The Spolchemie site was chosen as one of the NanoRem case study sites, to test two types of nanoparticles (NPs) (zerovalent iron - nZVI and iron oxide NPs) for in situ remediation of BTEX (Benzene, Toluene, Ethylbenzene, and Xylenes) contamination. Nanoremediation was seen as an opportunity to enhance the in situ biodegradation of the BTEX contaminants and to reduce the current remediation method of skimming free product from the groundwater surface waters and contining the use of a pump and treatment system that have been ongoing since 2005. Spolchemie is one of the leading synthetic resin manufacturers in Europe. Besides synthetic resins it also produces other chemicals (e.g. potassium and sodium hydroxide, epichlorohydrin, allylchloride, sodium hypochlorite, perchloroethylene, hydrochloric acid, liquid chlorine). This production site is located in an area of approx. 52 hectares at Usti nad Labem (Czech Republic) in the heart of Europe. The main Spolchemie complex comprises industrial buildings, roads and railway sidings, with a few vegetated areas. The site is in a rural setting. The plant was established in 1856, and began the production of inorganic chemicals followed by the manufacture of organic dyes at the turn of the 20th century, and from the middle of the last century Spolchemie started to produce resins and freons based on tetrachlormethane and tetrachlorethene.
The production, treatment, storage and distribution of these various products has led to extensive contamination of the subsurface by chlorinated ethenes and methanes and organic solvents including BTEX compounds, which in many cases have dispersed widely from the original source areas. Some parts of the subsurface are also contaminated by high concentrations of iron and other inorganics (mainly chlorides and sulphates) which have increased the salinity of the groundwater.
A number of groundwater monitoring campaigns has been undertaken followed by a preliminary site investigation. Based on this work a Conceptual Site Model (CSM) has been developed detailing the subsurface conditions followed by a preliminary risk analysis. This initial CSM was refined by further targeted investigation and subsequent updating of the risk analysis. This work indicated that remediation requirements would be complex. With further funding being secured, the CSM was expanded following delineation of the contamination, geological and hydrogeological surveys, well logging, development of a hydrogeological model of the site and a remediation feasibility study. Exploration of the site is still ongoing to further improve the conceptual site model and review further the most appropriate overall remedial strategy.
Six contamination plumes have been identified at Spolchemie, based on the type of contamination, geology and hydrogeology [see Box 1] of the subsurface areas identified in the conceptual site model.
BOX 1 – Geology and Hydrogeology at the site
The geological formations underlying the site are com-plex with the lower geological formations consisting of Mesozoic Cretaceous siltstones and claystones (thickness of several tens of metres) overlain by Tertiary Miocene tuffitic clays. From north to south of the site the thick-ness of the tuffite clays decreases, and is infilled by over-burden of Cretaceous sediments. Overlying the Mesozoic and Tertiary sediments is a Quaternary terrace formed mainly by fluvial sediments and deluvio fluvial sediments of the Bilina River, the Elbe River and Klissky Stream. The Quaternary terrace consists of gravel, sand and gravel with large boulders with an average thickness of 6m. The Quaternary terrace is overlain by aolian loess loams, which are located at a depth of 1.5 to 3.5 m below ground level (max. thickness 2.5 m) with made ground overlying that. This consists of backfill of various thick-nesses of clay, loam, sand, tarmacadam, pieces of brick and concrete.
The groundwater levels mirror the interface of the loess overburden in the overlying Quaternary terrace deposits. The groundwater level is from 3.0 to 4.0 m below ground level. The general horizontal groundwater flow direction is South East to South East East to the Bilina and Elbe
The general remedial concept is based on a combination of pump and treat technology, a passive reactive barrier and enhancing physical, chemical and biological in situ methods. The different methods being applied depending on the character of the contamination. For example permanganate infiltration or in situ oxidation accompanied by heating and sparging by a modified Fenton process, supported by venting, are being applied in the source zones, with pump and treat being combined with biological processes such as dehalogenation in a treatment station. This is being monitored in detail by molecular biology analysis in collaboration with the Technical University of Liberec.
The main principle underpinning the remediation design being considered is to pump the contaminated groundwater, treat it above ground and then allow the treated groundwater to infiltrate back into the ground. The costs associated with this type of pump and treat approach tend to be very high, and its operating lifetime tends to be rather long. Nanoremediation may offer a way of dealing with the source terms in situ so reducing the requirement for pathway management, and therefore lowering pump and treat costs and treatment time. NanoRem will explore this concept at this site.
The NanoRem case study at Spolchemie
The NanoRem case study at Spolchemie includes two large scale field tests.
Test Site 1: Two contamination plumes in the western part of the Spolchemie area, with Chlorinated Hydrocarbon Contamination (CHCs), are being treated by a 500 m long impermeable underground wall with 10 reactive gates filled with zerovalent iron chips. A pump and treat remedial system was also installed to decrease the concentration of CHCs on the inlet side of the wall. However, routine monitoring showed an overflow of contamination behind the wall from a secondary contamination source (storage tank) was occurring remediation option. This field test is being conducted by AQUATEST with participation of several NanoRem partners (TUL, Nanoiron, Palacky University in Olomouc and VEGAS Stuttgart). Detailed monitoring including installation of new wells for vertical contaminant distribution is being carried out in collaboration with VEGAS including the use of micro pumps installed in the original ZVI system for nanoparticle monitoring in the field test. A preliminary tracer test has already been undertaken. nZVI (NanoFer 25S) supplied by Nanoiron will be injected in the autumn of 2014.
Test Site 2: The middle part of the Spolchemie site was also extensively contaminated by BTEXs. A general approach in this area has been to excavate the contaminated soils from the unsaturated zone in the source zone area and then remediate the underlying aquifer by pump and treat. The pumping of free phase from several wells is also ongoing. Treated water is discharged back into the ground. Enhanced in situ bioremediation has been identified as a suitable remediation technology to treat residual free phase product and BTEX compounds in this area based on laboratory and pilot tests. Tests confirmed the ability of natural microflora to degrade the present contamination under anoxic conditions with nitrate being used as an electron acceptor. This has created an opportunity for NanoRem to look at nanoremediation and in situ bioremediation processes working in tandem, using of oxidic NPs (based on Goethite) as another possible electron acceptor. The NanoRem partners involved in this trial are the Helmholtz Institute in Muenchen, UNIVI and VEGAS Stuttgart.This area of the site has been investigated in detail. Additional wells have also been drilled and tracer tests undertaken before application to precisely delineate the plume. Undisturbed soil samples were taken for laboratory test verification (reactivity and migration tests) to assist with the NanoRem field test design.
Permitting: Permission for NPs application (for both sites) required negotiation with multiple agencies: the Municipality of Usti nad Labem, the Regional Authority, Czech Inspection of Environment, Ministry of Environment and Ministry of Finance. The permitting process was facilitated by an open process of discussion over many years, which provides information in detail about the whole remediation process, including the preliminary studies of proposed technologies, which are first applied as a small pilot test in the areas covered by the hydraulic barrier.
Spolchemie site remediation and NanoRem field site application