Final 100 Percent RD.pdf

N00129_001714

NEW_LONDON_NSB

SSIC 5090.3b

FINAL 100 PERCENT DESIGN REPORT NON COMPREHENSIVE

ENVIRONMENTAL RESPONSE COMPENSATION AND LIABILITY ACT SOIL

AND GROUNDWATER LOWER SUBBASE OPERABLE UNIT 4 (OU 4) ZONES 1

AND 2 NSB NEW LONDON CT

05/04/2018

APTIM FEDERAL SERVICES LLC

Approved for public release: distribution unlimited.

Rev. 2, dated April 2018

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Submitted to:

NAVFAC Mid-Atlantic 9324 Virginia Avenue, Building Z144 Norfolk, VA 23511

Submitted by:

APTIM Federal Services, LLC 150 Boush Street, Suite 701 Norfolk, Virginia 23510

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Prepared by: Date: May 4, 2018

Benjamin Porter Engineer

Reviewed by: ________________________ Date: May 4, 2018 David Crispo, P.E.

Senior Project Engineer

Approved by: Date: May 4, 2018

Steve Carriere, PMP Project Manager

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Final 100% Design Report May 2018 iii

Table of Contents ________________________________________________

List of Tables ................................................................................................................................................. v List of Appendices ......................................................................................................................................... v Acronyms and Abbreviations ........................................................................................................................ vii

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

1.1 Purpose and Scope .............................................................................................................. 1-1

1.2 Regulatory Framework ......................................................................................................... 1-2

1.2.1 CERCLA .................................................................................................................. 1-2

1.2.2 Connecticut Remediation Standard Regulations ..................................................... 1-3

1.3 Site History and Historical Land Use .................................................................................... 1-4

1.4 Soil Conditions ..................................................................................................................... 1-5

1.5 Hydrogeological Conditions .................................................................................................. 1-6

1.6 Site Hydrologic Conditions ................................................................................................... 1-7

1.7 Site Conceptual Model ......................................................................................................... 1-8

1.7.1 Zones 1 and Zone 2 ................................................................................................ 1-9

1.7.1.1 Zone 1 ....................................................................................................... 1-9

1.7.1.2 Zone 2 ..................................................................................................... 1-11

1.8 Pre-Design Investigation .................................................................................................... 1-11

1.8.1 Groundwater Investigation ..................................................................................... 1-11

1.8.2 Bench-Scale Treatability Testing ........................................................................... 1-12

1.9 Selected Remedy ............................................................................................................... 1-13

1.9.1 Biosparge .............................................................................................................. 1-13

1.9.2 Monitored Natural Attenuation ............................................................................... 1-14

1.9.3 Land Use Controls ................................................................................................. 1-14

1.9.4 Long-Term Monitoring ........................................................................................... 1-16

2.0 Design Requirements ..................................................................................................................... 2-1

2.1 Description of Selected Remedy .......................................................................................... 2-1

2.2 Performance Standards ........................................................................................................ 2-1

3.0 Implementation ............................................................................................................................... 3-1

3.1 Pre-Construction Activities ................................................................................................... 3-1

3.2 Mobilization and Site Preparation ......................................................................................... 3-2

3.2.1 Security Control ....................................................................................................... 3-2

3.2.2 Erosion and Sediment Control ................................................................................. 3-2

3.2.3 Utilities ..................................................................................................................... 3-2

3.2.4 Ancillary Facilities .................................................................................................... 3-2

3.2.4.1 Construction Office Trailers and Sanitary Facilities ................................... 3-3

3.2.4.2 Equipment and Material Staging Areas ..................................................... 3-3

3.2.4.3 Waste Storage Areas ................................................................................ 3-3

3.3 Construction and Remediation Activities .............................................................................. 3-3

3.3.1 Phase I .................................................................................................................... 3-4

3.3.1.1 Well Installation ......................................................................................... 3-4

3.3.1.2 Phase I Sampling ...................................................................................... 3-4

3.3.2 Phase II ................................................................................................................... 3-4 iv

Table of Contents (continued) _____________________________________

3.3.2.1 Well Installation ......................................................................................... 3-4

3.3.2.2 Compressor Sizing Test ............................................................................ 3-5

3.3.2.3 Installation and System Set-up.................................................................. 3-6

3.3.2.4 Biosparge System Operations .................................................................. 3-6

3.3.2.5 System Demobilization .............................................................................. 3-8

3.3.2.6 Waste Disposal ......................................................................................... 3-8

3.4 Monitoring, Sampling, and Analysis ...................................................................................... 3-8

3.4.1 Air Quality Monitoring .............................................................................................. 3-8

3.4.2 Waste Characterization ........................................................................................... 3-9

3.4.3 Phase I Monitoring .................................................................................................. 3-9

3.4.4 Biosparge System Operation Monitoring ................................................................. 3-9

3.4.5 Biosparge System Remediation Performance Monitoring ....................................... 3-9

3.4.6 Survey ................................................................................................................... 3-10

3.5 Post-Construction Activities ................................................................................................ 3-10

3.5.1 Land Use Control Implementation Actions ............................................................ 3-10

3.5.2 Long-Term Monitoring ........................................................................................... 3-12

3.6 Post-Remedial Action Maintenance .................................................................................... 3-12

4.0 Permitting ........................................................................................................................................ 4-1

5.0 Schedule and Sequence ................................................................................................................. 5-1

6.0 Quality Assurance/Quality Control Plan .......................................................................................... 6-1

7.0 References ..................................................................................................................................... 7-1 v

List of Tables ___________________________________________________

Table 1 Groundwater Monitoring Schedule Table 2 Biosparge System Monitoring Schedule Table 3 Summary of LUC Implementation Actions

List of Appendices _______________________________________________

Appendix A Design Drawings Appendix B Technical Memorandum, Pre-Design Investigation Groundwater Sampling (AGVIQ, 2016) Appendix C FINAL Report of Findings for Bench Scale Evaluation of Ozone and Air Sparging for Destruction of TPH, NSB-NLON, Groton, Connecticut Appendix D Department of the Navy—Land Use Instructions Appendix E Technical Specifications Appendix F Blower Cut Sheet Appendix G Pressure Loss Calculations Appendix H Land Use Control Compliance Inspection Checklists vi vii

Acronyms and Abbreviations ______________________________________ µg/L micrograms per liter AGVIQ AGVIQ Environmental Services APP Accident Prevention Plan bgs below ground surface Brown & Root Brown & Root Environmental CERCLA Comprehensive Environmental Response, Compensation, and

Liability Act CGS Connecticut Guideline Statutes COC contaminant of concern Cr(VI) hexavalent chromium CTDEEP Connecticut Department of Energy and Environmental Protection DEC Direct Exposure Criteria DGI Data Gap Investigation DO dissolved oxygen DoD Department of Defense ELUR Environmental Land Use Restriction EPA U.S. Environmental Protection Agency ETPH extractable total petroleum hydrocarbons Final RAP Final Remedial Action Plan for Zones 1 and 2 at Naval Submarine

Base – New London, Groton, Connecticut FS Feasibility Study I/C Industrial/Commercial IRP Installation Restoration Program LTM long-term monitoring LUC land use control mg/kg milligrams per kilogram MNA monitored natural attenuation MW monitoring well NAPL nonaqueous phase liquid NAVFAC Naval Facilities Engineering Command Navy U.S. Department of the Navy NSB Naval Submarine Base NLON New London O&M operation and maintenance O&MM Operation & Maintenance Manual ORP oxidation-reduction potential OU Operable Unit PDI Pre-Design Investigation PMC Pollutant Mobility Criterion POL petroleum, oil, and lubricants psi pounds per square inch PQCP Project Quality Control Plan QAPP Quality Assurance Project Plan viii

Acronyms and Abbreviations (continued) ____________________________

RAC remedial action contractor RAWP Remedial Action Work Plan RCSA Regulation of Connecticut State Agencies RD Remedial Design RDEC Residential Direct Exposure Criteria RI Remedial Investigation ROD Record of Decision ROI radius of influence RSR Remediation Standard Regulations SAP Sampling and Analysis Plan scfm standard cubic feet per minute SWPC Surface Water Protection Criteria Tetra Tech Tetra Tech NUS TOC total organic carbon TPH total petroleum hydrocarbons U.S. United States USGS U.S. Geological Survey UST underground storage tank VOC volatile organic compound

1-1

1.0 Introduction

1.1 Purpose and Scope

The purpose of this document is to provide the 100% Remedial Design (RD) for the selected remedy for non-Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) petroleum hydrocarbon-related constituent–impacted soil and groundwater in Zones 1 and 2 at the Lower Subase, also known as Operable Unit (OU) 4, at Naval Submarine Base (NSB) - New London (NLON) in southeastern Connecticut, in the towns of Ledyard and Groton (Appendix A, Drawing G-001, Cover Sheet). Zones 1 and 2 encompass Site 10 and Site 11 (Zone 1) and the former fuel distribution lines (Zone 2) on the Lower Subase. Zones 1 and 2 were previously investigated as part of the CERCLA process, and a Feasibility Study (FS) was completed in June 2010 and a Record of Decision (ROD) was signed in August 2012 for CERCLA contaminants at OU4; however, contamination associated with non-CERCLA contaminants was identified. Therefore, the non-CERCLA remediation for Zones 1 and 2 was placed in the United States (U.S.) Department of the Navy’s (Navy’s) petroleum, oil, and lubricants (POL) program to be investigated and remediated in accordance with the Connecticut Department of Energy and Environmental Protection (CTDEEP) Remediation Standard Regulations (RSRs). To this end, in June 2013, a Remedial Action Plan for non-CERCLA contaminants at Zones 1 and 2 was completed and submitted to the CTDEEP and approval was received on October 12, 2016. There are CERCLA remedies that overlap with non-CERCLA remedies, and these are discussed throughout the text of this document when applicable.

NSB-NLON is situated on the eastern bank of the Thames River, approximately 6 miles north of Long Island Sound. It is bordered to the east by Connecticut Route 12, to the south by Crystal Lake Road, and to the west by the Thames River. The northern border of the site is a low ridge that trends approximately east–southeast from the Thames River to Baldwin Hill.

OU4 includes approximately 33 acres of land along the Thames River that extends from just south of Pier 2 to just north of Pier 33 (Appendix A, Drawing C-001, Overall Site Plan).

Building 175, located just north of Pier 33, is included within the OU4 study area. The OU4 of NSB-NLON is bordered on the west by the Thames River and on the east by the Providence and Worcester Railroad. A quay (retaining) wall runs along the Thames River for the entire length of OU4. OU4 contains 15 piers and berths for submarine docking; facilities for submarine maintenance, repair, and overhaul; and industrial and administrative buildings. During the development of remedial actions for the site, OU4 was divided into zones for evaluation (Zones 1 through 7). There are nine Installation Restoration Program (IRP) sites located within the seven zones; two are located within Zone 1, and no IRP sites exist in Zone 2.

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The NSB-NLON facility is highly developed along the Thames River in the vicinity of OU4.

Adjacent to the northern boundary of NSB-NLON, the land is relatively undeveloped, with scattered residences. Further north, the land is residential, commercial, recreational, and open space. To the immediate south of NSB-NLON along the Thames River, the land is primarily residential with open spaces. Along the Thames River, tributary streams and wetlands are prevalent.

In January 1995, the Navy, U.S. Environmental Protection Agency (EPA), and State of Connecticut signed a Federal Facility Agreement for NSB-NLON, which ensures that environmental impacts associated with past and present activities at NSB-NLON are thoroughly investigated and that appropriate remedial action is pursued to protect human health and the environment.

This 100 Percent RD incorporates technologies recommended in the approved Final Remedial Action Plan for Zones 1 and 2 at Naval Submarine Base – New London, Groton, Connecticut (Final RAP; Tetra Tech NUS [Tetra Tech], 2013) for remediation. The approved Final RAP for Zones 1 and 2 recommended targeted ozone/air sparging as the remedial approach; however, due to site-specific constraints identified in Section 1.9 of this document, the ozone technology will not be implemented. For Zone 1 and Zone 2, biosparge—a type of air sparge—will be used as the primary remediation method.

The Final RAP presented the selected remedies for soil and groundwater at Zone 1 (Sites 10 and

11) and Zone 2 (no formal site number assigned, but includes fuel distribution lines). Remedies were chosen based on the evaluation of multiple technologies compared to remedial goals and site-specific constraints. The CTDEEP concurred with the selected remedies.

Based on a review of the applicable CTDEEP RSRs, as compared to contaminants of concern (COCs), biosparge injections in conjunction with monitored natural attenuation (MNA) and long-term monitoring (LTM) were chosen as the selected remedy to be implemented in Zone 1 and Zone 2.

1.2 Regulatory Framework

1.2.1 CERCLA

Although the subject of this document is non-CERCLA contamination, Zones 1 and 2 (OU4) were previously investigated under CERCLA. CERCLA contaminants, including polycyclic aromatic hydrocarbons, lead, and mercury, were identified and investigated via the CERCLA process. A FS was completed in June 2010, and a ROD was signed in August 2012 for CERCLA contaminants at OU4. The CERCLA remedy for Zone 1 includes land use controls (LUCs) and monitoring. The ROD determined No Further Action for CERCLA contaminants at Zone 2.

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During the investigation of CERCLA contaminants, non-CERCLA contaminants were identified.

Data from CERCLA investigations (FS Report, Soil and Groundwater Pre-Design Investigation [PDI] Completion Report, and FS Addendum) along with a 2016 PDI Report, discussed in Section 1.8, were used as part of the 100% design for non-CERCLA contaminants. The non-CERCLA remediation for Zones 1 and 2 was placed in the Navy’s POL program to be investigated and remediated in accordance with the CTDEEP RSRs.

1.2.2 Connecticut Remediation Standard Regulations

The Regulations of Connecticut State Agencies (RCSA) Sections 22a-133k-1 through 22a-133k-3, inclusive, comprise the RSRs. These are supported by RCSA 22a-133q-1, which provides regulations governing the implementation of Environmental Land Use Restrictions (ELURs). These regulations are applicable to various sites in Connecticut including those undergoing investigation and remediation under the Property Transfer Program, an administrative order from the CTDEEP, or under one of the CTDEEP Voluntary Remediation Programs. The RSRs contain numerical, default criteria used to determine the need for remediation of soil associated with a release area that are based on the potential for human health impacts from direct exposure to contaminants in soil, the Direct Exposure Criteria (DEC), and on the potential for contaminants in the soil to have an adverse impact on groundwater, the Pollutant Mobility Criteria (PMC). Likewise, the RSRs contain numerical, default criteria for contaminated groundwater associated with a release area. Criteria are established to protect surface water resources, the Surface Water Protection Criteria (SWPC), and to protect human health from contaminants that may volatilize from contaminated groundwater, the Volatilization Criteria. Criteria are also established for some site settings to protect groundwater as a drinking water supply, the Groundwater Protection Criteria. Although OU4 is not currently in a program or under order, the RSR criteria are used as part of the remedial design. A summary of applicable criteria to the site is discussed in the following paragraphs.

Due to the proximity of the Thames River, the SWPC are applicable to OU4. The CTDEEP surface water designated use and criteria for Zones 1 and 2 and is Class GB. The “GB” designation includes groundwater that is hydraulically connected to surface water bodies and is presumed not suitable for human consumption without treatment. Based on the GB designation for Zones 1 and 2 groundwater and the planned LUCs (discussed in Section 1.9.3), the RSR criteria that apply to soil data are the GB PMC and Industrial/Commercial (I/C) DEC. The Residential Direct Exposure Criteria (RDEC) are the RSR default criteria, and the RSRs permit ELURs that restrict future use of a site to non-residential uses, compared to the I/C DEC.

Although an ELUR is not planned for Zones 1 and 2, a LUC, implemented in accordance with the Department of Defense (DoD) Policy on Land Use Controls Associated with Environmental Restoration Activities (2001), is part of the remedy. As discussed in Section 1.9.3, a LUC will limit site use to I/C use only in the same way an ELUR would. Should the property be

1-4 transferred, an ELUR will be completed prior to the transfer of the property in accordance with RSRs.

1.3 Site History and Historical Land Use

In 1867, the State of Connecticut donated a 112-acre parcel of land on the eastern bank of the Thames River to the Navy. In 1868, the Navy officially designated the property a Navy Yard, which was used to moor small craft and obsolete warships and served as a coaling station for the Atlantic fleet. The Navy designated the site a submarine base in 1916. During World War I, facilities at the base were extensively expanded; 6 piers and 81 buildings were added. In 1917, a submarine school was established, and in 1918, the Submarine Medical Center was founded.

The facility underwent another period of growth during World War II. Between 1935 and 1945, the Navy added more than 180 buildings and acquired land adjacent to NSB-NLON, expanding the facility from 112 acres to 497 acres. The growth of NSB-NLON continued after World War II, and in 1946, the Medical Research Laboratory was established. In 1968, the status of the submarine school was changed from an Activity to a Command, and the submarine school became the largest tenant activity on the base. The Naval Submarine Support Facility was established in 1974, and the Naval Undersea Medical Institute was established the following year. Currently, NSB-NLON consists of more than 207 buildings on 687 acres of land and provides base command for naval submarine activities in the Atlantic Ocean. NSB-NLON also provides housing for Navy personnel and their families and supports submarine training facilities, military offices, medical facilities, and facilities for submarine maintenance, repair, and overhaul.

Most of the Lower Subase construction from approximately Pier 15 to the south, took place in the early 1900s with a major expansion from 1935 to 1940. In 1946, the waterfront, north of Pier 15, was developed extensively to accommodate berthing of the reserve fleet. The area was dredged and filled, and bulkheads, piers, support buildings, and utilities were constructed.

Battery overhaul was one of the largest operations at the Lower Subase until the advent of nuclear-powered submarines. Lead-acid battery maintenance and overhaul activities were conducted until the mid-1950s. A classified materials incinerator was also operated in the Lower Subase until 1967. It is possible that the resulting ash was disposed in portions of the Lower Subase. Petroleum products were used by the Navy throughout the Lower Subase. Releases of petroleum products to the environment may have occurred because of leaks from underground storage tanks (USTs) and fuel distribution lines, vehicle and locomotive maintenance operations and associated waste disposal practices, and marine fueling activities. Other ship and submarine maintenance activities (e.g., sandblasting and painting) were also conducted in the Lower Subase and adjacent Thames River.

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Detailed summaries regarding site operational history can be found in the following reports:

• Lower Subase Remedial Investigation for Naval Submarine Base - New London Groton, Connecticut (Brown & Root Environmental [Brown & Root], 1999)

• Feasibility Study for Operable Unit 4, Lower Subase, Naval Submarine Base New London, Groton, Connecticut (Tetra Tech, 2010)

• Lower Subase (Operable Unit 4) Soil and Groundwater Pre-Design Investigation Completion Report and Feasibility Study Addendum (Tetra Tech, 2012)

• Final Remedial Action Plan for Zones 1 and 2 at Naval Submarine Base - New London Groton, Connecticut (Tetra Tech, 2013)

1.4 Soil Conditions

NSB-NLON is situated in the Eastern Uplands region of Connecticut (Atlantic Environmental Services, Inc., 1992). The area has irregular hills of exposed bedrock with poorly drained uneven valleys between them. The bedrock is metamorphosed rock of sedimentary and igneous origin and is faulted and folded. The major low-angle fault in the area is the Honey Hill Fault, which trends east to west and is located approximately 6 miles north of NSB-NLON. The fault does not cross the facility boundary.

The following five bedrock formations underlie the NSB-NLON: Alaskite Gneiss, Granitic Gneiss, Mamacoke Formation, Plainfield Formation, and Westerly Granite (U.S. Geological Survey [USGS], 1967). The Alaskite Gneiss and Granitic Gneiss are orange pink to light gray, medium-grained, granitic gneisses; the Mamacoke Formation is a light to dark gray, medium-grained, biotite-quartz-feldspar gneiss; the Plainfield Formation is dark green hornblende-biotite-quartz-plagioclase gneiss; and the Westerly Granite consists of gray, fine- to medium-grained, equigranular granite. The Mamacoke Formation, Alaskite Gneiss, and Granite Gneiss are the only formations underlying the Lower Subase.

The surficial geology of NSB-NLON consists of unconsolidated glacial materials deposited during the Wisconsian Glaciation (USGS, 1960) and includes stratified drift and glacial till.

Stratified drift consists of deposits of sorted silt, sand, and gravel that were deposited by glacial meltwater streams. Glacial till consists of a non-stratified, dense, heterogeneous mixture of clay, silt, sand, and rock fragments placed by glacial ice. Stratified drift at NSB-NLON is mapped as terraces flanking the Thames River valley (USGS, 1960). The 20- and 30-foot elevation terraces of stratified drift border the eastern edge of the Lower Subase. A thin veneer of glacial till mantles most of the bedrock in the area. Till is exposed only on bedrock highs and probably underlies outwash materials in valleys. The till thickness varies considerably, but averages less than 10 feet (USGS, 1960).

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Other surficial deposits are post-glacial river and floodplain deposits (alluvium), backfill material of reworked and quarried till and drift, and debris fill (USGS, 1960). Fill material is mapped in the former location of Crystal Lake, in the southern half of the Lower Subase, at the former Defense Reutilization and Marketing Office along the Thames River, and in an area east of the Torpedo Shops. Generally, fill material underlying the southern half of the Lower Subase thickens from 5 feet along its eastern edge to approximately 20 feet along the Thames River.

Debris fill material is primarily sand and gravel with isolated areas of wood, fly ash, brick and concrete fragments, and metal fragments.

A silty sand layer underlies the sand and gravel backfill and debris fill in Zones 1 and Zone 2. A medium to coarse sand layer underlies the sand and gravel backfill and overlies the silty sand.

The silty sand layer contains shell and wood fragments and varying amounts of clay. The sand and silty sand units are interpreted as natural deposits of stratified drift. The bottom of the silty sand unit in Zones 1 through 2 was not encountered in borings to a maximum depth of 34 feet.

In 1940, the Navy constructed a wooden platform and quay wall in the southern portion of the Lower Subase. The wooden platform is believed to be in place shoreward of the current quay wall between Pier 2 and Pier 15, within Zones 1, 2, 3, and 4. The presence of the wooden platform has been confirmed by as-built drawings, borings, and excavations between Piers 2 and 6 and at Pier 10. The wooden platform is 4 inches thick and supported by 10- to 12-inch-square wooden joists and 8-inch-diameter timber pilings. A steel bulkhead along the Thames River was constructed in 1952 of steel sheet piling and supports. During construction of the bulkhead, the quay wall and wooden platform were covered with approximately 6 to 7 feet of sand and gravel fill, and the area was paved for vehicular access along Albacore Road. The quay wall is located approximately 4 feet east of the steel bulkhead, immediately beneath the paved surface. Void spaces of 3 to 8 feet occur beneath the wooden platform and are separated by sand and gravel fill. Natural river deposits of silt and sand underlie the void spaces (Tetra Tech, 2010).

1.5 Hydrogeological Conditions

The general direction of groundwater flow at NSB-NLON is westerly across the facility toward the Thames River, with the water table surface following the topography and bedrock surface locally. High hydraulic potentials develop within the three bedrock highs in the northern, central, and southern areas of the base. Precipitation infiltrates into the overburden and bedrock and flows radially from areas of high elevation toward areas of low elevation. Groundwater flows toward the two valleys and ultimately toward the Thames River, or directly from the western edges of the three hills toward the Thames River.

In most cases, groundwater elevations at NSB-NLON well clusters are similar in the bedrock and overburden, which suggests that the bedrock and overburden are hydraulically connected and that groundwater flow directions are similar. However, at a few well clusters, the difference in

1-7 groundwater elevations between the bedrock and overburden is several feet. In these areas, the bedrock and overburden have a weak hydraulic connection, and local groundwater flow directions may vary.

A drainage basin map of Connecticut, in the Connecticut Geological and Natural History Survey (1974), shows that a major basin divide is present along the ridges of Baldwin Hill. To the east of Baldwin Hill, surface and subsurface waters are part of the Southeast Coast Major Basin. Water from this basin is not expected to travel toward the base. To the west of Baldwin Hill, surface waters and groundwater are part of the Thames Major Basin and ultimately discharge into the Thames River.

The vertical component of groundwater flow is predominantly downward in upland areas of NSB-NLON. However, at the bases of the hills, the bedrock surface flattens and the overburden thickens. In these areas, upward gradients may occur locally, resulting in shallow bedrock groundwater discharge into the overburden (stream valleys and wetland seeps). Near the Thames River, upward gradients exist, as is typical for groundwater in major stream valleys. Whether an upward or downward gradient develops depends on factors such as bedrock surface elevation, thickness of the overburden, topographic features, permeability, distance to the river, and tidal stage (Tetra Tech, 2010).

Recent hydrogeological data collected at the site indicate groundwater flows southwesterly in the area around Zone 1 and Zone 2. Groundwater velocity within Zones 1 and 2 was estimated as about 1.63 feet per day (AGVIQ Environmental Services [AGVIQ], 2016).

1.6 Site Hydrologic Conditions

The Thames River is a tidally-influenced river. The tides of the Thames River influence the discharge of groundwater from NSB-NLON on a daily basis. The following conclusions were reached in the Lower Subase Remedial Investigation (RI) regarding tidal influences on groundwater discharge from NSB-NLON: (1) during low tide, the hydraulic gradient is toward the Thames River and results in the greatest discharge rate of groundwater to the river; (2) during high tide, the hydraulic gradient along the Thames River is reversed and flow occurs from the river to the Lower Subase, temporarily halting the discharge of groundwater from the base to the river; and (3) the reversal in hydraulic gradient resulting from tidal influences occurs only near the river, generally within 300 feet, and does not seem to significantly alter groundwater flow in other areas of NSB-NLON (Tetra Tech, 2010).

During the Phase II RI, seasonal variations of the groundwater table across NSB-NLON were recorded during monthly groundwater level measurements. The data showed that during periods of limited recharge (i.e., summer and early fall), hydraulic gradients along bedrock highs (where there is limited overburden thickness) decrease and groundwater discharge from these areas

1-8 decreases; conversely, during periods of significant recharge (late fall and spring), hydraulic gradients and groundwater discharge in these areas increase. The data also showed that hydraulic gradients in portions of NSB-NLON where there is significant overburden (i.e., valleys and floodplain) remain relatively constant (with the exception of tidal-related variations) throughout the year as does groundwater discharge (Brown & Root, 1999).

1.7 Site Conceptual Model

To evaluate the effect of the uncontrolled hazardous waste sites within the base on human health and the environment, conceptual site models for the zones of the Lower Subase were developed to identify contaminant sources, contaminant release mechanisms, transport routes, and receptors under current and future land use scenarios, and were presented in the zone-specific sections of the FS. The five primary sources of contamination to the Lower Subase soil have been identified to be: (1) battery maintenance and overhaul activities, (2) leaks of petroleum products from USTs and fuel distribution lines, (3) vehicle and locomotive maintenance operations and associated waste disposal practices, (4) disposal of ash from the classified materials incinerator, and (5) ship and submarine maintenance activities (e.g., sandblasting and painting) at the former marine railway (Tetra Tech, 2010). The primary source of contamination for the non-CERCLA– related contamination in Zones 1 and 2 is historic leaks of petroleum products from USTs and fuel distribution lines.

Potential receptors under current land use are adult recreational users exposed to surface water, shellfish, and finfish; full-time employees exposed to surface soil and groundwater; and construction workers exposed to surface/subsurface soil and groundwater. Potential receptors under future land use are adult recreational users exposed to surface water, shellfish, and finfish and full-time employees, construction workers, and hypothetical adult and child residents exposed to surface/subsurface soil and groundwater. CTDEEP has classified groundwater beneath OU4 as within a GB-classified area (a non-drinking water source area) (CTDEEP, 1996), which indicates that the area has been used for long-term industrial or commercial development and that a public water supply service is available. Water beneath the Lower Subase is not currently used for domestic, commercial, or industrial purposes, and it is not anticipated that the water will be used for these purposes in the future; therefore, consumption of groundwater was not evaluated as an exposure pathway for either current or future receptors. No complete exposure pathways exist for human receptors for sediment because of the depth (ranging from -16 to -40 feet) of the Thames River adjacent to the Lower Subase. Although human consumption of shellfish and finfish was evaluated as an exposure pathway, other factors, including the significant depth of the river adjacent to NSB-NLON, CTDEEP’s existing ban on recreational shellfish harvesting from the Thames River near the Lower Subase, and the subase security boundary installed by the Navy to prevent public access, minimize human exposure to surface water, shellfish, and finfish. The land surface of the Lower Subase contains a substantial

1-9 amount of paved area and very little maintained lawn; therefore, it does not provide suitable ecological habitat. Ecological receptors in the Thames River adjacent to the Lower Subase, the only potential ecological habitat, are limited to benthic invertebrates, fish and other aquatic organisms, and piscivorous birds (Tetra Tech, 2010).

Based on review of the RSRs as compared with COCs found in non-CERCLA soil and groundwater in both zones, remedies described in the Final RAP were developed to reduce the risk to current and/or future receptors and attenuate COC concentrations in groundwater to a level below RSR criteria prior to reaching the Thames River. The following section presents the selected remedies for Zones 1 and 2.

1.7.1 Zones 1 and Zone 2

1.7.1.1 Zone 1

Zone 1 extends from Darter Road south of Building 89 to the southern side of Corvina Road. The Providence and Worcester Railroad runs along the eastern border of the zone, and the Thames River forms the western border of the zone. Approximately 90 to 95 percent of Zone 1 is paved or covered with buildings, and the land surface slopes gently toward the Thames River. Zone 1 is covered primarily by buildings, concrete, or paving, although some small sections are covered by grass.

The main building in Zone 1 is the power plant (Building 29). There are three sites of concern in Zone 1: (1) IRP Site 10–Fuel Storage Tanks and Tank 54-H, (2) IRP Site 11–Power Plant Oil Tanks, and (3) Building 89 UST. These sites are shown in Appendix A, Drawing C-002, Zones 1 and 2 Existing Site Conditions.

IRP Site 10 included five concrete USTs located southwest of Building 107 that were placed into service during World War II. Three of the tanks had 125,000-gallon capacities and were used to store diesel fuel from 1954 to 1987. From 1954 to 1989, two other 25,000-gallon tanks were used to store lubrication and hydraulic oils. A sixth 30,000-gallon tank, 54-H, located adjacent to and north of the 125,000-gallon tanks, was used as a reclamation tank for the other five tanks.

The Navy decommissioned four of the tanks in 1987. In 1989, the Navy decommissioned the 25,000 gallon tanks and installed new steel tanks within the shells of these two tanks to provide secondary containment.

IRP Site 11 includes four 170,000-gallon USTs that were located adjacent to and east of Building 29. These tanks were installed during World War II. Two tanks were used to store No. 6 fuel oil pumped from the tank farm at the southern end of NSB-NLON; one tank was used to store diesel oil and one tank was used to store waste oil generated by the bilge water-oil recovery system at the power plant. Past oil leakage was apparent when the old tanks were cleaned; however, the old tanks were repaired and were used as containment structures for three

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150,000-gallon steel USTs. Two of the three 150,000 gallon USTs (northern and southern tanks) were abandoned during the period of 2010 and 2011.

The former Building 89 UST was located adjacent to Zone 1. The UST had a capacity of 3,000 gallons, was installed in 1982 and used for storage of No. 2 fuel oil for power motors operated in Building 89. The tank was installed to a concrete pad with steel tie-downs to prevent floatation. In 1993, the tank failed tightness testing and was removed by excavation in 1994.

Post-excavation soil samples analyzed for total petroleum hydrocarbons (TPH) indicated concentrations were below CTDEEP cleanup criteria.

Historical fuel lines from the tank farm distributed fuel oil to Zones 1 and 2. Some of these fuel lines have been decommissioned and some remain in place. According to the FS (Tetra Tech, 2010), in 1996, pressure leak testing was performed on the lines and valves in the fuel distribution system within and adjacent to Zone 1. A section of polyvinyl chloride or fiberglass pipe in the diesel oil line at Pier 12 was deemed to be compromised because it failed to hold air at 20 pounds per square inch (psi) during a pneumatic test. The Navy’s Public Works Department replaced this section of pipe. The other sections of line and various valves tested in the portion of the fuel oil distribution system within or adjacent to Zone 1 passed the pressure leak testing. In 1996, pressure leak testing was done on the sections of the lines and valves in the portion of the distribution system within Zone 2, and those sections passed the testing. The lines were subsequently abandoned in place. Other utilities located in Zone 1 include steam/condensate, water, sanitary sewer, storm sewer, natural gas, and electrical.

Soil data collected during the FS and 2012 Data Gap Investigation (DGI) performed by Tetra Tech indicated extractable total petroleum hydrocarbon (ETPH) concentrations that exceeded the I/C DEC RSRs in saturated soils at depths ranging from 8 to 12 feet below ground surface (bgs), located across Zone 1. Kriging statistical analysis performed by Tetra Tech during the DGI indicated ETPH soil concentrations that exceeded I/C DEC criteria in the saturated zone (Tetra Tech, 2013). There were no exceedances within the unsaturated zone.

Groundwater data collected during the FS and DGI indicated multiple exceedances of SWPC located across Zone 1. Data collected during the FS indicated ETPH concentrations ranging up to 16,000 micrograms per liter (µg/L). Groundwater samples collected during the DGI demonstrated ETPH concentrations ranging up to 33,000 µg/L (Tetra Tech, 2013).

Nonaqueous phase liquid (NAPL) was found in one well during historic gauging events in Zone 1, with an approximate thickness of 0.5 feet. An estimated 1,100 gallons of ETPH was calculated based on locations where NAPL was observed and where TPH soil concentrations exceeded 25,000 milligrams per kilogram (Tetra Tech, 2013).

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Based on the results from the previous investigations at Zone 1, it was determined that the petroleum-related impacts to soil and groundwater that were encountered are likely the result of possible leaks or historical spills associated with the former onsite USTs and subsurface fuel oil distribution lines.

1.7.1.2 Zone 2

Zone 2 extends from the southern boundary of Zone 1 along Corvina Road south to Capelin Road to North of Building 31. The Providence and Worcester Railroad runs along the eastern border of Zone 2, and the Thames River forms the western border of Zone 2. The ground surface of Zone 2 slopes gently to the Thames River, and approximately 90 to 95 percent of the surface is paved or covered with buildings. Multiple buildings exist in Zone 2 including Buildings 17, 20, 38, 75, 328, and 548. Utilities including former subsurface fuel line, steam/condensate, water, sanitary sewer, storm sewer, natural gas, and electrical exist in Zone 2.

Historical soil data collected during the FS indicated ETPH concentrations were below the I/C DEC criteria for the majority of Zone 2, with the exception of the northern boundary adjacent to Zone 1. Kriging statistical analysis performed by Tetra Tech for the DGI indicated ETPH soil concentrations exceeding the I/C DEC criteria in the saturated zone. There were no ETPH exceedances in soil in the unsaturated zone of Zone 2. Groundwater data collected during the FS indicated ETPH exceedances of the SWPC at one location (well 13MW6) within Zone 2 (Tetra Tech, 2013).

Based on the previous investigations conducted at Zone 2, it was presumed that the petroleum-related contamination at this area is associated with the former subsurface fuel oil distribution lines and historical releases that occurred within Zone 1.

1.8 Pre-Design Investigation

The PDI was performed in Zones 1 and 2 during the spring of 2016. The PDI included installation of additional monitoring wells, collection of groundwater samples from the new and existing wells, collection of groundwater samples from temporary borings, and collection of groundwater and soil samples for bench-scale treatability testing.

1.8.1 Groundwater Investigation

Four additional monitoring wells were installed during the PDI within Zones 1 and 2.

Groundwater samples were collected from each of the four new monitoring wells, four existing monitoring wells, and five temporary sampling points. All groundwater samples were analyzed for RSR metals and ETPH. The location of these wells is shown on Figure 5 from the PDI Technical Memo found in Appendix B (AGVIQ, 2016).

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Results from the groundwater investigation demonstrated SWPC exceedances at three well locations; two exceedances occurred in Zone 1 at locations up and downgradient of the power plant (wells TMW4 and 1MW1S), and one exceedance occurred in Zone 2 located near the northern boundary with Zone 1 (well TMW2). Figure 5 from the PDI Technical Memo illustrates the groundwater concentrations observed during the PDI and includes a plot of the delineation of ETPH in exceedance of SWPC (Appendix B).

NAPL was found at one location upgradient to the power plant (well TMW4). A new 2-inch-diameter well (TMW4) was installed for the observation of the NAPL during the PDI.

1.8.2 Bench-Scale Treatability Testing

Bench-scale tests were conducted at PRIMA Environmental Laboratory located in El Dorado Hills, California. The bench-scale tests were conducted from March to May 2016. The bench-scale tests were conducted using site soil and groundwater collected during the PDI. The bench-scale tests were conducted to evaluate the effectiveness of ozone and air sparge to degrade the TPH. In addition, the bench-scale tests were utilized to assess for mobilization of hexavalent chromium (Cr(VI)) and manganese. The four objectives of the laboratory test included the following:

• Determine if ozone treatment would adequately degrade TPH

• Determine if ozone treatment would be more effective than air sparging

• Determine if air sparging or ozonation could mobilize Cr(VI) and if so, at what concentrations

• Determine if air sparging or ozonation could mobilize manganese and if so, at what concentrations

Laboratory column tests demonstrated that ozone could effectively degrade TPH in site soil, but more ozone than the stoichiometric demand would be needed to achieve complete destruction.

Application of two times the theoretical dose destroyed 54 percent of TPH, though only about half of the ozone applied was consumed within the column. Application of air alone destroyed 12 percent of the TPH mass during the same duration (11 days).

Batch tests demonstrated 0.5 milligrams of Cr(VI) per 1 kilogram soil could be mobilized during ozone application. These data indicate that up to 4,760 µg/L of Cr(VI) could potentially be mobilized into groundwater during ozone application, which is greater than the SWPC (110 µg/L). There was no Cr(VI) mobilization observed during the air sparge tests.

Concentrations of manganese indicated decreased groundwater concentrations during both ozone and air sparge application.

The complete bench-scale report is included in Appendix C.

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1.9 Selected Remedy

The Final RAP prepared by Tetra Tech identified targeted “ozone/air sparging” as the most appropriate remedial alternative for Zones 1 and 2. Based on additional considerations, ozone will not be conducted as part of the remedial efforts in Zones 1 and 2. Ozone will not be implemented for the following reasons:

• A natural gas line, which is critical to the power plant and pier and facility operations, is located within the area requiring treatment in Zone 1. The construction of the gas line is steel, which is incompatible with ozone (Ozone Solutions, 2015). Use of ozone would lead to the corrosion of the gas line, which would pose a significant risk for shutdown of plant/base operations and create an overall safety risk.

• Multiple utilities of various construction materials are located throughout the treatment area. Ozone has the potential to be corrosive to other utilities (e.g. steam, air, and high-pressure water lines) within the area.

• Potential for mobilization of Cr(VI) during ozone injections, thus resulting in the exceedance of SWPC downgradient at the Thames River.

The Final RAP presented ozone/air sparge in conjunction with MNA and LTM as a selected remedy for Zones 1 and 2. Due to the constraints mentioned previously, the ozone technology will not be implemented. Air sparge involves the injection of air into the subsurface to facilitate contaminant attenuation. There are two primary mechanisms by which contaminants attenuate due to air sparging: (1) stimulation of biological aerobic degradation through delivery of oxygen into the subsurface, and (2) the partitioning of volatile compounds from the dissolved phase into injected air, which can then be recovered with a soil vapor extraction system.

Due to the chemical nature and age of the contaminants, air stripping is not expected to be a significant attenuation mechanism with the air sparge system. For this reason, the designed air sparge system is optimized to stimulate contaminant attenuation through aerobic biodegradation.

Air sparge systems optimized to stimulate biodegradation are sometimes referred to as “biosparge” systems. Within this document, the terms “biosparge” and “air sparge” are both applicable to the system design and are used interchangeably.

The selected remedy for Zone 1 and Zone 2 soil and groundwater includes: (1)…