U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY Regional sampling of waters and sediments variably impacted by mine drainage in the Denver West 1: 100,000 quadrangle, October, 1994: Preliminary data compiled by Sigrid Asher-Bolinder from data and analyses obtained by Sigrid Asher-Bolinder, William M. Aubrey, III, Linda C. S. Gundersen*, F. Allan Hills, Bill Larson, Megan McCoy, John McHugh, Allen L. Meier, Elwin L. Mosier, James K. Otton, Douglass E. Owen, Charles T. Pierson, Christopher J. Potter,Jacques F. Robertson, R. Randall Schumann, Kathleen S. Smith, Mark R. Stanton,Karen J. Wenrich, and Robert A. Zielinski* *Co-project Leader Open-File Report 95-0804 This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. MS 939, Box 25046, Federal Center Denver, CO 80225 1995 Regional sampling of waters and sediments variably impacted by mine drainage in the Denver West 1: 100,000 quadrangle, October, 1994: Preliminary data compiled by Sigrid Asher-Bolinder from data and analyses obtained by Sigrid Asher-Bolinder, William M. Aubrey, III, Linda C. S. Gundersen*, F. Allan Hills, Bill Larson, Megan McCoy, John McHugh, Allen L. Meier, Elwin L. Mosier, James K. Otton, Douglass E. Owen, Charles T. Pierson, Christopher J. Potter,Jacques F. Robertson, R. Randall Schumann, Kathleen S. Smith, Mark R. Stanton,Karen J. Wenrich, and Robert A. Zielinski* *Co-project Leader This database, identified as OFR95-0804, has been approved for release and publication by the Director of the USGS. Although this database has been subjected to rigorous review and is substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review Furthermore, it is released on condition that neither the USGS nor the United States Government may be held liable for any damages resulting from its authorized or unauthorized use. The database can be downloaded via 'anonymous ftp' from a USGS system named greenwood.cr.usgs.gov (136.177.48.5). The files are located in a directory named pub/open-file-reports/ofr950804. The data are presented as two spreadsheet computer files created in Microsoft Excel, version 5.0 saved as Lotus 1-2-3 worksheets, dwwat.wk1 and dwsed.wk1. The data are preliminary in nature and incomplete because data for dissolved anions and for trace elements in sediments are still pending. The purpose of this preliminary data release is to alert interested individuals and groups of the USGS's efforts to characterize the geochemical signature of past mining activities in this environmentally sensitive area. The database manager is: Robert A. Zielinski (303) 236-4719 rzielinski@usgs.gov U.S. Geological Survey Box 25046, Mail Stop 974 Denver, CO 80225 During the last century portions of the Colorado Front Range immediately west of Denver have been sites of extensive mining for base and precious metals and uranium. These largely abandoned mines and prospects are potential sources of radionuclides, heavy metals, and other toxic trace elements to major drainages that are the present source of industrial, domestic, and recreational waters to adjacent urban areas. The U.S Geological Survey (USGS) is interested in contributing its expertise to ongoing studies of the environmental impact of past mining activities in the area. Towards this end, a new project was established in October, 1994, "Environmental Impact of Abandoned Uranium Mines in the Front Range of Colorado". The initial study area for this project is the Denver West 1:100,000 quadrangle, which includes all of Clear Creek and Gilpin Counties, the northern half of Jefferson County, and parts of Summit, Grand, and Boulder Counties. The study area includes the important Central City-Idaho Springs mining district, the Schwartzwalder uranium mine and associated uranium occurrences, other areas of low grade sulfide mineralization, and areas largely devoid of mineralization. 2 This report presents some preliminary chemical data for water and sediment samples collected by project members during mid-October, 1994 at nearly 90 sites in the Denver West quad. The purpose of this initial sampling was to provide a regional-scale synoptic overview of the chemical variability of waters as a function of geology and land use, including past mining activities. Water samples are assumed to be representative of a period of low flow in the annual hydrologic cycle in which ground-water return contributes substantially to stream flow. Areal coverage is extensive enough to include water and sediment samples from heavily mined areas and also from variably mineralized areas largely undisturbed by mining activities. Geographically based inspection of the chemical data allows for interesting comparisons based on differences in geology and/or land use. The data also serve as a useful reference for comparison with previous analyses of water and sediments in more geographically restricted portions of the Denver West quad. Water samples were collected by depth-wise sampling at equally spaced intervals along a traverse of the stream perpendicular to its flow. At least four liters of water were collected in polyethylene bottles and combined in a larger plastic carboy. Aliquots of the mixed composite were taken for streamside measurements of temperature, pH, and specific conductance. Approximately two liters of raw water were transferred to a screw-capped polyethylene bottle and placed under refrigeration for transfer to the laboratory. Samples were returned to the laboratory within one day of collection. An aliquot of 125 ml of raw water (RA) was acidified to pH <2 with ultrapure nitric acid. The remaining sample was filtered through a cellulose acetate membrane of 0.45 micrometer opening. Alkalinity was then determined by titrations of 20-50 ml with standard acid. The remaining filtered sample was divided into unacidified (FU) and acidified fractions (FA) for subsequent analyses of anions and cations respectively. Sediment samples of 2-3 kg dry weight were taken as composited grab samples after water sampling was completed. Sediments were collected from areas of quiet water within the main channel. Sampling spots included the downstream sides of large boulders, quiet pools, or shallow backwaters along sand or gravel bars. Samples were collected away from stream banks to avoid potential contamination by slope wash. Sediments were collected with plastic scoops and were placed into plastic buckets lined with plastic bags. Excess water was decanted from samples after ten minutes or more of settling. Upon their return to the laboratory, sample bags were opened and the samples were air-dried at 40*C. Each sample was passed through a sieve of 2 mm opening and coarser materials were discarded. Five hundred grams of the <2 mm size fraction was saved for analysis , and the remaining material was further separated into specific size fractions for analysis. Most of the entries on the spreadsheets are self explanatory or include text that describe the nature and location of each sample, estimates of stream flow, types of splits analyzed, and the method of analysis. Additional questions regarding details of sampling and analysis or future plans for sampling under this project should be directed to either of the co-project leaders, Linda C. S. Gundersen at 703/648-6471 (lgundersen@usgs.gov) or Robert A. Zielinski at 303/236-4719 (rzielinski@usgs.gov). We thank U.S. Geological Survey volunteer P. K. Cavey for her help in sampling. This phase of the project also benefited from the support and advice of USGS colleagues Kevin F. Dennehy, Robert A. Kimbrough, Janice S.Heiny, and Gregory B. O'Neill. 3