Site-Specific Health and Safety Plan (HASP) - Laschools.org

APPENDIX A
COLUMN TEST FOR DETERMINING SORBED HEXAVALENT CHROMIUM
Heavy concentrations of hexavalent chromium have been found on one of the parcels of
the Los Angeles Unified School District site in South Gate. In order to determine
potential approaches to clean up the site it is necessary to know whether the hexavalent
chromium is present only in the dissolved form in the groundwater or it is also sorbed on
soil particles. If the hexavalent chromium is present in the sorbed form, its presence
could potentially be of much greater duration.
In the saturated zone water is present both free flowing among the solid particles and in
pores and cavities within the particles. Thus, when the sample of soil is filtered, a
significant amount of the hexavalent chromium may still be present as dissolved
hexavalent chromium. The dissolved hexavalent chromium in the pores contains the
same concentration of hexavalent chromium as the groundwater. In order to assess
whether all the hexavalent chromium is dissolved or some of it is adsorbed, it is
necessary to leach all the hexavalent chromium out of the soil. In so doing the dissolved
hexavalent chromium will leach out first, followed by the sorbed material.
The testing to determine if a significant amount of hexavalent chromium is present as
dissolved material consists of determining if the total amount of hexavalent chromium
recoverable from the soil exceeds the amount which would be present in the water
retained by the soil.
Procedure
1. Collect a sample of saturated zone soil and a sample of the groundwater
preferably from the same boring and at the same depth. Both samples must be
taken from a location known to contain hexavalent chromium.
2. Filter the groundwater and determine the concentration of hexavalent
chromium in the groundwater.
3. Take a 1 – 5 gram sample of the soil and place it in a tared glass dish to
determine the water content of the soil. Weigh the dish with the sample and
subtract the weight of the dish to determine the exact weight (W1) of the
sample. Do not use aluminum pans because hexavalent chromium, if present
in significant concentrations in the soil, will corrode the aluminum.
4. Dry the soil at 100 – 105 o C to constant weight. Determine the weight of the
dry sample (W2) by subtracting the weight of the dish from the weight of the
dish with the dry sample.
5. Determine the weight of the water in the sample by subtracting the dry weight
of the sample from the wet weight of the sample (W1 – W2). If one assumes a
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