Evaluation and Reporting on Contaminant Hydrogeological

12-12-01

Conditions at the Tajiguas Landfill

Page 12 of 24

S

ECTION

B

Sample Analyses

On Page 2-47, the draft EIR states that

“Groundwater quality for current landfill operations is monitored via eight

monitoring wells and one lysimeter.”

The current eight groundwater monitoring wells used to monitor the existing

landfill are insufficient to identify subsurface flow pathways and contaminant

migration, and is more appropriate for a single gas station underground storage tank

site.

On page 3.3-43 of the draft EIR, it states that VOCs are the main contaminants of

concern and that their apparent decrease in concentrations is due to effective

control systems which minimize the impacts to downgradient groundwater from the

landfill. This statement admits that the landfill is adversely impacting downgradient

groundwater and yet does not explain the character nor the gravity of these impacts.

Aside from the fact that there is an insufficient number of groundwater monitoring

wells in the most critical locations necessary to evaluate groundwater quality

conditions throughout and adjacent to the existing landfill, it is a likely possibility,

based upon recent groundwater monitoring lab data, that gasoline constituents as

well as chlorinated solvents are emanating from point sources from the landfill mass.

The following is the table of contaminants identified within the landfill.

1,4-Dichlorobenzene

1,1-dichloroethane

cis-1,2-Dichloroethene

trans-1,2-dichloroethene

cis-1,2--dichloroethylene

2-methylbutane

1,4-Dichlorobenzene

Methyl t-Butyl Ether

Trichioroethene (TCE)

Hexavalent chromium

benzothiazole

chlorobenzene

chlorodifluoromethane

methoxytrimethylsilane

fluorotrimethylsilane

trimethylsilanol

trimethylsilane (2-methoxyethyl)

1,2,4- trimethylbenzene

vinyl chloride