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HV0C,51F.X REMOVAL • The bubble zone,-A-as still expanding during the ten-day test Based upon the time sequence. a long axis extending outs ab --cards out 30 m(98 ft) in a westerly and easterly direction would be reached.with a minor axis (at right angles) of about 18 m (59 fit Each well would then treat a region 61 m (200 ft) long;by about 30 5 in (100 ft) wide and 27 m (90 ft) deep Although an elliptical zone exists here,the occurrence of bubbles at mimwell 126 about day five complicates the picture We must aNcume that a hurled gravel ctreamhed, ahneit 10 m (i-1 ft) wide,was originally intercepted and either small streamlets{braided streams) intercepted it Or some secondary fracturing by air pockets was occurring to create the offshoot to miniwell 126 A geological basis exists for assuming gravel streambeds originating east-west across the region from glacial streams Side connections could occur(see Table 2) GROUNDWATER FLOW-CIRCULATION PATTERN DEFE41MON -- Dingy groundwater flow measurements were perfor-mod with a KVA Model 40 GeoFlo R meter prior to the startup and during the operation to determine backgroundsvelocityW and changes Initial measurements indicated a flow near the spargewell(TW) _ " direction it a velocjjr of'TietWE= -2 ml.6 ftp and-24 in (8 ft)per day,coinciding with the direction of movement of the plume Additional measurements were taken after beginning injection to determine the velocity of groundwater eddies created by the double-screen well system and nsmg bubbles which expand the treatment zone both vemcally and horizontally across the site The observed change in direction and rate coincided with a slow vertical mixing rate set up at right angles to the main axis of mixing. At well A(which is 5.4 m [18 ft] east of TW)the change was measured at about i9 m (3 ft)per day in an easterly direction. At well B (which is 1 I m [36 ft] west of TW) a velocity change of 15 m ( 5 ft)per day occurred towards the TW well Well A is shallow (13 m [43 ft]below grade)and well B significantly lower(15 m [49 ft]below grade) Groundwater moving in towards the spargewel}would reach a maximum at about 27 in (71 ft) below grade The outward gyre(Figure 5)would reach a maximum velocity at about 12 m (39 ft) The vertical eddy for mixing appeared to reach a velocity with a diameter of about 20 m (66 ft)by day ten of the test,with an estimated velocity of about 3 3 m(10.8 ft)per day. This is slow by normal standards and probably the result of loss of pressure along the narrow gravel streambed, intercepted between 20m and 25 m deep(65 6 ft and 82 ft) RESULTS The site held a combination of a lower dissolved chlorinated solvent plume, dominated by TCE principally and PCE,and an upper dissolved fuel spill, dominated by BTEX compounds. A large region of the wells exhibited elevated HVOCs in groundwater, with initial samples from wells D,B,C, and mmiwell 129 (14m to 15 m [46 ft to 49 ft]) showing concentrations of 2,100 ggll, 14,500 µg11, 12,500 µg11, and 1,450 gg/l, respectively, well above the 800 µg11 originally expected Groundwater from the spargeweil (TW)and wells A,B,C, and D exhibited total BTEX concentrations ranging from 62 to 95 ggll Concentration of HVOCs located in the gravel zone underwent immediate rapid reduction(wells TW, D, 129) Nearby wells located at right angles(probably in fine sands)to the buried gravel streambed, showed a slower removal, converging on a logarithmic decay rate • Those in the outlying wells,mainly requiring recirculation to treat the groundwater,tended to 6