ARCHIVED REPORTS_XR0012921 - Laserfiche WebLink

Home Browse Search

r . Comment 3: "Why are the UVB monitoring wells to be placed 1 foot from the UVB well? How will installation of wells so close together be accomplished? If that is the limit of the zone of influence,this does not appear very effective." Response 3: The placement of the two monitoring wells does not indicate the limit of the UVB well zone of influence. Instead,the placement of the two monitoring wells will allow the monitoring of the stripping efficiency of the UVB system. The percent stripping efficiency is defined as (1- Cout/ C;,,) x100, where Co,,t is the concentration of volatile and semivolatile hydrocarbon constituents in groundwater leaving the upper screen of the UVB well, and C;,, is the concentration of volatile and semivolatile hydrocarbon constituents in groundwater entering the lower screen of the UVB well. In order to collect representative samples of the groundwater entering and leaving the lower and upper screens of the UVB well, respectively, the two monitoring wells should be installed as close to the UVB well as practically possible. Although Section 2.3 of the Groundwater Remediation System Technical Plan indicates that the monitoring wells will be installed at a distance of 1 foot fro the UVB well borehole, it was subsequently decided to install the monitoring wells further away, at a distance of 2 feet from the UVB well, in order to avoid any damage to the UVB well packing. Comment 4: "Will-the downgradient contamination, outside the circulation zone, be affected by the increased aeration and ground water flowrates within the circulation zone? If so, how will it be affected and how will the parameters will be measured?" Response 4: A UVB system removes volatile and semivolatile hydrocarbons in groundwater primarily through mass transfer in the air stripper located within the well. Secondarily, the increase in dissolved oxygen concentration in groundwater in the air stripper enhances the rate of biodegradation. Therefore, the increase in dissolved oxygen concentration in groundwater leaving the UVB well will enhance the rate of biodegradation within the circulation cell, as well as downgradient within the UVB well release zone. Increased groundwater flowrates within the UVB circulation cell will not affect the downgradient contamination, because groundwater velocity outside the circulation cell corresponds to the natural Darcian groundwater velocity at the site. The dissolved oxygen concentration in groundwater leaving the upper screen of the UVB well will be compared to the dissolved oxygen concentration at monitoring wells outside the circulation cell, both within the capture zone in the upgradient direction and the release zone in the downgradient direction.