# Estimation of Saprolite Thickness Needed to Remove _E. coli_ from Wastewater
## 3 Results and Discussion  
### Saprolite Properties  
Selected properties of the saprolites studied are shown in Table 2. The sites are listed in increasing estimated thickness of saprolite below septic drainlines needed to remove _E. coli_ from wastewater. Three saprolite horizons were included for Site 5, which had a thick saprolite zone, bringing the total number of samples to 14 for the 12 sites overall. Due to the differing thicknesses in the overlying soil, the depths of saprolite ranged from 50 to 395 cm across sites. Textures ranged from sand to clay loam, and clay percentages ranged from 2 to 30%. In situ K\({}_{\mathrm{sat}}\) values ranged from 0.7 cm/d (highest clay percentage) to 233 cm/d (highest sand percentage). However, on average, the sites had K\({}_{\mathrm{sat}}\) values < 10 cm/d. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Site No.** & \begin{tabular}{c} **Depth** \\ **Range** \\ \end{tabular} & **Sand** & **Silt** & **Clay** & **\begin{tabular}{c} **TEXTURAL** \\ **CLASS** \\ \end{tabular} & **In Situ K\({}_{\text{sat}}\)** & **\begin{tabular}{c} **Cation Exchange** \\ **Capacity** \\ \end{tabular} & **No. of Cores** & \
\begin{tabular}{c} **Volume of Cores** \\ **\(\leq\) 10 μm Diam. \({}^{\dagger\dagger}\)** \\ \end{tabular} & **
\begin{tabular}{c} **Estimated Sapphire** \\ **Thickness for OSWMS** \\ \end{tabular} \\ \hline \multicolumn{2}{c}{**cm**} & \multicolumn{2}{c}{-**\%**} & \multicolumn{2}{c}{**cm/d**} & \multicolumn{2}{c}{**cm/d**} & \multicolumn{2}{c}{**cm/cm\({}^{3}\)**} & \multicolumn{2}{c}{**cm**} \\ \hline Wake & 95-120 & 44 & 26 & 30 & Clay loom & 0.7\({}^{\dagger\dagger}\) & 4 & 19 & 0.47 \(\pm\) 0.08 & 36 \\
9 & 185-255 & 57 & 21 & 22 & Sandy clay loom & 21 & 1 & 22 & 0.38 \(\pm\) 0.09 & 45 \\
5\(<\)1 & 80-142 & 79 & 14 & 7 & Loamy sand & 3 & 6 & 14 & 0.37 \(\pm\) 0.08 & 46 \\
5\(<\)C3 & 125-200 & 83 & 15 & 2 & 2 & 6 & 10 & 0.37 \(\pm\) 0.15 & 46 \\
12 & 76-70 & 73 & 23 & 4 & Sandy loom & 13 & 1 & 14 & 0.36 \(\pm\) 0.08 & 47 \\
8 & 370-395 & 66 & 28 & 6 & - & 41 & 29 & 11 & 0.34 \(\pm\) 0.08 & 50 \\
6 & 135-200 & 73 & 21 & 6 & - & 69 & 2 & 9 & 0.33 \(\pm\) 0.05 & 52 \\
3 & 60-90 & 79 & 16 & 5 & Loamy sand & 7 & 9 & 15 & 0.32 \(\pm\) 0.05 & 53 \\
2 & 195-210 & 62 & 28 & 10 & Sandy loom & 77 & 3 & 15 & 0.31 \(\pm\) 0.06 & 55 \\
115-210 & 68 & 27 & 5 & - & 27 & 11 & 8 & 0.28 \(\pm\) 0.10 & 61 \\
5\(<\)C4 & 200-246 & 87 & 11 & 2 & Sand & - & 6 & 2 & 0.25 \(\pm\) N0 & 68 \\ \(7\) & 50-150 & 87 & 8 & 5 & Loamy sand & 9 & 9 & 6 & 0.25 \(\pm\) 0.11 & 68 \\ Knight. & 115-135 & 77 & 16 & 7 & - & 5 & 2 & 21 & 0.23 \(\pm\) 0.06 & 74 \\
10 & 135-200 & 91 & 4 & 5 & Sand & 233 & 1 & 15 & 0.15 \(\pm\) 0.06 & 113 \\ \(r\) values & 0.63* & \(-\)0.066* & \(-\)0.04 & \(-\)0.0 & 0.00* & \(-\)0.16 & \(-\) & 0.09* & 10 \\ \hline \hline \end{tabular}  
* Geometric mean, number of measurements made per site ranged from 2 to 11 with a mean of 6.\({}^{\dagger\dagger}\) Mean \(z\) standard deviation.
* Indicative value is significant at the 0.05 level.  
\end{table} 
Table 2: Selected properties for sapplices studied and estimated thickness of sapplice needed to filter _E. coli_ from wastewater using Equation (3). Correlation coefficients show relationship between a property and estimated sapplice thickness. Cation exchange capacities were generally low (<10 cmol\({}^{+}\)/kg (Table 2)), suggesting that physical filtration is the major factor in the removal of _E. coli_ rather than adsorption of _E. coli_ onto the negatively-charged mineral particles. [PERSON] [25] conducted batch sorption experiments to understand the attachment kinetics of bacteria in the presence of humic acid and clay colloids. Results indicated that the adsorption of bacteria onto porous media was enhanced by the presence of high surface area and high cation exchange capacity clay-textured soil, unlike the materials studied here.