Evaluating Natural Attenuation

Shu-Chi Chang, Ph.D., P.E., P.A.Assistant Professor1 and Division Chief2

1Department of Environmental Engineering2Division of Occupational Safety and Health,

Center for Environmental Protection and Occupational Safety and Health

National Chung Hsing University

May 2, 2007

Course plan

5/2: Midterm and Evaluating NA 5/9: Evaluating NA and Biobarrier (4

hours) 5/16: Air sparging case study, GW

and soil sampling demonstration (4 hours)

5/23: Modeling natural attenuation or guest speaker on NA (1 hour)

Course plan

5/30: Modeling natural attenuation 6/6: Case study 1 6/13: Case study 2 6/20: Student presentation. Each

group will have 30 minutes. 6/27: Final examination

Outline Chemical and geochemical data Lines of evidence Documented loss of contaminant mass of

plume stabilization Analytical data confirming intrinsic

bioremediation Microbiological data Estimating biodegradation rates Screening natural attenuation of PHCs Screening natural attenuation of chlorinated

solvents

Analytical data Several broad categories: source term and

sorption parameters, contaminants and daughter compounds, electron acceptors, metabolic by-products, and general quality parameters.

The analytes listed in the tables in next few pages are useful for

Estimating the composition and strength of a NAPL source

Showing that natural attenuation is occuring Evaluating the relative importance of the various

natural attenuation mechanism

Soil-sediment analytical parameters

Data quality objectives

GW parameters useful for evaluating natural attenuation (I)

GW parameters useful for evaluating natural attenuation (II)

GW parameters useful for evaluating natural attenuation (III)

GW analytical data quality objectives (II)

GW analytical data quality objectives (III)

Source term and sorption parameters Continuing source: mobile or

residual NAPL, or contaminant sorbed to the aquifer matrix

Degree of weathering of the NAPL, and its composition and strength-> amount of aqueous phase NAPL

TOC content is important to judge the sorption and possible retardation

Contaminant and daughter compounds Method 8020 can be used if site

contamination is limited to petroleum hydrocarbons.

Method SW 8020a is used if only chlorinated solvents of PHCs mixed with solvent are found in the subsurface

The dissolved concentration of combined BTEX and trimethylbenzene should not exceed 30 mg/L for a JP-4 spill or about 135 mg/L for a gasoline spill.

Electron acceptors and metabolic by-products Again, dissolved oxygen (DO), nitrate,

Mn(IV), Fe (III), sulfate, and CO2 (for methanogenesis).

Again, observe from the reduced form: Fe(II), Mn(II)

Readily measurable by-products: Fe(II), CO2, H2S, CH4, C2H6, C2H4, alkalinity, lowered redox potential, chloride, and hydrogen.

General water quality parameters

pH Temperature: Q10 rule Conductivity Those values better to be

measured “fresh”

General groundwater sampling consideration

Type: Monitoring wells: most common

and versatile but may be biased Monitoring points

Geoprobe®

Drive by cone penetrometer, hydraulic percussion, manually powered equipment

Grab sampling locations Hydraulic punch, Geoprobe, cone

penetrometer, hand-driven

Geoprobe®

Cone penetrometer technology (CPT)

Groundwater sampling Generic classification

Grab: Bailer (most common) Advantages: can be used at any depth Disadvantages: aeration and agitation

Suction lift: peristaltic pump Advantages: no cross contamination, no turbulence

(better DO and redox potential measurement) Disadvantages: limited depth, offgassing

Positive displacement: submersible pump Advantages: Deep withdraw, high volume Disadvantages: size limitation, rigorous

decontamination

Bailer

Peristaltic pump

Submersible pump

Light drilling machine

Well-head measurement Flow-through cell

<5% Height If bubbles were observed,

slow down If still has bubbles, replace

the tubing Bailer

Slowly immersing into water

Downhole measurement Care for decon

A few tips

Sample should be collected directly from the pump

Avoid aeration No air in the container and sealed

well

Lines of evidence used to evaluate natural attenuation Historical trends in contaminant data

showing plume stabilization and/or loss of contaminant mass overtime

Analytical data showing Depletion of electron acceptors and donors Increasing metabolic by-product Decreasing parent compounds Increasing daughtor compounds

Microbiological data that support the occurrence of biodegradation.

Documented loss of contaminant mass or plume stabilization

Visual tests of plume stabilization Statistical tests of plume

stabilization Mann-Whitney U test Mann-Kendal test

Visual tests of plume stabilization

Statistical tests of plume stabilization Mann-Whitney U test

Statistical tests of plume stabilization

Mann-Kendall test Well data Data comparison Menn-Kendall statistic

Statistical tests of plume stabilization

Mann-Kendal test

Analytical data confirming intrinsic bioremediation Electron acceptors Daughter compounds Metabolic by-products Spatial distribution of e donors, e

acceptors, metabolic by-products, and daughter compounds

Deducing the distribution of TEAPs in GW

Electron acceptors, by-products, and daughter compounds Electron acceptors

DO Nitrate Sulfate

By-products Fe(II) and Mn(II) H2S CH4 CO2 Alkalinity Redox potential Dissolved hydrogen Chloride

Daughter compounds

Spatial distribution of e donors, e acceptors, metabolic by-products, and daughter compounds

Microbiological data

Estimating biodegradation rates

Screening for NA of PHCs

Screening of NA of chlorinated solvents