Virginia Coastal PlainGroundwater Issues

 

David K. Paylor

March 27, 2015

Geology 101

Virginia Physiographic Provinces

COASTAL

PLAIN

PIEDMONT

BLUE RIDGEVALLEY A

ND RID

GE

APP. PLATEAU

CONFININGUNITS

CONFINED AQUIFERS

UNCONFINEDAQUIFER

IMPACT

CRATER

BED

RO

CK

Coastal PlainAquifer System

WEST

EAST

AQUIFERS• YORKTOWN-EASTOVER

• PINEY POINT

• AQUIA

BASEMENT BEDROCK

FLUVIAL SEDIMENTS

MARINE SEDIMENTSPOTOMAC AQUIFER

VA Coastal Plain Aquifer Cross-Section

McFarland & Bruce, 2006

Groundwater Terms and Concepts

Well Water Levels IndicateDirection of Flow

AQUIFER

HIGH WATERLEVEL

LOW WATERLEVELFLOW

Well Water Levels IndicateDirection of Flow

AQUIFER

LOW

HIGH

FLOW

AQUIFER

FLOW

CONFINING UNIT

Well Water Levels IndicateDirection of Flow

AQUIFER

LOW

HIGH

AQUIFER

HIGH

LOW

LEAKAGEDOWN

LEAKAGEUP

Cone of Depression

Confined Aquifer

Not a bathtub drain–actually a

drop in pressure

The pressure in the aquifer changes with distance from the well.

Potentiometric Surface

Groundwater Management in Virginia

Long-term Scientific Study

1913

19451988

1999

2006

2010

Scientific Milestones• Regional studies (late 1970s –early 1980s)• Hydrologic Framework I (1988)• Coastal Plain Groundwater Flow Model I (1990)• Coastal Plain Groundwater Flow Model II (1998)• Chesapeake Bay Impact Crater (1999)• Land Subsidence Study (2002)• Hydrologic Framework II (2006)• Coastal Plain Groundwater Flow Model III (2009)• Eastern Shore Model I (2009)• Groundwater Quality Trend Study (2010)• Program Peer Review (2011)• Potomac Aquifer Study (2013, pending publication)

Virginia Groundwater Withdrawals by Aquifer

Legislative History of GW Management

• Virginia Well Capping Law (1956)• Groundwater Management Act of 1973• 1986 Amendments to Act of 1973• Ground Water Management Act of 1992

• Private Wells (32.1-176.4, VDH-1986)

GW Management Areas

Management Area 6/17/13 Management Area

Management Issues

• Reversal of the hydraulic gradient (groundwater flow) leads to salt water intrusion

• Declining water levels• Subsidence and loss of storage

Reversal of Hydraulic Gradient and Saltwater Intrusion

Groundwater Pumping and Reversal of Hydraulic Gradient

Salt Water Intrusion - Upconing

Pumping draws the salt water upwards into the well.

Salinity Within the Aquifer System

Heywood and Pope, 2009

Groundwater Level Declines

Artesian Characteristics Lost Over Time

Long Term Water Level Decline

LONG-TERM DECLINE

Decline from Pre-Pumping Levels

-250

+100

-180

+150

100%

77%

POTOMAC AQUIFER

WEST EAST

+140

+50

PRE-PUMPING LEVEL

PRESENT-DAY LEVEL

+30

FRANKLIN80%

LAND SURFACE

FLOW

Simulated Change in Storage of Water in the Potomac Aquifer from Pre-development to 2008

Values >1 indicate head is below the 80% criterion

Legend

Available Storage Used

PCT_USED

0.00 - 0.10

0.11 - 0.25

0.26 - 0.50

0.51 - 0.75

0.76 - 1.00

1.01 - 72.50

Head Below Unit Top

Land Subsidence and Loss of Storage

Land Subsidence

-1.6

-2.4

-2.8

-4

-3.6

-1.2

-0.8

-4.4

-2

-1.2

-2

-2

-1.6

-2

-3.2

-3.2

0 25Miles

0 25Miles

West Point

Franklin

Suffolk

Chesa

peake

Bay

Franklin ExtensometerOct. 1979 – Dec. 1995Depth = 255 m

Suffolk ExtensometerJune 1982 – Dec. 1995Depth = 484 m

Rates of Elevation Change (1940-1971) mm/yearHoldahl and Morrison, 1974

Measurement of Compaction and Subsidence

Major Pumping Centers

5 0

4 0

3 0

2 0

1 0

0

CU

MU

LAT

IVE

CO

MP

AC

TIO

N (

mm

)

1980 1985 1990 1995

5 0

4 0

3 0

2 0

1 0

0

CU

MU

LAT

IVE

CO

MP

AC

TIO

N (

mm

)

SUFFOLK3.7 mm/yr

FRANKLIN1.6 mm/yr

Subsidence Record

MONITORING DISCONTINUED

Conclusions

• Water levels continue to decline in the primary aquifers.

• Land is subsiding.• Salt water intrusion is occurring.• Primary aquifers are not being pumped sustainably for the long-term.

Other States’ Responses

• Maryland – No irrigation withdrawals from the Potomac Aquifer. No new permits in areas where water levels have reached 80% of pre-development head.

• North Carolina – Reduce all existing withdrawals from the Potomac Aquifer by 30-75% over 15 years. Began 2006. State provided funds to convert to other sources. No new withdrawals from Potomac Aquifer.

• Georgia–South Carolina – Designated areas where no additional withdrawals are allowed and other areas where only incremental withdrawals are allowed. Mandatory conservation to reduce existing max withdrawals and GW monitoring.

• Savannah-Hilton Head Regional Management Area – Pumping limited based on areas reaching 500 mg/l Chloride in less than 113 years.

• Florida – Regional pumping caps on all withdrawals. All withdrawals including agr. are metered and conservation/efficiency mandated. 

Options Resulting From Peer Review

• Regulatory options include:– Reduce pumping– Spread out pumping– Modify management goals– Issue permits in regional or aquifer groupings– Implementation of greater water conservation

• Program recommendations include:– More data collection:

• water levels• water quality• land subsidence

– Implement new generation modeling tool– Increase program resources

Short-term Actions

• Amend GWMA regulations to:– Expand the management area– Determine regulatory compliance using full area of impact– Use land surface instead of pre-pumping head– Add greater clarity on expectations for use of alternative sources and water 

conservation• Implement use of new (2009) model• Collaborate with other agencies:

– Specific data on well location and construction– Un-captured withdrawals

• Reinstate GW quality sampling within chloride network starting with 20-25 samples/year

• Allow for drought contingencies in permits

Short-term Actions Under Review

• Begin moving existing pumps above the top of the Potomac Aquifer 

• Improvements to groundwater withdrawal reporting

• Continue to increase GW quality samples to 50 per year

• Work with VEDP and local governments regarding availability of GW in recruitment locations

• Review program and funding resources

Other Longer-term Policy Options

• Optimize the new model to spread out withdrawals and evaluate impact

• Add subsidence package to the model • Evaluate drawdown criteria for subsidence/salt water intrusion

• Continue to increase annual GW quality samples 

Other Longer-term Policy Options(cont.)

• Facilitate greater use of alternatives such as wastewater reuse, surface water conjunctive use, and water recycling

• Consider additional regulatory changes• Evaluate need for an across the board reduction target and implementation schedule

Questions?