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Section 3 <br />Field Data Collection Procedures <br />testing will be selected. All sediment samples will be submitted for geotechnical grain <br />size testing by the wet-sieve method following ASTM D-422 and ASTM D-2217 <br />(ASTM 2002, ASTM 1998). <br />3.1.4 Streambed Vertical Hydraulic Gradient Testing <br />The vertical hydraulic gradient across the streambed will be measured at each <br />transect at a location nearest to the center of the channel as defined by the bank full <br />water line at each transect. Field conditions may require that the location be moved to <br />another location along the transect. <br />The vertical hydraulic gradient between the stream and groundwater will be <br />determined by comparing the water level in a temporary streambed piezometer with <br />the water level (stage) of the stream. Each piezometer will consist of a 1-inch diameter <br />pipe with either a 4-inch to 8-inch long wire-wrapped stainless steel screen with a <br />drive point at the bottom. The top of the screen will be set 2.5 to 3 feet below the <br />streambed, a depth anticipated to be adequate to provide data on vertical gradients. <br />Installation will be accomplished by driving the piezometer into the streambed. <br />Water levels inside the piezometer will be measured with an electric water level meter <br />and the relative stream stage will be determined by measuring the surface water level <br />outside of the temporary piezometer using the same measuring point as for the <br />groundwater measurement. The difference in water levels between the groundwater <br />and the stream will provide an indication of the vertical direction of water flow at the <br />time of measurement. This information can then be used with the streambed <br />conductance to estimate the groundwater flux across the streambed during the time of <br />measurement. <br />In addition, at the four locations with SEO/USGS gaging stations and adjacent <br />monitoring wells (Henderson, Kersey, Balzac or Atwood, and Julesburg), the water <br />levels in the existing monitoring wells and the stage height on the SEO/USGS staff <br />gage will be recorded to assist determination of whether groundwater is discharging <br />to the stream (head in aquifer is higher than stream stage) or whether the stream is <br />recharging the groundwater (head in aquifer is lower than stream stage). At other <br />locations, all water levels will be referenced to the temporary benchmark that will be <br />placed at each location and surveyed later. <br />3.1.5 Streambed Hydraulic Conductivity Testing <br />Adjacent to one coring location at each of the up to 30 transect sites, aconstant-head <br />injection test will be performed to determine the hydraulic conductivity of the <br />streambed sediments using the method described by Cardenas and Zlotnik (2003). <br />This will be done using the temporary piezometer installed to measure the vertical <br />hydraulic gradient across the streambed. The piezometer's screened interval will be <br />driven to a depth interval corresponding to the depth from which a sample was <br />collected for grain-size analysis to develop an empirical relationship between the <br />grain-size analysis and hydraulic conductivity determined by hydraulic testing. <br />`~ ~ <br />3-3 <br />FINAL SPDSS T33 WORK PLAN &3-OS.DOC <br />