landfill gas impacts to shallow groundwater
DESCRIPTION
LANDFILL GAS IMPACTS TO SHALLOW GROUNDWATER. What is the real issue?. Steve Wampler, AquAeTer, Inc. Louis Bull, Waste Management Groundwater Protection Program. How significant are LFG groundwater impacts at MSW landfills?. - PowerPoint PPT PresentationTRANSCRIPT
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LANDFILL GAS IMPACTS TO LANDFILL GAS IMPACTS TO SHALLOW GROUNDWATERSHALLOW GROUNDWATER
Steve Wampler, AquAeTer, Inc.
Louis Bull, Waste Management Groundwater Protection Program
What is the real issue?
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How significant are LFG groundwater How significant are LFG groundwater impacts at MSW landfills?impacts at MSW landfills?
• One consultant’s opinion (mine) – Gas usually is the cause of groundwater impacts we have observed at landfills
• Another consultant’s opinion (not mine) – 90% of groundwater issues at MSW landfills are LFG-caused
• A major landfill operator’s opinion – At modern, lined landfills, 100% of observed groundwater impacts attributed to LFG
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Regulatory Agency OpinionsRegulatory Agency Opinions
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Regulatory agency opinionsRegulatory agency opinions
Do you know of instances in your State where LFG is the cause of elevated VOCs concentrations at MSWLF monitoring wells?
NO YES
CA, CO, MT, NM, OK, SC, TN, VA, WY
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Regulatory agency opinionsRegulatory agency opinions
Do you know of instances in your State where LFG is the cause of elevated inorganics concentrations at MSWLF monitoring wells?
NO
CA, CO, MT, OK, SC, TN, VA
YES
NM, WY
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Regulatory agency opinionsRegulatory agency opinions
Where groundwater at an MSWLF has been impacted by VOCs, can you estimate the percent of the time the following are the cause?
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How does LFG impact groundwater?How does LFG impact groundwater?
Migration can place gas in close proximity to water in the vadose or saturated zones
VOCs in gas can partition into the water or cause geochemical changesthat can increase vadose zone constituent solubility (often metals)
Gas is generated
Gas pressure rises
Gas movement begins
Gas might move into vadose zone
SOURCE
PATHW
AY
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9Groundwater impacts at MSW landfills are the exception, not the rule!
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The ‘Areal’ PathwayThe ‘Areal’ Pathway
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Exposed screen well
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The ‘Intrawell’ PathwayThe ‘Intrawell’ Pathway
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Source / PathwaySource / PathwayDetermine the cause of the Determine the cause of the
observed groundwater impactsobserved groundwater impacts
– Determine that the cause is not leachate
– Determine that the cause is not an ‘alternate source’ (not related to the landfill)
– If not leachate or another cause, it’s likely LFG moving along:
• LFG areal pathway
• LFG intra-well pathway
• Combination
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Is LFG the cause of the observed Is LFG the cause of the observed groundwater impacts?groundwater impacts?
FIRST: “Desktop Study” to consider the available information
Use available information to determine if conditions appear to support the hypothesis that LFG has caused the observed impacts
NEXT: Collect additional information
If available are not conclusive, supplemental data collection can ‘fill the gaps’
If characteristics not consistent with an LFG-cause are identified in this process, the explanation likely lies elsewhere
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Review Available InformationReview Available Information
What are the observed impacts?
Where do the observed impacts occur?
Do they relate to known sources? (sumps, recent construction, gas system changes)
Is LFG (CO2, Methane and VOCs) present in
perimeter gas probes?
groundwater monitoring wells?
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Are VOCs present in groundwater among Are VOCs present in groundwater among those often associated with LFG?those often associated with LFG?
benzenedichlorodifluoromethane1,1-dichloroethanedichloromethane (methylene chloride)tetrachloroethene trichloroethene1,1,1-trichloroethanevinyl chloridexylene
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Are inorganic SSIs among those Are inorganic SSIs among those often associated with LFG?often associated with LFG?
Why would inorganic compounds occur in groundwater affected by LFG?
Which inorganic compound concentrations might show significant increase?
– alkalinity– bicarbonate– calcium– magnesium
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Consider the location of impactsConsider the location of impacts relative to possible sources relative to possible sources
Up-gradient groundwater impacts
Closed cells
Down-gradient groundwater impacts
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Continue review of available dataContinue review of available data
Consider VOC partitioning potential using Henry’s Law
Compare leachate inorganic chemistry to up-gradient and down-gradient groundwater chemistry
• Use Stiff and Trilinear (Piper) diagrams to consider changes in groundwater and leachate chemistry over time
Consider site hydrogeology and the characteristics of the monitoring system
• Vadose zone stratigraphy
• Well construction
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Monitoring well screenedMonitoring well screenedinterval can be importantinterval can be important
Top of sand pack
Top of well screen
Groundwater surface
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Supplemental Data CollectionSupplemental Data Collection
Leachate sampling and analyses Determine site-specific leachate chemistry
Isotope analyses Attempt to differentiate the natural groundwater from groundwater
containing leachate
Well headspace sampling Test the hypothesis that the well does/does not provide a gas migration
pathway
Vadose zone gas sampling Test the hypothesis that the vadose zone does/does not provide a gas
migration pathway.
Groundwater sampling Obtain representative sample from below the groundwater surface while
removing gas from the well
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What influences the onset ofWhat influences the onset of LFG impacts to groundwater? LFG impacts to groundwater?
Gas generation changes
Landfill operations changes
Placement of low K interim and final covers
Vadose zone stratigraphy
Gas travel time through the vadose zone
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0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004
VO
C C
on
cen
trat
ion
(u
g/L
)
1,1-DCA
PCE
Final Cover Construction
On-set of VOC detections after final cover construction – Washington
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On-set of VOC detections after final cover construction – New Mexico
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
VOC
Conc
entra
tion
(ug/
L)
Methylene Chloride
Tetrachloroethene
Final Cover Construction
Passive venting
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The occurrence of LFG impacts to The occurrence of LFG impacts to groundwater can be prevented by:groundwater can be prevented by:
Corrective measures for gaspassive or active venting
Delay final cover placement construct based on gas generation
Use alternative final covergas-permeable covermethane oxidation possible
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After gas-related impacts occur,After gas-related impacts occur, the effective responses are: the effective responses are:
Targeted control of the gas source in the waste masspassive gas ventingactive gas venting
Use modified procedures to obtain representative groundwater samples submerged screen wellsgas purging during sampling low-flow or no-flow sampling methods
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Regulatory agency opinionsRegulatory agency opinions
Might you view an instance of groundwater impacts caused by LFG as possibly different from one caused by leachate with regard to your regulatory requirements for: ASSESSMENT or CORRECTIVE ACTION?
No Comment: (none)
Never: OK, TN
Maybe: CA, CO, MT, NM, SC, VA, WY
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What do the regulations require? What do the regulations require?
A verified exceedence of a water-quality criterion triggers a variety of requirements under Federal and or State regulations
– U.S. - 40 CFR 258.54(c)– Colorado - 6 CCR 1007, B4(C) in CO
Under strict application of the regulations, the cause of the exceedence is irrelevant.
While considering the regulations, remember that
effectively addressing gas impacts to groundwater requires the combination of source control and alternate monitoring methods.
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Requirements that follow a verified VOC detection or other SSI
If the cause is LFG, could there be a more direct route to regulatory compliance?
Detection Monitoring
Corrective Action
AssessmentNotifications
Assessment planAdditional sampling
Additional monitoring
Verified Exceedence
Alternate Source Demonstration
Assessment of Corrective Measures
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If the cause of the observed impact is determined to be LFG
AND
– The extent of impacts is small (on-site)
– The concentrations are low, probably well below risk-based criteria
– The distance or groundwater travel time to potential human receptors is large
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There is a more direct route to regulatory compliance!
Detection Monitoring
Source ControlCorrective
Action
AssessmentNotifications
Assessment planAdditional sampling
Additional monitoring
Verified Exceedence
Alternate Source Demonstration
Assessment of Corrective Measures
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LANDFILL GAS IMPACTS TO LANDFILL GAS IMPACTS TO SHALLOW GROUNDWATERSHALLOW GROUNDWATER
These impacts do occur,
They can be recognized,
This is a problem that often can be corrected relatively quickly, and
The OWNER/OPERATOR and the REGULATOR can work together to accomplish this !