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The two curves become essentially identical, again, after about 0.7 pore <br />volumes of effluent are produced. The data indicate that practically all <br />of the readily soluble materials were leached from the samples by the <br />time 1.5 pore volumes of effluent were produced. <br />The effluent from both tests was periodically sampled for chemical <br />analysis. The results for samples collected at the beginning, near the <br />midpoint, and near the end of the tests are shown in Table 31, Results <br />of Chemical Analysis. <br />The change in water quality in the river resulting from waters <br />passing through the backfilled channel is estimated from the mass balance <br />equation: <br />CdQd = CuQu + CbQb <br />where C is concentration, Q is discharge rate, and the subscripts d, u <br />and b refer to downstream, upstream and backfill, respectively. Because <br />the backfilled channel will not change the quantity of flow in the river, <br />the discharges upstream and downstream of the backfilled channel are <br />equal. Therefore, the mass balance equation is rewritten as: <br />C - Cd - Cu = Qb/Qu <br />so that the change in concentration can be calculated directly. <br />Estimates of high, low and average discharge for the river have <br />been made in previous studies and will be used here for Qu. The <br />following two subsections present the estimations of Qb and Cb. In the <br />final subsection, equation 2 is used to compute the change in water <br />quality. <br />The elevation of the ground water in materials adjacent to the <br />river is approximately equal to the elevation of the water surface in the <br />stream. It is expected, therefore, that the lower portion of the <br />backfill placed in the channel will be wetted and that ground water will <br />flow through the wetted section in the direction of the axis of the old <br />channel. The area of the wetted section will change seasonally as <br />directed by the <br />RN -6 2.05-82 (Repaginated 10/21/16) <br />