Tributaries Committee Draft Funding Request Page 1
A. Overview
The Tributary Streamflow Technical Committee has focused their efforts on developing a prioritized list of stream and stream segments that are most likely to benefit from low flow restoration or enhancement to help maintain and recover salmon runs.
The overall objective of this prioritization is to eventually improve flows and associated water temperatures for salmon in prioritized streams. Restoring groundwater contributions to streams has the potential to enhance both the quality and quantity of instream habitat, and to mitigate the trend toward warmer water temperatures in local watersheds.
A proven methodology for restoring groundwater contributions to stream flow is to reduce groundwater extraction from wells at locations that are hydraulically connected to impaired streams and stream segments. “Resting” or “pausing” groundwater extraction from selected wells during selected time periods can result in significant increases in stream flow and significant decreases in stream temperature. The scope of work described below is aimed at demonstrating potential improvements in-stream flow and temperature conditions through seasonal pausing of groundwater extraction from wells that have been identified by utilities or individuals as candidates for source exchange/substitution.
B. Background.
Most of the water supply wells in WRIA 8 and 9 are completed in either shallow unconfined aquifers or in semi-confined or “leaky” aquifers. Shallow unconfined aquifers are in most direct continuity with streams. The connection for wells in leaky, semi-confined aquifers is less direct, but not necessarily less important. In a leaky aquifer, a portion of the water extracted by the wells may originate from storage in the pumped aquifer and a portion may come from leakage through confining layers. When pumping first begins, the water comes primarily from storage in the pumped aquifer. As time goes on, more of the water that is extracted originates as leakage through the confining layer. The leakage and flow reductions are largest in the immediate vicinity of the well and wells in close proximity to streams are more likely to impact stream flow than wells that are most distant from streams.
The steady-state or equilibrium impact of groundwater extraction on stream flow was considered by the USGS in a modeling study (Morgan and Jones, 1999). This study, which was completed using a three-dimensional computer model, focused specifically on
DRAFT Document, Subject to Revision (June 5, 2006) – Page 1

Tributaries Committee Draft Funding Request Page 2 effects of ground-water withdrawals on discharge to streams and springs in small basins typical of the Puget Sound lowland. While this modeling study was useful for identifying long-term impacts, it cannot be used to evaluate the effects of pausing or resting wells because it did not consider transient or time-varying effects.
Recent analytical tools and field work has demonstrated that wells tend to have more local and more immediate effects than was perhaps previously appreciated (Hunt et al, 2001; Hunt, 2003a; Hunt, 2003b; Hunt, 1999; Nyholm et al, 2003; Sophocleous et al.,
1995). These relatively simple analytical tools can be used to identify stream segments that are most likely impacted by a specific well and to estimate the response time for reductions in stream flow caused by groundwater extraction at these wells. Estimates of the response times and spatial distribution of these impacts can be used to help identify specific wells that offer the best opportunity for improving in-stream flow and temperature conditions through seasonal pausing of groundwater extraction.
C. Scope and Activities
This effort will have four primary tasks, as summarized below.
Task 1 will involve compiling and integrating recent studies and reports that describe or relate to benefits derived from resting or pausing groundwater extraction. Both generic studies and studies specific to the Puget Sound region will be included in this compilation and integration. Available studies that consider both the hydraulic and thermal benefits of resting or pausing groundwater extraction will be reviewed and compiled.
Task 2 will involve characterizing a select number of groundwater wells in WRIA’s 8 and 9. This task will identify site-specific characteristics that are important for quantifying the magnitude, timing, and distribution of stream flow impacts from groundwater extraction. Characteristics will include well construction and operation information (e.g., length and depth of well screen and well pumping rates), hydrogeological parameters that control stream impact (e.g., storage coefficients, hydraulic conductivity values, aquifer and confining unit thicknesses), distances from impaired stream channels, and characteristics of impaired stream channels (e.g., base flow and peak temperatures). The wells that will be considered in this task will be identified by owners of municipal water supply wells who are interested in having their wells evaluated for source substitution or source exchange purposes.
Task 3 will involve modifying the USGS steady-state groundwater model developed for simulating aquifer systems in the Puget Sound lowlands (Morgan and Jones, 1999) so that it can be used to simulate transient or time-varying effects of groundwater extraction.
The transient model will then be used to identify well characteristics and hydrogeologic conditions necessary to obtain significant flow improvements from seasonal resting.
Task 4 will combine the results of the computer simulations developed in Task 3 with the well characterization data identified in Task 2 to evaluate potential improvements in in-
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Tributaries Committee Draft Funding Request Page 3 stream flow conditions through seasonal pausing of specific groundwater extraction wells. This task will include an assessment of the percent and timing of in-stream flow restored, the length of stream benefiting from flow restoration, and a recommendation on the period of time to pause withdrawals to maximize benefit to stream flow during the
July – October low flow period. Under this task, wells that are characterized under Task
2 will be divided into relatively broad categories that relate to their potential for flow restoration from seasonal pausing. In terms of potential benefits to stream flows during critical months, example categories might include “very unlikely,” “very likely”, and
“uncertain based on available data.”
Task 5 will be used to a compare the results of a site-specific analysis with the more
“semi-generic” analysis described under Task 4. This task will be completed in collaboration with a volunteer owner of a municipal water supply well. It is assumed that the owner of this well will have existing site-specific information that could be used to evaluate seasonal impacts on stream flow for different pumping strategies. In an ideal situation, a site-specific computer model would be available. This site-specific model would be modified as needed and applied to consider potential stream flow benefits from seasonal pausing. This task would be completed in close cooperation with the volunteer owner.
D. Deliverables.
The following set of deliverables is proposed :
Task 1

Technical memorandum or report that summarizes recent studies relate to benefits derived from resting or pausing groundwater extraction.
Task 2

Description of candidate groundwater wells with relevant characteristics that relate to potential benefits from seasonal pausing or resting.
Task 3

Computer code used for three-dimensional, transient simulations.

Technical memorandum or report describing computer simulations used to identify well characteristics and hydrogeologic conditions necessary to obtain significant flow improvements from seasonal resting.
Task 4

Evaluation of potential opportunities for improving in-stream flow conditions through seasonal pausing of groundwater extraction.
 Technical memorandum or report describing methods and results used to quantify potential impacts.
Task 5
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Tributaries Committee Draft Funding Request Page 4

Technical memorandum describing site-specific analysis and comparison with more generic analysis completed under Task 4.
E. Cost
The cost of completing the tasks described above will depend upon the number of wells that are considered using the screening tool and the availability of information related to these wells. Table 1 provides estimated costs of each of the four tasks proposed for this scope of work assuming approximately 10-20 candidate wells will be proposed by municipalities, utilities, and other owners of water supply systems that rely on groundwater resources. These wells will be divided into relatively broad categories, as described under Task 4. The collaboration with a well owner described under Task 5 assumes approximately 200 hours of time.
F. Timetable
Table 1 includes estimates of the time required to complete the tasks described above. The total time to compete this scope of work is approximately 6 months. This includes development of the technical memoranda and reports referenced in the task list.
References
Hunt, B. Unsteady stream depletion from ground water pumping , Ground Water; Vol.
37(1), 1999.
Hunt, B., Weir, J., and Clausen, B. A stream depletion field experiment , Ground Water,
39(2), 283–289, 2001.
Hunt, B., Unsteady stream depletion when pumping from semiconfined aquifer , J.
Hydrologic Eng., 8(1), 12–19. 2003a.
Hunt, B., Field-Data Analysis for Stream Depletion , J. Hydrologic Eng, Vol. 8(4), 2003b.
Morgan, D. S. and J.L. Jones, Joseph, Numerical model analysis of the effects of groundwater withdrawals on discharge to streams and springs in small basins typical of the
Puget Sound lowland, Washington, Water Supply Paper 2492, Reston, Virginia, 1999
Nyholm, T., S. Christensen, and K.R. Rasmussen, Flow depletion in a small stream caused by groundwater abstraction from wells , Ground Water, 40(4), 425-437, 2002.
Sophocleous, M. A., Koussis, A., Martin, J. L., and Perkins, S. P., Evaluation of simplified stream-aquifer depletion models for water rights administration, Ground
Water, 33(4), 579–588, 1995.
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Tributaries Committee Draft Funding Request
Task
Table 1: Estimated time and costs for completing scope of work
Description
Estimated
Time
Estimated
Cost
1
2
3
4
5
TOTAL
Compile and integrate recent studies and reports that describe or relate to benefits derived from resting or pausing groundwater extraction
Identify characteristics of individual candidate wells
Modify USGS steady-state groundwater model and complete simulations
Categorize specific wells that provide opportunities for improving in-stream flow conditions
Perform site-specific evaluation using an existing groundwater model for a volunteer well owner affecting a priority stream
1 month
1 month
3 months
1 month
2 months
8 months
$3,000
$4,000
$15,000
$4,000
$20,000
$46,000
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