WATER QUALITY AND EVALUATION OF RAW-WATER-ROUTING SCENARIOS, CHICKAHOMINY, DIASCUND CREEK, AND LITTLE CREEK RESERVOIRS, SOUTHEASTERN VIRGINIA, 1983-86 By Dennis D. Lynch U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 92-4034 Prepared in cooperation with the DEPARTMENT OF PUBLIC UTILITIES, CITY OF NEWPORT NEWS, VIRGINIA Richmond, Virginia 1992 U.S. DEPARTMENT OF THE INTERIOR MANUEL LUJAN, Jr., Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director For additional information write to: Copies of this report can be purchased from: District Chief U.S. Geological Survey U.S. Geological Survey, WRD Books and Open-File Reports Section 600 West Broad Street Box 25425 Room 606 Denver Federal Center Richmond, Virginia 23230 Denver, CO 80225 CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATED WATER-QUALITY UNITS Multiply By To obtain Length inch (in.) 2.54 centimeter foot (ft) 0.3048 meter mile (mi) 1.609 kilometer Area square mile (mi2) 259 hectare square mile (mi2) 2.590 square kilometer square foot (ft2) 0.09290 square meter Volume million gallons (Mgal) 3,785 cubic meters billion gallons (Bgal) 3,785,000 cubic meters Flow cubic foot per second (ftVs) 0.02832 cubic meter per second inch per year (in/yr) 25.4 millimeter per year million gallons per day (Mgal/d) 0.003785 million cubic meters per day million gallons per yr (Mgal/yr) 0.003785 million cubic meters per year mile per hour (mi/h) 1.609 kilometer per hour Mass pound (Ib) 453.6 gram pound (Ib) 0.4536 kilogram gram(g) 0.03527 ounce, avoirdupois kilogram (kg) 2.205 pound, avoirdupois ton 0.9072 megagram Sea level; In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929~a geodetic datum derived from a general adjustment of the first-order level nets of the United States and Canada, formerly called Sea Level Datum of 1929. In this report, chemical concentrations in water are expressed in milligrams per liter (mg/L) or micrograms per liter (jig/L); 1,000 ^g/L =1 mg/L. Specific conductance of water is expressed in microsiemens per centimeter at 25 degrees Celsius (pS/cm). This unit is equivalent to micromhos per centimeter at 25 degrees Celsius. Temperature in degrees (°C) can be converted to degrees Fahrenheit (°F) by use of the following equation: °F = (1.8X°O CONTENTS Page Abstract.................................................................................................................................................. 1 Introduction........................................................................................................................................... 2 Purpose and scope............................................................................................................................... 6 Acknowledgments............................................................................................................................... 6 Description of study area........................................................................................................................... 7 Land use............................................................................................................................................... 7 Geology................................................................................................................................................ 8 Climate................................................................................................................................................. 8 Physical characteristics of the reservoirs......................................................................................... 9 Reservoir inflows and outflows...................................................................................................... 10 Chickahominy Reservoir............................................................................................................. 10 Historical flows....................................................................................................................10 Flows during 1983-86..........................................................................................................12 Long-term trends.................................................................................................................12 Hydraulic retention time.................................................................................................... 13 Diascund Creek Reservoir.......................................................................................................... 14 Little Creek Reservoir..................................................................................................................14 Methods of study.......................................................................................................................................19 Sampling procedures........................................................................................................................ 19 Sample preparation and analysis....................................................................................................22 Water quality of reservoirs.......................................................................................................................22 Chickahominy Reservoir..................................................................................................................22 Specific conductance....................................................................................................................23 pH and water temperature......................................................................................................... 30 Dissolved oxygen.........................................................................................................................30 Major inorganic constituents......................................................................................................35 Iron, manganese, and selected trace elements.........................................................................37 Nutrients and chlorophyll-a.......................................................................................................43 Diascund Creek Reservoir................................................................................................................49 Specific conductance....................................................................................................................49 pH and water temperature......................................................................................................... 52 Dissolved oxygen.........................................................................................................................53 Major inorganic constituents......................................................................................................56 Iron and manganese....................................................................................................................60 Nutrients, chlorophyll-a, and reservoir transparency............................................................ 66 111 CONTENTS-Continued Page Little Creek Reservoir.......................................................................................................................72 Specific conductance.................................................................................................................... 74 pH and water temperature......................................................................................................... 77 Dissolved oxygen......................................................................................................................... 78 Major inorganic constituents...................................................................................................... 82 Iron and manganese....................................................................................................................86 Nutrients, chlorophyll-a, and reservoir transparency ............................................................89 Evaluation of raw-water-routing scenarios........................................................................................... 96 Summary......................................................................................................................................................99 References cited........................................................................................................................................ 102 ILLUSTRATIONS Page Figures 1-3. Maps showing location of: 1. Physiographic provinces of Virginia and study area........................................... 3 2. Chickahominy Diascund Creek, and Little Creek Reservoir drainage basins and sites in study area............................................................................. 4 3. Sampling sites in Chickahominy, Diascund Creek, and Little Creek Reservoirs.................................................................................................. 5 4. Schematic of raw-water routing and average daily volumes used by city of Newport News, 1983-86..................................................................................................... 6 5. Bar graph showing mean monthly discharge of Chickahominy River near Providence Forge, 1943-87....................................................................................... 12 6-15. Graphs showing: 6. Depth-volume curve for Little Creek Reservoir.................................................