Project Summary
ESA was retained by a developer who had purchased a former chemical manufacturing operation with the intention of redeveloping the property into a product distribution warehouse and office complex. The property had been undergoing environmental investigation and remediation activities for approximately 20 years, and the previous owner was being required by the NJDEP to perform active remediation of groundwater due to historically high concentrations of various chlorinated volatile organic compounds (e.g., cVOCs). The previous owner’s environmental consultant had performed a remedial alternative analysis and, based upon their analysis, had opted for the installation and operation of a groundwater pump and treat system utilizing granulated activated carbon and thermal treatment to address the high concentrations of residual cVOCs.
Challenges
During ESA’s initial evaluation of the existing groundwater pump and treat system upon the clients purchase of the property, ESA’s Licensed Site Remediation Professional (LSRP) determined that the existing system had never been connected to a series of monitoring/extraction wells located throughout the site and, additionally, was not connected to the various utilities required for system operation. Furthermore, it was determined that the groundwater bearing zone requiring active remediation had low permeability clay beneath the entire site. ESA’s LSRP performed an evaluation of the system design parameters — particularly the very low hydraulic conductivity of the water bearing zone requiring remediation — and determined that operation of the existing system would be inefficient and would likely create significant operational issues after redevelopment of the site.
ESA’s other primary concern was that the existing monitoring/extraction well network was constructed of vertical wells that would likely have very little radius of influence due to the low permeability clay in which they are installed, as well as their location within the proposed warehouse/office building footprint, which presents significant obstacles for site redevelopment activities and for future well access.
Proposed Solution
In order to facilitate active remediation of the required water bearing zone while significantly reducing future well maintenance requirements and the costs associated with operating a pump and treat groundwater remediation system, ESA selected an alternative remedial approach utilizing the installation of a horizontal well network and in-situ remediation of residual cVOCs through the injection of chemical oxidizing compounds. The horizontal well system, while eliminating the need for access through the future building foundation, also provides for greater contact of the chemical oxidizing compounds with the residual mass located within the low-permeability clay. Additionally, because of the low-permeability clay, ESA designed a chemical injection program using an approximate 4% chemical oxidant to water solution, pulsing the compounds through the system at flow rates of less than 5 gallons per minute, alternating chemical injections with water, allowing the clay formation’s natural hydraulic gradient to assist in the remediation. This approach allows for the effective treatment of residual cVOC mass while reducing remedial costs by approximately 50%.
The delivery system selected by ESA is relatively small in size (approximately 10-ft. X 14-ft.), minimizing area requirements, and utilizes a pump that operates on solar power, eliminating the need for an electrical connection and ongoing electrical costs.
Outcome
By thoroughly evaluating site hydrogeology, future redevelopment requirements, and costs, ESA was able to design an efficient and cost-effective remedial design without compromising NJDEP remedial requirements. Consequently the client will not need to install vaults to access the existing vertical well network (which will be appropriately abandoned prior to site redevelopment), provide access for maintenance of the vertical well network and, lastly, will be able to sell the existing groundwater pump and treat system, significantly offsetting the costs of ESA’s alternative remedial system design.