Analysis and Comparison of the Wells in the Pleasant Valley Area of Ventura County - 1
1.0 INTRODUCTION
1.1 Purpose and Scope
This report compares the production capabilities of a group of high
capacity water wells of varying design drilled in the Pleasant Valley Basin near the
city of Camarillo, California (see Figure 1). Thirty four wells
were chosen for the study and represent different screen types in addition to
development and completion methods. The type of screens in the wells range from low
open area milled and punched slotted casing to higher open area continuous wire wrap
and horizontal louver shutter screen. The total depth and length of screen varies
considerably between wells as does the type of aquifer penetrated.
Because of the variety of screen types and development methods, the
Pleasant Valley area affords an excellent opportunity to study the relationship between
well yields and screen design.
The scope of the investigation included plotting of a typical
geologic cross section through the Pleasant Valley aquifers and a computer analysis and
comparison of specific capacities per foot of screen for each of the wells.
2.1.1 Shallow Aquifers
The upper strata of the Pleasant Valley Basin is composed of recent
and Upper Pleistocene alluvial sands, gravels, silts and clays. The aquifers in this
zone are generally unconfined and very in thickness from a few feet to several hundred
feet. The permeable lenses yield little water to wells owing to rapid thinning and
predominance of fine-grained materials. The shallow aquifers in the Pleasant Valley
Basin are equivalent but not connected with the Oxnard aquifer lying to the West.
2.1.2 Fox Canyon Aquifer
Underlying the Pleasant Valley area at depths from 400 to 1500 feet
is a prominent zone of marine sands and gravels known as the Fox Canyon Aquifer. The
Fox Canyon Aquifer is the lower-most member of the early Pleistocene San Pedro formation
and forms the major producing zone of the Pleasant valley ground-water Basin. The
aquifer is confined and is from 100 to 300 feet thick.
Figure 2 is a geologic cross section through
the Pleasant Valley Basin along Las Posas Road. As can be seen in the section, the Fox
Canyon aquifer is penetrated by most of the high yielding wells in the study area.
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