Both curves are estimates from the interpolated 3D model, not a survey.
They're built from the same kriged grid the 3D plume view itself is
drawn from — useful for comparing thresholds and getting a sense of
scale, not a substitute for a site-specific remediation design.
Estimated Volume Exceeding %RE
For a given %RE, this is simply the total estimated volume of soil
whose interpolated response is above that value. It says nothing
about how deep that material is or what sits above it. The entire
volume could theoretically be under the surface.
Estimated Excavation Volume to Surface
This curve is the estimated total volume that would have to be
excavated to fully remove everything exceeding a given %RE
threshold. This contains the original exceedance volume itself,
plus the overburden sitting above it. It's always at least as large
as the "Exceeding %RE" curve at the same threshold — and exactly
equal to it wherever the exceedance already reaches the surface.
This is computed per vertical column across the interpolated grid:
for each (easting, northing) location, we find the deepest cell
that still exceeds the threshold, since an excavation has to reach
all the way down to the bottom of the exceedance interval in that
column, even if there's a non-exceeding gap partway through it. The
volume from the surface down to that depth, summed across every
column that meets the exceedance criteria, is the excavation
estimate. Columns with nothing exceeding the threshold anywhere do
not contribute to the excavation volume estimate.
There is one known limitation: this method treats the interpolated
grid's own shallowest layer as the ground surface, which holds true
for a normal LIF sample where logging begins near ground level. A
site whose earliest logged reading starts unusually deep could see
this curve underestimate the true excavation volume near the
surface.
Reading the chart
Both curves share the same %RE threshold axis, spanning the lowest to
the highest estimate on the job's grid. Read a volume by picking a
threshold along the bottom and going up to a curve, or hover the
chart: a readout gives both curves' values at the threshold under
the pointer (click the chart and use the arrow keys to step through
thresholds instead). The vertical axis is logarithmic: each labeled
step (1, 10, 100, 1k, ...) is ten times the one below. The area
between the two curves is the estimated overburden: how much
additional material has to come out purely to reach the volume that
exceeds the given %RE.
The controls above the chart change what it shows:
Interpolated between borings counts only the
volume inside the borings’ footprint, the outline joining the
outermost borings, where every estimate has borings on more than
one side.
Extrapolated beyond borings counts only the
volume past that outline, where estimates reach beyond the
outermost borings and are less certain (see
the
extrapolated area).
Sum of interpolated and extrapolated, the
default, counts both: every estimate the borings support. The two
parts add up to it exactly, for the excavation curve too, since it
excavates whole columns and a column is either inside the
footprint or not.
The two checkboxes show or hide each curve;
they are also the chart’s legend.
m³ / yd³ switches the units (1 m³ = 1.31 yd³)
of the axis, the readout and the table.
The table under the chart gives both curves at 10, 25, 50 and
100 %RE for the area chosen, and the job’s
readme.txt lists them for all three. Export
Image saves the chart as it is showing, with the area and
curves named across its top. The download zip also holds a static
copy of the chart for the whole area, volume_chart.png,
shown below.
What is counted, and how uncertain it is
Each volume is a count of grid cells, each 3 m × 3 m ×
0.15 m (1.35 m³). A cell counts when its estimate is above the
threshold and it passes the
90% rule, the same
cells the 3D view draws. That has consequences to keep in mind before
quoting a number:
The sum includes estimates beyond your borings.
The drawn area can reach tens of meters past the outermost borings,
and every cell there counts in the sum. On a site where the plume
runs off the edge of the boring grid, a large share of the volume
can sit outside it, and the count simply stops where the drawn area
stops, so it is not a bound in either direction. Choose
Interpolated between borings to leave it out.
Thin layers come out thicker. Each input is the
highest reading in a 30 cm interval, and kriging spreads a layer
over the vertical range it fits. A smear zone a few tenths of a
meter thick in the logs can be twice that on the grid.
The ground is treated as flat. Depths are
below each boring's own ground surface; surveyed elevations aren't
used.
No error band. lif-viz doesn't put a range on
these numbers. Two thresholds a few %RE apart, or one more boring,
can change them a lot, especially on the steep left end of the
curves.
Use them to compare thresholds and get a sense of scale, alongside
the logs and the 3D view, not as a quantity for a remediation design
or bid.
