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i v <br /> 0 <br /> 16 A S S O C I A T E S I N C <br /> approximately 500 feet from the groundwater plume The shallowest aquifer is located <br /> approximately 20 feet below ground surface and is impacted This aquifer is currently <br />' classified as a drinking water source but is not generally used as such <br /> ♦ Criterion 2 <br /> This alternative would reduce the existing levels and volume of impacted groundwater over <br /> time by natural degradation and attenuation, but the rate of reduction is not known The <br /> possible migration of petroleum hydrocarbons caused by surface water flushing <br />' contaminants into the groundwater is minimal due to the asphalt and concrete surface on <br /> site The groundwater gradient direction has been consistently southwest with a magnitude <br /> of 0 0004 ft/ft which makes it unlikely that the plume will migrate off site in the short terra <br /> ♦ Criterion 3 <br /> This alternative would not immediately remediate groundwater to levels acceptable to <br /> regulatory agencies Natural degradation of residual hydrocarbons would occur over time <br /> ♦ Criterion 4 <br /> Additional costs for implementing this alternative are related to the costs associated with the <br /> continued monitoring to ensure natural attenuation is occurring and the permitting and <br /> destruction of existing wells at project completion The cost of this alternative is estimated <br /> to be about $12,000 per year for monitoring, $5,000 to $10,000 for enhancing <br /> biodegradation with introduction of oxygen if warranted, and $5,000 for a closure plan and <br />' well destruction <br />' ♦ Criterion 5 <br /> This alternative is effective in minimizing the health-based risks in the short term <br /> Exposure to humans by contamination releases to the air due to dust, or through ingestion or <br /> 1 dermal exposure to impacted groundwater is minimal during groundwater monitoring and <br /> well destruction activities but is otherwise nonexistent <br /> 1 ♦ Criterion 6 <br /> The long term effectiveness of this alternative is acceptable This alternative would reduce <br /> the toxicity and volume of the contaminants by natural biodegradation, but the rate of <br />' reduction is not known The possibility for health-based risks in the long term is low as <br /> long as the site remains surfaced and exposure of humans to impacted groundwater does not <br /> occur during any type of site excavation or structure demolition activities <br />' ♦ Criterion 7 <br /> Of all the alternatives the passive remediation approach is the easiest to implement <br /> iGroundwater monitoring activities would continue, but additional analysis of water samples <br /> would be implemented to ensure natural attenuation is occurring When concentrations <br /> have reduced to levels acceptable to the regulatory agencies or an apparent decreasing trend <br /> is evident, a closure plan will be submitted Well destruction permits would be obtained <br /> w 1130991reportslsumweh doc 10 <br />