Sierra Valley Aquifer Delineation and Ground Water Flow Prepared for Randy Wilson, Director Plumas County Planning Department 520 Main Street, Quincy, CA 95971 530-283-7011 and Sierra Valley Groundwater Management District Loyalton, CA By Burkhard Bohm Hydrogeologist CHG lic. #337 Plumas Geo-Hydrology PO Box 1922, Portola, CA 96122 530-836-2208 Final Report December 27, 2016 Page 1 of 69 Table of Contents 1. Introduction .............................................................................................................. 6 Previous work conducted in SV ................................................................................... 6 Scope of the current study ........................................................................................... 7 2. Groundwater Recharge Areas in Sierra Valley ......................................................... 8 Groundwater recharge area defined ............................................................................ 8 Aerial contributions of groundwater recharge ............................................................... 8 Ground water recharge centers ................................................................................... 9 Defining groundwater recharge centers in the Sierra Valley watershed .................... 10 3. Aquifer delineation ................................................................................................. 13 Background ............................................................................................................... 13 Geologic setting of the SVB ....................................................................................... 13 Structural Geology of the SVB ................................................................................ 13 Stratigraphy of SVB sediments ............................................................................... 14 Deep and shallow aquifers in Sierra Valley ............................................................ 15 Conceptual model of SVB hydrogeology .................................................................... 16 Sierra Valley hydrostratigraphic units ..................................................................... 17 Valley fill aquifer parameters .................................................................................. 18 Bedrock aquifer parameters ................................................................................... 19 Aquifer properties .............................................................................................. 19 Aquifer delineation ..................................................................................................... 20 Objectives .............................................................................................................. 20 Aquifers and depth to bedrock identified by means of drilling reports ..................... 21 Aerial photo intepretation ........................................................................................... 22 General .................................................................................................................. 22 Methodology .......................................................................................................... 23 Page 2 of 69 Results of aerial photo interpretation ...................................................................... 24 SVB structural geology and groundwater flow ........................................................... 24 Results of aquifer delineation ..................................................................................... 27 Depth to bedrock .................................................................................................... 27 Faults ..................................................................................................................... 28 The Chilcoot sub-basin as a recharge area ............................................................ 29 Potential significance of structural elements for groundwater modeling .................. 29 4. Groundwater Flow Based on Light Stable Isotopes and Chemistry ........................ 30 Study Objective ......................................................................................................... 30 Types of data collected .............................................................................................. 30 Sierra Valley upland waters .................................................................................... 30 Sierra Valley Basin aquifer waters .......................................................................... 30 Stream waters ........................................................................................................ 31 Concepts and assumptions in tracer data Interpretation ............................................ 31 The basics of stable light isotope hydrology ........................................................... 31 Concepts of isotope data interpretation .................................................................. 32 Concepts of geochemical data interpretation .......................................................... 33 Data collection ........................................................................................................... 34 Field data and sample collection ............................................................................ 34 Literature data ........................................................................................................ 34 Lab analysis ........................................................................................................... 34 Sample location maps and sample identification codes ............................................. 34 NOTE ........................................................................................................................ 37 Overview: isotopes in valley floor wells, upland springs and streams ......................... 38 Key Observations: .................................................................................................. 38 Searching for possible groundwater sources outside the Sierra Valley watershed . 39 Page 3 of 69 Isotope composition and well location .................................................................... 40 Central valley floor well characteristics ................................................................... 42 Groundwater mixing in the central trench wells ...................................................... 44 Indications of groundwater mixing in the central valley floor wells .......................... 46 Evaporation and irrigation return flow......................................................................... 48 Summary of central and northern valley floor well chemistry ...................................... 49 Geothermal effects on groundwater chemistry ........................................................... 49 Stream waters of northern Sierra Valley .................................................................... 50 Streams and groundwater recharge in southern Sierra Valley ................................... 51 Streamflow ............................................................................................................. 51 Groundwater recharge ........................................................................................... 52 The Little Truckee River Diversion ............................................................................. 53 Recharge areas – a preliminary assessment ............................................................. 54 Isotopic provenances and recharge areas .............................................................. 54 Recharge in the N and NW basin periphery ........................................................... 56 Recharge in the NE periphery ................................................................................ 57 Discussion and Conclusions ...................................................................................... 58 Further Recommendations: ....................................................................................... 59 5. The Sierra Valley Water Balance ........................................................................... 60 Introduction ................................................................................................................ 60 The components of the water balance ....................................................................... 62 Recharge areas ......................................................................................................... 62 Methods to prepare preliminary recharge estimates .................................................. 62 Hydrologic balance discharge method .................................................................... 63 Chloride mass balance method .............................................................................. 63 Chloride in precipitation .......................................................................................... 65 Page 4 of 69 Ground water chloride data .................................................................................... 65 Refined Maxey-Eakin method ................................................................................ 65 6. Bibliography ........................................................................................................... 66 Page 5 of 69 Previous work conducted in SV Groundwater data have been collected