Sustainable management of contaminated groundwater present beneath an industrial site located in western India using a combination of field techniques and desktop groundwater modeling approach

English Abstract:

Groundwater contamination at an industrial facility involved in the manufacturing of dyes and dye-intermediates operating for over 20 years affected down-gradient groundwater quality at various receptors which mainly include agricultural lands and residences. The colour of the groundwater varied from light-brown to dark-brown with some waters ranging from red to yellow. This triggered a regulatory action which mandated that the facility manage and contain the migration of contaminated groundwater.

Field investigations were carried out to identify the main source areas (a potential hazardous waste landfill unit and a waste storage yard on-site) to understand the nature (high colour, total dissolved solids [TDS] and Sulphates) and the extent of the contaminant plume. The hydrogeology of the site area primarily consists of two aquifers mostly separated by a clay lens but interconnected in the central portion of the site by highly permeable silt hole (lens). This geology along with the exisiting hydraulic gradients caused the movement of contaminated groundwater from the shallow to the deeper zones. To add, the groundwater flow in the area is affected by a host of factors including seasonal rainwater recharge and evapotranspiration, discharge from industries, residences and farms in the area surrounding the facility, discharge from the facility of interest and recharge/ leakage from a major irrigation canal passing just north of the site.

Therefore, a multi-layered 3D groundwater flow model was developed using MODFLOW, incorporating the above elements, to model the changing nature of the groundwater flow system to aid in the design of a hydraulic containment system (HCS), i.e., network of abstraction wells on-site, for effective containment of the plume and prevention of future migration to off-site locations. The quantity of groundwater being pumped daily from abstraction wells was constrained by the daily water requirement of the manufacturing process. Following the installation and commissioning of the HCS system, real-time groundwater monitoring data was used to recalibrate the groundwater model parameters. The recalibrated model better predicted groundwater flow resulting in optimization of abstraction well pumping rates aimed towards achieving containment as per the regulatory mandate.