WORK PLANS_FILE 1 - Laserfiche WebLink

Home Browse Search

• • Mr. Ron Rowe Page 2 of 6 • Plume Stability Cumulative groundwater sampling data indicate that the plume of dissolved hydrocarbon contamination originating from the onsite source is generally stable. Increasing concentrations of dissolved gasoline and MTBE beneath the southern portion of the property are unrelated to releases on the subject property. Insignificant Threat to Human Health or the Environment Average benzene concentrations in groundwater appear to be below the level that would cause a significant health risk to occupants of the property. The stability of the plume suggests that no significant threat to beneficial uses of groundwater at point and time of use exists. These circumstances suggest that natural attenuation may be the most appropriate remedy to complete the restoration of groundwater. In order to evaluate this, Ground Zero proposes to perform the following scope of work: • TASK 1 QUARTERLY GROUNDWATER MONITORING AND SAMPLING Ground Zero will perform quarterly groundwater monitoring and sampling at the site until directed otherwise. Sampling will include oxygenate and 1,2 DCA analyses for all monitoring wells and all vapor wells. Ground Zero will request appropriate reductions in the frequency and/or analytical suite from time to time based upon the adequacy of historical data in characterizing plume dynamics. In addition, we propose conducting at least one round of bioattenuation monitoring to include insitu measurements of dissolved oxygen and redox potential and analysis of water samples for nitrate, sulfate, alkalinity and ferrous iron. TASK 2 CONFIRMATION SOIL BORINGS AND VERTICAL DELINEATION The first purpose of this task is to document the existing concentrations of contaminants in the vadose zone where soil vapor extraction has been operating. Additionally, this task is intended to complete the vertical definition of contamination in the saturated zone and will serve to better characterize the lithology beneath the site. Initially, one CPT boring (CPT1) will be advanced to a depth of approximately 100 feet bgs, or more if the rig is capable, within the former tankpit. The CPT data will be used to assist in the selection of subsequent soil and groundwater sampling depths. CPT1 will be • twinned by confirmation soil boring CBI which will be drilled to a depth of 100 feet, or more if field evidence of contamination persists. Three additional borings (CB2 through mekkbsure\addmdum