of National Defense’s oversight agency for excavations on the Project – the Vietnam Russia Tropical Centre or VRTC – also collected confirmatory samples. The confirmatory sampling conducted by the CMC included sampling of the excavation floors and sidewalls (if applicable) and employed the multi‐increment sampling (MIS) method, which is a systematic, statistically‐based compositing methodology. The excess volume discovered in the 2013 dry season peaked concerns for the Project Team (USAID Agent Orange Team and USAID prime contractors) regarding overall excess volume for the Project. As such, TetraTech remobilized in the 2014 dry season to begin Phase 2 excavations early (expedited from 2015 dry season) and to continue excavating Phase 1 excess volumes. The expedited Phase 2 excavations revealed that the original design volumes were again inadequate to achieve the Project excavation goals in the Phase 2 area but gave the Project Team and the Mission time to react to the excess volume (i.e., additional dry seasons for excavation, planning for additional thermal phases, exploring containment options with the GVN, etc.). The majority of the excess volume was sediment with concentrations greater than the 150 ppt sediment excavation cleanup standard but below the 1,000 ppt soil excavation cleanup standard. A summary of the total excavated volume is broken out by calendar year in the Table 1 (next page). As shown in the table, the total contaminant volume was more than double the originally estimated 72,900 m3 and required four dry seasons (versus the planned two dry seasons) to complete.

Table 1.

Calenda

2013 2014 2015 2016

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Ministry of Natural Resources and Environment, Office 33, the Office of Government, the Ministry of Foreign Affairs, and the Ministry of Planning & Investment among others. Some in the meeting expressed a preference for comprehensive treatment; others conceded that no additional thermal treatment phases were required but questioned the backfilling and solidification/stabilization option. Some verbally acknowledged the logic of USAID’s proposal to contain the lower concentration sediments, but psychologically they did not like the idea of the material still being present at the Airport and the inability to access and treat the material with a cheaper technology in the future. They also expressed concern that future generations would be disappointed. Concurrently, at the political level, Senator Leahy sent a letter to President Sang (written by the Mission Director) dated December 12, 2014, urging the Vietnamese “government to consider [USAID] proposals from a broad perspective and to respond to them quickly” and that “doing so will sustain the quality of cooperation that is so important to the relationship and could be critically helpful as this added cost has not been obligated and may have to be offset by reductions in other assistance programs, including programs prioritized by our governments.” Ultimately, in a letter dated June 10, 2015, the GVN largely accepted all of the material reclassifications to reduce the overall excavation volume and solidified agreement that no additional thermal treatment phases were required. However, the GVN did not approve the containment proposal to backfill and stabilize/solidify the lower concentration, excess sediments in the former storage area/drainage ditch excavation, and instead, requested the material be “manageably isolated at a specific area in the Airport” as designated by ADAFC. An initial location was identified by ADAFC north of the western runway in the letter. The Project Team was not comfortable with this location for the untreated sediments as the area consists of several small lakes and vegetated lowlands, with characteristics similar to a wetland, which drains to Sen Lake. In addition, the location did not have the capacity for the excess volume, which at this time was understood to be approximately 50,000‐70,000 cubic meters. For the remainder of 2015, ADAFC and USAID discussions on how to manage the excess volume shifted to proposals made by Chemical Command (MND) to construct a landfill in the north runway area and/or moving the stockpiles to the north runway area until MND could secure funding for alternative treatment technologies, but no solutions were identified. Following a U.S. study tour of dioxin remediation projects in October 2015 (provided by USAID), MND agreed that the north runway area was not a good location for placement of the material either temporarily or permanently. In late 2015, USAID requested ADAFC to identify a stockpile location that: 1) can fit the entire volume of soil/sediment with dioxin concentrations between 150 and 1,000 ppt; and 2) is in an upland, commercially/industrially‐zoned area of the Danang Airport that does not contain low‐lying wetlands or lakes. USAID also confirmed the agreement between USAID and ADAFC that no amendment or stabilization/solidification technology would be required for stockpiling the excess soil/sediment, particularly if it is placed in an area designated for industrial land use. With the lead up to the May 2016 Phase 1 completion celebration event, the discussions accelerated to find a suitable, alternative location and determine a final stockpile design. ADAFC identified a location for the Excess Volume Stockpile Area (EVSA) in the southwest corner of the Danang Airport property near the former Pacer Ivy Storage Area. The area provided adequate space at an elevation above the groundwater table with no downstream water bodies and has a land use designation of

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industrial for up to 100 years. USAID’s CMC confirmed that the location is acceptable in February 2016. The location agreement was made in accordance with GVN regulation QCVN 45:2012/BTNMT that states commercial and industrial areas can contain soils with dioxin concentrations up to 1,200 ppt. The CMC then conducted a risk assessment based upon the new location in order to determine the appropriate engineering controls for the EVSA. The findings show that both cancer and non‐cancer risks are below levels of concern for all receptors (including potential future residents, trespassers, and construction workers) for the conceptual EVSA design for both dioxin and arsenic (there were no other contaminants of concern); and that while meaningful benefits could be shown by adding an HDPE liner to the stockpile cover, there is no meaningful additional benefit in terms of risk protection with the addition of a bottom liner and leachate collection system. (The additional bottom liner and leachate collection system was estimated to cost an additional $2 million USD.) The exposure point concentrations used for the risk assessment were 751 ppt for dioxin and 30 parts per million (ppm) for arsenic based on preliminary stockpile concentrations. These concentrations are well below the GVN hazardous waste thresholds for dioxin and arsenic of 100,000 ppt and 40 ppm, respectively, per GVN regulation QCVN 07:2009/BTNMT. The Vietnamese Ministry of National Defense approved the conceptual design (HDPE‐capped stockpile with no bottom liner or leachate collection system) in a letter to USAID dated August 11, 2016 (Decision #2907/BTL‐KHQS). As the final 2016 dry season excavations closed and the IPTD treatment structure was filled with material known to be greater than 1,000 ppt, USAID’s CMC more formally characterized the remaining stockpiled material to verify and document the average dioxin concentration of the EVSA material, although all sediment material in the three stockpiles was known to have dioxin concentrations less than 1,000 ppt based on prior characterization/confirmation samples collected during excavation activities. This was conducted by collecting three multi‐increment (MIS) samples (i.e. three samples collected and composited from a minimum of 30 points) for dioxin analysis from each of the three onsite, temporary stockpiles (i.e., DP‐1, TSSA‐1 and TSSA‐2). The three, MIS samples meet or exceed the QCVN 07:2009 minimum requirement of three random samples to determine the mean concentration of waste material. All samples were below 1,000 ppt (see Table 2 below). Table 2. Stockpile sampling to determine mean concentration of EVSA

Temporary Stockpile & Description Volume Concentration

DP‐1 DP‐1 contains primarily over‐excavated material from the Eastern Wetland, Eastern Area, and hummocky areas.

~20,000 m3 321 ppt

TSSA‐1 TSSA‐1 contains primarily sediment placed as it was excavated from Sen Lake.

~24,000 m3 751 ppt

TSSA‐2 TSSA‐2 contains primarily sediment from the Eastern Wetland, Eastern Area, and Sen Lake.

~24,000 m3 794 ppt

The volume‐weighted average of the three stockpiles, and therefore of the mean dioxin concentration of the EVSA material, is 650 ppt. This determination enabled finalization of the conceptual design and verified that the untreated, excess sediment was indeed less than the agreed

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upon 1,000 ppt threshold for the Project, as well as the 1,200 ppt industrial/commercial standard for dioxin in Vietnam (QCVN 45:2012/BTNMT). In addition, the actual mean concentration of 650 ppt is lower than the exposure point concentration of 751 ppt used for the risk assessment, further validating the recommendations of the risk assessment. USAID submitted the final detailed design for the EVSA in a letter dated September 8, 2016; this was approved by MND leadership in a letter dated February 13, 2017 (Decision #407/ BTL‐KHQS). Please see Annexes A and B, for the conceptual and final detailed EVSA designs, respectively.

Internal Approvals and Implementation

During the above negotiations with the GVN, USAID proceeded with internal sensitization to the excess volume, securing funds, and adjusting the procurement strategy for the Project: including hosting a site visit to the Danang site with both the Regional Environmental Advisor (REA) and the Bureau Environmental Officer (BEO) in October 2015; preparing an Activity Approval Design Amendment #5, approved by the Mission Director in December 2015; preparing a Determination & Findings and Justification & Approval for Other Than Full and Open Competition package, approved by the Agency Administrator in March 2016; working with the CMC to prepare the Final EMMP inclusive of activities relevant to the EVSA, approved by the REO and BEO in May 2016; preparing the IEE Amendment No. 3, approved by the REO and BEO in May 2016; and working with OAA to finalize modification of the Dig & Haul contractor’s award to include all excess volume excavations and related handling costs, as well as the EVSA construction activity, in June 2016.

Decision

While the GVN rejected USAID’s first (and preferred) proposal to backfill and stabilize/solidify the excess sediments onsite beneath the future taxiway extension, USAID and MND were able to reach a government‐to‐government solution to responsibly contain the lower concentration excess volume sediments. The EVSA design is a risk‐based, practical solution to mitigate the excess volume found during implementation of the Danang Project that is still protective of human health and the environment and enables Project completion within final cost and timing constraints. The Dig & Haul contractor will construct the EVSA between May 2017 and October 2017 under the oversight of the CMC, which will monitor operations as prescribed by the Final Phase 2 EMMP.

References:

USAID (2010). Environmental Assessment ‐ Environmental Remediation at Danang Airport. Hanoi, Vietnam: U.S. Agency for International Development in Vietnam. Hanoi, Vietnam. June.

USAID (2011). Final Remediation Work Plan ‐ Environmental Remediation at the Danang Airport. Hanoi, Vietnam. March 18.

USAID (2016). Final Project Environmental Mitigation and Monitoring Plan (EMMP) – Phase II and Site Restoration ‐ ‐ Environmental Remediation at the Danang Airport. Hanoi, Vietnam. May 20.

USAID (2016). Estimated Human Health and Ecological Risks Due to Arsenic and Dioxin in the Excess Volume Stockpile Area at the Danang Airport, Vietnam. Hanoi, Vietnam. June 24.

Annex A: Conceptual Design Letter to Air Defense Air Force Command for Excess Volume Stockpile Area

:fi\ USAID I VIETNAM ~ FROM THE AMERICAN PEOPLE

July 1, 2016

Major General Bui Anh Chung Vice Chief, Air Defense -Air Force Command Ministry of National Defense 167 Truong Chinh Street Hanoi, Vietnam

Subject: Recommended excess volume stockpile area (EVSA) design for the Environmental Remediation of Dioxin Contamination at Danang Airport Project

Dear Major General Chung,

First of all, we would like to express our appreciation for your continuing support to address the excess volume of sediment with dioxin concentrations higher than 150 part per trillion (ppt) but lower than 1,000 ppt. Identification of a location for the excess volume stockpile area (EVSA) near the former Pacer Ivy area was a significant development since USAID and the Government of Vietnam (GVN) began discussing this issue nearly two years ago (Attachment 1). The UXO clearance conducted by the Ministry of National Defense (MND) during March to May 2016 enabled USAID contractors to fully survey the location and complete the recommended stockpile construction plan as requested (see Attachment 2).

The attached design is based on the (i) topological survey and groundwater monitoring results; (ii) the average dioxin and arsenic concentrations in sediment to be stockpiled; (iii) the current Vietnamese regulations including the QCVN 07: 2009/BTNMT National Technical Regulation on Hazardous Waste Thresholds, QCVN 45:2012/BTNMT National Technical Regulation on allowed limits of dioxin in soils, and (iv) a risk assessment using United States Environmental Protection Agency (USEP A) dioxin standards and risk assessment procedures. The attached design with soil cap and top liner of high density polyethylene (HDPE) is a very technically and practically sound solution that complies with applicable Vietnamese and USEP A regulations to manage the excess sediment volume at the Environmental Remediation of Dioxin Contamination at Danang Airport Project (the "Project").

The current estimated excess sediment volume is from 60,000 to 70,000 cubic meters (m3)

with average dioxin and arsenic concentrations of 7 51 ppt and 3 8 milligrams per kilogram (mg/kg), respectively. These concentrations are well below the hazardous waste thresholds for dioxin and arsenic, as defined in QCVN 07: 2009/BTNMT, ofO.l parts per million (ppm) (or 100,000 ppt) and 40 ppm (40 mg/kg), respectively. Furthermore, based on the QCVN 45:2012/BTNMT regulation, this material can be used in industrial and commercial areas without treatment or containment since the dioxin concentration is below the threshold of 1,200 ppt for commercial or industrial land use scenarios.

We acknowledge the suggestions from Air Defense-Air Force Command (ADAFC) in their letter #876/BTL-KHQS dated March 21, 2016 regarding the design and construction of the EVSA and the suggestions from Chemical Command in the recent monthly meeting on June U.S. Agency for International Development USAID Vietnam, 15/F Tung Shing Square 2 Ngo Quyen Street Hanoi, Vietnam

Tel: 84+3-935-1260 Fax: 84-4-3-935-1265

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21, 2016 on whether the TCXDVN 320 - 2004 Vietnamese Design Standards for Hazardous Waste Landfills are applicable; however the material to be placed in the EVSA is not classified as a hazardous material per QCVN 07: 2009/BTNMT. Moreover, we have previously agreed that it is neither necessary nor required to build a landfill, but only to stockpile the excess sediment as discussed in the meeting on January 15, 2015 in Danang (see Attachment 3) and in other communications (please refer to Attachment 1) .

.In order to ensure that the proposed design will not adversely impact the environment or the health of residents in the surrounding areas, USAID conducted a risk assessment for the residual concentration of dioxin and arsenic present in the material to be stockpiled in the EVSA (see Attachment 4). The risk assessment evaluated potential human health cancer and non-cancer risks due to exposures to dioxin and arsenic for multiple pathways including: incidental ingestion of excess soil, dermal contact with excess soil, inhalation of excess soil, ingestion of groundwater, incidental ingestion of surface water while swimming, and dermal contact with surface water while swimming at the site. Exposure was evaluated using standard equations recommended by the USEP A for use at Superfund sites in the United States. The risk assessment findings shows that both cancer and non-cancer risks are below levels of concern for all receptors (including potential future residents, trespassers, and construction workers). The risk assessment also indicates that there is negligible additional benefit in terms of risk protection with the addition of a bottom liner as suggested by Chemical Command representatives.

Considering all the findings discussed above, the recommended EVSA design is a practical, science-driven solution that is protective of human health and the environment and goes above and beyond a basic stockpile. US AID cannot justify nor does it have the funds to support additiorial, unnecessary actions such as adding a bottom liner and leachate collection system to the design. If the GVN would like to proceed with a different design approach with GVN funds, USAID will hand over the excess sediment volume in the existing project stockpile areas to ADAFC as previously indicated, and USAID will not be held responsible for its ultimate disposition. Given the limited time to begin construction of the EVSA this dry season and to complete the EVSA by APEC 2017, a timely decision is warranted. USAID respectfully requests a decision on the proposed EVSA design by July 15, 2016.

Should the GVN accept USAID's recommended design, it is imperative that a regular inspection and maintenance plan be developed and implemented to ensure proper performance. At a minimum, the plan should include: regular mowing of grass (monthly or bimonthly); quarterly walk-through inspections looking for animal burrows into the cap system, growing shrubs/trees, erosion gullies, signs of subsidence, and confirming the integrity of the EVSA's surrounding berm, fence and signs; performing repairs to address any issues identified; and conducting inspections as needed following significant rainfall events with subsequent repairs including re-grassing and/or adding soil. With proper maintenance of the recommended design, leachate will not be generated. If there is no maintenance, any potential leachate impacts would be localized and could be managed through institutional controls such as limiting the installation of groundwater drinking water wells in the uppermost Holocene aquifer. USAID recommends that ADAFC requests funding to perform the above inspection and maintenance of the EVSA.

USAID concurs with ADAFC's recommendation to jointly sample the EVSA location with Vietnam Russia Tropical Centre (VR TC) to identify the baseline dioxin and arsenic concentrations of the area and will direct CDM Smith to coordinate directly with VRTC upon approval of the recommended EVSA design.

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Thank you for your continued support and effective partnership for this Project. We are looking forward to seeing your response. Should you need any additional information, please contact Mr. Nguyen Manh Phuc, USAID Environment and Social Development Office at 04-39352195 (office) or at 0977215703 (cell).

Sincerely,

Christopher Abrams Acting Mission Director

Cc: Col. Pham Quang Vu, Head of Military Science and Technology Office, Air Defense -Air Force Command, Ministry of National Defense

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Attachment 1

Timeline of Consultations on Excess Volume Stockpile

• Summer 2014 - Identification of excess volume issue • November 7, 2014- USAID submits formal proposal to backfill excess volume in the

former storage area and southern drainage ditch (with stabilization to address the airport's constructability concerns)

• January 15, 2015 -Agreement to stockpile with no stabilization/solidification (S/S) at monthly meeting with USAID and Col. Do Duy Kien (ADAFC) and Col Than Thanh Cong (Military Science Department)

• June 10, 2015 -MND's formal response to the November 2014 USAID proposal, requesting USAID to "manageably isolate" the excess volume at the north head of the western runway and direct its contractors to "survey [and] prepare a stockpile construction plan with management in the area"

• June 26, 2015 - survey of north head of the western runway completed; USAID and ADAFC monthly meeting discussion about USAID concerns with the north head of the western runway area (not enough capacity and proximity to lakes/wetlands)

• October 7, 2015 -ADAFC requests USAID to direct its contractors to prepare the "stockpile construction plan" in the north head of the western runway stating that "an amendment should be used to improve the soil's properties, prevent the contaminant migration and ensure the highest level of safety for long-term storage"

• October 13-16, 2015 - USAID Regional Environmental Advisor (REA) and Asia Bureau Environmental Officer (BEO) site visit

• November 3, 2015 - USAID letter to ADAFC stating that USAID cannot place the material in the north head of the western runway area; reiterates previous agreement that no S/S is required for stockpiling; and requests ADAFC to identify an alternate location

• November 10, 2015 -ADAFC agrees to find new excess volume location • February 25, 2015 - USAID provides conceptual design to ADAFC for the excess volume

stockpile area (EVSA) based on site visit to new location • June 21, 2015 - following completion ofUXO clearances, detailed topological survey,

groundwater monitoring, and risk assessment, USAID provides revised design with consideration of ADAFC's March 2016 comments

EVSA Design Elements

• Surface area provided by ADAFC is approximately 41,750 square meters. • Groundwater is 1.0-1.5 meters below the ground surface. • Current estimated excess volume is approximately 60,000 cubic meters (m3); the

maximum anticipated excess volume is 80,000 m3.

• Average dioxin and arsenic concentrations are 751 ppt and 38 mg/kg, respectively. These concentrations are well below the hazardous waste thresholds of dioxin and arsenic required in the QCVN 07: 2009/BTNMT of 0.1 parts per million (ppm or 100,000 ppt) and 40 ppm (40 mg/kg) respectively.

• Based on the QCVN 45:2012/BTNMT, this material is able to be used for industrial purposes without treatment since the dioxin concentration is below the 1,200 ppt threshold for dioxin in an industrial area.

• Average recommended slope is 3 percent from peak to berm. Stockpile cap system consists of geotextile, 40-mil HDPE liner, geo-composite for drainage, 50-centimer vegetated soil cap that is surrounded by a berm and security fence.

EVSA Design Risk Assessment Findings

• For cancer, risks are expressed in terms of the probability that site-related exposures will result in the occurrence of cancer. USEP A considers cumulative excess cancer risks that are below about lE-06 (lxl o-6 or 1 in 1,000,000) to be negligible, and risks above lE-04 (lxl0-4 or 1 in 10,000) to be sufficiently large that some form ofremedial action is desirable. Excess cancer risks that range between lE-04 and lE-06 are generally considered to be acceptable.

• Non-cancer risks are evaluated by computing hazard quotient (HQ) values for individual exposure pathways and summing them to compute the hazard index (HI). If the value of the HI is less than or equal to 1 (one), then risks of non-cancer effects are not of concern. If the value of HI exceeds 1, then there may be a risk of non-cancer effects, with the probability and/or severity tending to increase as the values of the HI becomes larger.

• All receptors (residents, trespasser, and construction worker) were evaluated to span the possible range of exposures from incidental ingestion of soil, dermal contact with soil, inhalation of soil, ingestion of groundwater from uppermost Holocene aquifer, ingestion of incidental surface water while swimming, and dermal contact with surface water while sw1mmmg.

• Three scenarios were evaluated with the following findings: Scenario 1 - stockpile with a soil cap meets GVN dioxin requirements and EPA's updated dioxin soil screening levels for cancer and non-cancer effects. Material is not hazardous waste per GVN regulations and is less than the applicable land use based soil standard for dioxin in the proposed stockpile area. Arsenic could be present in shallow groundwater. Scenario 2 - stockpile with a soil cap and a high density polyethylene (HDPE) top liner meets GVN and EPA requirements. No potential groundwater concerns. Scenario 3 - stockpile with a soil cap, HDPE top liner, and geo-synthetic clay with a HDPE bottom liner goes beyond both GVN and EPA requirements, no additional exposure pathways eliminated, costs significantly more than Scenario 2.

Attachment 2

The Proposed EVSA design

T3

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STAGIN

G AR

EA

S=4.330M2

OFFICE: 170-172 LE DAI HANH, WARD 7

Tel: +84 8 3766 1530

VINAUSENDIST 11, HO CHI MINH CITYTETRA TECH

3475 East Foothill Boulevard Pasadena

Tel:+1-626-351-4664, Web: tetratech.comCalifornia 91107-6024

ENVIRONMENTAL REMEDIATIONAT DA NANG AIRPORT THAI VINH CO., LTD

LAYOUT OF EVSA

STAGIN

G AR

EA

S=4.330M2

n

e

TETRA TECH3475 East Foothill Boulevard Pasadena

Tel:+1-626-351-4664, Web: tetratech.comCalifornia 91107-6024

ENVIRONMENTAL REMEDIATIONAT DA NANG AIRPORT

PROPOSED EVSA STOCKPILE

A

A

SECTION A-A

PROPOSED EVSA STOCKPILE

SC: 1/2000PLAN

SC: 1/250

DETAIL ASC: 1/50

DETAIL A

Attachment 3

The Monthly Meeting Minutes between Air Defense - Air Force Command and USAID on January 15, 2015

MONTHLY MEETING FOR ENVIRONMENTAL REMEDIATION AT DANANG AIRPORT PROJECT

AIR DEFENSE - AIR FORCE COMMAND (AD AFC) AND USAID

Venue:

Participants:

USAID:

AD AFC:

Airport:

CDM trailer, Danang Airport, Danang, Vietnam

Thursday, January 15, 2015

08:30 a.m. to 12:00 p.m.

Ms. Kyung Choe, Mr. Andrew Sayers-Fay, Ms. Maura Patterson, Mr. Nguyen Manh Phuc, Ms. Hoang Nghe Ha

Col. Do Duy Kien (ADAFC), Lieutenant Col. Tran Trong Hieu (ADAFC), Col. Than Thanh Cong: Department for Military Science, Col. To Van Thiep: Institute of New Technology - AMST, Mr. Trinh Khac Sau: VRTC

Mr. Le Hoai Nam

CDM Smith: Mr. Beau Sanders, Mr. Peter Chenevey, Mr. Alexis Lopez, Mr. Karl Tilgner

Tetra Tech: Dr. David Liu

TerraThenn: Mr. Jim Galligan, Mr. Glenn Anderson

Content:

1. Excess Volume Options

- Mr. Cong is in the process of gathering written comments from the attendees at the excess volume workshop held in December 2014. All comments from MND have been received, but he is still waiting on comments from Office 33 and the Pollution Control Department within MONRE. Comments have also been received from Senator Leahy. When all comments are received, he will prepare a summary letter and submit to MND. MND will then officially respond to the ADAFC and USAID proposal.

- Mr. Cong said that the comments received support Options 1 and 2, which relate to reclassification of materials from sediment to soil. Regarding Option 3, the comments are against placing the stabilized sediment in the drainage ditch area due to concerns about changes in the future land use, more stringent environmental regulations and/or new remediation technologies. Instead, it is suggested that the material be isolated somewhere else on site and monitored since it already meets the 1,000 ppt GVN standard.

- Ms. Choe inquired about when an official response would be provided. TetraTech needs to start excavation activities soon, so a response before Tet would be preferred.

- Mr. Cong stated that they will try to get a response by the end of January. The response will address all 3 options.

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- There was discussion regarding whether or not it was necessary to stabilize the sediment if it was just being placed in an isolated area. Dr. Liu pointed out that the main benefit of solidification/stabilization is increased strength (reduced leachability is a potential side benefit). The strength would not be necessary if it was going to be stockpiled. Mr. Cong said that isolating the sediment and preventing migration is good enough, and it is not necessary to solidify/stabilize.

- It was agreed to work out the details of the storage, isolation, and monitoring of the sediment at a later time, but Mr. Kien and Mr. Cong agreed that a third thermal treatment phase was not required and that stabilization/solidification was not necessary for the stockpiled material.

- Mr. Kien requested to hear from the Middle Airports Authority since they would be the key beneficiary of the proposal. Mr. Nam said that he was happy to hear the responses from MND since it will mean no more delays to the Airport construction projects. He supports Option 1 and Option 3, but would prefer keeping the same standard for the eastern wetland (Option 2). However, he is ok with MND's response. Mr. Nam indicated that the stockpile area for treated and isolated material should not be near West Lake because Sen Lake will be reduced in size as part of the airport expansion efforts and storm water retention/storage will already be limited at the Airport.

- Mr. Kien indicated that ADAFC will work with CDM to find a suitable location for both the treated and isolated (untreated, < 1,000 ppt) material.

2. MONRE Inspection

- Mr. Kien provided an update regarding the MONRE inspection. The initial COI,lclusions provided by the MONRE inspection team indicate that:

• The project has had some design changes from the Environmental Impact Assessment. The Project Management Unit needs to update these changes.

• AD AFC has to register as owner of a hazardous waste storage site and manage emissions.

• There was not enough information to support the claim that there were discharges directly from Sen Lake to the environment.

- MONRE inspection team has to report to the Vice Minister. Until then, the conclusions won't be final. ADAFC agrees with their initial conclusions.

3. Project Update

- Mr. Galligan provided an update of the temperatures within the pile, indicating that the additional L WIC cover has been completed, and that they are in the process of raising the heaters to focus on heating the 0 to 1 meter depth of soil. He anticipates reaching 335C in mid-February.

- Mr. Kien inquired about how long heating has been delayed. Ms. Patterson indicated that it was originally anticipated to be approximately 4 months. However, time was lost due to water infiltration in the pile in Fall 2013, the temporary plant shutdown in Summer 2014, and the cover cracking in October 2014. With all of these items, Phase 1 heating will be about 9 to 10 months, instead of 4 months. The delay will impact emptying and refilling of the pile. It's likely that only emptying will occur in 2015 and refilling the IPTD structure and Phase 2 heating will occur in 2016.

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Mr. Kien inquired about how long there was cracking and emissions from the pile, and what was the remedy for the issue. Mr. Galligan said that they increased the vacuum, installed a liner on top of the LWIC, installed a supplemental LWIC cover on top of the liner, and required people working on top of the pile to wear elevated PPE including respiratory protection (SCBAs ). Ms. Patterson added that more ambient air monitoring around the Project site monitoring is also being performed.

- Mr. Kien inquired about the purpose of the supplemental LWIC, who poured it, and their legal status as a subcontractor. Mr. Galligan said that the additional L WIC is to provide more insulation and expedite heating of the top layers in the pile. It was performed by a joint venture under Kruger consisting of Daleo, who installed the LWIC, and Lilama, who monitored the reports. Mr. Kien reiterated MONRE's requirement that all Vietnamese subcontractors must be working under an environmental license on the Project site. USAID agreed.

4. Site Walk/Tour

A site walk was held to look at the IPTD pile structure.

- Potential sites for storing and isolating the sediment were visited.

5. Capacity Building Training

- Ms. Patterson provided an overview of the next capacity building training activity, which will focus on environmental sampling and be held at the Bien Hoa Airbase. The proposed schedule is to travel Monday morning to Bien Hoa, have 1 Yz days of classroom and 2 Yz days of field training, and travel back Friday afternoon. The week of March 23rd was proposed.

- Mr. Kien agreed with the proposed date and agenda. USAID should prepare a letter with the time, schedule, and list of trainees, and ADAFC will inform the trainees.

6. US Ambassador Visit

- Ms. Choe said that the new US Ambassador may be visiting the site around February 9th. The schedule is being prepared by the Consulate, but it is anticipated that he will visit the site and have a site walk. Mr. Kien said that USAID should provide more details when available and advise on who should attend from ADAFC.

The meeting ended at 5:00 pm.

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Attachment 4

The Report on Estimated Human Health and Ecological Risk Assessment due to Arsenic and Dioxin in the Excess Volume Stockpile Area at the Danang Airport, Vietnam

1

Estimated Human Health and Ecological Risks Due to Arsenic and Dioxin in the Excess

Volume Stockpile Area at the Danang Airport, Vietnam

June 24, 2016 This document was produced for review by the United States Agency for International Development (USAID). It was prepared by CDM International, Inc. (CDM Smith).

ENVIRONMENTAL REMEDIATION AT DANANG AIRPORT

CONSTRUCTION MANAGEMENT AND OVERSIGHT

Environmental Remediation at Danang Airport Construction Management and Oversight

Estimated Human Health and Ecological Risks Due to Arsenic and Dioxin in the Excess Volume Stockpile Area at the Danang Airport, Vietnam

Prepared by: Erin Formanek, Teddy Marcum, Roger Olsen

Organization: CDM International, Inc. (CDM Smith)

Submitted to: Maura Patterson United States Agency for International Development (USAID) Contracting Officer's Representative (COR)

USAID Contract No.: AID-EDH-1-00-08-00023

USAID Order No.: AID-486-TO-12-00001

Date: June 24, 2016

CONTENTS SECTION 1 – SITE INTRODUCTION AND BACKGROUND ................................................ 1

SECTION 2 – HUMAN HEALTH RISK EVALUATION ........................................................... 4 2.1 Exposure Assessment .................................................................................................................... 4 2.2 Selection of Chemicals of Potential Concern .......................................................................... 5 2.3 Risk from Arsenic ........................................................................................................................... 5 2.4 Risk from Dioxin ........................................................................................................................... 10 2.5 Exposure Due to Fish Consumption ....................................................................................... 12 2.6 Uncertainties .................................................................................................................................. 12 2.7 Conclusions .................................................................................................................................... 13

SECTION 3 – ECOLOGICAL RISK EVALUATION ............................................................... 14

SECTION 4 – REFERENCES ..................................................................................................... 14

TABLES Table 1 Analytical Results .......................................................................................................................................... 5 Table 2 Site-Specific IVBA Results for Evaluation of Risks due to Incidental Ingestion of Soil .................. 6 Table 3 Estimated Concentrations of Arsenic in Groundwater and Surface Water ................................. 7 Table 4 Estimated Arsenic RME Non-Cancer HIs ............................................................................................... 8 Table 5 Estimated Arsenic RME Cancer Risks ...................................................................................................... 9 Table 6 Estimated Concentrations of Dioxin in Groundwater and Surface Water ................................. 10 Table 7 Estimated Dioxin RME Non-Cancer HIs ............................................................................................... 11 Table 8 Estimated Dioxin RME Cancer Risks ..................................................................................................... 11

Figures Figure 1 EVSA Location Map ...................................................................................................................................... 2

ATTACHMENTS A Exposure Parameters B Arsenic Risk Estimates C Dioxin Risk Estimates D Groundwater and Surface Water Concentrations Derivation

ACRONYMS/ABBREVIATIONS 2,3,7,8-TCDD 2,3,7,8-tetrachlorodibenzo-p-dioxin 95UCL 95% upper confidence level ADAFC Air Defense – Air Force Command AWQC ambient water quality criteria bgs below ground surface CDM Smith CDM International, Inc. cm centimeter COPC chemical of potential concern COR Contracting Officer’s Representative CRC collision-reaction cell CTE central tendency exposure DD former Drainage Ditch EA Environmental Assessment EPC exposure point concentration EVSA Excess Volume Stockpile Area GVN Government of Vietnam HDPE high density polyethylene HI hazard index HQ hazard quotient ICP inductively coupled plasma IPTD® In-Pile Thermal Desorption® IVBA In Vitro Bioaccessibility kg kilogram m meter m3 cubic meter mg/kg milligrams per kilogram m3/kg cubic meters per kilogram mg/L milligrams per liter MIS multi-increment sample mm millimeter MND Vietnamese Ministry of National Defense MS mass spectrometry PEF particulate emission factor ppt parts per trillion RBA relative bioavailability RME reasonable maximum exposure RSL Regional Screening Level SA former Storage Area SPLP Synthetic Precipitation Leaching Procedure TDI tolerable daily intake TSSA Temporary Sediment Storage Area

2

µg/L micrograms per liter U.S. United States USAID United States Agency for International Development USEPA United States Environmental Protection Agency VF volatilization factor

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1 Introduction and Background Large volumes of Agent Orange, a defoliant containing dioxin, primarily as the 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) congener, were used during the United States (U.S.)-Vietnam War. The former U.S. military base at Danang, now a Vietnamese military airbase and civilian airport, is one of the country’s most contaminated sites and is a Government of Vietnam (GVN) priority area for remediation to reduce the risk of human exposure to 2,3,7,8-TCDD (dioxin). The U.S. Agency for International Development (USAID) is the lead U.S. agency implementing the remediation program in Danang. USAID’s 2010 Environmental Assessment (EA) at Danang Airport selected In-Pile Thermal Desorption® (IPTD®) for dioxin treatment based on effectiveness, implementability, environmental impact, and cost (USAID 2010).

Phase 1 of the remediation program was completed in 2015, and post-treatment confirmation samples collected from the IPTD® pile demonstrated successful treatment of dioxin in approximately 45,000 cubic meters (m3) of soil, with concentrations well below the cleanup goal of 150 parts per trillion (ppt) of dioxin. Phase II of the remediation program is underway, with another 45,000 m3 of dioxin-contaminated material excavated and placed in the IPTD structure for thermal treatment in 2016 and 2017. Since the volume of contaminated material has exceeded the amount estimated by the EA, there is additional sediment material that has been excavated since it exceeded the dioxin sediment standard of 150 ppt. This remaining over excavation material is below 1,000 ppt dioxin.

In 2014, USAID and the Vietnamese Ministry of National Defense (MND), Air Defense – Air Force Command (ADAFC) first discussed alternatives for handling excavated soil/sediment with dioxin concentrations between 150 ppt and 1,000 ppt. USAID recommended stabilizing/solidifying the material and using it as backfill in the former Storage Area (SA) and former Drainage Ditch (DD). In 2015, ADAFC requested the material be stockpiled at a location designated by ADAFC rather than be stabilized/solidified and used as backfill in the SA and DD – an initial location was identified by ADAFC north of the western runway. In November 2015, USAID requested ADAFC to identify a stockpile location that: 1) can fit the entire volume of soil/sediment with dioxin concentrations between 150 and 1,000 ppt; and 2) is in an upland, commercially/industrially-zoned area of the Danang Airport that does not contain low-lying wetlands or lakes. USAID also confirmed the agreement between USAID and ADAFC that no amendment or stabilization/solidification would be required for stockpiling the excess soil/sediment, particularly if it is placed in an area designated for commercial/industrial land use. ADAFC identified a location for the Excess Volume Stockpile Area (EVSA) in the southwest corner of the Danang Airport property near the former Pacer Ivy Storage Area (see Figure 1), and USAID/CDM Smith confirmed that the location is acceptable in February 2016. This agreement was made in accordance with GVN regulation QCVN 45:2012/BTNMT that states commercial and industrial areas can contain soils with dioxin concentrations up to 1,200 ppt.

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1 2

EVSA location

Ponds 1 through 6

3

4 & 5

6

Figure 1 – EVSA Location Map

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Approximately 35,000 m3 of excess soil/sediment with dioxin concentrations less than 1,000 ppt has been excavated from the Project site and placed in Temporary Sediment Storage Area (TSSA)-1 and TSSA-2. This material, plus approximately 15,000 m3 of additional sediment to be excavated in 2016, will be placed in EVSA.

While the focus of the remediation program was to treat dioxin; sampling of site soil and sediment was conducted during the 2010 EA to determine whether other chemicals of potential concern (COPCs) were present in soil/sediment that might affect the remedial design, operation and maintenance of the remedy, and/or health and safety aspects of the remedy implementation. With one exception, all metal concentrations in site soil were below the U.S. Environmental Protection Agency (USEPA) industrial Regional Screening Levels (RSLs) (USEPA 2016). Arsenic concentrations at the site ranged from 6 to 328 milligrams per kilogram (mg/kg). The USEPA industrial RSL for inorganic arsenic in soil is 3.0 mg/kg; no RSL is established for sediment. According to GVN regulation QCVN 03-MT:2015/BTNMT (National Technical Regulation on the Allowable Limits of Heavy Metals in Soils), the allowable arsenic concentration in soil is 20 mg/kg for commercial land and 25 mg/kg for industrial land.

Due to a potential range of dioxin concentrations (150 to 1,000 ppt) and arsenic concentrations (6 to 328 mg/kg) in the material to be placed in the EVSA, CDM Smith conducted a risk evaluation in order to determine the appropriate engineering controls needed for construction of the EVSA. This report presents the complete results of the evaluation of human health and ecological risks due to dioxin and arsenic in the EVSA. Multiple receptors and exposure pathways were evaluated, and multiple EVSA construction scenarios were evaluated to estimate the level of risk associated with each scenario. The following five scenarios for EVSA construction were evaluated:

Scenario 1

• Slope = 1A) 2% and 1B) 5%

• 60 centimeter (cm) soil cover

• 1.5 meter (m) waste material

Scenario 2

• Slope = 2A) 2% and 2B) 5%

• 60 cm soil cover

• 1-millimeter (mm) (40-mil) thick high density polyethylene (HDPE) liner with 1 holes/defect per hectare

• 1.5 m waste material

Scenario 3

• Slope = 3A) 2% and 3B) 5%

• 60 cm soil cover

• 1-mm (40-mil) thick HDPE liner with 1 hole/defect per hectare

• Bentonite mat as a barrier layer

• 1.5 m waste material

• 1-mm (40-mil) thick HDPE liner with 1 hole/defect per hectare

• Bentonite mat as a barrier layer

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• 1 m silty to clayey sand

The modeling difference between the 2% slope and 5% slope were minimal, therefore, only the 2% slope scenarios were evaluated in the risk evaluation (i.e., only Scenarios 1A, 2A, and 3A were evaluated). In addition, the 2% slope scenario is more conservative for a risk evaluation since the drainage is less with more potential infiltration under the 2% slope scenario than the 5% slope scenario. Note that these scenarios assume the following:

• Construction of a berm and fence around the EVSA and placement of signs restricting access. • Regular mowing of grass (when it is 6-12 inches high, probably every 2 weeks or every month),

• Quarterly walk-through inspections looking for: animal burrows into cover, shrubs/trees growing (significant roots that could damage/penetrate liner), erosion gullies, inspection of subsidence, integrity of berm, fence, and signs.

• Inspection for erosion gullies following significant rainfall with subsequent repairs including regressing and/or adding soil.

2 Human Health Risk Evaluation

2.1 Exposure Assessment Several receptors were selected for the evaluation of potential human health risks. A future resident, a trespasser, and a construction worker were evaluated to span the possible range of exposures from incidental ingestion of soil, dermal contact with soil, inhalation of soil, ingestion of groundwater, incidental ingestion of surface water while swimming, and dermal contact with surface water while swimming at the site. Not all of these exposure pathways are complete for all receptors. For example, exposure to groundwater via ingestion is not a complete pathway for a trespasser. In addition, the soil exposure pathways (via incidental ingestion, dermal contact, and inhalation) are not complete for the resident and trespasser. The soil exposure pathway is not complete for the resident and trespasser because cover will be placed over the stockpile and there will be a berm and fence constructed around the stockpile as well as signage indicating that trespassing is not permitted.

Exposure was evaluated using standard equations recommended by the United States Environmental Protection Agency (USEPA) for use at Superfund sites. This results in a more conservative evaluation compared to utilizing GVN standards primarily due to the exposure pathways evaluated (e.g., dermal and inhalation as well as ingestion), the toxicity values used (i.e., oral slope factor vs. tolerable daily intake [TDI]), and the assumed mode of action for dioxin (i.e., linear non-threshold vs. non-linear threshold model). The exposure parameters were based on USEPA default guidelines or on professional judgment when default guidelines were not available (see Attachment A). Typically, attention is focused on intakes that are “average” or are otherwise near the central portion of the range, and on intakes near the upper end of the range (e.g., the 95th percentile). These two exposure estimates are referred to as central tendency exposure (CTE) and reasonable maximum exposure (RME), respectively. This evaluation focuses on RME estimates only, in order to be conservative. If risk estimates for RME receptors are below a level of concern, risk estimates for CTE receptors will be as well. Attachment B (arsenic) and Attachment C (dioxin) present a summary of risk estimates for both the CTE and RME receptors for informational purposes. The following exposure parameters were assumed for the receptors evaluated for RME.

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• An adult body weight of 80 kilograms (kg)1 and a child body weight of 15 kg;

• An exposure frequency for the resident, trespasser, and construction worker of 350, 52, and 225 days/year, respectively; and

• An exposure duration of 26 years for the resident/trespasser (child plus adult) and 25 years for the construction worker.

2.2 Selection of Chemicals of Potential Concern Previous investigations at the site revealed arsenic and dioxin are of potential concern. Therefore, this evaluation was focused on the evaluation of risks from arsenic and dioxin only.

2.3 Risk from Arsenic Analytical results for total arsenic measured in soil samples collected from Project site indicate total arsenic concentrations at the site ranged from 6 to 328 mg/kg. Analysis of leachable arsenic was not conducted on the untreated Project site soil/sediment; however, the treated soil/sediment from Phase 1 was analyzed for total arsenic and leachable arsenic. The Phase I treated soil/sediment arsenic results were used to determine the exposure point concentration (EPC) for soil (see Table 1). The arsenic concentration in these samples is not expected to differ substantially from the arsenic concentrations in untreated soil because the thermal treatment process has a relatively small impact if any on the total arsenic concentration in soil. USEPA’s ProUCL software was used to derive the EPC. The 95% Student’s-t upper confidence limit (95UCL) on the mean was selected for use in the risk estimates. The arsenic EPC for soil was 30 mg/kg.

Table 1. Analytical Results

Sample ID 1R-SL-P1-IPTD-0001

1R-SL-P1-IPTD-0002

1R-SL-P1-IPTD-0003

1R-SL-P1-IPTD-0004

1R-SL-P1-IPTD-0005

1R-SL-P1-IPTD-0006

Sample Description1 0-1 m

IPTD layer 1-2 m

IPTD layer 2-3 m

IPTD layer 3-4 m

IPTD layer 4-5 m

IPTD layer 5-6 m

IPTD layer Total arsenic2 20.4 mg/kg 20.3 mg/kg 23.1 mg/kg 18.7 mg/kg 17.7 mg/kg 36.3 mg/kg Leachable Arsenic3 0.0395 mg/L 0.0639 mg/L 0.244 mg/L 0.250 mg/L 0.238 mg/L 0.142 mg/L

Notes: 1 – Each sample represents a different horizontal layer of the 6 m deep IPTD pile. The samples were collected using multi-increment sample (MIS) methodology, by compositing 30 aliquots from the subject layer into one sample for analysis. The 30 aliquots for each sample were collected from a systematic random grid across the IPTD pile, each collected from the entire 1 m depth of the IPTD pile layer. 2 – Analyzed by USEPA Method 200.2/6020A (modified); Metals in Soil by collision-reaction cell (CRC) inductively coupled plasma (ICP) mass spectrometry (MS). 3 – Analyzed by Synthetic Precipitation Leaching Procedure (SPLP) USEPA Method 1312M; extraction fluid to soil ratio of 2:1 (milliliter to gram); 4.2 pH extraction solution. Digest analyzed by USEPA Method 200.2/6020A.

For soil, accurate assessment of the human health risks resulting from incidental ingestion of arsenic-containing soil requires knowledge of the bioavailability of arsenic from those soils. Oral bioavailability is defined as the amount of arsenic absorbed into the body following ingestion of soil or soil-like materials (e.g., sediment) that contain arsenic. Relative bioavailability (RBA) is the ratio of the absolute oral bioavailability of arsenic present in some test material (e.g., soil) to the absolute oral bioavailability of

1 Note, these exposure parameters are not typical values for the Vietnamese population. However, even if a site-specific body weight was used, the overall conclusions would remain unchanged.

5

arsenic in an appropriate reference material. The bioavailability of arsenic in soil may vary from site to site depending upon the chemical form of the arsenic present in the soil, as well as the physical and chemical characteristics arsenic-bearing soil particles. It is for this reason USEPA recommends the collection of site-specific data on RBA where such assessments are deemed feasible and valuable for improving the characterization of risk at the site. In-vitro bioaccessibility (IVBA) testing was not conducted on the untreated Project site soil/sediment; however, IVBA testing was conducted on the treated Phase 1 soil/sediment to determine the site-specific arsenic RBA of the treated soil. The arsenic concentration in these samples is not expected to differ substantially from the arsenic concentrations in untreated soil because the thermal treatment process has a relatively small impact if any on the total arsenic concentration in soil. IVBA analyses were performed by Dr. John Drexler at the University of Colorado in Boulder, Colorado. Table 2 presents the results of the IVBA testing. As seen, the estimated IVBA values ranged from 16% to 59%. These IVBA results are used to estimate the RBA using the regression equation provided in Diamond et al. (2016). As shown in Table 2, RBA values ranged from 16% to 50%, with an average of 36%. The RBA is used to adjust the toxicity values when evaluating soil ingestion exposure scenarios.

Table 2. Site-Specific IVBA Results for Evaluation of Risks due to Incidental Ingestion of Soil

Sample ID 1R-SL-P1-IPTD-0001

1R-SL-P1-IPTD-0002

1R-SL-P1-IPTD-0003

1R-SL-P1-IPTD-0004

1R-SL-P1-IPTD-0005

1R-SL-P1-IPTD-0006

Arsenic concentration (< 250 micron soil particle size fraction)1

23.7 mg/kg 25.0 mg/kg 26.9 mg/kg 23.6 mg/kg 25.8 mg/kg 34.8 mg/kg

Percent Arsenic IVBA 16% 38% 59% 50% 48% 40% Percent RBA, predicted based on Diamond et al., 2016

16% 33% 50% 43% 41% 34%

Note 1: The arsenic concentration used for the IVBA and RBA analysis represent the arsenic concentration for the fraction of soil particles less than 250 microns instead of the arsenic concentration for all the soil fractions. The < 250 micron soil particle size fraction is the portion that adheres to children’s hands and would be ingested.

Arsenic in soil can become suspended as airborne particulates due to natural processes (e.g., wind) or soil disturbance activities. The concentration of arsenic in air was estimated using a screening-level soil-to-air transfer model as outlined in USEPA’s Soil Screening Guidance (USEPA 1996). The model requires an estimate of the acreage, fraction of vegetative cover, and a location-specific dispersion model (Q/C) value for each zone/U.S. city. For the purposes of modeling air concentrations for this site, the vegetative cover was assumed to be 5%. The Q/C value for Miami, Florida at the minimum acreage available (0.5 acres) was selected. The minimum acreage was selected because cover will be placed on the stockpile. The resulting estimated particulate emission factor (PEF) was 1.05E+09 cubic meters per kilogram (m3/kg).

Arsenic concentrations in groundwater and surface water were estimated for three scenarios (1A, 2A, and 3A) using the inputs and modeling procedures described in Attachment D. The results of the modeling for each scenario are presented in Table 3. For Scenario 1A and 2A, the estimated groundwater concentration of arsenic range from 6.75E-05 to 0.110 milligrams per liter (mg/L) in a hypothetical groundwater well placed in the middle of the EVSA completed in the upper aquifer, and range from 1.86E-05 to 0.036 mg/L in a hypothetical downgradient groundwater well completed in the

6

upper aquifer and located 50 m downgradient from the southern boundary of the EVSA. For Scenario 3, the modeling resulted in 0.00% percolation thru the bottom layer and arsenic concentrations in both hypothetical groundwater sources of 0 mg/L.

Surface water arsenic concentrations were estimated for six ponds near the EVSA (see Figure 1). The estimated arsenic concentrations for the ponds did not span a wide range. For this reason, only the estimated concentrations for the pond with the highest estimated concentrations (Pond 1) are shown in Table 3, with the estimated concentrations for all ponds presented in Attachment D. For Scenarios 1A and 2A, arsenic concentrations range from 1.29E-05 to 0.025 mg/L in Pond 1. For Scenario 3, because there is no percolation through the bottom layer, the concentration of arsenic in water is 0 mg/L for all water sources.

Table 3. Estimated Concentrations of Arsenic in Groundwater and Surface Water Water Source

Scenario Well in Middle of EVSA1

Downgradient Well 50m from Southern Boundary

of EVSA1

Pond 1

0.25 mg/L Leachate

0.50 mg/L Leachate

0.25 mg/L Leachate

0.50 mg/L Leachate

0.25 mg/L Leachate

0.50 mg/L Leachate

1A 0.055 mg/L 0.110 mg/L 0.018 mg/L 0.036 mg/L 0.013 mg/L 0.025 mg/L 2A 6.75E-05 mg/L 1.35E-04 mg/L 1.86E-05 mg/L 3.71E-05 mg/L 1.29E-05 mg/L 2.57E-05 mg/L 3 0 mg/L 0 mg/L 0 mg/L 0 mg/L 0 mg/L 0 mg/L

Note 1: Groundwater wells were assumed to be completed in the uppermost Holocene aquifer with a groundwater level of 0.3 m below ground surface (bgs).

Toxicity values for both cancer and non-cancer were selected from USEPA recommended sources as summarized in the RSLs table (USEPA 2016).

Non-cancer risks are evaluated by computing hazard quotient (HQ) values for individual exposure pathways and summing them to compute the hazard index (HI). If the value of the HI is less than or equal to 1 (one), then risks of non-cancer effects are not of concern. If the value of HI exceeds 1, then there may be a risk of non-cancer effects, with the probability and/or severity tending to increase as the values of the HI becomes larger. Based on this approach, the calculated non-cancer risk estimates for the complete soil (incidental ingestion, dermal contact, and inhalation) (for construction workers only – the soil pathway is incomplete for residents and trespassers), groundwater (ingestion) and surface water (incidental ingestion and dermal contact) pathways are summarized below in Table 4. Note, risk estimates are not presented for Scenario 3 because the EPC is 0 mg/L for groundwater and surface water.

7

Table 4. Estimated Arsenic RME Non-Cancer HIs1,2

Scenario

Well in Middle of EVSA3 Downgradient Well 50m from southern boundary of EVSA3

Future Resident Trespasser

Worker4 Future

Resident Trespasser Worker4

Adult Child Adult Child Adult Child Adult Child

1A

0.25 mg/L Leachate 6 9 0.003 0.04 1 2 3 0.003 0.04 0.5

0.50 mg/L Leachate 11 18 0.005 0.09 3 4 6 0.005 0.09 1

2A

0.25 mg/L Leachate 0.007 0.01 0.000003 0.00004 0.04 0.002 0.003 0.000003 0.00004 0.04

0.50 mg/L Leachate 0.01 0.02 0.000005 0.00009 0.04 0.004 0.006 0.000005 0.00009 0.04

Notes: 1 – RME non-cancer HI values represent all complete exposure pathways (i.e., soil incidental ingestion/dermal contact/inhalation for workers, groundwater ingestion for residents, trespassers and workers, and surface water incidental ingestion/dermal contact for residents, trespassers and workers). 2 – RME non-cancer HIs shown in red exceed one, indicating there may be a risk of non-cancer effects and some form of remedial action is desirable. 3 – HIs were calculated assuming that receptors would ingest groundwater from the uppermost Holocene aquifer (groundwater level of 0.3 m bgs). However, per the Environmental Remediation at Danang Airport: Environmental Assessment in Compliance with 22 CFR 216 (USAID 2010), the sources of drinking water in this area are the Lower Pleistocene and Cambrian Ordovician aquifers which underlie an approximate 5 m thick aquitard. 4 – Construction worker.

As shown in Table 4, for Scenario 1A, RME non-cancer HIs are above 1 for the adult and/or child resident and below 1 for the adult and/or child trespasser regardless of the groundwater source and assumed leachate level (i.e., 0.25 mg/L and 0.50 mg/L leachate). For the construction worker, RME non-cancer HIs were only above 1 if the hypothetical well in the middle of the EVSA were used as a groundwater source and 0.50 mg/L leachate were assumed. For Scenario 2A, all RME non-cancer HIs were below 1 for all receptors, based on both groundwater sources and both leachate assumptions.

For cancer, risks are expressed in terms of the probability that site-related exposures will result in the occurrence of cancer. USEPA considers cumulative excess cancer risks that are below about 1E-06 (1x10-6 or 1 in 1,000,000) to be negligible, and risks above 1E-04 (1x10-4 or 1 in 10,000) to be sufficiently large that some form of remedial action is desirable. Excess cancer risks that range between 1E-04 and 1E-06 are generally considered to be acceptable, although this is evaluated on a case-by-case basis. The calculated cancer risk estimates are summarized below in Table 5.

8

Table 5. Estimated Arsenic RME Cancer Risks1, 2

Scenario

Well in Middle of EVSA3 Downgradient Well 50m from southern boundary of EVSA3

Future Resident4 Trespasser4

Worker5 Future

Resident4 Trespasser4 Worker5

Adult Child Adult Child Adult Child Adult Child

1A

0.25 mg/L Leachate 7E-04 4E-04 3E-07 2E-06 2E-04 2E-04 1E-04 3E-07 2E-06 8E-05


2A



Notes: 1 –RME cancer risk values represent all complete exposure pathways (i.e., soil incidental ingestion/dermal contact/inhalation for workers, groundwater ingestion for residents, trespassers and workers, and surface water incidental ingestion/dermal contact for residents, trespassers and workers). 2 – RME cancer risks shown in red are above 1E-04 (i.e., USEPA’s acceptable risk range), indicating that some form of remedial action is desirable. 3 – Cancer risks were calculated assuming that receptors would ingest groundwater from the uppermost Holocene aquifer (groundwater level of 0.3 m bgs). However, per the Environmental Remediation at Danang Airport: Environmental Assessment in Compliance with 22 CFR 216 (USAID 2010), the sources of drinking water in this area are the Lower Pleistocene and Cambrian Ordovician aquifers which underlie an approximate 5 m thick aquitard. 4 – Future resident and trespasser risks are for individual adult and child and do not represent the total lifetime risk which is the sum of the adult and child risk. 5 – Construction worker.

As shown in Table 5, for Scenario 1A, RME cancer risks are at or above USEPA’s acceptable risk range for the adult and/or child resident and within or below USEPA’s acceptable risk range for the adult and/or child trespasser regardless of the groundwater source and assumed leachate level (i.e., 0.25 mg/L and 0.50 mg/L leachate). For the construction worker, RME cancer risks were above USEPA’s acceptable risk range if the well in the middle of the EVSA were used as a hypothetical groundwater source regardless of the assumed leachate level (i.e., 0.25 mg/L or 0.50 mg/L leachate) and above USEPA’s acceptable risk range for the downgradient well if 0.50 mg/L leachate were assumed. For Scenario 2A, all RME cancer risks were within or below USEPA’s acceptable risk range for all receptors, based on both groundwater sources and both leachate assumptions.

Review of Attachment B reveals that RME non-cancer HIs above 1 and cancer risks above USEPA’s acceptable risk range are being driven by the groundwater ingestion pathway. Exposures were calculated assuming that receptors would ingest groundwater from the uppermost Holocene aquifer (groundwater level of 0.3 m bgs). However, per the Environmental Remediation at Danang Airport: Environmental Assessment in Compliance with 22 CFR 216 (USAID 2010), the sources of drinking water in this area are the Lower Pleistocene and Cambrian Ordovician aquifers which underlie an approximate 5 m thick aquitard. If the groundwater pathway (i.e., exposure via ingestion of groundwater) were eliminated by restricting the installation of groundwater wells in the uppermost Holocene aquifer, all RME non-cancer HIs would be below 1 and cancer risks would be below USEPA’s acceptable risk range for all receptors for all scenarios for soil and surface water exposures.

9

2.4 Risk from Dioxin The EPC for soil was assumed to be 751 ppt. This value is based on one, 30-point multi-increment sample (1R-SL-TSSA1-B-All-0001) collected from TSSA-1 (temporary onsite storage area that contains approximately 25,000 m3 of the material to be placed in the EVSA).

Dioxin in soil can become suspended as airborne particulates due to natural processes (e.g., wind) or soil disturbance activities as well as by volatilization. The concentration of dioxin in air was estimated using a screening-level soil-to-air transfer model as outlined in USEPA’s Soil Screening Guidance (USEPA 1996) and a volatilization factor derived using USEPA’s Supplemental Guidance for Developing Soil Screening Levels for Superfund Sites (USEPA 2002). The derivation of the PEF (1.05E+09 m3/kg) used in the dioxin risk estimates is presented in Section 2.3. The volatilization factor (VF) of 1.96E+06 m3/kg was derived based on USEPA (2002) assuming a 0.5-acre emission source, which is consistent with the area assumed for the derivation of the PEF value.

Dioxin concentrations in groundwater and surface water were estimated for three scenarios (1A, 2A, and 3A) using the inputs and modeling procedures described in Attachment D. The results of the modeling for each scenario are presented in Table 6. For Scenario 1A, the estimated groundwater concentrations of arsenic are 0.595 picograms per liter (pg/L) in a hypothetical groundwater well placed in the middle of the EVSA completed in the upper aquifer and 0.195 pg/L in a hypothetical downgradient groundwater well completed in the upper aquifer and located 50 m downgradient from the southern boundary of the EVSA. For Scenario 2A, the estimated concentrations are 7.24E-04 pg/L and 2.00E-04 pg/L. For Scenario 3, the modeling resulted in 0.00% percolation thru the bottom layer and dioxin concentrations in both hypothetical groundwater sources of 0 pg/L.

Surface water dioxin concentrations were estimated for six ponds located approximately 750 to 1,000 m downgradient from the EVSA (see Figure 1). The estimated dioxin concentrations for the ponds did not span a wide range. For this reason, only the estimated dioxin concentrations for the pond with the highest estimated concentrations (Pond 1) are shown in Table 6, with the estimated concentrations for all ponds presented in Attachment D. For Scenario 1A, the dioxin concentration was estimated at 0.137 pg/L in Pond 1. A dioxin concentration of 1.39E-04 pg/L was estimated in Pond 1 for Scenario 2A. For Scenario 3, because there is no percolation through the bottom layer, the concentrations of dioxin in water is 0 pg/L for all water sources.

Table 6. Estimated Concentrations of Dioxin in Groundwater and Surface Water Water Source

Scenario Well in Middle of EVSA1

Downgradient Well 50m from Southern Boundary of EVSA1

Pond 1

1A 0.595 pg/L 0.195 pg/L 0.137 pg/L 2A 7.27E-04 pg/L 2.00E-04 pg/L 1.39E-04 pg/L 3 0 pg/L 0 pg/L 0 pg/L

Note 1: Groundwater wells were assumed to be completed in the uppermost Holocene aquifer with a groundwater level of 0.3 m below ground surface (bgs).

10

Toxicity values for both cancer and non-cancer were selected from USEPA recommended sources as summarized in the RSLs table (USEPA 2015).

The calculated non-cancer risk estimates for the complete soil (incidental ingestion, dermal contact, and inhalation) (for construction workers only – the soil pathway is incomplete for residents and trespassers), groundwater (ingestion), and surface water (incidental ingestion and dermal contact) pathways are summarized below in Table 7. Note, risk estimates are not presented for Scenario 3 because the EPC is 0 mg/L for groundwater and surface water. As shown in Table 7, for both scenarios, RME non-cancer HIs are below 1 for all receptors, based on both groundwater sources.

Table 7. Estimated Dioxin RME Non-Cancer HIs1,2

Scenario Well in Middle of EVSA3 Downgradient Well

50m from southern boundary of EVSA3 Future Resident Trespasser

Worker4 Future Resident Trespasser

Worker4 Adult Child Adult Child Adult Child Adult Child

1A 0.03 0.04 0.00001 0.0002 0.9 0.008 0.01 0.00001 0.0002 0.9 2A 0.00003 0.00005 1E-08 2E-07 0.9 0.000009 0.00001 1E-08 2E-07 0.9

Notes: 1 – RME non-cancer HI values represent all complete exposure pathways (i.e., soil incidental ingestion/dermal contact/inhalation for workers, groundwater ingestion for residents, trespassers and workers, and surface water incidental ingestion/dermal contact for residents, trespassers and workers). 2 – No RME non-cancer HIs exceed one, indicating risks of non-cancer effects are not of concern. 3 – HIs were calculated assuming that receptors would ingest groundwater from the uppermost Holocene aquifer (groundwater level of 0.3 m bgs). However, per the Environmental Remediation at Danang Airport: Environmental Assessment in Compliance with 22 CFR 216 (USAID 2010), the sources of drinking water in this area are the Lower Pleistocene and Cambrian Ordovician aquifers which underlie an approximate 5 m thick aquitard. 4 – Construction worker.

The calculated cancer risk estimates are summarized below in Table 8. As shown in Table 8, for both scenarios, RME cancer risks are within or below USEPA’s acceptable risk range for all receptors, based on both hypothetical groundwater sources.

Table 8. Estimated Dioxin RME Cancer Risks1

Scenario Well in Middle of EVSA2 Downgradient Well

50m from southern boundary of EVSA2 Future Resident3 Trespasser3

Worker4 Future Resident3 Trespasser3

Worker4 Adult Child Adult Child Adult Child Adult Child

1A 7E-07 3E-07 3E-10 2E-09 3E-05 2E-07 1E-07 3E-10 2E-09 3E-05 2A 8E-10 4E-10 3E-13 2E-12 3E-05 2E-10 1E-10 3E-13 2E-12 3E-05

Notes: 1 –RME cancer risk values represent all complete exposure pathways (i.e., soil incidental ingestion/dermal contact/inhalation for workers, groundwater ingestion for residents, trespassers and workers, and surface water incidental ingestion/dermal contact for residents, trespassers and workers). No RME cancer risks are above 1E-04, indicating risks of cancer effects are negligible. 2 – Cancer risks were calculated assuming that receptors would ingest groundwater from the uppermost Holocene aquifer (groundwater level of 0.3 m bgs). However, per the Environmental Remediation at Danang Airport: Environmental Assessment in Compliance with 22 CFR 216 (USAID 2010), the sources of drinking water in this area are the Lower Pleistocene and Cambrian Ordovician aquifers which underlie an approximate 5 m thick aquitard. 3 – Future resident and trespasser risks are for individual adult and child and do not represent the total lifetime risk which is the sum of the adult and child risk. 4 – Construction worker.

11

2.5 Exposure Due to Fish Consumption Fish tissue measurements for arsenic and dioxin were not available, thus, it is not possible to directly calculate potential risks from fish consumption. However, USEPA has derived ambient water quality criteria (AWQC), which are protective of human consumption of fish that can be used to evaluate potential exposures from a fish consumption scenario. The estimated surface water arsenic concentrations in Pond 1 range from 1.29E-05 to 0.025 mg/L (see Table 3) depending on the scenario and assumed leachate concentration, which is equivalent to 0.0129 micrograms per liter (µg/L) to 25 µg/L. Arsenic concentrations for Scenario 1A are greater than the USEPA AWQC value for arsenic that is protective of human health consumption of fish (0.14 µg/L), however, values for Scenario 2A are below the USEPA AWQC.

In addition, the estimated surface water dioxin concentrations in Pond 1 range from 1.39E-04 to 0.137 pg/L (see Table 6) for Scenarios 1A and 2A. These concentrations are equivalent to 1.39E-10 µg/L and 1.37E-07 µg/L. The dioxin concentration for Scenario 1A (1.37E-07 µg/L) is greater than the USEPA AWQC value for dioxin that is protective of human health consumption of fish (5.10E-09 µg/L), while the value for Scenario 2A (1.39E-10 µg/L) is below the AWQC value for dioxin.

Recognizing that the surface water concentrations were estimated and because the AWQC values have built in assumptions regarding fish tissue bioaccumulation rates, measured concentrations of arsenic and dioxin in fish tissue over time would be helpful to observe impacts of groundwater infiltration into the ponds and more accurate risk estimates could be computed.

2.6 Uncertainties Quantitative evaluation of the risks to humans from environmental contamination is frequently limited by uncertainty regarding a number of key data items, including concentration levels in the environment, the true level of human contact with contaminated media, and the true dose-response curves for non-cancer and cancer effects in humans. This uncertainty is usually addressed by making assumptions or estimates for uncertain parameters based on whatever limited data are available. Because of these assumptions and estimates, the results of risk calculations are themselves uncertain, and are likely overestimated rather than underestimated due to the conservative nature of assumptions made. Additionally, risks are presented for RME in this report, which represent high-end exposures; CTE risk estimates represent average exposures and are included in the Attachment B (arsenic) and Attachment C (dioxin) to provide a range of risk estimates that may occur at the site. It is important for risk managers and the public to keep this in mind when interpreting the results of the risk evaluation. For some scenarios and receptors, risks based on CTE estimates are below a level of concern, where the RME estimates are above a level of concern (e.g., risks to the adult resident for Scenario 1A and the downgradient well 50 m from the southern boundary of the EVSA [0.25 mg/L leachate] are below a level of concern based on CTE estimates, but not RME estimates as shown in Attachment B-2).

Measured concentrations of arsenic and dioxin in fish tissue prior to soil/sediment placement and over time after soil/sediment placement would allow for a more accurate estimation of risk.

12

2.7 Conclusions Below is a summary of the main risk findings for arsenic.

Scenario 1A:

• Non-cancer and cancer risks are above levels of concern for residents and construction workers.

• Groundwater from either hypothetical source (well in the middle and the downgradient well) is driving risk for non-cancer and cancer for the resident and construction worker. If groundwater was not consumed, risks are below a level of concern for all receptors.

• Fish consumption would not be advisable based on comparison of surface water values estimated for all ponds to the USEPA AWQC value.

Scenario 2A:

• Non-cancer and cancer risks are below levels of concern for residents, trespassers, and construction workers.

• Fish consumption is not expected to pose a significant risk based on comparison of surface water values estimated for all ponds to the USEPA AWQC value.

Scenario 3:

• Since there is no percolation through the bottom layer, there are no non-cancer and cancer risks, and fish consumption is not a risk.

Below is a summary of the main risk findings for dioxin.

Scenario 1A:

• Non-cancer and cancer risks are below levels of concern for all receptors.

• Fish consumption would not be advisable based on comparison of surface water values estimated for all ponds to the USEPA AWQC value.

Scenario 2A:

• Non-cancer and cancer risks are below levels of concern for all receptors.

• Fish consumption is not expected to pose a significant risk based on comparison of surface water values estimated for all ponds to the USEPA AWQC value.

Scenario 3:

• Since there is no percolation through the bottom layer, there are no non-cancer and cancer risks, and fish consumption is not a risk.

Based on the above findings, it can be seen that there is a meaningful benefit by adding the HDPE liner to the stockpile cover in Scenario 2 when compared to Scenario 1. Since the findings of the risk assessment for Scenario 2 and 3 are the same, there are no meaningful benefits to Scenario 3 resulting from the inclusion of an HDPE bottom liner.

13

3 Ecological Risk Evaluation For the ecological risk evaluation, risks were evaluated for ecological species that may be adversely impacted due to groundwater migration to the ponds. Risks were not evaluated for terrestrial wildlife receptors that may be present on the EVSA. The rationale for this being that the habitat is not intentionally supportive of these receptors, indeed the presence of burrowing mammals will be actively monitored and discouraged, and migration on and off the EVSA is limited due to the fencing that will be installed. Below is a summary of the ecological screening-level evaluation for arsenic and dioxin for the ponds.

For arsenic, a screening-level evaluation of ecological risks for aquatic receptors was performed using a commonly used screening value, i.e., the USEPA AWQC value for aquatic life. The aquatic life criterion is the highest concentration of a pollutant or parameter in water that is not expected to pose a significant risk. The AWQC values for arsenic are 340 µg/L and 150 µg/L for acute and chronic exposures, respectively. The estimated surface water arsenic concentrations in Pond 1 range from 1.29E-05 to 0.025 mg/L (see Table 3) depending on the scenario and assumed leachate concentration, which is equivalent to 0.0129 µg/L to 25 µg/L. A comparison of the estimated concentrations to both the acute and chronic AWQC values indicates that levels of arsenic in the ponds are not likely of concern.

For dioxin, a screening-level evaluation of ecological risks for aquatic receptors was performed using dioxin values recommended by USEPA for evaluating risks to aquatic life and associated wildlife (USEPA 1993). The aquatic life criterion is the highest concentration of a pollutant or parameter in water that is not expected to pose a significant risk. A range of screening values (low risk to high risk) may be used for comparison to estimated dioxin levels. For screening purposes, the high risk to sensitive species values were selected, values range from 0.4 pg/L to 5 pg/L for the protection of mammalian wildlife, avian wildlife, and fish. The estimated surface water dioxin concentrations in Pond 1 range from 1.39E-04 to 0.137 pg/L (see Table 6) for Scenarios 1A and 2A. A comparison of the estimated concentrations to both the lowest of the values that are protective of high risk to sensitive species (0.4 pg/L) indicates that levels of dioxin in the ponds are not likely of concern.

4 References Gary L. Diamond, Karen D. Bradham, William J. Brattin, Michele Burgess, Susan Griffin, Cheryl A. Hawkins, Albert L. Juhasz, Julie M. Klotzbach, Clay Nelson, Yvette W. Lowney, Kirk G. Scheckel & David J. Thomas (2016) Predicting oral relative bioavailability of arsenic in soil from in vitro bioaccessibility, Journal of Toxicology and Environmental Health, Part A, 79:4, 165-173, DOI: 10.1080/15287394.2015.1134038.

USAID. 2010. Environmental Remediation at Danang Airport: Environmental Assessment in Compliance with 22 CFR 216, July.

USEPA. 1993. Interim Report on Data and Methods for Assessment of 2,3,7,8-Tetrachlorodibenzo-p-dioxin Risks to Aquatic Life and Associated Wildlife. Office of Research and Development. Washington, DC. EPA/600/R-93/055.

USEPA. 1996. Soil Screening Guidance: User’s Guide. Second Addition. Office of Solid Waste and Emergency Response. Washington, DC. July.

14

USEPA. 2002. Supplemental Guidance for Developing Soil Screening Levels for Superfund Sites. Office of Solid Waste and Emergency Response. OSWER 9355.4-24. December.

USEPA. 2016. Regional Screening Levels. http://www.epa.gov/region9/superfund/prg/. May.

15

http://www.epa.gov/region9/superfund/prg/

ATTACHMENT A

Exposure Parameters

ATTACHMENT A‐1. EXPOSURE PARAMETERS FOR CENTRAL TENDENCY EXPOSURE

ValueSource/

NoteValue

Source/

NoteValue

Source/

NoteValue

Source/

NoteValue

Source/

Note

Body Weight kg 80 10 15 1 80 10 15 1 80 10Exposure Frequency days/year 350 1 350 1 26 4, e 26 4, e 225 10Exposure Duration years 20 10 6 1 20 10 6 4, f 25 1Averaging Time (Noncarcinogenic) days 7,300 1, a 2,190 1, a 7,300 1, a 2,190 1, a 9,125 1, aAveraging Time (Carcinogenic) days 25,550 1, a 25,550 1, a 25,550 1, a 25,550 1, a 25,550 1, a

Ingestion Rate of Soil (IRsoil) mg/day 50 3, bHIF, non‐cancer kg/kg/day 3.9E‐07 7

HIF, cancer kg/kg/day 1.4E‐07 7Skin Surface Area Available for Contact (SA) cm2 3,470 10Adherence Factor (AF) mg/cm2 0.12 10Event Frequency events/day 1 5Dermal Absorption Fraction (ABS) unitless 0.03 5, gConversion Factor kg/mg 1.0E+06 ‐‐

HIF, non‐cancer kg/kg/day 9.6E‐08 7

HIF, cancer kg/kg/day 3.4E‐08 7

Exposure Time (ET) hr/day 8 4, iTWF, non‐cancer 2.1E‐01 7

TWF, cancer 7.3E‐02 7

Ingestion Rate of Water (IRgw) L/day 1.4 1, 2 0.4 6, c 0.7 3HIF, non‐cancer L/kg/day 1.7E‐02 7 2.6E‐02 7 5.4E‐03 7

HIF, cancer L/kg/day 4.8E‐03 7 2.2E‐03 7 1.9E‐03 7

Ingestion rate mL/hr 50 2 50 2 50 2 50 2 50 2Exposure Frequency days/year 25 4 50 4 25 4 50 4 25 4Event Frequency events/day 1 4 1 4 1 4 1 4 1 4Event Time hrs/event 0.5 e 1 e 0.5 e 1 e 0.5 eConversion Factor mg/ug 0.001 ‐‐ 0.001 ‐‐ 0.001 ‐‐ 0.001 ‐‐ 0.001 ‐‐

HIF, non‐cancer L/kg/day 2.1E‐05 7 4.6E‐04 7 2.1E‐05 7 4.6E‐04 7 2.1E‐05 7

HIF, cancer L/kg/day 6.1E‐06 7 3.9E‐05 7 6.1E‐06 7 3.9E‐05 7 7.6E‐06 7

Exposed Skin Surface Area cm2 20,900 10 6,378 10 20,900 10 6,378 10 20,900 10Exposure Frequency days/year 25 4 50 4 25 4 50 4 25 4Dermal Permeability Coefficient (Kp) cm/hr 1.0E‐03 5 1.0E‐03 5 1.0E‐03 5 1.0E‐03 5 1.0E‐03 5Exposure Time (ET) hrs/day 0.5 e 1 e 0.5 e 1 e 0.5 eConversion Factor L/cm3 0.001 ‐‐ 0.001 ‐‐ 0.001 ‐‐ 0.001 ‐‐ 0.001 ‐‐



Sources:

[1] USEPA 1991. Risk Assessment Guidance for Superfund. Volume 1: Human Health Evaluation Manual, Supplemental Guidance, Standard Default Exposure Factors. Interim Final. OSWER Directive 9285.6‐03

[2] USEPA 1989. Risk Assessment Guidance for Superfund, Volume 1, Human Health Evaluation Manual (Part A). Office of Emergency and Remedial Response, Washington, D.C. EPA/540/1‐89/002. December.

[3] USEPA 1997. Exposure Factors Handbook.

[4] Profressional judgment.

[5] USEPA 2004. Risk Assessment Guidance for Superfund, Volume 1, Human Health Evaluation Manual (Part E). Office of Solid Waste and Emergency Response, Washington, D.C. EPA/540/R/99/005. July.

[6] USEPA 2002d. Child‐Specific Exposure Factors Handbook. Interim Report. EPA‐600‐P‐00‐002B. September 2002.

[7] Calculated from exposure parameters shown.

[8] USEPA. 2011. Exposure Factors Handbook: 2011 Edition, EPA/600/R‐090/052F, September 2011.

[9] USEPA 2009. Risk Assessment Guidance for Superfund. Vol. 1: Human Health Evaluation Manual, Part F, Supplemental Guidance for Inhalation Risk Assessment. EPA‐540‐R‐070‐002.

[10] USEPA 2014. OSWER Directive 9200.1‐120. Human Health Evaluation Manual, Supplemental Guidance: Update of Standard Default Exposure Parameters.2014

[b] Table 4‐23. Mean recommended values for soil ingestion.

[c] Mean drinking water intake for 1‐10 year olds.

[d] Based on the geometric mean for a grounds keeper scenario (USEPA 2004a, Exhibit 3‐3).

[e] 1/2 RME frequency.

[f] Assumes tresspasser is a resident in the area so they would have a similar exposure duration.

[g] Dermal Absorption Fraction for arsenic.

[h] Hours/day spent breathing ambient air are default values in EPA, 2011,Table 16‐20. CTE is the 50th percentile.

[i] Assumed 8‐hour workday

General

Incidental Ingestion of Soil

Dermal Contact with Soil

Inhalation of Soil

[a] Averaging time expressed as days. Noncancer averaging time calculated by multiplying the exposure duration in years by 365 days/year and cancer averaging time calculated by multiplying a 70 year lifetime for cancer effects by 365 days/year.

Incidental Ingestion of Surface Water

Dermal Contact with Surface Water

Ingestion of Groundwater Pathway not complete, not evaluated

Pathway not complete, not evaluated Pathway not complete, not evaluated



Construction Worker

AdultExposure Pathway Parameter Unit

Resident Trespasser

Adult Child Adult Child

ATTACHMENT A‐2. EXPOSURE PARAMETERS FOR REASONABLE MAXIMUM EXPOSURE

ValueSource/

NoteValue

Source/

NoteValue

Source/

NoteValue

Source/

NoteValue

Source/

Note

Body Weight kg 80 10 15 1 80 10 15 1 80 10Exposure Frequency days/year 350 1 350 1 52 4, c 52 4, c 225 10Exposure Duration years 20 10 6 1 20 10 6 4, d 25 1Averaging Time (Noncarcinogenic) days 7,300 1, a 2,190 1, a 7,300 1, a 2,190 1, a 9,125 1, aAveraging Time (Carcinogenic) days 25,550 1, a 25,550 1, a 25,550 1, a 25,550 1, a 25,550 1, aIngestion Rate of Soil (IRsoil) mg/day 100 7

HIF, non‐cancer kg/kg/day 7.7E‐07 8HIF, cancer kg/kg/day 2.8E‐07 8

Skin Surface Area Available for Contact (SA) cm2 3,470 10

Adherence Factor (AF) mg/cm2 0.12 10Event Frequency events/day 1 5Dermal Absorption Fraction (ABS) unitless 0.03 5, eConversion Factor kg/mg 1.0E+06 ‐‐

HIF, non‐cancer kg/kg/day 9.6E‐08 8

HIF, cancer kg/kg/day 3.4E‐08 8

Exposure Time (ET) hr/day 8 4, iTWF, non‐cancer 2.1E‐01 8

TWF, cancer 7.3E‐02 8

Ingestion Rate of Water (IRgw) L/day 2.5 10 0.78 10 1 1HIF, non‐cancer L/kg/day 3.0E‐02 8 5.0E‐02 8 7.7E‐03 8

HIF, cancer L/kg/day 8.6E‐03 8 4.3E‐03 8 2.8E‐03 8

Ingestion rate mL/hr 50 2 50 2 50 2 50 2 50 2Exposure Frequency days/year 25 4 50 4 25 4 50 4 25 4Event Frequency events/day 1 4 1 4 1 4 1 4 1 4Event Time hrs/event 1 4 2 4 1 4 2 4 1 4Conversion Factor L/mL 0.001 ‐‐ 0.001 ‐‐ 0.001 ‐‐ 0.001 ‐‐ 0.001 ‐‐



Exposed Skin Surface Area cm2 20,900 10 6,378 10 20,900 10 6,378 10 20,900 10Exposure Frequency days/year 25 4 50 4 25 4 50 4 25 4Dermal Permeability Coefficient (Kp) cm/hr 1.0E‐03 7 1.0E‐03 7 1.0E‐03 7 1.0E‐03 7 1.0E‐03 7Exposure Time (ET) hrs/day 1 4 2 4 1 4 2 4 1 4Conversion Factor L/cm3 0.001 ‐‐ 0.001 ‐‐ 0.001 ‐‐ 0.001 ‐‐ 0.001 ‐‐



Sources:

[1] EPA 1991. Risk Assessment Guidance for Superfund. Vol. 1: Human Health Evaluation Manual, Supplemental Guidance, Standard Default Exposure Factors. Interim Final. OSWER Directive 9285.6‐03

[2] USEPA 1989. Risk Assessment Guidance for Superfund, Volume I, Human Health Evaluation Manual (Part A). Office of Emergency and Remedial Response, Washington, D.C. EPA/540/1‐89/002. December.

[3] USEPA 1997. Exposure Factors Handbook.

[4] Profressional judgment.

[5] USEPA 2004. Risk Assessment Guidance for Superfund, Volume 1, Human Health Evaluation Manual (Part E). Office of Solid Waste and Emergency Response, Washington, D.C. EPA/540/R/99/005. July.

[6] USEPA 2002a. Child‐Specific Exposure Factors Handbook. Interim Report. EPA‐600‐P‐00‐002B. September 2002.

[7] USEPA 2002b. Supplemental Guidance for Developing Soil Screening Levels for Superfund Sites. OSWER 9355.4‐24. December.

[8] Calculated from exposure parameters shown.

[9] USEPA 2009. Risk Assessment Guidance for Superfund. Vol. 1: Human Health Evaluation Manual, Part F, Supplemental Guidance for Inhalation Risk Assessment. EPA‐540‐R‐070‐002.

[10] USEPA 2014. OSWER Directive 9200.1‐120. Human Health Evaluation Manual, Supplemental Guidance: Update of Standard Default Exposure Parameters.2014

[b] 95th percentile drinking water intake rate for 1‐10 year olds.

[c] Assumes tresspassing occurs 1 time/week.

[d] Assumes tresspasser is a resident in the area so they would have a similar exposure duration.

[e] Dermal Absorption Fraction for arsenic.

[f] Hours/day spent breathing ambient air are default values in EPA, 2011,Table 16‐20. RME is the 95th percentile.

[g] Assumed 8‐hour workday

AdultUnitParameter

Construction Worker

Exposure Pathway

Resident

ChildAdult

Trespasser

Adult Child


[a] Averaging time expressed as days. Noncancer averaging time calculated by multiplying the exposure duration in years by 365 days/year and cancer averaging time calculated by multiplying a 70 year lifetime for cancer effects by 365 days/year.

General

Incidental Ingestion of Soil

Dermal Contact with Soil

Inhalation of Soil

Ingestion of Groundwater Pathway not complete, not evaluated

Incidental Ingestion of Surface Water




ATTACHMENT B

Arsenic Risk Estimates

Attachment B‐1. Arsenic Risk Estimates for Scenario Scenario 1a :Evaluated at Groundwater Well in Middle of EVSA (0.25 mg/L Leachate), and for Surface Water from Pond 1Panel A. Non‐Cancer Risks

CTE RME CTE RME CTE RME CTE RME CTE RME CTE RME CTE RME

Adult NA NA NA NA NA NA 3 6 0.0009 0.002 0.0004 0.0008 3 6

Child NA NA NA NA NA NA 5 9 0.02 0.04 0.002 0.005 5 9

Adult NA NA NA NA NA NA NA NA 0.0009 0.002 0.0004 0.0008 0.001 0.003

Child NA NA NA NA NA NA NA NA 0.02 0.04 0.002 0.005 0.02 0.04

Construction Worker

Adult 0.01 0.03 0.01 0.01 0.0004 0.0004 1 1 0.0009 0.002 0.0004 0.0008 1 1

Panel B. Cancer Risks


Adult NA NA NA NA NA NA 4E‐04 7E‐04 1E‐07 2E‐07 1E‐09 1E‐07 4E‐04 7E‐04

Child NA NA NA NA NA NA 2E‐04 4E‐04 7E‐07 1E‐06 9E‐09 2E‐07 2E‐04 4E‐04

Adult NA NA NA NA NA NA NA NA 1E‐07 2E‐07 1E‐09 1E‐07 1E‐07 3E‐07

Child NA NA NA NA NA NA NA NA 7E‐07 1E‐06 9E‐09 2E‐07 8E‐07 2E‐06

Construction Worker

Adult 2E‐06 4E‐06 2E‐06 2E‐06 9E‐09 9E‐09 2E‐04 2E‐04 1E‐07 3E‐07 6E‐08 1E‐07 2E‐04 2E‐04

Assumptions: Groundwater arsenic concentration: 0.055 mg/L, Pond 1 arsenic concentration: 0.013 mg/L.

HQ = hazard quotientCTE = central tendency exposureRME = reasonable maximum exposureNA = not available, pathway is not completemg/L = milligrams per liter

Pathway Risk

Resident

Trespasser

Receptor

Hazard IndexIncidental Ingestion

of SoilDermal Contact

with SoilInhalation

of SoilIngestion of

Groundwater

Non‐cancer HIs greater than 1 shown in Panel A and cancer risks above 1E‐04 (i.e., USEPA’s acceptable risk range) shown in Panel B are highlighted in red, indicating there may be a risk of non‐cancer or cancer effects and some form of remedial action is desirable.

Resident

Trespasser

Total RiskIncidental Ingestion


with SoilInhalation

of SoilIngestion of

GroundwaterIncidental Ingestion

of Surface WaterDermal Contact with

Surface Water

Receptor

HQ ValuesIncidental Ingestion


Surface Water

Attachment B‐2. Arsenic Risk Estimates for Scenario Scenario 1a :Evaluated at Groundwater Downgradient Well 50m from Southern Boundary of EVSA (0.25 mg/L Leachate), and for Surface Water from Pond 1Panel A. Non‐Cancer Risks






Construction Worker

Adult 0.01 0.03 0.01 0.01 0.0004 0.0004 0.3 0.5 0.0009 0.002 0.0004 0.0008 0.4 0.5







Construction Worker




Pathway Risk

Resident

Trespasser

Receptor



with SoilInhalation

of SoilIngestion of

Groundwater


Resident

Trespasser



with SoilInhalation

of SoilIngestion of



Surface Water

Receptor



Surface Water







Construction Worker

Adult 0.01 0.03 0.01 0.01 0.0004 0.0004 2 3 0.002 0.004 0.0008 0.002 2 3







Construction Worker




Pathway Risk

Resident

Trespasser

Receptor



with SoilInhalation

of SoilIngestion of

Groundwater


Resident

Trespasser



with SoilInhalation

of SoilIngestion of



Surface Water

Receptor



Surface Water







Construction Worker

Adult 0.01 0.03 0.01 0.01 0.0004 0.0004 0.6 0.9 0.002 0.004 0.0008 0.002 0.7 1







Construction Worker




Pathway Risk

Resident

Trespasser

Receptor



with SoilInhalation

of SoilIngestion of

Groundwater


Resident

Trespasser



with SoilInhalation

of SoilIngestion of



Surface Water

Receptor



Surface Water



Adult NA NA NA NA NA NA 0.004 0.007 0.0000009 0.000002 0.0000004 0.0000008 0.004 0.007

Child NA NA NA NA NA NA 0.006 0.01 0.00002 0.00004 0.000002 0.000005 0.006 0.01



Construction Worker

Adult 0.01 0.03 0.01 0.01 0.0004 0.0004 0.001 0.002 0.0000009 0.000002 0.0000004 0.0000008 0.03 0.04







Construction Worker




Pathway Risk

Resident

Trespasser

Receptor



with SoilInhalation

of SoilIngestion of

Groundwater


Resident

Trespasser



with SoilInhalation

of SoilIngestion of



Surface Water

Receptor



Surface Water







Construction Worker

Adult 0.01 0.03 0.01 0.01 0.0004 0.0004 0.0003 0.0005 0.0000009 0.000002 0.0000004 0.0000008 0.02 0.04







Construction Worker




Pathway Risk

Resident

Trespasser

Receptor



with SoilInhalation

of SoilIngestion of

Groundwater


Resident

Trespasser



with SoilInhalation

of SoilIngestion of



Surface Water

Receptor



Surface Water







Construction Worker

Adult 0.01 0.03 0.01 0.01 0.0004 0.0004 0.002 0.003 0.000002 0.000004 0.0000008 0.000002 0.03 0.04







Construction Worker




Pathway Risk

Resident

Trespasser

Receptor



with SoilInhalation

of SoilIngestion of

Groundwater


Resident

Trespasser



with SoilInhalation

of SoilIngestion of



Surface Water

Receptor



Surface Water







Construction Worker

Adult 0.01 0.03 0.01 0.01 0.0004 0.0004 0.0007 0.001 0.000002 0.000004 0.0000008 0.000002 0.02 0.04







Construction Worker




Pathway Risk

Resident

Trespasser

Receptor



with SoilInhalation

of SoilIngestion of

Groundwater


Resident

Trespasser



with SoilInhalation

of SoilIngestion of



Surface Water

Receptor



Surface Water

ATTACHMENT C

Dioxin Risk Estimates

Attachment C‐1. Dioxin Risk Estimates for Scenario Scenario 1a :Evaluated at Groundwater Well in Middle of EVSA , and for Surface Water from Pond 1Panel A. Non‐Cancer Risks






Construction Worker

Adult 0.4 0.8 0.1 0.1 0.002 0.002 0.005 0.007 0.000004 0.000008 0.000002 0.000003 0.5 0.9







Construction Worker


Assumptions: Groundwater arsenic concentration: 0.59 pg/L, Pond 1 arsenic concentration: 0.14 pg/L.

HQ = hazard quotientCTE = central tendency exposureRME = reasonable maximum exposureNA = not available, pathway is not completepicogram per liter

Trespasser

Resident

Incidental Ingestionof Soil

Dermal Contactwith Soil

Inhalationof Soil

Ingestion of Groundwater

Incidental Ingestionof Surface Water


Trespasser

Receptor

Pathway Risk

Total Risk




Receptor

HQ Values



with SoilInhalation

of Soil

Resident

Attachment C‐2. Dioxin Risk Estimates for Scenario Scenario 1a :Evaluated at Groundwater Downgradient Well 50m from Southern Boundary of EVSA , and for Surface Water from Pond 1Panel A. Non‐Cancer Risks






Construction Worker

Adult 0.4 0.8 0.1 0.1 0.002 0.002 0.001 0.002 0.000004 0.000008 0.000002 0.000003 0.5 0.9







Construction Worker




Trespasser

Resident



Inhalationof Soil




Trespasser

Receptor

Pathway Risk

Total Risk




Receptor

HQ Values



with SoilInhalation

of Soil

Resident

Attachment C‐3. Dioxin Risk Estimates for Scenario Scenario 2a :Evaluated at Groundwater Well in Middle of EVSA , and for Surface Water from Pond 1Panel A. Non‐Cancer Risks


Adult NA NA NA NA NA NA 0.00002 0.00003 4E‐09 8E‐09 2E‐09 4E‐09 0.00002 0.00003

Child NA NA NA NA NA NA 0.00003 0.00005 9E‐08 2E‐07 1E‐08 2E‐08 0.00003 0.00005



Construction Worker

Adult 0.4 0.8 0.1 0.1 0.002 0.002 0.000006 0.000008 4E‐09 8E‐09 2E‐09 4E‐09 0.5 0.9







Construction Worker




Trespasser

Resident



Inhalationof Soil




Trespasser

Receptor

Pathway Risk

Total Risk




Receptor

HQ Values



with SoilInhalation

of Soil

Resident

Attachment C‐4. Dioxin Risk Estimates for Scenario Scenario 2a :Evaluated at Groundwater Downgradient Well 50m from Southern Boundary of EVSA , and for Surface Water from Pond 1Panel A. Non‐Cancer Risks


Adult NA NA NA NA NA NA 0.000005 0.000009 4E‐09 8E‐09 2E‐09 4E‐09 0.000005 0.000009

Child NA NA NA NA NA NA 0.000007 0.00001 9E‐08 2E‐07 1E‐08 2E‐08 0.000007 0.00001



Construction Worker

Adult 0.4 0.8 0.1 0.1 0.002 0.002 0.000002 0.000002 4E‐09 8E‐09 2E‐09 4E‐09 0.5 0.9







Construction Worker




Trespasser

Resident



Inhalationof Soil




Trespasser

Receptor

Pathway Risk

Total Risk




Receptor

HQ Values



with SoilInhalation

of Soil

Resident

ATTACHMENT D

Groundwater and Surface Water Concentrations Derivation

1

Attachment D Groundwater and Surface Water Dioxin and Arsenic Concentration Derivation

Section 1 Introduction The objective of this analysis was to determine concentrations of dioxin and arsenic that may be present in groundwater and surface water as a result of leaching from stockpiling untreated soil/sediment in an Excess Volume Stockpile Area (EVSA) on the Danang Airport. Approximately 24,000 cubic meters of soil/sediment with dioxin concentrations less than 1,000 picogram/gram or parts per trillion (ppt) has been excavated from the Project site and placed in Temporary Sediment Stockpile Areas (TSSA-1 and TSSA-2). This material, plus additional sediment to be excavated in 2016, will be placed in the EVSA. The five hectare EVSA is located in a commercial/industrial area in the southwest corner of the Danang Airport property near the Pacer Ivy Storage Area.

In order to determine engineering controls to minimize dioxin and arsenic leaching to groundwater and subsequently being transported to surface water at levels that may pose a threat to human health, multiple EVSA construction scenarios were evaluated. The following scenarios for EVSA construction were modeled.

Scenario 1A and 1B • Slope = 2% (Scenario 1A) and 5% (Scenario 1B)• 60 cm soil cover• 1.5 m waste (untreated soil/sediment) material

Scenario 2A and 2B • Slope = 2% (Scenario 2A) and 5% (Scenario 2B)• 60 cm soil cover• 1-mm (40-mil) thick HDPE liner with 1 holes/defect per hectare• 1.5 m waste material

Scenario 3A and 3B • Slope = 2% (Scenario 3A) and 5% (Scenario 3B)• 60 cm soil cover• 1-mm (40-mil) thick HDPE liner with 1 hole/defect per hectare• Bentonite mat as a barrier layer• 1.5 m waste material• 1-mm (40-mil) thick HDPE liner with 1 hole/defect per hectare• Bentonite mat as a barrier layer• 1 m silty to clayey sand

Concentrations of dioxin and arsenic in groundwater were estimated at two hypothetical well locations: • a hypothetical groundwater well located in the middle of the EVSA, and• a hypothetical well located approximately 650 meters (m) downgradient from the southern

edge of the EVSA which is about 50 meters (m) from the southern airport boundary

2

In addition, concentrations of dioxin and arsenic were estimated in six downgradient surface water ponds as a result of groundwater transport from the EVSA. The six manmade aquaculture ponds are in the same area located about 650 m to 700 m southeast of the EVSA (Figure 1). Methods used to estimate dioxin and arsenic concentrations at these locations include: the United States Army Corp of Engineers (USACE) Hydrologic Evaluation of Landfill (HELP) Model and a simple mixing model (mixing infiltration/percolation and groundwater). The HELP model used was used to estimate percolation rates through the various EVSA construction materials and waste (untreated soil/sediment) material. Percolation rates were then used in a simple mixing model to determine dioxin and arsenic concentrations based on estimates of contaminant mass moving through the groundwater system. The following sections summarize the HELP model analysis, the mixing model evaluation, and the results.

Section 2 Help Model The HELP Model is a quasi-two-dimensional hydrologic model for conducting water balance analysis of landfills, cover systems, and other solid waste containment facilities. The model uses weather, soil and design data, runoff, infiltration, evapotranspiration, vegetative growth, soil moisture storage, lateral subsurface drainage, unsaturated vertical drainage, leakage through soil, and other parameters to evaluate design alternatives as judged by their water balance (Schroeder et. al. 1994). The HELP Model was used to predict percolation rates through the EVSA considering different soil cover compositions and additional HDPE liner options described below. The latest version (Version 3.07) of the HELP model was used to estimate percolation rates and volumes for Scenarios 1A through 3B. The difference in percolation/leakage rates between the 2% slope and 5% slope scenarios were minimal; therefore, only the 2% slope scenarios (slightly more conservative than 5% slope) are discussed in this memorandum (i.e., only Scenarios 1A, 2A, and 3A). The rates and volumes were based on a period of one year. As much site-specific information was input into the HELP model as possible. Site-specific weather, soil and design data were used to generate daily estimates of water movement across, into, through, and out of the EVSA. Site-specific assumptions used in the model are described briefly below and are summarized on Tables 1 and 2. Evapotranspiration Data:

Evaporative zone depth. This is the maximum depth from which water may be removed by evapotranspiration. In humid areas where moisture is readily available near the surface, grasses may have rooting depth of 15 to 60 cm. A depth of 60 was used in the model.

Maximum Leaf Area (LAI). LAI is the dimensionless ratio of the leaf area of actively transpiring vegetation to the nominal surface area of the land on which the vegetation is growing. The maximum LAI for bare ground is zero. For a poor stand of grass, the LAI could approach 1.0; for a fair stand of grass, 2.0; for a good stand of grass, 3.5; and for an excellent stand of grass, 5.0) For this analysis a good stand of grass was assumed, thus the LAI used was: 3.5.

Growing season. The model uses the start and ending dates of the growing season. A growing season of 300 days was used based on information obtained online for growing

3

seasons in provinces of Vietnam. Starting and ending growing season dates used in the model were: 32 (Start) – 332 (End) (Goggle Books 2015)

Normal average wind speed. The normal average wind speed was obtained online from the Weatherbase.com website (Weatherbase 2015). The average wind speed used in the model was: 8 kilometers per hour (km/h).

Normal average quarterly relative humidity. Average quarterly humidity measurements were obtained from the online Weatherbase.com website (Weatherbase 2015) and were estimated to be: (first quarter, 1Q) 86%, (2Q) 81%, (3Q) 79.67%, and (4Q) 85.67%.

Climatic Data (Temperature, Precipitation, and Solar Radiation):

Typically, daily averages for temperature, precipitation, and solar radiation are input into the model for one or more years. However, because only monthly averages for these parameters were available, the monthly average was used as the average for each day of that month. Average monthly values obtained from the online Weatherbase.com website (Weatherbase 2015) for the year 2014 were used in the model. Values used are shown in the HELP Model output (Attachment E-1).

Soil and Design Data: Design data describe the general properties of the EVSA area including area, percentage of area where runoff is possible, method of initialization of moisture storage, and layer data. Multiple layers with varying properties can be modeled. Four general types of layers can be used in the model: vertical percolation layers, lateral drainage layers, barrier soil liners, and geomembrane liners. The program models the flow of water through the four types of layers in different ways. For this analysis the waste (untreated soil/sediment) and soil cover layer types were assumed to be vertical percolation layers. The HDPE liner and bentonite mat were included as geomembrane liners and soil liners, respectively. A total of three scenarios were evaluated in this analysis varying cover composition and liner options. All scenarios assumed that the waste (untreated soil/sediment) was placed in the 5 hectare EVSA. All scenarios assumed a 60 cm soil cover was placed over a 1.5 m waste material layer. A 2% cover slope was assumed for all scenarios. Scenario 1A assumed only a soil cover was placed above the waste material. Scenario 2A assumed that a 40-mil thick HDPE liner with 1 holes/defect per hectare was placed beneath the soil cover. Scenario 3A assumed that a 40-mil thick HDPE liner with 1 holes/defect per hectare and a bentonite mat was placed beneath the soil cover and another liner with the same specifications was placed beneath the waste material. In addition, a bentonite mat and a 1 m silty to clayey sand layer was placed below the lower HPDE liner. Soil parameters were determined for the waste material (bottom layer in Scenario 1A and all other scenarios), soil bottom layer in Scenario 3A, and for cover materials (top layer all scenarios). Types of soil covers included clean common fill with various characteristics. Specifications for fill material call for the fill to be placed in 0.3 m lifts and then to “be compacted to 90 % of the modified Proctor (ASTM D1557) maximum dry density, or as otherwise directed by the USAID CoTR or “DESIGNATE””; this compaction results in fairly dense material. Tests show a maximum density of 1.87 g/cm3 at moisture content of 13.5%. Site-specific soil parameters used in the model include porosity, field capacity, wilting point, and saturated hydraulic conductivity. The runoff curve number was determined in the HELP Model using the slope of the EVSA, slope length, soil texture, and vegetation index. Two soil types were evaluated for the soil cover designated as texture 13 and texture 24 in the model (Table 4, HELP manual). Cover soil properties for texture 13 and texture 24 are summarized in Table 3. Soil

4

properties, waste properties, bentonite mat properties, HDPE properties and other design assumptions used in the model are shown in Tables 1(Texture 13) and 2 (Texture 24).

Table 3 Cover Soil Properties

Parameter Texture 13 Texture 24

Classification (USDA) SC (clayey sand) SCL (sandy clay loam, moderately compacted)

Classification (USCS) SC (clayey sand) SC (clayey sand) Total Porosity (vol/vol) 0.430 0.365 Field Capacity (vol/vol) 0.321 0.305 Wilting Point (vol/vol) 0.221 0.202 Saturated Hydraulic Conductivity (cm/sec) 3.3 ×10‐5 2.7 ×10‐6

Section 3 Mixing Model A simple mixing model was used to estimate concentrations of dioxin and arsenic in groundwater and nearby surface water resulting from leaching and transport of these contaminants in untreated soil/sediment stockpiled in the EVSA. The model calculated volumes of water entering the EVSA and volumes of water exiting the EVSA using site specific assumptions. Estimates of five different mixing volumes were calculated including:

the volume of water infiltrating the EVSA area from precipitation (rainfall) and percolating (transported through the placed material) into the groundwater,

the volume of groundwater entering the EVSA from upgradient, the volume of groundwater contained beneath the EVSA area, the volume of groundwater reaching the hypothetical downgradient groundwater receptor well,

and the volume of groundwater mixed with surface water in the 6 downgradient ponds; volumes for

ponds 1, 2, and 3 were estimated separately, and the volume for ponds 4, 5, 6 was grouped together.

The EVSA is located is in the “West of Airport-Han River Catchment” where groundwater flow is to the south. The aquifer most likely affected by leaching of contaminants from material placed in the EVSA is the Holocene Aquifer. The uppermost Holocene Aquifer consists of fine to medium sand and clayey sand and ranges in thickness from 8 m to 15 m. An aquitard, less than 5 m thick, underlies the unconfined Holocene Aquifer and is comprised mostly of clays. Groundwater levels range seasonally between 0.3 m to 3 m below ground level (bgl), with groundwater levels generally ranging between 2m to 3m bgl in the dry season. Average groundwater elevations measured at 3 piezometers at the EVSA ranged from 4.74 meters mean sea level (m MSL) at P-02 to 5.2 m MSL at P-03. The gradient calculated using measured groundwater levels from the EVSA piezometers was 0.002. The saturated thickness based on site-specific data was 9 m. The permeability of the Holocene aquifer ranges between 1.42 and 1.9 meters per day (m/d). Based on site-specific data the estimated aquifer permeability used in the model was 1.73 m/d. A simple box mixing model is used to estimate volumes of groundwater for the scenarios listed above. The calculations for all mixing volumes are shown in Table 5 (texture 13) and Table 6 (texture 24).

5

As an example, the volume of groundwater entering the well downgradient of the EVSA (V4) was estimated by multiplying the aquifer thickness by the distance to the downgradient well, by the length perpendicular to groundwater flow by the total porosity. The total mixing volume at this well is the sum of all contributing water volumes including: the volume of upgradient water entering the EVSA (V3), the volume of water infiltrating the EVSA(V1), the volume of groundwater beneath the EVSA(V2), and the volume of downgradient water of the EVSA entering the well (V4). Measured leachate data are not available for the soil/sediment samples that will be stockpiled in the EVSA. Arsenic concentrations in untreated soil/sediment samples ranged from 6 mg/kg to 328 mg/kg and averaged 174 mg/kg. However, arsenic concentrations in untreated soil/sediment are not expected to differ substantially from the arsenic concentrations in treated soil because the thermal treatment process has a relatively small impact, if any, on the total arsenic concentration in soil. Therefore, the arsenic leachate results from treated material are considered representative for untreated soils and were used in this analysis. Two arsenic leachate concentrations based on a modified (2 to 1 liquid to soil leaching ratio) Synthetic Precipitation Leaching Procedure (SPLP) were used in the mixing calculations: 250 micrograms per liter (µg/L) and 500 µg/L. The 250 µg/L was the highest measured arsenic concentration using the treated soil and modified SPLP. The 500 µg/L was estimated as a worst case considering that actual soil-water (precipitation) interactions occur at a lower water to soil ratio than used in the SPLP method. A dioxin leachate concentration was estimated using the average total organic carbon (TOC) measurements (1.085%) from sediment samples SAP501-1-21-Jan10 and SAP521-1-21-JAN-10 and a default organic carbon partition coefficient (Koc) of 257,000 cubic centimeters per gram (cm3/g) used in USEPA soil leaching models (USEPA 2011). The dioxin toxicity equivalence (TEQ) concentration used is 751 pg/g or parts per trillion (ppt), based on the result for sediment sample 1R-SL-TSSA1-B-All-0001; this result is the estimated dioxin TEQ concentration using ½ the detection limit for non-detected congeners and WHO 2005 TEF values (EPA 2010). This concentration represents about 25,000 m3 of the material to be stockpiled at the EVSA. The resulting dissolved concentration is 2.69 × 10-9 mg/L. The leachate calculation for dioxin is shown in Table 4. Using measured leachate concentrations for arsenic and the estimated leachate concentration for dioxin and the calculated mixing volumes assuming complete mixing, dioxin and arsenic concentrations were estimated for the locations described in Section 1. By assuming complete mixing, the resulting concentrations are best case (lowest) concentrations. A range of dioxin and arsenic concentrations in groundwater were estimated for each location based on changes in assumptions due to seasonal fluctuations, the value of the leachate concentration used, and the assumed cover and liner options. The average annual rainfall is 2,000 millimeters (mm) and approximately 75% of the total annual rainfall occurs during the rainy season which generally lasts from September to December. The actual calculations use the total amount of precipitation over a one-year period.

Section 4 Groundwater and Surface Water Results Dioxin and arsenic leachate is produced by water moving into, through, and out of the EVSA and subsequently migrating into and mixing with groundwater and adjacent areas. Leachate may be composed of liquids originating from a number of sources including precipitation, consolidation, and initial moisture storage. The baseline (existing load or mass) of dioxin and arsenic in groundwater was assumed to be zero. The load is the amount of dioxin or arsenic mass per time; in this analysis the dioxin and arsenic mass per year and volumes of water per year for each scenario were calculated. The resulting dioxin or arsenic

6

concentration (mg/L) for each scenario is calculated by dividing the contaminant mass per year (mg/yr) by the water volume per year (m3/yr) multiplied by a conversion factor for liters per cubic meter (L/m3). In general, predicted dioxin and arsenic concentrations in groundwater are conservative (highest) because concentration estimates assume that there is complete mixing of contamination occurring all at once with an original concentration of zero in groundwater. Site-specific conditions suggest that complete and immediate mixing of groundwater and leachate from the EVSA waste material is unlikely.

Scenario 1A In Scenario 1A the waste material is assumed to be covered by a soil cover; two soil cover types were evaluated. Each calculation and the associated assumptions for Scenario 1A for soil cover texture 13 and 24 are shown in Tables 5 and 6, respectively. As shown dioxin and arsenic concentrations in groundwater wells and ponds are slightly higher assuming a soil cover texture of 13. As expected arsenic concentrations are highest in the hypothetical well in the middle of the EVSA based on the 0.50 mg/L leachate concentration. Predicted arsenic concentrations for this well were 0.144 mg/L for texture 13 and 0.110 mg/L for texture 24 based on the 0.50 mg/L leachate concentration. Predicted arsenic concentrations for the well 50 m from the southern airport boundary were 0.050 mg/L for texture 13 and 0.036 mg/L for texture 24 based on the 0.50 mg/L leachate concentration. All predicted arsenic concentrations in groundwater wells are above the USEPA maximum contaminant level (MCL) for arsenic in drinking water (10 parts per billion or 0.01mlligrams per liter (mg/L)). Estimated dioxin concentrations are about 3 times higher in the hypothetical well in the middle of the EVSA than in the well 50 m from the southern airport boundary. Predicted dioxin concentrations for the well in the middle of the EVSA were 0.788 pg/L for texture 13 and 0.595 pg/L for texture 24. Predicted dioxin concentrations for the well 50 m from the southern airport boundary were 0.270 pg/L for texture 13 and 0.195 pg/L for texture 24. Predicted dioxin concentrations in groundwater wells were not above the USEPA MCL for dioxin in drinking water (3 ×10-8 mg/L or 30 pg/L). Pond 1 is closest to the EVSA and arsenic and dioxin concentrations were highest in this pond than in the other ponds evaluated. Predicted arsenic concentrations for Pond 1 were 0.035 mg/L for texture 13 and 0.025 mg/L for texture 24 based on the 0.50 mg/L leachate concentration. Predicted dioxin concentrations in Pond 1were 0.190 pg/L for texture 13 and 0.137 pg/L for texture 24.

Scenario 2A In Scenario 2A the waste material is assumed to be covered by a soil cover; two soil cover types were evaluated (textures 13 and 24). In addition, a 40-mil thick HDPE liner with 1 holes/defect per hectare was placed beneath the soil cover. Each calculation and the associated assumptions for Scenario 2A for soil cover texture 13 and 24 are shown in Tables 7 and 8, respectively. As shown, by including the HPDE liner, dioxin and arsenic concentrations in groundwater wells and ponds are significantly lower compared to Scenario 1A. Predicted arsenic concentrations for the well in the middle of the EVSA ranged from 0.0009 mg/L for texture 13 to 0.0001mg/L for texture 24 based on the 0.50 mg/L leachate concentration. Predicted arsenic concentrations for the well 50 m from the southern airport boundary were 0.0002 mg/L for texture 13 and 0.00004 mg/L for texture 24 based on the 0.50 mg/L leachate concentration. Predicted dioxin concentrations for the well in the middle of the EVSA were 0.005 pg/L for texture 13 and 0.0007 pg/L for texture 24. Predicted dioxin concentrations the well 50 m from the southern airport boundary were 0.001 pg/L for texture 13 and 0.0002 pg/L for texture 24. Neither arsenic or dioxin concentrations exceed USEPA MCLs. Predicted arsenic concentrations for Pond 1

7

were 0.0002 mg/L for texture 13 and 0.00002 mg/L for texture 24 based on the 0.50 mg/L leachate concentration. Predicted dioxin concentrations in Pond 1were 0.001 pg/L for texture 13 and 0.0001 pg/L for texture 24.

Scenario 3A In Scenario 3A the waste material is assumed to be covered by a soil cover and two soil cover types were evaluated (textures 13 and 24). Additionally, a 40-mil thick HDPE liner with 1 holes/defect per hectare and a bentonite mat was placed beneath the soil cover. Another HDPE liner with the same specifications was placed beneath the waste material. Finally, a bentonite mat and a 1 m silty to clayey sand layer was placed below the lower HPDE liner. Each calculation and the associated assumptions for Scenario 3A for soil cover texture 13 and 24 are shown in Tables 9 and 10, respectively. As shown, contaminants are not expected to leach into groundwater from the EVSA based on this construction; therefore, concentrations of arsenic and dioxin in groundwater and in the downgradient ponds are 0 (zero, or below analytical detection limits) assuming the baseline assumptions are correct.

Summary of the Mixing Model for Ponds Surface water dioxin and arsenic concentrations were estimated for six ponds southeast of the EVSA. Groundwater flowing beneath the EVSA was assumed to reach these ponds as a conservative measure; however, in reality this may not occur based on the actual groundwater directional flow. Future concentrations of dioxin and arsenic in the ponds assume that the baseline concentrations in the surface water is zero. The estimated mass of dioxin and arsenic in the ponds considers the volume of each pond and the mass of the contaminant in groundwater that mixes with water in each pond (Tables 5 through 10). The estimated dioxin and arsenic concentrations for ponds 1, 2 and 3 did not span a wide range within each scenario but were significantly higher for Scenario 1A than either Scenarios 2A or 3A. Concentrations of dioxin and arsenic in ponds 4, 5, 6 were generally an order of magnitude lower than in the other three ponds.

Section 5 Summary Concentrations of dioxin and arsenic that may be present in groundwater and surface water as a result of leaching from stockpiling untreated soil/sediment in an EVSA on the Danang Airport were estimated for a hypothetical well beneath the EVSA and for a downgradient well near the southern boundary of the Airport. In addition, concentrations of arsenic and dioxin were estimated for 6 surface water ponds southeast of the EVSA. Three scenarios considering varying soil cover compositions and liner options were evaluated. Predicted concentrations of dioxin and arsenic leaching from the EVSA to groundwater and transported to downgradient ponds water varied greatly depending on the engineering specifications for EVSA covers and liners. Under the most conservative construction scenario, Scenario 3A, arsenic and dioxin were not predicted to leach from the EVSA to groundwater; therefore, concentrations in groundwater and downgradient ponds were 0. Predicted concentrations for Scenario 2A were significantly lower than Scenario 1A. The maximum predicted concentration of arsenic in the well beneath the EVSA under Scenario 1A was 0.144 mg/L compared to 0.0009 mg/L under Scenario 2A. The maximum concentration of dioxin in the well beneath the EVSA under Scenario 1A was 0.778 pg/L compared to 0.005 pg/L under Scenario 2A. Predicted arsenic and dioxin concentrations in the downgradient well follow the same pattern with values under Scenario 2A being significantly lower than under Scenario 1A. Maximum predicted arsenic and dioxin concentrations in the downgradent well under Scenario 1A were 0.050 mg/L and 0.270pg/L, respectively. In comparison, the maximum predicted

8

arsenic and dioxin concentrations in the downgradent well under Scenario 2A were 0.0002 mg/L and 0.001 pg/L, respectively. Concentrations of arsenic and dioxin were predicted to be highest in Pond 1 out of the 6 ponds evaluated. Under Scenario 1A the maximum arsenic concentration in Pond 1 was 0.035 mg/L and 0.0002 mg/L under Scenario 2A. Under Scenario 1A the maximum dioxin concentration in Pond 1 was 0.190 pg/L and 0.0009 pg/L under Scenario 2A. Results for soil cover textures 13 and 24 are summarized in Table 11 and 12, respectively. A comparison of all results is presented in Table 13. The results of this analysis were used to evaluate possible impacts to human health and the environment.

Section 6 References Google Books. 2015. https://books.google.ie/books?id=iI8J-MsETeUC&pg=PA100&lpg=PA100&dq=%22length+of+growing+season+and+selected+provinces%22+%22vietnam%22&source=bl&ots=MmbjRsjgiR&sig=6mib63B59-5Xgg6ViMp9eAJhJ1c&hl=en&sa=X&ved=0CCAQ6AEwAGoVChMIr8-Lp8HaxgIVySqICh38jwUx#v=onepage&q=%22length%20of%20growing%20season%20and%20selected%20provinces%22%20%22vietnam%22&f=false United States Environmental Protection Agency (USEPA). 2010. Recommended Toxicity Equivalence Factors (TEFs) for Human Health Risk Assessments of 2,3,7,8-Tetrachlorodibenzo-p-dioxin and Dioxin-Like Compounds. Risk Assessment Forum. EPA/100/R-10/005. December.

United States Environmental Protection Agency (USEPA). 2011. Background Information for the Leaching Environmental Assessment Framework (LEAF) Test Methods. EPA/600/R-10/170. November. Schroeder, P. R., Aziz, N. M., Lloyd, C. M. and Zappi, P. A. 1994. The Hydrologic Evaluation of Landfill Performance (HELP) Model: User’s Guide for Version 3. EPA/600/R-94/168a, September 1994, U.S. Environmental Protection Agency Office of Research and Development, Washington, DC. Weatherbase. 2015. http://www.weatherbase.com/weather/weather.php3?s=55884&cityname=Da-Nang-Da-Nang-Vietnam&units=metric

Table 1 Assumptions Used in the HELP Model for Soil Cover Texture 13

60 cm Soil Cover, 60 cm Soil Cover, 60 cm Soil Cover, 60 cm Soil Cover, 60 cm Soil Cover, 60 cm Soil Cover,

1.5 m Waste Material, 1.5 m Waste Material, 1 mm HDPE Liner, 1 mm HDPE Liner, 1 mm HDPE Liner, 1 mm HDPE Liner,

Slope 2% Slope 5% 1.5 m Waste Material, 1.5 m Waste Material, Bentonite Mat, Bentonite Mat,

Slope 2% Slope 5% 1.5 m Waste Material, 1.5 m Waste Material,

1 mm HDPE Liner, 1 mm HDPE Liner,Bentonite Mat Bentonite Mat

Slope 2% Slope 5%

Landfill Capping Area ha 5 5 5 5 5 5Precipitation mm/yr 1,875.80 1,875.80 1,875.80 1,875.80 1,875.80 1,875.80Evaporative Zone Depth cm 60 60 60 60 60 60Leaf Area Index 3.5 (good stand) 3.5 (good stand) 3.5 (good stand) 3.5 (good stand) 3.5 (good stand) 3.5 (good stand)

Layer Type1 Soil Cover Texture # 13 13 13 13 13 13

Thickness m 0.6 0.6 0.6 0.6 0.6 0.6Porosity vol/vol 0.43 0.43 0.43 0.43 0.43 0.43Field Capacity vol/vol 0.321 0.321 0.321 0.321 0.321 0.321Wilting Point vol/vol 0.221 0.221 0.221 0.221 0.221 0.221Saturated Hydraulic Conductivity

cm/sec 3.30E-05 3.30E-05 3.30E-05 3.30E-05 3.30E-05 3.30E-05

4 HDPE Liner Texture # 35 35 35 35Thickness m 0.001 0.001 0.001 0.001Saturated Hydraulic Conductivity

cm/sec 2.00E-13 2.00E-13 2.00E-13 2.00E-13

Pinhole Density holes/ha 1 1 1 1Installation Defects defects/ha 1 1 1 1Placement Quality 3 (Good) 3 (Good) 3 (Good) 3 (Good)

3 Bentonite Matting Texture # 17 17Thickness m 0.006 0.006Porosity vol/vol 0.75 0.75Field Capacity vol/vol 0.747 0.747Wilting Point vol/vol 0.4 0.4Saturated Hydraulic Conductivity

cm/sec 3.00E-09 3.00E-09

1 Waste Material Texture # 10 10 10 10 10 10Thickness m 1.5 1.5 1.5 1.5 1.5 1.5Porosity vol/vol 0.398 0.398 0.398 0.398 0.398 0.398Field Capacity vol/vol 0.244 0.244 0.244 0.244 0.244 0.244Wilting Point vol/vol 0.136 0.136 0.136 0.136 0.136 0.136Saturated Hydraulic Conductivity

cm/sec 1.20E-04 1.20E-04 1.20E-04 1.20E-04 1.20E-04 1.20E-04

4 HDPE Liner Texture # 35 35Thickness m 0.001 0.001Saturated Hydraulic Conductivity

vol/vol 2.00E-13 2.00E-13

Pinhole Density vol/vol 1 1Installation Defects vol/vol 1 1Placement Quality cm/sec 3 (Good) 3 (Good)

3 Bentonite Matting Texture # 17 17Thickness m 0.006 0.006Porosity vol/vol 0.75 0.75Field Capacity vol/vol 0.747 0.747Wilting Point vol/vol 0.4 0.4Saturated Hydraulic Conductivity

cm/sec 3.00E-09 3.00E-09

1 Natural Ground Texture # 10 10Thickness m 1 1Porosity vol/vol 0.398 0.398Field Capacity vol/vol 0.244 0.244Wilting Point vol/vol 0.136 0.136Saturated Hydraulic Conductivity

cm/sec 1.20E-04 1.20E-04

Slope Length m 112 112 112 112 112 112Slope % 2 5 2 5 2 5Soil Texture 13 13 13 13 13 13 Vegetation 4 4 4 4 4 4Runoff Curve Number 83.5 83.9 83.5 83.9 83.5 83.9

Model OutputsRunoff mm/yr 4.34 4.695 1,060.42 1,059.76 1,063.19 1,064.17Runoff (% of precipitation) 0.23 0.25 56.53 56.5 56.68 56.73Evapotranspiration mm/yr 754.522 754.522 810.964 811.628 812.572 812.732Evapotranspiration (% of precipitation)

40.22 40.22 43.23 43.27 43.32 43.33

Lateral Drainage Collected mm/yr - - - - - -

Lateral Drainage Collected (% of precipitation)

- - - - - -

Bedding Infiltration mm/yr 1,116.94 1,116.58 5.224 5.483 0.000* 0.000*Bedding Infiltration (% of precipitation)

59.54 59.53 0.28 0.29 0 0

Peak infiltration to groundwater m3/day 1,172.10 1,044.44 3.689 4.278 0 0

Runoff Curve Number Information

Barrier Soil

Vertical Percolation

Scenario 3A Scenario 3BScenario 1A Scenario 1B Scenario 2AHELP Model InputsDa Nang, Vietnam

19 th May 2016

Geomembrane Liner

Scenario 2B


Geomembrane Liner

Barrier Soil


Table 2 Assumptions Used in the HELP Model for Soil Cover Texture 24

60 cm Soil Cover, 60 cm Soil Cover, 60 cm Soil Cover, 60 cm Soil Cover, 60 cm Soil Cover, 60 cm Soil Cover,

1.5 m Waste Material, 1.5 m Waste Material, 1 mm HDPE Liner, 1 mm HDPE Liner, 1 mm HDPE Liner, 1 mm HDPE Liner,

Slope 2% Slope 5% 1.5 m Waste Material, 1.5 m Waste Material, Bentonite Mat, Bentonite Mat,

Slope 2% Slope 5% 1.5 m Waste Material, 1.5 m Waste Material,

1 mm HDPE Liner, 1 mm HDPE Liner,

Bentonite Mat Bentonite Mat

Slope 2% Slope 5%

Landfill Capping Area

ha 5 5 5 5 5 5

Precipitation mm/yr 1,875.80 1,875.80 1,875.80 1,875.80 1,875.80 1,875.80Evaporative Zone Depth

cm 60 60 60 60 60 60

Leaf Area Index 3.5 (good stand) 3.5 (good stand) 3.5 (good stand) 3.5 (good stand) 3.5 (good stand) 3.5 (good stand)

Layer Type

1 Soil Cover Texture # 24 24 24 24 24 24Thickness m 0.6 0.6 0.6 0.6 0.6 0.6Porosity vol/vol 0.365 0.365 0.365 0.365 0.365 0.365Field Capacity vol/vol 0.305 0.305 0.305 0.305 0.305 0.305Wilting Point vol/vol 0.202 0.202 0.202 0.202 0.202 0.202Saturated Hydraulic Conductivity

cm/sec 2.70E‐06 2.70E‐06 2.70E‐06 2.70E‐06 2.70E‐06 2.70E‐06

4 HDPE Liner Texture # 35 35 35 35Thickness m 0.001 0.001 0.001 0.001Saturated Hydraulic Conductivity

cm/sec 2.00E‐13 2.00E‐13 2.00E‐13 2.00E‐13

Pinhole Density holes/ha 1 1 1 1

Installation Defects defects/ha 1 1 1 1

Placement Quality 3 (Good) 3 (Good) 3 (Good) 3 (Good)

3 Bentonite Matting Texture # 17 17

Thickness m 0.006 0.006Porosity vol/vol 0.75 0.75Field Capacity vol/vol 0.747 0.747Wilting Point vol/vol 0.4 0.4Saturated Hydraulic Conductivity

cm/sec 3.00E‐09 3.00E‐09

1 Waste Material Texture # 10 10 10 10 10 10Thickness m 1.5 1.5 1.5 1.5 1.5 1.5Porosity vol/vol 0.398 0.398 0.398 0.398 0.398 0.398Field Capacity vol/vol 0.244 0.244 0.244 0.244 0.244 0.244Wilting Point vol/vol 0.136 0.136 0.136 0.136 0.136 0.136Saturated Hydraulic Conductivity

cm/sec 1.20E‐04 1.20E‐04 1.20E‐04 1.20E‐04 1.20E‐04 1.20E‐04

4 HDPE Liner Texture # 35 35Thickness m 0.001 0.001Saturated Hydraulic Conductivity

cm/sec 2.00E‐13 2.00E‐13

Pinhole Density holes/ha 1 1

Installation Defects defects/ha 1 1

Placement Quality 3 (Good) 3 (Good)3 Bentonite Matting Texture # 17 17

Thickness m 0.006 0.006Porosity vol/vol 0.75 0.75Field Capacity vol/vol 0.747 0.747Wilting Point vol/vol 0.4 0.4Saturated Hydraulic Conductivity

cm/sec 3.00E‐09 3.00E‐09

1 Natural Ground Texture # 10 10Thickness m 1 1Porosity vol/vol 0.398 0.398Field Capacity vol/vol 0.244 0.244Wilting Point vol/vol 0.136 0.136Saturated Hydraulic Conductivity

cm/sec 1.20E‐04 1.20E‐04

Slope Length m 112 112 112 112 112 112Slope % 2 5 2 5 2 5Soil Texture 24 24 24 24 24 24Vegetation 4 4 4 4 4 4Runoff Curve Number

86.7 87 86.7 87 86.7 87

Model Outputs

Runoff mm/yr 342.541 351.974 1,090.91 1,090.82 1,091.43 1,091.37Runoff (% of precipitation)

18.26 18.76 58.16 58.15 58.19 58.18

Evapotranspiration mm/yr 753.451 753.965 784.212 784.309 784.33 784.395

Evapotranspiration (% of precipitation)

40.17 40.19 41.81 41.812 41.813 41.817

Lateral Drainage Collected

mm/yr ‐ ‐ ‐ ‐ ‐ ‐

Lateral Drainage Collected (% of precipitation)

‐ ‐ ‐ ‐ ‐ ‐

Bedding Infiltration mm/yr 779.62 769.862 0.674 0.673 0.000* 0.000*

Bedding Infiltration (% of precipitation)

41.56 41.04 0.04 0.04 0 0

Peak infiltration to groundwater m3/day 471.233 477.677 1.866 1.865 0 0

Geomembr

ane Liner

Scenario 2B

Vertical

Percolation

Geomembr

ane Liner

Barrier Soil

Vertical

Percolation

Scenario 3A Scenario 3BScenario 1A Scenario 1B Scenario 2AHELP Model Inputs

Da Nang, Vietnam

19 th May 2016

Runoff Curve Number Information

Barrier Soil

Vertical

Percolation

Page 1 of 1

Table 4 Estimation of Dioxin Concentration in Groundwater

Kd (L/g) = sorbed concentration (mg/kg)/ dissolved concentration ( mg/L)Kd= Koc x focDioxins Koc (cm3/g) 257,000 Default Koc value used in leaching models 1

foc 1.085Kd (L/g) 278,845

pg/g 751mg/kg 7.51E‐04

Dissolved Conc. mg/L 2.69E‐09

1

Sample 1R‐SL‐TSSA1‐B‐All‐0001; result is 751 ppt Dioxin TEQ (using NDs at ½ the detection limit and WHO 2005 values)

Average of sediment TOC from SAP501‐1 21‐JAN‐10 and SAP521‐1 21‐JAN‐10

Dioxin TEQ in material to be stockpiled

Assumptions Used to Estimate Dioxin Leachate Concentration

United States Environmental Protection Agency (USEPA). 2011. Background Information for the Leaching Environmental Assessment Framework (LEAF) Test Methods. EPA/600/R-10/170. November.

Page 1 of 1

Table 5. Mixing Model Assumptions for Scenario 1A, Texture 13

DaNang Airport

Best case scenario using simple mixing model and assuming complete mixing:Potential Mixing Volumes per year:V1 = infiltration over EVSA

V1= HELP model estimate for leakage through Layer 2

Precipitation (m/yr)

Bedding Infiltration

Rate (% of

precipitation) =EVSA Area (m

2)

Leakage

through EVSA

Layer 2‐V1

(m3/yr)

2 59.54% 50,000 55,847

V2 = groundwater volume under EVSA V2= Aquifer thickness * Area of treated material placement *Porosity

Aquifer Thickness (m)Stockpile Placement

Area (m2) Total Porosity (%) V2 (m3/yr)

9 50,000 30 135,000

V3 = upgradient groundwater entering EVSAV3 Estimated based on Darcy's Law Q=KiA

Aquifer Thickness (m)Length perpendicular to

GW Flow (m)

Cross Sectional Area

Perpendicular to

Groundwater Flow (K)

(m2)

Groundwater

Gradient (i)

Hydraulic

Conductivity

(K) (m/yr) V3 (m

3/yr)

9 224 2016 0.002 630.72 2,543

V41 = volume entering receptor well downgradient of EVSA V4= Aquifer thickness * Distance to downgradient well * length perpendicular to groundwater flow* porosity

Aquifer Thickness (m)Distance to

Downgradient Well (m)

Length perpendicular

to GW Flow (m)

Total Porosity

(%) V4 (m

3/yr)

9 600 224 30 362,880

Groundwater flow velocity (max during rainy season and high water table) Velocity = hydraulic conductivity * gradient / effective porosity

Hydraulic Conductivity

(K) (m/yr)

Groundwater Gradient

(i)Effective Porosity

Groundwater

Velocity (m/yr)

630.72 0.002 0.2 6.3

Mass of leached arsenic per yearMass (mg /yr)= V1(Stockpile Area* Infiltration Rate) *leachate concentration * 1000 L/m 3

Leachate Concentration (mg/L) 0.25 0.5Mass of leached arsenic per year (mg/yr) 1.40E+07 2.79E+07

Mass of leached dioxin per year Mass (mg /yr)= V1(Stockpile Area* Infiltration Rate) *leachate concentration * 1000 L/m 3

Dioxin Dissolved Conc. (mg/L) 2.69E‐09Mass of leached dioxin per year (mg/yr) 1.50E‐01

COC Concentration in hypothetical groundwater well in middle of EVSA:

For Mixing Volume assume complete mixing of V1 + V2 + V3

V1 (m3/yr) V2 (m

3/yr) V3 (m

3/yr)

Mixing Volume

(m3/yr)

55,847 135,000 2,543 193,390Concentration of arsenic = Mass of leached arsenic per year/ Mixing Volume *1000 L/m 3

Mass (mg/yr) ‐for 0.25

mg/L LeachateArsenic Conc. (mg/L)

Mass ‐ for 0.50 mg/L

Leachate

Arsenic Conc.

(mg/L)

1.40E+07 0.072 2.79E+07 0.144Concentration of dioxin = Mass of leached dioxin per year/ Mixing Volume *1000 L/m 3

Mass (mg/yr) Dioxin Conc. (mg/L) Dioxin Conc. (pg/L)

1.50E‐01 7.78E‐10 0.778

COC Concentration in hypothetical groundwater well 50 m from southern airport boundary downgradient of stockpile :

For Mixing Volume assume complete mixing of V1 + V2 + V3 + V4 1

V1 (m

3/yr) V2 (m3/yr) V3 (m3/yr) V41 (m3/yr)

Mixing Volume

(m3/yr)

55,847 135,000 2,543 362,880 556,270Concentration of arsenic = Mass of leached arsenic per year/ Mixing Volume *1000 L/m 3




Leachate

Arsenic Conc.

(mg/L)



1.50E‐01 2.70E‐10 0.270

Page 1 of 2


DaNang Airport

Estimate of Concentrations in Downgradient Ponds

V42 = volume entering pond downgradient of EVSA V4= Aquifer thickness * Distance to downgradient pond * length perpendicular to groundwater flow* porosity

Pond Aquifer Thickness (m) Distance to Pond (m)Length perpendicular

to GW Flow (m)

Total Porosity

(%) V4 (m

3/yr)

10% of V4

(m3/yr)

Pond 1 9 750 224 30 453,600 45,360 Pond2 9 750 224 30 453,600 45,360Pond 3 9 875 224 30 529,200 52,920Ponds 4,5,6, 9 1000 224 30 604,800 60,480

Concentrations of COCs in groundwater inflow:

Assume no surface water contamination from EVSA to area ponds (material covered), 0 mg/L starting COC conc.For mixing volume assume complete mixing of V1 + V2 + V3 + V4

Pond V1 (m3/yr) V2 (m

3/yr) V32 (m

3/yr) V42 (m

3/yr)

Total Volume

migrating to

pond (m3/yr) ‐

V5

Arsenic Conc

(mg/L) ‐for

0.25 mg/L

Leachate

Arsenic

Conc (mg/L)

‐for 0.5

mg/L

Leachate

Dioxin Conc

(mg/L)

Pond 1 55,847 135,000 2,543 453,600 646,990 0.022 0.043 2.32E‐10Pond2 55,847 135,000 2,543 453,600 646,990 0.022 0.043 2.32E‐10Pond 3 55,847 135,000 2,543 529,200 722,590 0.019 0.039 2.08E‐10

Ponds 4,5,6, 55,847 135,000 2,543 604,800 798,190 0.017 0.035 1.88E‐10

Pond Length (m) Width (m) Depth (m)Pond volume

(m3)

Total Mixing

Volume ( m3)

Arsenic Mass

(mg/yr)

Entering Pond

‐for 0.25 mg/L

Leachate

Arsenic

Conc (mg/L)

in Pond ‐for

0.25 mg/L

Leachate

Arsenic

Mass

Entering

Pond

(mg/yr) ‐for

0.50 mg/L

Leachate

Arsenic Conc

(mg/L) in Pond

‐for 0.50 mg/L

Leachate

Dioxin Mass

(mg/yr)

Entering

Pond

Dioxin Conc (mg/L)

in Pond

Dioxin Conc

(pg/L) in Pond

Pond 1 200 100 0.5 10,000 55,360 979 0.018 1,958 0.035 1.05E‐05 1.90E‐10 0.190Pond2 200 100 0.6 12,000 57,360 979 0.017 1,958 0.034 1.05E‐05 1.84E‐10 0.184Pond 3 300 100 0.7 21,000 73,920 1,023 0.014 2,045 0.028 1.10E‐05 1.49E‐10 0.149Ponds 4,5,6, 250 200 1.2 60,000 120,480 1,058 0.009 2,116 0.018 1.14E‐05 9.46E‐11 0.095

Concentration in Groundwater

Page 2 of 2

Table 6. Mixing Model Assumptions for Scenario 1A, Soil Cover Texture 24

DaNang Airport





Rate (% of


2)

Leakage

through EVSA

Layer 2‐V1

(m3/yr)

2 41.56% 50,000 38,981




9 50,000 30 135,000



GW Flow (m)


Perpendicular to


(m2)

Groundwater

Gradient (i)

Hydraulic

Conductivity

(K) (m/yr) V3 (m

3/yr)

9 224 2016 0.002 630.72 2,543





to GW Flow (m)

Total Porosity

(%) V4 (m

3/yr)

9 600 224 30 362,880



(K) (m/yr)



Groundwater

Velocity (m/yr)

630.72 0.002 0.2 6.3







V1 (m3/yr) V2 (m

3/yr) V3 (m

3/yr)

Mixing Volume

(m3/yr)

38,981 135,000 2,543 176,524Concentration of arsenic = Mass of leached arsenic per year/ Mixing Volume *1000 L/m 3




Leachate

Arsenic Conc.

(mg/L)



1.05E‐01 5.95E‐10 0.595



V1 (m

3/yr) V2 (m3/yr) V3 (m3/yr) V41 (m3/yr)

Mixing Volume

(m3/yr)

38,981 135,000 2,543 362,880 539,404Concentration of arsenic = Mass of leached arsenic per year/ Mixing Volume *1000 L/m 3




Leachate

Arsenic Conc.

(mg/L)



1.05E‐01 1.95E‐10 0.195

Page 1 of 2

Table 6. Mixing Model Assumptions for Scenario 1A, Soil Cover Texture 24

DaNang Airport




to GW Flow (m)

Total Porosity

(%) V4 (m

3/yr)

10% of V4

(m3/yr)





3/yr) V32 (m

3/yr) V42 (m

3/yr)

Total Volume

migrating to

pond (m3/yr) ‐

V5

Arsenic Conc

(mg/L) ‐for

0.25 mg/L

Leachate

Arsenic

Conc (mg/L)

‐for 0.5

mg/L

Leachate

Dioxin Conc

(mg/L)

Pond 1 38,981 135,000 2,543 453,600 630,124 0.015 0.031 1.67E‐10Pond2 38,981 135,000 2,543 453,600 630,124 0.015 0.031 1.67E‐10Pond 3 38,981 135,000 2,543 529,200 705,724 0.014 0.028 1.49E‐10

Ponds 4,5,6, 38,981 135,000 2,543 604,800 781,324 0.012 0.025 1.34E‐10


(m3)

Total Mixing

Volume ( m3)

Arsenic Mass

(mg/yr)

Entering Pond

‐for 0.25 mg/L

Leachate

Arsenic

Conc (mg/L)

in Pond ‐for

0.25 mg/L

Leachate

Arsenic

Mass

Entering

Pond

(mg/yr) ‐for

0.50 mg/L

Leachate

Arsenic Conc

(mg/L) in Pond

‐for 0.50 mg/L

Leachate

Dioxin Mass

(mg/yr)

Entering

Pond

Dioxin Conc (mg/L)

in Pond

Dioxin Conc

(pg/L) in Pond

Pond 1 200 100 0.5 10,000 55,360 702 0.013 1,403 0.025 7.56E‐06 1.37E‐10 0.137Pond2 200 100 0.6 12,000 57,360 702 0.012 1,403 0.024 7.56E‐06 1.32E‐10 0.132Pond 3 300 100 0.7 21,000 73,920 731 0.010 1,462 0.020 7.87E‐06 1.07E‐10 0.107Ponds 4,5,6, 250 200 1.2 60,000 120,480 754 0.006 1,509 0.013 8.13E‐06 6.75E‐11 0.067


Page 2 of 2


DaNang Airport





Rate (% of


2)

Leakage

through EVSA

Layer 2‐V1

(m3/yr)

2 0.28% 50,000 261




9 50,000 30 135,000



GW Flow (m)


Perpendicular to


(m2)

Groundwater

Gradient (i)

Hydraulic

Conductivity

(K) (m/yr) V3 (m

3/yr)

9 224 2016 0.002 630.72 2,543





to GW Flow (m)

Total Porosity

(%) V4 (m

3/yr)

9 600 224 30 362,880



(K) (m/yr)



Groundwater

Velocity (m/yr)

630.72 0.002 0.2 6.3







V1 (m3/yr) V2 (m

3/yr) V3 (m

3/yr)

Mixing Volume

(m3/yr)

261 135,000 2,543 137,804Concentration of arsenic = Mass of leached arsenic per year/ Mixing Volume *1000 L/m 3




Leachate

Arsenic Conc.

(mg/L)

6.53E+04 4.74E‐04 1.31E+05 9.48E‐04Concentration of dioxin = Mass of leached dioxin per year/ Mixing Volume *1000 L/m 3


7.03E‐04 5.10E‐12 5.10E‐03



V1 (m

3/yr) V2 (m3/yr) V3 (m3/yr) V41 (m3/yr)

Mixing Volume

(m3/yr)

261 135,000 2,543 362,880 500,684Concentration of arsenic = Mass of leached arsenic per year/ Mixing Volume *1000 L/m 3




Leachate

Arsenic Conc.

(mg/L)

6.53E+04 1.30E‐04 1.31E+05 2.61E‐04Concentration of dioxin = Mass of leached dioxin per year/ Mixing Volume *1000 L/m 3


7.03E‐04 1.40E‐12 1.40E‐03

Page 1 of 2


DaNang Airport




to GW Flow (m)

Total Porosity

(%) V4 (m

3/yr)

10% of V4

(m3/yr)





3/yr) V32 (m

3/yr) V42 (m

3/yr)

Total Volume

migrating to

pond (m3/yr) ‐

V5

Arsenic Conc

(mg/L) ‐for

0.25 mg/L

Leachate

Arsenic

Conc (mg/L)

‐for 0.5

mg/L

Leachate

Dioxin Conc

(mg/L)

Pond 1 261 135,000 2,543 453,600 591,404 1.10E‐04 2.21E‐04 1.19E‐12Pond2 261 135,000 2,543 453,600 591,404 1.10E‐04 2.21E‐04 1.19E‐12Pond 3 261 135,000 2,543 529,200 667,004 9.79E‐05 1.96E‐04 1.05E‐12

Ponds 4,5,6, 261 135,000 2,543 604,800 742,604 8.79E‐05 1.76E‐04 9.47E‐13


(m3)

Total Mixing

Volume ( m3)

Arsenic Mass

(mg/yr)

Entering Pond

‐for 0.25 mg/L

Leachate

Arsenic

Conc (mg/L)

in Pond ‐for

0.25 mg/L

Leachate

Arsenic

Mass

Entering

Pond

(mg/yr) ‐for

0.50 mg/L

Leachate

Arsenic Conc

(mg/L) in Pond

‐for 0.50 mg/L

Leachate

Dioxin Mass

(mg/yr)

Entering

Pond

Dioxin Conc (mg/L)

in Pond

Dioxin Conc

(pg/L) in Pond

Pond 1 200 100 0.5 10,000 55,360 5 9.05E‐05 10 1.81E‐04 5.40E‐08 9.75E‐13 9.75E‐04Pond2 200 100 0.6 12,000 57,360 5 8.73E‐05 10 1.75E‐04 5.40E‐08 9.41E‐13 9.41E‐04Pond 3 300 100 0.7 21,000 73,920 5 7.01E‐05 10 1.40E‐04 5.58E‐08 7.55E‐13 7.55E‐04Ponds 4,5,6, 250 200 1.2 60,000 120,480 5 4.41E‐05 11 8.83E‐05 5.73E‐08 4.76E‐13 4.76E‐04


Page 2 of 2

Table 8. Mixing Model Assumptions for Scenario 2A

DaNang Airport



Precipitation (m/yr)Bedding Infiltration Rate

(% of precipitation) =EVSA Area (m2)

Leakage

through EVSA

Layer 2‐V1

(m3/yr) 2 41.56% 50,000 37

V2 = groundwater volume under EVSA

V2= Aquifer thickness * Area of treated material placement *Porosity



9 50,000 30 135,000



GW Flow (m)


Perpendicular to


(m2)

Groundwater

Gradient (i)

Hydraulic

Conductivity (K)

(m/yr) V3 (m3/yr)

9 224 2016 0.002 630.72 2,543





to GW Flow (m)

Total Porosity

(%) V4 (m3/yr)

9 600 224 30 362,880



(K) (m/yr)



Groundwater

Velocity (m/yr)

630.72 0.002 0.2 6.3

Mass of leached arsenic per yearMass (mg /yr)= V1(Stockpile Area* Infiltration Rate) *leachate concentration * 1000 L/m3

Leachate Concentration (mg/L) 0.25 0.5

Mass of leached arsenic per year (mg/yr) 9.29E+03 1.86E+04

Mass of leached dioxin per year Mass (mg /yr)= V1(Stockpile Area* Infiltration Rate) *leachate concentration * 1000 L/m3




V1 (m3/yr) V2 (m3/yr) V3 (m3/yr)Mixing Volume

(m3/yr)

37 135,000 2,543 137,580Concentration of arsenic = Mass of leached arsenic per year/ Mixing Volume *1000 L/m3




Leachate

Arsenic Conc.

(mg/L)

9.29E+03 6.75E‐05 1.86E+04 1.35E‐04Concentration of dioxin = Mass of leached dioxin per year/ Mixing Volume *1000 L/m3


1.00E‐04 7.27E‐13 7.27E‐04


For Mixing Volume assume complete mixing of V1 + V2 + V3 + V41

V1 (m3/yr) V2 (m3/yr) V3 (m3/yr) V41 (m

3/yr)

Mixing Volume

(m3/yr)

37 135,000 2,543 362,880 500,460Concentration of arsenic = Mass of leached arsenic per year/ Mixing Volume *1000 L/m3




Leachate

Arsenic Conc.

(mg/L)

9.29E+03 1.86E‐05 1.86E+04 3.71E‐05Concentration of dioxin = Mass of leached dioxin per year/ Mixing Volume *1000 L/m3


1.00E‐04 2.00E‐13 2.00E‐04

Page 1 of 2


DaNang Airport




to GW Flow (m)

Total Porosity

(%) V4 (m3/yr)

10% of V4

(m3/yr)




Pond V1 (m3/yr) V2 (m3/yr) V32 (m3/yr) V42 (m

3/yr)

Total Volume

migrating to

pond (m3/yr) ‐

V5

Arsenic Conc

(mg/L) ‐for

0.25 mg/L

Leachate

Arsenic

Conc (mg/L) ‐

for 0.5 mg/L

LeachateDioxin Conc

(mg/L)

Pond 1 37 135,000 2,543 453,600 591,180 1.57E‐05 3.14E‐05 1.69E‐13Pond2 37 135,000 2,543 453,600 591,180 1.57E‐05 3.14E‐05 1.69E‐13Pond 3 37 135,000 2,543 529,200 666,780 1.39E‐05 2.79E‐05 1.50E‐13

Ponds 4,5,6, 37 135,000 2,543 604,800 742,380 1.25E‐05 2.50E‐05 1.35E‐13


(m3)

Total Mixing

Volume ( m3)

Arsenic Mass

(mg/yr)

Entering Pond

‐for 0.25 mg/L

Leachate

Arsenic

Conc (mg/L)

in Pond ‐for

0.25 mg/L

Leachate

Arsenic

Mass

Entering

Pond

(mg/yr) ‐for

0.50 mg/L

Leachate

Arsenic Conc

(mg/L) in Pond

‐for 0.50 mg/L

Leachate

Dioxin Mass

(mg/yr)

Entering Pond

Dioxin Conc (mg/L)

in Pond

Dioxin Conc

(pg/L) in Pond

Pond 1 200 100 0.5 10,000 55,360 1 1.29E‐05 1 2.57E‐05 7.68E‐09 1.39E‐13 1.39E‐04Pond2 200 100 0.6 12,000 57,360 1 1.24E‐05 1 2.48E‐05 7.68E‐09 1.34E‐13 1.34E‐04Pond 3 300 100 0.7 21,000 73,920 1 9.97E‐06 1 1.99E‐05 7.94E‐09 1.07E‐13 1.07E‐04Ponds 4,5,6, 250 200 1.2 60,000 120,480 1 6.28E‐06 2 1.26E‐05 8.15E‐09 6.76E‐14 6.76E‐05


Page 2 of 2


DaNang Airport





Rate (% of precipitation)

=EVSA Area (m

2)

Leakage

through EVSA

Layer 2‐V1

(m3/yr) 2 0.00% 50,000 0




Area (m2)

Total Porosity (%) V2 (m3/yr)

9 50,000 30 135,000



GW Flow (m)


Perpendicular to


(m2)

Groundwater

Gradient (i)

Hydraulic

Conductivity

(K) (m/yr) V3 (m3/yr)

9 224 2016 0.002 630.72 2,543

V41 = volume entering receptor well downgradient of EVSA

V4= Aquifer thickness * Distance to downgradient well * length perpendicular to groundwater flow* porosity




to GW Flow (m)

Total Porosity

(%) V4 (m

3/yr)

9 600 224 30 362,880



(K) (m/yr)



Groundwater

Velocity (m/yr)

630.72 0.002 0.2 6.3





Dioxin Dissolved Conc. (mg/L) 2.69E‐09Mass of leached dioxin per year (mg/yr) 0.00E+00



V1 (m3/yr) V2 (m3/yr) V3 (m3/yr)

Mixing Volume

(m3/yr)





Leachate

Arsenic Conc.

(mg/L)

0.00E+00 0.00E+00 0.00E+00 0.00E+00Concentration of dioxin = Mass of leached dioxin per year/ Mixing Volume *1000 L/m3


0.00E+00 0.00E+00 0.00E+00



V1 (m

3/yr) V2 (m3/yr) V3 (m3/yr) V41 (m3/yr)

Mixing Volume

(m3/yr)





Leachate

Arsenic Conc.

(mg/L)



0.00E+00 0.00E+00 0.00E+00

Page 1 of 2


DaNang Airport




to GW Flow (m)

Total Porosity

(%) V4 (m

3/yr)

10% of V4

(m3/yr)





3/yr) V32 (m

3/yr) V42 (m

3/yr)

Total Volume

migrating to

pond (m3/yr) ‐

V5

Arsenic Conc

(mg/L) ‐for

0.25 mg/L

Leachate

Arsenic

Conc (mg/L)

‐for 0.5

mg/L

Leachate

Dioxin Conc

(mg/L)

Pond 1 0 135,000 2,543 453,600 591,143 0.00E+00 0.00E+00 0.00E+00Pond2 0 135,000 2,543 453,600 591,143 0.00E+00 0.00E+00 0.00E+00Pond 3 0 135,000 2,543 529,200 666,743 0.00E+00 0.00E+00 0.00E+00

Ponds 4,5,6, 0 135,000 2,543 604,800 742,343 0.00E+00 0.00E+00 0.00E+00


(m3)

Total Mixing

Volume ( m3)

Arsenic Mass

(mg/yr)

Entering Pond

‐for 0.25 mg/L

Leachate

Arsenic

Conc (mg/L)

in Pond ‐for

0.25 mg/L

Leachate

Arsenic

Mass

Entering

Pond

(mg/yr) ‐for

0.50 mg/L

Leachate

Arsenic Conc

(mg/L) in Pond

‐for 0.50 mg/L

Leachate

Dioxin Mass

(mg/yr)

Entering

Pond

Dioxin Conc (mg/L)

in Pond

Dioxin Conc

(pg/L) in Pond

Pond 1 200 100 0.5 10,000 55,360 0 0.00E+00 0 0.00E+00 0.00E+00 0.00E+00 0.00E+00Pond2 200 100 0.6 12,000 57,360 0 0.00E+00 0 0.00E+00 0.00E+00 0.00E+00 0.00E+00Pond 3 300 100 0.7 21,000 73,920 0 0.00E+00 0 0.00E+00 0.00E+00 0.00E+00 0.00E+00Ponds 4,5,6, 250 200 1.2 60,000 120,480 0 0.00E+00 0 0.00E+00 0.00E+00 0.00E+00 0.00E+00


Page 2 of 2


DaNang Airport





Rate (% of precipitation)

=EVSA Area (m

2)

Leakage

through EVSA

Layer 2‐V1

(m3/yr) 2 0.00% 50,000 0




Area (m2)

Total Porosity (%) V2 (m3/yr)

9 50,000 30 135,000



GW Flow (m)


Perpendicular to


(m2)

Groundwater

Gradient (i)

Hydraulic

Conductivity

(K) (m/yr) V3 (m3/yr)

9 224 2016 0.002 630.72 2,543

V41 = volume entering receptor well downgradient of EVSA

V4= Aquifer thickness * Distance to downgradient well * length perpendicular to groundwater flow* porosity




to GW Flow (m)

Total Porosity

(%) V4 (m

3/yr)

9 600 224 30 362,880



(K) (m/yr)



Groundwater

Velocity (m/yr)

630.72 0.002 0.2 6.3





Dioxin Dissolved Conc. (mg/L) 2.69E‐09Mass of leached dioxin per year (mg/yr) 0.00E+00



V1 (m3/yr) V2 (m3/yr) V3 (m3/yr)

Mixing Volume

(m3/yr)





Leachate

Arsenic Conc.

(mg/L)



0.00E+00 0.00E+00 0.00E+00



V1 (m

3/yr) V2 (m3/yr) V3 (m3/yr) V41 (m3/yr)

Mixing Volume

(m3/yr)





Leachate

Arsenic Conc.

(mg/L)



0.00E+00 0.00E+00 0.00E+00

Page 1 of 2


DaNang Airport




to GW Flow (m)

Total Porosity

(%) V4 (m

3/yr)

10% of V4

(m3/yr)





3/yr) V32 (m

3/yr) V42 (m

3/yr)

Total Volume

migrating to

pond (m3/yr) ‐

V5

Arsenic Conc

(mg/L) ‐for

0.25 mg/L

Leachate

Arsenic

Conc (mg/L)

‐for 0.5

mg/L

Leachate

Dioxin Conc

(mg/L)

Pond 1 0 135,000 2,543 453,600 591,143 0.00E+00 0.00E+00 0.00E+00Pond2 0 135,000 2,543 453,600 591,143 0.00E+00 0.00E+00 0.00E+00Pond 3 0 135,000 2,543 529,200 666,743 0.00E+00 0.00E+00 0.00E+00

Ponds 4,5,6, 0 135,000 2,543 604,800 742,343 0.00E+00 0.00E+00 0.00E+00


(m3)

Total Mixing

Volume ( m3)

Arsenic Mass

(mg/yr)

Entering Pond

‐for 0.25 mg/L

Leachate

Arsenic

Conc (mg/L)

in Pond ‐for

0.25 mg/L

Leachate

Arsenic

Mass

Entering

Pond

(mg/yr) ‐for

0.50 mg/L

Leachate

Arsenic Conc

(mg/L) in Pond

‐for 0.50 mg/L

Leachate

Dioxin Mass

(mg/yr)

Entering

Pond

Dioxin Conc (mg/L)

in Pond

Dioxin Conc

(pg/L) in Pond

Pond 1 200 100 0.5 10,000 55,360 0 0.00E+00 0 0.00E+00 0.00E+00 0.00E+00 0.00E+00Pond2 200 100 0.6 12,000 57,360 0 0.00E+00 0 0.00E+00 0.00E+00 0.00E+00 0.00E+00Pond 3 300 100 0.7 21,000 73,920 0 0.00E+00 0 0.00E+00 0.00E+00 0.00E+00 0.00E+00Ponds 4,5,6, 250 200 1.2 60,000 120,480 0 0.00E+00 0 0.00E+00 0.00E+00 0.00E+00 0.00E+00


Page 2 of 2

Table 11. Summary of Mixing Model, Texture 13

DaNang Airport

Arsenic

Concentration

(mg/L) assuming

0.25 mg/L

leachate

Arsenic

Concentration

(mg/L) assuming

0.50 mg/L

leachate

Dioxin TEQ

Concentration

(pg/L)

Arsenic

Concentration

(mg/L) assuming

0.25 mg/L

leachate

Groundwater

Arsenic Mass (mg)

Based on 0.50

mg/leachate conc

Dioxin TEQ

Concentration

(pg/L)

1A 0.072 0.144 0.778 0.025 0.050 0.2702A 4.74E‐04 9.48E‐04 5.10E‐03 1.30E‐04 2.61E‐04 1.40E‐033A 0.0 0.0 0.0 0.0 0.0 0.0

Scenario

Assumes 10%

Infiltration

Arsenic

Concentration

(mg/L) assuming

0.25 mg/L

leachate

Arsenic

Concentration

(mg/L) assuming

0.50 mg/L

leachate

Dioxin TEQ

Concentration

(pg/L)

Arsenic

Concentration

(mg/L) assuming

0.25 mg/L

leachate

Arsenic

Concentration

(mg/L) assuming

0.50 mg/L

leachate

Dioxin TEQ

Concentration

(pg/L)

Arsenic

Concentration

(mg/L) assuming

0.25 mg/L

leachate

Arsenic

Concentration

(mg/L) assuming

0.50 mg/L

leachate

Dioxin TEQ

Concentration

(pg/L)

Arsenic

Concentration

(mg/L) assuming

0.25 mg/L

leachate

Arsenic

Concentration

(mg/L) assuming

0.50 mg/L

leachate

Dioxin TEQ

Concentration

(pg/L)

1A 0.018 0.035 0.190 0.017 0.034 0.184 0.014 0.028 0.149 0.009 0.018 0.0952A 9.05E‐05 1.81E‐04 9.75E‐04 8.73E‐05 1.75E‐04 9.41E‐04 7.01E‐05 1.40E‐04 7.55E‐04 4.41E‐05 8.83E‐05 4.76E‐043A 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Scenario

Downgradient well 50m from southern boundary of

EVSA

Pond 2 Pond 3 Pond 4,5,6

Well in Middle of EVSA

Pond 1

Page 1 of 1

Table 12. Summary of Mixing Model for Soil Cover Texture 24

DaNang Airport

Arsenic

Concentration

(mg/L) assuming

0.25 mg/L

leachate

Arsenic

Concentration

(mg/L) assuming

0.50 mg/L

leachate

Dioxin TEQ

Concentration

(pg/L)

Arsenic

Concentration

(mg/L) assuming

0.25 mg/L

leachate

Groundwater

Arsenic Mass (mg)

Based on 0.50

mg/leachate conc

Dioxin TEQ

Concentration

(pg/L)

1A 0.055 0.110 0.595 0.018 0.036 0.1952A 6.75E‐05 1.35E‐04 7.27E‐04 1.86E‐05 3.71E‐05 2.00E‐043A 0.0 0.0 0.0 0.0 0.0 0.0

Scenario

Assumes 10%

Infiltration

Arsenic

Concentration

(mg/L) assuming

0.25 mg/L

leachate

Arsenic

Concentration

(mg/L) assuming

0.50 mg/L

leachate

Dioxin TEQ

Concentration

(pg/L)

Arsenic

Concentration

(mg/L) assuming

0.25 mg/L

leachate

Arsenic

Concentration

(mg/L) assuming

0.50 mg/L

leachate

Dioxin TEQ

Concentration

(pg/L)

Arsenic

Concentration

(mg/L) assuming

0.25 mg/L

leachate

Arsenic

Concentration

(mg/L) assuming

0.50 mg/L

leachate

Dioxin TEQ

Concentration

(pg/L)

Arsenic

Concentration

(mg/L) assuming

0.25 mg/L

leachate

Arsenic

Concentration

(mg/L) assuming

0.50 mg/L

leachate

Dioxin TEQ

Concentration

(pg/L)


Scenario

Downgradient well 50m from southern boundary of

EVSA

Pond 2 Pond 3 Pond 4,5,6

Well in Middle of EVSA

Pond 1

Page 1 of 1

Table 13. Summary of Mixing Model, Texture 13 and Texture 24

DaNang Airport

Arsenic

Concentration

(mg/L) assuming

0.25 mg/L leachate

Arsenic

Concentration (mg/L)

assuming 0.50 mg/L

leachate

Dioxin TEQ

Concentration (pg/L)

Arsenic

Concentration

(mg/L) assuming

0.25 mg/L

leachate

Groundwater Arsenic

Mass (mg) Based on 0.50

mg/leachate conc

Dioxin TEQ


Arsenic

Concentration

(mg/L) assuming

0.25 mg/L leachate

Arsenic

Concentration

(mg/L) assuming

0.50 mg/L leachate

Dioxin TEQ


Arsenic


assuming 0.25 mg/L

leachate

Groundwater

Arsenic Mass (mg)

Based on 0.50

mg/leachate conc

Dioxin TEQ


1A 0.072 0.144 0.778 0.025 0.050 0.270 0.055 0.110 0.595 0.018 0.036 0.1952A 4.74E‐04 9.48E‐04 5.10E‐03 1.30E‐04 2.61E‐04 1.40E‐03 6.75E‐05 1.35E‐04 7.27E‐04 1.86E‐05 3.71E‐05 2.00E‐043A 0.0 0.0 0.0 0.0 0.0 0.0 0 0 0 0 0 0

Scenario

Assumes 10%

Infiltration

Arsenic

Concentration

(mg/L) assuming

0.25 mg/L leachate

Arsenic


assuming 0.50 mg/L

leachate

Dioxin TEQ


Arsenic

Concentration

(mg/L) assuming

0.25 mg/L

leachate

Arsenic Concentration

(mg/L) assuming 0.50

mg/L leachate

Dioxin TEQ


Arsenic

Concentration

(mg/L) assuming

0.25 mg/L leachate

Arsenic

Concentration

(mg/L) assuming

0.50 mg/L leachate

Dioxin TEQ


Arsenic


assuming 0.25 mg/L

leachate

Arsenic

Concentration

(mg/L) assuming

0.50 mg/L leachate

Dioxin TEQ



Scenario

Assumes 10%

Infiltration

Arsenic

Concentration

(mg/L) assuming

0.25 mg/L leachate

Arsenic


assuming 0.50 mg/L

leachate

Dioxin TEQ


Arsenic

Concentration

(mg/L) assuming

0.25 mg/L

leachate

Arsenic Concentration

(mg/L) assuming 0.50

mg/L leachate

Dioxin TEQ


Arsenic

Concentration

(mg/L) assuming

0.25 mg/L leachate

Arsenic

Concentration

(mg/L) assuming

0.50 mg/L leachate

Dioxin TEQ


Arsenic


assuming 0.25 mg/L

leachate

Arsenic

Concentration

(mg/L) assuming

0.50 mg/L leachate

Dioxin TEQ



Pond 1 Pond 2 Pond 3 Pond 4,5,6

Texture 24

Scenario

Texture 13

Well in Middle of EVSA Downgradient well 50m from southern boundary of EVSA

Pond 1 Pond 2 Pond 3 Pond 4,5,6

Texture 13 Texture 24

Well in Middle of EVSA Downgradient well 50m from southern boundary of EVSA

Page 1 of 1

Annex B: Final Detailed Design Information for Excess Volume Stockpile Area

1

Detailed Design Information for the Excess Volume Stockpile Area (EVSA)

Environmental Remediation of Dioxin Contamination at Danang Airport

1.0 Introduction On 1 July 2016, the United States Agency for International Development (USAID) submitted to the Air Defense Air Force Command (ADAFC) a recommended design for the Excess Volume Stockpile Area (EVSA). This letter also provides a timeline of consultations and the risk assessment report that influenced the EVSA design. ADAFC responded on 11 August 2016 (Letter No. 2907/BTL-KHQS) providing acceptance of the conceptual design and requested a detailed design for the EVSA. The purpose of this document is to provide additional background and detailed information to support the EVSA design.

2.0 Background Information Location, Site Conditions, and Topography The EVSA is located in the southwest area of the Airport near the former Pacer Ivy Storage area. The site area encompasses approximately 5 hectares (ha) and generally consists of flat land with brush and trees. Clearance of unexploded ordnance (UXO) in the area was conducted by the Ministry of National Defense (MND) during March to May 2016 and enabled the Excavation and Construction Contractor (ECC) to conduct a topographic survey (see Figure 1). As indicated, the EVSA location generally grades from the north to south-southwest with elevations ranging from 7 meters (m) above mean sea level (msl) to 5 m msl.

Groundwater The ECC installed three groundwater piezometers (P-1, P-2, and P-3) at the locations indicated on Figure 1 to enable measurement of groundwater depths. Construction details for each piezometer are provided on Figure 2 and show that the piezometers extend to 2.05 to 2.25 m below the ground surface. Measurements conducted between April and June 2016 indicate that the depth to groundwater ranged from 1.83 m to 1.95 m P-1, 1.13 m to 1.44 m at P-2, and 1.97 m to 2.02 m at P-3 (Figure 2a).

Sampling The ground surface of the EVSA was sampled to determine the baseline concentrations of dioxin and arsenic in surface soil. The Construction Management Contractor (CMC) collected one (1) confirmation-level, 30-point composite sample using the multi-increment sampling (MIS) method from the entire EVSA footprint for dioxin and arsenic analysis. Results indicated the surface soils in the EVSA contains dioxin at a concentration of 7.89 parts per trillion (ppt) toxic equivalent (TEQ) (i.e., pg TEQ/g), and arsenic at a concentration of 2.82 parts per million (ppm) (i.e., mg/kg).

3.0 EVSA Design Layout and Design Details The configuration of the EVSA is provided in Figure 3 and the construction sequence is identified in Figure 4. Key design details include the following:

Detailed Design Information for the EVSA

2

A 40-m by 108-m gravel-surfaced area for equipment parking, material storage, and field office will be constructed between the east side of the EVSA and existing Airport ring road. Access to the EVSA will be through this area.

A 0.5-m high soil containment berm (Figures 5 and 6) will be constructed along the perimeter of the EVSA to facilitate placement of soil/sediment and management of any stormwater during construction. The area within the containment berm is approximately 4.3 ha.

Following placement of material in the EVSA, a cover system will be constructed to reduce the infiltration of precipitation into the stockpile (Figure 6) and eliminate exposure pathways. The composition of the cover system (from bottom to top) will be a barrier layer consisting of a 1 millimeter (mm) thick high density polyethylene (HDPE) geomembrane liner; a 4.4-mm thick geonet composite drainage layer to remove water above the HDPE liner; a 40 centimeter (cm) layer of soil; and a 10-cm top soil layer of sufficient organic content to sustain vegetative growth. Specification information for the HDPE liner and geonet composite are provided in Figure 8.

As indicted in the plan view in Figure 5 and cross section in Figure 6, the top surface of the EVSA will generally be sloped at 3 percent to promote drainage. It is estimated that the maximum height of the EVSA will be approximately 4 m above the existing ground surface.

Stone will be placed on the outside slope of the containment berm (Figure 6) to create a toe drain, provide erosion protection, and promote a natural sheet-flow of rainwater runoff from the EVSA cover.

A 2.4-m high permanent security fence (Figures 5 and 7) will be installed around the perimeter of the EVSA to control access to the area.

Volumes and Storage Capacity Material to be placed in the EVSA is currently stockpiled in Drying Pad Number 1 (DP-1), Temporary Sediment Stockpile Area (TSSA)-1, and TSSA-2. It is estimated that about 55,000 to 60,000 cubic meters (m3) of material is stockpiled in these three areas. The configuration of the EVSA shown in Figure 5 has a storage capacity of approximately 60,000 m3. Since there is likely to be shrinkage from compaction (i.e., placing the material into the EVSA in a denser condition than it is currently at in the stockpiles), it can be seen that all material from the stockpiles will fit within the EVSA. The configuration of the EVSA will be adjusted in the field during construction to accommodate the actual, in-place compacted volume of material. This could involve moving the containment berm inwards to reduce the EVSA footprint and/or reducing the cover slope of the EVSA to a minimum of 2 percent.

Construction and Filling Sequence The anticipated construction and filling sequence for the EVSA is provided in Figure 4. Following site preparation activities (i.e., surveying, installation of silt fence, clearing of vegetation, and grading and proof rolling the existing ground surface), the perimeter containment berm and internal access/haul roads will be constructed. Material will be hauled from the DP-1, TSSA-1, and TSSA-2 and spread and compacted in the EVSA. In general, the sequence of placement will be from north to south and east to west. Once subareas of the EVSA have been filled to final grade, installation of the cover system will begin and will continue as more subareas are completed. The perimeter security fence will be erected upon completion of the cover system.

Groundwater Monitoring Wells As mentioned in Section 2, three groundwater piezometers were installed to monitor groundwater depths in the EVSA. Based on the groundwater measurements performed from April to June 2016, P1 and P-2 are located on the down-gradient side of the EVSA and P-3 is located on the upgradient

Detailed Design Information for the EVSA

3

side. It is proposed that these piezometers remain in place and be used for potential future shallow groundwater quality monitoring (to be performed by MND). During construction, the piezometers will be protected to prevent damage from construction equipment and activities.

T3

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CURENT TOPOGRAPHY OF EVSA AND LOCATIONS OF EXISTING GROUNDWATER PIEZOMETER WELLS (P-01 TO P-03) FIG-01

ENVIRONMENTAL REMEDIATIONAT DA NANG AIRPORT FIG-02DETAILS OF GROUNDWATER PIEZOMETER WELL CONSTRUCTION

DETAILS P-01

COVER

h2 msl =6.627m

DETAILS OF GROUNGWATER PIEZOMETER WELL CONSTRUCTION SC: 1/10

DETAILS OF P-02

COVER

h1(msl)=6.260m elev. top of casing

h2(msl)=5.893m elev. existing ground surface elev. existing ground surface

E E

bentonite

h3(ms1)=4.448m elev. bottom of casing

1----+--+---+--+--------------1 QilEF OF PARTY 1----+--+---+--+--------------1 SUPERINTENDENT------1----+--+---+--+--------------1 QA/QC ENGINEER 1----+--+---+--+--------------1 SHEET CHK'D BY 1-=--+-~+,-,,---+~-+--~~~---------1 APPRO'IED BY

REV. DATE DRWN. CHKD REMARKS. DATE ---------NO.

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DETAILS OF P-03

COVER

h1(msl)=7.468m elev. top of casing

h2(msl)=7.171m elev. existing ground surface

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bentonite


NOTE: -ALL DIMENslONs IN DRAWING ARE CM.

PROJECT NO. FILE NAME:

SHEET NO.

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GROUNDWATER ELEVATION MONITORINGFIG-02a


PROPOSED EVSA SITE LAYOUTFIG-03


EVSA SEDIMENT PILE CONSTRUCTION SEQUENCEFIG-04


PLAN VIEW OF EVSA SEDIMENT PILE FIG-05


CROSS SECTIONS AND DETAILS OF EVSA SEDIMENT PILEFIG-06


DETAILS OF SECURITY FENCE FOR EVSA SEDIMENT PILE AREAFIG-07


SPECIFICATIONS FOR SEDIMENT PILE COVERHDPE LINER AND GEOSYNTHETIC DRAINAGE NET FIG-08

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