1.1 MB pdf - Bolsa Chica Lowlands Restoration Project

SECTION 3: ANALYSIS
the regression analyses to show the low end of the dose-response curve (e.g., low
concentration/low response). Sediment data that were from samples in which survivorship
differed significantly from the controls were retained for further screening as follows (note:
all screening values, including those derived from the regression analyses are presented as
part of the effects profile at the end of this section):
1. Chemical concentrations were screened against available ER-Ls. Data below ER-Ls were
excluded from the regression analysis for that chemical because it was considered
unlikely that concentrations lower than the ER-L would cause significant mortality.
Instead, the observed mortality was considered more likely to have been caused by
another chemical present in that sample.
2. If the chemical was an inorganic and ER-Ls were unavailable, then concentrations were
screened against the Bolsa Chica background values. Data below the upper limit of
background were excluded from the regression analysis because it was considered
unlikely that chemicals at background levels would cause significant mortality. It was
considered more likely that other chemicals in that sample caused the observed
mortality.
3. If a data point was greater than the ER-L, but lower than background, it was excluded
from the regression analysis if mortality in the bioassay was greater than 50 percent.
Although some toxicity could be expected to occur if chemical concentrations exceeded
the ER-L, it was not likely that mortality would exceed 50 percent even if the
background level for that inorganic chemical was elevated within the Bolsa Chica
Lowlands.
Pore water data were screened as follows:
1. Chemical concentrations were screened against the California Water Quality Standards
for chronic exposure. Concentrations that were below the chronic CTR were excluded
from the regression analyses because concentrations lower than the chronic standard
should not cause significant toxicity. Instead, it was considered more likely that another
chemical in the water sample caused the observed effects.
2. Chemical concentrations exceeding California Water Quality Standards chronic values
were retained for the regression analyses.
3. If a California Water Quality Standard value was not available for a given chemical, it
was retained for regression analyses.
Five out of the 45 total pore water samples contained ammonia. Of these, three samples
(R11C2-1, R32C2-1, and R38C1-1) were considered to have ammonia concentrations that
would be toxic to test organisms, and two (R3C1-1 and FOSN01-1) were considered to have
ammonia concentrations that would potentially be toxic to test organisms. The presence of
ammonia was not clearly tied to significance vs. controls, so the samples were not removed
from the database. Rather, they were screened on a chemical-specific basis for data
reduction for the regression analysis.
The results of this screening process are presented in Appendix F, Table F-1 for sediment
and Table F-2 for pore water. The regression analyses were then performed on data retained
after the screening process had been completed.
ERA REPORT 3-32 SAC/143368(003.DOC)
7/31/02