A quality-assurance plan has been developed for use by the sediment laboratory of the U.S. Geological Survey Montana Water Science Center in conducting activities related to the analysis of suspended sediment. The plan documents quality-assurance policies for sediment-laboratory certification, personnel responsibilities and training, documentation requirements, and laboratory safety. The plan also documents quality-assurance procedures related to laboratory equipment and supplies, sample management, sample analysis, analytical quality control, and data management.

This report describes the policies and procedures used by the Montana District sediment laboratory of the U.S. Geological Survey to assure the quality of suspended-sediment data. Suspended-sediment concentration and percentage of sediment finer than 0.062 millimeter (sand-silt separation) for stream samples are routinely analyzed by standard methods. Qualitycontrol practices and documentation are used to identify and minimize errors for the various types of equipment and procedures used for sample processing and reporting of analytical results. Data are systematically evaluated by technical review and verification prior to final approval and release of suspended-sediment data.

Base-flow measurement 27 "'N.:RIVER site and number where dit •,;.• water-quality sample 1 48° 26 14% was taken 'RICH L .4. ANG 25 24

Selected hydrogeologic data from the Judith basin, central Montana, have been compiled for use as the physical basis of a groundwater model prepared as part of a 4-year study of Cenozoic and Mesozoic aquifers of the northern Great Plains area of Montana. Records of 1,124 wells and 640 springs are tabulated in the report; most of these data have been collected since 1959. Lithologic logs of 68 wells are also included. Chemical data for wells and springs include 290 water samples analyzed for major cation and anion concentrations and 189 water samples analyzed for miscellaneousconstituent concentrations. The locations of wells and springs listed in the report are shown on a map at a scale of 1:250,000. ALBERTA 49V-1'-M3°S ASKATCHEWAN 109° 107°K >5°I DAHO 0 SO IOO ISO KILOMETERS I 50 100 MILES Well I5NI8E25CBCB02 Figure 2.-Well and spring numbering system. DATA PRESENTATION This report includes records of 1,124 wells and 640 springs that have been retrieved from the GroundWater Site Inventory (GWSI) part of the U.S. Geological Survey's National Water Data Storage and Retrieval System (WATSTORE). For these data to appear in table 1 or 2, the following criteria had to be met: (1) The site is located in the study area, and (2) the principal contributing aquifer is designated. Approximately 180 of the wells listed in table 1 have been inventoried in 1978 through 1980 as part of the data-collection effort for the northern Great Plains aquifer study in Montana. The remaining wells and springs are historic data from previously published reports that recently have been stored in the GWSI data base. Most of these data have been collected since 1959. Wells and springs are listed in tables 1 and 2 and their locations are shown on plate 1. The specific conductance and temperature values listed in these tables are onsite determinations made at the time of inventory. The discharge values listed in the well tables were measured under the operating conditions at the time of inventory, and they do not necessarily represent a maximum well yield. Lithologic logs of 68 wells inventoried in 1980 in the Judith basin are in table 3. They are representative of the typical lithologic sequence penetrated by wells in this area. Most of these logs were obtained from State records; a few came from drillers' records. The lithologic descriptions appear as reported by well drillers, except for minor word changes made for a consistent presentation. Data in tables 4 and 5 have been retrieved from the WATSTORE Water Quality File and consist of the results of all available analyses for well or spring sites in the study area. Table 4 consists of major cation and anion concentrations for 290 water samples. Table 5 consists of miscellaneous-constituent concentrations for 189 water samples. Approximately 160 of these samples were collected from 1978-80. The analyses were performed by the

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