AbstractUpland placement of dredge sediments has the potential to provide beneficial reuse of suitable sediments for agricultural uses or urban soil reconstruction. However, the use of many dredge materials is limited by contaminants, and most established screening protocols focus on limiting major contaminants such as heavy metals and polycyclic aromatic hydrocarbons and generally ignore fundamental agronomic parameters. Since 2001, we have placed over 450,000 m3 of Potomac River fresh water dredge materials and 250,000 m3 of saline materials from various locations into monitored confined upland facilities in Charles City, VA, and documented their conversion to agricultural uses. Groundwater and soil quality monitoring has indicated no adverse effects from material placement and outstanding agricultural productivity for the freshwater materials. Once placed, saline materials rapidly leach and ripen with quick declines in pH, electrical conductivity, and sodicity, but potentials for local groundwater impacts must be considered. Our experience to date indicates that the most important primary screening parameter is acid-base accounting (potential acidity or lime demand), which should become a mandatory analytical requirement. Our second level of acceptance screening is based on a combination of federal and state residual waste and soil screening standards and basic agronomic principles. High silt+clay and total organic C may also limit rapid use of many dredge materials due to extended dewatering times and physical limitations. This dredge material screening system separates potential upland placement candidates into three soil quality management categories (unsuitable, suitable, and clean fill) with differing monitoring requirements. Similar use of these sediments in urban soil reconstruction is also recommended.

Beneficial Use of Dredge Materials for Soil Reconstruction and Development of Dredge Screening Protocols

Sara C. Koropchak, W. Lee Daniels,* Abbey Wick, G. Richard Whittecar, and Nick Haus

The United States Army Corps of Engineers (USACE) maintains over 40,000 km of waterways and over 400 ports across the United States, which includes

the maintenance dredging of >200 million m3 of material annu-ally (USACE, 2014a; Brandon and Price, 2007). Dredged mate-rials may be disposed of as waste or placed for a beneficial use, depending on physical and chemical properties and on the con-taminant levels of the dredge sediment (USEPA and USACE, 2004). Over 70% of dredge materials are disposed of via ocean placement or placement into disposal impoundments or islands, with approximately 30% designated for some form of beneficial use. In general, there are three categories of beneficial dredge use: engineered uses, agricultural and product use, and environmen-tal enhancement (USACE, 2014b). More specifically, beneficial uses include habitat development, aquaculture, beach nourish-ment, recreation, agriculture, mine reclamation, shoreline sta-bilization, and industrial use/construction (Brandon and Price, 2007). As disposal sites become more limited, material is increas-ingly being considered for upland placement for agriculture as well as covers for mines and landfills. In this paper, we contend that significant amounts of dredge materials have great potential for use as agricultural soil media or as components of manufac-tured soils used for urban soil reconstruction and/or brownfields rehabilitation.

Beneficial utilization projects where high-value agricultural or horticultural soils are produced have been occasionally documented in the literature, most notably in the United States for programs focused on Illinois River sediments (Darmody and Marlin, 2002, 2008; Darmody et al., 2004; Ebbs et al., 2006), which were used successfully for urban renewal projects in Chicago and for landscape development in public parks in central Illinois. Dredge materials from the mid-Atlantic United States have been successfully combined with other residuals to produce manufactured soils for wider applications for brownfield redevelopment, gardening, and landscaping applications (Lee, 2001). Similar findings and potential applications have been reported for Ireland (Sheehan and Harrington, 2012; Sheehan

Abbreviations: EC, electrical conductivity; PAH, polycyclic aromatic hydrocarbon; SSL, soil screening level; TOC, total organic carbon; USACE, United States Army Corps of Engineers; WWB, Woodrow Wilson Basin.

S.C. Koropchak and W.L. Daniels, Dep. of Crop and Soil Environmental Sciences, 0404, Virginia Tech, 185 Ag Quad Lane, Blacksburg, VA 24061; A. Wick, Dep. of Soil Science, North Dakota State Univ., Walster Hall, Fargo, ND 58108-6050; G.R. Whittecar, Dep. of Ocean, Earth & Atmospheric Sciences, Old Dominion Univ., Norfolk, VA 23529; N. Haus, Dep. of Soil Science, Univ. of Wisconsin, Madison, WI 53706. Assigned to Associate Editor Alex Chow.

Copyright © 2015 American Society of Agronomy, Crop Science Society of Ameri-ca, and Soil Science Society of America. 5585 Guilford Rd., Madison, WI 53711 USA. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. J. Environ. Qual. doi:10.2134/jeq2014.12.0529 Received 10 Dec. 2014. Accepted 27 Feb. 2015. *Corresponding author (wdaniels@vt.edu).

Journal of Environmental QualitySOIL IN THE CITY

SPECIAL SECTION

Journal of Environmental Quality

et al., 2010). However, adverse effects of metal sulfide oxidation from upland placed dredge materials in Belgium have also been noted by Cappuyns et al. (2006), along with similar reports of acid sulfate soil formation in a range of dredge spoil materials placed in the mid-Atlantic United States (Fanning and Fanning, 1989; Demas et al., 2004). Related concerns regarding metal release by oxidizing and weathering sulfidic sediments have been voiced by Caille et al. (2003), Singh et al. (2000), and many others.

A synthesis of the literature cited above along with our detailed review (Haus, 2011) indicates that dredge materials destined for consideration for upland placement can be separated into two broad groupings—freshwater and saline—with widely different management criteria and potential constraints. It is also clear that although the USEPA and USACE (2004) and the USACE (2014a,b) have established general criteria for screening dredge sediments for beneficial use versus simple disposal, more detailed and specific criteria to support local or state decision-making and the development of upland dredge placement monitoring programs are not in existence, with the exception of the New Jersey program (NJDEP, 1999). To date, most local or state authorities have fallen back on the use of USEPA regional soil screening levels (SSLs) (USEPA, 2014) that are more commonly used as clean-up targets for contaminated sites and can set unrealistically low standards for certain levels of total metals such as As that may not reflect actual bioavailability of those elements or compounds in a field utilization setting. For example, the current residential SSL for As is 0.67 mg kg-1, whereas native background As levels in Virginia soils are an order of magnitude higher (Smith et al., 2005).

The purpose of this paper is to review, summarize, and synthesize the long-term (15-yr) results of our collaborative dredge spoil characterization and utilization program that is cooperative with Weanack Land LLC (Weanack; see Fig. 1) in Charles City, VA. Weanack is located directly adjacent to the James River on the grounds of historic Shirley Plantation and has been accepting low-contaminant dredge materials for conversion to agricultural uses and mined land reclamation

since 2000. To date, this program has included large-scale applications of both freshwater and saltwater dredge materials to produce agricultural crops and monitored demonstration plots to examine the feasibility of liming acid–forming materials and the biodegradation of polycyclic aromatic hydrocarbons (PAHs). In a parallel effort, we have evaluated over 20 candidate dredge materials for upland placement and developed a detailed and novel screening template approach that categorizes potential dredge materials based on their potentials for restricted versus unrestricted use as upland soil media.

In this paper we review and summarize our collective research and monitoring results from a range of long-term field, laboratory, and greenhouse studies where we have focused on three primary objectives: (i) to determine the feasibility of transforming a range of freshwater and saline dredge spoil materials into productive agricultural soils, (ii) to identify specific chemical and mineralogical properties of fresh dredge spoil materials that might limit their use as agricultural soils and to investigate appropriate remediation strategies where indicated, (iii) to monitor the effect of placing large volumes of dredge materials into upland leaching environments on local ground and surface water quality, and (iv) to develop a set of dredge material screening criteria acceptable to local regulators that would allow for more uniform determination of their suitability for upland placement and that would differentiate the level of postplacement monitoring required.

The various studies described and summarized in this paper are presented in their actual order of occurrence, although multiple studies were often ongoing at the same time. Monitoring and field research will continue through 2020 and beyond.

Freshwater Dredge Materials: Woodrow Wilson Bridge

Before 1999, no major upland utilization program for dredge materials had occurred in Virginia, although the use of sands for beach nourishment and fine-silty materials for tidal marsh enhancement was common. In 1999, the states of Maryland and Virginia initiated a joint project to widen the Woodrow

Fig. 1. Location and site maps of dredge spoil confined upland utilization facilities (CUFs) at Weanack LLP in Charles City County, Virginia. Most dredge materials arrive via barge through Port Tobacco in the center of the photo and are pumped to the CUFs. The Woodrow Wilson Basin receives freshwater dredge materials, whereas the Earle Basin receives saline materials. Figure by Nick Haus (Univ. of Wisconsin, Madison, WI).

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Wilson Bridge, just downstream from Washington, DC on the Potomac River. Although this reach of the river was tidal, salinity levels were very low, and the majority of the sediment was presumably derived from silty topsoil sediments from the combined Shenandoah and Potomac River watersheds. Other than small naval yard activity just upstream at Alexandria, VA and Anacostia, MD, industrial effluent inputs to the river system were historically low. Starting in early 2000 and continuing intermittently for over 5 yr, approximately 500,000 m3 of freshwater tidal sediments generated during the construction of the bridge were transported by barge to Weanack. Before excavation, the material was analyzed for a variety of parameters and was found to be very low in organic contaminants and metals, low in organic matter, moderate in pH, and loam to silt-loam in texture (Tables 1–3). All measured inorganic constituents, including pesticides, herbicides, and other man-made compounds, were found to be below USEPA Region III Risk Based Criteria for residential soil, with the exception of As. The sediment also easily met all USACE beneficial use criteria. The project was approved by the Virginia Department of Environmental Quality under its Virginia Pollution Abatement (VPA) permitting program, which is used for the management of a wide array of monitored land application of waste programs.

The permit required (i) detailed analyses of inbound and postplacement dredge materials and (ii) extensive ground and surface water monitoring as described below.

These dredge materials were placed into an upland confined use facility at Weanack (Fig. 1) designated as the Woodrow Wilson Basin (WWB), which was constructed above a formerly reclaimed sand and gravel mine. The site was excavated to variable depth (-2 to -4 m) below original grade, and a berm was built around the area to prevent sediment loss due to surface water flow and is operated as a zero discharge facility. The basin is unlined and therefore has direct contact with shallow groundwater. During material placement from 2000 to 2006, we began quarterly monitoring (pH, electrical conductivity [EC], dissolved organic C, temperature, and water level) and annual water analyses for metals and other federal Safe Drinking Water Act defined contaminants from an extensive groundwater monitoring network (Fig. 2). Overall, results from these hydrogeologic studies indicate that the study area has a very complex pattern of aquifers and aquitards typical of the upper Coastal Plain (McFarland, 1997). Essentially, the WWB sediments infiltrate the vast majority of precipitation, and because the facility is zero-discharge due to the surrounding berm, the local water table forms an elevated

Table 1. Basic chemical (Mehlich I extractable) and particle size analysis of Woodrow Wilson dredge from samples collected in 2001 (n = 12) and 2005 (n = 16) after initial placement (data adapted from Daniels et al., 2007).

Year pH P K Ca Mg Zn Mn Cu Fe B Total sand

Total silt

Total clay

Textural class†

—————————————————— mg kg-1 —————————————————— ————— % —————2001 6.9 21 55 2808 198 50 126 8.6 300 0.6 nd‡ nd nd nd2005 7.2 17 91 2243 163 22 84 5.5 186 0.6 35 49 16 SIL to SIL/L

† L, loam; SIL, silt.

‡ Not determined.

Table 2. Concentrations and screening criteria for selected metals in various dredge materials described in this study.

Parameter

NJDEP dredge

placement criteria†

USEPA Region 3 soil

screening levels‡

USEPA Part 503 biosolids

USGS soil background

metal§VA

exclusion criteria¶

VA clean upland fill#

Woodrow Wilson Bridge (n = 4)

Earle naval weapons

station (n = 4)

Cheatham naval annex

(n = 6)

Maryland Port

Authority (n = 1)Industrial

soilResidential

soilExcep. quality VA levels

—————————————————————————————— mg kg-1 ——————————————————————————————Aluminum –†† 110,000 7,700 – – – – 13,005 53,491 15,956 30,600Antimony 14 47 3.1 – – 410 14 <2.2 <1.8 <6.7 <51.3Arsenic 20 3.0 0.67 41 5 41 20 <3.8 6.0 7.7 34.0Barium 700 22,000 1,500 – 244 19,000 700 124.8 – 46.7 67.3Beryllium 1 230 16 – <1 2,000 160 1.08 <0.86 <1.35 <0.513Cadmium 39 98 7 39 <0.1 810 39 <0.58 <0.38 <1.24 2.01Calcium – – – – – – – 2,993 15,775 2,936 6,740Zinc 1,500 35,000 2,300 2,800 41 7,500 1,500 205 65 93 –

† New Jersey Department of Environmental Protection (NJDEP) (1999).

‡ USEPA Region 3 soil screening levels have been merged into a regional document developed with input from Regions III, VI, and IX. Values from May 2014 version. Values are for Residential Soil and Industrial Soil screening levels. Values listed for antimony (metallic), arsenic (inorganic), and cadmium are for diet and not soil exposures (USEPA, 2014).

§ Background metal levels specific to the state of Virginia (Smith et al., 2005).

¶ The Virginia exclusion standards generally represent the higher of USEPA RBC Industrial, NJDEP, or USEPA 503 EQ levels for a given parameter as available in 2008. Values exceeding these limits are questionable for acceptance. These are the values of the 2014 Virginia Pollution Abatement permit for Weanack Land LLC.

# Virginia clean fill criteria are based primarily on NJDEP residential cleanup criteria and manually adjusted for known issues with agricultural production/bioavailability. These are the values of the 2014 Virginia Pollution Abatement permit for Weanack Land LLC. Values between the clean fill and exclusion criteria require a variation of the current management strategy.

†† No data/exclusion criteria available for the specific parameter.

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mound within the basin relative to surrounding groundwater levels. Since placement, there have been no significant changes in groundwater quality. However, several parameters have occasionally been elevated. Elevated levels (5–10 mg L-1) of nitrate N were noted in the early 2000s after either revegetation efforts on the surrounding berms or row crop fertilization efforts. Several downgradient wells also occasionally produced low pH (<5.0) and elevated Fe (>4 mg L-1); these values were presumed to be due to periodic seasonal oxidation of the underlying Shirley Formation, which is known to be sulfidic in its upper part (Mixon et al., 1989). Tang et al. (2004) originally expressed concerns that trace metals could potentially be released and mobilized by these sediments as they oxidized and weathered after placement, but no evidence for this has been noted in over 12 yr of post-placement monitoring. More detailed information on the geologic conditions of the study area is presented in full in Daniels et al. (2007).

During summer 2001, a gently sloped, well-drained area inside of the berm in the southwest corner of the WWB (near well 47) had dewatered and cured adequately for planting winter wheat (Triticum aestivum L.) as well as the installation of an agricultural compost amendment experiment (Daniels et al., 2007). Within 1 yr after placement, the sediments had dewatered and oxidized down to a depth >50 cm (Fig. 3) and had developed a combination of coarse prismatic structure

at depth and moderate fine and medium subangular blocks in their surface Ap horizons. The surface soils were neutral pH with high levels of plant-available nutrients (Table 1). The compost

Table 3. Concentrations and screening criteria of selected organic compounds in the presented dredge materials.

Parameter

NJDEP dredge

placement criteria†

USEPA Region 3 soil screening levels‡ VA exclusion

criteria§VA clean

upland fill¶

Woodrow Wilson Bridge

(n = 4)

Earle naval weapons

station (n = 8)

Cheatham naval annex

(n = 6)

Maryland Port

Authority (n = 1)

Industrial soil

Residential soil

——————————————————————————— mg kg-1 ———————————————————————————Benzo(k)fluoranthene 0.9 29 1.5 21 0.9 0.09 <0.36 <0.06 0.09Benzo(ghi)perylene –# – – – – 0.12 <0.41 <0.05 0.16Benzo(a)pyrene 0.66 0.29 0.015 0.66 0.21 0.19 <0.37 <0.06 0.17Pentachlorophenol 6 4 0.99 9 6 <0.32 <3.18 <0.94 0.26Phenanthrene – – – – – 0.21 <1.42 <0.08 0.21Phenol 10,000 25,000 1,800 180,000 10,000 <0.09 <0.62 <1.14 <0.51Pyrene 1,700 2,300 170 17,000 1,700 0.31 <1.19 <0.10 0.34

† New Jersey Department of Environmental Protection (NJDEP) (1999).

‡ USEPA Region 3 soil screening levels have been merged into a regional document developed with input from Regions III, VI, and IX. Values from May 2014 version. Values are for Residential Soil and Industrial Soil screening levels. (USEPA, 2014)

§ The proposed Virginia exclusion standards generally represent the higher of USEPA RBC Industrial, NJDEP, or USEPA 503 EQ levels for a given parameter as available in 2008. Values exceeding these limits are questionable for acceptance. These are the values of the 2014 VA Department of Environmental Quality Virginia Pollution Abatement permit for Weanack Land LLC.

¶ Proposed Virginia clean fill criteria are based primarily on NJDEP residential cleanup criteria and manually adjusted for known issues with agricultural production/bioavailability. Values between the clean fill and exclusion criteria require a variation of the current management strategy. These are the values of the 2014 Virginia Pollution Abatement permit for Weanack Land LLLC.

# No data/exclusion criteria available for the specific parameter.

Fig. 2. Map of Woodrow Wilson Basin (WWB) and monitoring well locations. The dashed line represents the edge of a local Coastal Plain scarp that divides local groundwater low regimes. Wells to the north and east are generally upgradient, and wells to the south and west are downgradient.

Journal of Environmental Quality

application experiment was a completely randomized design with four replications and measured corn (Zea mays L.) yields in 2002 and 2003 after placement of yard waste compost over a series of loading rates (0, 56, 112, 224, and 336 Mg ha-1). The full details of the experimental design and setup are reported in Daniels et al. (2007). The plots received no additional lime or N fertilizer applications in either year, but they did receive P+K. Corn yields in 2002 were not affected by compost loading rates, but all treatment yields were significantly higher than the local (Charles City) county average (Table 4). This was despite the fact

that 2002 was a very dry year and the plots were not irrigated. In 2003, yields were lower due to substantial wildlife herbivory (Table 4) and possibly the fact that 2003 was a very wet year, and the subsoils may have been saturated. Soil wetness was also interpreted as the reason for the significantly lower yields associated with the highest compost rate in 2003. Anecdotal reports from the landowner (based on GPS yield monitor data) indicate that this field has consistently been among the highest yielding fields in the county for all years between 2004 and 2014. For example, in 2007, this basin yielded nearly double the soybean yield (5700 kg ha-1) compared with the county average for that year (2891 kg ha-1).

Development of Dredge Spoil Screening Criteria

By the mid-2000s, it was clear that the WWB dredge utilization project was highly successful and had produced a very productive postplacement landform. Subsequently, regional regulatory authorities and the dredging industry began proposing upland placement into confined utilization facilities for a wide range of potential projects. Both entities (regulators and contractors) expressed an interest in the development of a set of dredge material screening criteria that would allow more uniform determination of their suitability for conversion to agricultural soils. Thus, from 2008 onward we focused a large collective effort on developing a set of sediment screening criteria, which were based on a combination of (i) soil screening levels used by USEPA (2005, 2014) for setting cleanup levels for contaminated sites, (ii) upland dredge spoil placement criteria developed by the New Jersey Department of Environmental Protection (NJDEP, 1997), and (iii) modifications by our group to account for agronomic plant growth needs and certain agronomically nonsensical standards as discussed below. In certain instances, we also relied on USEPA 503 standards for biosolids (USEPA, 1994) to set certain limits for “clean fill.” We have used this classification system since the mid-2000s to screen over 20 dredge materials proposed for upland utilization at Weanack, and it formed the basis of a 2014 Virginia Department of Environmental Quality permit (VPA) revision, where it was formally accepted.

An example of our dredge spoil quality screening system is presented in Tables 2 and 3. The data are drawn from a full spreadsheet version that specifies a range of acceptable parameter levels for over 130 different parameters. Certain threshold values in the criteria are based on older (2004 and 2008) USEPA human health–based SSLs that were higher than current (2014) SSL values, as shown in the tables. The base document is an Excel spreadsheet that allows for entry of sample characterization data

Table 4. Corn yields from Weanack/Shirley Plantation for freshwater dredge materials receiving five wood waste compost loading rates. Limited P+K and no N fertilizer was added (details available in Daniels et al., 2007).

YearCompost treatment County average

yield†0 Mg ha-1 56 Mg ha-1 112 Mg ha-1 224 Mg ha-1 336 Mg ha-1

—————————————————————————— kg ha-1 ——————————————————————————2002 13,090a‡ 15,820a 16,100a 13,790a 14,630a 9,7302003 7,350a 7,910a 7,910a 8,190a 4,900b 9,590

† County average yields obtained from the USDA National Agricultural Statistics Service.

‡ Treatment yield levels by year followed by different letters are different at p ≤ 0.05 (F-protected LSD).

Fig. 3. Dredge soil profile from April 2002. Image was taken in April 2002 immediately adjacent to compost soil amendment experiment. The rapid oxidation front is clearly evident and extended to >70 cm. The subsoil was dominated by a coarse prismatic structure, which was inherited from the initial dewatering and consolidation collapse of the initially wet (30–40% solids) original dredge materials. The surface Ap horizon was pH 7.0, 100% base-saturated silt loam. By 2012, the depth of oxidation extended to >1.5 m. Photo by W.L. Daniels (Virginia Tech, Blacksburg, VA).

Journal of Environmental Quality

into appropriate review fields with instructions for the proposer to bold/highlight all exceedances. This system is novel in that it proposes two tiers of “acceptable materials” with different levels of permitting, management, and monitoring requirements. One of the center columns in Tables 2 and 3 lists screening levels that we apply to separate “clean fill” from material with moderate levels of contaminants. From a regulatory perspective, these materials are presumably suitable for upland use without intensive soil and groundwater monitoring requirements once the material properties have been confirmed via inbound sediment sampling and analysis. However, site placement mapping and minimum fill location requirements need to be documented for these materials. The other center column in Tables 2 and 3 contains what we consider to be “exclusion criteria” where one or more exceedances (of average or individual sample preshipping characterization values) would prevent upland utilization. Another column in Tables 2 and 3 lists the current (2014) USEPA Region 3 risk-based SSLs, which are intended for use in contaminated site cleanup. However, they are often used by state agencies and consultants as generic screening criteria for other applications. Based on our collective experience in this area since 2001, it is obvious that a number of materials that will be proposed and available for upland placement are going to fall somewhere between our “clean fill” and “exclusion” criteria as explained above. These materials should continue to be regulated via a site-specific permit with soil and water quality monitoring criteria tailored to the nature of the inbound sediments and the characteristics of the utilization site.

The various screening levels given in Table 2 were originally developed primarily from human health risk assessment protocols that may be not appropriate for the intended uses discussed here. For example, the USEPA (2014) residential site soil screening level for As is 0.67 mg kg-1 (Table 2), whereas the normal background As level in native Virginia soils is approximately 5 mg kg-1 (Smith et al., 2005). The use of this standard for screening dredge materials for use as soil materials is therefore clearly inappropriate. Similarly, the USEPA industrial SSL for Zn is 35,000 mg kg-1 because Zn is not particularly toxic when ingested or inhaled by humans at target doses. However, elevated Zn in soils, particularly when associated with sulfates, can be phytotoxic at soil pH levels <7.5 (Chaney et al., 2000; Stuczynski et al., 2007), and we therefore adjusted the Zn screening levels for our system based on agronomic and soil literature.

In addition to the conventional screening criteria presented in Tables 2 and 3, our screening protocol requires that all proposed sediments be carefully screened for acid production potential (e.g., potential acidity or acid–base accounting), soluble salts, and other properties such as texture and total organic C (TOC). It is our opinion that detection and rejection of acid-forming materials (lime demand of >5 Mg per 1000 Mg material) is the most important single criterion for evaluating dredge materials for upland use. We have also found that materials that are higher than 70% silt+clay (as described below for the Earle and Cheatham sediments) and >5% TOC may take extended periods of time to dewater, may be massive and require additional amendments, and may complicate post-placement tillage and crop management regimes.

Saline Dredge Material: Earle Naval Weapons Station

In 2005–2006, a subsequent large-scale upland application of dredge materials at Weanack placed approximately 300,000 m3 of saline dredge material from the Earle Naval Weapons Station in New Jersey. The material was analyzed before placement, and several PAHs were found to be slightly above the USEPA residential use standards (Tables 2 and 3), although, as discussed below, soluble salts were the primary concern in terms of agricultural applications. A clay-lined basin (Fig. 4) was constructed directly to the east of the Woodrow Wilson Basin in 2004 for the placement of these materials in 2005 and 2006. Details on the dewatering and chemical transformation of these highly saline sediments into normal soils are detailed by Haus (2011) and summarized here (Fig. 5). Upon initial dewatering, the solution phase of these soils was essentially that of seawater (pH 9.9; EC, 37 ds m-1) with high Na saturation. These dredge materials were very high in silt+clay (>80%) and were pumped into the basin as an ~15% solids water slurry, which led to further segregation of fines in the slack water portions of the impoundment. The dewatering process took much longer than for the WWB materials and began by the development of large (~50 cm wide) polygons of soil surrounded by deep cracks (>50 cm) and a series of irreversible flocculation steps that appeared to expel considerable amounts of Na to pore waters. By 2007, the EC in the surface 15 cm of soil had dropped to 2.5 ds m-1 with a pH of 7.0, whereas the EC of the nearby ponded surface water remained >5 ds m-1. Deep soil sampling by Haus (2011) revealed that bulk salts and Na were concentrating at depths of 1.5 to 3 m under the surface, apparently perched above the underlying compacted clay liner. Haus (2011) fully described and classified

Fig. 4. Map of Earle sediment basin. The Woodrow Wilson Basin (WWB) lies to the west, across the ephemeral drain shown running south toward Eppes Creek. Major upgradient (north and east) and downgradient (south and west) monitoring wells are shown. Well 53 has shown excursion of saline water over time.

Journal of Environmental Quality

the resultant 3-yr-old dredge soils as predominantly Typic Halaquepts and Fluventic Epiaquepts.

Before material placement, we began quarterly well monitoring (pH, EC, dissolved organic C, temperature, and water level) and annual water analyses for metals and other Safe Drinking Water Act–specified contaminants at multiple groundwater monitoring locations (Fig. 4). To date, the only

changes in external water quality have been significantly elevated EC and Cl- levels (from 2011 to 2014) in one downgradient well (well 53; Fig. 4), likely due to the fact that a section of the enclosing dike immediately north and upgradient was underlain by a former gravel roadbed that was not removed during basin and dike construction. This appeared to allow considerable migration of the saline waters under the dike and south toward well 53. No such salt migration has been noted at two other downgradient monitoring locations, however, and the gravel roadbed was removed in 2012 and the area was resealed with compacted clays.

Due to the presence of saline surface soil and waters, by 2009 only a few weedy species had begun to invade into the dry soil edges of the Earle Basin and the frequently ponded areas remained unvegetated. To facilitate the transition of this material to productive agricultural soil, a soil amendment experiment was conducted in 2009 and 2010 (Wick et al., 2011a). This study measured German millet (Setaria italica L.) yields and biomass of invasive species in plots treated with (i) a loamy topsoil cap of 20 cm, tilled (TS); (ii) 30% sand by volume tilled into the top 20 cm of the dredge material (30% sand); or (iii) no amendment, tilled (Control). The topsoil cap treatment was based on the local availability of topsoil stockpiles from older local sand mining operations, and the sand treatment was indicated as being needed by the very high initial silt+clay (>80%) content of the Earle dredge materials. These three treatments were replicated four times in a completely randomized design. Each treatment plot was split in half; one half left was as-is (noncompost), and the other half was treated with compost at a loading rate of 78.4 Mg ha-1 (dry compost). After treatment installation, all plots were seeded with German millet and treated with fertilizer (40 mg N kg-1 and 200 mg P ha-1) and lime (300 kg ha-1, 0.1% dry weight). A parallel study was conducted in the Virginia Tech greenhouse in March of 2009.

German millet and other species (invasive) were clipped from the field site in 2009 and 2010. In composted treatments in both years, there were no significant differences in millet, invasive, or total biomass among the three main treatments (Table 5). In the noncomposted treatments in both years, the 30% sand treatment produced the highest millet and total biomass but did not differ from the control treatment. After all millet was harvested, all plots were no-till drill seeded to

Fig. 5. Soil profile exposure in coarse-textured area of Earle Basin in 2008, 1 yr after final placement of materials. The differently colored layers represent coarser textured (brown) and finer textured (black) sediment layers with different levels of Fe oxidation. Surface salts are dominantly sulfates. Upon initial dewatering, the solution phase of these soils was highly saline (pH 9.9; EC, 37 ds m−1) with high Na saturations. By 2007, the electrical conductivity in the surface 15 cm of soil had dropped to 2.5 ds m−1 with a pH of 7.0. Photo by W.L. Daniels (Virginia Tech, Blacksburg, VA).

Table 5. Plant biomass for 2009 German millet (Setaria italica L.), other species (invasive), and total as well as 2010 total biomass grown on various soil amendment treatments (details available in Wick et al., 2011a).

Compost NoncompostControl 30%S† TS‡ Control 30%S TS

—————————————————————————— kg ha-1 ——————————————————————————2009

German millet 3455a§ 2751a 2547a 3276ab 4382a 1517bOther 612.3a 893.0a 828.2a 1052a 987a 1467a¶Total 4067a 3644a 3375a 4328ab 5369a¶ 2984b

2010Total 4007a 4302a 3897a§ 4121a 4319a 3364b

† Thirty percent sand by volume added to the Earle Basin dredge materials.

‡ Topsoil cap applied to the Earle Basin dredge materials.

§ Moderately significant differences (F-protected LSD; p < 0.10) are shown across treatments with different letters.

¶ Significant differences within treatment among compost/noncompost splits (p < 0.05).

Journal of Environmental Quality

winter wheat. In general, soil EC was lower in the topsoil and 30% treatments after vegetation establishment regardless of compost additions (Table 6). Overall, soil EC decreased and pH increased as plots were seeded to millet and wheat. Changes in soil pH and EC were much slower in the control treatment compared with the topsoil and 30% sand treatments. Complete results of soil chemistry and development from the field study are presented in Wick et al. (2011a).

This experiment and associated agronomic demonstrations on other areas of the Earle basin demonstrated that once soil EC drops to moderate levels, these materials can be quite productive. However, it was also obvious that appropriate weed control measures need to be taken early in the dredge material conversion process to limit competition by invasive weeds. It is also interesting to note that, similar to the work reported above for the WWB sediments, adding significant amounts of high-quality compost had little effect on either system. Thus, it would appear that such amendments are not necessary for the conversion of these materials to agricultural production.

Additional Earle Basin Studies and Site History

Since the amendment study was completed in 2011, Weanack Land LLC placed over 70,000 m3 more dredge material from the Cheatham Naval Annex in York, VA. This material was placed over the underlying Earle sediments between 2012 and 2013 (Tables 2 and 3). The material was very low in contaminants and deemed to be “clean fill,” but based on a potential peroxide acidity (Ondorff and Daniels, 2004) of 10.1 Mg agricultural lime per 1000 Mg for around 20% of the materials shipped, we advised blending agricultural lime with the material as it was placed. Rationale for this recommendation is described in below. The Cheatham materials were also high in silt+clay (>75%), followed a similar dewatering and salt+Na leaching process as the underlying Earle sediments, and successfully supported a winter wheat crop in 2013/2014 that produced 4100 kg ha-1. The high silt+clay content of these materials (Earle and Cheatham) leads to extended dewatering and consolidation times and significant surface elevation subsidence. The materials also cure initially into very large (>25 cm) blocks that are massive and structureless and therefore demand extensive tillage to allow for adequate aggregation over time.

Table 6. Soil electrical conductivity (EC) and pH for Earle Basin dredge materials receiving sand and topsoil with/without compost amendments (78 Mg ha-1) in a field experiment (details available in Wick et al., 2011a).

Treatment (date) EC pH EC pH

dS m-1 dS m-1

Compost (0–5 cm) Noncompost (0–5 cm)Preinstall (16 Apr. 2009) Control 7.67a,A† 4.59a,C 4.47a,A 4.91a,B 30%S‡ 6.18a,A 4.31a,B 6.28a,A 4.79a,A TS§ 4.73a,A 4.90a,C 3.14a,A 4.89a,CMillet (7 Sept. 2009) Control 3.36a,B 5.65b,B 3.24a,A 5.32a,B 30%S 1.32b,B 5.99ab,A 1.92b,B 5.50a,A TS 1.15b,A 6.21a,B 0.846b,B 6.25a,BWheat (22 June 2010) Control 2.74a,B 6.74ab,A¶ 2.72a,A 5.98b,A 30%S 1.62b,B 6.60b,A 2.23a,B 6.39b,A TS 0.995b,A 7.71a,A 1.35b,B 7.24a,A

Compost (5–20 cm) Noncompost (5–20 cm)Preinstall (16 Apr. 2009) Control 6.64a,A 4.77a,B 4.23a,A 5.24a,A 30%S 5.14a,A 5.42a,B 4.15a,A 5.35a,A TS 4.01a,A 5.79a,B 3.34a,A 5.25a,CMillet (7 Sept. 2009) Control 3.28a,B 5.71b,A 3.88a,A 5.17b,A 30%S 1.75b,B 5.80b,B 2.42a,A 5.36b,B TS 0.90b,B 6.34a,B 1.73a,B 6.30a,BWheat (June 2010) Control 3.49a,B 6.39b,A 3.22a,A 5.70b,A 30%S 2.07ab,B 6.59b,A 2.47a,A 6.55b,A TS 1.24b,B 7.41a,A 1.08b,B 7.07a,A

† Significant differences are shown across treatments with lowercase letters, uppercase letters indicate a change across dates within treatment. Analysis via ANOVA (p < 0.05) followed by mean separations.

‡ Thirty percent sand by volume added to the Earle Basin dredge materials.

§ Topsoil cap (15 cm) applied to the Earle Basin dredge materials.

¶ Significant differences within treatment by compost/noncompost splits. Analysis via ANOVA (p < 0.05) followed by mean separations.

Journal of Environmental Quality

In general, low levels of PAHs commonly limit the potential upland beneficial use of many sediments, particularly those from former industrial areas and shipyards. Additional studies on the mechanisms and extent of biodegradation of PAHs in contaminated sandy freshwater sediments from the nearby Appomattox River were completed in test cells adjacent to the Earle Basin by Tracey et al. (2008) and in a greenhouse environment by Haus (2011). Total PAHs dropped by more than 50% over 2 yr in both studies, but smaller decreases were noted for more recalcitrant four- and five-ring PAHs.

Management of Acid-Forming Dredge Material: Maryland Port Authority

Many dredged materials become acidic in the presence of oxygen due to the presence of sulfides in excess of neutralizing compounds (e.g., carbonates [Demas et al., 2004]). The formation of acidic materials often results in the mobilization of heavy metals and groundwater contamination (Cappuyns et al., 2006; Caille et al., 2003; Singh et al., 2000) and is highly problematic for vegetation establishment and soil formation. Therefore, it is important to identify and reject materials with significant acid-forming potentials and to develop best management practices when acid-forming dredge material cannot be avoided to minimize impacts to groundwater and maximize vegetation establishment. In 2010, Weanack received 150 m3 of dewatered acid-forming dredge material from the Maryland Port Authority Cox Creek facility. This material was selected from a wider range of dredge materials managed by Maryland Port Authority due to it being representative of a much larger volume of materials potentially available for upland utilization but also containing moderate levels of sulfides, which could be potentially limiting. Before accepting the material, it was screened for a variety of parameters (heavy metals, pesticides, organics, nutrients, potential peroxide acidity, salinity, pH, and

particle size), and certain summary properties are presented in Tables 2 and 3. Based on an H2O2 oxidation method for estimating potential acidity (Orndorff and Daniels, 2004), a liming rate of 12.5 Mg CaCO3 per 1000 Mg dredge sediment was prescribed. Two variations of liming treatments were tested against an unlimed control: (i) a layered application where lime and dredge were applied in alternating layers during placement and (ii) a bulk-blended application where lime was mixed with dredge material before placement. Three clay-lined 4.5 × 8 × 1.2 m research cells were constructed for the placement of the control, blended lime, and layered lime treatments by May 2010. Before dredge material placement, three zero-tension lysimeters were installed in each cell to collect leachate. Any leachate that was not collected in lysimeters was directed to an overflow tank to prevent uncontrolled release of leachate into groundwater. Leachate was first pumped from all nine lysimeters in July 2010 and subsequently sampled approximately monthly through 2012, after which the lysimeters were pumped approximately quarterly. Electrical conductivity and pH were measured immediately, and the remaining sample was filtered through a 0.45-µm filter. Filtered samples were treated with 6 mol L-1 HNO3 to a pH of 2.0 and analyzed for dissolved Fe and Mn. Details on monitoring and analytical methods used for this study are given in Wick et al. (2011b).

After over 4 yr of sample collection, EC decreased more than 6-fold in both the blended lime and layered lime treatments but decreased less than 4-fold in the control treatment (Fig. 6). However, the mean EC of the layered lime treatment was initially more than 3.5 mS cm-1 higher than the mean EC of the blended lime or control treatments. Moreover, by November 2011, the treatments did not significantly differ from one another within the same treatment date. The change in mean pH within the three liming treatments was more erratic than the change in EC. Mean pH in the control treatment fluctuated somewhat but overall did not change over the course of the experiment (Fig.

Fig. 6. Mean electrical conductivity (EC) of Maryland Port Authority Cox Creek leachate in the control, blended lime, and layered lime treatments. Error bars represent 1 SE above and below mean values.

Journal of Environmental Quality

7). The blended treatment initially appeared to increase pH more than the layered treatment, but 2014 samples indicated pH may have decreased again, whereas the layered treatment pH was circumneutral. However, the layered treatment pH was consistently more variable among the three lysimeters than the blended treatment.

Aside from an initial peak in the beginning of the study, Fe concentrations remained fairly constant in the control and blended lime treatments (Fig. 8). Iron concentrations in the layered lime treatment were higher than in the control and blended lime treatments, although concentrations decreased and

stabilized over the final 2 yr. In general, Mn concentrations in leachate decreased in the layered lime, blended lime, and control treatments from the beginning of the experiment (Fig. 9). The blended lime treatment produced consistently less Mn than the control and layered lime treatments. The layered lime treatment initially had the highest Mn concentrations, eventually becoming approximately equal to the control treatment.

Revegetation of these materials was difficult regardless of lime treatments. The surface of even the bulk blended lime treatment supported <20% living vegetation for 2 yr (Wick et al., 2011b) and only approached >70% in 2014. The control plots remained

Fig. 7. Mean pH of Maryland Port Authority Cox Creek leachate in the control, blended lime, and layered lime treatments. Error bars represent 1 SE above and below mean values.

Fig. 8. Mean total dissolved Fe of Maryland Port Authority Cox Creek leachate in the control, blended lime, and layered lime treatments. Error bars represent 1 SE above and below mean values.

Journal of Environmental Quality

largely unvegetated through 2014. The dark surface color of these materials coupled with their moderate to high initial EC levels apparently killed germinating seedlings and prevented invasion of local weedy species. The combined results from this experiment clearly support efforts to identify and exclude potentially acid-forming materials rather than assuming they can be adequately treated via bulk liming. Although bulk liming clearly has a positive effect on pH and metal leaching (Fe and Mn), it does not prevent it, and certain levels of groundwater contamination should be expected.

ConclusionsAlthough the studies summarized in this paper have been

performed in an agricultural environment, we contend that our results and findings are also directly applicable to the potential for utilization of similar materials in urban environments. The chemical and physical properties of the materials studied here, particularly the freshwater dredge, are very similar to those detailed by Darmody and Marlin (2002, 2008) and would be quite useful for urban soil reconstruction or brownfield redevelopment. Detailed groundwater and soil quality monitoring indicate no adverse effects from material placement and outstanding agricultural productivity for the freshwater materials. Once placed, saline materials also rapidly leach and ripen with quick declines in pH, EC, and sodicity, but potentials for negative local groundwater impacts must be considered.

Our combined experience to date indicates that the most important primary screening parameter is acid–base accounting (potential acidity or lime demand), which should become a mandatory analytical requirement. Potential acidity is much more commonly encountered in saline source dredge materials and is rarely seen in freshwater materials. High silt+clay and TOC may also limit the use of many dredge materials for physical and logistical reasons or may require much longer times for dewatering and stabilization. In summary, we believe that

a wide range of freshwater dredge materials should be actively considered and pursued for use as topsoiling materials in urban environments. Saline materials may also have some utility, but local issues with internal drainage and salt migration would need to be considered. If moderately acid-forming materials (<10 Mg lime demand per 1000 Mg) are used for soil reconstruction, their adverse properties (both soil and water quality) can be adequately and rapidly remedied via bulk-blending appropriate amounts of agricultural lime, but some elevation in soil EC and local leaching of metals should be expected.

Although many dredge materials are highly suitable for upland placement, others do contain significant contaminants, and detailed pre-dredge screening programs need to be applied that address both typical organic (e.g., PAHs) and inorganic (e.g., metals) contaminants along with more conventional agronomic parameters like EC. The dredge material screening system described here separates potential upland placement candidates into three soil quality management categories (unsuitable, suitable, and clean fill) with differing monitoring requirements. The potential for the use of dredge sediments (particularly from fresh water) for agricultural soil and urban soil reconstruction sites should not be overlooked.

AcknowledgmentsThis work was supported by Weanack Land LLC. The authors thank Charles H. Carter III for support and Charles (Chee) Saunders of Cardno for regulatory compliance reporting.

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