ARCHIVED REPORTS XR0009502 - Laserfiche WebLink

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' Work Plan Page 4 Former Manna Pro Site Project No 207 3 August 16, 1999 ' Since the GTI study was completed in 1996, groundwater levels have risen several feet This fact in conjunction with the known distribution of gasoline to depths in excess of 50 ' feet, mean that a substantial volume of the total contaminant plume lies below the groundwater surface Unfortunately, this deeper groundwater contamination is not likely to be efficiently mitigated by the methods proposed by GTI We suggest that vapor ' extraction can be an important part of a remedial action plan, but will not be useful in remediating hydrocarbon contamination situated more than a short distance beneath the groundwater surface Air sparging to introduce oxygen into the subsurface and mobilize ' contaminants may address the deep contamination plume Infected air will encourage the growth of aerobic bacteria and should also help to mobilize light hydrocarbons As these mobilized hydrocarbons move through and up the water column, down gradient vapor ' extraction wells may be used to extract the mobilized hydrocarbons One drawback of this remedial method is that the vapor extraction and the air sparging may both tend to generate a local rise in the level of groundwater Hydrocarbons may tend to migrate ' "down-hill" radially away from this localized groundwater "mound" We suggest that an effective way to capture and destroy fugitive hydrocarbons would be to contain the plume with a passive oxygen barrier This barrier could be constructed by placing magnesium ' dioxide in soil borings around the groundwater plume This material is available under the trade name, Oxygen Releasing Compound (ORC) By encouraging bacterial attack of the hydrocarbons, this material can retard the horizontal migration of the plume due to remedial activities while simultaneously degrading the down gradient end of the plume 1.3.2 Scope of Work The tasks described in this Work Plan encompass the following principal elements ' • Conduct a water well survey to identify all groundwater production wells located within 2,000 feet of the point of release s Install a deep soil boring to be converted to a groundwater monitoring well The intent of this well is to determine the depth of the deepest detectable gasoline impacted groundwater at a point near the point of release The screened interval of the well will be placed dust beneath the deepest detectable petroleum hydrocarbons, as determined in the field during installation of the boring • Install and operate a pilot vapor extraction system Given the change in ground water level which has occurred since 1996, the pilot vapor extraction data documented in the earlier GTI report should be re-evaluated A new vapor extraction well will be constructed and used for the completion of this portion of the pilot study Insofar as all of the screens in the existing wells are submerged beneath the groundwater surface, it will be necessary to construct two new vapor extraction monitoring wells to monitor the effectiveness of vapor extraction at the site 2937 Veneman Ave,##13240 Geo-Phase Environmental Inc Phone(209)569-0293 Modesto, CA 95356 Fax(209)569-0295