## 3 Results  
### Tracer Test Results  
As discussed above in Section 2.2.1, remedial design modeling suggested a 9.5 lpm (2.5 gpm) recirculation flow rate to achieve an approximate 26-day travel time between injector-extractor wells. The dense, high-resolution geologic characterization achieved during the installation of the wells and the tracer test results, however, indicated that the first arrival and median travel times were much shorter than 26 days, at recirculation flow rates between 15.1 and 20.4 lpm (4.0 and 5.4 gpm). The difference between design and operational flows and travel times was due to heterogeneities in the shallow zone geology, which consisted of a general firing of the materials from the water table to the aquitard. This resulted in higher permeable zones in the upper portions of the aquifer and channels or braids of coarse materials interbedded and intermittent throughout. At the EL, EVO, and source zone test cells, between approximately 1892.7 and 2271.3 L (500 and 600 gallons) of bromide tracer stock solution was injected into the recirculation flow stream at rates ranging between approximately 15.1 and 18.9 L per hour (4 and 5 gallons per hour, respectively). The flows were adjusted upward from the design flow rates until the pressure responses recorded at the extraction and injection wells were approximately equal to the pressure responses at these wells predicted in the numerical flow model used for the remedial design. Average bromide stock solution concentrations ranged between approximately 1250 mg/L and 3000 mg/L. Care was taken to keep the injected bromide concentration below 100 mg/L to reduce its antiseptic properties. Tracer testing was not conducted in the dairy whey test cell.  
Breakthrough and peak detections of the bromide tracer at the extraction wells varied from test cell to test cell. At the EL and EVO test cells, breakthrough was detected at the extraction wells 18 h after injection started. The peak detection times and concentrations varied between these test cells. In the EL test cell the peak detection occurred after 6.9 days of injection, and in the EVO test cell the peak detection occurred 5.4 days post injection. The peak concentrations detected at the EL and EVO test cells were approximately 50 mg/L and 80 mg/L bromide, respectively. These peak concentrations were between approximately 50% and 70% of the injected bromide concentration and indicated variability in hydrodynamic dispersion, likely a measure in the degree of heterogeneity in different areas of the water-table aquifer.  
In the source zone test cell, a total of 2400.0 L (634 gallons) of tracer stock solution, at an average bromide concentration of 1250 mg/L, was injected. The average feed rate of the tracer stock solution was 20.4 L per hour (5.4 gallons per hour). Breakthrough of the bromide tracer was detected 96 h later in EW-3, with the peak detection occurring after 48 days of injection and recirculation. Compared with the other test cells, these results confirm the low permeability zones present at the base of the shallow aquifer and the need for segregating the source zone injection wells.  
The USEPA semi-analytical ground-water flow simulation program RESSQC, a computational module of Wellhead Protection Analysis (WHPA), was used to delineate the time-related capture zone around the extraction wells and tracer fronts around injection wells. The volume of the capture zone at time of maximum breakthrough was modeled for each test cell. Ultimately, the flow model calibrated to the results of the tracer tests was used to assess full-scale operational modes, where injected amendments could be mixed with greater contact and long travel paths could be developed to extend travel times and improve contact with bio-amendments within the hotspot treatment area.