ARCHIVED REPORTS_XR0006230 - Laserfiche WebLink

Home Browse Search

asci IU mo I y M itv No sy A r 4 ,/54 Figure 7 presents a view of the separating stream surfaces of all three water bodies in connection with the flow around a UVB The natural groundwater flow comes from the left side (In Figure 7b the three water bodies were artificially separated for clarification.) ' At the left side of Figure 7, the separating stream surface of the contaminated groundwater captured by the UVB can be seen In the center a water body is shown which consists of cleaned groundwater and shows the circulation flow around the UVB. At the right side of Figure 7, the separating stream surface of the cleaned groundwater flowing downstream is displayed The calculation has accounted for the following dimensionless parameters- Q/(Hlv) = 30, a/H = 0 25, and KH/K, = 5 The screen lengths ' at the bottom and top are the same- ar = as = a Diagrams for the Dimensioning of WB Installations Absence of Natural Groundwater Flow. At sites without natural groundwater flow, the sphere of influence (R) of a UVB is of special interest R is dependent on the anisotropy (horizontal over vertical hydraulic conductivity- KH/Kv), on the thickness (H) of the aquifer, and on the length of the screen sections ar and as at the top and bottom of the aquifer (see Fig 8) or the ratio a/H (when the same length of the screen section is used for both, then only a is referred to) Although R is mathematically mfinilf., it is, in practice, defined as the horizontal distance from the well axis to the farthest point at which circulation flow is still significant. Ina dimensionless description, R has been made dependent on the ratio QR/Q,where QR is that water quantity,which circulates within the distance R from the well. The ratio QR/Q, which is prescribed for practical reasons, describes the strength of a circulation flow at the distance R from the well. In Figure 9a, results are presented for ratios Qs/Q = 0 98 and 0.8 and for a = ar = as in a dimensionless diagram. The sphere of influence (R) is independent of the dis- charge through the well, but strongly dependent on the anisotropy KH/K,,. Within usual proportions, the length of the screen sections has only a small influence. For a UVB with ' separating plate and additional pump, a totally screened well casing should be avoided because of hydraulic shortcircuiting. Figure 9b presents a dimensionless diagram that describes the differences (eh) of the hydraulic heads between the top and bottom of a double-screened well through which ==H Ah =hT-he ( Or ; 0 - 2nr f vrdz ' hv,1zl z,H12 T ' K ; l .v ° H KH 0 ' z h a he 1 s UVB Figure 8. Notation in a vertical cross section. 9