Natural gas gathering operations in the Sacramento Basin have resulted in limited impacts to shallow groundwater. At most sites, detectable BTEX compounds in soil and groundwater are low or nonexistent. Groundwater plumes are small (<400 feet) and stable or shrinking over time. While diesel-range organic concentrations exceed water quality standards at all active sites, they are primarily degrading to non-hydrocarbon polar compounds through natural biodegradation processes. As a result of intrinsic biodegradation and natural attenuation, the majority of condensate releases from natural gas gathering facilities has been degraded, with less than 10% of the original mass remaining at most sites according to soil and groundwater concentration mapping and mass estimates.

1. Limited Impacts of Natural Gas Gathering Operations
on Shallow Groundwater in the Sacramento Basin
James A. Lehrman, PG, CHG
Jim.Lehrman@parsons.com
Walnut Creek, California
Current Conditions at Most Sites
 Little or no detectable BTEX in soil or groundwater (GW)
 GW plumes are small (<400’) and stable or shrinking
 Diesel range organic (DRO) concentrations exceed
water quality objects (WQOs) at all open sites (primary
regulatory driver)
 DRO concentrations exceed gasoline range organic
(GRO) concentrations in GW on average by a ratio of
>10:1 (puzzling…)
Approach/Activities Results/Lessons Learned
Typical Natural
Gas Gathering
Site
Natural gas, condensate and formation
water (typically >7,000’ bgs)
Dry natural
gas to end
users
Condensate releases from
dehydrators, ASTs, sumps,
etc.
In order to better understand the nature of the impacts:
 Collected fresh unweathered condensate from NGG
product storage tanks and weathered free product (FP)
from GW monitoring wells
 Compared the results of a suite of FP analytical tests
including hydrocarbon fractionation
 Analyzed GW samples from 16 sites for DRO w/ and
w/out gravity separation (GS) and silica gel cleanup
(SGC) from 2011 through 2014 (307 samples)
 Mapped the plumes using historical and recent data w/
and w/out SGC
Condensate Composition
Degradation of Hydrocarbons
To Polar Compounds
Biodegradation of (TPHg/GRO) can result in polar compounds
that are measured (elute) as TPHd/TEPH/DRO because the
polar compounds have higher boiling points than hydrocarbon
with the same number of carbon atoms. - CA LUFT Manual, 2012
Typical NGG Site Cross Section
Typical NGG Site GW Plume
Typical NGG Site Mass Reduction
Shrinking and Degrading to Polars
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
DRO w/GS DRO w/SGC DRO w/SGC & GS
Average
PercentRemaining(%)
19%
81%
12%
(16 Sites, 66 Wells, 13 Events)
w/GS & SGCw/SGCw/GS
19% 81% 88%
DRO
Avg.%Remaining
Reduction in DRO
with & w/o Gravity Separation
and Silica Gel Cleanup
Un-weathered
Weathered
AliphaticsAromatics
Unweathered
Weathered
Evidence of the loss of
the light fraction and
bioattenuation
#1 #2 #3
#4 #5 #6
with DRO in Soil Iso-concentration Overlay
Original Release
Mass Remaining
from Natural Attenuation –
Compared to estimated Original Release
 Natural Gas Gathering (NGG) sites are located within or
adjacent to gas fields throughout the Sacramento Basin
 NGG operations removed liquids (water and condensate)
from raw gas prior to transmission in pipelines since the
1940’s
 Condensate:
 Volatile
 High API gravity unrefined petroleum
 Similar to gasoline
 High % BTEX and carbon range of approximately C6 to
C16
 Environmental investigations performed at ~78 NGG sites;
most showed little or no impacts
 Remediation (i.e., source removal) conducted at ~15 sites
 17 sites/cases currently open with ongoing monitoring;
~61 closed
DRO ≈ Polars in Groundwater
octane (C8H18) BP = 125°C octanol (C8H18O) BP = 195°C
n‐hexane (C6H14) BP = 69°C caproic acid (C6H12O2) BP = 205°C
Polar compounds a have higher solubility and lower vapor pressure, therefore
lower Henry’s constant (than petroleum compounds)
 Most of the released condensate at NGG sites has
attenuated
 Remaining hydrocarbons are effectively insoluble
and strongly sorbed to soil in the smear zone
 Dissolved phase DRO is virtually all polar non-
hydrocarbons
 Intrinsic biodegradation is occurring at the NGG sites
and producing polar compounds as metabolic by-
products
 Comparison of GW data over time indicates plumes
are:
 Shrinking
 Less than 400 feet in length, and
 Limited to shallow GW w/in the vicinity of NGG
operations
 Based on detailed mapping of soil and GW
concentrations and current mass in place
calculations for 10 sites:
 Mass remaining is <10% of the original release for most
sites, even those with no prior engineered remediation
 The ratio of hydrocarbon mass (soil:groundwater) is
typically ~ 10,000:1
Background
Study Area: Sacramento Basin