HomeMy WebLinkAboutSWP272264(2) CITY OF RENTON
Predesign Report For
Production Well Nos. 10 & 12
Well Drilling and Wellhead Construction
2 i '2-'-1
August 1993
City of Renton:
Ronald Olsen, Water Utility Engineer
City of Renton
200 Mill Avenue S.
Renton, Washington 98055
Work (206)277-6207
Prepared By:
8383 158th Avenue ME
Suite 200
Redmond, Washington 98052
(206) 869-1488
CHAPTER 1
INTRODUCTION
This report summarizes the engineering concepts and design and planning criteria used for the
proposed development of two water production wells on the Maplewood Golf Course in the City
of Renton. This report will also serve as the Project Report for the Washington State Department
of Health (DOH) requirements as outlined in WAC 246-290-110, and Source Approval as outline
in WAC 246-190-130. The information presented in this report has been reviewed by a
representative from the City of Renton.
A. PROJECT OBJECTIVES
This project involves the installation of two water production wells within the Maplewood Golf
rCourse in the City of Renton. These production wells will provide additional water supply to
the City's water system. The specific objectives of this project are listed below.
U 1. Expand the City's existing water production wellfield within the Maplewood Golf
Course.
2. Study the flow of water through aquifers within the Maplewood area. This objective
includes gathering geologic and hydrologic data during well drilling. A better
understanding of aquifer hydrology will permit the future development of a Wellhead
Protection Area for the Maplewood Wellfield.
3. Collect and analyze groundwater samples from each water production well. Results of
this analysis will provide a baseline of groundwater quality for comparison with future
analyses, demonstrate compliance with drinking water MCL's, and indicate treatment
requirements.
B. PURPOSE OF PREDESIGN REPORT
The general purpose of this Predesign Report is to provide a basis for decision-making during
construction of these production wells. Unforeseen situations which commonly arise during the
production well drilling and wellhead design and construction process can be dealt with
efficiently by reviewing the goals, objectives, and information presented in this Predesign Report.
The specific items in this Predesign Report are summarized below.
1. The background of the City's water production well development efforts.
2. A summary of geologic and hydrologic data of the Maplewood area.
3. Details for the proposed production well installation,including locations and construction
designs.
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CHAPTER ONE
4. A discussion of sources of contamination and groundwater flow paths.
5. A discussion of proposed production well pumping test and procedures.
6. A water quality assessment plan for sampling and analysis of groundwater from each
production well.
7. An environmental assessment of the proposed improvements.
C. AUTHORIZATION
On December 21, 1992, the City of Renton authorized RH2 Engineering to provide engineering
and hydrogeological services for the construction of two additional water production wells within
the Maplewood Golf Course. The project is to include hydrogeologic services for the drilling,
developing, and testing each water production well and the design and construction inspection
for the wellhead improvements.
D. BACKGROUND INFORMATION
The City of Renton's water supply comes from groundwater wells located with the City limits.
In the past, the City's groundwater resources have provided high quality, potable water for the
City's water customers. In recent years, the City has taken an active role in protecting the
quality of its groundwater through various programs and projects. However, the City has had
six known contaminations of the aquifer which provides a major portion of the City's water
supply. Detailed background information regarding the City's water supplies is presented below.
1. Cedar River Delta Water Supply Sources
The City of Renton relies primarily on groundwater for supply of its water system. Ninety
percent (90%) of the City's water supply is pumped from a shallow aquifer in the Delta area
beneath Liberty and Cedar River Parks. Development of groundwater from this downtown
aquifer has successfully provided substantial volumes of high quality water. The combined water
supply capacity for these six (6) groundwater wells is approximately 12,800 gpm. Another seven
percent (7%) of the City's water supply is pumped from PW-5R which is located in the
Kennydale area in the northern section of the City. The remaining three percent (3%) of the
City's water supply originated at a spring located in the Springbrook area in the southern portion
of the City. The City is currently meeting its water supply need; however, build out under
existing zoning in the City will double water demands. 10
2. Maplewood Golf Course Water Supply Sources 10
In 1987, the City pursued the development of a second wellfield within the recently purchased
Maplewood Golf Course located in the Cedar River Valley in the eastern section of the City.
The City began with the drilling and testing of an 8-inch well in 1987. In 1988,
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Introduction
the City proceeded with the drilling of two water production wells, PW-10 and 11. PW-11 was
a successful well with a capacity of 2,500 gpm; however, PW-10 was not successful and was
eventually converted to a monitoring well OBW-1.
In 1989, the City drilled another well, PW-17, adjacent to PW-11. PW-17 was a successful well
with a capacity of 1,500 gpm. therefore, the combined capacity of PW-11 and 17 is 4,000 gpm.
The Maplewood Aquifer is much deeper than the Cedar River Delta Aquifer. The screens for
PW-11 and 17 are in excess of 300 feet below the ground surface. This may provide greater
protection of the groundwater resource from surface contaminants. However, the existing
groundwater quality in the Maplewood Aquifer is poorer than the Cedar River Delta Aquifer.
The Maplewood Aquifer has elevated levels of iron and manganese and measurable levels of
hydrogen sulfide.
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i CHAPTER 3
GROUNDWATER HYDROLOGY
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Several studies have been conducted which investigate the geology and hydrogeology within the
Maplewood area. The most recent studies include the 'Work Plan for the Monitoring Well Installation
Project," (RH2 Engineering and PGG, 1991) "Hydrogeologic Report for Maplewood Production Wells
PW-11 and PW-17," (Pacific Groundwater Group, 1990), and "Monitoring Well Installation Project
Report", (RH2 and PGG, 1993). The following is a summary of the hydrogeology presented in these
reports. Figure 3 presents the geologic features within the Renton area along with estimated bedrock
contours. Two geologic cross-sections are also presented in Figures 4 and 5.
A. AQUIFER DESCRIPTIONS
There are three primary aquifer units within the Maplewood area. The first is an alluvial aquifer called
the "Cedar Valley Alluvial Aquifer" which is shallow and bounded by the valley walls. The second
aquifer is the "Maplewood Production Aquifer" which is located near the bedrock in the Maplewood Golf
Course area. The third aquifer is called the "Deep Aquifer" which is located one mile east of the
Maplewood Golf course. This Deep Aquifer is tapped by an artisan well with a static pressure of 60 psi
at the ground surface.
The Cedar Valley Alluvial Aquifer provides a water source for an irrigation well located at the Maplewood
Golf Course and domestic water supply well located in Wasmeta Park. The aquifer bottom occurs at a
depth of about 50 feet below land surface. Measured depths to groundwater are generally within 15 feet
of the land surface. Some degree of hydraulic continuity with the Cedar River is likely, but previous
studies have not investigated this aspect.
The Maplewood Production Aquifer has been well documented through the installation of several
monitoring and production wells in the Maplewood Golf Course area, and is believed to extend northward
into hydrostratigraphically correlated zones beneath the North Uplands. Two recently completed
production wells, PW-I1 and PW-17, yield a combined flow of 4000 gpm. The aquifer is encountered
at elevations ranging from approximately 40 to -220 feet mean sea level (MSL) beneath the golf course,
and -160 to -220 feet MSL beneath the North Uplands. Its thickness varies from approximately 50 feet
beneath the golf course to 150 feet beneath the North Uplands. Testing of PW-II and 17 has shown it
to be confined and leaky. The aquifer does not extend to the south and west due to the presence of
bedrock and does not exist one mile east of the Maplewood production wells based on the log of the deep
exploration well. Aquifer recharge is believed to occur predominantly from the North Uplands. Aquifer
discharge occurs in the Cedar Valley via upward flow to the Cedar Valley Alluvial Aquifer east of The
Narrows. Other recharge and discharge point(s) may exist, but have not been documented.
The North Uplands aquifer system consists of a stratified series of glacially deposited aquifers. The
uppermost of these aquifers occurs in the Vashon recessional outwash deposits which cover the top of the
uplands. Other permeable glacial deposits alternate with low permeability deposits beneath the recessional
outwash. The aquifers are currently not used for water supply due to their limited thicknesses, available
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CHAPTER THREE
drawdown, and permeabilities (relative to other aquifers). Recharge to the upland aquifer system occurs
from rainfall and septic drainage from residential development atop the uplands. The aquifer system
discharges to the Cedar Valley Alluvial Aquifer via springs emanating from the valley wall and infiltrating
into the valley floor, and possibly to the Maplewood Production Aquifer via downward flow.
B. AQUIFER PROPERTIES
Existing literature and technical reports provide good definition of aquifer properties in the Maplewood
Production Aquifer, and relatively moderate definition in the Cedar Valley Alluvial Aquifer. Aquifer
properties include thickness(b),hydraulic conductivity(K),transmissivity M,and storage coefficient(S).
Testing was performed during installation of the new monitoring wells to augment existing aquifer/aquitard
property data. This section summarizes both existing and recently obtained hydraulic data.
Documented tests of the Cedar Valley Alluvial Aquifer to estimate aquifer properties are relatively limited.
Hydraulic conductivity in the Maplewood area was calculated to be 460 feet/day based on testing a
shallow well (GeoEngineers Inc, 1986). The aquifer appears to be unconfined in Maplewood and the
storage coefficient should be correspondingly large. A constant-rate pumping test was conducted in the
borehole for MW-33 to estimate transmissivity in the Alluvial Aquifer slightly east of The Narrows.
Analysis by the method of Jacob-Cooper (Lohman, 1979) yields an estimated T value of 20,200 gpd/ft.
The corresponding hydraulic conductivity is on the order of 80 ft/day given a saturated aquifer thickness
of 33 feet.
Aquifer properties have been characterized in the Maplewood Production Aquifer based on constant-rate
testing of Production Wells 17 and 11. Transmissivities estimated for these wells range from 49,000 to
67,000 gpd/ft, and corresponding hydraulic conductivities range from 94 to 128 ft/day (aquifer thickness
70 feet). Storage coefficient was estimated to be approximately 0.0006. A leaky aquifer response was
observed,however leakage analysis was inconclusive(Pacific Groundwater Group, 1990). Recent attempts
to measure the transmissivity of the laterally contiguous sediments beneath the North Uplands were
unsuccessful due to the inability to sufficiently stress the aquifer.
Hydraulic properties were estimated for the aquitard which overlies the Maplewood Production Aquifer
and underlies the Alluvial Aquifer. "Slug" (positive and negative displacement)tests were performed upon
MW-37 and MW-38 during their construction, and were analyzed with the method of Horvslev (1951).
The analysis assumed that vertical conductivity is assumed to be one-tenth of horizontal conductivity.
Estimated values of horizontal hydraulic conductivity ranged from approximately 0.14 to 10 feet/day
(5X 10-5 to 4X 10-3 cm/sec).
Aquifer properties have not been documented for the Vashon recessional aquifer and other related Vashon
drift deposits. Transmissivity and storage coefficients for the 'Deep Aquifer" encountered in the
exploration well east of the Maplewood Golf Course have been estimated to be 19,500 gpd/ft and 0.00024,
respectively (Golder, 1991).
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Groundwater Hydrology
C. GROUNDWATER ELEVATIONS, GRADIENTS, AND FLOW PATTERNS
Water levels were measured in selected City of Renton monitoring wells on August 20-21, 1992 and
January 22, 1993. Potentiometric elevations were calculated for all monitoring wells visited.
1. Horizontal Gradients
MA sufficient number of monitoring wells exist to describe the horizontal component of groundwater
gradients in the Delta Aquifer, Cedar Valley Alluvial Aquifer and in the Maplewood Production Aquifer.
Horizontal gradients in the Delta Aquifer and Cedar Valley Alluvial Aquifer can be evaluated together,
because these surficial aquifers are hydraulically coupled through The Narrows. The horizontal gradients
occur in a down-valley direction. An inferred steeper gradient in the vicinity of The Narrows is qualitative
and based on the decreased cross-sectional area available for groundwater flow.
Horizontal gradients in the Maplewood Production Aquifer are relatively steep between wells completed
in the laterally contiguous sediments beneath the North Uplands and wells completed in the sediments
beneath the golf course. Assuming lateral continuity between the completion zones of MW-35D, MW-
36D, and MW-37D, a south-southwestem gradient of approximately 0.024 exists. The horizontal gradient
between wells completed in the Maplewood Production Aquifer beneath the golf course is less steep and
rdirected more towards the west. The direction of the horizontal gradient component is down valley (west)
with a magnitude of approximately 0.006.
r2. Vertical Gradients
The vertical component of groundwater flow was assessed by comparing water levels in shallow and deep
rcompletions of nested monitoring wells. Multiple completion wells in which water levels were measured
include MW-34,MW-35,MW-36, MW-37 and MW-38. Data shows that upward gradients ranging from
approximately 0.007 to 0.01 predominate in the Maplewood area, whereas larger magnitude downward
gradients are evident beneath the North Uplands. Upward vertical gradients are known to occur from the
"Deep Aquifer" encountered east of the golf course, based on its flowing artisan condition.
The magnitude of upward vertical gradients in the golf course vicinity is fairly comparable in MW-36,
MW-37, and MW-38. Vertical gradients,while consistently downward in Well MW-34 beneath the North
Uplands, vary in magnitude between aquifers. MW-34 is completed in the Vashon recessional deposits
and two zones within the sediments hydrostratigraphically correlated with the Maplewood Production
Aquifer. The relatively large (0.62) downward gradient between MW-34S and MW-34M suggests that
the Vashon recessional deposits (MW-34S) are effectively perched. Geologic information (a thick
sequence of low permeability glacial sediments between the two completions) supports this theory.
Potentiometric elevations in MW-34D show that the downward vertical gradient extends to the deeper
(MW-34D) zone beneath the North Uplands. Vertical gradient information for MW-35 is currently
unavailable, but also appears to have a downward vertical gradient.
Production Wells 10 and 12
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CHAPTER THREE
3. Groundwater Flow Patterns
Groundwater flow in the shallow Cedar Valley Alluvial Aquifer system is largely down valley (west-
northwest) and radial towards City of Renton pumping wells in the downtown Delta Aquifer. Dominantly
horizontal flow is likely in the Alluvial Aquifer based on its relatively high permeability. East of The
Narrows, where upward vertical gradients occur, the Alluvial Aquifer receives recharge from the
Maplewood Production Aquifer and slight upward flow may exist within the lower portion of the Alluvial
Aquifer itself. West of The Narrows,flow patterns in the Delta Aquifer are largely controlled by pumping
of the City of Renton downtown wellfield. Both horizontal and vertical flow components vary with
pumping schedules.
Groundwater flow within the Maplewood Production Aquifer beneath the golf course is likely to be
dominantly horizontal. Although the horizontal gradient within the aquifer(0.006)is only slightly smaller
than the upward vertical gradient across the overlying aquitard (0.01), the horizontal aquifer permeability
(94-128 ft/day) is much larger that the vertical aquitard permeability(0.014-1 ft/day). The role of upward
vertical groundwater flow as a discharge pathway may be significant,however,considering the areal extent
of the Alluvial Aquifer into which upward flow can occur. Upward vertical flow may also play a greater
role closer to the bedrock narrows west of the golf course. In this vicinity, bedrock boundaries are
encountered to the west at The Narrows and to the south at the uplands; higher heads are encountered in
the laterally contiguous sediments to the north and northeast; and the aquifer pinches out to the east.
Upward vertical discharge is likely because there appears to be nowhere else for groundwater to flow.
Groundwater flow in the stratified glacial aquifer system beneath the North Uplands may have both
horizontal and vertical components. Springs along the northern Cedar Valley wall indicate a horizontal
component of flow within the stratified aquifer system, but water level data are insufficient to quantify
the horizontal component. High downward vertical gradient components indicate that downward recharge
is occurring to the beneath the North Uplands. The upward vertical flow documented beneath the
Maplewood golf course suggests a hydraulic circulation pattern with recharge to the laterally contiguous
sediments beneath the North Uplands flowing into the Maplewood Production Aquifer and discharging
upward within the Cedar Valley. In this case, groundwater discharge occurs from the Maplewood
Production Aquifer to the overlying Alluvial Aquifer and eventually the Cedar River.
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