1.1 MB pdf - Bolsa Chica Lowlands Restoration Project

SECTION 3: ANALYSIS
Cadmium
Background levels of cadmium in the Bolsa Chica Lowland sediments are estimated to be
< 0.66 mg/Kg dw. This value represents the 91st and 95th percentile levels for the all sample
and surface data sets, respectively. This data set had a large number of nondetect values
(i.e., flagged with “U” in the database) that occur at higher concentrations in the data set.
The resulting cumulative percent plots (Appendix E, Figures E-10a, E-11, and E-12) show
a two-stepped curve. There were 368 samples out of the total 581 samples that were nondetects.
The same value (0.66 mg/Kg) was at the 91st percentile level for the all sample data
set when the nondetect values were removed. The resulting cumulative percent plot
(Appendix E, Figure E-10b) shows a smooth curve rising to the break point, where the curve
becomes discontinuous and starts to rise more steeply. A similar value of < 0.65 mg/Kg dw
was estimated from the subsurface sample data set (86th percentile).
Chromium
Background levels of chromium in the Bolsa Chica Lowlands are estimated to be
< 43 mg/Kg dw. This value represents the 94th and 90th percentile value for the all sample
and surface data sets, respectively. A lower value (< 32 mg/Kg dw) was estimated from the
subsurface sediment samples that represents the 96th percentile value for that data set. All
three cumulative percent plots for chromium rise in a relatively smooth line to the break
points, where the curves become less continuous and begin to rise more sharply
(Appendix E, Figures E-13 through E-15).
Cobalt
The background level of cobalt for the Bolsa Chica Lowlands was estimated to be
< 10.1 mg/Kg dw. This value represents the 93rd and 94th percentile value for the all
sample and subsurface groups, respectively. A slightly lower value (< 10 mg/Kg dw) was
estimated from the surface sediment data, representing the 91st percentile level. All three
cumulative percent plots for cobalt rise in a relatively smooth line to the break points,
where the curves become less continuous and begin to rise more sharply (Appendix E,
Figures E-16 through E-18).
Copper
Background levels for copper in the Bolsa Chica Lowland sediments were estimated to be
< 26.1 mg/Kg dw. This value was derived from the all sample data and represented the 91st
percentile level. A slightly higher value was estimated from the surface (< 30 mg/Kg dw)
sediment sample data set (91st percentile). A lower value was estimated from the subsurface
(< 20.6 mg/Kg dw) sediment sample data set (94th percentile). Figure 3-2 shows the
cumulative percent plot for all the copper samples and the break point in the curve where
the upper limit of the background level was estimated. All three cumulative percent plots
for copper rise in a relatively smooth line to the break points, where the curves begin to rise
more sharply (Appendix E, Figures E-19 through E-21).
Lead
Background levels for lead in the Bolsa Chica Lowland sediments were estimated to be
< 48 mg/Kg dw. This value represents the 95th and 92nd percentile levels for the all sample
and surface data sets, respectively. A lower value of < 17.3 mg/Kg dw was estimated from
SAC/143368(003.DOC) 3-15 ERA REPORT
7/31/02