Evaluating Safe Yield for Supply WellsEvaluating Safe Yield for Supply Wellsin an Aquifer with in an Aquifer with

Fresh Water / Salt Water InterfaceFresh Water / Salt Water Interface

Gregory NelsonGregory Nelson11, Liliana Cecan, Liliana Cecan11, Charles , Charles McLaneMcLane11, and Maura Metheny, and Maura Metheny11

11McLane Environmental, LLC, Princeton, NJ USAMcLane Environmental, LLC, Princeton, NJ USA

SWIM 2008SWIM 2008

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IntroductionIntroduction Safe YieldSafe Yield

Aquifer Characterization for Safe Yield AnalysisAquifer Characterization for Safe Yield Analysis Delineation of the Fresh Water / Salt Water InterfaceDelineation of the Fresh Water / Salt Water Interface Characterization of the Density DistributionCharacterization of the Density Distribution Characterization of the Horizontal and the Vertical Hydraulic Characterization of the Horizontal and the Vertical Hydraulic

ConductivityConductivity

Salinity Impact Safe Yield Analysis (Case Study)Salinity Impact Safe Yield Analysis (Case Study) Site GeologySite Geology Aquifer CharacterizationAquifer Characterization Traditional Safe YieldTraditional Safe Yield Salinity Impact Safe YieldSalinity Impact Safe Yield

Conclusions / RecommendationsConclusions / Recommendations

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Safe YieldSafe Yield Safe Yield: Manage the water resource by striking a balance between Safe Yield: Manage the water resource by striking a balance between

meeting community water demands while avoiding deleterious hydrologic meeting community water demands while avoiding deleterious hydrologic and environmental impactsand environmental impacts

Typical MethodsTypical Methods Specific capacitySpecific capacity

Long-term pumping test (5 – 10 days)Long-term pumping test (5 – 10 days)

Hydrologic impact limitsHydrologic impact limits

Specific CapacitySafe Yield Determination

dd

Specif ic Capacity

Pumping rate

Time

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Safe Yield for a Coastal AquiferSafe Yield for a Coastal Aquifer

A safe yield analysis in coastal settings should A safe yield analysis in coastal settings should take into consideration salinity impacts caused take into consideration salinity impacts caused by pumpingby pumping Requires more detailed aquifer characterizationRequires more detailed aquifer characterization Requires application of a salinity transport modelRequires application of a salinity transport model

Predevelopment InterfaceRegional Thinning

Local Upconing

Pumping Well

Predevelopment InterfaceRegional Thinning

Local Upconing

Pumping Well

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Aquifer CharacterizationAquifer CharacterizationDelineation of the Fresh Water / Salt Water Interface and Density DistributionDelineation of the Fresh Water / Salt Water Interface and Density Distribution

Density distribution and an accurate delineation of Density distribution and an accurate delineation of the fresh water / salt water interface before, during the fresh water / salt water interface before, during pumping phase and during recovery phase of a pumping phase and during recovery phase of a pumping test yield important information in pumping test yield important information in determining a safe yield for the well fielddetermining a safe yield for the well field

Transition Zone

P1

P2P3

P4P5

P6

Dep

th

Concentration / Density / Electrical Conductivity

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Aquifer CharacterizationAquifer CharacterizationCharacterization of the Horizontal and the Vertical Hydraulic ConductivityCharacterization of the Horizontal and the Vertical Hydraulic Conductivity

Salt water intrusion and Salt water intrusion and upconing is sensitive to upconing is sensitive to horizontal and vertical horizontal and vertical hydraulic conductivityhydraulic conductivity

Low vertical hydraulic Low vertical hydraulic conductivity below the conductivity below the pumping well will dampen pumping well will dampen upconingupconing

Method: “Pumping Test Method: “Pumping Test Analyses in an Aquifer Analyses in an Aquifer with Fresh Water/Salt with Fresh Water/Salt Water Interface” – Liliana Water Interface” – Liliana CecanCecan

TPW-1 Pumping test

1.0E-4 0.001 0.01 0.1 1. 10.0.001

0.01

0.1

1.

10.

100.

Time (day)

Dis

plac

emen

t (ft)

Obs. WellsTPW-01OW-11SOW-11IOW-11D

Aquifer ModelLeaky

SolutionHantush-Jacob

ParametersT = 8.259E+4 ft2/dayS = 0.023491/B = 1.0E-5 ft-1

Kz/Kr = 0.05129b = 270. ft

Predevelopment InterfaceRegional Thinning

Local Upconing

Pumping Well

Predevelopment InterfaceRegional Thinning

Local Upconing

Pumping Well

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Safe Yield Analysis (Case Study)Safe Yield Analysis (Case Study)Cape Cod Site GeologyCape Cod Site Geology

Glacial sediments deposited in a Glacial sediments deposited in a lacustrine deltaic system 15,000 lacustrine deltaic system 15,000 years ago (Oldale 1992)years ago (Oldale 1992)

Glacial sediments extend 900 ft Glacial sediments extend 900 ft below ground surface to crystalline below ground surface to crystalline bedrock (Masterson 2004)bedrock (Masterson 2004)

Aquifer system is composed of Aquifer system is composed of several fresh water lenses – the several fresh water lenses – the site lies in the Pamet Lens (Walter site lies in the Pamet Lens (Walter and Whealan 2004)and Whealan 2004)

Average recharge is 24 in/yr Average recharge is 24 in/yr (Masterson 2004)(Masterson 2004)

Groundwater flow is radial toward Groundwater flow is radial toward the Atlantic Ocean (East), Cape the Atlantic Ocean (East), Cape Cod Bay (West), Pilgrim Lake Cod Bay (West), Pilgrim Lake (North), and Herring River (South)(North), and Herring River (South)

88

Safe Yield Analysis (Case Study)Safe Yield Analysis (Case Study)Aquifer CharacterizationAquifer Characterization

Southeast Northwest

salt water interface transition zone

boundaries

99

Safe Yield Analysis (Case Study)Safe Yield Analysis (Case Study)Aquifer CharacterizationAquifer Characterization

1010

0

200

400

600

800

1000

0 10 20 30 40 50 60 70

Time (Years)

Co

nc

en

tra

tio

n (

mg

/L)

Stronger Anisotropy Weaker Anisotropy MCL of 500 mg/L

Safe Yield Analysis (Case Study)Safe Yield Analysis (Case Study)Aquifer CharacterizationAquifer Characterization

Figure 2 Measured and Simulated Results

-300

-280-260

-240

-220

-200

-180

-160-140

-120

-100

-80

-60

-40-20

0

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

Salt Water Concentration (mg/L)

Ele

vati

on

(ft.

am

sl)

Test Well

Simulated after 10 Days

Initial Concentration

Measured after 10 Days

Measured before Pumping

Figure 2 Measured and Simulated Results

-300

-280-260

-240

-220

-200

-180

-160-140

-120

-100

-80

-60

-40-20

0

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

Salt Water Concentration (mg/L)

Ele

vati

on

(ft.

am

sl)

Test Well

Simulated after 10 Days

Initial Concentration

Measured after 10 Days

Measured before Pumping

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Safe Yield Analysis (Case Study)Safe Yield Analysis (Case Study)Traditional Safe YieldTraditional Safe Yield

Available drawdown (Available drawdown (dddd): 20 ft): 20 ftSpecific capacity (Specific capacity (SCSC): 35 gpm / ft dd): 35 gpm / ft dd

Safe Yield rate: Safe Yield rate: SC SC x x dd = dd = 700 gpm 700 gpm ≈ 1 MGD≈ 1 MGD

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Safe Yield Analysis (Case Study)Safe Yield Analysis (Case Study)Salinity Impact Safe YieldSalinity Impact Safe Yield

A pumping rate of 1 MGD causes fouling of the A pumping rate of 1 MGD causes fouling of the well within 50 yrswell within 50 yrs

A pumping rate of 0.7 MGD causes upconing, A pumping rate of 0.7 MGD causes upconing, but the concentration does not exceed the MCLbut the concentration does not exceed the MCL

0

200

400

600

800

1000

0 10 20 30 40 50 60 70 80 90 100

Time (Years)

Co

nc

en

tra

tio

n (

mg

/L)

0.72 MGD Well Concentration MCL of 500 mg/L 1.0 MGD Well Concentration

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Conclusions / RecommendationsConclusions / Recommendations

Despite a growing awareness of salt water intrusion and Despite a growing awareness of salt water intrusion and upconing, safe yield pumping rate regulations still do not upconing, safe yield pumping rate regulations still do not require assessment of potential salinity impacts caused require assessment of potential salinity impacts caused by pumpingby pumping

Accurate delineation of the interface and density Accurate delineation of the interface and density distribution can be helpful in estimating a safe yield distribution can be helpful in estimating a safe yield pumping rate in coastal aquiferspumping rate in coastal aquifers

Proper characterizing of the horizontal and vertical Proper characterizing of the horizontal and vertical hydraulic conductivity are essential in determining safe hydraulic conductivity are essential in determining safe yield pumping rate estimatesyield pumping rate estimates

The safe yield pumping rate estimated with consideration The safe yield pumping rate estimated with consideration of salinity impacts is potentially lower then a rate of salinity impacts is potentially lower then a rate estimated using traditional methodsestimated using traditional methods

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ReferencesReferences

Masterson, J.P., 2004, Simulated interaction between Masterson, J.P., 2004, Simulated interaction between freshwater and saltwater and effects of ground-water freshwater and saltwater and effects of ground-water pumping and sea level change, Lower Cape Cod aquifer pumping and sea level change, Lower Cape Cod aquifer system, Massachusetts: U.S. Geological Survey system, Massachusetts: U.S. Geological Survey Scientific Investigations Report 2004-5014, 72 p.Scientific Investigations Report 2004-5014, 72 p.

Oldale RN (1992) Cape Cod and the Islands, the Geologic Oldale RN (1992) Cape Cod and the Islands, the Geologic Story. Parnassus Imprints, East Orleans, Story. Parnassus Imprints, East Orleans, Massachusetts, 208 p.Massachusetts, 208 p.

Walter, D.A., and Whealan, A.T., 2004, Simulated water Walter, D.A., and Whealan, A.T., 2004, Simulated water sources and effects of pumping to wells and surface sources and effects of pumping to wells and surface waters, Sagamore and Monomoy flow lenses, Cape waters, Sagamore and Monomoy flow lenses, Cape Cod, Massachusetts: U.S. Geological Survey Scientific Cod, Massachusetts: U.S. Geological Survey Scientific Investigation Report 2004-5181, 85 p.Investigation Report 2004-5181, 85 p.

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AcknowledgementsAcknowledgements

The authors wish to thank Mark White of The authors wish to thank Mark White of Environmental Partners Group and Andrew Miller Environmental Partners Group and Andrew Miller of Head First for many hours of discussions that of Head First for many hours of discussions that have helped to improve this paper.have helped to improve this paper.

We’d also like to thank John Masterson of the U.S. We’d also like to thank John Masterson of the U.S. Geologic Survey for discussions on the U.S.G.S. Cape Cod Geologic Survey for discussions on the U.S.G.S. Cape Cod SEAWAT model.SEAWAT model.

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