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Nordroc 2012

CHARACTERIZATION OF DNAPL CONTAMINATION CONTAINING THE ORGANOPHOSPHOROUS PESTICIDE PARATHION

Torben H. Jørgensen1*, Kirsten Rügge1, Lars Nissen1, Lars R. Bennedsen2, Neal D. Durant4, Leah MacKinnon4, Freddy S. Petersen3, and Morten Bondgaard5,

1 (COWI, Denmark), 2(Rambøll, Denmark), 3 (Kogsgaard Miljø, Denmark), 4 (Geosyntec Consultants, USA), 5 (Region Midtjylland, Denmark )

* COWI, Vestre Stationsvej 7, 5000 Odense, Denmark, tjr@cowi.dk

Case Study - Groyne 42

Groyne 42” is an old pesticide dumpsite, heavily contaminated with 200-300 tons of chemicals, mainly parathion (organophosphorous insecticide), also with mercury

NorthPestClean (2010-2013)

Project Objectives:

1. Test the effect of in situ alkaline hydrolysis for treating the organophosphorus pesticides

2. Test three in situ techniques to enhance delivery and contact between the reagent (caustic soda) and the contaminants.

Principle of Alkaline hydrolysis

› Increasing pH to about pH 12 (by adding NaOH) induces alkaline hydrolysis of parathion.

› The hydrolysis products (e.g. p-nitrophenol PNP) have relatively low toxicity, are water soluble and can be removed by pump-and-treat.

Overall approach of the project

3 test cell

Target area

This presentation focuses on the results from the initial characterization (DNAPL distribution)

Phase Activities

Initial Draining

Injection of Caustic Soda

Alkaline hydrolysis

Draining

Characterization of efficiency

Initial

Characterisation

Cycle 1

Cycle 3 ?

Same approach as cycle 1 -

Testing enhancemant methods:

- Delivering methods

- Vibrations

- Recirculation

- Surfactants

Cycle 2

Not fully defined yet

Contamination (DNAPL), geology,

hydrogelogi

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DNAPL

DNAPL (Dense non-aqueous phase liquids)

A liquid that is denser than water and only slightly soluble in water.

Type of contaminants

› Chlorinated solvents (e.g. PCE and TCE), creosote, coal tar, PCB oils and some Pesticides (eg. Parathion)

Residual DNAPL

› Immobile disconnected small drops of organic liquid (DNAPL)

Mobile DNAPL A continuous distribution of DNAPL (Pools or strings)

› Detailed description of geology, hydrogeology, DNAPL distribution and contaminant mass

› 9 boreholes in each 3 test cell

› >400 soil samples

› 90 water samples

› Each sample was analysed for 10-20 parameters

Initial characterization

10 m

10

m

› In the target area the geology consists of well sorted medium grained sand

› locally we observe more fine- grained sand layers with lower permeability.

› The sand layer is underlain by silt layer

› The geology in the target area is not divided in 2 sublayers as expected – but more homogenious

Geology

Shift from medium grained to fine grained

Visual DNAPL observations

DNAPL was visually observed:

› On top of the silt layer (mobile and residual)

› In the sand layer in finer grained sub-units (Residual and some mobile DNAPL)

› In groundwater above the silt layer

Contaminant Mass calculation of Ethylparathione – EP3

Mass in test cell is calculated (270 m3 soil)

Mass in each sub cell is calculated (5.5 m3 soil)

In each location - samples every ½ meter

Saturated soil samples from 9 borings

Test cell 1 Test cell 2 Test cell 3

Samples (#) 58 58 56

Soil volume (m3) 280 270 270

Total Mass (kg) ~600 ~1.000 ~800

About 99.7 % of the total EP3 mass is found in the sediment (DNAPL & sorbed).

What did the initial characterization show?

Concentrations of EP3 >1300 mg/kg

High concentrations of EP3 in all depth in the Target area

Updated conceptual model based on the initial characterization

› DNAPL is distributed in the whole treatment area

› DNAPL is situated in more fine grained sediments (fine sand)

› No subdivison of the sandlayer (Testarea)

Initial CM Revised CM

12

How can we use the results from the initial characterization?

› Important to deliver NaOH uniformly across the whole treatment area to treat all DNAPL

› Delivering NaOH to the DNAPL seems easier than initially expected due to broader distribution of DNAPL in sand

› NaOH can be added with traditionally screened injection wells

Conclusions

› DNAPL occurs in more fine grained sediments (fine sand) all over the treatment area

› About 99.7 % of the total EP3 mass is found in the sediment (DNAPL & sorbed).

› Fine resolution sampling changed conceptual model significantly , improving remedy design

› The remediation approach has to be based on a fully understanding of the geology, hydrogeology and contamination distribution (Conceptual model)

› Effective remedy design for DNAPL typically requires detailed site characterization

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Thank you - Questions

For more information visit

www.northpestclean.dk

EP3 concentrations in soil samples

Preliminary conceptual model

› Before the investigation took place we expected:

› only to observe DNAPL in the bottom of the target area in a fine-grained sand layer just above the silt layer

› Most of the mass will typical be present as DNAPL (typical > 90 %)

› DNAPL source zones can persist for many decades and, even hundreds of years

› DNAPLs can migrate to significant depths below the water table

› Presence of DNAPL will be important when we select remedy techniques Many (most) traditional remediation techniques are not efficient against DNAPL eg. Pump & Treat, Air sparging, Soil vapor extraction, Permeable barriers, Phytoremediation

› Presence of DNAPL will increase time and cost for remediation

Why should we focus on DNAPL?

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Overall (initial) conceptual model of the site

Presence of parathion DNAPL

Target area for remediation