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� . . � � Appendix I <br /> Subtask B.1 - Evaluation of Seepage and Evaporation Losses <br /> A program of field investigation will be developed to determine potential seepage from <br /> Friends Creek during periods when the stream channel is used to convey groundwater <br /> to Lake Decatur. <br /> Harza will install and measure water table levels in "mini-piezometers" at up to five <br /> locations along Friends Creek to identify which reaches of the Creek are influent or <br /> effluent, and to estimate permeability of bed and bank materials in various stream <br /> reaches. Each location will have from one to three piezometers implanted directly in the <br /> streambed. If levels in the piezometers are below stream level, the reach is effluent. <br /> Seepage losses would be indicated. If piezometer levels are higher than stream level, the <br /> reach is influent. Locations for piezometer installations will be selected on the basis of <br /> site investigation and review of documents obtained from sources including the USGS <br /> and the SCS. <br /> In addition to installation of mini-piezometers, shallow auger holes will be bored adjacent <br /> to the five "mini-piezometer" locations. These borings will provide information on the <br /> soil profiles adjacent to the stream bed. Auger hole sites will be selected based on data <br /> indicating typical subsurface conditions along the stream. One-inch diameter piezometers <br /> will be installed in each auger hole. Water table levels will then be measured in the <br /> one-inch piezometers and in the "mini-piezometers" and correlated with stream surface <br /> elevations to measure groundwater gradients between the stream and the piezometers. <br /> In addition, permeability tests will be performed in each piezometer to estimate K values <br /> for use in predicting seepage losses. <br /> Since water table elevations generally fluctuate during a year, seasonal variations of the <br /> water table will be considered in estimating the seepage loss. <br /> Potential seepage losses from the channel will be estimated using Darcy's equation. <br /> Q = K x A x dh/dl <br /> where <br /> K = coefficient of permeability <br /> A = potential flow area <br /> dh/dl = hydraulic gradient <br /> The value of K will be determined from data collected by the field program described <br /> above, supported by published data from the USGS and other sources. Flow area will <br /> s9ioiz <br /> A893092N-APP.I I-2 <br />