## 2 Materials and Methods
### Pilot Test Procedures
#### 2.3.2 Biorecirculation Testing  
The tracer study incorporated into the recirculation testing was a critical step in understanding the travel time between injection and extraction wells and the expected flow and dispersion of the bio-amendments in situ. Bromide (in the form of sodium bromide salts) was used as the conservative (non-adsorbing) tracer. The tracer was added to the injection well at the manifold using chemical metering pumps. Monitoring of the tracers was accomplished using two methods: bromide probes installed in each of the test cell extraction wells (EW-3, HSE-11, and HSE-14) and sampling of the extraction well manifold. Extraction manifold samples were submitted for bromide laboratory analysis. Bromide probes were programmed to record bromide concentration at a frequency of once every half hour and bromide results were logged in the probe's on-board datalogger. The datalogger was accessed and data downloaded weekly. Furthermore, samples were collected for laboratory bromide analyses during the recirculation testing. In addition, each batch of stock tracer solution was sampled and submitted for bromide analysis so that the injection concentration calculations could be checked for accuracy. Baseline Recirculation Sampling and Analysis  
Immediately prior to the additional bio-amendments to the test cell recirculation, the flow stream from the extraction well was sampled to assess the homogenization of the groundwater within the test cell. Similar to the pre-pumping baseline sampling, baseline recirculation samples were field screened (temperature, dissolved oxygen, pH, redox potential and specific conductance) and submitted for a full suite of laboratory analyses. Electron Donor Addition  
Upon completion of the baseline sampling tasks, the electron donor/nutrient test began. The electron donor volumes and recirculation requirements were established using the tracer test results. An injection of a nutrient mix was also included with each injection of electron donor. The nutrient mix was a yeast fermentation metabolite provided by JRW Bioremediation, LLC. It was added to accelerate the growth of the microbial populations. All the field test cells received supplemental injection of EVO. EVO was chosen as the electron donor for all four test cells primarily because vinyl chloride had begun to form in the EVO test cells but not in the EL or dairy whey test cells. Table 1 summarizes electron donor used at each test cell. EVO Test Cell (HIS-19/HSE-14): The EVO used was a soybean oil-based product with a total organic carbon concentration of approximately 510 mg/L. Approximately 1381.7 L (365 gallons) of EVO and 283.9 L (75 gallons) of nutrient mix were fed as a stock solution into the injection well recirculation flow stream at an approximate feed rate of 15.1 L per hour (4 gallons per hour). Dosing of the EVO and nutrient mix required over five days. During and after the injection, recirculation was continued until the end of the 5-month testing period. Due to decreasing total organic carbon (TOC) concentrations measured in the extraction well discharge, supplemental electron donor addition was performed in the middle of the testing period. HSI-19 received approximately 946.4 L (250 gallons) of EVO solution over a 6h period and 227.1 L (60 gallons) of nutrient mix injected over a 2h period as a supplemental EVO dose. Source Zone Test Cell (IW-2S, IW-2D/EW-3: EVO and Hydrogen Gas Infusion): The source zone test cell was slightly different than the hotspot test cell in that injection wells within the shallow aquifer and within the source zone were split into two wells: a collocated shallow and deep injection well. This change was implemented because the deeper sediments above the aquitard were lower in permeability compared with the upper portion of the shallow aquifer, and these deeper sediments were significantly more contaminated.