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16 USBR Monitoring of Reed Wash N ~ N a:. USBR stage One monitoring program entails collecting of ground- water and surface-water data in a hydrologically isolated basin called the Reed Wash in Grand Valley, which includes about 10,000 acres. Reclamation established a hydrosalinity monitoring network before construction of stage One and continued monitoring afterward. It is bounded on the east and west ridges by impervious mancos shale, and unweathered shale in the subsurface forms a restricted outlet which permits measurement of all drainage flow at a single point. See figure IV-1 & IV-2 for location of monitoring stations. The network consisted of gauging stations at the hydrologic boundaries to record water and salt entering and leaving the basin and gauging stations within the basin to record drain flows and salt. These data are used to develop salt and water budgets to determine the salt pickup from irrigation. A network of 100 wells, 80 sampled bimonthly and 12 sampled monthly were installed to measure water chemistry and depth to water table and explain hydro-geol-chemistry processes. Eight wells had continuous monitoring. The well network is used to examine salt loading mechanisms, to support the salt load pickup determination, and to document the existing and post project water table levels (Figures IV-3). The mean total disolved solids in terms of anions (CI, HC03, S04) and cations (Ca, Na, Mg) is shown in Figure IV-8. The inflow and outflow monitoring data are used to directly estimate the salt load reduction in the salt and water budgets, while other data provides evidence by quantifying associated hydro-chemical phenomena. Data in Table IV-5 demonstrate no change in before and after concentration of salinity in the drain flow: Before Condition 1976 to 1980 - 4307 mg/l salinity concentration 5.88 tns/ac-ft After condition following installation of practices 1981 to 1983 - 4314 mg/L salinity concentration 5.88 tns/ac-ft