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season in 80 to 100 existing observation wells upstream and 80 to 120 existing we11s <br />downstream. When necessary, up to a total of 10 replacement wells or supplemental wells in <br />each of the two study regions will be drilled using flight augers, outfitted with sand filters if <br />necessary, and cased with slotted PVC. Multiprobes will be used to measure electrical <br />conductivity (EC) (as specific conductance at 25°C), temperature, pH, dissolved oxygen (DO), <br />and oxidation reduction potential (ORP) of the ground water. Periodically, water samples will be <br />gathered from a subset of 10 to 20 wells once or twice per year and analyzed in the laboratory to <br />determine correlation of EC to total dissolved solids (TDS) and to specific salt ions. In <br />collecting, storing, transporting, and analyzing water samples protocols approved by the <br />Colorado Water Quality Control Division (CWQCD) for its funded project with CSU will be <br />followed. Plans are underway to conduct more frequent measurements in the LARB study <br />regions subject to pending financial support from other local, state, and/or federal sources. In <br />addition, periodic samples for TDS, specific salt ions, dissolved Se, and dissolved U will be <br />available from a subset of about 100 wells in the study regions of the LARB from the CSU <br />project funded by CWQCD. <br />Task 2b: Installation and Monitoring of New Ground Water Observation Wells in the UARB <br />It is initially recommended that 20 to 30 monitoring wells be installed in the alluvial deposits <br />within the new representative study region of the UARB. Stratified random sampling will be <br />used for preliminary siting of wells within the alluvium of the main stem and tributaries along <br />the `study region. Final locations will be adjusted based upon accessibility and in consultation <br />with personnel from USGS and other cooperating agencies. This will include consideration of <br />the location of about 50 existing domestic pumping wells in which the USGS currently is <br />planning to monitor water levels. The Division 2 Office of the Colorado Division of Water <br />Resources (CDWR) will be contacted to determine the need for permits to install these wells in <br />the UARB; however, it has been assumed in this proposal that fees for any well permits will be <br />waived by CDWR, as has been the case with past and on-going CSU studies in the LARB. <br />Observation wells installed by this project are expected to be drilled using flight augers to depths <br />of up to about 100 ft, outfitted with sand filters if necessary, and cased with slotted PVC. <br />Bentonite will be packed around the annulus of each well near the ground surface to discourage <br />entry of water from the surface. Direct push technology, whereby casings are hydraulically <br />forced into the graund rather than placed after drilling, also will be explored as a possible cost- <br />saving measure. Some type of visual or electroconductivity logging will be used to describe <br />aquifer lithology during well installation, depending on available resources and technical <br />expertise. Samples will be gathered at 10 to 20-ft depth intervals during drilling and will be <br />stored for eventual analysis of grain size distributions. Funds will not be available under the <br />current project for conducting this analysis (using sieves and hydrometers) but hopefully the <br />analysis can be completed under funding from related projects or with later supplemental <br />funding. Water levels, EC, temperature, pH, DO, and ORP in these wells will be manually <br />measured with multiprobes bi-weekly to monthly throughout the year, depending upon <br />hydrologic conditions (e.g., seasonal response to snowmelt-induced recharge) and observed <br />6