WORK PLANS - Laserfiche WebLink

Home Browse Search

�. .i 5.0 ALTERNATIVE DEVELOPMENT AND ANALYSIS Two remedial alternatives developed based on the technologies discussed in Section 4.0 will be reviewed to determine the most appropriate to expedite site closure given site conditions and constraints. The alternatives are: 1.In Situ Bioremediation 2. Data Gaps Sampling and Low Risk Site Closure r 5.1 Alternative 1 —In Situ Bioremediation ` Alternative 1 consists of using a direct-push drill rig and injecting ORC®through steel rods into the subsurface treatment area Injection locations will need to spaced 10 feet apart in a grid pattern throughout ` the source area,encompassing a treatment area of approximately 55 feet by 75 feet. Approximately 48 injection locations would be required to adequately distribute oxygen throughout the estimated significant portion ofthe contaminant plume. This estimate was approximated byusing an estimate ofthe groundwater velocity to distribute the dissolved oxygen. The velocity ofthe groundwater at the site was estimated to be 20.1 feet per yearbased on hydraulic conductivity(slug test data)(W ESTON, 1992)and the current groundwater gradient of 0.009 ft/ft. The direct-push deliverymethod calls for drive rods with an inner diameter of at least 5/8 of an inch to be _ pushed to the bottom ofthe contaminated saturated zone. The ORC®is then mixed with water to create a slung,which is injected as the rods are withdrawn. For grid-based treatments,one to two reapplication may be necessary over the duration of the project as determined by groundwater monitoring. Each reapplication will most likely be done over a smaller area and the dose amount less than the initial application. It is estimated that the ORC®will be replaced approximately every 8 to 12 months as it is used UP. Changes in the contaminant levels will be monitored by groundwater sampling to determine when the process will be discontinued. It is likely that multiple injection events will be required. Groundwater ` samPlin will beperformed quarterly, will include wells MW-2 MW-2A MW-3A MW-6 MW-7, MW-9,and the two new wells. WESTON recommends that the two wells outlined in Sections 4.3.2 and ` 4.3.3 be installed under this alternative to adequately address the vertical extent of contamination and direction of groundwater flow at the site. 5.1.1 Effectiveness The effectiveness of Alternative 1 is unknown. Biodegradation ofBTEX compounds occurs under most ~ circumstances when supplied with oxygen. Because oxygen is generated in the contaminant source area, the source is destroyed in place. This technology is more effective than other technologies that try to remove the source through diffusion or other mass tranfermechanisms. The effectivenessofAltemative 17