recommended practices for baseline …...recommended practices for baseline sampling of water...
TRANSCRIPT
RECOMMENDED PRACTICES FOR BASELINE SAMPLING OF WATER SOURCES IN AREAS OF SHALE OIL AND GAS DEVELOPMENT
GWPC ANNUAL FORUM
Lisa J. Molofsky, Stephen D. Richardson, Jenna S. Kromann, Ann P. Smith, and John A. Connor GSI Environmental Inc.
Anthony W. Gorody Universal Geoscience Consulting, Inc.
Fred Baldassare Echelon Applied Geosciences
BASELINE SAMPLING OF WATER SOURCESWhat is it?
2
Water Source
Proposed Well Pad
What is Baseline Sampling?
aka: Baseline sampling or Pre-Drill survey
Sampling of water sources within a defined distance from the proposed location of oil and gas (O&G) development
What Water Sources?
Residential water wells, springs, and/or surface waters that are intended for human or livestock consumption
Why Collect Baseline Samples?
Required by 13 state agencies overseeing O&G activities
Evaluate whether reported changes in local water quality are naturally occurring or the result of nearby drilling
BASELINE SAMPLING OF WATER SOURCESWhat States have Regulations?
3
KEY POINT: Thirteen states have final regulations on pre-drill sampling of water sources in areas of shale oil and gas development
BASELINE SAMPLING OF WATER SOURCESWhat States have Regulations?
4
KEY POINT: Thirteen states have final regulations on pre-drill sampling of water sources in areas of shale oil and gas development
• Alaska
• California
• Colorado
• Idaho
• Illinois *
• Michigan
• Nevada
• North Carolina *
• Ohio
• Pennsylvania *
• Tennessee
• West Virginia *
• Wyoming
* Presumption of Liability: The burden of proof remains with the oil and gas operator in cases of alleged water quality impacts to nearby water supplies.
Final Regulations for Baseline Sampling of Water Sources
BASELINE SAMPLING OF WATER SOURCESWhat Guidance is Out There?
5
Numerous oil and gas and environmental organizations support implementation of pre-drill (baseline) sampling programs
EPA SAB: Review of the EPA’s Draft Assessment of the Potential Impacts of Hydraulic Fracturing for Oil and Gas on Drinking Water Resources
6
Regulations&
Guidance
Information Resources
Sample Collection&
Analyses
Data Analysis&
Management
Case Study1
2
3
4
5
BASELINE SAMPLING OF WATER SOURCESWhat’s Our Goal?
Develop recommended practices for improved sample collection
methods and data interpretation for pre-drill and post-drill
sampling programs
Baseline Sampling of Residential Water Wells
Baseline Sampling of Residential Water Wells
7
Regulations&
Guidance
Information Resources
Sample Collection&
Analyses
Data Analysis&
Management
Case Study1
2
3
4
5
BASELINE SAMPLING OF WATER SOURCESWhat’s Our Goal?
For Today’s Talk…
Discuss key challenges with baseline sampling of dissolved gases at residential water wells
Present results from field studies in Northeastern Pennsylvania to support the recommended practices development
1
2
8
BASELINE SAMPLING CHALLENGESRegulations and Guidance
KEY POINT:Regulations contain similar key elements, but details within each element can vary.
Key elements of regulations:
Location: type of water supply, radial distance, number of sampling locations
Timeframe: sampling frequency, time period before and after production
Methods: sample location, procedures, purging
Analytical: field parameters, analytical suite, action levels
Reporting: operator to water well owner or state agency, public reporting
Regulations vary between states1
BASELINE SAMPLING CHALLENGESResidential Water Wells
Majority of baseline sampling efforts focus on residential water wells, but…
Well construction information is often limited
Open hole construction results in mixed conditions (different fractures supply water)
Sampling is conducted at the surface from the water well system (e.g., outlet of the pressure tank)
Guidance for sampling of monitoring wells does not directly apply to residential water wells
KEY POINT: Residential water wells create additional complications for environmental sampling and assessment of risk 9
Residential wells are not monitoring wells
(Adapted from PA DCNR, 2012)
2
BASELINE SAMPLING CHALLENGESDissolved Gas Sampling at the Surface
At depth, methane concentrations greater than solubility can be maintained (pressure >1 atm)
As water is pumped to surface (1 atm), reduction in pressure decreases methane solubility, resulting in exsolution if methane concentrations are sufficiently elevated
Under effervescing conditions, it can be difficult to capture a water sample that is representative of the dissolved concentration in the aquifer
KEY POINT: Collecting a representative dissolved gas sample can be difficult depending on collection method. 10
Collecting dissolved gas samples can be challenging3
>1atm
1atm
BASELINE SAMPLING CHALLENGESUnderstanding Natural Methane Variability
Methane is naturally occurring in the subsurface in many regions
4
Other Challenges… Berea Shale, E. Kentucky
BASELINE SAMPLING CHALLENGESUnderstanding Natural Methane Variability
Methane is naturally occurring in the subsurface in many regions
4
Other Challenges…
January October
20
Me
than
e C
on
c. (m
g/L
)
10
15
5
0
Pre-Drill Post-Drill
Differentiating natural variability in groundwater quality from induced variability can be complicated
PADEP Threshold = 7 mg/L
5
KEY POINT: There are factors unrelated to unconventional oil and gas development that can affect residential water quality results
BASELINE SAMPLING OF WATER WELLSWhat are the Key Factors?
Sampling Methods Temporal Variability Key Factors
STUDY GOAL: Develop recommended practices for the collection and interpretation of baseline dissolved methane data from residential water wells. 13
Well Purging
STUDY DESIGNResidential Water Wells in NE Pennsylvania
.Well Completion
Open hole; completed in Catskill and Lock Haven Formations, and glacial till
Well Depths 25 - 438 ft. BTOC
Casing Volumes 30 - 388 gallons
Methane Concentrations
Low: < 5 mg/L Medium: 5 – 15 mg/LHigh: > 15 mg/L
Residential Well Details
12 residential water wells in Bradford and Susquehanna Co., NE Pennsylvania
All wells were >2,500 ft. from the nearest existing or proposed gas well location
Sampling Procedures
Wells were purged at a flowrate of ~3 gpm
Field parameters (temp., pH, and spec cond.) were monitored during purging
Flowrate was reduced to <0.5 gpm to sample
Samples were collected after the pressure tank and prior to any pre-treatment devices
15
EFFECT OF SAMPLE COLLECTION METHODSStudy Findings
At dissolved methane concentrations below 20 mg/L, the three sample collection methods provide comparable results.
Sample Collection Methods1
Open System“Direct Fill”
Semi-closed System“Inverted Bottle”
Closed System“Isoflask”
16
EFFECT OF SAMPLE COLLECTION METHODSStudy Findings
At dissolved methane concentrations below 20 mg/L, the three sample collection methods provide comparable results.
Inverted VOA sampling method provides no advantage relative to Direct-Fill VOA sampling method.
Sample Collection Methods1
Open System“Direct Fill”
Semi-closed System“Inverted Bottle”
17
EFFECT OF SAMPLE COLLECTION METHODSStudy Findings
At dissolved methane concentrations below 20 mg/L, the three sample collection methods provide comparable results.
Inverted VOA sampling method provides no advantage relative to Direct-Fill VOA sampling method.
Direct Fill method can be used for samples that are not effervescing.
Sample Collection Methods1
Open System“Direct Fill”
Closed System“Isoflask”
Use a fully closed sampling system for collecting effervescing samples.
18
EFFECT OF WELL PURGINGStudy Findings
There appears to be no real benefit to purging larger volumes of water (e.g., 3 casing volumes).
Well Purging2
Met
han
e (
mg/
L)3
Cas
ing
Vo
lum
es
Pu
rge
d
Methane (mg/L)“No Purge”
19
EFFECT OF WELL PURGINGStudy Findings
There appears to be no real benefit to purging larger volumes of water (e.g., 3 casing volumes).
Concept of purging until parameters stabilize may not achieve desired goal of obtaining representative sample of stable water source.
Well Purging2
Stabilization Criterion: ±5%
Recommend purging a consistent volume prior to each sampling event (e.g. 2-3 pressure tank volumes).
20
VARIATIONS IN METHANE OVER TIMEStudy Findings
A 2-fold change in methane concentration over time represents that upper range of natural variability for the wells tested.
Change in methane concentrations greater than this magnitude may be indicative of non-natural variability and warrant further investigation.
Temporal Variability3
21
UNDERSTANDING NATURAL METHANE OCCURRENCEStudy Findings
Large changes in methane concentration should be compared to changes in concentrations of sodium and other indicator parameters (e.g., chloride, specific conductivity, total dissolved solids).
Key Factors / Relationships 4
Changes in both is likely related to changes in mixing dynamics within the well and indicative of natural methane occurrence.
STUDY FINDINGSOther Factors
What are the effects of the following factors on resulting dissolved methane concentrations at the study residential water wells?
Effect Laboratory Variability
More work is needed to evaluate key factors affecting variability in dissolved gas results between labs
22
Effect of Preservatives
Effect of Pressure Tank
No significant change in dissolved methane concentrations for duplicate sample with or without preservative
No significant difference between samples collected before and after the pressure tank
Water Level
Water level variations did have some impact on methane concentrations
23
Key Research Questions
What is the effect of common sample collection methods on dissolved methane concentrations in residential water wells?
1
What is the magnitude of variability in dissolved methane concentration, isotopic signature, and other water quality parameters over time?
What are the key relationships that can help us better understand the occurrence of natural methane?
What is the effect of purging practices on dissolved methane concentrations in residential water wells?
2
4
RESULTSRecommended Practices
3
Molofsky, L.J., Richardson, S.D., Gorody, A.W., Baldassare, F.; McHugh, T.E.; and J.A. Connor (2016). Effect of Different Sampling Methodologies on Measured Methane Concentrations in Groundwater Samples, Groundwater.
Molofsky, L.J., Connor, J.A., McHugh, T.E., Richardson, S.D., Woroszlyo, C., P.A. Alavarez (2016). Environmental Factors Associated with Natural Methane Occurrence in the Appalachian Basin, Groundwater.
Molofsky, L.J., Connor, J.A., Wylie, A.S., Wagner, T., and S.K. Farhat (2013). Evaluation of Methane Sources in Groundwater in Northeastern Pennsylvania, Groundwater, Vol. 51, Issue 3: 333-349.
Molofsky, L.J., Connor, J.A., Wylie, A.S., Wagner, T., and S.K. Farhat (2011). Methane in Pennsylvania water wells unrelated to Marcellus Shale fracturing, Oil and Gas Journal, Dec. 5, 2011: 54 – 67.
24
REFERENCES
Department of Energy National Energy Technology Laboratory
Research Partnership to Secure Energy for America
25
Universal Geoscience Consulting
Echelon Applied Geosciences
Moody & Associates, Inc.
Eurofins Lancaster Laboratories
Isotech Laboratories
PADEP Bureau of Laboratories
ACKNOWLEDGEMENTSThanks to our Teaming Partners
Stephen D. Richardson, Ph.D, P.E.
GSI Environmental Inc.
(512) 346-4474
Jenna Kromann, E.I.T, G.I.T
GSI Environmental Inc.
(512) 346-4474
Ann P. Smith, P.E., BCEE
GSI Environmental Inc.
(512) 346-4474