A GROUNDWATER CHARACTERIZATION OF SQUALICUM VALLEY LAKE WHATCOM WATERSHED, WHATCOM COUNTY, WA Niki Thane – MS Geology, WWU • Dr. Robert Mitchell – WWU Figure 6. Schematic representation of the fractured bedrock mountain-valley aquifer system. ? ? ? INTRODUCTION This study is designed to characterize the discrete confined groundwater aquifer in Squalicum Valley, the largest glacial basin in the Lake Whatcom watershed east of Bellingham, WA (Figure 1). Lake Whatcom receives a substantial portion of recharge from groundwater; approximately 80% of the lake watershed is fractured bedrock (Chuckanut Formation) that is estimated to provide less than 30% of the groundwater recharge budget for the lake. Valleys filled with late Fraser glacial deposits discharge the remainder. Squalicum Valley alone is hypothesized to provide more than 20% of the lake’s groundwater recharge (Pitz, 2005). Glacial sediments are recharged mainly by pressurized flow through the fractured bedrock, though a small amount of groundwater recharge may come from direct precipitation. Lake Whatcom is subject to a Total Maximum Daily Load (TMDL)restoration plan for water quality. To facilitate the TMDL, two points near shore in Agate Bay, at the lakeshore of Squalicum Valley, were sampled for seepage values (Pitz, 2005). These values, however, may not be representative of the entire Squalicum Valley aquifer system, which contains a confined aquifer that discharges further lakeward. Our goal is to fully characterize the confined aquifer system in Squalicum Valley. We will characterize the hydrogeology with Groundwater Modeling Systems software (GMS), provide new estimates for bedrock recharge to valley sediments, and determine general groundwater volumes, flow patterns and potential discharge from the valley into Lake Whatcom. FIELD METHODS Individual permissions from private and group well owners were required for this study. The WA State Department of Ecology well log database contains more than 240 well driller’s logs for the Squalicum Valley area. Logs were reconciled to current tax parcel divisions, street addresses, and property owners. Letters and information were sent with prepaid RSVP cards, and of 143 responses returned, just 18 requested the option of “no further contact.” Additional permissions were garnered by personal visits to residences, and through information sharing between neighbors for a total of 125 permitted wells (Figure 1 ). Precise survey grade GPS positions and elevations were collected using a Trimble 5700, Trimmark3 Radio, and Zephyr and R6-2 satellite antennas. Aquifer piezometric water elevations will be modeled relative to mean sea level. Water levels in non-flowing wells were measured with a Ravensgate sonic water level meter accurate to 0.1 of a foot. Flowing artesian wells were measured by pressure gauge where possible, and converted to piezometric elevation. April and September 2012 water levels illustrate seasonal high- and low-water levels. A subset of wells were sampled quarterly to validate seasonal fluctuations throughout the valley. MODELING METHODS Model boundaries were defined in GMS beyond the edges of the confined aquifer to map the projected contact between bedrock and glacial deposits, and the underwater surfacing of the confined aquifer below lake shore elevation (Figure 1 ). The Chuckanut Sandstone bedrock was built in the preliminary model as a base TIN with depth to bedrock interpolated from 42 wells drilled completely through aquifer sediments (Figure 2; Figure 3 ). For the purpose of initial mapping, 22 scattered wells where dense clay was encountered below the aquifer were simplified as aquifer-contacting bedrock. Lake Whatcom bathymetry files will be used to determine underwater elevations for extrapolating the extent of the aquifer into the lakebed (Mitchell et al, 2010). Model stratigraphy was developed from 125 well driller’s logs. Seventy-five client well logs were pinpointed with precise GPS locations and elevations, and model layers designated according to the method of Allen et al (2008). An additional 50 well logs were placed at tax-parcel- and satellite-image-interpreted locations using approximate surface elevations from LiDAR data (Figure 1 ). Due to inconsistent descriptions of sediments in the upper units of Squalicum Valley, model layers have been simplified to the distinctive break between highly transmissive gravels of the confined aquifer and the silt/clay-rich confining layers above (Figure 2; Figure 4 ). Modern wells are rarely completed in unconfined or perched lenses in Squalicum Valley due to the nearly complete extent of the productive confined aquifer. Aquifer conductivity will be defined by specific capacity tests recorded on driller’s logs using a modified Theis equation for screened wells by Ferris and others (1962) (Kahle and Olsen, 1995). For wellbores with an open end, a screened interval of 5 feet will be assumed for the purposes of conductivity modeling (Arihood, 2009). The bedrock recharge contact throughout this small-scale discrete aquifer system will be set as a seasonal constant in the final model, rather than as the zero-flow boundary common in large-scale studies. The lakeshore boundary condition will also be modeled as a constant elevation head, once the projection of the confining layer into the lake depths is defined and we can calculate consequent pressures of the overlying lake water. Perennial and large seasonal streams will not need to be modeled as drains, because cross-section modeling has shown they recharge and discharge from unconfined aquifer layers and do not substantially impact confined aquifer dynamics other than at the bedrock edges of the system. (Figure 1 ). PRELIMINARY RESULTS A model of stratigraphy from 125 well logs shows that glacial deposits slope gently south-southwest toward the Lake Whatcom basin, and that the confined aquifer is continuous throughout the valley (Figure 4 ). Modern wells are sparse in the NE portion of the valley because most households are served by a Group B water association. Resting on bedrock, or on a thin discontinuous stratum of dense clay, the dominant aquifer unit is water-rich, highly transmissive gravel and sand from 0.5-78 feet thick (possibly up to 115 ft), with >90% of the known values less than 30 ft. This unit is not fully saturated in all areas of the valley, and does not contact the land surface above lake level. The deep aquifer is capped and confined by a stratum of mixed silty-clay drift from 0-281 feet thick, with 75% of the wellbore records showing thicknesses less than 130 ft. This layered drift and mixed recessional outwash is a highly heterogeneous unit containing discontinuous unconfined watery lenses and perched aquifers. Hydrostatic water levels are elevated above the contact with the confining strata throughout much of the valley, particularly toward the lake, and in the central portion of the valley between small bedrock ridges (Figure 5). Wells along the shore are flowing artesian with pressures as great as 37 psi due to the confining clay layer surfacing below lake level. There is a potential for groundwater from the confined aquifer to discharge further from the lake shore than would be seen from an unconfined system discharging into a lake. Water availability and water levels are extremely variable for wells completed in Chuckanut Sandstone on the flanking hills (Figure 6). A few productive fracture zones have been encountered, even a few high elevation artesian flowing wells! Many homeowners use filters and fine-sediment flocculants, and must pump slower than 3 gpm on demand to keep a large storage tank filled. Many on Squalicum Mtn report they experience water shortages during the summer. REFERNECES Allen, D.M., Schuurman, N. Deshpande, A. and Scibek, J. 2008. Data Integration and Standardization in Cross-Border Hydrogeological Studies: Hydrostratigraphic Model Development. Environmental Geology, 53:1441–1453. Arihood, L.D., 2009, Processing, analysis, and general evaluation of well-driller records for estimating hydrogeologic parameters of the glacial sediments in a ground-water flow model of the Lake Michigan Basin: Scientific Investiga-tions Report 2008-5184, 26 p. Kahle, S. C.; Olsen, T. D. 1995. Hydrogeology and quality of ground water on Guemes Island, Skagit County, Washington. USGS Water-Resources Investigations Report: 94-4236. Mitchell, R., G. Gabrisch, and R. Matthews, Lake Whatcom Bathymetry and Morphology. November 2010. Report to the City of Bellingham, WA. Pitz, C. 2005. Lake Whatcom Total Maximum Daily Load Groundwater Study. Washington State Department of Ecology. Publication No. 05-03-001. 90 p. Figure 1. LiDAR DEM of North Lake Whatcom area, showing Squalicum Valley field area and Lake Whatcom. Surface morphology exhibits evidence of lateral glacial moraines, sub-glacial fluting, and the outburst flood from a small late glacial ice tongue in the north of Squalicum Valley. Figure 2. Six wellbore cross-sections and a TIN representing the glacial contact with bedrock create this fence diagram of the Squalicum Valley confined aquifer. The blue layer indicates water bearing sediments, and the red shows confining sediments. Figure 5. Purple half circles indicate April 2012 static water levels in 39 client wells completed in the Squalicum Valley confined aquifer. N Lake Whatcom Figure 3. Distribution of 42 points of known aquifer thickness, in feet. A A’’ A’ Figure 3. Longitudinal cross-section with 5x vertical exaggeration. The blue strata of aquifer sediments is not fully saturated in the north of the valley. N West side of valley East side of valley A A’ A’’ A
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
-
A GROUNDWATER CHARACTERIZATION OF SQUALICUM VALLEY
LAKE WHATCOM WATERSHED, WHATCOM COUNTY, WA
Niki Thane – MS Geology, WWU • Dr. Robert Mitchell – WWU
Figure 6. Schematic representation of the fractured bedrock mountain-valley aquifer system.
?
?
?
INTRODUCTION This study is designed to characterize the discrete confined groundwater aquifer in Squalicum Valley, the largest glacial basin in the Lake Whatcom watershed east of Bellingham, WA (Figure 1). Lake Whatcom receives a substantial portion of recharge from groundwater; approximately 80% of the lake watershed is fractured bedrock (Chuckanut Formation) that is estimated to provide less than 30% of the groundwater recharge budget for the lake. Valleys filled with late Fraser glacial deposits discharge the remainder. Squalicum Valley alone is hypothesized to provide more than 20% of the lake’s groundwater recharge (Pitz, 2005). Glacial sediments are recharged mainly by pressurized flow through the fractured bedrock, though a small amount of groundwater recharge may come from direct precipitation. Lake Whatcom is subject to a Total Maximum Daily Load (TMDL)restoration plan for water quality. To facilitate the TMDL, two points near shore in Agate Bay, at the lakeshore of Squalicum Valley, were sampled for seepage values (Pitz, 2005). These values, however, may not be representative of the entire Squalicum Valley aquifer system, which contains a confined aquifer that discharges further lakeward. Our goal is to fully characterize the confined aquifer system in Squalicum Valley. We will characterize the hydrogeology with Groundwater Modeling Systems software (GMS), provide new estimates for bedrock recharge to valley sediments, and determine general groundwater volumes, flow patterns and potential discharge from the valley into Lake Whatcom.
FIELD METHODS
Individual permissions from private and group well owners were required for this study. The WA State Department of Ecology well log database contains more than 240 well driller’s logs for the Squalicum Valley area. Logs were reconciled to current tax parcel divisions, street addresses, and property owners. Letters and information were sent with prepaid RSVP cards, and of 143 responses returned, just 18 requested the option of “no further contact.” Additional permissions were garnered by personal visits to residences, and through information sharing between neighbors for a total of 125 permitted wells (Figure 1).
Precise survey grade GPS positions and elevations were collected using a Trimble 5700, Trimmark3 Radio, and Zephyr and R6-2 satellite antennas. Aquifer piezometric water elevations will be modeled relative to mean sea level.
Water levels in non-flowing wells were measured with a Ravensgate sonic water level meter accurate to 0.1 of a foot. Flowing artesian wells were measured by pressure gauge where possible, and converted to piezometric elevation. April and September 2012 water levels illustrate seasonal high- and low-water levels. A subset of wells were sampled quarterly to validate seasonal fluctuations throughout the valley.
MODELING METHODS
Model boundaries were defined in GMS beyond the edges of the confined aquifer to map the projected contact between bedrock and glacial deposits, and the underwater surfacing of the confined aquifer below lake shore elevation (Figure 1).
The Chuckanut Sandstone bedrock was built in the preliminary model as a base TIN with depth to bedrock interpolated from 42 wells drilled completely through aquifer sediments (Figure 2; Figure 3). For the purpose of initial mapping, 22 scattered wells where dense clay was encountered below the aquifer were simplified as aquifer-contacting bedrock.
Lake Whatcom bathymetry files will be used to determine underwater elevations for extrapolating the extent of the aquifer into the lakebed (Mitchell et al, 2010).
Model stratigraphy was developed from 125 well driller’s logs. Seventy-five client well logs were pinpointed with precise GPS locations and elevations, and model layers designated according to the method of Allen et al (2008). An additional 50 well logs were placed at tax-parcel- and satellite-image-interpreted locations using approximate surface elevations from LiDAR data (Figure 1). Due to inconsistent descriptions of sediments in the upper units of Squalicum Valley, model layers have been simplified to the distinctive break between highly transmissive gravels of the confined aquifer and the silt/clay-rich confining layers above (Figure 2; Figure 4). Modern wells are rarely completed in unconfined or perched lenses in Squalicum Valley due to the nearly complete extent of the productive confined aquifer.
Aquifer conductivity will be defined by specific capacity tests recorded on driller’s logs using a modified Theis equation for screened wells by Ferris and others (1962) (Kahle and Olsen, 1995). For wellbores with an open end, a screened interval of 5 feet will be assumed for the purposes of conductivity modeling (Arihood, 2009).
The bedrock recharge contact throughout this small-scale discrete aquifer system will be set as a seasonal constant in the final model, rather than as the zero-flow boundary common in large-scale studies.
The lakeshore boundary condition will also be modeled as a constant elevation head, once the projection of the confining layer into the lake depths is defined and we can calculate consequent pressures of the overlying lake water.
Perennial and large seasonal streams will not need to be modeled as drains, because cross-section modeling has shown they recharge and discharge from unconfined aquifer layers and do not substantially impact confined aquifer dynamics other than at the bedrock edges of the system. (Figure 1).
PRELIMINARY RESULTS
A model of stratigraphy from 125 well logs shows that glacial deposits slope gently south-southwest toward the Lake Whatcom basin, and that the confined aquifer is continuous throughout the valley (Figure 4). Modern wells are sparse in the NE portion of the valley because most households are served by a Group B water association.
Resting on bedrock, or on a thin discontinuous stratum of dense clay, the dominant aquifer unit is water-rich, highly transmissive gravel and sand from 0.5-78 feet thick (possibly up to 115 ft), with >90% of the known values less than 30 ft. This unit is not fully saturated in all areas of the valley, and does not contact the land surface above lake level.
The deep aquifer is capped and confined by a stratum of mixed silty-clay drift from 0-281 feet thick, with 75% of the wellbore records showing thicknesses less than 130 ft. This layered drift and mixed recessional outwash is a highly heterogeneous unit containing discontinuous unconfined watery lenses and perched aquifers.
Hydrostatic water levels are elevated above the contact with the confining strata throughout much of the valley, particularly toward the lake, and in the central portion of the valley between small bedrock ridges (Figure 5). Wells along the shore are flowing artesian with pressures as great as 37 psi due to the confining clay layer surfacing below lake level. There is a potential for groundwater from the confined aquifer to discharge further from the lake shore than would be seen from an unconfined system discharging into a lake.
Water availability and water levels are extremely variable for wells completed in Chuckanut Sandstone on the flanking hills (Figure 6). A few productive fracture zones have been encountered, even a few high elevation artesian flowing wells! Many homeowners use filters and fine-sediment flocculants, and must pump slower than 3 gpm on demand to keep a large storage tank filled. Many on Squalicum Mtn report they experience water shortages during the summer.
REFERNECES
Allen, D.M., Schuurman, N. Deshpande, A. and Scibek, J. 2008. Data Integration and Standardization in
Cross-Border Hydrogeological Studies: Hydrostratigraphic Model Development. Environmental Geology,
53:1441–1453.
Arihood, L.D., 2009, Processing, analysis, and general evaluation of well-driller records for estimating
hydrogeologic parameters of the glacial sediments in a ground-water flow model of the Lake Michigan
Basin: Scientific Investiga-tions Report 2008-5184, 26 p.
Kahle, S. C.; Olsen, T. D. 1995. Hydrogeology and quality of ground water on Guemes Island, Skagit
County, Washington. USGS Water-Resources Investigations Report: 94-4236.
Mitchell, R., G. Gabrisch, and R. Matthews, Lake Whatcom Bathymetry and Morphology. November
2010. Report to the City of Bellingham, WA.
Pitz, C. 2005. Lake Whatcom Total Maximum Daily Load Groundwater Study. Washington State
Department of Ecology. Publication No. 05-03-001. 90 p.
Figure 1. LiDAR DEM of North Lake Whatcom area, showing Squalicum Valley field area and Lake Whatcom.
Surface morphology exhibits evidence of lateral glacial moraines, sub-glacial fluting, and the outburst flood
from a small late glacial ice tongue in the north of Squalicum Valley.
Figure 2. Six wellbore cross-sections and a TIN representing the glacial contact
with bedrock create this fence diagram of the Squalicum Valley confined aquifer.
The blue layer indicates water bearing sediments, and the red shows confining
sediments.
Figure 5. Purple half circles indicate April 2012 static water levels in 39 client wells completed in the Squalicum Valley
confined aquifer.
N Lake Whatcom
Figure 3. Distribution of 42 points of known aquifer thickness, in feet.
A
A’’
A’
Figure 3. Longitudinal cross-section with 5x vertical exaggeration. The blue
strata of aquifer sediments is not fully saturated in the north of the valley.
N
West side of valley
East side of valley
A
A’
A’’
A
Related Documents
![1 Climatic zoneskula.geol.wwu.edu/rjmitch/climate.pdfFigure 1.1 Global distribution of climatic zones [1] ... Chapter 1 Energy Comfort and Buildings 4. ... TAREB Energy, Enviroment](https://static.cupdf.com/doc/110x72/5aaed76e7f8b9aa8438c9324/1-climatic-11-global-distribution-of-climatic-zones-1-chapter-1-energy-comfort.jpg)
