NOTE ON WELL SITING AT CORNER OF CASTLE VALLEY DRIVE AND SHAFER LANE FOR TOWN OF CASTLE VALLEY, GRAND COUNTY, UTAH

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1 NOTE ON WELL SITING AT CORNER OF CASTLE VALLEY DRIVE AND SHAFER LANE FOR TOWN OF CASTLE VALLEY, GRAND COUNTY, UTAH Authors: Dr. Kenneth E. Kolm, Hydrologic Systems Analysis, LLC., Golden, Colorado and Paul K.M. van der Heijde, Heath Hydrology, Inc., Boulder, Colorado Prepared For: Town of Castle Valley, Utah July 2017

2 Note On Well Siting At Corner Of Castle Valley Drive And Shafer Lane For Town Of Castle Valley, Grand County, Utah The HESA completed by Kolm and van der Heijde (March 2016) of the surface water and groundwater systems in the Castle Valley (TCV) study area makes extensive use of existing GIS databases and maps of geologic, hydrogeologic and hydrologic characteristics, collected specifically for this study. Additional data layers and evaluations were needed to illustrate the HESA particularly with respect to the hydrogeological characteristics of the rock types present and the significance of hydrostructures. The results of the HESA of the TCV area provide support for, among others, the evaluation of a proposed well for the Town of Castle Valley near the northern corner of the Castle Valley Drive and Shafer Lane intersection at about ft from Shafer Lane, and about ft from Castle Valley Drive on parcel (Utah GIS, 2017) (see Figure 1). Note that this well is identified as TCV well 2, in contrast to a proposed culinary well at end of Shafer Lane near Castle Creek (Kolm and van der Heijde, December 2016). Figure 1. Location of Proposed Well Site (Site 2) and Parcel Numbers (Utah GIS 2017). The hydrogeology at the location of proposed well 2 indicated a highly permeable sequence of unconsolidated sands and gravels (Quaternary alluvial fan deposits/stream alluvium) underlain by a zone of fractured bedrock of the Permian Cutler Formation.(Bedrock high K- zone) (Figure 2). In the absence of a confining unit at the top of the aquifer, the aquifer is considered unconfined with a freely moving water table. 1

3 Figure 2. Hydrogeology in the Vicinity of Proposed Well Site 2 (from Kolm and van der Heijde, 2016). Figure 3. Thickness of Unconsolidated Valley Fill Deposits in the Vicinity of Proposed Well Site 2 (UGS 2004); and Underground and Spring Diversions (Utah Division of Water Rights, Utah GIS 2017). 2

4 Earlier investigators identified a relatively shallow bedrock ridge in the vicinity of well site 2 (UGS, 2004), limiting the saturated thickness to about ft. (Figure 3). According to these investigators, this ridge shows a sharp drop off directly northeast and southwest of the proposed well site. Literature indicates a permeability range for the sand and gravels of 1-10 ft/day and a unconfined effective storage coefficient or specific yield of Saturated thickness in the vicinity of the well varies from about 50 ft to 100ft or more. Being located at the edge of the Permian Cutler Bedrock High-K Zone hydrostructure, the saturated thickness at the proposed well site may increase somewhat, but this may also decrease the water quality further, if screened into or if water is drawn up from. Existing wells in the vicinity of proposed well site 2 are all partially penetrating in the unconsolidated sands and gravels. None have been screened into bedrock. The nearest well (Goff well) is about 285ft NNE from the proposed well site (Figure 4, Table 1). Figure 4. Well locations in the Vicinity of the Proposed Well Site 2 According to the Utah Division of Water Right's Online Database (Accessed June 2017). In an unconfined aquifer the top of the aquifer is the water table itself; as the water table declines around the pumped well, the saturated thickness decreases causing the transmissivity (T=k * m; where k = permeability in ft/d and m = saturated thickness in ft) to decrease. This leads to complex non-linear equations of which the solutions for determining the drawdown at some distance of the pumping well may be conservatively approximated by assuming a constant saturated thickness. Another consideration in calculation of drawdowns due to pumping in the vicinity of a well in an unconfined aquifer is the process of gravity drainage of pore space or "delayed yield". This process can be taken into consideration for larger pumping times by using a drawdown- 3

5 dependent correction. Again, a conservative approach to the calculation of drawdowns in the vicinity of a pumping well is to neglect this effect which leads to larger computed drawdown away from the well than occur in reality. WIN (Utah Water Right Database) Owner Distance from Well 2 (ft, direction) Water Depth (ft) Bore Hole Depth (ft) Main Lithology Parcel Goff 285 NNE Sand, gravel TCV 540 W Sand, gravel Stoughton 630 SSW Sand, gravel Pike 655 SE Sand, gravel TCV 735 SW Clay, sand, gravel Holoman 820 SW Sand, gravel Price 925 ENE Sand, gravel Diggs 975 NW Sand, gravel; last 5ft conglomerate TCV 1017NE Sand, gravel to 128; clay, silt, sand in last 4ft Prickett 1065 SE Sand, gravel Brown 1180 SSE Sand, gravel Sikora 1200 NW Sand, gravel Rogers 1385 E Sand, gravel 228 Table 1. Well Log Data of Wells in the Vicinity of the Proposed Well Site 2 (from the Utah Division of Water Right's Online Database, Accessed June 2017) The following drawdowns where calculated for a constant pumping date of 125 gpm using a solution to the Theis equation provided on-line by the Utah Division of Water Rights ( (Table 2). The calculations assume that continuous pumping starts at time = 0 days and continues without interruptions until the time of calculation of the drawdowns. If the pumping is intermittent, the water table will recuperate to some extent during the down time and will start declining again from the recuperated levels upon restarting pumping. For calculation purposes the location of the proposed well is set at 95 ft from Shafer Lane, and 95 ft from Castle Valley Drive in northern corner of intersection on parcel (Figure 1). It is assumed that the aquifer is homogeneous and isotropic, meaning that the effects of pumping on water levels in the aquifer are propagated equally in all directions. 4

6 Time since start pumping (days) k=1.0 ft/d m=50 ft T=50 ft2/d Sy=0.1 k=1.0 ft/d T=100 ft2/d Sy = 0.1 k=1.0 ft/d T=100 ft2/d Sy=0.2 k=10.0 ft/d T=1000 ft2/d Sy 0.1 k=10.0 ft/d T=1000 ft2/d Sy= < < < < < Table 2. Drawdown in ft at Distance r=285ft for a Pumping rate of 125 gpm at the Proposed Well Site 2. (k= permeability; m=saturated thickness; T=transmissivity; Sy=specific yield). Note that to obtain drawdowns for a constant pumping rate of 250 gpm, the drawdowns in Table 2 need to be multiplied by a factor 2. The results listed in Table 2 indicate that the larger drawdowns are found assuming the lower limit for permeability, saturated thickness and specific yield values. If continuous pumping does not exceed a 7-day period, most drawdown values at 285ft from well are less than 1ft. Further than 285 ft away from the pumping well drawdowns will be significantly less than shown in Table 2. Also, if the well is pumped intermittently, drawdowns will be less than shown in Table 2. It should be noted that the water quality in the direct vicinity of the proposed well site is rather poor (up to 2000 mg/l TDS; UGS 2004). (Figure 5). Figure 5. Groundwater Quality in the Vicinity of the Proposed Well Site 2 Expressed in Terms of TDS (UGS 2004). 5

7 References: Kolm, K.E, and P.K.M. van der Heijde. March Hydrologic Assessment of the Surface Water and Groundwater Resources of Castle Valley, Utah: Part 1: Hydrologic and Environmental System Analysis (HESA) and Preliminary Water Budget. Report prepared for the Town of Castle Valley, Grand County, Utah. Kolm, K.E, and P.K.M. van der Heijde. December Hydrologic Assessment of the Surface Water and Groundwater Resources of Castle Valley, Utah: Part 2: HESA-Based Siting of Culinary Well for Town of Castle Valley. Report prepared for the Town of Castle Valley, Grand County, Utah. Lowe and others. (UGS) Ground-water Quality Classification and Recommended Septic Tank Soil Absorption System Density Maps, Castle Valley, Grand County, Utah UGS Special Study 113. UTAH GIS 2017: State Geographic Information Database (SGID) web site: UDWR 2017: Utah Division of Water Rights Interactive Diversions Map: 6