Southern Sierra Critical Zone Observatory
KGR135 SUP Amendment Proposal
Project Director/Principal Investigator: Roger Bales
Affiliation and contract information: University of California, Merced
Southern Sierra Critical Zone Observatory. RBales@ucmerced.edu
Field Manager contact: mmeadows@ucmerced.edu
Collaborators: Cliff Riebe, Anthony O’Geen, Peter Hartsough, Matthew Meadows
Project Title: Geoprobe and Geophysics of the Critical Zone
Project proposal:
We would like to do additional monitoring into the deeper saprolite and bedrock
at the Soaproot Saddle and Shorthair Creek tower sites (see attached map and GPS
locations). This project has two components: Geoprobe and Geophysics. A major thrust
of our proposed work is to quantify weathering, fracture spacing and orientation, water
content, and the size and distribution of macropores and subsurface corestones. By
coupling direct measurements of subsurface properties from the Geoprobe together with
indirect measurements from Geophysics we will address the fundamental,
methodological problem of calibrating geophysical surveys, which are relatively easy to
apply over broad scales and minimally invasive. Hence it is important that the Geoprobe
measurements are co-located with the geophysical surveys insomuch as possible.
Geoprobe:
The purpose of this component is to collect a small number of physical samples
for analysis, while also allowing for the installation of water monitoring wells in the
subsurface, when possible. Based on field observations and physical restrictions, we
propose using use two different methods that are appropriate for each site: 1) at Soaproot
Saddle we will use a Geoprobe (http://geoprobe.com/) sonic drilling rig to collect
samples down to ~10m and install monitoring wells at these sites, 2) at Shorthair Creek
we will use a handheld rotary coring drill. We chose the Geoprobe, largely because it
was inexpensive (we have one available at UC Davis) and is very low impact (less than
4.6 lb/in2 surface load). The Geoprobe runs on a track, which minimizes disturbance to
off-road areas. We propose to do dry drilling so would not be introducing any water or
other drilling fluids. We would like to attempt 7-11 drilling locations per site, which may
go as deep as 12m with at Soaproot Saddle but limited to less than 5m at Shorthair Creek.
Soaproot Saddle geoprobing will likely occur along the E-W main access road. Shorthair
Creek geoprobing will likely occur along two, approximately 600 foot, transects N-S and
E-W. Wells will be completed with 2" PVC, slotted in the bottom ~2m for monitoring
subsurface water. We do not expect to encounter any groundwater while drilling in late
summer/early fall. However, we do expect instrumentation in the wells to reveal
transient groundwater during the winter. We plan to collect continuous soil and rock
cores from all the wells which will be analyzed for physical and chemical properties of
the saprolite and deep water therein. Location is flexible but will generally be with the
vicinity of the existing flux towers at Soaproot Saddle (37° 1'51.85"N, 119°15'23.15"W)
and Shorthair Creek (37° 3'59.75"N, 118°59'18.51"W) but in an area not in conflict with
the existing/future NEON instrumentation at Soaproot Saddle. Please see attachments for
general location, although final locations may be different.
Project Request Form
Page 1
Geophysics:
The purpose of this component is to obtain a better understanding of the geology
and regolith formation at Soaproot Saddle and Shorthair Creek using non-invasive
geophysical techniques. Our geophysical surveys will include seismic refraction,
resistivity, ground-penetrating radar, nuclear magnetic resonance, gravity and magnetics
along transects near our current flux tower sites.
None of the geophysical techniques will result in significant or lasting disturbance
to the landscape. The gravity and magnetic surveys are completely passive and can be
conducted with instruments carried over the ground by a team of two researchers.
Seismic refraction and resistivity surveys are more labor intensive, requiring a team of
four or five researchers, because of the amount of equipment involved. However both
techniques are minimally invasive and can be conducted at the same time to minimize
disturbance. In seismic refraction surveys, a connected line of 96 geophones is distributed
across the surface at regular intervals. Geophones need to be in solid contact with the
ground, and have a two-inch spike on one end so that they can be driven into the soil. On
removal, after our survey, we will backfill the small holes thus produced. Seismic
refraction surveys measure the velocity and attenuation of seismic energy in the
subsurface. Hence seismic energy must be applied to the subsurface. This is done with a
sledge hammer applied with vigor to a steel plate. To obtain a distributed view of the
subsurface over the entire transect, we will need apply energy to multiple “shot points”
along the transects. At each shot point a series of 5-10 blows is needed to optimize the
signal-to-noise ratio in the seismic data. In resistivity surveys, an array of connected
electrodes (similar to the geophones) is distributed and driven into the top 2-3 inches of
soil for the resistivity surveys. The resistivity surveys measure resistance of the
subsurface to passing a current. Hence a current must be applied to the subsurface to
obtain measurements; this is accomplished with pulses of current routed through the
electrodes from a car battery. The applied current is minimally invasive and should have
no effect on biota. Geophysical transects will run along the same or similar transects as
the Geoprobing, and along several perpendicular transects in the area.
Project location:
Project location will be within footprint of existing Flux Towers: Soaproot Saddle
(37° 1'51.85"N, 119°15'23.15"W) and Shorthair Creek (37° 3'59.75"N, 118°59'18.51"W)
[see attached map and coordinates]. Non-invasive geophysics lines may also run
perpendicular and/or outside of transects.
Duration of use and activity periods:
Project duration should be 1-2 weeks of on-site activity for each portion of the
project (Geoprobe and Geophysics). Project timeframe is August to December, 2013 and
continuing Spring to early Winter 2014. All Geoprobe activity will occur within a short
2-7 day period, likely in 2013 including a team of 4-6 people. Geophysics activity would
likely occur in 2014 including a team of 5-10 people. Access to monitor installed wells
would continue into the future and have a limited number of people (1-2 people for 1 day
per visit).
Project Request Form
Page 2
Describe any markers, including tags, flagging, stakes, or other to be used. Will
GPS location data be collected at these locations?
No permanent markers or stakes are needed. We request to install PVC well
casing into the geoprobe holes when appropriate and potentially instrument them with
water monitoring equipment. Well casing can be flush with surface or may protrude less
than 5 inches above surface.
Do you intend to publish your results?
Yes. We plan on publishing and will acknowledge the contributions of the Sierra
National Forest in published materials. Current and future publications can be accessed
through our website: http://criticalzone.org/sierra
Will project include use of toxic chemicals, animal or human test subjects?
No
Date: August 1, 2013
Project Request Form
Page 3