MORGAN VALLEY HYDROGEOLOGY STUDY By Janae Wallace, Mike Lowe, Jon King, Walid Sabbah, and Kevin Thomas Utah Geological Survey

View to northwest of Weber River and Morgan Valley

OBJECTIVES CHARACTERIZE RELATIONSHIP OF GEOLOGY TO GROUND-WATER CONDITIONS –Compile geologic map and cross sections –Develop hydrostratigraphy –Determine thickness of valley-fill aquifer (use gravity survey to make isopach map) –Define hydrogeologic setting (map recharge/discharge areas) –Compile water-yielding characteristics, including fractured- rock aquifers DEVELOP WATER BUDGET FOR DRAINAGE BASIN DETERMINE WATER QUALITY –Mostly valley-fill data (52 wells) from previous UGS study, added 10 bedrock wells/springs CLASSIFY GROUND WATER IN VALLEY-FILL AQUIFER DETERMINE HIGH NITRATE SOURCE THROUGH STABLE ISOTOPE DATA ENVIRONMENTAL TRACER DATA FOR 10 ALLUVIAL; 10 BEDROCK WELLS/SPRINGS (AGE DATING)

METHODS Geologic map – simplified geologic map compiled from several sources with most of the younger surficial deposits stripped off (King) Three cross sections produced to attempt to define locations and offsets on faults, thicknesses of Tertiary cover, and likely underlying pre-Tertiary units – geology below Morgan Valley is likely more complicated than shown (King) Aquifer characteristics estimated included specific capacity, transmissivity, hydraulic conductivity and storativity – from specific capacity using TGUESS algorithm or aquifer test by others (Sabbah) Gravity survey included 350 data points throughout valley (Thomas) Defined hydrogeologic setting on presence or absence of thick clay layers and direction of vertical hydraulic gradient (Lowe) Developed water budget from PRISM annual precipitation data for last 10 years, annual evapotranspiration data derived from current landuse and natural vegetation data, and other available data (Sabbah) Standard water-quality sampling procedures, 2004 and 2009: general chemistry, nutrients, stable isotopes/environmental tracers, and age dating (Wallace)

HYDROGEOLOGIC SETTING - 1 Geologic units range from Proterozoic to Holocene age (lithologic columns for Morgan Valley area and Willard thrust sheet) Area is structurally complex, mostly related to three major episodes of mountain building (Early Proterozoic deformation, high-grade metamorphism, and igneous intrusion; Cretaceous compression and development of Sevier fold and thrust belt; and late Cenozoic extension, resulting in basin-and-range-type features, including normal faults and trough shared by Ogden and Morgan Valleys Potential fractured-rock aquifers are identified on lithologic columns (mostly carbonates, with some sandstones/quartzites) In many areas, potential fracture-rock aquifers covered by thick sequences of Tertiary units (such as Wasatch Formation and Norwood Tuff)

Blue indicates formation has potential water-bearing properties (potential aquifer)

Blue indicates formation has potential water-bearing properties (potential aquifer)

Geologic Map By Jon King Tertiary units

HYDROGEOLOGIC SETTING - 2 Cross sections indicate that thickness of Tertiary units may make fractured-rock aquifers prohibitively deep (thousands of feet) for water wells in many areas and structural complexity makes targeting specific rock units risky where covered by these Tertiary units (also, not all geologic units exist in subsurface at all locations) Ground-water flow in fractured rock aquifers largely controlled by structure, especially dip, and water-yield to wells largely controlled by amount of fracturing encountered by well Compiled water-yielding characteristics for fractured-rock aquifers highly variable, even for aquifers with more than one set of data, and data from aquifer tests conducted by others may be of variable quality (reported transmissivities from square feet/day with highest reported for Wasatch Formation [valley fill?])

HYDROGEOLOGIC SETTING - 3 Valley-fill aquifer has historically been the most important aquifer in Morgan Valley. Many wells screened in both Quaternary and Tertiary. Many wells shallow. Generally unconfined with flow from valley margins to valley center and then downstream toward head of Weber Canyon Thickness of valley fill is 0 at valley margins, is less than 200 feet in much of the valley, but may be greater than 600 feet thick near towns of Morgan and Enterprise Valley-fill is predominantly coarse grained (gravel and sand) and is a primary recharge area (vulnerable to contamination from activities on the land surface) Valley fill is productive aquifer with transmissivities ranging from square feet/day based on our data (U.S.G.S. report estimated 40,000-50,000 for a Morgan City well). Areas of high transmissivity correspond to areas with great aquifer thickness)

Cottonwood Creek Weber River East Canyon Creek Schematic block diagram showing groundwater conditions

Location of gravity stations And cross section locations

Isopach map (showing relatively valley-fill thickness)

Different Types of Recharge/Discharge Scenarios

Recharge-area map All Primary Recharge

Sc = Q/S Q – pumping rate S -drawdown

T = bk b = aquifer thickness k = hydraulic conductivity TGUESS algorithm using Sc data – Implements Cooper-Jacob approximation of Theis equation

k = T/b T – transmissivity B – aquifer thickness

S = Sy + (Ss x b) Sy – specific yield Ss – Specific storage b – aquifer thickness

Integrated land use and natural vegetation map used for estimating ET

Estimated ET rates for dominant vegetation and land use

Summary of Integrated Water Budget for Morgan Valley

Water-Quality Data -Overall quality -Classification -Nitrate -Environmental Tracers

WATER-QUALITY RESULTS TDS RANGE: 91 – 1,018 mg/L; (437 av) BEDROCK: mg/L; (526 av) NITRATE RANGE: <0.01 – 12.8 mg/L; AVERAGE NITRATE 2.6 mg/L BEDROCK NO 3 :<0.01 – 28 mg/L (1.4; 4.6) 4 WELLS EXCEEDED MCL FOR NO 3 (including 1 bedrock well) ; 2 FOR ARSENIC

TOTAL-DISSOLVED-SOLIDS MAP Kilometers

GROUND WATER CLASS TDSBENEFICAL USE CLASS IA/IB0 to 500 mg/LPRISTINE/ IRREPLACABLE CLASS II500 to 3,000 mg/L DRINKING WATER CLASS III3,000 to 10,000 mg/L LIMITED USE CLASS IV>10,000 mg/LSALINE

CLASSIFICATION MAP

TDS and Location of Bedrock samples

NITRATE CONCENTRATION

Location of public supply well (formerly Wilkinson Dairy) this picture Was taken during the development phase of the housing project. The Water from this well has been sampled numerous times and relatively High nitrate concentrations persist (latest sampled yielded ~9 mg/L)

View upgradient of Hardscrabble Canyon (no apparent land use to contribute nitrate, but some wells in the area have persistent, but sporadic nitrate concentrations)

Fields taken from USGS

N well Nitrate 28 mg/L

well Nitrate 28 mg/L N

WELLS SAMPLED FOR ENVIRONMENTAL TRACERS ‘ Miles Kilometers

Environmental Tracer/Age Data

C C C* -Tritium C carbon -14 Modern *C carbon -14 Modern Tritium age

Overall younger water for alluvial samples-- longer residence time for older water in bedrock?

CONCLUSIONS OVERALL GROUND-WATER QUALITY: 98% PRISTINE - 2% DRINKING-WATER OVERALL LOW NO 3 CONCENTRATION- 4 wells > 10 mg/L OXYGEN-NITROGEN ISOTOPES: Manure/Septic and Soil N (mixed?) Modern-Age and Mixed-Age Water (all 3 Carbon-14 wells Modern; 2 Tritium are pre- bomb water, 6 Tritium are Modern; 12 are Mixed) -overall historical recharge age Nitrate likely human related-localized (not NPS)

CONCLUSIONS Geology is complex with potential fractured-rock aquifers covered by thick Tertiary deposits in many areas Penetrating targeted fractured-rock aquifers in these covered areas may be hit or miss and well yield will be determined by amount of fractures intercepted by well Valley-fill aquifer safer target and generally productive - may make more sense to target valley-fill aquifer and pump water to where it is needed Valley fill is greatest (>600 feet) in center of valley near towns of Morgan and Enterprise Coarse-grained valley fill vulnerable to surface sources of pollution Valley fill contains mostly high quality ground water. Nitrate an issue in some areas. Widespread use of septic tanks combined with shallow depth of some wells may be a future concern Water budget indicates inflows exceed outflows – water deficit