Evaluation and Reporting on Contaminant Hydrogeological

12-12-01

Conditions at the Tajiguas Landfill

Page 6 of 24

enough or as underflow in alluvial fill or fractured bedrock below the channel.” It is

clear that intensely fractured rock likely exists in bedrock below the channel and can

be very permeable allowing contaminated underflow to bypass the interceptor

trench. The original topography and Pila Creek bed are shown on GeoSolv

Original

Topography of Vicinity of Pila Creek

map.

The Collection Trench Profile and Details cross section also verifies that the 20 to

35 feet of soil exposures on the east and west sides of the trench are permeable

alluvium. (

See GeoSolv Tajiguas Landfill Map

) This provides migratory pathways for

contaminated groundwater to bypass the trench and contaminate groundwater in

the Monterey Shale formation, at the Arroyo Quemada community and the beaches

beyond.

Since the community of Arroyo Quemada utilize groundwater from the

Monterey/Alluvium hydrogeologic unit for domestic supply, the landfill is posing a

threat to groundwater with potential and or existing drinking water beneficial uses

(see page 3.3-49 of the EIR). Furthermore, unless otherwise indicated within the

Basin Plan or a formal Regional Board Order which de-designates a surface or

groundwater body’s beneficial use designation, groundwater in the Rincon,

Vaqueros and Sespe-Alegria, and the Gaviota hydrogeologic units are considered to

have potential or existing drinking water beneficial use designations. Therefore,

contaminated groundwater in the Rincon in direct contact with the contaminated

groundwater that saturates the landfill mass, is considered to be drinking water and

should be treated as such. The draft EIR conspicuously leaves out the beneficial use

designations for the groundwater in the Rincon Hydrologic Unit.

On page 3.3-17 of the Draft EIR the Monterey Formation is stated to consist of

“weathered and fractured Monterey Formation shales and siltstones south of the

existing landfill, as well as valley bottom alluvial and colluvial deposits in the lower

canyon area.” Since the monitoring wells, located down gradient of the interceptor

trench, are founded in colluvium, contaminated groundwater underflow in the

fractured shales and siltstone may escape the grossly inadequate monitoring system

and reach the beach and ocean.

Since, based on the preceeding discussion, the interceptor trench does not

prevent all groundwater from escaping the landfill, it is necessary to establish its

overall effectiveness.

The surface run-off in the upper portion of the Pila Creek watershed is captured in

three retention basins located directly north of the current landfill. One is an out-of-

channel basin and two are in-channel basins located at an approximate elevation of

400 to 500 feet above MSL. All three retention basins are unlined and are