Attachment_1_Data_Gap_Inv_Rpt_Pgs_1-1000.pdf

F i na l

Alakanuk Federal Scout Readiness Center

Data Gap Investigation Report

Prepared for

Alaska Army National Guard Fort Richardson, Alaska

Contract No. W90FYQ-09-D-003 Delivery Order 2Z01

June 2013

949 East 36th Avenue

Suite 500 Anchorage, AK 99508

Contents Section Page

Acronyms and Abbreviations ............................................................................................................................ v

1. Introduction ...................................................................................................................................... 1-1

1.1 Goals and Objectives of Data Gap Investigation ............................................................................. 1-1

1.2 Report Organization ........................................................................................................................ 1-1

2. Site Background ................................................................................................................................ 2-1

2.1 Site Location and Climate ................................................................................................................ 2-1

2.2 Site Characteristics .......................................................................................................................... 2-1

2.2.1 Surface Water ..................................................................................................................... 2-2

2.2.2 Hydrogeology ...................................................................................................................... 2-2

2.3 Site Description and History ............................................................................................................ 2-2

3. Previous Investigations and Remedial Actions .................................................................................... 3-1

3.1 1998 Preliminary Assessment/Site Investigation ............................................................................ 3-1

3.2 2002 Interim Remedial Action ......................................................................................................... 3-2

3.3 2004 Alternate Cleanup Level Demonstration ................................................................................ 3-2

4. Data Gap Analysis ............................................................................................................................. 4-1

4.1 Project Screening Levels .................................................................................................................. 4-1

4.1.1 Soil Screening Levels ........................................................................................................... 4-1

4.1.2 Groundwater Screening Levels ........................................................................................... 4-1

4.2 Data Quality Objectives ................................................................................................................... 4-2

4.3 Conceptual Site Model .................................................................................................................... 4-3

4.4 Identification of Data Gaps .............................................................................................................. 4-4

5. Field Activities ................................................................................................................................... 5-1

5.1 Site Reconnaissance ........................................................................................................................ 5-1

5.2 Sample Locations ............................................................................................................................. 5-1

5.3 Soil Sampling .................................................................................................................................... 5-1

5.4 Groundwater Sampling .................................................................................................................... 5-6

5.5 Quality Control ................................................................................................................................. 5-6

5.5.1 Field Duplicate Samples ...................................................................................................... 5-6

5.5.2 Equipment Blanks ............................................................................................................... 5-7

5.5.3 Trip Blanks .......................................................................................................................... 5-7

6. Contamination Assessment ............................................................................................................... 6-1

6.1 Nature and Extent of Soil Contamination ........................................................................................ 6-1

6.2 Nature and Extent of Groundwater Contamination ........................................................................ 6-1

6.3 Groundwater Use Determination .................................................................................................... 6-1

7. Cumulative Risk Assessment .............................................................................................................. 7-1

7.1 Assessing Cumulative Risk ............................................................................................................... 7-1

7.2 Cumulative Risk Results ................................................................................................................... 7-1

8. Conclusions and Recommendations ................................................................................................... 8-1

8.1 Conclusions ...................................................................................................................................... 8-1

8.2 Proposed Soil Site-Specific Cleanup Levels ...................................................................................... 8-1

8.3 Recommended Remedial Actions .................................................................................................... 8-2

8.3.1 Contaminated Soil .............................................................................................................. 8-2

8.3.2 Contaminated Groundwater .............................................................................................. 8-3

ANC123540003/ES012512133101ANC III

CONTENTS

8.4 Estimated Soil Volume ..................................................................................................................... 8-3

8.5 Summary .......................................................................................................................................... 8-3

9. References ........................................................................................................................................ 9-1

Appendixes

A Field Notes, Boring Logs, and Well Logs B Data Quality Evaluation and Laboratory Reports (laboratory reports provided electronically only) C Hydrocarbon Risk Calculator – Cumulative Risk Results (source files provided electronically only)

Tables

4-1 Soil Screening Levels ..................................................................................................................................... 4-2 4-2 Groundwater Screening Levels ..................................................................................................................... 4-2 5-1 Field Screening Results for Soil ..................................................................................................................... 5-5 5-2 Monitoring Well and Groundwater Elevations ............................................................................................. 5-6 6-1 Soil Results for DRO, GRO, and BTEX ............................................................................................................ 6-2 6-2 Soil Results for PAHs ..................................................................................................................................... 6-9 6-3 Groundwater Results for BTEX, DRO, and GRO .......................................................................................... 6-17 6-4 Groundwater Results for PAHs ................................................................................................................... 6-19 7-1 Cumulative Risk Assessment ........................................................................................................................ 7-2 7-2 Risk Assessment of Petroleum Hydrocarbons in Soil ................................................................................... 7-2 8-1 Soil Ingestion Cleanup Levels ........................................................................................................................ 8-2 8-2 Soil Inhalation Cleanup Levels ...................................................................................................................... 8-2

Figures

2-1 Alakanuk Location Map .................................................................................................................................2-5 2-2 Site Features and Historical Sample Locations ..............................................................................................2-7 4-1 Conceptual Site Model...................................................................................................................................4-5 4-2 Conceptual Exposure Model ..........................................................................................................................4-7 5-1 Soil and Groundwater Sample Locations .......................................................................................................5-3 6-1 Soil Sampling Results .....................................................................................................................................6-7 6-2 Groundwater Sampling Results ...................................................................................................................6-15 8-1 Proposed Area of Soil Excavation ..................................................................................................................8-5

IV ANC123540003/ES012512133101ANC

Acronyms and Abbreviations °F degrees Fahrenheit

AAC Alaska Administrative Code

ACL alternate cleanup level

ADEC Alaska Department of Environmental Conservation

ADNR Alaska Department of Natural Resources

ARNG Army National Guard

AST aboveground storage tank

ASTM ASTM International bgs below ground surface

BTEX benzene, toluene, ethylbenzene, and xylenes

Clearwater Clearwater Environmental, Inc.

CSM conceptual site model

DCRA Alaska Department of Commerce, Community, and Economic Development, Division of Community and Regional Affairs

DGI data gap investigation

DQO data quality objective

DRO diesel-range organics

EPA U.S. Environmental Protection Agency

EPH extractable aliphatic and aromatic petroleum hydrocarbons

ERM/Hart Crowser ERM-West, Inc., and Hart Crowser, Inc.

FSRC Federal Scout Readiness Center ft2 square feet

GPS global positioning system

GRO gasoline-range organics

HI hazard index

Hoefler Consulting Group

HRC hydrocarbon risk calculator

IC institutional control

IRA interim remedial action mg/kg milligrams per kilogram mg/L milligrams per liter

NAPL nonaqueous-phase liquid

PA preliminary assessment

PAH polynuclear aromatic hydrocarbon

ANC123540003/ES012512133101ANC V

ACRONYMS AND ABBREVIATIONS

PID photoionization detector

PVC polyvinyl chloride

RRO residual-range organics

SI site investigation

SL screening level

SPLP synthetic precipitation leaching procedure

TOC total organic carbon

UFP-QAPP Unified Federal Program-Quality Assurance Project Plan

VPH volatile aliphatic and aromatic petroleum hydrocarbons yd3 cubic yards

VI ANC123540003/ES012512133101ANC

1. Introduction This data gap investigation (DGI) report provides background information, summarizes previous investigations, describes the updated conceptual site model (CSM), and provides the results of the recently completed field investigation at Alakanuk Federal Scout Readiness Center (FSRC). The report includes recommendations for further remedial actions.

This work was conducted under National Guard Bureau Contract W90FYQ-09-D-003, Task Orders 2Z01 and 2Z03.

1.1 Goals and Objectives of Data Gap Investigation

The goal of this DGI was to ensure that the Alaska Army National Guard (ARNG) has all the environmental data necessary to conduct remedial actions at Alakanuk FSRC to allow divestiture of the leased property without the use of institutional controls (ICs).

To fulfill this goal, the following primary project objectives of the DGI at Alakanuk FSRC were established:

• Ensure that adequate data are available to delineate the extent of petroleum-contaminated soil and groundwater related to previous heating oil spills and releases at Alakanuk FSRC in accordance with Title 18, Chapter 75, Section 335, of the Alaska Administrative Code (18 AAC 75.335), which requires that, before proceeding with site cleanup under the site cleanup rules, a responsible person characterize the extent of hazardous substance contamination at the site including:

− Identifying each (potential) hazardous substance at the site, including the concentration and extent of contamination; this information must be sufficient to determine cleanup options without ICs

− Evaluating the potential threat to human health, safety, and welfare, as well as to the environment, from site contamination

− Locating sources of known site contamination, including a description of potential releases into soil, sediment, groundwater, or surface water

− Evaluating the size of the contaminated area, including the concentrations and extent of any soil, sediment, groundwater, or surface water contamination

− Identifying the vertical depth to groundwater and the horizontal distance to nearby wells, surface water, and water supply intakes

− Evaluating the potential for surface water runoff from the site and the potential for surface water or sediment contamination

− Identifying the soil type and determining whether the soil is a continuing source of groundwater contamination

• Evaluate the possibility of establishing alternative cleanup levels (ACLs) for soil

• Identify appropriate remedial alternatives

1.2 Report Organization

The findings resulting from site activities are provided in the following sections:

• Section 1–Introduction. The introduction presents an overview of the DGI, including goals and objectives and report organization.

• Section 2–Site Background. The regional setting and site background information is presented in this section.

ANC123540003/ES012512133101ANC 1-1

1 INTRODUCTION

• Section 3–Previous Investigations and Remedial Actions. This section summarizes information from previous preliminary assessments (PAs), site investigations (SIs), and remedial actions conducted at Alakanuk FSRC.

• Section 4–Data Gap Analysis. This section summarizes project screening levels (SLs), data quality objectives (DQOs), identified data gaps, and the CSM.

• Section 5–Field Activities. This section describes and summarizes methods and procedures used to investigate the affected soil for Alakanuk FSRC.

• Section 6–Contamination Assessment. This section assesses the extent of contamination across the site for all affected media, utilizing historical and recently obtained data.

• Section 7–Cumulative Risk Assessment. Analytical results are analyzed to establish the potential risk to humans and the environment associated with the existing site contamination.

• Section 8–Recommendations. This section presents conclusions derived from the investigation data, presents proposed ACLs, and estimates the volume of contaminated soil that will require remedial action.

• Section 9–References. This section lists sources referenced in the text.

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2. Site Background This section summarizes the site location, climate, characteristics, and history of Alakanuk FSRC.

2.1 Site Location and Climate

The City of Alakanuk is located at the east entrance of Alakanuk Pass, the major southern channel of the Yukon River, 15 miles from the Bering Sea (Figure 2-1). The city lies within the Yukon Delta National Wildlife Refuge and is situated 8 miles southwest of Emmonak, approximately 162 air miles northwest of Bethel. Alakanuk FSRC lies (approximately) at latitude 62.68340331 degrees north and longitude −164.65781450 degrees west, based on the 1984 (revised 2004) world geodetic system (WGS 84) datum, and within Section 14 of Township 030N, Range 082W of the Seward Meridian.

The original FSRC was constructed in 1959 as a single-story, 20- by 60-foot, Butler-type, prefabricated structure on Lot 3 of U.S. Survey 4092. In 1967, erosion along Alakanuk Pass threatened the town. As a result, the entire community was forced to relocate approximately 3 miles upstream. U.S. Department of Interior, Bureau of Land Management, officials approved the FSRC relocation and selected a site on Lot 8, Block 6, Tract B, of U.S. Survey 4405, Alakanuk Townsite, Alaska. The Old FSRC was removed in 1970, but was not placed on the new lot because of unsafe ice. Instead, the building was placed in an unspecified, temporary location, where it remained for 2 years. In 1972, the move was completed and the building was relocated to its present location. A 1997 survey conducted at the old townsite confirmed that the Yukon River had completely eroded the former FSRC location (ERM-West, Inc., and Hart Crowser, Inc. [ERM/Hart Crowser] 1999).

Alakanuk FSRC is located approximately 800 feet south of Alakanuk Pass. An unnamed lake lies approximately 300 feet south of the FSRC. Surrounding properties include private residences to the east and west, and school grounds approximately 600 feet to the east.

The climate of Alakanuk is subarctic, averaging 60 inches of snowfall and 19 inches of total precipitation per year.

Temperatures range from −25 degrees Fahrenheit (°F) to 79°F. Heavy winds are frequent during fall and winter (Alaska Department of Commerce, Community, and Economic Development, Division of Community and Regional Affairs [DCRA], 2012).

2.2 Site Characteristics

Alakanuk lies within the Yukon River Delta area, adjacent to the mouth of the Yukon River. The coastal area is underlain by Cenozoic gravel and silts, basalts, and (possibly) granodiorite. The surface soil consists of older coastal deposits of interlayered alluvial and marine sediments, including coastal delta deposits at the mouth of the river. Onsite soil consists of brown or gray sandy silt or silty sand to 5 feet below ground surface (bgs), mixed with organic material to 1 foot bgs. Vegetation at the FSRC consists of grasses, with heavy concentrations of willows and alders on the perimeter (Photograph 1).

The area around Alakanuk is underlain by discontinuous permafrost, which causes polygonal-patterned ground and ice wedges to be prevalent. Alaska Department of Natural Resources (ADNR) well logs identify two wells as having been present in the area (ADNR, 2012). Neither log suggests the presence of permafrost. Many buildings in the city are constructed on pilings or thick gravel pads that limit heat transfer between the structure and the frozen ground to protect

PHOTOGRAPH 1

Grasses surround the FSRC building, and there are dense willows and alders at property boundaries.

Looking north.

ANC123540003/ES012512133101ANC 2-1

2 SITE BACKGROUND

permafrost from thawing. Thaw bulbs within the permafrost may be present in areas devoid of vegetation or adjacent to bodies of water. Permafrost has not been detected onsite to 5 feet bgs.

2.2.1 Surface Water

Alakanuk is characterized by low-lying, moist, flat topography. Surface water occurs in shallow depressions and ponds throughout the area. Stream channels are low in gradient and are typically meandering, with wide floodplains. Meander cutoffs and oxbow lakes are prevalent. The area is susceptible to flooding, and the U.S. Army Corps of Engineers has established minimum building elevation recommendations. Erosion and riverbank sloughing along the larger rivers is a problem in the region. The original village (3 miles downstream of the current city) was endangered and eventually moved in 1970 because of bank erosion.

Surface flow from the FSRC site may move south toward an unnamed lake located approximately 300 feet from the FSRC or may move north toward Alakanuk Pass. Surface water is likely to remain ponded onsite as depression storage and to either evaporate or infiltrate.

2.2.2 Hydrogeology

The soil profile that has historically been encountered at Alakanuk FSRC (previous investigations are discussed in Section 3) has generally consisted of a silty sand or sandy silt to 5 feet bgs. Permafrost has not been encountered in any borings advanced at the site. A perched layer of water has been encountered at 1.5 to 2 feet bgs, ranging from 1 to 1.5 feet in thickness but appearing only seasonally. This perched layer of water was not present during site excavation activities conducted in May 2002 (Clearwater Environmental, Inc. [Clearwater], 2005), but has been present during other investigations (ERM/Hart Crowser, 1999; Hoefler Consulting Group [Hoefler], 2005).

Given the slight rise in elevation at the site, this perched layer is likely connected hydraulically to the surface water that is present along the perimeter of the site.

Groundwater aquifers in Alakanuk generally produce insufficient amounts of water to be viable drinking water resources. ADNR well logs identify two wells as having been present in the area (ADNR, 2012). One well was located at the former townsite (more than 3 miles away from the FSRC) and was completed in an aquifer of fine sand at 89 feet bgs; this well had a static water level of 3.5 feet bgs. The other well was located near the new high school, which is approximately 600 feet to the east of the FSRC, and was drilled to 103 feet bgs in blue and black clay and silts with organics. Frost was encountered only in the top 2 feet of the boring when the well was drilled in June 1978. This well produced insufficient amounts of water for development and was considered a dry hole.

2.3 Site Description and History

Alakanuk FSRC is currently an inoperable scout readiness center that was originally established at its current location in 1972. Buildings and equipment remaining at the FSRC are (Photograph 2 and Figure 2-2):

• A 20- by 60-foot, prefabricated scout readiness center known as the Old FSRC that was built in 1959

• A 30- by 40-foot, metal, prefabricated scout readiness center built in 1986 that is attached to the Old FSRC with an enclosed walkway (1986 FSRC)

• A 30- by 50-foot, prefabricated scout readiness center known as the New FSRC, which was built after 2005 and is located east of the older structure

• Two double-walled, 1,500-gallon fuel oil aboveground storage tanks (ASTs) (installed after 1999)

• A hazardous materials storage locker

PHOTOGRAPH 2

New FSRC (tan building) at left, Old (original) FSRC (grey building) in center, 1986 FSRC (green building) at right. Looking south.

2-2 ANC123540003/ES012512133101ANC

• A storage van located north of the New FSRC

Abandoned or removed equipment and materials relevant to the DGI are:

• A 3,000-gallon, single-walled AST that was removed between 1990 and 1995

• A generator shed that was removed between 1998 and 2002

ANC123540003/ES012512133101ANC 2-3

2-4 ANC123540003/ES012512133101ANC

CH2MHILL

FIGURE 2-1

Alakanuk Location Map Alakanuk FSRC Data Gap Investigation Alakanuk, Alaska

North

403507 ES012512133101ANC_DGI_Alakanuk_LocMap_05.ai 02/25/13 cts

Approximate scale in feet

5002500

Alakanuk Federal Scout Readiness Center

Alakanuk Pass

Vicinity Map A R C T I C O C E A N

B E R I N

G S E

A

Bethel

Nome

Anchorage

Alakanuk

2-6 ANC123540003/ES012512133101ANC

\\SHARES.CRITIGEN.COM\PROJECTS\ARNG_10410956\MAPFILES\ALAKANUK\FIG_2-2_ALAKANUK_SAMPLELOCS_HISTORICAL.MXD SRUDOLPH 3/6/2013 1:12:03 PM

VICINITY MAP

ALA005

Former AST Tank Cradle

Existing

1,500-gallon

AST

Hazardous Material

Storage Locker1986 Federal Scout Readiness Center

Old Federal Scout Readiness

Center

Former Generator

Shed

New Federal Scout Readiness Center

Storage Van

Covered Walkway

ALA-ACL-011

ALA-ACL-012

B-01

B-02

ALA-ACL-001

ALA-ACL-002

ALA-ACL-003

ALA-ACL-004

ALA-ACL-005

ALA-ACL-006

ALA-ACL-007

ALA-ACL-008

ALA-ACL-009

ALA-ACL-010

B-06

B-07

B-08

B-09

B-10

B-1B

B-2B

ALA001

ALA002

ALA003

ALA004

ALA006

SB1

SB3

SB4

SB5

0 2512.5

Feet

LEGEND

Federal Scout Readiness Center (FSRC)

Old FSRC

Storage Van

Former Shed

AST

Former AST Tank Cradle

Hazardous Material Storage Locker

Approximate Extent of Previous IRA Excavation

Themes from CAD Drawing

US Survey

Subdivision Lot

Easement Line

Water Supply

Sewer Line

Historical Sample Location

Mountain Village

Savoonga Gambell

Saint Mary’s

Alakanuk

Emmonak

Stebbins

Kotlik

Eek

Tununak

Nightmute

Kipnuk

Kwethluk

Akiak

Nunapitchuk Kasigluk

Tuntutuliak

Toksook Bay Napakiak

Napaskiak

A L A S K A

FIGURE 2-2

Site Features and Historical Sample Locations Alakanuk FSRC Data Gap Investigation Alakanuk, Alaska

ALA-ACL-011

ALA-ACL-012

ALA-ACL-010

B-09

B-10

ALA001

ALA002

ALA003

ALA004

ALA006

ALA005

Old Federal Scout Readiness

Center

Former Generator

Shed

Notes:

1. Location of historical samples is approximate based on historical figures and on orthophotography courtesy of Alaska Department of Commerce, Division of Community & Regional Affairs (DCRA), 1-foot pixels.

2. Location of excavation is approximate based on historical figures.

3. Definitions:

AST = aboveground storage tank

2-8 ANC123540003/ES012512133101ANC

3. Previous Investigations and Remedial Actions This section briefly discusses known spills, previous investigations, and the results of each investigation at Alakanuk FSRC. SLs discussed in this section are based on those used at the time of each investigation unless otherwise noted. Figure 2-2 presents historical sample locations and known site features at Alakanuk FSRC.

In May 1985, an estimated 400 gallons of No.1 fuel oil was released from the old AST on the western side of the Old FSRC. The spill was caused by a broken weld on an outlet pipe beneath the single-walled tank. The ground was frozen and covered with 12 to 24 inches of ice and snow at the time of the spill. ARNG personnel removed oil-saturated snow and used absorbent pads to collect free product; an estimated 100 gallons of fuel was recovered. The contaminated snow and absorbent pads were burned at the city landfill (ERM/Hart Crowser, 1998).

A 1990 spill prevention control and countermeasure plan referenced leaks in the fuel supply line between the old tank and the building (Ogden Environmental and Energy Services, Inc., 1999).

The following environmental investigations have been conducted at Alakanuk FRSC:

• PA records review conducted by ERM/Hart Crowser in 1998 (ERM/Hart Crowser, 1998)

• SI conducted by ERM/Hart Crowser in 1998 (ERM/Hart Crowser, 1999)

• Interim remedial action (IRA) conducted by Clearwater in 2002 (Clearwater, 2005)

• ACL demonstration project performed by Hoefler in 2004 (Hoefler, 2005)

3.1 1998 Preliminary Assessment/Site Investigation ERM/Hart Crowser conducted a PA/SI at Alakanuk FSRC in 1998 (ERM/Hart Crowser, 1998 and 1999). The SI included surface and subsurface soil sampling and groundwater sampling. The final report identified a maximum surface soil concentration of diesel-range organics (DRO) as 13,000 milligrams per kilogram (mg/kg), in a soil sample collected from boring B-05, at the site of the former AST. The maximum subsurface soil DRO concentration, 23,000 mg/kg, was identified in a sample from the same location. Laboratory results for benzene, toluene, ethylbenzene, and xylenes (BTEX); gasoline-range organics (GRO); and polynuclear aromatic hydrocarbons (PAHs) in soil samples were all less than Alaska Department of Environmental Conservation (ADEC) cleanup levels.

A groundwater sample was collected from a wellpoint installed within the perched layer of water adjacent to boring B-10. Because of poor recovery of the well, only a sample of groundwater for DRO analysis was obtained at B-10. A groundwater sample was also collected from the open borehole at boring B-05 and was submitted for analysis of DRO, GRO, and BTEX. DRO was detected at 46 milligrams per liter (mg/L) in the sample from B-05 and at 30 mg/L in the sample from B-10. GRO was detected at 26 mg/L in the sample from B-05. These concentrations were greater than the 18 AAC 75.345, Table C, cleanup levels for groundwater (1.5 mg/L for DRO and 1.3 mg/L for GRO). However, the groundwater samples from both locations were reportedly very turbid; as a result, the GRO and DRO results were likely to have been biased high.

A soil sample was collected from the area where significant DRO contamination in soil had been identified (B-05 at 13,000 mg/kg) to assess the potential for leaching to groundwater, using synthetic precipitation leaching procedure (SPLP) analysis. Results of leachate analysis indicated a DRO leachate concentration of 4.5 mg/L, which exceeds the 18 AAC 75, Table C, cleanup level of 1.5 mg/L for DRO in groundwater.

Risk-based cleanup levels (based on ADEC Method 2) were proposed for the site. Assuming those cleanup levels, it was concluded that 40 to 60 cubic yards (yd3) of soil contained DRO in concentrations that exceeded the proposed risk-based cleanup level of 10,250 mg/kg. ADEC did not approve the proposed cleanup levels.

ANC123540003/ES012512133101ANC 3-1

3 PREVIOUS INVESTIGATIONS AND REMEDIAL ACTIONS

3.2 2002 Interim Remedial Action In May and June 2002, based on the findings of the SI, Clearwater performed an IRA at Alakanuk FSRC by excavating soil contaminated with DRO in concentrations greater than the ADEC Method 1, Category B, cleanup level of 200 mg/kg for the under-40-inch zone (Clearwater, 2005). A total of 21 tons of DRO-contaminated soil was removed and sent to an approved offsite thermal remediation facility. The perched layer of water that had been identified during the SI (ERM/Hart Crowser, 1999) was not encountered. The IRA was successful in removing much of the soil that contained DRO in high concentrations (greater than 200 mg/kg) from the main spill area. However, results of confirmation sampling indicated that concentrations of DRO that remained in soil after the IRA exceeded the project cleanup level.

Soil samples from the bottom of the excavation contained DRO at concentrations of 1,300 mg/kg (ALA001) and 821 mg/kg (ALA004), both exceeding the ADEC Method 1 cleanup level for DRO (200 mg/kg). DRO concentrations detected in confirmation samples collected from the excavation walls (ALA002, ALA003, ALA005, and ALA006) also exceeded the Method 1 cleanup level goal for DRO.

Analysis for DRO was performed for SPLP on samples from ALA001 and ALA003. DRO concentrations detected in the leachate of these samples were 2.53 mg/L and 4.73 mg/L, respectively. The sample from ALA008 was analyzed for total organic carbon (TOC) and reported as containing TOC at a concentration of 17,300 mg/kg. Because this sample was not analyzed for DRO, no information exists as to whether a significant portion of the TOC result might be attributable to hydrocarbon contamination.

3.3 2004 Alternate Cleanup Level Demonstration In 2004, Hoefler conducted an ACL demonstration project to develop potentially applicable contaminant ACLs for Alakanuk FSRC (Hoefler, 2005). A total of 12 soil borings were advanced and sampled at depths from 1.5 to

2.0 feet bgs. The total depths of the borings were limited by the perched water layer. All soil samples were analyzed for DRO, with select samples analyzed for GRO, BTEX, and TOC and analyzed by SPLP for GRO, BTEX, and DRO. Three groundwater samples were collected from drive-points set at 3.5 to 4 feet bgs and were analyzed for GRO, DRO, and BTEX.

Eight background samples (from locations ALA-ACL-001 through ALA-ACL-008) were collected in areas on the northern and eastern sides of the site that had been confirmed during the SI and the IRA as free of DRO contamination. DRO detections ranged from 8.75 to 14.2 mg/kg in samples from these locations. These low DRO concentrations presumably were resulting from natural biogenic material in the soil.

The soil data for the contaminated area confirmed the findings of the SI and the IRA, with notable detections of petroleum constituents in samples from the immediate vicinity of the former AST location at the western side of the Old FSRC. DRO detections ranged from 585 to 9,880 mg/kg and GRO detections ranged from 1.88 to

75.9 mg/kg in samples from this area. Significant contamination was identified in a sample collected in an area of dense brush approximately 30 feet south of the site of the former AST: this sample, from ALA-ACL-009, contained the second-highest DRO concentration (1,930 mg/kg) and the highest GRO concentration (75.9 mg/kg). BTEX compounds were detected in all soil samples that had been collected near the former tank location, but at concentrations less than cleanup levels. The highest benzene concentration (0.0342 mg/kg) was detected in a sample from the site of the former AST. The second-highest benzene concentration (0.0265 mg/kg) was found in the sample from ALA-ACL-009.

Samples of perched water were collected from three locations to characterize soil contaminant impacts to this resource. The locations were selected to assess impacts on groundwater at the point of release (ALA-ACL-012) and at nearby presumed upgradient (ALA-ACL-008) and presumed downgradient (ALA-ACL-011) locations. Field observations suggested a very slight gradient of flow to the south. The maximum DRO and GRO concentrations—

14.6 mg/L and 3.1 mg/L, respectively—were detected in water from ALA-ACL-011. Both detections are above ADEC cleanup levels.

3-2 ANC123540003/ES012512133101ANC

4. Data Gap Analysis This section summarizes how SLs and DQOs were established for the DGI and how previous investigation data were used, and presents the CSM of site conditions and the means of potential exposure at Alakanuk FSRC. This section also presents the data gaps identified for Alakanuk FSRC that were examined during the DGI.

4.1 Project Screening Levels

SLs are conservative, predominantly risk-based values used to characterize and determine the nature and extent of contamination in soil and groundwater. SLs are intended to be used for screening purposes only; exceedance of an SL is not necessarily an indication of unacceptable risk. Details about the SL selection process for each medium are provided in the Unified Federal Program-Quality Assurance Project Plan (UFP-QAPP) published as Final Work Plan for Site Characterization at 21 Alaska Federal Scout Readiness Centers (CH2M HILL, 2011).

4.1.1 Soil Screening Levels

Soil SLs are established in consideration of cumulative exposure of human receptors to contaminants in soil (and sediment) through direct contact and outdoor inhalation, as well as protection of groundwater. The project SLs established for Alakanuk FSRC were based on ADEC cleanup levels provided in 18 AAC 75.

As presented in 18 AAC 75.340(a)(2), proposed soil cleanup levels for a site must be based on an estimate of the reasonable maximum exposure expected to occur under current and future site conditions. Soil SLs may be developed using ADEC Method 2 for soil contaminated with chemicals other than petroleum hydrocarbons, as set out in Table B1 of 18 AAC 75.341(c), and for soil contaminated with petroleum hydrocarbons, as set out in Table B2 of 18 AAC 75.341(d). The ADEC Method 2 cleanup levels presented in Tables B1 and B2 were determined for three potential exposure pathways—direct contact/ ingestion, inhalation, and migration to groundwater— depending on the climatic zone in which the soil is located (arctic zone, under-40-inch zone, or over-40-inch zone).

The cleanup levels from Table B1 or B2 that apply to Alakanuk FSRC are based on the exposure pathway with the most stringent value calculated for a site within the under-40-inch climatic zone. Based on available data, all three exposure pathways were considered potentially complete for Alakanuk FSRC.

The project SLs are shown in Table 4-1. The project SLs for GRO and DRO in soil were set equal to the ADEC Method 2 cleanup levels for the migration-to-groundwater pathway; for residual-range organics (RRO) in soil, the SL was set equal to the ADEC Method 2 cleanup level for the ingestion pathway. For chemicals other than petroleum hydrocarbons, to account for possible cumulative risk associated with multiple chemical exposure routes such as direct contact and outdoor inhalation, cleanup levels were divided by a factor of 10. The SL for a specific chemical in soil was determined to be the lowest of the adjusted ADEC Method 2 direct contact or outdoor inhalation cleanup level and the ADEC Method 2 migration-to-groundwater cleanup level. Because of the extensive list of possible contaminants, only SLs for BTEX compounds are shown in Table 4-1.

4.1.2 Groundwater Screening Levels

Groundwater SLs are established in consideration of potential cumulative exposure of human receptors to contaminants through drinking of groundwater. As defined in 18 AAC 75.345(b)(1), contaminated groundwater must meet the cleanup levels in Table C of 18 AAC 75.345(b)(1) if the current use or the reasonably expected potential use of the groundwater, determined under 18 AAC 75.350, is a drinking-water source. In addition, 18 AAC 75.345(g) states that groundwater that is closely connected hydrologically to nearby surface water may not cause a violation of the water quality standards in 18 AAC 70 for surface water.

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4 DATA GAP ANALYSIS

TABLE 4-1

Soil Screening Levels Alakanuk Federal Scout Readiness Center Data Gap Investigation

Contaminant of Concern

ADEC Method 2 Cleanup Level Exposure Route of Primary Concern

Proposed ADEC Method 2 Soil Cleanup Level

Project Screening

Level Direct Contact/

Ingestion Outdoor

Inhalation Migration to Groundwater

Gasoline-range organics 1,400 1,400 300 Migration to GW 300 300

Diesel-range organics 10,250 12,500 250 Migration to GW 250 250

Residual-range organics 10,000 22,000 11,000 Ingestion 10,000 10,000

Benzene 150 11 0.025 Migration to GW 0.025 0.025

Toluene 8,100 220 6.5 Migration to GW 6.5 6.5

Ethylbenzene 10,100 110 6.9 Migration to GW 6.9 6.9

Xylenes (total) 20,300 63 63 Inhalation 63 6.3

Note: All values are presented in milligrams per kilogram.

ADEC = Alaska Department of Environmental Conservation GW = groundwater Source: 18 AAC 75.341, Tables B1 and B2, under-40-inch zone

For DRO, GRO, and RRO, the project SLs were set equal to the cleanup levels in Table C. For all other compounds, SLs were derived by dividing the cleanup levels in Table C by a factor of 10 to account for possible cumulative risk associated with multiple chemical exposures. Table 4-2 summarizes the project SLs for GRO, DRO, RRO, and BTEX compounds only at Alakanuk FSRC.

TABLE 4-2

Groundwater Screening Levels Alakanuk Federal Scout Readiness Center Data Gap Investigation

Contaminant of Concern

18 AAC 75 Groundwater Cleanup Level

(mg/L)

18 AAC 70 Water Supply, Aquiculture, Cleanup Level

(µg/L) Project Screening Level

(mg/L)

Gasoline-range organics 2.2 -- 2.2

Diesel-range organics 1.5 -- 1.5

Residual-range organics 1.1 -- 1.1

Benzene 0.005 -- 0.0005

Toluene 1.0 -- 0.1

Ethylbenzene 0.7 -- 0.07

Xylenes (total) 10 -- 1.0

Total aromatic hydrocarbons -- 10 --

Total aqueous hydrocarbons -- 15 --

-- = not analyzed µg/L = micrograms per liter AAC = Alaska Administrative Code mg/L = milligrams per liter Source: 18 AAC 75.345, Table C, and 18 AAC 70.020(b)(5)(A)(iii)

4.2 Data Quality Objectives

DQOs were established to provide benchmarks against which the quality of fieldwork and the quality of the resulting analytical data could be evaluated. The DQOs specified the type, quality, quantity, and uses of the data

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needed to adequately support environmental decisions for Alakanuk FSRC. The DQOs could be fulfilled by using either existing data or data to be gathered during the 2011−2012 DGI.

Historical (previous investigation) data were evaluated for usability following the general procedures outlined in the UFP-QAPP (CH2M HILL, 2011). Data that (1) had been properly validated, (2) had been derived through use of ADEC-approved or U.S. Environmental Protection Agency (EPA) approved analytical methods, and (3) reflected analytical detections greater than the limits of detection or lower than the SLs were considered usable for the purposes of determining the extent of contamination. Those data that were considered usable were also retained to characterize the site. Data that had been collected prior to the 2000 IRA and were from samples collected within the limits of the excavation were not considered usable because they were not representative of current site conditions.

Three DQOs were established for the 2011−2012 DGI for Alakanuk FSRC. The DQOs established the type and quantity of data necessary to determine the nature and extent of contamination in the soil and groundwater at the FSRC and specified the quality and quantity of data required to assess cumulative human health risk.

• DQO 1 established what data were necessary to determine whether further sampling of the soil would be required to define the nature and extent of contamination (and, secondarily, to support a remedial decision and cost savings for future remedial actions). The lateral extent of soil contamination would be adequately defined only if all soil samples surrounding the potential source or release location contained concentrations of all target analytes below SLs.

• DQO 2 established the type and quantity of data that were necessary to determine whether groundwater was present, contaminated, and acting as a transport mechanism to nearby surface water bodies.

• DQO 3 was established to determine the type and quantity of data required to ascertain whether current or hypothetical residents, occupational workers, or construction/excavation workers might be exposed to constituent contaminant concentrations that could pose potentially unacceptable risks.

Identified data gaps are discussed in Section 4.4.

4.3 Conceptual Site Model

A CSM integrates (1) existing information and working assumptions about the physical site conditions; (2) the nature, occurrence, and distribution of chemicals; and (3) fate-and-transport processes. The CSM for Alakanuk FSRC is based on the current understanding of site history and conditions.

As a pure product, heating oil is less dense than water and is referred to as light nonaqueous-phase liquid (NAPL).

When released to the ground surface, NAPL products spread laterally across the ground surface and infiltrate into the soil. The extent of lateral spreading across the ground surface is a function of quantity and rate of release and the permeability of the surface soil. The infiltrating product from a surface spill tends to flow primarily vertically under the influence of gravity through larger air-filled soil pores, although capillary forces may cause some lateral spreading. When released in sufficient quantities, NAPL product can migrate downward through soil and accumulate at the capillary fringe of the groundwater table surface. When the soluble portion of heating oil dissolves in groundwater, the specific gravity of the aqueous plume is nearly the same as that of uncontaminated groundwater, and the plume moves with the groundwater flow. The insoluble portion of heating oil typically is absorbed by the soil particles or becomes disconnected globules in the soil pore spaces. Because the known spills at Alakanuk FSRC are at least one decade old, it is very likely that gravity drainage and flow of the NAPL product to a point of immobility have already occurred.

The CSM for the Alakanuk FSRC site integrates information about leaks and spills of heating oil from the site of the former AST along the western side of the Old FSRC. Each spill and leak of heating oil has spread both laterally and vertically from its point of release, resulting in surface and subsurface soil hydrocarbon contamination (Figure 4-1).

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The conceptual model for exposure at Alakanuk FSRC, including past or current sources of contamination, chemical release mechanisms, transport/exposure media, potential exposure points, potential exposure routes, and potential receptors, is incidental human ingestion of surface soil and dermal contact with the soil (Figure 4-2).

Groundwater is present at Alakanuk FSRC; therefore, the groundwater pathway is also considered a complete exposure pathway. Dermal contact with surface water is considered a potential exposure pathway. Ingestion of surface water or aquatic organisms affected by contamination is possible but unlikely. Because of the relatively flat topography, substantial drainage channel flow is not expected. Because of the slow and dispersive nature of drainage, it is unlikely that contaminant concentrations would reach the Yukon River (which would be unlikely to cause exceedances of surface water quality standards if it did occur).

Alakanuk is prone to flooding. Although exposure to floodwaters contaminated by contact with contaminated soil is a potentially complete pathway, the amount of potential exposure to contaminated floodwater is considered insignificant. Alakanuk is subject to flooding roughly once every 10 to 20 years, for a period of 1 to 7 days. If a flood occurred in the spring, it would be caused by an ice jam on the river, and it is very likely that the ground would be solidly frozen, eliminating the possibility of downward migration of surface water. If a flood occurred in the fall, it would likely be caused by a heavy rain event locally or upriver, and the rise in the river would be quick and dramatic (the groundwater table would not have time to rise to the ground surface, so downward migration would be the only means of interaction [no upward migration would occur]). If surface water did become exposed to contaminated soil and reached equilibrium with the contamination, the surface water would be undergoing substantial movement during the flood event, and there would be an immense amount of mixing (dilution) occurring. The concentration levels within the surface water would be insignificant.

Groundwater is considered a potentially complete exposure pathway. All potentially complete ecological exposure pathways are considered insignificant because of the small size of the site and the presence of more optimal habitat nearby.

4.4 Identification of Data Gaps

Historical site use and previous investigation findings suggest that the primary source of contamination at Alakanuk FSRC is associated with spills and leaks from the former heating oil AST. Data collected during previous investigations indicated the presence of DRO in surface and subsurface soil subsequent to the 2000 IRA near the site of the former AST west of the Old FSRC.

Groundwater at the site has been encountered to date. However, flow direction and the lateral extent of the contamination in the groundwater were unknown.

The data gaps that needed to be filled to complete the delineation of the extent of contamination at the site and to support risk assessment efforts were as follows:

• The lateral and vertical extent of DRO contamination present in soil at concentrations greater than the SL had not been adequately delineated. Consequently, additional subsurface soil data were needed to adequately characterize the extent of DRO contamination in the soil.

• The lateral extent of DRO contaminated groundwater at concentrations greater than the SL had not been adequately delineated. Consequently, groundwater data were needed to determine the extent of DRO contamination in the groundwater and to determine whether the contaminated groundwater was migrating offsite.

• PAH, BTEX, extractable aliphatic and aromatic petroleum hydrocarbon (EPH), and volatile aliphatic and aromatic petroleum hydrocarbon (VPH) data were limited or not available. The EPH and VPH data would aid in differentiating between aliphatic and aromatic hydrocarbons for the remaining contamination. Those data could be used to help the study team to generate future site-specific cleanup levels for residual hydrocarbons.

Actions taken to fill these data gaps are discussed in Section 5.

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Contaminated Soil and Groundwater

Perched Groundwater

Hydrocarbon mass from leaking AST is sufficient to reach and mix with seasonal perched groundwater and to migrate below the groundwater table.

NAPL Contaminated Soil Source Area

NAPL Contaminated Soil Source Area

Frozen Soil

Confining Layer

CH2MHILL

FIGURE 4-1

Conceptual Site Model Alakanuk FSRC Data Gap Investigation Report Alakanuk, Alaska

403507 ES012512133101ANC_DGI_Alakanuk_ConceptualSiteModel_02.ai 03/5/13 cts

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Discharge

Elements of a complete exposure pathway

Chemical release mechanisms Short-Term

W orkers

Transport or exposure media

Potential Receptors

Terrestrial Vegetation

Aquatic R esources

R ecreational U ser

H ypothetical R esidents

Subsistence G atherers/H unters

Terrestrial Birds and M am m als

Potential exposure routes

Potential exposure points

Past or current sources of contamination

Gill uptake X

Ingestion and dermal contact

Animal (e.g., bird) uptake/consumption

Surface Runoff

Infiltration, percolation and leaching Groundwater Seeps

Offsite wetland and bog areas

Ingestion and dermal contact

X

Onsite and offsite

Direct contact by receptors

= Potentially complete pathway (to be addressed quantitatively)

= Pathway considered minor (to be addressed qualitatively) Blank = Incomplete pathway

X = Exposure route is not complete

Note: Exposure pathways assume current conditions of the site.

Potential Human and Ecological Exposures Alakanuk FSRC Data Gap Investigation Alakanuk, Alaska

FIGURE 4-2

Animal (e.g., bird) uptake/consumption

Vegetation (e.g., berries) uptake/consumption

Dusts and vapors in ambient air

XOnsite and offsite

Onsite Dust generation through wind Inhalation dermal…