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An aerial view of the Pioneer Park in Hanau.

© Stadt Hanau / Thomas Feuerhahn

Ground­wa­ter reme­di­a­tion the gentle way

Once the site of a mili­tary instal­la­tion, the “Pioneer Park” quar­ter of Hanau, Germany, is now being trans­formed into a hous­ing area for 5,000 resi­dents. Yet before the modern living space can fully come to life, reme­di­a­tion is needed for cont­a­m­i­nated ground­wa­ter in two sections of the soon-to-be neighborhood.

Hanau is one of Germany’s up-and-coming towns. Located east of Frank­furt, Hanau is home to numer­ous large compa­nies and is on the way towards devel­op­ing into a major city. This also trans­lates into high demand for new and afford­able hous­ing. So when the roughly 50-hectare site of a former mili­tary barracks became vacant in 2008, it made sense for the city to turn this into useful real estate.

An attrac­tive resi­den­tial quarter

Since 2018, the site has under­gone trans­for­ma­tion into a modern resi­den­tial quar­ter. The largest resi­den­tial construc­tion project in the Rhine-Main area, Pioneer Park is conve­niently located, border­ing directly on the Bulau Forest and Nature Reserve. Inside the site itself, numer­ous green spaces are being created, while the streets are based on the fan shape already laid down by the former barracks. Most of the devel­op­ment is being built from scratch. Ulti­mately, 5,000 people will find a comfort­able home within Pioneer Park.

Resi­dents already began moving into the first apart­ments and houses as early as 2020. But before the entire area can be converted, the condi­tion of the soil and ground­wa­ter needed care­ful scrutiny. After all, sites previ­ously used for mili­tary purposes often reveal some form of cont­a­m­i­na­tion. And indeed, two areas cover­ing a total of 11,000 square meters (1.1 hectares) showed the pres­ence of chlo­ri­nated volatile organic compounds (VOCs). “The source of the cont­a­m­i­na­tion was chem­i­cal clean­ing agents, includ­ing those from the barracks’ former dry clean­ing facil­ity,” explains Mike Mueller, EMEA Busi­ness Manager for Soil & Ground­wa­ter Reme­di­a­tion at Evonik Active Oxygens. “Some of these solvents seeped under­ground, and from there, VOCs entered the ground­wa­ter.” This was a prob­lem, as VOCs are harm­ful to health. And because the pollu­tant takes a long time to degrade natu­rally – and even then, usually incom­pletely – the decom­po­si­tion needs to be helped along.

Envi­ron­men­tally friendly reme­di­a­tion solution

A good reme­di­a­tion solu­tion was needed. To find the right measure, site devel­oper LEG Hessen-Hanau GmbH – an enter­prise of the BIG BAU Group – together with the City of Hanau contracted global infra­struc­ture consul­tancy AECOM. A preferred approach quickly emerged: An active ingre­di­ent was to be injected into the substrate that would accel­er­ate degra­da­tion of the pollu­tants. As it so happened, Evonik Active Oxygens is head­quar­tered in the Hanau area – and is itself a major supplier of sophis­ti­cated tech­nolo­gies for soil and ground­wa­ter remediation.

The degra­da­tion of VOCs can be tricky. A biolog­i­cal or chem­i­cal approach alone is often not enough. That is why Evonik’s EHC® Reagent was selected for the task. This prod­uct is composed of controlled-release organic carbon, with nutri­ents derived from a grain-milling by-prod­uct, and micronized zero valent iron (ZVI), sourced from scrap iron. The use of these recy­cled ingre­di­ents thus makes EHC® not only safe to handle and easy to apply, but also an espe­cially sustain­able prod­uct. It is also highly effec­tive against VOCs. Mueller says: “EHC® Reagent trig­gers phys­i­cal, chem­i­cal, and micro­bi­o­log­i­cal processes. Inject­ing this substance into the subsoil under high pres­sure reli­ably leads to the rapid and perma­nent destruc­tion of VOCs in groundwater.”

The appli­ca­tion method for EHC® Reagent is also advan­ta­geous. Evonik worked together with its field tech­nol­ogy part­ner Sensatec GmbH to pursue “in-situ chem­i­cal reduc­tion” (ISCR). Mueller explains: “With ISCR, we are apply­ing the prod­uct directly into the ground. There is no need to pump out the ground­wa­ter, process it, and put it back again. Compared to such a ‘pump-and-treat’ method, ISCR saves energy, time, and costs.” This also helps make the approach more sustain­able. In fact, a well-designed ISCR appli­ca­tion such as this one can gener­ate signif­i­cantly lower carbon diox­ide (CO2) emis­sions than alter­na­tive reme­di­a­tion measures.

Convinc­ing results

EHC® Reagent had already proven its effec­tive­ness many times before, start­ing with soil and ground­wa­ter reme­di­a­tion projects in the U.S. That is why, in the summer of 2020, a pilot test was carried out within the cont­a­m­i­na­tion hotspot in Pioneer Park in order to judge its effec­tive­ness in the Hanau setting. In prepa­ra­tion, AECOM and Sensatec had obtained a precise picture of the compo­si­tion of the subsoil and the distri­b­u­tion of pollu­tants. They used this high-reso­lu­tion infor­ma­tion to inject the solid mixture at several points into the ground under high pres­sure and with pinpoint accu­racy. Subse­quent monthly measure­ments of the ground­wa­ter confirmed the desired effect: The VOCs, which had been leak­ing into the ground for decades, were almost completely degraded after just eigh­teen months. After the pilot test, any remain­ing detectable substances were signif­i­cantly below the permis­si­ble limit values for groundwater.

“For us, the measure­ment results confirmed that the ISCR proce­dure has once again done an excel­lent job,” says Mueller. “We there­fore proceeded to treat the remain­ing cont­a­m­i­nated areas in the first half of 2023, with full support from the local regu­la­tory agency.” As with the pilot test, special­ists from Evonik’s part­ner Sensatec took on the tech­ni­cal appli­ca­tion. At 73 smaller drill points, they used injec­tion probes to push EHC® Reagent up to 12 meters into the subsur­face, where the suspen­sion once again began its work to degrade VOCs. Today, the qual­ity of the ground­wa­ter is on track toward the spec­i­fied limits.

For Hanau’s Lord Mayor Claus Kamin­sky, this approach toward the pollu­tant prob­lem is exem­plary: “It is impor­tant to us that the soil and ground­wa­ter qual­ity in Pioneer Park is completely within accept­able para­me­ters. Thanks to the compa­nies involved and Evonik’s active ingre­di­ent, we are well on our way. The fact that Evonik, a company from the imme­di­ate vicin­ity, had the right solu­tion ready makes it all the better for me. It’s an excel­lent exam­ple of commu­nity at work.”

The project part­ners are also satis­fied. “We are advanc­ing the appli­ca­tion of sustain­able, in situ reme­di­a­tion tech­nolo­gies in Germany, and the Pioneer Park site is a show­case exam­ple of their success,” remarked Gordon Bures, Reme­di­a­tion Engi­neer at Sensatec’s Berlin office. And Peter Martus, AECOM Envi­ron­men­tal Team Leader in Germany, said: “We have designed a sustain­able solu­tion which reflects Pioneer Park’s ambi­tion to create a climate-friendly neigh­bor­hood. Work­ing in collab­o­ra­tion with project part­ners to test and iden­tify the best solu­tions for the project, the inno­v­a­tive approach we chose now means that the project can move at a faster pace than if we had used tradi­tional reme­di­a­tion methods.”

An award-winning example

The jury of the 2024 German Brown­field Awards was also convinced by the results. On 16 May 2024, the Pioneer Park ground­wa­ter reme­di­a­tion project took the bronze medal in the cate­gory “Espe­cially Sustain­able” due to its posi­tive social, economic, and envi­ron­men­tal impact.

With EHC® Reagent, Evonik Active Oxygens offers a proven means of completely reme­di­at­ing tough VOC cont­a­m­i­na­tions in a short period of time. In view of the large number of areas in Germany that were formerly used for indus­trial, commer­cial, or mili­tary purposes, the demand for the envi­ron­men­tally friendly, effec­tive, and cost-savings reme­di­a­tion method is on the rise..