City of Kent Wellhead Protection Program, Clark, Kent, and Armstrong Springs

266 Pages·2012·14.34 MB·English

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Earth and Environmental Technologies
City of Kent
Wellhead Protection Program
Clark, Kent, and
Armstrong Springs
Prepared for
City of Kent
0
J-3508-01
April 2, 1996
Funded through a Centennial
Fund Grant No. G9400034
f-
PROPERTY OF STATE OF WASHINGTON
DEPAP.TMENT OF ECOLOGY LIBRARY
Hart Crowser
J-3508-01
CONTENTS
EXECUTIVE SUMMARY Vll
1.0 INTRODUCTION 1-1
1.1 Scope of Kent's WHPP and Report Organizaiion 1-2
1.2 Coordination of Wellhead Protection Program Development 1-2
1.3 Existing Data Sources 1-2
1.4 The Groundwater Sources 1-3
2.0 HYDROGEOLOGY 2-1
2.1 Topography and Drainage 2-1
2.2 Surface Water Features 2-1
2.3 Surficial Geology 2-2
2.4 Recharge and Infiltration Potential 2-2
2.5 Water Quality 2-3
• 2.6 Principal Geologic Units 2-4
2. 7 Subsurface Geology and Groundwater Flow 2-6
3.0 WELLHEAD PROTECTION AREA (WHPA) DELINEATION 3-1
3.1 Capture Zones Based on Numerical Modeling 3-1
3.2 Surface Water Divide as Recharge Area 3-3
3.3 Assessment of Data Uncertainties 3-3
3.4 Composite Wellhead Management Area - Kent/Covington WHPA 3-4
3.5 Areas Highly Susceptible to Contamination 3-7
4.0 POTENTIAL SOURCES OF GROUNDWATER CONTAMINATION 4-1
4.1 Contaminant Source Inventory Methodology 4-1
4.2 Historical and Cu"ent Land Use 4-1
4.3 Potential Contaminant Sources Identified in Regulatory Databases 4-3
4.4 Other Groundwater Quality Concerns 4-8
4.5 Establishing Risk Priority for Potential Contaminant Sources within the WHPA4-12
5.0 EXISTING REGULATORY PROGRAMS 5-1
5.1 Introduction 5-1
•
5.2 Existing Regulatory Programs 5-1
5.3 South King County GWMP Strategies Planned for Risk Reduction 5-9
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CONTENTS (Continued)
6.0 WELLHEAD PROTECTION MANAGEMENT STRATEGIES 6-1
6.1 Introduction 6-1
6.2 Wellhead Protection Tasks 6-1
6.3 Management and Cooperation Strategies 6-3
6.4 Land Use Strategies 6-3
6.5 Regulotory Strategies 6-4
6. 6 Planning Strategies 6-4
6. 7 Data Management Strategies 6-5
6.8 Education Strategies 6-6
7.0 MONITORING PLAN 7-1
7.1 Water Level and Water Quality Monitoring Recommendations 7-1
7.2 Future Model Refinement 7-5
• 8.0 SPll..L RESPONSE 8-1
8.1 Introduction 8-1
8.2 National, State, and Local Spill Response Plans 8-1
8.3 Spill Response Organizations 8-2
9.0 KENT WHPP CONTINGENCY OPTIONS 9-1
9.1 Introduction 9-1
9.2 Short-Tenn Contingency Plan 9-2
9.3 Long-Tenn Contingency Plan 9-3
9.4 Pennanent Replacement Contingency Plan 9-4
9.5 Contingency Procedures and Emergency Phone Numbers 9-5
10.0 REFERENCES 10-1
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• CONTENTS (Continued)
TABLES
2-1 Nitrate Levels in Kent's Water Sources 2-4
4-1 Potential Contaminant Sources Listed by Type 4-19
4-2 Confirmed and Suspected Contaminated Sites 4-20
4-3 Leaking Underground Storage Tank Sites 4-20
4-4 Operational Underground Storage Tank Sites 4-21
4-5 Current and Former Contaminated Underground Storage Tank Sites 4-21
4-6 Solid Waste Landfill Sites 4-22
4-7 Resource Conservation and Recovery Act Sites 4-22
4-8 Pesticides Used in WHP A 4-23
4-9 Covington/Kent Wellhead Protection Program Overall Risk Prioritization 4-13
4-10 Covington/Kent Wellhead Protection Program Risk Sub-Prioritization - 4-13
Proximity to Source
4-11 Covington/Kent Wellhead Protection Program Risk Sub-Prioritization - 4-14
Type of Contamination
• 4-12 Covington/Kent Wellhead Protection Program Risk Sub-Prioritization - 4-16
· Contaminated Media
4-13 Risk Ranking for Kent Springs 4-24
4-14 Risk Ranking for Clark Springs 4-25
4-15 Risk Ranking for Armstrong Springs 4-26
4-16 Overall Risk Ranking for WHPAs 4-18
5-1 Programs Related to Groundwater Quality and Quantity 5-12
5-2 Programs Related to Groundwater Quality Only 5-13
5-3 Programs Related to Groundwater Quantity Only 5-15
6-1 Wellhead Management Tasks 6-7
6-2 Three Main Ways to Organize Wellhead Protection Tasks 6-10
6-3 Common Tasks for All Risk Areas 6-11
6-4 Tasks for Residential Risk Areas 6-12
6-5 Tasks for Transportation/Pipeline Corridors Risk Areas 6-13
6-6 Tasks for Industrial Commercial Risk Areas 6-14
6-7 Tasks for Mining Risk Area 6-15
6-8 Tasks for Forestry Risk Area 6-16
6-9 Management Strategies 6-17
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• CONTENTS (Continued)
FIGURES
1-1 Site Vicinity Map
2-1 Surficial Geology and Cross Section Location Map
2-2 Clark Springs Area
Generalized Geologic Cross Section Cl-Cl' and C2-C2'
2-3 Clark Springs Area
Generalized Geologic Cross Section C3-C3' and C4-C4'
2-4 Kent Springs Area
Generalized Geologic Cross Section Kl-Kl' and K2-K2'
2-5 Kent Springs Area
Generalized Cross Section K3-K3'
2-6 Armstrong Springs Area
Generalized Geologic Cross Section Al-Al'
2-7 Armstrong Spring Area
Generalized Geologic Cross Section A2-A2'
• 2-8 Armstrong Springs Area
Generalized Geologic Cross Section A3-A3'
2-9 Armstrong Springs Area
Generalized Cross Section A4-A4'
2-10 Armstrong Springs Area
Generalized Cross Section A5-A5'
2-11 Armstrong Springs Area
Generalized Geologic Cross Section A6-A6'
2-12 Groundwater Elevation Contour Map
3-1 Modeled Capture Zones and Surface Water Divide Map
3-2 Kent/Covington Wellhead Protection Area Map
3-3 Aquifer Susceptibility Map
Kent/Covington WHPA
4-1 Land Use Zoning and Relevant Features Map
4-2 Potential Sources - Regulatory Database Listings
4-3 Other Potential Sources
7-1 Groundwater Monitoring Plan Map
8-1 Fire Districts Spill Response Jurisdiction Map
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CONTENTS (Continued)
APPENDIX A
HYDROGEOLOGIC DATA ANALYSIS A-1
Precipitation Data Summary and Analysis A-1
Water Level Data Collection A-1
Groundwater Elevation Data and Water Level Hydro graphs A-2
Groundwater Production Data A-2
TABLES
A-1 Landsburg Monthly Total Precipitation A-4
A-2 Summary of Well Construction Data for Wells Monitored A-6
A-3 Monthly Monitoring Data from Kent Watersheds A-7
A-4 Groundwater Elevation Data - City of Kent Monitoring Program A-8
A-5 Armstrong Springs Water Production Summary A-9
A-6 Kent Springs Water Production Summary A-ll
A-7 Clark Springs Water Production and Streamflow Summary A-13
FIGURES
A-1 Monthly Total Precipitation and Cumulative Departure
Landsburg Station
A-2 Armstrong Springs Water Levels
A-3 Kent Springs Water Levels
A-4 Clark Springs Well No. 1
A-5 Armstrong Springs Water Production
A-6 Kent Springs Water Production
A-7 Clark Springs Water Production
APPENDIXB
GROUNDWATER MODELING PROCEDURES B-1
Approach and Parameter Selection B-1
Model Calibration B-7
Capture Zone Delineation B-8
Sensitivity Analysis and Model Limitations B-9
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CONTENTS (Continued)
TABLES
B-1 Runoff Zone Calculations for Kent Numerical Model B-12
B-2 River Node Parameters B-13
FIGURES
B-1 Model Boundaries
B-2 Pumping Test Transmissivity Data
B-3 Hydraulic Conductivity Distribution
B-4 Bottom Elevation Distribution
B-5 Recharge Distribution
B-6 Precipitation-Recharge-Runoff Relations
Used in Groundwater Model
B-7 Predicted versus Observed Groundwater Elevation
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APPENDIX C
MANAGEMENT TASK DATABASE
APPENDIXD
CITY OF KENT SPILL RESPONSE PLAN
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EXECUTIVE SUMMARY
A wellhead protection program (WHPP) is being developed by the City of Kent (City) for the
Clark, Kent, and Armstrong Springs water supply sources. The wellhead protection program is
designed to protect groundwater resources supplying public wells used for drinking water.
Development of the wellhead protection program is mandated by the 1986 Amendments to the
Safe Drinking Water Act and the Washington State Drinking Water Regulations (WAC 246-290-
135). The wellhead protection program builds on the South King County Groundwater
Management planning process and is an important local tool for protecting groundwater quality.
Delineation of wellhead protection areas helps to identify the most important areas of focus for
protecting water supplies and the most appropriate areas to focus limited funding resources.
This project began in 1991 when the City applied to the Washington State Department of
Ecology (Ecology) for a Centennial Fund Grant to help fund the program development. A Grant
was awarded in 1992. The City is conducting program development efforts with the Covington
Water District and Water District No. 111 who are simultaneously developing wellhead
protection programs. Coordination efforts have occurred through a Project Review Committee
set up for review and input to the process and including representatives from the three purveyors
as well as the Seattle-King County Health Department, the State Department of Health, and
Ecology's Water Quality Program.
•
Hydrogeology and Wellhead Protection Area Delineation
The City derives its water from shallow, highly transmissive, glacial outwash aquifers without
significant confining layers between ground surface and the depth of groundwater withdrawal.
Infiltration of precipitation is the principal source of recharge to the groundwater system in the
study area. Infiltration is high in the permeable outwash sediments that comprise much of the
area, particularly in the eastern foothills where precipitation averages 58 inches per year. The
till-capped uplands provide recharge through runoff to the surrounding, highly permeable
outwash channel deposits. Surface water features like Lake Sawyer provide some additional
recharge to the groundwater system.
Groundwater flow in the area is predominantly east to west from the high recharge area of the
foothills east of Clark Springs through two principal aquifers, the Vashon Recessional Outwash
(Qvr) and the deeper, older Qc(2) glacial deposits. In the western area, till lies between the
recessional outwash and the deeper Qc(2) aquifer in some locations; however, at the City's Kent
Springs and Armstrong Springs properties the till seems to be absent, and these two aquifers are
connected. In these areas the aquifer is more highly susceptible to contamination.
The east to west flow pattern creates capture zones that extend eastward from the wellheads.
The wellhead capture wnes were delineated through development of a regional groundwater flow
model. The groundwater flow model, based in MODFLOW, was used in conjunction with a
• particle tracking model, PATII3D, to define 1-, 5-, and 10-year time of travel zones. An
assessment of data uncertainties and coordination of management efforts with the area water
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