VI International Seminar on Remediation and Redevelopment of Contaminated Sites. Natural attenuation and biological remediation a contradiction? Thilo Schenk IBL Umwelt- und Biotechnik GmbH Heidelberg, Germany
Concerned parties in remediation projects authority / public authority / public consulting company owner / company obliged for remediation remediation company
Influencing factors of remediation projects ENVIRONMENT TIME MONEY Target values Target values Reasonable means Reasonable means
Basic questions 1. Active reduction of contaminants = remediation technologies or Passive reduction of contaminants? = natural attentuation 2. Why focused on biological remediation?
Definition of NA I NA according to EPA OSWER directive (1999): The natural attenuation processes that are at work in such a remediation approach include a variety of physical, chemical or biological processes that, under favorable conditions, act without human intervention to reduce the mass, toxicity, mobility, volume, or concentration of contaminants in soil or groundwater.
Definition of NA II When it comes to money the abbreviation NA may also be interpreted as NO ACTION
Mechanisms of Natural Attenuation Differentiation between non-degradative and degradative mechanisms non-degradative mechanisms sorption, volatilization, dispersion, dilution, chemical or biological stabilization, transformation advection no NA-process but major mechanism driving contaminants downgradient degradative mechanisms biotic use of contaminants as primary growth source or co-metabolism = co-oxidation of contaminants abiotic hydrolysis, radioactive decay
Main technical preconditions for MNA The term Monitored Natural Attenuation (MNA) is used when NA processes are implemented into a remediation procedure. no direct danger for human health is indicated spreading of contaminant(s) can be controlled detrimental effects for groundwater and soil are accepted for a certain time within a defined space usability of soil and groundwater can be achieved within an appropriate time frame the source of contamination is removed or the hazardous risk of the source is already reduced to an extent that under technical and economic efforts a removal is not useful
Time frame for MNA The time period for a MNA measure has to be defined for each contamination individually. It should be reasonable. Time period for MNA should follow up a conventional decontamination measure which leads to an equivalent reduction of contaminants. General rule: Time period for active measure + 10 years In Germany a reasonable time frame for MNA is seen within 10-30 years
MNA costs MNA is not for free. Costs arise by: Planning: monitoring plan, contingency concept, approval by authorities Construction: drilling of monitoring wells, sentry wells Calculation: evaluation of degradation rates Prognosis: groundwater transportation model Monitoring: contaminants & indirect parameters Costs for MNA vary in a broad range between and are comparable to p&t-procedures.for small and mid-sized contaminations MNA is more expensive than conventional remediations. For bigger contaminations and Mega-sites MNA sometimes is the only cost effective approach.
Conclusions MNA is useful in such contaminations in which 1. the defined three lines of evidence are fulfilled 2. old contaminations are given, in case of excavation of the center of contamination an easy and effective intervention is possible 3. contaminations have big extensions / long plumes 4. direct access to center(s) of contamination is not possible 5. low concentrations and spread plumes are observed
Biological remediation procedures In-situ Ex-situ Unsaturated soil zone Saturated soil zone off-site on site - Bioventing - Bioslurping - Hydraulic circle - Biosparging - Bioslurping - Landfarming - Pile Biological remediation procedures are state-of-the art technologies
Definition of ENA ENA stands for Enhanced Natural Attenuation. ENA remediation represents a temporary intervention in the relevant area (compartment) combined with a subsequent control of NA processes within this area and its downstream. From legal point of view ENA characterizes a goaloriented intervention. Therefore ENA can be designated as an active remediation technology which in general leads to a better acceptance for the remediation approach even if the amount of the driving forces for the degradation lies in NA processes itself.
Devil s workshop, the Dr. Freund case In 1948 the chemical company Dr. Freund was established. During operation there many accidents occurred. After a severe explosion in 1979 claiming the death of a worker the company was shut down by authorities. The company site was acquired by the municipality of Sandhausen who started the assessment and consequently the remediation
Overview contamination situation Zweckverband Hardtgruppe water works (drinking water protection zone I) CHC-plume Dr. Freund Groundwater flow dicrection Former chemical company Dr. Freund (remediated since 1996) Scale 1:25000
Spectrum of contamination Totally over 120 different compounds 3 relevant groups of contamination Center of contamination: CHC (chlorinated hydrocarbons), BTEX (aromatic hydrocarbons), TPH (mineraloil hydrocarbons) Plume: only CHC
Remediation infrastructure - Center of contamination
Detailed view contamination situation ML 395 distant downstream - low CHC concentration ML 394 ML 391 ML 396 B 380 B 381 B 98 near downstream - B high 373 CHC concentration B 379 B 300 ML 324 B 98 F 19 former center of contamination B 372 B 97 ML 392 B 375 B 299 B 305 ML 393 B 96 B 371 B 307 B 306 B 99 Biologically remediated (1990-1996) B 106
Characteristics of CHC plume Near downstream = active area Contaminant concentration Contaminants max. 2.500 µg/l, average 500 µg/l cis-dichloro-ethene and vinyl chloride Contaminated area 15.000 m² Far downstream = passive area Contaminent concentration Contaminant 80 µg/l trichloroethene Contaminated area 60.000 m²
ENA-remediation concept for active area groundwater treatment plant 05m 10m 15m 20m PCE & TCE groundwater flow direction 25m 30m 35m 40m CIS & VC 45m multilevel monitoring well extraction well infiltration well
Definition of plume according to ENA concept ML 395 ML 394 control area ML 391 ML 396 ML 2 ML 3 B 381 Maßstab 50 m 100 m 150 m ML 1 B 380 B 98 B 373 Legende: Weiterer Abstrom B 379 passive area B 99 B 300 B 372 B 97 B 375 B 299 ML 392 B 374 active area B 123 ML 393 B 100 B 305 B 96 B 106 B 371 B 307 B 306 ML 324 B 98 ML 1 Abstromfahne (gemäß Modellrechnung) Abgrenzung des nahen Abstroms Multilevelbrunnen Brunnen Multilevelbrunnen neu/ Abstromsicherung Aktivbereich Passivbereich F 19 Naher Abstrom Dateiname:...San\Sandhausen\Graphik\SDHHW1.dsf Auftraggeber:Gemeinde Sandhausen Kontrollbereich Erstellt:23.02.1998 Name: rei Geändert: 02.08.2001 Name: SN Auftrag- Nr.:201589 Maßstab: 1:3.000 Anlage- Nr.: 1 UMWELT ABFALL SICHERHEIT Geändert: 06.02.2004 Name: SN Projekt: Dr. Freund Sandhausen Übersichtsplan der Abstromfahne und der Grundwasseraufschlüsse
Contaminants in the groundwater downstream Contaminants are CHC (Chlorinated HydroCarbons) CHC is a group of different single substances Used substances in the former chemical company Perchloroethene = PCE, Trichloroethene = TCE Metabolites (biologically formed under reductive conditions) cis-dichloroethene = CIS, Vinylchloride = VC
Contaminant degradation 1 Contaminants are degraded by microorganisms in a two-stage process. First the original contaminants (parent products) PCE and TCE are transformed under reductive conditions into the intermediates Cis and VC. Under oxidative conditions these metabolites (daughter products) subsequently are mineralized into untoxic end products (water, carbon dioxide and chloride).
Contaminant degradation 2 In the Dr. Freund project the first step of CHC degradation has to be activated due to the fact that no longer electrondonators (aromatic hydrocarbons) are delivered from the center of the contamination. This is achieved by the addition of nutrients and organics into the infiltration water of the upper zones of the groundwater creating a hydraulic cycle. This is the active part ot the operation which is based on the construction of wells, horizontal drillings for pipes and a treatment plant for the extracted groundwater. The second step of CHC degradation proceeds without any further human intervention due to the favorable oxidative conditions in the aquifer and is monitored for 3 years.
Project progression of ENA measure active area passive area control area redox potential strictly anaerobic anaerobic slightly aerobic aerobic primary phase active hydaulic cycle for metabolization of PCE and TCE to CIS and VC hydraulic barrier if threshold 1 for CHC is exceeded monitoring of endproducts of biological degradation (ethene / carbondioxide) & mobilized contaminants control phase secondary phase interuption of active hydraulic cycle verification of efficiency of natural NA degradation processes for CIS and VC under undisturbed groundwater conditions monitoring of contaminants a) positive proof for effective NA processes monitored NA monitored NA monitored NA b) negative proof for effective NA processes active hydraulic cycle with addition of oxygen to mineralize CIS and VC hydraulic barrier if threshold 1 for CHC is exceeded monitoring of contaminants
Remediation infrastructure B 98 B 373 N extraction well B 300 B 374 Legende: Einzugsbereich der Förderpumpe B 372 B 97 B 299 B neu B 375 ML 392 I 4 I 1 I 2 infiltration well I 3 B 305 B 123 ML 393 B 100 B 96 B 106 B 371 ML 392 B 372 Multilevelbrunnen Sanierungsbrunnen Infiltrationsbrunnen Standort Sanierungsanlage Rohrleitung B 307 B 306 B 99 seepage well Dateiname:projekte\san\sandhausen\sand2001\S0000196.dsf Erstellt:15.03.2001 Name:SN/MM Auftrag- Nr.:991589 Anlage- Nr.: 2 Maßstab: UMWELT 1:1000 ABFALL SICHERHEIT 17 960726 Auftraggeber:Gemeinde Sandhausen Geändert:02.08.2001 Name:SN/TSCH Geändert: 06.02.2004 Name: SN Projekt:Dr. Freund Sandhausen Lageplan der Förder- und Infiltrationsbrunnen im Aktivbereich F 19
Construction works for ENA project
Situation after 1,5 years of operation Reduction of CHC concentration approx. 35% Conversion of PCE and TCE to metabolites 60%
Project costs ENA-remediation: 776.000,00 (drilling of wells, pipe-installation, plant construction, operation, analysis & documentation P&T remediation: 2.500.000,00 to 3.100.000,00 time of operation: 17 years to 22 years
Summary Nature helps itself if injured. NA processes (resp. biological degradation) take place without human intervention. NA is effective if favorable conditions are given. Then MNA can be performed as a remediation procedure. MNA is not for free and needs big efforts to realize. MNA is cost effective for bigger and complex projects. ENA is useful to achieve remediation target levels within a short period of time. ENA acception by authorities is higher. ENA combines biological state-of-the-art technologies with the NA approach and in the end saves time and money.