Appendix A Hydrology Documents... Appendix A – Hydrology Report A-2 1939-1940, 1950-1957, and 1977-1998

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  • Appendix A Hydrology Report Prepared by: The RETEC Group, Inc. 2409 Research Blvd., Suite 106 Fort Collins, Colorado 80526 RETEC Project Number: APC02-18086-410 Prepared for: Anadarko Petroleum Corporation P.O. Box 10 Midwest, Wyoming 82643 Prepared by: DRAFT ____________________________________________________

    Margaret C. Zebley, P.E., Project Engineer Reviewed by: DRAFT ____________________________________________________

    Robert Friesen, P.E., Supervising Engineer

    October 25, 2004

  • Table of Contents

    A-i

    1 Introduction................................................................................................... A-1 2 Hydrologic Data............................................................................................ A-1

    2.1 USGS Data........................................................................................ A-1 2.2 2003 – 2004 Field Data..................................................................... A-2

    3 Hydrologic Conditions.................................................................................. A-2 3.1 Salt Creek Conditions ....................................................................... A-3

    3.1.1 Salt Creek Watershed............................................................ A-3 3.1.2 Salt Creek Hydrologic Conditions ........................................ A-3

    3.2 Powder River Conditions.................................................................. A-4 3.2.1 Powder River Watershed ...................................................... A-4 3.2.2 Powder River Hydraulic Conditions..................................... A-5

    3.3 Salt Creek Comparison to Powder River .......................................... A-5 3.4 Groundwater Uses............................................................................. A-6

    4 Produced Water Discharges.......................................................................... A-6 4.1 NPDES Permits and Discharge Locations........................................ A-6 4.2 Effects of Produced Water Discharges ............................................. A-6

    5 Effects of Discontinuing Produced Water Discharges.................................. A-7 5.1 Predicted Salt Creek Flow Characteristics........................................ A-8 5.2 Predicted Powder River Flow Characteristics .................................. A-8 5.3 Agricultural Uses .............................................................................. A-8 5.4 Future Allocations............................................................................. A-8

    6 Conclusions................................................................................................... A-9 7 References................................................................................................... A-10 List of Tables Table A-1 Produced Water Discharges to Salt Creek Table A-2 Salt Creek Annual Flows and Estimated Available Flows List of Figures Figure A-1 USGS Gage Locations Figure A-2 October 2003 and April 2004 Flow Measurements Figure A-3 Salt Creek Mean Monthly Flows Figure A-4 Mean Monthly Flow Rate Comparison Between Salt Creek and

    Powder River Figure A-5 Annual Flow Comparison Between Salt Creek and Powder River Figure A-6 Comparison of Minimum Mean Monthly Flows Salt Creek, Powder

    River, and Produced Water Discharges Figure A-7 Salt Creek Contribution to Powder River Figure A-8 NPDES Permitted Discharges

  • Table of Contents

    A-ii

    List of Acronyms ac-ft acre-feet AMSL above mean sea level cfs cubic feet per second HUC Hydrologic Unit Code NPDES National Pollutant Discharge Elimination System PRCD Powder River Conservation District RETEC The RETEC Group, Inc. UAA Use Attainability Analysis USEPA United States Environmental Protection Agency USGS United States Geological Survey

  • Appendix A – Hydrology Report

    A-1

    1 Introduction This report evaluates available data for the hydrology of Salt Creek and the Powder River downstream of its confluence with Salt Creek and is presented in support the Salt Creek Use Attainability Analysis (UAA). The goal of this evaluation is to analyze the hydrology of the Salt Creek basin, the contributions of the basin to the Powder River, and to evaluate possible effects of eliminating currently permitted produced water discharges to Salt Creek.

    This report includes the following sections:

    • Section 2 discusses the hydrologic data used in this evaluation

    • Section 3 discusses permitted produced water discharges to Salt Creek

    • Section 4 includes an evaluation of hydrologic conditions in the Salt Creek and the Powder River

    • Section 5 discusses predicted changes to the Salt Creek water budget if permitted discharges were discontinued

    • Section 6 presents the conclusions of this report

    • Section 7 provides references cited in this report.

    2 Hydrologic Data Data used for evaluation of hydrologic conditions in Salt Creek and the Powder River were obtained from the United States Geological Survey (USGS) and from recent field sampling events performed by the Powder River Conservation District (PRCD) and The RETEC Group, Inc. (RETEC). Following is a discussion of data that were used in this evaluation.

    2.1 USGS Data Hydrologic data for the Salt Creek drainage (Hydrologic Unit Code [HUC] 10090204) consist of flow discharge data collected from a USGS stream gage (Station 06313400) located on Salt Creek near Sussex, Wyoming, as shown in Figure A-1. The gage was operated from 1976 to 1993, barring occasional periods of equipment malfunction.

    Powder River (HUC 10090202) flow data were also collected from a stream gage operated by the USGS (Station 06313500). This gage is located on the Powder River immediately downstream of the confluence with Salt Creek at Sussex, Wyoming (Figure A-1). The gage was operated during the years of

  • Appendix A – Hydrology Report

    A-2

    1939-1940, 1950-1957, and 1977-1998. Since 1998, flow has been collected on a continuous basis, barring occasional periods of equipment malfunction.

    Due to the different monitoring periods for each gaging station: (Salt Creek: 1977-1993; Powder River: 1939-1940, 1950-1957, and 1977-1998), and incompleteness of data prior to 1970, the comparison between the Salt Creek and Powder River gages is limited to the years from 1977 to 1993. Also, the nearest gage upstream of the confluence between Salt Creek and the Powder River is over 11 miles upstream of Sussex, rendering upstream flow data comparison questionable. Therefore, this evaluation relies primarily on USGS data from the stations near Sussex, Wyoming.

    2.2 2003 – 2004 Field Data Recent hydrologic data for Salt Creek and the Powder River were developed from 2003 and 2004 water quality monitoring performed by the PRCD sampling program (October 2003) and the RETEC synoptic sampling program in April 2004. The main objective of the PRCD monitoring and RETEC sampling was the monitoring and evaluation of water quality parameters on Salt Creek. However, flow data taken during the water quality sampling events were included in this evaluation.

    The PRCD has been monitoring water quality in the Salt Creek watershed under a Section 319 grant from the United States Environmental Protection Agency (USEPA). The District conducted monthly water quality monitoring from April 2003 through the end of the water year in October 2003. Recently, the District reinitiated monthly monitoring starting in April 2004 and will conclude in October 2004.

    The RETEC synoptic surveys were undertaken, in order to characterize high- flow conditions and baseflow conditions. Samples and flow measurements were collected in 11 locations as shown in Figure A-2. Details of the sampling event are provided in the Water Quality Report (Appendix B). Multiple data points in the same month were averaged to represent one flow value.

    3 Hydrologic Conditions Data were reviewed to provide an evaluation of the hydrologic conditions of Salt Creek. This evaluation was performed to generate a baseline scenario of conditions within the Salt Creek basin that currently include produced water discharges to the creek. The evaluation also includes a discussion of conditions within the Powder River and the contribution of Salt Creek flows to the Powder River.

  • Appendix A – Hydrology Report

    A-3

    3.1 Salt Creek Conditions Following is a discussion of the characteristics of the Salt Creek watershed and hydrologic conditions of the creek.

    3.1.1 Salt Creek Watershed The Salt Creek drainage covers an area of approximately 806 square miles encompassing parts of Natrona County, Johnson County, and Converse County, Wyoming (PRCD, 2004) as shown in Figure A-1. Elevation within the basin range varies 6,020 feet (ft) above mean sea level (AMSL) near the headwaters at the southern extent of the basin, to approximately 4,390 ft AMSL at the confluence with the Powder River in the north (PRCD, 2004). The drainage area of Salt Creek upstream of the USGS stream gage 06313400 covers approximately 769 square miles and includes every significant tributary and water source in the basin. The USGS gage sits at an elevation of 4,480 AMSL. Several tributaries feed into Salt Creek, including Teapot Creek, Cottonwood Creek, Castle Creek, Dugout Creek, and Meadow Creek.

    The watershed is semi-arid, receiving approximately 13 to 15