Environmental Projects

Coal Tar Recovery Success at a
Former Manufactured Gas Plant Site

INNOVATIVE ENGINEERING SOLUTIONS, INC. is currently providing consulting services at a former manufactured gas plant (MGP) located in the North East US. We have been responsible for completing response actions at this site starting with the Comprehensive Site Assessment (including a human health risk assessment) through design, implementation and operation of the selected remedial action alternative.

During subsurface explorations, dense non aqueous phase liquid (DNAPL), that was similar to coal tar, was observed at thicknesses greater than 8 feet above silty clay layer. Downward movement of the DNAPL appears to be limited by the low permeability and configuration of the perching layer.

Initial DNAPL recovery efforts were conducted using a basic timed-pump removal system from the bottom of the 9 recovery wells using 6 peristaltic pumps (operating on timers). During the approximate year of operation, more than 8,000 gallons of fluid (primarily DNAPL) were recovered and disposed off –site.

Based on the successful operation of limited DNAPL recovery effort and the results of pump tests, an expanded DNAPL recovery system was designed and constructed.

The expanded system includes the continued use of 9 existing recovery wells and 11 new wells for fluid collection using both pneumatic pumps and peristaltic pumps; separating NAPL and water from the collected fluids using an aboveground oil-water separator; transferring the NAPL to a storage tank for removal from the site; and treating the water using a bag filter to remove particulates, liquid phase granular activated carbon (GAC) to remove organics, and ion exchange resin to remove cyanide prior to discharge to the sanitary sewer system. Construction of the expanded DNAPL recovery system was completed in 4 months to meet DEP deadlines. Since startup of the system in December 2003, over 60,000 gallons of DNAPL have been recovered and disposed offsite and over 1,800,000 gallons of water have been treated and discharged to the local sewer system.

The rate of DNAPL recovery has reduced from a high of 78 gallons per day during the first year of operation to 10 gallons per day of DNAPL. This reduction in daily DNAPL recovery was anticipated and in response, IESI has been pilot testing enhanced recovery methods (e.g., pH adjustments, surfactants, solvents, etc.). The pilot test is ongoing and is showing encouraging results for continued use of the recovery system.