4.7.0 Macro Molecules (Cell 4)

The University of Arizona, in cooperation with the U.S. EPA, operated the macromolecule test cell.  The cell is approximately 3m by 5m in surface area and instrumented as shown in  Figure 4.7.0.1. The injection wells are along the south side of the cell and labeled 244x. The extraction wells are along the north side of the cell and labeled 245x. The locations labeled 249x are the locations where post remediation cores were collected. Multilevel samplers are designated 241x, 242x, and 243x. Objects with the designation xx6x are small diameter screened wells installed to monitor the head during the experiments. This cell was located in the most contaminated region of the test area.   Looking at the site description drawing, this cell is located in the middle of one of the disposal pits.  The high concentrations were also detected and mapped during the preliminary characterization with resistively and through core analysis.  Difficulties were encountered during the installation of the sheet pile and it was believed that the bottom of the sheet pile was not in contact with the clay.  To improve the likelihood of a bottom seal, a pit was dug and the sheet piles driven an additional 1.5 m into the formation.  During the well installation and soil sampling, workers needed to use supplied air due to the toxicity of the volatile substances emanating from the cuttings.

Essentially seven studies were performed. Initially, the formation was sampled by coring the formation during the installation of wells and multilevel samplers. Descriptive logs of the wells cored are available in the database in the table Boring Logs.   The core samples were analyzed for a group of chemicals initially believed to be representative of the site and of regulatory concern.  The selected chemicals represented several classes of contaminants. Following the installation of the instrumentation, the formation was allowed to re-equilibrate before any additional measurements were made.  Ground-water samples were collected under both static and dynamic conditions.  Injecting uncontaminated ground water into the formation, simulating a forced gradient flush or water flood, created the dynamic flow conditions.  The static samples would be representative of the maximum concentration that would be anticipated in water samples from this location.  Ground-water sampling was followed by a pre-remediation tracer study.  The pre-remediation tracer study was designed to estimate the mass of NAPL in the formation.  Once the pre-remediation tracer study was completed, the remedial technology was implemented and its performance monitored.  At the termination of the remedial demonstration, the three characterization steps were repeated in reverse order. A time line for the activities is shown in Table 4.7.0.2.  An analysis of this data permits an evaluation of the technology.

Cyclodextrin molecules are helical structures with a hydrophobic interior and a hydrophilic exterior. The objective was to use the characteristic of the molecule to transport the hydrophobic molecules through the formation since the molecule itself moves through the formation as easily as water. Essentially, this is a solubilization process since the cyclodextrin increases the hydrophobic "carrying capacity" of the fluid. The amount of remedial fluid required to achieve a cleanup level is related to the partition coefficient between the cyclodextrin and the individual contaminants and how cyclodextrin preferentially carries the different contaminants.

Table 4.7.0.1 Operating Conditions for the Experiments
Parameter
Activity
Pre-Remediation Tracer Demonstration Post-Remediation Tracer
Average Saturated Thickness (m)  ND ND  ND 
Average Head Across Cell (m) ND  ND  ND 
Average Influent Flow rate (lpm) ND  ND  ND 
Average Effluent Flow rate (lpm)  4.29  4.58  4.32

Table 4.7.0.2 Study Sequence
Test Activity Fluid injected *  Total flux rate (l/m)- volume (l) Duration
Core and install instrumentation Collect soil samples None   3/12/96 - 3/14/96 
Ground-water sampling Collect water samples None    5/27/96
Pre-remediation tracer Establish flow field Water  4.6 lpm  ?
  Inject tracer suite 1  br,eth,pen,hex,dmp,methep  4.6 lpm  6/6/96
  Maintain flow field Water  4.6 lpm  6/6/96 - 6/16/96
Remedial technology Establish flow field  Water  4.6 lpm  
  Inject remedial fluid 10% cyclodextrin  4.6 lpm  7/20/96-7/31/96
         
  Remove hpcd Water  4.6 lpm  7/31/96 - 8/5/96
Post-remediation tracer Establish flow field  Water   simultaneous with above
  Inject tracer suite 2  br,eth,pen,hex,dmp,methep  4.6 lpm  8/6/96 - 8/7/96
  Maintain flow field  water  4.6 lpm  8/7/96 - 8/13/96
Ground-water sampling Collect water samples None    8/19/96
Core  Collect soil samples None    9/18/96 - 9/20/96
* br = bromide, eth = ethanol, pen = pentanol, hex = hexanol, dmp = 2,2-dimethyl-3-pentanol, methep = 6-methyl-2-heptanol.

4.7.1    Core Analysis

Decane and undecane are typical for the chemicals that were entering the chemical waste pit from the fire training area up-gradient and the dichlorobenzene was probably introduced directly into the pit. The figures plot the concentration of the individual contaminants as a function of depth without regard for spatial location within the test cell.  Black data were the data collected prior to remediation and the blue data were the observations collected after remediation.  The vertical bars are the means for the values over the bar's depth zone;  95% confidence limits are plotted, where possible, with the limits represented by the small + at the center of the bar.  The two magenta lines depict the vertical extent of the target zone and the surface area within the cell is printed at the top of the figure.   At the top of the figure, several different methods are reported to calculate the mean concentration and total mass in the target zone of the test zone.  The decane and undecane show very similar distributions throughout the profile with little variability sample to sample.  It appears that the target zone for the remediation test only captured the lower portion of the contamination and that there was a definite decrease in concentration as one looks deeper into the profile.  The dichlorobenzene is much more variable with depth than either the decane or undecane.  All of the chemicals in this cell were sufficiently high in concentration to indicate that there should be no significant error in interpreting the results.  The removal efficiency, in general, is greater than 70%.  In general, the more soluble compounds were removed more effectively than less soluble compounds suggesting that the cyclodextrin behaved as a solubilizing agent rather than a mobilizing agent.  The least soluble compounds decane and undecane showed very little, approximately 30%, removal.  Displays for the individual chemicals are attached in the following figures: benzene, dichlorobenzene, decane, ethylbenzene, m-xylene, naphthalene, o-xylene, 1,1,1-trichloroethane, trichloroethene, trimethylbenzene, toluene,  and  undecane.

Table 4.7.1.1 Summary of Core Data Based on Boxcar Averaged Results
Chemical Pre-Remediation concentration (mg/kg) Post-Remediation concentration (mg/kg) Fraction Removed
dichlorobenzene 130 27 0.79
1,1,1-trichloroethane 3.8 0.91 0.76
toluene 16 4.7 0.71
o-xylene 14 4.3 0.69
m-xylene 5 1.4 0.72
naphthalene 7.2 1.5 0.79
trimethylbenzene 7.9 4.0 0.49
decane 68 50 0.26
undecane 250 170 0.32
ethylbenzene 2.8 0.64 0.77
trichloroethene 6.8 0.71 0.90
benzene 0.25 0.034 0.86

If one evaluates the performance of cyclodextrin based on fraction of mass removed, the performance does not look like one of the better performers. However, if one evaluates the mass of contaminant removed as a function of the number of pore volumes of remedial fluid used it begins to look like one of the better systems.

4.7.2 Tracer Analysis

A summary of the tracer activities is shown it the following table:
Table 4.7.2.1 Summary of Traer Activities
Tracer Pre-Remediation Post-Remediation
Concentration (mg/l) Total Mass Injected (g) Mass Recovered 

(g)*

 Concentration (mg/l) Total Mass Injected (g) Mass Recovered 

(g)*
Bromide  292  438  340  304  432  203
2,2-dimethyl-3-pentanol  531  796  553  619  879  798
hexanol  983  1475    871  1237  
pentanol  1083  1624    797  1132  
Tracer Volume (l)
 1500
  1420
Injection Time (min)
 331
  313
* Based on zero moment of extrapolated data.

One would anticipate good conservation of mass for bromide. In the pre-remediation study, only 78% of the bromide was recovered. In the post-remediation study, only 47% of the bromide was recovered.  When mass conserve is not observed with bromide in a closed system one begins to question the internal consistency of the rest of the data. For this reason, we only discuss the tracer data on a qualitative basis rather than making quantitative conclusions based on the data. The pre-remediation tracer showed relatively uniform flow across the cell and the NAPL saturation estimates are reasonable for the highly contaminated conditions that were observed with the core data.  In the post-remediation tracer analysis, two observations can be made.  First, the time of travel is significantly less than almost one half the travel time for the pre-remediation study.  Second, the apparent NAPL saturation has increased significantly.  This suggests that either there was significant biofouling of the formation because of the readily degradable sugar molecule that was used to increase the solubilization, or that a significant portion of the sugar had gelled in the formation reducing the permeability and showing a partition coefficient to the tracers.  Even from a qualitative standpoint, significant changes were observed in the aquifer properties and the long-term implications of this change should be investigated before the technique is implemented in a full-scale operation.

Table 4.7.2.2. Summary of Extraction Well 1 Tracer Analysis
Extraction Well 1
Pre-remediation
 Post-remediation
  conservative (bromide) 2,2-dimethyl 
-3-pentanol		 NAPL Saturation conservative (bromide) 2,2-dimethyl 
-3-pentanol		 NAPL Saturation
Pulse duration (days)  0.230      0.217    
zero moment data   61.861  90.957    30.049  170.078  
zero moment extrapolated 65.408  95.691    30.269  109.569  
first moment / zero moment data (days)  1.720  2.711  0.083  0.624  2.174  0.405
first moment extrapolated / zero moment (days)  2.243  3.243  0.0673  0.631  2.311  0.432
Convective Dispersive Model      0.045      0.280
dispersivity (m)  0.275  0.339    1.870  0.255  
est. initial conc. (mg/l)  209.725  1.405    163.943  403.675  
mean time of travel (days)  1.052  281.096    0.516  1.593  
Stochastic model      0.044      0.259
variance in travel time  0.967  0.986    0.935  0.993  
travel time (days)  1.098 
1.454
    0.546  1.596  
est. initial conc. (mg/l)  271.997 312.126    167.455  384.059  

Figure 4.7.2.1  Extraction Well 1 Pre-remediation tracer analysis 2-2,dimethyl-3-pentanol
Figure 4.7.2.1.b  Extraction Well 1 Pre-remediation tracer analysis 2-2,dimethyl-3-pentanol log
Figure 4.7.2.2  Extraction Well 1 Post-remediation tracer analysis 2,2-dimethyl-3-pentanol
Figure 4.7.2.2.b  Extraction Well 1 Post-remediation tracer analysis 2,2-dimethyl-3-pentanol log
Figure 4.7.2.3  Extraction Well 1 Post-remediation tracer analysis hexanol
Figure 4.7.2.3.b  Extraction Well 1 Post-remediation tracer analysis hexanol log
Figure 4.7.2.4  Extraction Well 1 Post-remediation tracer analysis methylheptanol
Figure 4.7.2.4.b  Extraction Well 1 Post-remediation tracer analysis methylheptanol log
 

Table 4.7.2.3. Summary of Extraction Well 2 Tracer Analysis
Extraction Well 2
Pre-remediation
 Post-remediation
  conservative (bromide) 2,2-dimethyl 
-3-pentanol		 NAPL Saturation conservative (bromide) 2,2-dimethyl 
-3-pentanol		 NAPL Saturation
Pulse duration (days)  0.230      0.217    
zero moment data  56.806  81.850    35.287  111.488  
zero moment extrapolated  58.790  83.420    35.461  117.341  
first moment / zero moment data (days)  1.239  2.120  0.105  0.481  2.101  0.585
first moment extrapolated / zero moment (days)  1.645  2.317  0.059  0.485  2.444 0.699 
Convective Dispersive Model      0.089      0.251
dispersivity (m)  1.333  0.311    9.886  0.316  
est. initial conc. (mg/l)  251.586  289.441    278.879  430.926  
mean time of travel (days)  0.772  1.283    0.506  1.451  
Stochastic model      0.104      0.247
variance in travel time  0.997  0.937    0.984  1.00  
travel time (days)  0.770 
1.364
    0.512  1.451  
est. initial conc. (mg/l)  270.960 379.727    236.876  430.926  

Figure 4.7.2.5  Extraction Well 2 Pre-remediation tracer analysis 2,2-dimethyl-3-pentanol
Figure 4.7.2.5.b  Extraction Well 2 Pre-remediation tracer analysis 2,2-dimethyl-3-pentanol log
Figure 4.7.2.6  Extraction Well 2 Post-remediation tracer analysis 2,2-dimethyl-3-pentanol
Figure 4.7.2.6.b  Extraction Well 2 Post-remediation tracer analysis 2,2-dimethyl-3-pentanol log
Figure 4.7.2.7  Extraction Well 2 Post-remediation tracer analysis hexanol
Figure 4.7.2.7.b  Extraction Well 2 Post-remediation tracer analysis hexanol log
Figure 4.7.2.8  Extraction Well 2 Post-remediation tracer analysis methylheptanol
Figure 4.7.2.8.b  Extraction Well 2 Post-remediation tracer analysis methylheptanol log

Table 4.7.2.4. Summary of Extraction Well 3 Tracer Analysis
Extraction Well 3
Pre-remediation
 Post-remediation
  conservative (bromide) 2,2-dimethyl 
-3-pentanol		 NAPL Saturation conservative (bromide) 2,2-dimethyl 
-3-pentanol		 NAPL Saturation
Pulse duration (days)  0.230      0.217    
zero moment data  60.487  88.141    31.785  148.193  
zero moment extrapolated  61.373 89.659    31.953  158.086  
first moment / zero moment data (days)  1.188  2.320 0.142  0.593  2.192 0.444 
first moment extrapolated / zero moment (days)  1.278  2.487 0.140  0.599  2.622  0.555
Convective Dispersive Model     0.077      0.365 
dispersivity (m)  1.867  0.493    0.924  0.367  
est. initial conc. (mg/l)  301.528  309.650    152.722  608.762  
mean time of travel (days)  0.978  1.536    0.445  1.654  
Stochastic model      0.073     0.323 
variance in travel time  0.985  1.001    0.839  1.009  
travel time (days)  0.990  1.214    0.496  1.689  
est. initial conc. (mg/l)  305.238  424.112    173.912  593.570  

Figure 4.7.2.9  Extraction Well 3 Pre-remediation tracer analysis 2,2-dimethyl-3-pentanol
Figure 4.7.2.9.b  Extraction Well 3 Pre-remediation tracer analysis 2,2-dimethyl-3-pentanol log
Figure 4.7.2.10  Extraction Well 3 Post-remediation tracer analysis 2,2-dimethyl-3-pentanol
Figure 4.7.2.10.b  Extraction Well 3 Post-remediation tracer analysis 2,2-dimethyl-3-pentanol log
Figure 4.7.2.11  Extraction Well 3 Post-remediation tracer analysis hexanol
Figure 4.7.2.11.b  Extraction Well 3 Post-remediation tracer analysis hexanol log
Figure 4.7.2.12  Extraction Well 3 Post-remediation tracer analysis methylheptanol
Figure 4.7.2.12.b  Extraction Well 3 Post-remediation tracer analysis methylheptanol log

4.7.3    Extraction Analysis

Two alternatives could be utilized to interpret the data in the estimation of overall performance.  If there were a complete analysis of the NAPL, one could estimate the initial mass of a particular contaminant based on tracer data estimates of the NAPL saturation and the mole fraction of the individual contaminant in the NAPL.  Samples of NAPL were collected from several locations around the site and analyses performed.  When a NAPL is sampled in this manner, the fraction collected is what is readily mobile.  It is necessary to assume that this NAPL is in equilibrium (i.e., having the same composition) with the rest of the NAPL in the immediate area.  If there is a "pitch" portion to the NAPL, this fraction may not be in equilibrium with the energetically free NAPL, creating a potential bias to the results.  Using core data creates a different set of biases.  The core samples that were analyzed represent only a subsample of the total core removed from the formation.  Much of the formation is occupied by cobbles that were too large to be included in the analysis.  Since a significant portion of the formation was occupied by cobbles, the estimated mass is likely less than the actual presented value.  This is not a significant problem when comparing core data to core data but may be a significant problem when using core data as an estimate for the starting mass in the individual test cell.  In addition to this problem, the geometry of the test cell creates dead zones or at least zones that are difficult to access.  Thus, the remedial fluid may not have been in contact with all of the contamination.  In the analysis presented here, core data was used as a starting point.

Data appears to be internally reasonably consistent with the core data with similar removal fractions for 1,2,4-trimethylbenzene, ethylbenzene, toluene, and  naphthalene.  It appears from the elution curve of the macromolecule that the delivery of the remedial fluid was consistent across the cell.  One would anticipate that the analysis would be constant with the core data.  The results for three of the chemicals show strange variability well to well: undecane, decane, and trichloroethene.  The concentration for undecane in well 2 is approximately 10 times the concentration in the other wells.  If well 2 were the correct values and wells 1 and 3 miss reported by a factor of 10, the data would appear much more consistent with the core data.  Dichlorobenzene  appears to have eluted nearly 100% based on the elution curves while only 50% based on the core data.  Either the core data underestimates the mass removed or the remedial fluid swept a volume greater than the target zone.  Note that in the  core data figure dichlorobenzene there is a significant amount of contaminant above the target region. The elution curve for o-xylene, is significantly less than the mass removed based on core analysis.  Since GC/MS performed the core analysis and the elution curves were analyzed by GC, it is believed that the GC analysis is less reliable and it is likely the cyclodextrin was masking some of the o-xylene.
 

Table 4.7.3.1 Summary of Mass Removed in Elution Curve
Chemical Initial mass * (g) Mass extracted (g) Fraction removed
dichlorobenzene
5400
  5278  0.97
decane
5400
 62.4  0.01
naphthalene
660
 404  0.61
o-xylene
 1800
 111.95  0.01
undecane
 21000
 296  0.01
ethylbenzene
 300
  101  0.66
toluene
 2900
  733  0.75
trimethylbenzene
 770
 203.6  0.26
* Initial mass estimate based on geostatistical analysis