Formatted Title

Optimizing Injection Dosage of Enhanced In Situ Bioremediation Substrate and Incorporating Interactive Data Visualization Software for System Management

Background/Objectives

A confidential client in California had the dilemma of groundwater impacted by chlorinated solvents below a building where access is limited and a range of hydraulic conductivity from approximately less than 1 feet/day to 3 feet/day with limited downward migration. Previous investigation activities detected the presence of dissolved chlorinated volatile organic compounds (CVOCs) of approximately 240,000 µg/L from past industrial activities.

CDM Smith designed, constructed, and now operates an 11 extraction well/11 injection well enhanced in situ bioremediation (EISB) recirculation system to distribute electron donor amendment for anaerobic bioremediation of contaminated groundwater in a confined aquifer. Eleven extraction wells and 11 injection wells recalculate groundwater and intermittently inject amendment at around 5 gallons per minute. Two circulation loops were established. The higher concentration loop recirculated water from the 11 extraction wells centered around eight injection wells. The other outer loop consisted of three injection wells west of and parallel to the high concentration recirculation loop. The outer loop and was added to address a lower concentration arm extending from the high concentration plume. Well placement encompassed a 500x500 ft area.

During EISB operations, pressure, flow and pump run status data were evaluated and managed to help achieve site-specific remediation goals. The objective is to discuss using PowerBI™ to automate and optimize system operations along with substrate dosing.  

Approach/Activities

The EISB system consisted of electric submersible groundwater extraction pumps, groundwater conveyance system, influent bag filters in parallel, donor metering pump, groundwater booster pumps, and injection wells. Flow meters, pressure transducers, and solenoid-actuated valves play a critical role in the implementation and operation of the EISB system. The CVOCs are degraded by anaerobic bacteria (Dehalococcoides, Dhc) in strongly reducing conditions. The speed of the degradation is increased by providing an electron-donating compound (in this case 60% sodium lactate) to the bacteria in the vicinity of the plume. A targeted concentration of sodium lactate is blended into the extracted groundwater prior to re-injection at approximately 4% sodium lactate/96% water, by volume, for approximately 30 hours each week. This has resulted in an average donor injection concentration of 0.7% sodium lactate over the entire EISB implementation. Minute-by-minute data collection of key process parameters such as flow, pressure, and pump run status are downloaded by the operator on a weekly basis for evaluation and optimization purposes.

Results/Lessons Learned

This system will continue to be operated until site-specific remediation goals are achieved. The system is difficult to balance hydraulically as some wells have pipes that go in multiple directions and some wells syphon flow at a disproportionate rate compared to others. Management of key process data is instrumental in helping the system operate smoothly. Multiple attempts to optimize dosing injection time duration (of the electron-donating compound) demonstrated a continuous 30-hour injection each week was the ideal time to inject sodium lactate. A continuous 43-hour injection led to the fouling of the system flow meter downstream of the booster pump. Daily sodium lactate injections of 6 hours 5 days per week resulted in exceedances of the targeted concentration of sodium lactate and potential for biofouling.

In the beginning of the system operations, all data were downloaded onto a thumb drive and transferred via secure file transfer links to be uploaded and managed in Excel™. As time progressed, the process became time consuming and would often result in data quality issues. This required multiple quality control measures to ensure there were no data discrepancies. The data were moved to an EQuIS™ database, where data quality checking and the ability to process high volume data, in a SQL server database, are built-in features. Then a PowerBI™ dashboard, connected to EQuIS™, was set up to assist with visualizing and reviewing these data in near real-time. These tools dramatically reduced effort expended, along with project costs, when evaluating data to optimize operations. Visualizations generated by Excel™ and PowerBI™ will be presented. Ultimately, increased substrate aids in reducing CVOCs though caution should be taken so that fouling of the system pipelines/wells do not hinder system performance.