What is karst?
A landscape formed Non-Point Source Pollution of Karst Groundwater: primarily by dissolution A Poorly Recognized National Crisis of the bedrock, typically: * limestone * dolomite * marble * gypsum * halite George Veni, Ph.D. Executive Director National Cave and Karst Research Institute Carlsbad, New Mexico USA
How karst aquifers form: Non-karst vs. karst aquifers Fractures capture water and are enlarged into conduits Porous media Fracture Karst
Adapted from: Groundwater: a primer (Moore et al., 1995)
How karst aquifers form: Hydrologic cycle for karst aquifers
Fractures capture water and are enlarged into conduits
As conduits enlarge, they capture water from surrounding fractures and enlarge at ever-increasing rates
When the conduit becomes large enough for human entry it is called a cave. From: Living with Karst (Veni and DuChene, 2001) Groundwater velocity, age, and chemistry vary between diffuse, fracture, and conduit flow Distribution of karst in the United States
How much water occurs in conduits?
Conduits store ~ 6% Conduits move ~ 94 - 99%
Exposed Carbonate Karst Buried Carbonate Karst Exposed Evaporite Karst Buried Evaporite Karst Unconsolidated Pseudokarst Volcanic Pseudokarst
From: Veni et al., 2001, American Geological Institute
Percent of U.S. underlain by karst: 20-25%, possibly >40% Percent of U.S. groundwater supplies provided by karst aquifers: ~40%
Groundwater contamination through sinkhole collapse
Karst aquifers are the most vulnerable due to rapid recharge and travel, and no filtration
Complex contaminant dispersal and storage mechanisms in karst: Groundwater recharges through point and non-point features “Bathtub ring” and other effects in conduits and fractures
Map adaptation by Bob Richards, courtesy of Edwards Aquifer Authority Artificial recharge allows controlled experimental monitoring Almost immediate response to recharge (typically 10-90 minutes) of vadose zone and comparison to natural recharge events Minimum 6-20% of applied water measured in caves as recharge
BunnyBunny Hole: Hole Temperature,Temperature, conductivity conductivity, and surface precipitation precipitation atfor SiteDrip Site A1, A1, June June 20052005
0.8 19.5 PrecipitationPrecipitation 0.7 WaterConductivity Conductivity WaterTemperature Temperature 19
0.6
18.5 0.5
0.4 18
0.3 17.5 Temperature (C) Conductivity (mS/cm )
Precipitation (cm/15 minutes) 0.2
17 0.1
0 16.5
27/05/05 120 27/05/05 2136 28/05/05 0712 28/05/05 1648 29/05/05 0224 29/05/05 120 29/05/05 2136 30/05/050712 30/05/05 1648 31/05/05 0224 31/05/05 120 31/05/05 2136 01/06/05 0712 01/06/05 1648 02/06/05 0224 02/06/05 120
Date (dd/mm/yy, time)
Known sites of urban groundwater contamination in the Edwards Aquifer Rural non-point pollution: (Edwards Aquifer Authority, April 2004) Loss of contaminants and soil reduces agricultural productivity and increases groundwater pollution and sedimentation in caves Site County Material Texas Industrial Services Uvalde PCE S&S Trailer Park Uvalde Nitrate Braun Station Bexar Cryptosporidium Helotes Well Bexar Fecal Coliform Kelly AFB Bexar VOCs Randolph AFB Bexar Oil Camp Stanley Bexar VOCs Camp Bullis Bexar VOCs Ram Texaco Bexar BTEX West Avenue Landfill Bexar PCE Jones - Maltsberger PST Bexar BTEX R & H Oil Bexar Oil, VOCs Dyno-Nobel Comal VOCs, SVOCs Reliable Battery Site Bexar VOCs, Metals
But these do not account for sites affected by non-point sources
Are current groundwater sampling protocols adequate How widespread is non-point contamination in the U.S. karst? to identify contaminants in karst aquifers?
* * *
* * *
Exposed Carbonate Karst Buried Carbonate Karst Exposed Evaporite Karst Buried Evaporite Karst Unconsolidated Pseudokarst Volcanic Pseudokarst
From: Edwards Aquifer Authority, 2001 From: Veni et al., 2001, American Geological Institute How serious are the consequences? How do you reduce the risk of non-point source contamination in karst? E. Coli contamination, Walkerton, Ontario, May 2000 Learn about karst, use karst-appropriate research methods, use karst data and experts
720 hour travel time from MODFLOW
5 hour travel time from tracer test
26 hour travel
time from tracer test
0 1,000
meters
7 dead, 2,300 ill
Use hydrographs to identify flow regimes Geophysics are useful for site-specific investigations and aquifer properties by well and springflow calculations Microgravity Microgravity + Electrical resistivity
(
sinkhole
Modified from: Center for Cave and Karst Studies (2000) From: Karst Geomorphology and hydrology (Ford and Williams, 1989)
Potentiometric mapping Tracer testing is the most valuable tool in karst hydrogeology From: Ray, 2003 Useful but not always completely accurate in karst
* 1630
* 1160 Tracer tests: •Identify source and fate * 1480 •Quantify dilution * 850 * 1550 •Quantify dispersion •Quantify time of travel •Delineate drainage basins * 1360 * 960 * 1200
* 800 * 1330
* 680 * 1190
* 800
Modified from: Hydrogeologic framework of the Edwards-Trinity Aquifer (Barker & Ardis , 1996) Tracer testing is the most valuable tool in karst hydrogeology Tracer testing is the most valuable tool in karst hydrogeology
Tracer tests: Tracer tests: •Identify source and fate •Identify source and fate •Quantify dilution •Quantify dilution •Quantify dispersion •Quantify dispersion •Quantify time of travel •Quantify time of travel •Delineate drainage basins •Delineate drainage basins •Identify stage-based variables •Identify stage-based variables •Are empirical, repeatable data
From: Quinlan & Ewers, 1981 From: Quinlan & Ewers, 1981
Management strategies to limit NPS pollution in karst Factors and strategies to limit NPS pollution in karst •Karst aquifers cannot be adequately managed or protected on a feature-by-feature basis Limit impervious cover to 15%
BMPs?
Factors and strategies to limit NPS pollution in karst Factors and strategies to limit NPS pollution in karst •Karst aquifers cannot be adequately managed or protected on a feature-by-feature basis •Karst aquifers cannot be adequately managed or protected on a feature-by-feature basis •Effective management requires a drainage basin approach to water management •Effective management requires a drainage basin approach to water management Basin-based management addresses Basin-based management addresses * total water development and use * total water development and use * total pollutant loading * total pollutant loading * ecological and regulatory boundaries * ecological and regulatory boundaries •Determine the karst aquifer’s capacity for pollutant loading Factors and strategies to limit NPS pollution in karst Factors and strategies to limit NPS pollution in karst •Karst aquifers cannot be adequately managed or protected on a feature-by-feature basis •Karst aquifers cannot be adequately managed or protected on a feature-by-feature basis •Effective management requires a drainage basin approach to water management •Effective management requires a drainage basin approach to water management Basin-based management addresses Basin-based management addresses * total water development and use * total water development and use * total pollutant loading * total pollutant loading * ecological and regulatory boundaries * ecological and regulatory boundaries •Determine the karst aquifer’s capacity for pollutant loading •Determine the karst aquifer’s capacity for pollutant loading •Manage point and non-point contaminant to those limits •Manage point and non-point contaminant to those limits •Buffer the limits based on uncertainties and potential for accidents
Factors and strategies to limit NPS pollution in karst Factors and strategies to limit NPS pollution in karst •Karst aquifers cannot be adequately managed or protected on a feature-by-feature basis •Karst aquifers cannot be adequately managed or protected on a feature-by-feature basis •Effective management requires a drainage basin approach to water management •Effective management requires a drainage basin approach to water management Basin-based management addresses Basin-based management addresses * total water development and use * total water development and use * total pollutant loading * total pollutant loading * ecological and regulatory boundaries * ecological and regulatory boundaries •Determine the karst aquifer’s capacity for pollutant loading •Determine the karst aquifer’s capacity for pollutant loading •Manage point and non-point contaminant to those limits •Manage point and non-point contaminant to those limits •Buffer the limits based on uncertainties and potential for accidents •Buffer the limits based on uncertainties and potential for accidents •Understand the limits of engineered mitigation measures •Understand the limits of engineered mitigation measures •Never underestimate the vulnerability of karst, which cannot be adequately measured based on the presence or distribution of karstfeatures
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