AUTHORS

John H. Rodgers Jr. � Department ofForestry and Natural Resources, ClemsonUniversity, Clemson, South Carolina 29634;jrodger@clemson.edu

John Rodgers received his Ph.D. from VirginiaPolytechnic Institute and State University in1977. Currently, he is a professor at ClemsonUniversity, director of the Ecotoxicology Pro-gram in the Department of Forestry and NaturalResources, and codirector of the Clemson En-vironmental Institute. His research involvesa quest for accurate risk characterizations anddevelopment of sustainable risk mitigationtactics.

James W. Castle � Department of Environ-mental Engineering and Earth Sciences,Clemson University, Clemson, South Carolina29634; jcastle@clemson.edu

Jim Castle is a professor in the Department ofEnvironmental Engineering and Earth Sciencesat Clemson University, where he conducts re-search on geological and environmental aspectsof energy resources. Prior to joining Clemsonin 1995, he worked as a geologist for CabotOil and Gas and Chevron. He received a Ph.D. ingeology from the University of Illinois.

ACKNOWLEDGEMENTS

The articles contained within the EnvironmentalGeosciences special issues on constructed wet-land treatment systems were presented, intheir entirety or in part, during a special tech-nical session at the 14th Annual Clemson Hy-drogeology Symposium, Clemson University,South Carolina, on March 30, 2006. We thankthe authors and attendees for participatingin the technical session and also thank ScottBrame for organizing an outstanding Sympo-sium. We appreciate the helpful commentsby reviewers of the manuscript.

Constructed wetland systemsfor efficient and effectivetreatment of contaminatedwaters for reuseJohn H. Rodgers Jr. and James W. Castle

ABSTRACT

Using a basic biogeochemical approach, constructed wetland treat-

ment systems (CWTSs) can be designed to renovate contaminated

waters for beneficial reuse. The purpose of this article is to present

the fundamental design strategy for CWTSs for a variety of contami-

nated waters. In designing a CWTS, the contaminants of concern

are identified in the water to be treated, and effective biogeochem-

ical pathways by which the targeted constituents can be transferred

or transformed are determined. Specific transfer processes in wet-

land cells of a CWTS include sorption, volatilization, precipitation

(and settling), and bioconcentration. Transformation processes in

the wetland cells include photolysis, hydrolysis, speciation and ioni-

zation, oxidation, reduction, and biotransformation. Physicalmodels

(pilot-scale CWTSs) are built according to the process-based design,

and their performance is measured in terms of rate and extent of

removal of targeted constituents as well as functional parameters

indicating readiness to perform. Demonstration-scale systems may

be used to provide additional site-specific data. Full-scale CWTSs

are designed for site conditions, and performance is monitored as

part of the operation and maintenance to ensure treatment. A va-

riety of contaminated waters can be treated effectively and effi-

ciently using well-designed CWTSs.

INTRODUCTION

As the limited supply of fresh waters is more intensively and ex-

tensively used, waters formerly considered wastewaters present an

opportunity for treatment by constructed wetland treatment sys-

tems (CWTSs), so thewaters can be beneficially reused or discharged

to augment receiving aquatic system flows. High costs associated

with traditional or conventional water treatment approaches have

prompted interest in the development of innovative and efficient

Environmental Geosciences, v. 15, no. 1 (March 2008), pp. 1–8 1

Copyright #2008. The American Association of Petroleum Geologists/Division of EnvironmentalGeosciences. All rights reserved.

DOI:10.1306/eg.11090707019

approaches. Volumes of contaminated waters are in-

creasing, and costs of conventional treatment methods

are escalating exponentially because of increasingly strin-

gent regulations regarding surface discharge and re-

injection under the Clean Water Act (CWA) through

the National Pollutant Discharge Elimination System

(NPDES) and SafeDrinkingWater Act throughUnder-

ground Injection Control (UIC). Development of new

approaches for treatment of contaminated waters could

turn this current liability into an asset that can be reused

for a variety of purposes.

Contaminated waters are produced from many

sources in relatively high volumes and commonly con-

tain a variety of constituents that limit discharge or re-

use of the water. Although salinity of some contam-

inated waters may be low enough to meet NPDES

discharge limits, concentrations of other constituents in

these waters may preclude discharge, prompting a need

for treatment or disposal. Constituents such as organics

and inorganics (e.g., metals and metalloids) are com-

monly of concern in these waters. Specifically designed

CWTSs have been used to treat the various constituents

independently, and research is emerging indicating the

potential of these systems for effectively and efficiently

treating waters containing complex mixtures of con-

taminants. Successful remediation of diverse waters has

been achieved with this treatment strategy including

stormwater runoff, nutrient-enriched agricultural run-

off water, flue-gas desuflurizationwater, acidmine drain-

age, municipal wastewater, and other waters contain-

ing elevated concentrations of inorganics and organics

(Cronk, 1996; Hawkins et al., 1997; Barton and Ka-

rathanasis, 1998; Knight et al., 1999; Gillespie et al.,

2000; Huddleston et al., 2005; Murray-Gulde et al.,

2005).Wetlands harbor unique reactions not occurring

in other aquatic or terrestrial systems. Constructed wet-

lands can be poised or buffered to ensure that desired

reactions (transfers and transformations) affecting the

constituents targeted for treatment proceed at predict-

able rates over long periods of time (e.g., decades). The

use of CWTSs offers several specific advantages:

1. low construction cost

2. low operational and maintenance costs

3. reliability

4. flexibility in design, so the approach is applicable to

a wide range of water quality and quantity

The purpose of this article is to present the funda-

mental design strategy for CWTSs for a variety of con-

taminated waters as an introduction to a series of ar-

ticles illustrating this approach. The specific objectives

of this article are (1) to summarize the approach for

designing, constructing, and measuring the performance

of CWTSs to effectively and consistently treat contam-

inated waters and (2) to introduce the following arti-

cles in this series on CWTSs for specific contaminated

waters.

METHODS

The approach used in these studies involves strategic

design of the CWTS for each situation and site. The

initial step is to thoroughly characterize the water to

be treated. This includes both quality and quantity (i.e.,

water balance, periodicity, etc.). This step is followed

or accompanied by identifying and confirming targeted

constituents and treatment performance goals for the

CWTS. Then, the CWTS is specifically designed based

on biogeochemistry and macrofeatures (i.e., hydrosoil,

vegetation, and hydroperiod), promoting the desired re-

actions. The design is followed by a pilot-scale study to

confirm performance and function of the constructed

systems. To provide additional data and assurances re-

garding performance at a particular site, a demonstration-

scale CWTS may be used. Subsequently, the full-scale

CWTS is assembled, and treatment performance ismoni-

tored by comparison of inflow to outflow concentrations

of targeted constituents in the water.

IDENTIFY TARGETED CONSTITUENTS ANDDETERMINE PERFORMANCE GOALS

To initiate the design of a CWTS for specific contam-

inated waters, a comprehensive analysis is conducted

for each water. Constituents measured in contaminated

waters include water chemistry parameters and mea-

surable trace inorganic (i.e., elemental analyses) and or-

ganic compounds.Water chemistry parameters typically

include pH, alkalinity, hardness, dissolved oxygen, con-

ductivity, suspended solids, biochemical oxygen demand,

and chemical oxygen demand.Data on the composition

of each contaminatedwater are obtained from chemical

analyses of water samples, published journal articles,

and review of product labels (for chemical additives,

treatment chemicals, etc.).

Constituents of concern (COC) for treatment are

identified as elements or compounds observed in a par-

ticular water at sufficient concentrations to cause signif-

icant adverse effects in receiving systems. Constituents

2 Constructed Wetland Systems for Treating Contaminated Waters

of concern may cause toxicity to testing species used

for NPDES permitting or may impair potential reuse

of the treated water (e.g., scaling, biofouling, and cor-

rosion). Constituents of concern are identified based on

physical and chemical composition (i.e., elements or

compounds), concentrations, NPDES permits, water

quality criteria, and toxicity data (published literature

or laboratory testing). When toxicity measurements

(7-day static and renewal Ceriodaphnia dubia experi-

ments) are not available from literature reviews, water

quality criteria established by the U.S. Environmental

ProtectionAgency (USEPA) can be used presumptively

to identify an element or compound as a constituent

of concern.

Reuse or discharge criteria for a specific water at a

site are regulated based on the intended use for the

treated water. Water usages can include irrigation, rec-

reation, and drinking water for human consumption.

Irrigation water standards or permitted limits of con-

taminants are established by the U.S. Department of

Agriculture. Recreational water (i.e., water quality cri-

teria) and drinking water standards are proposed by the

USEPA. Discharge permits for treated waters, estab-

lished and regulated by the NPDES (USEPA, 1991),

involve site location, total maximum daily loading lim-

its, monthly average contaminant discharge limits, and

toxicity testing requirements. The requirements for re-

use and discharge for a water at a site establish the treat-

ment performance goals.

DESIGN CONSTRUCTED WETLANDTREATMENT SYSTEM

Theoretical Basis

These CWTSs are based on biogeochemical reactions

occurring in natural wetlands that do not occur widely

in other aquatic or terrestrial systems. By manipulating

components of these treatment systems (i.e., environ-

mental conditions), contaminants can be targeted for

removal through controlled processes to decrease their

solubility and bioavailability to aquatic species. Through

transfers and transformations, specifically designed

CWTSs can alter the physicochemical and biogeochem-

ical characteristics of targeted constituents in waters.

For example, potentially toxic inorganic elements

(e.g., Cu, Zn, Hg, Se, and As) can be transferred to the

solid phase and transformed into stable solids within

the treatment systems. Organics can be retained and

chemically altered by abiotic and biodegradation pro-

cesses that can occur throughout the reactors or cells in

specifically designed constructed wetlands.

Specific transfer processes inwetland cells of aCWTS

include sorption, volatilization, precipitation (and set-

tling), and bioconcentration (Table 1). Sorption occurs

by hydrophobic chemicals (including oil, some pesti-

cides, and organometallics) adsorbing to surfaces of

plants and hydrosoil particles. Volatilization involves

the transfer of chemicals having high vapor pressure (or

low solubility), such as low-molecular-weight organics,

from the water surface to the atmosphere. Transpira-

tion can contribute to transfer of chemicals by vola-

tilization. Treatment by precipitation involves a solid

phase separating from a solution and then settling caused

by gravity. During bioconcentration, a targeted chem-

ical or compound is transferred from the aqueous phase

by plant uptake.

Transformation processes in the wetland cells in-

clude photolysis, hydrolysis, speciation and ionization,

oxidation, reduction, and biotransformation. Photoly-

sis may be either direct or indirect and occurs during

light absorption by the chemical or reactive intermedi-

ate. Hydrolysis involves the introduction of a hydroxyl

group (OH�) into a chemical structure and is com-

monly promoted by acids or bases. Treatmentmay occur

by speciation, which is the transformation to alterna-

tive forms of an element or compound (e.g., hydra-

tion). Oxidation in wetland cells can decrease aqueous

concentrations of oil and grease by the transformation

of organic molecules and can transform specific metals

to less bioavailable and less soluble species (e.g., Fe2+

to Fe3+, forming Fe2O3). During reduction, specific

targeted metals (e.g., Hg, Cu, Pb, and Zn) can be re-

moved from the aqueous phase by the formation of

sulfideminerals as sulfate is reduced, resulting in species

that are less soluble. Chlorinated organic compounds

are subject to dehalogenation during some reductive

processes. Biotransformation involves the enzyme-

catalyzed transformation of chemicals such as biode-

gradable organics.

Specific design characteristics, such as hydrosoil

composition and type of plants, are incorporated in

the CWTSs to promote conditions needed for the pre-

ferred transfers or transformations (Table 1). Because

these systems are robust, most variations of inflows

and concentrations of contaminants do not require

alterations or additions to the system during treatment.

Thus, the CWTSs must be poised to make the required

reactions possible and likely. The process-based design

ofCWTSs is based on sound biogeochemical theory and

modeling, as well as in published literature. Predictions

Rodgers and Castle 3

Table 1. Treatment Processes in Wetland Cells of CWTSs

Treatment Process Biogeochemical Conditions in CWTS

CWTS Components

Examples of Constituents RemovedHydrosoil Plants

TransfersSorption* Availability and generation of

surfaces

Low ratio of sand to clay; high

organic matter content; porous

Large mass of roots and shoots Hydrophobic chemicals (e.g., oil

and grease, some pesticides,

organometallics)

Volatilization Presence of water surface and

transpiration

Exposure to atmosphere (e.g.,

during drawdown)

Plants with high transpiration rates Chemicals with high vapor

pressure or low solubility;

low-molecular-weight organics

Precipitation, settling,

and sedimentation

Low flow rate (less than approximately

10 cm/s [4 in./s]) conducive to

settling (Stokes law)

Not applicable Flow baffles to maintain low flow

rate and prevent short-circuiting

Solids and precipitates

Bioconcentration

(plant uptake)

Prolific vegetation in contact with

the water

Favorable particle size and

nutrients to support vegetative

growth

Large mass in contact with water Hydrophobic chemicals (e.g., oil

and grease, some pesticides,

organometallics)

TransformationsPhotolysis Sunlight intensity and light absorption Not applicable Minimize shading Low-molecular-weight organics

Hydrolysis Acid, basic, or neutral environment

depending on targeted constituents

Not applicable Not applicable Pesticides

Speciation and

ionization

Presence of reactive ions or electrons

(e.g., oxidation, reduction)

Refer to oxidation and reduction

(below)

Refer to oxidation and reduction

(below)

Metals and organics

Oxidation Redox (Eh) >�50 (approximately);

pH slightly acidic to near neutral

High ratio of sand to clay; low

organic matter content

Rhizosphere aeration; large radial

oxygen loss

Organics (e.g., oil and grease);

some metals (e.g., Fe)

Reduction Redox (Eh) <�150 (approximately);

pH near neutral to slightly basic

Low ratio of sand to clay; high

organic matter content

Small radial oxygen loss; root

metabolism in anaerobic

environment

Metals (e.g., Hg, Cu, Pb, Zn);

organochloride chemicals subject

to dehalogenation

Biotransformation and

biodegradation

Presence of organisms and enzymes

capable of transforming targeted

constituents

Favorable particle size and

nutrients to support microbial

growth

Plants that support periphytic and

rhizosphere microbial growth

Biodegradable organics

*Adsorption to organic and inorganic surfaces; absorption by plants not used in these systems.

4Constructed

Wetland

Systemsfor

TreatingContam

inatedWaters

of rates, speciation, and extents of transfers and trans-

formations of COC guide the design of the pilot-scale

CWTSs. Some elements and some waters are not ame-

nable to treatment by CWTSs, and the constituents

must be treated using conventional, energy-driven meth-

ods (e.g., treatment of chloride by reverse osmosis).

Pilot Scale

Pilot-scale studies provide crucial information and im-

portant benefits such as (1) rigorous testing of hypoth-

eses embodied in replicated physical model CWTSs as

well asmeasuring performance under varied conditions;

(2) instilling confidence in potential owners regard-

ing the robust seasonal performance of these systems;

(3) ensuring regulatory approval and decreasing the

time required to obtain a permit to construct for the

full-scale system; and (4) providing refined rate coef-

ficients and extents of removal to improve full-scale

designs.

Each pilot-scale CWTS is designed and assembled

to efficiently and effectively remediate the identified

COC through chemical, physical, and biological (i.e.,

microbial) pathways by decreasing the constituents’

concentration, bioavailability, and toxicity from inflow

to outflow of the CWTS. Published literature and re-

search with the COC are used in the design process.

This information includes Eh-pH diagrams, chemical

modeling programs (e.g., MINTEQA2), complexation

reactions, solubility products, reduction-oxidation reac-

tions, and data from other pilot- and full-scale CWTSs.

Pilot-scale study provides data regarding the feasibility

of this approach for treating a site water. Results from

pilot-scale study serve to decrease uncertainties and

confirm design features for the demonstration-scale and

full-scale CWTSs.

Demonstration Scale

A demonstration-scale CWTS can be useful in chal-

lenging and novel situations where few data or minimal

experience exist. These systems are particularly useful

for site-specific information such as performance and

costs. Often, these demonstration-scale systems are de-

signed so that they can be readily converted into a part

of the full-scale CWTS if the initial experiments and

results are positive. Demonstration-scale CWTSs are

designed based on information obtained from the pilot-

scale study. They may be built either unenclosed or in

a greenhouse, depending on local conditions and treat-

ment requirements. An engineering design for the

demonstration-scale CWTS should include all facets of

construction and components required for effective treat-

ment of the site water, including individual component

description, specifications, manufacturer, and cost. A

site survey is needed early in the process. Reliable and

experienced contractors must be identified for con-

struction activities, such as site preparation, excavation,

and plumbing, as well as planting the demonstration-

scale CWTS. A permit from regulatory authorities may

be needed for construction of the demonstration-

scale CWTS, particularly if any discharge to an aquatic

system is anticipated (an NPDES permit may also be

needed). As for the pilot-scale systems, demonstration-

scale CWTSs are assembled with careful selection of

hydrosoil, vegetation, and hydroperiod. The hydrosoil

is analyzed and amended as needed to achieve the ap-

propriate redox conditions and promote plant growth.

The plats are commonly densely planted to minimize

acclimation time for the wetland. Hydroperiod condi-

tions aremanaged initially to promote rapid plant growth

and development. Flow control structures are particu-

larly important for demonstration-scale CWTSs. The

demonstration-scale system provides site-specific data

and an opportunity for more intensive and extensive

sampling (relative to the pilot-scale system).

Full Scale

Design and construction of a full-scale CWTS requires

most of the same considerations as for the pilot-scale

and demonstration-scale systems. Typically, the acclima-

tion period for a full-scale CWTS ranges from 6 months

to more than 1 yr, depending on a variety of factors

such as local climate and weather conditions, season of

construction, timing and density of planting, and regu-

lation of initial hydrologic conditions. CWTSs are de-

signed specifically for site conditions aswell as thewater

to be treated. Systems may be designed for surface flow

or, at sites where having no exposed water is preferred,

for subsurface flow (Figure 1). At some sites, coman-

agement of stormwater or other water sources may

be used with the water to be treated to adjust ionic

strength and create viable treatment conditions. Other

sites may require the use of reverse osmosis or other

techniques to deal with high-ionic-strength waters.

MONITOR TREATMENT PERFORMANCE

Performance of a CWTS can be evaluated initially by

comparing concentrations of COC in the inflow to

Rodgers and Castle 5

concentrations in the outflow. Many NPDES permits

also require toxicity testing with a sensitive sentinel

aquatic animal species, and no toxicity should be ob-

served at the instream discharge dilution or concentra-

tion. Toxicity testing can discern unanticipated conse-

quences such as antagonism or synergism that may not

be considered in parameter-specific discharge limits from

the NPDES permit.

Treatment performance monitoring may also

involve sampling to determine the readiness of the

CWTS to perform. These measurements may include

parameters such as sediment redox, organic matter

content, and acid-volatile sulfide production, as well

as plant density to assess both the biogeochemical

conditions and plant health and vigor within the

system. Redox (reduction-oxidation potential), which

is a measure of the ability to donate or accept electrons,

strongly influences biogeochemical reactions occurring

within the wetland. Assessment of treatment perfor-

mance over time may also include functional measure-

ments as indicators of how the CWTS is performing

(versus if the CWTS is performing). Other measure-

ments of treatment performance may include costs or

economic benefits relative to conventional treatment or

emerging advances in treatment technology.

DISCUSSION: CASE STUDIES

Articles in this special issue of Environmental Geosci-ences and in a second special issue to follow illustrate the

biogeochemical approach for designing and constructing

Figure 1. Design profiles for cells of CWTSs: (A) surface-flow CWTS; (B) subsurface-flow CWTS. Components (hydrosoil, vegetation,and hydroperiod) are selected to produce conditions that promote specific biogeochemical treatment processes (Table 1). Hydrosoil(planting medium) contains sand, clay, and organic matter, with proportions dependent on desired conditions. Examples of vegetationinclude Schoenoplectus californicus (bulrush) when reducing conditions are needed and Typha latifolia (cattail) to promote oxidizingconditions. Hydroperiod is managed initially for rapid plant growth and then to sustain treatment performance. The length of wetlandcells in typical full-scale CWTSs ranges from a few to more than 100 m (330 ft).

6 Constructed Wetland Systems for Treating Contaminated Waters

wetland treatment systems for divergent contaminated

waters. Our article provides the theoretical basis for

design, construction, and treatment performance of the

systems and presents an overview of CWTSs. The fol-

lowing articles present case studies of CWTSs for treat-

ing various types of water. The second article in this issue

by Huddleston et al. (Design of a Constructed Wetland

System for Treatment of Copper-Contaminated Waste-

water) illustrates the use of a pilot-scale study to design

a full-scale system for treating copper-contaminated

water. The pilot-scale CWTS incorporated theoretical

design into a physical system that could be used tomake

performance measurements. It demonstrates the value

of a pilot-scale study to discern removal rate coefficients

as well as the expected extent of removal of the targeted

constituent.

Results from the pilot-scale study by Huddleston

et al. were applied to designing a full-scale CWTS, as

discussed by Murray-Gulde et al. in the third article

(Evaluating Performance of a Constructed Wetland

Treatment SystemDesigned to Decrease Bioavailable

Copper in aWaste Stream). The full-scale system, con-

structed at the Savannah River Site in South Carolina,

incorporates internal thermodynamic processes and

design criteria for decreasing copper in industrial pro-

cess water and stormwater runoff. Initial performance

data presented byMurray-Gulde et al. demonstrate the

effectiveness of the CWTS design in removing copper

from the water column and in removing toxicity asso-

ciated with the bioavailable fraction of copper.

The fourth article, by Nelson and Gladden (Full-

Scale Treatment Wetlands for Metal Removal from

Industrial Wastewater), addresses long-term operation

and performance of the CWTS constructed at the Sa-

vannah River Site and discussed in the article byMurray-

Gulde et al. Nelson and Gladden present results of mon-

itoring the CWTS for the reduction in concentrations

of metals, including copper and mercury, and illustrate

the system’s success inmeeting regulatory requirements.

Their results demonstrate the stability of thermody-

namic processes in the CWTS and sustained perfor-

mance of the system.

A second special issue of Environmental Geosci-ences will include two articles on CWTSs for treating

natural-gas storage-produced waters and two articles

on CWTSs for flue-gas desulfurization (FGD) waters.

The first article, by Johnson et al. (Feasibility of a Con-

structed Wetland Treatment System for Simulated

Natural-Gas Storage-Produced Waters), illustrates the

application of CWTSs to treatment of waters produced

fromnatural-gas storage fields. A pilot-scale CWTSwas

designed and constructed based on characteristics of gas-

storage–produced waters and on desired biogeochem-

ical processes for treatment. Treatment effectiveness of

the system was demonstrated by measuring perfor-

mance in terms of decreased concentrations of targeted

constituents and decreased toxicity. Many of the results

presented by Johnson et al. are applicable not only to

the wide diversity of gas-storage–produced waters, but

also to other types of oil- and gas-produced waters.

The second of two articles on treating natural-gas

storage-produced waters by Kanagy et al. (Hydrosoil

Conditions in a Pilot-Scale ConstructedWetland Treat-

ment System for Natural-Gas Storage-Produced Wa-

ters) illustrates the function of hydrosoil characteristics

in treatment using the pilot-scale CWTS built for gas-

storage–produced waters and discussed by Johnson et

al. Wetland reactors were designed to promote specific

biogeochemical reactions for transfer or transforma-

tion of metals from the water column. As reactors ac-

climated following construction, hydrosoil conditions

developed that promoted the desired reactions, which

resulted in the successful treatment of simulated pro-

duced waters. Results confirm that the hydrosoil of

CWTSs can be designed to achieve specific conditions

and functions.

The third article in the second special issue by Eggert

et al. (Performance of Pilot-Scale Constructed Wetland

Treatment Systems for Flue Gas Desulfurization Wa-

ters) illustrates the application of constructed wetland

systems for treating FGDwaters. Performance data from

a pilot-scale CWTS designed specifically for FGD wa-

ters demonstrate the effective treatment and provide

parameters for designing full-scale systems for onsite

treatment of waters produced by FGD at coal-fired

power plants. These data also illustrate the diversity of

FGD waters as well as the robust nature of the CWTS

design in accommodating this diversity.

The final article by Mooney and Murray-Gulde

(Constructed TreatmentWetlands for Flue-Gas Desul-

furizationWaters: Full-ScaleDesign,Construction, and

Performance) integrates engineering considerations

in building a full-scale CWTS with results from a case

study of an operating system. Performance data from

the case study demonstrate that the full-scale system

can achieve a decrease inmercury and selenium concen-

trations to targeted levels and provide NPDES compli-

ance. The article illustrates that advantages (including

lower cost) over conventional treatment can be realized

by incorporating appropriate design parameters, such

as those developed from pilot-scale studies, into build-

ing a full-scale CWTS.

Rodgers and Castle 7

CONCLUSIONS

The design strategy that we have presented represents

a novel approach for renovating contaminated waters

from a variety of sites. Based on fundamental biogeo-

chemistry, the primary goal is to convert COCs to less

bioavailable and less toxic forms commonly sequester-

ing them in sediments. The approach is to design the

system for a specific site using sequential steps that pro-

vide information leading to effective and efficient treat-

ment. Performance monitoring includes goals for reuse

or discharge of treated water as well as for function of

the system.

The case studies presented in this special issue of

Environmental Geosciences and in a following special

issue illustrate unique designs for the waters and the

sites and follow the sequential design strategy. The wa-

ters in these case studies range from industrial and storm-

water at the Savannah River Site to energy-related pro-

duced waters. Produced waters encompass those derived

from extraction of fossil fuels as well as waters from

thermoelectric power generation. Constituents targeted

for treatment in these waters are chlorides, metals, met-

alloids, and organics. The diversity in composition and

concentrations of targeted constituents, as well as differ-

ences among sites, prompt flexibility in designs. Spe-

cific designs for the diverse waters were developed and

assessed in pilot-scale studies (articles by Huddleston

et al., Johnson et al., Kanagy et al., and Eggert et al.).

Full-scale systems based on these specific designs are

providing data that demonstrate long-term performance

contributing to regulatory acceptance and cost benefits

(articles by Nelson and Gladden, Murray-Gulde et al.,

Mooney and Murray-Gulde).

REFERENCES CITED

Barton, C. D., and A. D. Karathanasis, 1998, Aerobic and anaerobicmetal attenuation processes in a constructed wetland treating acidmine drainage: Environmental Geosciences, v. 5, p. 43–56.

Cronk, J. K., 1996, Constructed wetlands to treat wastewater fromdairy and swine operations: A review: Agriculture, Ecosystemsand Environment, v. 58, p. 97–114.

Gillespie, W. B. Jr., W. B. Hawkins, J. H. Rodgers Jr., M. L. Cano,and P. B. Dorn, 2000, Transfers and transformations of zinc inconstructed wetlands: Mitigation of a refinery effluent: Ecologi-cal Engineering, v. 14, p. 279–292.

Hawkins, W. B., J. H. Rodgers Jr., W. B. Gillespie Jr., A. W. Dunn,P. B. Dorn, and M. L. Cano, 1997, Design and construction ofwetlands for aqueous transfers and transformations of selectedmetals: Ecotoxicology and Environmental Safety, v. 36, p. 238–248.

Huddleston, G. M. III, J. H. Rodgers Jr., C. Murray-Gulde, and F. D.Mooney, 2005, Designing constructed wetlands for mitigatingrisks from flue gas desulfurization wastewater, in K. J. Hatcher,ed., Proceedings of the 2005 Georgia Water Resources Confer-ence, April 25–27, Athens, Georgia.

Knight, R. L., R. H. Kadlec, and H. M. Ohlendorf, 1999, The use oftreatment wetlands for petroleum industry effluents: Environ-mental Science and Technology, v. 33, p. 973–980.

Murray-Gulde, C. L., G. M. Huddleston III, K. V. Garber, and J. H.Rodgers Jr., 2005, Contributions of Schoenoplectus californicusin a constructed wetland system receiving copper contaminatedwastewater: Water, Air, and Soil Pollution, v. 163, p. 355–378.

USEPA, 1991, Technical support document for water quality-basedtoxics control: U.S. Environmental Protection Agency, EPA/505/2-90-001, 335 p.

8 Constructed Wetland Systems for Treating Contaminated Waters