Formatted Title

Application of a Groundwater Model for the Planning of Groundwater Remediation at a Former Industrial Site 

Background/Objectives

The former chemical industry site is a 34-hectare brownfield area in the east of a German city. The site was used from 1842 until 2010 for tar oil distillation, leather processing and the production of dyes. As a result of the long-standing use of the site, the soil and groundwater are contaminated with inorganic (e.g., arsenic, lead) and predominantly aromatic organic (e.g., chlorobenzene, BTEX, aniline, PAH, β-naphthol) compounds. The site has been inaccessible and secured since 2010. Almost all industrial facilities, unusable buildings and infrastructure were demolished and the area was cleared. The site is now to be developed into both a forward-looking commercial location for global companies, startups and artists as well as a local recreation area for the city's citizens. To remediate the contaminated groundwater, hydraulic securing and remediation measures were conducted site-wide beginning in 1993, and only in the northeast of the study area beginning in 2012. To plan groundwater remediation strategies and to investigate the effects of remediation on groundwater conditions, a three-dimensional finite element groundwater flow model was built and calibrated.

Approach/Activities

The model covers an area of approximately 1.2 km² and includes the entire subsurface (fill, Quarternary) from the ground surface to the uppermost layer of the Rupelton (Tertiary). As a basis for the model development, a conceptual hydrogeological site model was previously developed using the existing data. The steady-state groundwater flow model was calibrated using real groundwater conditions for September 2015 and verified for October 2008. According to the hydrogeological maps, groundwater in the Quarternary aquifer of the study area flows predominantly to the northeast and northwest due to a Rupelton sill along a river. The river is located at the northern model boundary and a small creek is running through the northeastern side of the study area. A groundwater plateau forms in the central part of the site, resulting from delayed groundwater discharge.

The model was used to plan and optimize various groundwater securing measures, e.g., for sensitivity analyses to gain a greater understanding for the processes on site or to optimize the pumping regime. In addition, prognosis calculations were carried out for various scenarios and evaluated based on their impact on groundwater conditions: e.g., the effect of a sealing wall along the river or the influence of various canal construction works in the study area.

Results/Lessons Learned

Sensitivity analyses of groundwater recharge and the water level at the river had different impacts. A change in the river water level, for example, showed no major impact on groundwater flow conditions. Similarly, lowering the groundwater recharge did not influence the groundwater conditions. However, increasing the groundwater recharge by 30% needed to be adjusted by higher pumping rate of the remediation wells. As part of the preparation of framework and partial remediation plans, several groundwater extraction wells were planned in the area of the small creek and in the northwestern site area to capture the contaminated groundwater. The number of wells, the location of the wells, and their extraction rates were optimized through various simulations. The construction of a sealing wall along the river is expected to cause a rise in groundwater table and more flow towards the small creek. If the remediation wells are not operating, this may result in an overflow.

The results from these simulations show how the remediation strategies can be brought into practice and efficiently planned to provide a cost-effective solution for such contaminated sites.