Laserfiche WebLink
! I Yl J_1111E E F�h Fi, '� `�:..y. — .M�_..�` � <<' r b t.. Kti✓",...n f ' c �.�.t w^ ; F . .-az.. <br /> I R ^JSs _ ,. 1'.. ";S ,.�:,...+�y. r 4'i•. _ '1 .a Z t_.... �J J 3..3...—..4-.x—.N..`e..4 __ <br /> _ 1 <br /> t <br /> 15 February 2000 <br /> AGE-NC Project No 98-0448 <br />' Page 24 of 33 <br /> natural attenuation <br /> I91 IN-SITU ATR SPARGING <br /> IAS utilizes air injection to volatilize dissolved hydrocarbons and strip volatile hydrocarbons from <br />' ground water and transfer the hydrocarbons into the vadose zone in a vapor state, where they can be <br /> recovered by SVE Air sparging is commonly conducted concurrently with an SVE system <br /> I <br /> 91 1 Principles <br />' IAS induces the transfer of hydrocarbons from a dissolved state in ground water to soil gas in the <br /> vadose zone by creating an intense concentration gradient between the two regimes Commonly, a <br /> SVE well is surrounded by specifically designed air injection(sparging) wells that are screened only <br /> Attie saturated zone(t,q,below ground water"low capacity blower connected to the injection <br /> wells forces air under pressure into the saturated zone, producing air bubbles that strip dissolved <br /> contaminants from the ground water and rise to the soil-air-water interface Upon reaching the <br /> unsaturated zone, the volatilized hydrocarbons are drawn toward the extraction well by the <br /> subsurface air flow induced by the vacuum potential <br /> I <br /> 9 12 Basic System Design <br /> Injection wells are screened within the saturated zone and normally have limited screened intervals ' <br /> J Y <br />' typically five to ten feet Since most of the air escapes from the upper part of the interval where head <br /> pressure is the least,1ittle is gained by increasing the length of the screen interval The IAS system <br /> must be combined with vapor extraction,to contain vapor stnpped from the ground water <br /> The radius of influence of a sparging well is dependent on site lithology and the depth of the <br /> sparging well Sandy soil types tend`to produce a larger radius of influence, clayey soil types tend <br />' to produce a more limited radius of influence <br /> Unless injection wells are properly located, channeling of air flow streams may occur and <br /> contamination pockets may be bypassed This problem is more common where firie-grained strata <br /> having low permeability are interbedded with coarse-grained strata in the saturated zone Air flow <br /> is retarded within fine-grained strata, and hydrocarbon recovery is poor <br /> I <br /> Advanced GecEnwronmentei,Inc <br />