BUILDING STRONG ® TNT Source Area Ground Water Remediation Former Nansemond Ordnance Depot Formerly Used Defense Site June 2, 2016

BUILDING STRONG ® TNT Site - History  Long History Going Back To 1987 With First Discovery of Crystalline TNT.  2011 Modeling and Treatability Study – Construct site models for groundwater flow and TNT transport and to quantify rates associated with natural attenuation and in- situ bioremediation.  2012 RI Report Update - The RI Update Report recommended an FS, primarily to address the presence of explosives in the soils and groundwater.  2014 Data Gap Evaluation – Current Phase.

BUILDING STRONG ® Modeling and Remediation Study  In 2011 Virginia Tech University completed two studies.  Modeling Study - The aim of this work was to simulate groundwater flow and solute transport at the TNT Area.  Treatability Study - The primary objective was to evaluate the effectiveness of both monitored natural attenuation (MNA) and enhanced bioremediation at the TNT Area.

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TNT Site – Geology TABB Formation: The TABB formation is the top layer of the saturated zone and consists of a variety of soil types ranging from silty and sandy clays to clayey and silty sands to sands of varying grain sizes (IT Corporation 1992). This is referred to as the upper unit of the Columbia Group or the Columbia Aquifer in other site reports (MicroPact 2006). This formation extends from the water table surface to around 20 ft below mean sea level or 35 ft below ground surface. The TABB formation transmits groundwater and acts as an unconfined aquifer. Discontinuous Clay Layer: Underlying the TABB formation is a discontinuous clay layer of varying width and thickness. The clay layer is considerably thicker in the southern part of the TNT source area, but thins out and eventually disappears north of the soccer field area. The clay layer acts as a potential aquitard or confining unit; however, historical drilling throughout FNOD indicates the clay layer to be formed of multiple discontinuous clay lenses, which would lead to a hydraulic connection between the overlying unconfined TABB formation and underlying semi- confined Yorktown formation at various points within the extent of the clay layer itself. Yorktown Formation: The Yorktown formation is the deeper aquifer encountered at FNOD, approximately 35 feet below the ground surface. It is overlain by the discontinuous clay layer in the southern part of the TNT Area, and the unconfined TABB formation in the northern part. The Yorktown formation is a marine unit, comprising primarily of quartz sand, shell hash and some clay (CAPE 2008). It transmits groundwater and acts as a semi-confined aquifer.

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TNT Site – Transport  Model: The groundwater flow model for the TNT Area was developed within GMS v7.1 (Groundwater Modeling System), MODFLOW 2000 is a FORTRAN code that is widely used for simulating groundwater flow at different sites with varying conditions, and is used in conjunction with solute transport codes including MT3DMS and SEAM3D.  Findings: TNT migrate downward due to the strong vertical hydraulic gradient through low conductivity material and into the permeable lower region of the TABB formation and the upper region of the Yorktown. From there, contaminants move laterally to the James River. However, the primary pathway from the TNT source area is the horizontal migration through the TABB formation in a northern direction.  Groundwater Velocity at MW-11(mound) 0.3 ft/day, at MW-25s (no mound) 23.5 ft/day  Horizontal extent of the TNT plume along the direction of groundwater flow is 1050 ft.  Vertical extent of the TNT plume at source location at least 45 ft bgs.

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TNT Site – Attenuation  The decrease in concentrations with time could be attributed to the source removal activities since 1988, as well as the in-situ anaerobic reductive biodegradation process due to the indigenous microbial population in the aquifer matrix. It could be inferred that the TNT and ADNT plumes have been shrinking since then, which would suggest MNA as a viable remediation alternative.  The presence of 2-ADNT and 4-ADNT strongly indicates the presence of anaerobic reductive biodegradation of TNT occurring naturally in the sub- surface. Under reducing conditions, indigenous microbial populations present in the aquifer matrix have been shown to reduce TNT to 2-ADNT and 4- ADNT simultaneously.  An overall decrease of 28% for total TNT mass and 40% for total ADNT mass in the aquifer was observed within 50 years. The total mass decrease increased to 49% for TNT and 63% for ADNTs after a total duration of 100 years.

BUILDING STRONG ®  Treatability study found that microorganisms capable of degrading TNT were confirmed to be present in the TNT Area sediments. Results of bench- scale microcosms conducted to assess the treatability of TNT demonstrated that TNT-degradation rates were significantly enhanced in laboratory microcosms using ethanol and lactate as electron donors relative to controls containing representative background levels of organic matter.  Injection of solutions to enhance TNT/ADNT biodegradation (i.e., biostimulation compounds (food) and bioaugmentation culture (more bacteria)) is a feasible option in the TABB formation in the vicinity of the TNT Source Area.  Enhanced Anaerobic Bioremediation (EAB) will result in an increased rate of TNT/ADNT biodegradation by a factor of at least 5-10 times above the current rate of natural attenuation.  The reduction achieved is greater than 99%, with remaining total mass less than 1% of the initial total mass for both TNT and its degradation products ADNTs after 100 years.

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TNT Site – Data Gap Issues