I

Soil washing is a physical- chemical process in which a contaminated soil matrix is separated so that each fraction can be properly trea fed.

zziz!&&e I& GROUND POLLUTION - Sensing & Monitoring PART 7

Soil washing yields 82% clean backfill return

David M. Keyser Design Engineer

Alternative Remedial Technologies. Inc

Tampa, Florida

n June 28, 1993, Alternative Re- medial Technologies, Inc. (ART) began the first full-scale soil wash-

ing operation in the US. The location of the project was the King of Prussia (KOP) Technical Corp. site-a Superfund site in Winslow Township, NJ (Fig. 1). Our goal was to remediate 19,200 tons of soil that had been contaminated with chromium, copper, and nickel. The project was suc- cessfully completed on October 10,1993.

ART was formed in 1992 as the result of a joint venture between Heidemij of the Netherlands and Geraghty & Miller (G&M) Inc., based in Plainview, NY. Heidemij had been performing soil washing in Europe for ten years, and G&M is a major environ- mental consulting and engineering firm.

Bill Leeder System Designer

Schulz Control Designs. Inc.

Mississauga, Ontario, Canada

Soil washing is a physical-chemical process in which the contaminated soil matrix is separated. This makes it possible to individually apply the most effective treatment to each fraction. As a result, up to 90 percent of the soils processed can be returned to the site as clean backfill. Soil washing also releases owners and respon- sible parties from certain long-term opera- tions and maintenance obligations by restoring the site to its natural condition and eliminating the ongoing need to pro- vide long-term O&M (operations and maintenance) and monitoring.

The KOP site The ten-acre KOP site is locatedtin

southern New Jersey, within the Pinelands

FIG. I: This soil washing system, installed at a Superfund site in Winslow, NJ, removed chromium, copper, and nlckel from the fen-acre site. The system rendered clean backfill wlih up to 90% of the contaminants removed from the soil.

Al

National Reserve, adjacent to the State of New Jersey's Winslow Wildlife Refuge. The KOP Technical Corpor- ation purchased the site in 1970 to oper- ate an industrial waste recycling cen- ter. The operation failed, and in 1985 the site was placed on the NPL list.

During site operations, wastes were stored in six lagoons. Environ- mental Protection

JGUST 1994 I&CS 39

1

GROUND POLIU77ON - Sensing & Monitoring PART 7 , I t- Agency (EPA) studies revealed high levels of chromium, copper, and nickel contami- nation in the soils. A Record of Decision (ROD) was issued for the site in 1990, and soil washing was specified as the cleanup technology to be used for remediating the soils. A group of five potentially responsi- ble parties (PRPs) was issued a unilateral administrative order to implement the requirements of the ROD.

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Site activities scaled to a model Our first step in planning the design of

the on-site soil washing plant was to per- form treatability and bench-scale, studies. During the treatability study, we separated site materials into particle-size fractions, and constructed a percent finer particle-size distribution curve. We then analyzed each

resulting fraction for the target contami- nants. Next, we conducted bench scale studies to determine the treatment units to be used in the full-scale operation.

Because soil washing was new to the EPA, some questions were left from the treatability study. To fully show the ability of the proposed system to remediate KOP soils, we conducted a demonstration run at our full-scale Heidemij plant in Moerdijk, The Netherlands. With the approval of the EPA and VROM (the Dutch agency that’s equivalent to the EPA), 165 tons of contam- inated soils and sludges were shipped from the KOP site to Moerdijk. We per- formed a one-day operation with the equipment configured as we’d recom- mended in our preliminary design for the KOP soil washing plant. The demonstra-

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clockwise, from above) FIG. 2: The soii washing process consisfs of four major subsysfems: screen- ing, sepamfion, coarse frac- fion freafment, and sludge management.

FIG 3: Confrol panels of ART’S soil washing facilify include the maln control panel and motor confrol center for all modules In the plant.

FIG. 4: The control system uses a Uiockner-Moeller PS- 316 PLC with local capacify of 1024 inputs and 1008 out- puts. If connects to fhe motor control center and to three Suconet networks using PS-3s as slaves. The ten modules are shown as MDl through MD 10.

I I-r I Future - Message display -. - Color grophics

40 I&CS AUGUST 1994

tion run treated the KOP soils to levels well below the ROD-specified standards of 483 mg/kg for chromium, 3,571 mg/kg for copper, and 1,935 mg/kg for nickel (see table, below). The operation was successful in demonstr'lting the effectiveness of soil washing in treating KOP site soils, and the EPA gave ART approval to proceed with full-scale remediation.

Following the demonstration run, SALA International was contracted by ART to manufacture the soil washing plant. Upon delivery of the plant, we constructed it right on the site, and conducted a pilot run on 1,000 tons of contaminated site- soils. Our pilot run was very successful; we again achieved cleanup levels below the ROD-s peci f ied standards . The res u 1 t s prompted the EPA to grant prompt

sand, will be dewatered and, after analysis, returned to the site as clean backfill.

The fines are forwarded to a thicken- ing unit and converted into a 50-60% dry solids filter cake. This cake will contain the concentrated contaminants and must be disposed of at an approved facility.

Soil washing plant design The soil washing plant used at the KOP

Technology site is of modular design for ease of mobility from site to site. The follow- ing ten modules or equipment units make up the major parts: (1) feeding module, (2) screening module, (3 ) pump module, (4) conditioning module, (5) flotation module, (6) operations module, (7) thickening mod- ule (8) filter module, (9) water supply mod- ule, and (10) reagent module.

A on Soil washing plant's !:$it Prod. control system ROD std ~"xl) 1,935 2,300 Process control of

483 4,700 the soil washing plant 3,571 5,900 , is accomplished by

approval to proceed with the cleanup.

The soil washing Process

of four major subsystems: 1. Screening, 2. Separation, 3. Coarse fraction treatment, 4. Sludge management.

As you c m see in Fig. 2, during the process a working pile is excavated in the field. The materials are then screened, pro- ducing both a field-screened oversize and process oversize. The final screened prod- uct (material less than 2 mm) is formed into a wet slurry and introduced into the hydrocycloncs, which effect the separation of coarse (sand) and fine-grained materi- als. Sand is discharged from the bottom of the unit, while fine-grained materials are discharged from the top. Each fraction is then fed to the next processing phase.

The sand flows by gravity to the froth flotation unit and is contacted with a sur- factant. The froth, which is subsequently formed, con hiins the contaminants from the sand fraction, and will be combined with the fii1c.s. The underflow, the clean

The ART soil washing process consists

the use of the follow- ing five integrated control circuits: 1. Feeding, 2. Screening/hydrocycloning, 3. Flotation/ dewatering, 4. Sludge management, 5. Support functions.

agement circuit, all circuits are dependent upon one another for start-up and shut- down. In general, the support functions circuit must be running before other cir- cuits can be started. Start-up then contin- ues by turning on circuits 3, 2, and 1 in order. Shutdown occurs by first shutting off the feeding circuit, then circuits 2 and 3.

Motor fault sensors, flow sensors, level controls and other sensors are used to monitor start-up, general operations, and shutdown. More details these and other elements of the control system follow.

The operations module houses the main control panel and the motor control center for all of the modules in the plant. This module also serves as the plant office. The concept behind the motor control panel was to keep the panel as clean and simple as possible to not only help cut operator training time, but also to speed

With the exception of the sludge man- .

AUGUST 1994 I&CS 4 1

GROUND POLLUTION - Sensing & Monitoring PART^

up the location of problem areas. The main control panel (Fig. 3) con-

sists of four sections. The first section is for major alarms and tank levels. The second is for motor status and alarm with pilot lights that operate in the order of start-up sequence. The third section is the main sta- tus pilot lights and main control push but- tons, while the last section is for display meters, feed and product mass rates, pH, cyclone feed rate and thickener torque. All the pilot lights are IDEC 16 mm light emit- ting diodes, which were selected for their long life and trouble-free operation. The six main control push buttons control the five main circuits, with one being a spare.

Program control logic follows the process and instrumentation diagram (P&ID) flow circuits to allow the operator to start the plant in a step-by-step sequence to allow pumps to balance out. If there’s a

major fault (Le., major motor trips) the pro- grammable controller (PLC) will shut down the plant in a safe sequence to pre- vent overflows or other potential equip- ment problems. The PLC program has fail- safe rules programmed to prevent the build-up of product in sumps and flotation cells. This prevents surging during opera- tions, and major spills during an emer- gency shutdown. For maintenance purpos- es and safety, all manual functions are remote to the control panels on the mod- ules so the operators can safely control the equipment manually.

The main programmable controller is a Klockner-Moeller PS-316 with local capacity of 1024 inputs and 1008 outputs. Three Suconet networks, using Klockner- Moeller PS-3s as slaves, are also used. Each network can be expanded up to a total of eight PS-3s , which provides the capability

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of 128 inputs, 128 outputs, 32 analog inputs, and 8 analog outputs (Fig. 4).

Sensors, used in the plant include Milltronics inline weigh belt scales and tank level sensors (ultrasonic type with 4- 20 mA outputh Great Lakes Instruments pH sensors, and Krohne flowmeters (Alto- flux magnetic inductive flowmeter).

Sensors used external to the plant, but of great importance to a soil washing site, included X-ray fluorescence sample test- ing. We used this device to quantify conta- mination in samples of soil before process- ing was started, and before entering and exiting the plant. As a backup, we also sent duplicate samples to outside lab?.

Operations summary We performed the KOP project with

full EPA oversight, and in accordance with the approved Site Operations Plan. The

overall analytical results for the project are tabulated in the table on p 41. We were able to meet the ROD-specified levels, and achieve our goals for soil remediation.

As we said earlier, the soil washing operation was completed on October 10, 1993, and the facility was disassembled and removed from the site. The site even- tually will be revegetated and restored to its natural condition. The entire project treated 19,200 tons yielding a clean backfill return of 82%.

(This was based on an article that ran in the Dec. 2993 issue of ECON Magazine.)

The author, David M Keyser, will be available to answer any questions you may have about this article He can be reached at (813) 264- 3506 during normal business hours.

for more information, circle 163 on one of the /&CS Reader Service Cards in this issue

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ROSEMOUNTINALY TICAL FISHER-ROSEMOUNT" Managing The Process Better. 01994 Rosemount Analytical Inc

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