United States Department of The Army EPA-823-B-98-O04

Environmental Protection US Army Corps of Engineers Februa~ 1998

Agency

Office of Water (4305)

?zEPA Evaluation of Dredged Material

[m]

I I Proposed For Discharge in II-II

Waters of the U.S. - Testing U.S. Army Corps

of Engin-rs Manual

Inland Testing Manual
EVALUATION OF DREDGED MATERIAL

PROPOSED FOR DISCHARGE IN WATERS OF THE U.S. - TESTING MANUAL

(INLAND TESTING MANUAL)

Prepared by

ENVIRONMENTAL PROTECTION AGENCY

OffIce of Water

Office of Science and Technology

Washington, D.C.

and

DEPARTMENT OF THE ARMY

United States Army Corps of Engineers

Operations, Construction, and Readiness Division

Washington, D.C.

February 1998
APPENDIX B

GUIDANCE FOR EVALUATION

OF EFFLUENT DISCHARGES

FROM CONFINED DISPOSAL

FACILITIES
i

TABLE OF CONTENTS

Page No.

Table of Contents i

List of Tables iii

List of Figures iv

APPENDIX B - GUIDANCE FOR EVALUATION OF EFFLUENT DISCHARGES

FROM CONFINED DISPOSAL FACILITIES . . . . . . . . . . . . . . . . . B-1

B1.0 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1

B1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1

B1.2 Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-3

B1.3 Regulatory Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-3

B1.4 Applicability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-4

B1.4.1 Hydraulic Filling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-4

B1.4.2 Flow Through Dikes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-4

B1.4.3 Mechanical Filling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-5

B1.4.4 Surface Runoff and Leachate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-5

B2.0 OVERVIEW OF EVALUATIONS FOR EFFLUENT DISCHARGES . . . . . . B-5

B2.1 Water Quality Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-6

B2.2 Mixing Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-6

B2.3 Basis of Evaluations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-6

B2.4 Contaminant Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-7

B2.5 Tiered Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-7

B2.6 Tier II: Water Quality Evaluations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-9

B2.6.1 Screen Relative to WQS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-9

B2.6.2 Testing for Evaluation of Effluent Water Quality . . . . . . . . . . . . . . . . . . . . . B-9

B2.7 Tier III: Toxicity Evaluations .................................. B-10

B3.0 TESTING PROCEDURES FOR EFFLUENT DISCHARGES ........... B-11

B3.1 Data Requirements .......................................... B-11

B3.1.1 Disposal Area Design ......................................... B-12

B3.1.2 Sampling Requirements ....................................... B-12

B3.2 Column Settling Tests ........................................ B-12

B3.2.1 Apparatus ................................................. B-14

B3.2.2 Test Procedure ............................................. B-14

B3.2.3 Data Analysis .............................................. B-18

B3.2.4 Determination of Effluent Suspended Solids Concentration ............. B-21

B3.2.5 Determination of Field Mean Retention Time ....................... B-22

B3.3 Effluent Elutriate Test Procedure ................................ B-23

B3.3.1 Apparatus ................................................. B-23

B3.3.2 Test Procedure ............................................. B-24
ii

B3.3.3 Chemical Analyses ........................................... B-26

B3.3.4 Dissolved Concentrations of Contaminants ......................... B-26

B3.4 Water Column Toxicity Test Procedure ........................... B-26

B3.4.1 Apparatus ................................................. B-26

B3.4.2 Test Procedure ............................................. B-27

B4.0 EXAMPLE CALCULATIONS .................................. B-28

B4.1 Example 1: Evaluation of Effluent Water Quality For an Existing

Disposal Area .............................................. B-28

B4.1.1 Project Information .......................................... B-28

B4.1.2 Effluent Elutriate Testing ...................................... B-29

B4.1.3 Column Settling Tests ........................................ B-30

B4.1.4 Prediction of Effluent Suspended Solids Concentration ................ B-31

B4.1.5 Prediction of Contaminant Concentrations ......................... B-31

B4.2 Example 2: Determination of Disposal Area Requirements to Meet a

Given Effluent Quality Standard ................................ B-31

B4.2.1 Project Information .......................................... B-31

B4.2.2 Column Settling Tests ........................................ B-32

B4.2.3 Determination of Allowed Effluent Suspended Solids Concentration ...... B-32

B4.2.4 Determination of Ponded Volume and Surface Area .................. B-33

B5.0 REFERENCES ............................................. B-35
iii

LIST OF TABLES

Page No.

Table B1. Summary of Data Requirements for Prediction of the Quality of Effluent from

Confined Dredged Material Disposal Areas. B-13

Table B2. Observed Flocculent Settling Data. B-19

Table B3. Percentage of Initial Concentration and Suspended Solids Concentrations vs.

Time, Assumed Depth of Influence of 2 ft. B-20

Table B4. Recommended Resuspension Factors for Various Ponded Areas and Depths. B-22
iv

LIST OF FIGURES

Page No.

Figure B1. Schematic of Supernatant Water Interaction in an Active Confined Disposal

Facility. B-2

Figure B2. Flowchart Illustrating Approach for Evaluating Potential Effluent Impacts from

Confined Dredged Material Disposal Areas. B-8

Figure B3a. Specifications for Settling Column and Plan for Sedimentation Column. B-15

Figure B3b. Plans for Top and Bottom Columns. B-16

Figure B4. Concentration Profile Diagram. B-19

Figure B5. Plot of Supernatant Suspended Solids Concentration vs. Time from Column

Settling Tests. B-20
B-1

APPENDIX B - GUIDANCE FOR EVALUATION OF EFFLUENT DISCHARGES FROM

CONFINED DISPOSAL FACILITIES

B1.0 INTRODUCTION

B1.1 Background

Dredged material may be placed in diked disposal areas sometimes called confined disposal facilities

(CDFs). CDFs may be considered as an alternative for contaminated dredged material that is

unsuitable for disposal in open water. Possible contaminant migration pathways for confined disposal

facilities include effluent discharges to surface water during filling operations, surface runoff due to

precipitation, leachate into groundwater, volatilization to the atmosphere, and direct uptake by plants

and animals. Subsequent cycling through food webs to animal populations living in close association

with the dredged material should also be considered. Each pathway may have its own standards and

criteria defined by the water quality certification or other applicable laws and regulations. If standards

or criteria are not met, management options may be considered including operational modifications,

treatment or containment options such as covers or liners.

This appendix provides technical guidance for evaluation of the effluent pathway. Guidance for

evaluation of other pathways and for management actions and control measures for CDFs is found in

USACE/EPA (1992).

Dredged material may be placed in CDFs in several ways. The most common method of filling is by

direct hydraulic pipeline from cutterhead dredges. Pumpout operations from hopper dredges or

hydraulic reslurry from barges results in intermittent hydraulic filling. Direct mechanical placement of

dredged material from barges (or possibly from trucks) can be done with equipment located at the

CDF. All of these operations result in some sort of effluent discharge, defined for purposes of this

manual as that material discharged directly to receiving waters during the filling operation (this would

include water discharged directly over weir structures or through filter cells or retaining dikes).

A schematic of an active hydraulically filled CDF is shown in Figure B1. Dredged material hydraulically placed in a confined disposal area settles, resulting in a thickened deposit of material overlaid

by a clarified supernatant. The supernatant waters are discharged from the site as effluent during

active dredging operations. The effluent may contain both dissolved contaminants and suspended

solids.
B-2

Figure B1. Schematic of Supernatant Water Interaction in an Active Confined Disposal Facility.

Supernatant waters from confined disposal sites are discharged after a retention time of up to several

days. Furthermore, actual withdrawal of the supernatant is governed by the hydraulic characteristics of

the ponded area and the discharge weir. Several factors influence the concentration of suspended

particles present in supernatant waters. Fine particles become suspended in the disposal area water

column at the point of entry due to turbulence and mixing. The suspended particles are partially

removed from the water column by sedimentation. However, particle concentrations may be maintained by flow of water through the slurry mass during settling. Wind and/or surface wave action may

also resuspend additional particles.
B-3

B1.2 Purpose and Scope

The purpose of this appendix is to describe procedures for evaluation of effluent discharges from

CDFs. The procedures provide an estimation of potential contaminant release and/or biological effect

under laboratory-simulated confined disposal conditions and consider the sedimentation behavior of

dredged material, the retention time of the proposed containment area, and the physicochemical environment in ponded water during active disposal into the containment area.

B1.3 Regulatory Considerations

The quality of effluent discharged from these sites is an environmental concern and is regulated as a

discharge under Section 404 of the Clean Water Act. In addition, Section 401 provides the States a

certification role as to project compliance with applicable State water quality standards; effluent

standards may be set as a condition of the certification.

The discharge of effluent from a CDF is defined as a dredged material discharge in 33 CFR

323.2 (d):

...the term "discharge of dredged material" means any addition of dredged material

into, including any redeposit of dredged material within, the waters of the United

States. The term includes, but is not limited to, the following: ...the runoff or

overflow from a contained land or water disposal area...

Nationwide general permit 16 (33 CFR 330, Appendix A, part B (16)) authorizes the return water

from an upland, contained dredged material disposal area, where the quality of the return water is

controlled by the State through Section 401 Certification procedures. For all non-upland CDFs, and

for all CDFs in which contaminated sediments may be discharged, an evaluation of potential

contaminant impacts of the discharge will be necessary.

General permits are not intended to apply to projects involving the dredging or the discharge of

contaminated material. In addition, Section 230.10 (c)(1) of the Guidelines states that no discharge of

dredged material shall be permitted which will result in significant adverse impacts on municipal

water supplies. Section 230.50 (a) defines municipal water supplies as surface or groundwater

directed to the intake of any municipal or private water supply system. Therefore, the potential

impacts of leachate into groundwater must also be considered.

There are three types of general permits issued by the USACE, nationwide permits, regional general

permits and programmatic general permits. Nationwide permits are issued by the Chief of Engineers
B-4

and apply nationwide. Regional permits are issued by district and division engineers and are

applicable on district or State-wide basis. Programmatic permits are issued (by the Chief of

Engineers, as well as district and division engineers) to other federal, State or local agencies with the

intention of providing the appropriate level of environmental protection and avoiding unnecessary

duplication of effort with the agency regulatory activities at issue.

There are currently four nationwide permits that pertain to dredging and the discharge of dredged

material. One authorizes the discharge and return water from confined disposal areas (provided the

associated dredging is authorized pursuant to Section 10 of the River and Harbor Act of 1899); two

other nationwide permits authorize the dredging and discharge, respectively, of up to 25 cubic yards

of material; and a fourth authorizes maintenance dredging of existing marina basins (provided that

the dredged material is deposited on uplands; return water from a confined disposal area requires

separate authorization pursuant to section 404 of the Clean Water Act). As stated in the preamble to

the nationwide permit regulations (FR56, 226, November 22, 1991), the USACE depends on its

districts’ knowledge of potentially contaminated areas and on the discretionary authority of district

and division engineers to develop special conditions and/or require individual permits where

contaminated sediments are present. General permits are not intended to apply to projects involving

the dredging or the discharge of contaminated materials.

B1.4 Applicability

B1.4.1 Hydraulic Filling

The techniques for evaluation of effluent discharges described in this appendix are specifically

designed for the case of hydraulic placement of material into CDFs with the effluent discharge

occurring from an outlet pipe or weir structure or structures. Hydraulic placement can be in the form

of direct pipeline inflow from cutterhead or similar hydraulic suction dredges, intermittent hydraulic

placement from hopper dredge pumpout operations, or intermittent hydraulic placement by reslurrying

material from barges (which may have been filled by mechanical dredges). Such placement

operations would normally have an effluent discharge flowrate roughly equal to that of the inflow.

B1.4.2 Flow Through Dikes

Some CDFs may be designed to allow flow of effluent water through filter cells or permeable dike

sections. The techniques described in this appendix may be applied to this case, but the influence of

the filter media in adsorption of contaminants from the effluent discharge should be considered

(Krizek et al., 1976).
B-5

B1.4.3 Mechanical Filling

Dredged material may be placed in some CDFs by direct mechanical means such as rehandling from

barges or by truck. Although such filling operations normally involve handling relatively little free

water, there may still be an effluent discharge. Also, there may be ponded water in the CDF before

filling begins, especially for CDFs constructed in water. For the case of mechanical filling, the

effluent discharge involves the free water which is released during the mechanical placement

operation or the existing pond water which is displaced by the operation. No laboratory-developed

and field-verified techniques now exist for the case of direct mechanical placement of materials in

CDFs, however the procedures described here may be used in the interim for the case of mechanical

placement and are considered conservative for such evaluations.

B1.4.4 Surface Runoff and Leachate

Long-term geochemical changes may occur following disposal, site dewatering, and subsequent

drying of the dredged material. The quality of the surface runoff or leachate to surface water or

groundwater from disposal sites after these long-term changes occur may be markedly different from

that of the effluent discharged during active disposal. The techniques described in this appendix

apply only to conditions during active filling of the site and do not account for long-term

geochemical changes. Therefore, they should not be used to evaluate the quality of surface runoff or

leachate. In accordance with 33 CFR 336.1 (b)(8) and Corps Regulatory Guidance Letter 87-8, the

technical procedures contained in USACE/EPA (1992) should be used as a guide for developing the

appropriate tests and evaluating surface runoff and leachate and possible management options.

B2.0 OVERVIEW OF EVALUATIONS FOR EFFLUENT DISCHARGES

The discharge of effluent from CDFs has the potential for water column effects only. Any solids in

the effluent would be dispersed and mixed. Because CDFs are designed to retain virtually all of the

solid fraction of dredged material, the evaluation of benthic effects is usually not applicable.

The evaluation of water column effects resulting from effluent discharges uses a tiered approach

generally patterned after that for discharges of material into open water. General guidance in the

main body of this manual [pertaining to Tier I evaluations (Sections 4.0 and 4.1), selection of

contaminants of concern (Section 4.2), sample collection and preservation (Section 8), analytical

procedures (Section 9) and general procedures for toxicity tests (Section 10)] is applicable for

evaluation of effluent discharges.
B-6

B2.1 Water Quality Standards

Section 401 of the CWA requires that all Federal permits and licenses, including those for effluent or

other discharges into waters of the United States, authorized pursuant to Section 404 of the CWA,

must be certified as complying with applicable State water quality standards (WQS). Violations of

any applicable State water quality standard apply at the edge of a State designated mixing zone.

The process for adoption of State WQS is prescribed at 40 CFR 131. States must issue, condition,

deny, or waive a Water Quality Certification for activities permitted or conducted by USACE,

certifying that no adverse water quality impacts will occur based on determinations of compliance

with applicable State WQS which have been adopted in accordance with the above regulation. State

water quality standards consist of designated uses, narrative and numeric criteria designed to support

those uses, and anti-degradation provisions.

B2.2 Mixing Zones

The evaluation of effluent discharges must consider the effects of mixing and dispersion.

Section 230.3(m) of the Guidelines defines the mixing zone:

The term "mixing zone" means a limited volume of water serving as a zone of initial

dilution in the immediate vicinity of a discharge point where receiving water quality

may not meet quality standards or other requirements otherwise applicable to the

receiving water. The mixing zone should be considered as a place where wastes and

water mix and not as a place where effluents are treated.

Mixing zones are normally defined by the State regulatory agency as part of the 401 water quality

certification. Detailed procedures for evaluation of mixing zones for CDF discharges are found in

Appendix C.

B2.3 Basis of Evaluations

Chemical analyses are performed for contaminants that may be released from dredged material placed

in CDFs and the results are compared to water quality standards for these contaminants after

allowance for mixing. This provides an indirect evaluation of potential biological impacts. If water

quality standards are met for all contaminants of concern, the material discharged as effluent in the

water column may also be evaluated for toxicity after mixing. Toxicity tests provide information on

the toxicity of contaminants not included in the water quality standards, and indicate possible
B-7

interactive effects of multiple contaminants. Bioaccumulation from the material discharged as

effluent in the water column is typically considered to be of minor concern due to the short exposure

time and low exposure concentrations resulting from rapid dispersion and dilution.

B2.4 Contaminant Controls

If the testing and associated analysis of the effluent pathway indicates applicable water quality

standards will not be met after consideration of mixing, appropriate contaminant controls may be

considered to reduce impacts to acceptable levels. Controls for effluent may include modification of

the operation (e.g., use of a smaller dredge with reduced inflow rate, providing increased ponded area

and depth of the CDF, or relocation of the inflow and effluent discharge points), or treatment of

effluent to remove contaminants. Additional information on contaminant controls is found in

USACE/EPA (1992).

B2.5 Tiered Approach

The tiered approach for evaluation of water column effects for effluent discharges from CDFs is

generally patterned after that for discharges of material into open water (Section 3.1). The Tier I

evaluations should be conducted as described in Section 4.0. Procedures in this appendix for

evaluation of effluent discharges are performed in Tiers II and III. A flowchart illustrating the

approach for evaluating potential effluent impact is shown in Figure B2. Detailed descriptions of the

test procedures are given in Section B3.0. Tier IV evaluations for effluent discharges, if deemed

required, would be performed considering the guidance in Section 11.3.

Tier II evaluations for effluent discharges consist of determinations of a screen relative to WQS

compliance and perhaps conduct of additional water column testing. Water column testing should be

conducted only if shown by the evaluation to be necessary. Water column impacts are evaluated (if

necessary) by comparison of applicable water quality standards to the contaminant concentrations in

the effluent discharge after consideration of mixing. Water column impact must also be evaluated by

toxicity testing in Tier III when there are contaminants of concern for which applicable WQS are not

available or where interactive effects are of concern.
B-8

Figure B2. Flowchart Illustrating Approach for Evaluating Potential Effluent Impacts from

Confined Dredged Material Disposal Areas.
B-9

B2.6 Tier II: Water Quality Evaluations

B2.6.1 Screen Relative to WQS

The screen relative to WQS determines the need for additional testing by considering the bulk

concentration of contaminants in the dredged material, the mixing at the disposal site, and applicable

water quality standards. If the need for additional testing is not demonstrated, the effluent discharge

complies with WQS. If additional testing is needed, it is conducted according to the guidance in

Section B3.0 as appropriate.

The screen involves a determination of whether the water quality standards, after consideration of

mixing, would be met if the bulk concentration of contaminants present in the sediment were to be

completely dissolved in the inflow water flowing into the CDF and discharged as effluent from the

disposal site.

The contaminant that would require the greatest dilution is determined by calculating the dilution that

would be required to meet the applicable water quality standard. To determine the dilution (D) the

following equation is solved for each contaminant of concern:

D = [(Cs x SS/1000) — Cwq]/(Cwq — Cds)

where Cs = concentration of the contaminant in the dredged material expressed as

micrograms per kilogram (μg/Kg), on a dry weight basis;

SS = suspended solids concentration in the CDF inflow expressed as grams

per liter (g/L);

1000 = conversion factor, g to Kg;

Cwq = WQS in micrograms per liter (μg/L); and

Cds = background concentration of the contaminant at the disposal site in

micrograms per liter (μg/L).

The mixing zone evaluation is then made for the contaminant that would require the greatest dilution.

If the concentration after mixing is below the applicable water quality standard, the effluent discharge

complies with WQS. If this concentration exceeds the applicable water quality standard, additional

testing must be conducted according to the guidance in Sections B2.6.2 and B3.0.

B2.6.2 Testing for Evaluation of Effluent Water Quality

The Tier II water column evaluation considers concentrations of contaminants of concern released

from the dredged material (in contrast to bulk concentrations used in Section B2.6.1), after allowance
B-10

for initial mixing, compared with applicable water quality standards. The evaluation therefore

requires a prediction of the CDF effluent quality.

The prediction of the quality of effluent from CDFs must account for the dissolved concentration of

contaminants. An effluent elutriate procedure has been developed for this purpose (Palermo, 1986,

1988; Palermo and Thackston, 1988a and b). This test defines dissolved concentrations of contaminants in milligrams per liter, and considers the geochemical changes occurring in the disposal area

during active disposal operations. Refinements and extensions of column settling test procedures

(Averett et al., 1988; Montgomery et al., 1983; and Palermo and Thackston, 1988c) have also been

developed to define the concentration of SS in the effluent for a given operational condition (i.e.,

ponded area and depth, inflow rate, and hydraulic efficiency). The column test results can be used to

evaluate the turbidity of the effluent if a relationship between TSS and turbidity is defined for the

sediment under consideration.

Predicted contaminant concentrations based on the results of a effluent elutriate test can be used with

applicable water quality standards to determine if the discharge is in compliance with the standards

after consideration of mixing. To determine the dilution (D) required to meet the standards, the

following equation is solved for each contaminant of concern:

D = (Cee - Cwq)/(Cwq - Cds)

where Cee = concentration of the dissolved contaminant in the effluent elutriate in

micrograms per liter (μg/L). All other terms are as previously defined in

Section B2.6.1.

The mixing zone evaluation is then made for the contaminant that would require the greatest dilution.

If the concentration after mixing is below the applicable water quality standard, the discharge

complies with WQS. Otherwise, it does not.

B2.7 Tier III: Toxicity Evaluations

Tier III testing assesses the impacts of contaminants in the dredged material on appropriate sensitive

organisms to determine if there is potential for the dredged material to have an unacceptable adverse

impact. The Tier III assessment methods are toxicity tests, which use lethality as the primary

endpoint because the importance of this endpoint is easily interpreted. These acute tests use

organisms representative of the water column at the disposal site. The recommended procedures for

water column toxicity tests for evaluation of effluent discharges are conducted in generally the same

manner as those for discharges of material into open water (Section 11.1). The only exception is that

the toxicity test medium is prepared using an effluent elutriate procedure.
B-11

The results of the water column toxicity tests must be interpreted considering the effects of mixing.

If the concentration of dissolved plus suspended contaminants, after allowance for mixing, does not

exceed 0.01 of the toxic (LC50 or EC50) concentration beyond the boundaries of the mixing zone,

the discharge is predicted not to be acutely toxic to water column organisms. If the concentration of

dissolved plus suspended contaminants, after allowance for mixing, exceeds 0.01 of the toxic

concentration, the discharge is predicted to be acutely toxic to water column organisms.

B3.0 TESTING PROCEDURES FOR EFFLUENT DISCHARGES

This section describes the data requirements, testing procedures, and evaluation techniques necessary

to predict effluent contaminant concentrations for the Tier II evaluation and to conduct water column

toxicity tests for the Tier III evaluation. Example calculations are presented as appropriate.

The predictive techniques can be applied to evaluate the performance of existing sites and to design

new sites. For existing sites, the technique can be used to predict the effluent quality for a given set

of anticipated operational conditions (known flow and containment area size). In a similar manner,

the required operational conditions for a new site (size, geometry, maximum allowable dredge size,

etc.) can be determined to meet a given effluent quality requirement by comparing the predicted

effluent quality for a variety of assumed operational conditions. In either case evaluation of effluent

quality must be considered in conjunction with a sound design of the CDF for retention of suspended

solids and initial storage of the sediments to be dredged.

B3.1 Data Requirements

Data requirements for prediction of effluent quality and effluent TSS include those pertaining to

operational considerations (i.e., CDF site characteristics and dredge characteristics) and those

pertaining to the properties of the dredged material (i.e., contaminant release characteristics and

sedimentation characteristics). Data relating to operational considerations are usually determined by

the disposal area design and by past experience in dredging and disposal activities for the project

under consideration or for similar projects. Data relating to the dredged material characteristics must

be obtained by sampling the sediments to be dredged and testing them. A summary of the data

requirements for effluent quality prediction is given in Table B1.
B-12

B3.1.1 Disposal Area Design

When the quality of the effluent from a CDF is of concern, the design, operation, and management of

the site should be carefully controlled. This includes aspects relating to both the volume required for

effective sedimentation and the storage capacity of the site. Procedures for such evaluations are

presented in Engineer Manual 1110-2-5027 (USACE, 1987), and should be considered prior to the

prediction of the quality of the effluent for the project. These design procedures will determine the

surface area and ponding depth required to achieve effective sedimentation, the required containment

volume for storage (including required freeboard), and the proper sizing of weir structures. The

prediction of the quality of the effluent described in this appendix is an extension and refinement of

the design procedures. A list of data items required from the design evaluation is shown in Table B1.

The process described in Section 4.2 should identify which contaminants are of concern and which

therefore should be considered for subsequent analysis in the effluent elutriate testing. The effluent

elutriate tests and the column settling tests provide the remaining data required for prediction of the

quality of the effluent.

B3.1.2 Sampling Requirements

Samples of channel sediment and water from the dredging site are required for conducting effluent

elutriate tests and column settling tests, and toxicity tests, and for characterizing the sediment to be

dredged. The level of effort, including number of sampling stations, quantity of material, and any

schemes used for compositing samples, is highly project-specific. If at all possible, the sampling

operations required for sediment characterization (both physical and chemical), design and evaluation

of the disposal site, and conducting the effluent elutriate tests or toxicity tests should be conducted

simultaneously to avoid duplication of effort. Note that water from the dredging site is used in tests

for evaluation of effluent discharges. Dredging site water is used since the effluent discharge only

involves a small fraction of dredged material solids and the fractionation of contaminants to the

dissolved phase will be influenced primarily by that water. Note that disposal site water samples must

also be taken and analyzed for evaluation of mixing. The guidance in Section 8 should be used for

obtaining samples.

B3.2 Column Settling Tests

Settling tests are necessary to provide data for design or evaluation of disposal areas for retention of

suspended solids. These tests are designed to define the settling behavior of a particular sediment and

to provide information concerning the volumes occupied by newly placed layers of dredged material.
B-13

Table B1. Summary of Data Requirements for Prediction of the Quality of Effluent from

Confined Dredged Material Disposal Areas.

Data Required Symbol Source of Data

Dredge inflow rate Qi Project information; site design

Dredge inflow solids Ci Project information; site design

concentration

Ponded area in disposal site Ap Project information; site design

Average ponding depth in Dp, Dpw Project information; site design

disposal site and at the weir

Hydraulic efficiency factor HEF Dye tracer or theoretical

determination

Effluent total suspended SSeff Laboratory column settling tests

solids concentration

Dissolved concentration of Cdiss Effluent elutriate tests

contaminant in effluent

* This summary includes only those data required for effluent quality prediction. It is assumed

that the disposal area under consideration is designed for effective sedimentation and storage

capacity. Data requirements for such design or evaluation are found in EM 1110-2-5027

(USACE, 1987).
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For purposes of effluent water quality prediction, the column setting tests need only be performed if

there are water quality standards for total suspended solids or turbidity. If standards exist for turbidity,

a sediment-specific correlation of suspended solids and turbidity must be developed.

Sedimentation of freshwater slurries of concentration less than 100 g/L can generally be characterized

as flocculent settling. As slurry concentrations are increased, the sedimentation process may be

characterized as a zone settling process, in which a clearly defined interface is formed between the

clarified supernatant water and the more concentrated settled material. Zone settling also occurs when

the sediment/water salinity is approximately 3 ppt or greater. Flocculent settling also describes the

behavior of residual suspended solids in the clarified supernatant water above the sediment/water

interface for slurries exhibiting an interface. The procedures described below define the sedimentation

of suspended solids under flocculent settling conditions or above the settled material/water interface

under zone setting conditions. The settling test procedures consist of withdrawing samples from the

settling column at various depths and times and measuring the concentrations of suspended solids.

B3.2.1 Apparatus

An 8-inch diameter settling column such as shown in Figure B3 is used. The test column depth

should approximate the effective settling depth of the proposed disposal area. A practical limit on the

depth of the test is 6 ft. The column should be at least 8 in. in diameter with interchangeable sections

and with sample ports at 1/2-ft or closer intervals. The column should have provisions to bubble air

from the bottom to keep the slurry mixed during the column filling period.

B3.2.2 Test Procedure

The following test procedure should be used:

Step 1. Mix the sediment slurry to a suspended solids concentration C equal to the expected

concentration of the dredged material influent Ci . The slurry should be mixed in a container with

sufficient volume to fill the test column. Field studies indicate that for maintenance dredging of finegrained material, the disposal concentration will average about 150 grams per liter. This concentration

should be used in the test if better data are not available.

Step 2. Pump or pour the slurry into the test column using compressed air or mechanical agitation to

maintain a uniform concentration during the filling period. Any coarse material which settles to the
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Figure B3a. Specifications for Settling Column and Plan for Sedimentation Column.
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Figure B3b. Plans for Top and Bottom Columns.
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bottom of the mixing container during transfer of the slurry to the test column need not be added to

the column.

Step 3. When the slurry is completely mixed in the column, cut off the compressed air or mechanical

agitation and immediately draw off samples at each sample port and determine their suspended solids

concentration. Use the average of these values as the initial slurry concentration at the start of the test.

The test is considered initiated when the first samples are drawn.

Step 4a. If an interface has not formed during the first day, flocculent settling is occurring in the

entire slurry mass. Allow the slurry to settle and withdraw samples from each sampling port at regular

time intervals to determine the suspended solids concentrations. Record the water surface height and

time at the start of the sampling period. Analyze each sample for total suspended solids. Substantial

reductions of suspended solids will occur during the early part of the test, but reductions will decrease

with longer retention times. Therefore, the intervals can be extended as the test progresses.

Recommended sampling intervals are 1, 2, 4, 6, 12, 24, 48 hours, etc., until the end of the test. As a

rule, a 50-milliliter sample should be taken from each port. Continue the test until either an interface

can be seen near the bottom of the column and the suspended solids concentration in the fluid above

the interface is less than 1 gram per liter or until the suspended solids concentrations in extracted

samples shows no decrease.

Step 4b. If an interface forms the first day, zone settling is occurring in the slurry below the interface,

and flocculent settling is occurring in the supernatant water. For this case, samples should be

extracted from all side ports above the falling interface. The first of these samples should be extracted

immediately after the interface has fallen sufficiently below the uppermost port to allow extraction or

sufficient sample can be withdrawn from the surface without disturbing the interface. This sample can

usually be extracted within a few hours after the beginning of the test. Record the time of extraction,

water surface height, and port height for each port sample taken and analyze each sample for

suspended solids. As the interface continues to fall, extract samples from all ports above the interface

at regular time intervals. As before, a suggested sequence of sampling intervals would be 1, 2, 4, 6,

12, 24, 48, 96 hours, etc. The samples should continue to be taken until either the suspended solids

concentration of the extracted samples shows no decrease or for a maximum time of 15 days. For this

case, the suspended solids in the samples should be less than 1 gram per liter, and filtration will be

required to determine the concentrations. The data should be expressed in milligrams per liter for

these samples. In reducing the data for this case, the concentration of the first port sample taken

above the falling interface is considered the initial concentration SSo .
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B3.2.3 Data Analysis

A flocculent data analysis procedure, as outlined in the following paragraphs, is required. Example

calculations are also shown in Section B3.4.

Step 1. Arrange the flocculent settling test data from the laboratory test as shown in Table B2 and

compute values of the depth of sampling below the fluid surface, z. In computing the fractions of

suspended solids remaining φ, the highest concentration of the first port samples taken is considered

the initial concentration SSo.

Step 2. Plot the values of φ and z using the data from the table as shown in Figure B4, forming a

concentration profile diagram. Concentration-depth profiles should be plotted for each time of sample

extraction.

Step 3. Use the concentration profile diagram to graphically determine percentages of suspended

solids removed R for the various time intervals for the anticipated ponding depth Dpw (the minimum

recommended ponding depth is 2 feet). This is done by graphically determining the area to the right

of each concentration-depth profile and its ratio to the total area above the depth Dpw. The removal

percentage is:

R Area to right of profile

Total area (100)

Step 4. Compute the percentage P remaining as simply 100 minus the percentage removed, or:

Step 5. Compute values for suspended solids for each time of extraction as:

P 100 R

SSt Pt(SSo)

Arrange the data as shown in Table B3.

Step 6. Plot a relationship for suspended solids concentration versus time using the value for each

time of extraction, as shown in Figure B5. An exponential or power curve fitted through the data

points is recommended.
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Table B2. Observed Flocculent Settling Data.

Sample Extraction

Time

t (h)

Depth of Sample

Extraction

z (ft)

Suspended Solids

SS (mg/L)

Fraction of Initial SS

(percent)

3

3

7

7

14

14

14

24

24

24

48

48

48

0.2

1.0

1.0

2.0

1.0

2.0

3.0

1.0

2.0

3.0

1.0

2.0

3.0

93

169

100

105

45

43

50

19

18

20

15

7

14

55

100

59

62

27

25

30

11

11

12

9

4

8

Figure B4. Concentration Profile Diagram.
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Table B3. Percentage of Initial Concentration and Suspended Solids Concentrations vs. Time,

Assumed Depth of Influence of 2 ft.

Sample Extraction

Time

t (h)

Removal Percentage,

Rt

Remaining Percentage,

Pt

Suspended Solids

SS (mg/L)

3

7

14

24

48

14

47

78

90

94

86

53

22

10

6

145

90

37

17

10

Figure B5. Plot of Supernatant Suspended Solids Concentration vs. Time from Column Settling

Tests.
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By repeating steps 4 through 6 for each of several values of Dpw , a family of curves showing

suspended solids remaining versus retention time for each of several assumed ponding depths may be

developed. These curves may be used for prediction of effluent suspended solids concentrations under

ideal, quiescent settling conditions for any estimated ponding depth and field mean retention time.

Simply enter a curve with the estimated field mean retention time Td, and select the value of effluent

suspended solids predicted by the column test SScol. Guidance for determination of the field mean

retention time is given in Section B3.2.5. Guidance for adjusting the value derived from the column

test for anticipated resuspension is given in the Section B3.2.4.

B3.2.4 Determination of Effluent Suspended Solids Concentration

A prediction of the concentration of total suspended solids in the effluent must consider the anticipated

actual mean retention time in the disposal area and must account for possible resuspension of settled

material because of wind-generated turbulence. The relationship of supernatant suspended solids

versus time developed from the column settling test is based on quiescent settling conditions found in

the laboratory. The anticipated actual mean retention time in the disposal area under consideration can

be used to determine a predicted suspended solids concentration from the relationship. This predicted

value can be considered a minimum value which could only be achieved in the field if there were little

or no turbulence or resuspension of settled material. However, an adjustment for anticipated

resuspension is necessary for real conditions. The minimum expected value and the value adjusted for

resuspension would provide a range of anticipated suspended solids concentrations for use in

predicting the total concentrations of contaminants in the effluent. The value adjusted for anticipated

resuspension is:

where

SSeff SScol × RF

SSeff = suspended solids concentration of effluent considering anticipated resuspension, mg

suspended solids/L of water

SScol = suspended solids concentration of effluent as estimated from column settling tests, mg

suspended solids/L of water

RF = resuspension factor selected from Table B4

Table B4 summarizes recommended resuspension factors based on comparisons of suspended solids

concentrations predicted from column settling tests and field data from a number of sites with varying

site conditions. For dredged material slurries exhibiting flocculent settling behavior, the concentration

of particles in the ponded water is on the order of 1 g/L or higher. The resuspension resulting from

normal wind conditions will not significantly increase this concentration. Therefore, an adjustment for

resuspension is not required for the flocculent settling case.
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Table B4. Recommended Resuspension Factors for Various Ponded Areas and Depths.

Resuspension Factor for Anticipated Average Ponded Depth

Anticipated Ponded Area Less than 2 ft. 2 ft. or Greater

Less than 100 acres 2.0 1.5

Greater than 100 acres 2.5 2.0

B3.2.5 Determination of Field Mean Retention Time

Estimates of the field mean retention time for expected operational conditions are required for

selecting appropriate settling times in the effluent elutriate test and for determination of suspended

solids concentrations in the effluent. Estimates of the retention time must consider the hydraulic

efficiency of the disposal area, defined as the ratio of mean retention time to theoretical volumetric

retention time. Field mean retention time Td can be estimated for a given flow rate and ponding

conditions by applying a hydraulic efficiency correction factor (HECF) to the theoretical detention time

as follows:

where

Td

T

(HECF)

Td = mean detention time, h

T = theoretical detention time, h

HECF = hydraulic efficiency correction factor (HECF > 1.0) defined as the inverse of the

hydraulic efficiency

The theoretical detention time is calculated as follows:

where

T

Vp

Qi

(12.1)

ApDp

Qi

(12.1)

Vp = volume ponded, acre-ft

Qi = average inflow rate, cfs

Ap = area ponded, acres

Dp = average depth of ponding, ft

12.1 = conversion factor, acre-ft/cfs to h

The hydraulic efficiency correction factor HECF can be estimated by several methods. The most

accurate estimate is that made from dye tracer studies to determine Td at the actual site under
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operational conditions at a previous time, with the conditions similar to those for the operation under

consideration. This approach can be used only for existing sites.

Alternatively, the ratio Td/T = 1/HECF can be estimated from the equation:

Td

T

0.9











 1 exp 0.3 L

W

where L/W is the length-to-width ratio of the proposed basin. The L/W ratio can be increased greatly

by the use of internal spur dikes, resulting in a higher hydraulic efficiency and a lower required total

area. In the absence of dye tracer data or values obtained from other theoretical approaches, a value

for HECF of 2.25 may be used based on field studies conducted at several sites (Montgomery, 1983;

Montgomery et al., 1983).

B3.3 Effluent Elutriate Test Procedure

The effluent elutriate tests should be conducted, and appropriate chemical analyses should be

performed, as soon as possible after sample collection. The volume of elutriate sample needed for

chemical analyses will vary depending upon the number and types of chemical analyses to be

conducted. The volume required for each analysis, the number of parameters measured, and the desired

analytical replication will influence the total elutriate sample volume required. A 4 L cylinder is

normally used for the test, and the supernatant volume available for sample extraction will vary from

approximately 500 to 1,000 mL, depending on the sediment properties, settling times, and initial

concentration of the slurry. It may be necessary to composite several extracted sample volumes or to

use large diameter cylinders to obtain the total required volume.

B3.3.1 Apparatus

The following items are required:

a. Laboratory mixer, preferably with Teflon shaft and blades.

b. Several 4 L graduated cylinders. Larger cylinders may be used if large sample

volumes are required for analytical purposes. Nalgene cylinders are acceptable for

testing involving analysis of inorganic compounds such as metals and nutrients. Glass

cylinders are required for testing involving analysis of organic compounds.

c. Assorted glassware for sample extraction and handling.
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d. Compressed air source with deionized water trap and tubing for bubble aeration of

slurry.

e. Vacuum or pressure filtration equipment, including vacuum pump or compressed air

source and an appropriate filter holder capable of accommodating 47-, 105-, or 155-

mm-diam filters.

f. Presoaked filters with a 0.45 μm pore-size diameter.

g. Plastic sample bottles, 500 mL capacity for storage of water and liquid phase samples

for metal and nutrient analyses.

h. Wide-mouth, 1 gal capacity glass jars with Teflon-lined screw-type lids for sample

mixing. These jars should also be used for sample containers when samples are to be

analyzed for pesticides.

Prior to use, all glassware, filtration equipment, and filters should be thoroughly cleaned. Wash all

glassware with detergent, rinse five times with tap water, place in a clean 10 percent (or stronger)

HC acid bath for a minimum of 4 h, rinse five times with tap water, and then rinse five times with

distilled or deionized water. Soak filters for a minimum of 2 h in a 5 M HC bath, and then rinse

10 times with distilled water. It is also a good practice to discard the first 50 mL of water or liquid

phase filtered.

B3.3.2 Test Procedure

The step-by-step procedure for conducting the effluent elutriate test is outlined below.

Step 1 - Slurry preparation. The sediment and water from the proposed dredging site should be mixed

to a concentration approximately equal to the expected average field inflow concentration. If estimates

of the average field inflow concentration cannot be made based on past data, a slurry concentration of

150 g/L (dry weight basis) should be used. Predetermine the concentration of the well-mixed sediment

in grams per liter (dry weight basis) by oven drying a small subsample of known volume. Each 4 L

cylinder to be filled will require a mixed slurry volume of 3-3/4 L. The volumes of sediment and

water to be mixed for a 3-3/4 L slurry volume may be calculated using the following expressions:

Vsediment 3.75 Cslurry

Csediment
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and

where

Vwater 3.75 Vsediment

Vsediment = volume of sediment, in L

3.75 = volume of slurry for 4 L cylinder, L

Cslurry = desired concentration of slurry, g/L (dry weight basis)

Csediment = predetermined concentration of sediment, g/L (dry weight basis)

Vwater = volume of disposal site water, in L

Step 2 - Mixing. Mix the 3-3/4 L of slurry by placing appropriate volumes of sediment and water

from the proposed dredging site in a 1 gal glass jar and mixing for 5 min with the laboratory mixer.

The slurry should be mixed to a uniform consistency, with no unmixed agglomerations of sediment.

Step 3 - Aeration. The prepared slurry must be aerated to ensure that oxidizing conditions will be

present in the supernatant water during the subsequent settling phase. Bubble aeration is therefore

used as a method of sample agitation. Pour the mixed slurry into a 4 L graduated cylinder. Attach

glass tubing to the aeration source and insert the tubing to the bottom of the cylinder. The tubing can

be held in place by insertion through a predrilled No. 4 stopper placed in the top of the cylinder.

Compressed air should be passed through a deionized water trap, through the tubing, and bubbled

through the slurry. The flow rate should be adjusted to agitate the mixture vigorously for 1 h.

Step 4 - Settling. Remove the tubing, and allow the aerated slurry to undergo quiescent settling for a

time period equal to the anticipated field mean retention time, up to a maximum of 24 h. If the field

mean retention time is not known, allow settling for 24 h. Guidance for estimating the field mean

retention is given in Section B3.2.5.

Step 5 - Sample extraction. After the appropriate period of quiescent settling, an interface will usually

be evident between the supernatant water, with a low concentration of suspended solids above, and the

more concentrated settled material below the interface. Samples of the supernatant water should be

extracted from the cylinder at a point midway between the water surface and interface using syringe

and tubing. Care should be taken not to resuspend the settled material.

Step 6 - Sample preservation and analyses. The sample should be analyzed as soon as possible after

extraction. Dissolved concentrations of desired analytes in milligrams per liter should be determined.

Filtration using 0.45 μm filters should be used to obtain samples for analysis of dissolved

concentrations. Samples to be analyzed for dissolved pesticides or polychlorinated biphenyls

(PCBs) must be free of particles but should not be filtered due to the tendency for these materials to

adsorb on the filter. However, particulate matter can be removed before analysis by high-speed
B-26

centrifugation at 10,000 times gravity using Teflon, glass, or aluminum centrifuge tubes (Fulk et al.,

1975).

B3.3.3 Chemical Analyses

Chemical analyses of the effluent elutriate samples should be performed according to the guidance in

Section 9.

B3.3.4 Dissolved Concentrations of Contaminants

The dissolved concentrations of chemical contaminants in the effluent elutriate are compared with

water quality standards after consideration of mixing.

B3.4 Water Column Toxicity Test Procedure

The procedures for performing toxicity tests to evaluate water column effects of effluent discharges

from CDFs are generally the same as those for evaluation of dredged material discharges in open

water (see Section 5.1). However, the preparation of the dredged material (dissolved plus suspended

contaminants) should done using the effluent elutriate procedure as described below.

The volume required for each analysis, the number of parameters measured, and the desired analytical

replication will influence the total elutriate sample volume required. A 4 L cylinder is normally used

for the test, and the supernatant volume available for sample extraction will vary from approximately

500 to 1,000 mL, depending on the sediment properties, settling times, and initial concentration of the

slurry. It may be necessary to composite several extracted sample volumes or to use large diameter

cylinders to obtain the total required volume.

B3.4.1 Apparatus

The following items are required:

a. Laboratory mixer, preferably with Teflon shaft and blades.

b. Several 4 L graduated cylinders. Larger cylinders may be used if large sample

volumes are required for analytical purposes. Nalgene cylinders are acceptable for

testing involving analysis of inorganic compounds such as metals and nutrients. Glass

cylinders are required for testing involving analysis of organic compounds.

c. Assorted glassware for sample extraction and handling.
B-27

d. Compressed air source with deionized water trap and tubing for bubble aeration of

slurry.

e. Wide-mouth, 1-gal capacity glass jars with Teflon-lined screw-type lids for sample

mixing. These jars should also be used for sample containers when samples are to be

analyzed for pesticides.

Prior to use, all glassware should be thoroughly cleaned. Wash all glassware with detergent, rinse five

times with tap water, place in a clean bath for a minimum of 4 h, rinse five times with tap water, and

then rinse five times with distilled or deionized water.

B3.4.2 Test Procedure

The step-by-step procedure for conducting the effluent elutriate test for use in toxicity tests is outlined

below.

Step 1 - Slurry preparation. The sediment and water from the proposed dredging site should be mixed

to a concentration approximately equal to the expected average field inflow concentration. If estimates

of the average field inflow concentration cannot be made based on past data, a slurry concentration of

150 g/L (dry weight basis) should be used. Predetermine the concentration of the well-mixed sediment

in grams per liter (dry weight basis) by oven drying a small subsample of known volume. Each 4 L

cylinder to be filled will require a mixed slurry volume of 3-3/4 L. The volumes of sediment and

water to be mixed for a 3-3/4 L slurry volume may be calculated using the following expressions:

and

Vsediment 3.75 Cslurry

Csediment

where

Vwater 3.75 Vsediment

Vsediment = volume of sediment, in L

3.75 = volume of slurry for 4 L cylinder, L

Cslurry = desired concentration of slurry, g/L (dry weight basis)

Csediment = predetermined concentration of sediment, g/L (dry weight basis)

Vwater = volume of dredging site water, in L

Step 2 - Mixing. Mix the 3-3/4 L of slurry by placing appropriate volumes of sediment and water

from the proposed dredging site in a 1-gal glass jar and mixing for 5 min with the laboratory mixer.

The slurry should be mixed to a uniform consistency, with no unmixed agglomerations of sediment.
B-28

Step 3 - Aeration. The prepared slurry must be aerated to ensure that oxidizing conditions will be

present in the supernatant water during the subsequent settling phase. Bubble aeration is therefore

used as a method of sample agitation. Pour the mixed slurry into a 4 L graduated cylinder. Attach

glass tubing to the aeration source and insert the tubing to the bottom of the cylinder. The tubing can

be held in place by insertion through a predrilled No. 4 stopper placed in the top of the cylinder.

Compressed air should be passed through a deionized water trap, through the tubing, and bubbled

through the slurry. The flow rate should be adjusted to agitate the mixture vigorously for 1 h.

Step 4 - Settling. Remove the tubing, and allow the aerated slurry to undergo quiescent settling for a

time period equal to the anticipated field mean retention time, up to a maximum of 24 h. If the field

mean retention time is not known, allow settling for 24 h. Guidance for estimating the field mean

retention is given in Section B3.2.5.

Step 5 - Sample extraction. After the appropriate period of quiescent settling, an interface will usually

be evident between the supernatant water, with a low concentration of suspended solids above, and the

more concentrated settled material below the interface.

The liquid plus the material remaining in suspension after the settling period represents the 100 percent

liquid plus suspended particulate phase. Carefully siphon the supernatant, without disturbing the

settled material, and immediately use it for toxicity testing. With some very fine-grained dredged

materials, it may be necessary to centrifuge the supernatant for a short time. The suspension should be

clear enough at the first observation time for the organisms to be visible. The general guidance in

Section 10 should be followed in performing the toxicity tests.

B4.0 EXAMPLE CALCULATIONS

B4.1 Example 1: Evaluation of Effluent Water Quality For an Existing Disposal Area

This example illustrates the evaluation of a proposed effluent discharge for an existing CDF in which

effluent standards exist for dissolved contaminants and total suspended solids.

B4.1.1 Project Information

Dredged material from a maintenance project will be placed in an existing disposal site. The ponded

area will be approximately 35 acres. The design indicated that the surface area is adequate for

sedimentation if a minimum ponding depth of 2 ft is maintained. The dredging equipment and pumping conditions anticipated will result in a flow rate of approximately 30 cfs. A dye tracer test was
B-29

previously run at this disposal site under similar operational conditions, and the field mean retention

time was 20 h. Previous sampling of inflow from the dredge pipe under similar conditions indicated

that the influent solids concentration was approximately 150 g/L, which is considered a conservative

maximum.

The quality of effluent must be predicted and compared with applicable water quality standards so that

the acceptability of the proposed discharge may be evaluated. A field evaluation of dispersion at the

disposal site determined that a dilution factor of 38 would occur in the mixing zone. For purposes of

this example, copper is the parameter requiring the greatest dilution and will be used to illustrate the

calculations. The water quality standard for dissolved copper at the perimeter of the mixing zone was

set at 0.004 mg/L, while that for total suspended solids was set at 50 mg/L. (Note that these values are

for purposes of example calculations only.)

B4.1.2 Effluent Elutriate Testing

Effluent elutriate tests were conducted on samples of sediment and disposal site water from three

stations at the site. The effluent elutriate tests were run at the anticipated influent concentration, in

this case 150 g/L. Sediment samples for each sampling station to be tested were homogenized, and a

sediment concentration of 450 g/L was determined by oven drying a sample of known volume. The

volumes of sediment and water mixed for this sample for a 3-3/4 L slurry volume were determined as:

Vsediment 3.75 Cslurry

Csediment

3.75 150

450 1.25 L

and

Vwater 3.75 Vsediment 3.75 1.25 2.50 L

The effluent elutriate tests were completed with the retention time used in the tests equal to the

anticipated field mean retention time of 20 h. Samples were extracted for the replicate tests and

analyzed for dissolved concentrations of desired parameters. The mean concentration of dissolved

copper was 0.06 mg/L.
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B4.1.3 Column Settling Tests

A column setting test was required because of the water quality standard for suspended solids.

Samples from all stations were homogenized into a composite for the column settling test. The test

used for prediction of effluent suspended solids was run at a slurry concentration of 150 g/L, equal to

the anticipated influent slurry concentration. The interface was formed early in the test. Samples were

extracted from settling column ports at 3, 7, 14, 24, and 48 h. Data for the solids concentrations and

for various depths and extraction times are shown in Table B2.

The concentration-depth profile diagram was then constructed from the data, and is shown in

Figure B4. Ratios of suspended solids removed as a function of time were then determined

graphically using the step-by-step procedure described previously. Since an interface formed in the

test, the slurry mass was undergoing zone settling. Therefore, the initial supernatant solids

concentration SSo was assumed to be the highest concentration of the first samples taken, 169 mg/L.

The concentration-depth profile diagram was therefore constructed using 169 mg/L as φ =

100 percent. The lower horizontal boundaries for the area determinations corresponded to a range of

assumed depths of withdrawal influence at the outlet weir, in this case 1, 2, and 3 ft. An example

calculation of the removal ratio for the concentration-depth profile at t = 14 h and a depth of

influence of 2 ft is:

* Areas are designated by circled numbers in Figure B5. The areas were determined by planimeter.

R14

Area to right of the profile

Total area

Area 1230

Area 1240 0.78

The portion remaining at t = 14 h is:

P14 1 R14 1 0.78 0.22

The value for the suspended solids remaining is:

SS14 P14 (SSo) 0.22 (169) 37 mg/L

Values at other times were determined in a similar manner. The summary data are shown in

Table B3. Similar calculations for other assumed ponding depths were made. Curves were fitted to

the data for total suspended solids versus retention time for depths of influence of 1, 2, and 3 ft and

are shown in Figure B5.
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B4.1.4 Prediction of Effluent Suspended Solids Concentration

A value for the estimated effluent suspended solids can be determined for quiescent settling conditions

using the column test relationship. In this case, the field mean retention time of 20 h corresponds to a

suspended solids concentration of 24 mg/L, as shown in Figure B5. This value should be adjusted for

anticipated resuspension using the factors shown in Table B4. In this case, for a surface area less than

100 acres and an assumed average ponding depth of 2 ft, the resuspension factor is 1.5. The predicted

total suspended solids concentration in the effluent is calculated as :

SSeff SScol × RF 24 mg/L × 1.5 36 mg/L

The acceptability of the discharge for suspended solids can be evaluated by comparing the estimated

effluent concentration with the water quality standard, considering the appropriate mixing zone. For

suspended solids, the estimated concentration of 36 mg/L is less than the water quality standard of

50 mg/L, therefore the discharge is acceptable for suspended solids prior to considering mixing.

B4.1.5 Prediction of Contaminant Concentrations

The acceptability of the proposed discharge for contaminants can be evaluated by comparing the

estimated effluent concentrations with applicable water quality standards, considering an appropriate

mixing zone. For a mixing zone dilution of 38 and a copper standard of 0.004 mg/L, the

concentration of copper at the point of discharge must be less than 0.15 mg/L. The estimated concentration of 0.06 mg/L from the effluent elutriate test at the point of discharge is less than the limiting

value of 0.15 mg/L. The discharge would therefore be acceptable.

B4.2 Example 2: Determination of Disposal Area Requirements to Meet a Given

Effluent Quality Standard

This example illustrates the evaluation of a proposed effluent discharge for a new CDF in which

effluent standards are defined in terms of total suspended solids. The required retention time of the

new CDF to meet the standards is determined.

B4.2.1 Project Information

A disposal area is planned for contaminated sediment from a small maintenance dredging project.

Dredging equipment traditionally used in the project area is capable of flow rates up to 15 cfs.
B-32

Available real estate in the project vicinity is scarce, with the maximum available area limited to

60 acres. The disposal area required to meet applicable water quality standards must be determined.

The CDF design indicated that a minimum ponded surface area of 20 acres was required for effective

sedimentation, assuming a flow rate of 15 cfs and an assumed minimum ponding depth of 2 ft. A

mixing evaluation was conducted using a computer model and a dilution factor of 1.8 was estimated

for the allowable mixing zone. The water quality standard for TSS is 10 mg/L (Note that this value is

for purposes of example calculations only).

B4.2.2 Column Settling Tests

Column settling tests were performed, and the resulting concentration-depth profile was developed as

was illustrated in Example 1. The column tests were run at a concentration of 150 g/L for this

example. For simplicity, the test results from column tests used in the first example will also be used

in this example (see Figures B4 and B5).

B4.2.3 Determination of Allowed Effluent Suspended Solids Concentration

Since this example requires determination of the disposal site characteristics necessary to meet a given

water quality standard, the calculations would proceed in a manner similar to Example 1, but in

reverse sequence. The concentration of effluent suspended solids required to meet water quality

standards must first be determined. For a dilution of 1.8, the TSS concentration at the point of discharge must be less than 18 mg/L.

An appropriate value should be selected from Table B4 for the resuspension factor. The minimum

ponding depth of 2 ft required by the site design was selected. A resuspension factor of 1.5 was

selected, corresponding to an available area <100 acres and the selected ponding depth of 2 ft.

The value of 18 mg/L of SS which must be achieved at the point of discharge includes anticipated

resuspension. The corresponding value for total suspended solids concentration under quiescent

settling conditions is determined as:

or transposed,

Seff SScol × RF

SScol

SSeff

RF

18 mg/L

1.5

12 mg/L
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The disposal area must provide a retention time which will allow the necessary sedimentation. The

required retention time to achieve 12 mg/L under quiescent settling conditions may be determined

from the relationship of suspended solids versus retention time for the laboratory column. Using the

concentration profile data and the selected depth of ponding at the weir of 2 ft, the relationship for

suspended solids versus field mean retention was developed as was previously shown in Figure B5.

Using Figure B5, 12 mg/L corresponds to a field mean retention time of 36 h. To determine the

required disposal site geometry, the theoretical volumetric retention time should be used. Since no

other data were available, the hydraulic efficiency correction factor was assumed to be 2.25. The

theoretical volumetric retention time was calculated as:

Td

T

(HECF)

or transposed,

T Td (HEF) 36 (2.25) 81 h

B4.2.4 Determination of Ponded Volume and Surface Area

The required disposal area ponded volume can now be determined using data on anticipated flow rate

and the theoretical volumetric retention time. Since the dredging equipment available in the project

area is capable of flow rates up to 15 cfs, the high value should be assumed.

The ponded volume required is calculated as:

or transposed,

T

Vp

Qi

(12.1)

Vp

TQi

12.1

81 h × 15 cfs

12.1 100 acre ft

A ponding depth of 2 ft is the minimum allowed. This same depth should be maintained over the

entire ponded surface area and at the weir. The disposal site should therefore encompass

approximately 50 acres of ponded surface area with an average depth of 2 ft if the dredge selected for

the project has an effective flow rate not greater than 15 cfs. The surface area of 50 acres required to
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meet the water quality standard controls the design instead of the calculated surface area of 20 acres

required for effective sedimentation.
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B5.0 REFERENCES

Averett, D. E., M.R. Palermo and R. Wade. 1988. Verification of procedures for design of dredged

material containment areas for solids retention. Technical Report D-88-2, U.S. Army Engineer

Waterways Experiment Station, Vicksburg, MS.

Fulk, R., D. Gruber and R. Wullschleger. 1975. Laboratory study of the release of pesticide and PCB

materials to the water column during dredging and disposal operations. Contract Report D-75-

6, prepared by Envirex, Inc., under contract to the US Army Engineer Waterways Experiment

Station, Vicksburg, MS.

Krizek, R.J., J.A. FitzPatrick and D.K. Atmatzidis. 1976. Investigation of effluent filtering systems

for dredged material containment facilities. Contract Report D-76-8, prepared by Dept. of

Civil Engineering, Northwestern University, under contract to the U.S. Army Engineer

Waterways Experiment Station, Vicksburg, M.S.

Montgomery, R.L. 1983. Methodology for design of fine-grained dredged material containment areas

for solids retention. Technical Report D-78-56, U.S. Army Engineer Waterways Experiment

Station, Vicksburg, MS.

Montgomery, R. L., E. L. Thackston and F. Parker. 1983. Dredged material sedimentation basin

design. J. Environ. Engineer, Am. Soc. Civil Engineers. 109.

Palermo, M. R. 1986. Development of a modified elutriate test for predicting the quality of effluent

discharged from confined dredged material disposal areas. Technical Report D-86-4, U.S.

Army Engineer Waterways Experiment Station, Vicksburg, MS.

Palermo, M. R. 1988. Field evaluations of the quality of effluent from confined dredged material

disposal areas. Technical Report D-88-1, U.S. Army Engineer Waterways Experiment Station,

Vicksburg, MS.

Palermo, M. R. and E. L. Thackston. 1988a. Test for dredged material effluent quality. J. Environ.

Engineer., Am. Soc. Civil Engineers 114: 1295-1309.

Palermo, M. R. and E. L. Thackston. 1988b. Verification of predictions of dredged material effluent

quality. J. Environ. Engineer., Am. Soc. Civil Engineers 114: 1310-1330.
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Palermo, M. R. and E.L. Thackston. 1988c. Refinement of column settling test procedures for

estimating the quality of effluent from confined dredged material disposal areas. Technical

Report D-88-9, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS.

USACE. 1987. Confined Disposal Material. Engineer Manual 1110-2-5027, Office, Chief of

Engineers, U. S. Army Corps of Engineers, Washington, D.C.

USACE/EPA. 1992. Evaluating Environmental Effects of Dredged Material Management Alternatives -

A Technical Framework. EPA842-B-92-008, U.S. Environmental Protection Agency and U.S.

Army Corps of Engineers, Washington, D.C.