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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?