Evaluation and Reporting on Contaminant Hydrogeological

12-12-01

Conditions at the Tajiguas Landfill

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and the depth of the 100-year, 24-hours storm is 7.85 inches. The average annual

runoff is five inches per year.

Rainfall in the northernmost portion of the Pila Creek watershed is a 20.01 inches

per year area-weighted average and 18.34 inches per year area weighted average

precipitation for the lower watershed area (Santa Barbara County Public Works

Department - Solid Waste and Utilities Division, 2001). The calculated runoff from the

upper and lower watershed areas are estimated to be 25 AF per year and 21 AF per

year, respectively; resulting in a total combined runoff of 46 AF per year.

Geologic materials identified during field mapping and drilling consist of

Quaternary-age alluvium, colluvium and artificial fill which overly Tertiary-age

bedrock consisting of the Rincon Shale and the Monterey Formation. The alluvium

consists of recent stream-laid deposits of Canada de Ia Pila Creek and occurs in a

narrow zone in the canyon bottom. Recent alluvium unconformably overlies fill and

colluvial soil in the valley bottom. The older alluvium unit underlies artificial fill and

colluvial soils and overlies Rincon Shale. The older alluvium consists of silty to

locally gravelly sand and is similar to the recent alluvium in composition. Colluvium

consists of a heterogeneous mass of soil or rock fragments deposited by sheetflow

or gradual accumulation at or near the base of a slope.

The contact between the Rincon Shale and the Monterey Formation trends

roughly east-west on both sides of the canyon and dips approximately 50 to 60

degrees to the south. The contact between the two appears to be transitional over a

10 to 20 foot thick zone.

A zone of weathered bedrock, generally less than ten feet thick, is present over

most of site area.

The Rincon Shale is the bedrock formation that underlies most of the landfill area

as well as a broad area to the north. It is predominantly a grey to olive-drab

mudstone containing ½ to 2 foot thick interbeds of orange-brown weathering

dolomitic limestone, foraminiferal marl and pale yellow brown to olive-brown

bentonitic, lithic-vitric tuff at the top of the formation.

Bedding in the Rincon Shale and the Monterey Formation at the site trend

approximately east-west and homoclinally dip about 60 degrees to the south. Local

variations in strike and dip occur, most of which appear to be related to faulting.

A fault zone is observed in a surface outcrop approximately 500 feet east of the

canyon bottom, near the Rincon to Monterey contact. This fault zone strikes N80E

and dips approximately 80 degrees to the south. The fault shows a reverse sense of