Your Partner from Concept to Completion

Background/Objectives. This platform presentation will detail the first and second injection events at a former manufactured gas plant (MGP) now owned and managed by the City of Boulder, Colorado. The work area is currently developed as a parking lot, skating rink (in Winter) and historic building for which special considerations must be made. Background information will be provided about previous activities at the site including excavation of 12,000 tons of MGP solid waste, 3,000 gallons of MGP product and 60,000 gallons of impacted groundwater in 2012. The two injection events have utilized caustic activated persulfate (Peroxychem’s Klozur SP) at up to 27 previously installed injection wells. Discussions will include modifications to the well network based on newly-discovered solid MGP waste and changes to the persulfate concentrations to address this new waste.     

Approach/Activities. In October 2017, twenty five injection wells were installed utilizing hollow stem auger to approximately 25 feet below ground surface (bgs). During drilling, solid MGP waste was discovered at locations previously unknown. Because of this new MGP waste, the persulfate solution concentration was increased and redistributed to target these areas. Following installation, 125,000 pounds persulfate and 190,000 pounds caustic as 89,000 gallons solution were injected across the wells. Lesser volumes were injected into wells which exhibited lower concentrations of target constituents. A follow-up injection event was completed in May 2019 to address remaining elevated PAHs in groundwater. Additionally, four additional wells were installed prior to injection based on recent groundwater sampling in the area. During the second injection event, 115,000 pounds persulfate and 168,000 pounds caustic as 66,000 gallons solution were injected across the wells.  

Results/Lessons Learned. Post-injection results will be presented along with a summary of previous remediation efforts at the site to evaluate effectiveness. Additionally, field modifications will be discussed and evaluated for efficacy due to changes in contaminant mass distribution observed in select areas of the site. Post-injection laboratory data will be presented and compared to historical concentrations with focus on mass reduction as compared to previous events. Focus will be provided on changes that were made based on real time site data and evaluation of this methodology for other remediation projects.   

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