2
A person was considering developing a potential sand
deposit located on a property in the Gulf Coastal Plain
a few miles coastward from the Piedmont Uplands. The
property purportedly was underlain with high quality con-
struction sand. The property lies partially in a bottomland
floodplain of a sluggish river with backwater ponds and
swamps. Swamp forests consist mostly of oak-dominated
hardwoods. The bulk of the property lies on a gently slop-
ing valley side with terraces covered with a mixture of hard-
wood/pines and dense overgrown clear-cut areas.
Potential Minerals Reported
Two existing geologic reports described the potential for
sand on the property. One report stated, “The sand encoun-
tered proved to be fine to coarse grain and fits the specifi-
cation for construction, mortar and specialty sands [golf
courses, blasting, grinding, etc.]” Even more convincing,
that same report stated “The test drilling of 70 plus test
holes on the 300 acres ***shows a tremendous amount of
course sand and lesser amount of gravel.” (Text in bold ital-
ics emphasized by me.) The report backs up the claim by
including sieve analyses and logs of test holes in the report
and by referring to logs of drill holes in other older reports.
Existing Technical Reports
There was a conspicuous absence of geology in both reports.
The only discussion of geology in the first report was the
statement, “Geologically, the material deposits are located
in high terrace gravels of quaternary age. These deposits are
described as ‘lenticular beds of poorly sorted sand, ferruginous
sand, silt, clay, and gravelly sand. Sand consists primarily of
very fine to very coarse poorly sorted quartz grains, gravel com-
posed of quartz, quartzite, and chert pebbles.’ ”
In the absence of geology, the entire evaluation of the
sand was based entirely on drill hole logs that contained
lengthy sections of tan or pink silty sand. And kicking the
dirt in a casual reconnaissance of the site could leave a trust-
ing person with the impression that the site indeed con-
tained “such quantities of sand.”
In-Depth Geologic Study
I was retained by a client to evaluate the existing reports
and to opine on the report’s description of the quality and
quantity of sand.
The data gleaned from the existing reports were of
uncertain and conflicting quality. There were considerable
discrepancies between test hole logs and sieve analyses. In
addition, the Fineness Modulus* was reported for a num-
ber of samples, but some of the values reported were not
correctly calculated. My reconnaissance visit revealed much
sand but the presence of pinkish sand in the higher terraces
seemed oddly out of place compared to the tannish sand in
the floodplain. Consequently, my initial review of the exist-
ing data lead left me with a low level of confidence.
A new geologic study and drilling program were pro-
posed to increase the confidence level of the sand resource
estimates. Two USGS regional geologic maps were accessed
to evaluate the regional geology 1) a digital geologic map
of the state, and 2) a map showing surficial materials of the
area. Both of those maps would have been available to the
authors of the client-supplied reports, although the latter
report may not have been available as a digital product.
Of the twenty drill holes I had planned, only 13 were
completed. Shortly after drilling commenced it became evi-
dent that there was much more silt and clay in the pink silty
sand deposits than was described in the existing reports.
Sand suitable for use as concrete was encountered in only
three of the new bore holes all three were in the modern
flood plain (i.e., the first terrace above the stream surface).
The remaining ten drill holes, all located on terraces above
the modern floodplain, were barren of sand suitable for use
as construction or other more demanding applications.
Six side-by-side analyses (see Figure 1 for an example)
were conducted comparing the test hole logs in the existing
reports to logs from new drill holes located very nearby.
Four of the six comparisons were significantly different
clean sand that had been reported in the existing drill holes
was totally absent or was excessively laden with silt. This
cast doubt on all the old drill holes.
A brief analysis of the regional geology was conducted
as part of the study. The regional study extended into the
piedmont where particular attention was given to a map
unit described as micaceous saprolite. The saprolite (shown
by the purple section in Figure 1) formed on a gneissic rock
directly along strike with the purported sand deposit. It
was determined that the pink, micaceous silty, clayey sand
described in the existing reports was the same as the silty
saprolite exposed along strike in the nearby Piedmont.
The original sand report that had been prepared without
*The fineness modulus is an empirical value that describes the
average size of particles in a sample of aggregate. It is calculated
by adding the total percentage of the sample of an aggregate
retained on each of a specified series of sieves, dividing the sum
by 100.
A person was considering developing a potential sand
deposit located on a property in the Gulf Coastal Plain
a few miles coastward from the Piedmont Uplands. The
property purportedly was underlain with high quality con-
struction sand. The property lies partially in a bottomland
floodplain of a sluggish river with backwater ponds and
swamps. Swamp forests consist mostly of oak-dominated
hardwoods. The bulk of the property lies on a gently slop-
ing valley side with terraces covered with a mixture of hard-
wood/pines and dense overgrown clear-cut areas.
Potential Minerals Reported
Two existing geologic reports described the potential for
sand on the property. One report stated, “The sand encoun-
tered proved to be fine to coarse grain and fits the specifi-
cation for construction, mortar and specialty sands [golf
courses, blasting, grinding, etc.]” Even more convincing,
that same report stated “The test drilling of 70 plus test
holes on the 300 acres ***shows a tremendous amount of
course sand and lesser amount of gravel.” (Text in bold ital-
ics emphasized by me.) The report backs up the claim by
including sieve analyses and logs of test holes in the report
and by referring to logs of drill holes in other older reports.
Existing Technical Reports
There was a conspicuous absence of geology in both reports.
The only discussion of geology in the first report was the
statement, “Geologically, the material deposits are located
in high terrace gravels of quaternary age. These deposits are
described as ‘lenticular beds of poorly sorted sand, ferruginous
sand, silt, clay, and gravelly sand. Sand consists primarily of
very fine to very coarse poorly sorted quartz grains, gravel com-
posed of quartz, quartzite, and chert pebbles.’ ”
In the absence of geology, the entire evaluation of the
sand was based entirely on drill hole logs that contained
lengthy sections of tan or pink silty sand. And kicking the
dirt in a casual reconnaissance of the site could leave a trust-
ing person with the impression that the site indeed con-
tained “such quantities of sand.”
In-Depth Geologic Study
I was retained by a client to evaluate the existing reports
and to opine on the report’s description of the quality and
quantity of sand.
The data gleaned from the existing reports were of
uncertain and conflicting quality. There were considerable
discrepancies between test hole logs and sieve analyses. In
addition, the Fineness Modulus* was reported for a num-
ber of samples, but some of the values reported were not
correctly calculated. My reconnaissance visit revealed much
sand but the presence of pinkish sand in the higher terraces
seemed oddly out of place compared to the tannish sand in
the floodplain. Consequently, my initial review of the exist-
ing data lead left me with a low level of confidence.
A new geologic study and drilling program were pro-
posed to increase the confidence level of the sand resource
estimates. Two USGS regional geologic maps were accessed
to evaluate the regional geology 1) a digital geologic map
of the state, and 2) a map showing surficial materials of the
area. Both of those maps would have been available to the
authors of the client-supplied reports, although the latter
report may not have been available as a digital product.
Of the twenty drill holes I had planned, only 13 were
completed. Shortly after drilling commenced it became evi-
dent that there was much more silt and clay in the pink silty
sand deposits than was described in the existing reports.
Sand suitable for use as concrete was encountered in only
three of the new bore holes all three were in the modern
flood plain (i.e., the first terrace above the stream surface).
The remaining ten drill holes, all located on terraces above
the modern floodplain, were barren of sand suitable for use
as construction or other more demanding applications.
Six side-by-side analyses (see Figure 1 for an example)
were conducted comparing the test hole logs in the existing
reports to logs from new drill holes located very nearby.
Four of the six comparisons were significantly different
clean sand that had been reported in the existing drill holes
was totally absent or was excessively laden with silt. This
cast doubt on all the old drill holes.
A brief analysis of the regional geology was conducted
as part of the study. The regional study extended into the
piedmont where particular attention was given to a map
unit described as micaceous saprolite. The saprolite (shown
by the purple section in Figure 1) formed on a gneissic rock
directly along strike with the purported sand deposit. It
was determined that the pink, micaceous silty, clayey sand
described in the existing reports was the same as the silty
saprolite exposed along strike in the nearby Piedmont.
The original sand report that had been prepared without
*The fineness modulus is an empirical value that describes the
average size of particles in a sample of aggregate. It is calculated
by adding the total percentage of the sample of an aggregate
retained on each of a specified series of sieves, dividing the sum
by 100.