Porewater Collection and Risk Evaluation 27 th Alabama Water Resources Conference Orange Beach, AL...

Porewater Collection and Risk Evaluation

27th Alabama Water Resources Conference

Orange Beach, AL

Jacob Gruzalski

Environmental Standards, Inc.

Acknowledgements

I would like to thank the following individuals for their significant contributions and input: Dr. Bill Rogers - Tennessee Valley Authority Dr. Neil Carriker - Tennessee Valley Authority Mr. Rock Vitale - Environmental Standards, Inc. Mr. David Thal - Environmental Standards, Inc. Dr. James Markwiese - Environmental

Standards, Inc.

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Objectives

Define Porewater Reason for Porewater Collection and Analysis Importance of Proper Porewater Sampling Overview of Case Studies Conclusions

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Porewater Basics

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Sediment

Sediment is naturally occurring material that is broken down by processes of weathering and erosion and transported by wind, water, or ice.

Sediment is comprised of an aqueous and solid phase.

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Porewater – Definition

Porewater is the water filling the spaces between grains of the solid phase of sedimento Sand, silt, and clay

Porewater is the aqueous phase of sediment

By definition porewater cannot exist separate from the solid phase of sediment in the environment

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Porewater – Ecological Significance

Sediment porewater is a primary exposure pathway of contaminants to the benthic community.

These organisms then have the potential of introducing contaminants into the food chain (fish, aerial feeding birds).

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Pictorial Conceptual Site Model

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Why Analyze Porewater?

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Why analyze porewater?

To collect complete information on sediment contamination

Chemical concentration profiles in sediment porewater are widely used in studies and investigations into contaminant exposure, fate, and transport.

To evaluate potential exposure pathwayso Bioavailable vs. Totalo Line of evidence in ecological risk assessmentso Toxicity testing

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Why analyze porewater? (cont.)

An understanding of porewater in relation to

sediment properties provides for the following:

o Complete picture of the exposure to the

benthic aquatic environment;

o Comprehensive identification of contaminant

sources and sinks and their extent;

o Prediction of contaminant flux across the

sediment-water interface.11

Why analyze porewater? (cont.)

Evaluating concentrations in porewater is important to differentiate bioavailability of the contaminant from total concentration of the contaminant in the sediment.

This is possible only if porewater data truly reflects the in-situ conditions.

Many sampling and processing techniques do not address the possibility of geochemical transformation during porewater collection and extraction.

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Porewater Collection

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Porewater Collection

Collection and processing methods have the potential to cause geochemical changes to the porewater, primarily through oxidation.

This oxidation can lead to biased results that do not accurately represent the natural conditions.

Results can be biased to indicate both higher and lower concentrations compared to in-situ conditions.

What does this mean? The collection and processing technique selected should

be able to produce the most “realistic” data possible

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Case Studies

Ubatuba Bay, Brazil, River Study Tennessee Valley Authority Kingston Ash Recovery Project

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Ubatuba Bay, Brazil, River Study

Aim of study to present results of chemical analysis of ammonium ions from porewater extracted in oxygen-free environment

Sediment samples collected from four river estuaries on Ubatuba Bay in southeast Brazil

Historically, rivers have received discharges of raw sewage 16

Ubatuba Bay, Brazil, River Study (cont.)

Six samples collected from each location and split into two groups

One sample group processed in oxygen-free environment and other sample group exposed to the atmosphere

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Ubatuba Bay, Brazil, River Study (cont.)

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Tennessee Valley Authority Kingston Ash Recovery Project (TVA KRP)

Large release of fly ash spilled from containment area at the Kingston, TN, fossil plant in December 2008.

Approximately 5.4 million cubic yards of ash released from containment area with the majority discharging into the Emory River.

Two high flow storm events shortly after release

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December 22, 2008

TVA KRP

In addition to the chemical constituents in fly ash (primarily metals – As, Se), this release also had the ecological impacts of large deposits of ash on the bottom of the river

Fly ash removed from the Emory River by hydraulic and mechanical dredging

Extensive sampling and monitoring program executed throughout the life of the project (ongoing)

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TVA KRP – Porewater Sampling

Due to the nature of the project, multiple organizations are involved

Porewater samples have been collected by TVA and third-party researchers

Sampling occurred over multiple years at same general locations

Multiple porewater sampling methodologies have been implemented

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As Porewater vs Total (sediment)

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As Porewater (mg/L) Total As – Sediment (mg/kg)

As Sequential Extraction Procedure

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SEP Fraction

Water Soluble Ion Exchangeable Carbonate Bound Fe/Mn Oxide Bound

Arse

nic

(mg/

kg)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

ref 180d 600d ref 180d 600d ref 180d 600d ref 180d 600d

Days post spill (d)

mg/kg

TVA KRP - Summary

PW vs Total As concentrations between the collection methods suggest aerobic technique results in biased (high) data

Sediments included in TVA study have little to no sulfides

SEP data and previously published literature suggest Fe oxide is binding potentially bioavailable As.

Exposure to atmosphere during processing releases As to the porewater

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Summary

If porewater sample collection is planned, proper

collection and processing methods are essential.

The documented effects of oxidation of porewater

during collection drives the need for collection and

processing of porewater in oxygen-free environment.

Improper sample collection can lead to biased data

not reflective of in-situ conditions.

Evaluating in-situ conditions needed to assess

bioavailability of contaminants.25

QUESTIONS?

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Porewater Collection and Risk Evaluation 27 th Alabama Water Resources Conference Orange Beach, AL...

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