1. Overview of Groundwater Concepts and Catalina Island Water Resources.

2. Avalon Canyon Watershed.

3. Avalon Canyon Bedrock Wells. Construction Plan, Groundwater Monitoring, and Aquifer Testing.

4. Avalon Canyon Bedrock Wells, Permitting for a

Municipal Water Supply Well.

Avalon is heavily dependent on the Middle Ranch well field and the adjacent Thompson Reservoir for it’s water supply.

Avalon is heavily dependent on the Middle Ranch well field and the adjacent Thompson Reservoir for its water supply.

Middle Ranch alluvial aquifer (consisting of sand and gravel) and Thompson Reservoir both store all of their accessible water within a 50 foot thickness. California defines a shallow well as less than 200 feet deep, an intermediate well as 200 to 600 feet, and a deep well as over 600 feet.

Avalon is heavily dependent on the Middle Ranch well field and the adjacent Thompson Reservoir for it’s water supply.

Middle Ranch alluvial aquifer (consisting of sand and gravel) and Thompson Reservoir both store all of their accessible water within a 50 foot thickness. California defines a shallow well as less than 200 feet deep, an intermediate well as 200 to 600 feet, and a deep well as over 600 feet.

The shallow depth of the Middle Ranch well field and Thompson Reservoir make them vulnerable to drought. The island has been under water rationing 26 percent of the time since 1966.

Avalon is heavily dependent on the Middle Ranch well field and the adjacent Thompson Reservoir for it’s water supply.

Middle Ranch alluvial aquifer (consisting of sand and gravel) and Thompson Reservoir both store all of their accessible water within a 50 foot thickness. California defines a shallow well as less than 200 feet deep, an intermediate well as 200 to 600 feet, and a deep well as over 600 feet.

The shallow depth of the Middle Ranch well field and Thompson Reservoir make them vulnerable to drought. The island has been under water rationing 26 percent of the time since 1966.

Extend the water supply at Middle Ranch and delay the onset of regulatory rationing.

Santa Catalina Island Watersheds

A watershed is a basin-like landform defined by highpoints and ridgelines. All the water that falls in a watershed drains into a larger body of water: an aquifer, a river, a lake, an ocean.

Santa Catalina Island has about 70 individual watersheds – each of which drain into the Pacific Ocean.

The five largest watersheds on the island are: - Middle Canyon (5,700 acres) - Cottonwood (3,229 acres) - Silver Canyon (2,613 acres) - Little Harbor (2,603 acres) - Avalon Canyon (2,551 acres)

#1 Middle Canyon

#5 Avalon Canyon

#4 Little

Harbor

#2 Cottonwood

#3 Silver

Canyon

Avalon

Two Harbors

Middle Canyon 5,700 acres above Thompson Reservoir

Avalon Canyon 2,551 acres

Middle Canyon above Thompson Reservoir is 2.2 times as large in area as Avalon Canyon.

In the 1890’s shallow (alluvial) wells were constructed in Avalon Canyon. Wells constructed too close to the ocean eventually became salty.

In 1904 Avalon Well No. 2 was constructed in the alluvium at the golf course. It is currently pumping about 65 acre ft per year. Today’s health regulations prevent this well from being used for drinking water.

In the 1950’s the Golf Links well was constructed in the bedrock to a reported depth of 990 feet (590 feet below sea level) as a water supply for the City of Avalon.

Wells were constructed into bedrock in the 1920’s for the St. Catherine Hotel. Wells No. 2 and 3 are still in existence and are 85 ft below sea level. They are not known to have ever experienced salt water intrusion, despite producing 25,000 gallons day for over 20 years.

These wells are still functional and produce fresh water, but today’s health regulations for well construction prevent them from being used for drinking water.

There is at least as much groundwater stored in the bedrock aquifer under the Avalon Canyon watershed (more than 1,000 acre feet) as there is surface water in Thompson Reservoir when it is full.

On average, about 300 to 400 acre feet of water per year recharges the Avalon Canyon watershed, but the amount of recharge varies from year to year and not all of that water can be captured by wells in the bedrock and alluvial aquifers.

Avalon Canyon and Middle Creek Canyon have the same rock type (quartz diorite) and similar hydrogeologic properties. However, we can currently only estimate the amount of water that can be pumped from new wells in Avalon Canyon.

Monitoring water levels hourly in 5 existing wells (4 alluvial wells and the Golf Links bedrock well) to evaluate how water levels change in response to drought and precipitation events.

Water quality testing in selected wells to establish baseline water chemistry conditions.

Geophysical studies to assist in determining where to drill potentially productive wells.

Drilling test wells.

Encountered groundwater at about top of bedrock at a depth of about 100 ft.

Drilled to 644 ft below ground surface. Most water was found in a fractured zone at about 460 ft bgs.

Preliminary water production rate about 25 gpm.

Water quality is typical for island with a total dissolved solid content estimated at about 1,000 parts per million.

Results are about what we expected. We are exploring the bedrock aquifer for water.

Complete as a drinking water well by installing well casing according to California regulations.

Conduct a short duration pumping test to determine the well’s water production rate.

Collect water samples, transport to a certified laboratory, and determine groundwater chemistry in the bedrock aquifer.

After completing Test Well AV-BR-1 as a drinking water well, include the well in the Canyon’s automated water level monitoring program. Share data with SCE’s Groundwater Management and Sustainability Program.

Move to Test Well No. 2 site and construct another test boring. Complete as a well if conditions are favorable.

Review results from Test Wells Nos. 1 and 2.

Drill and test additional new wells to determine if they represent feasible conditions for a new water resource.

Conduct additional environmental and engineering studies and determine sustainable pumping rates and annual pumping amounts.

Apply for permits to develop a new municipal water supply.

Establish a groundwater monitoring plan that actively tracks water level and water quality changes in alluvial and bedrock aquifers. Adjust pumping rates and annual quantities to avoid unwanted consequences.

Possible salt water intrusion into aquifers.

Possibly lowering groundwater level in the bedrock aquifer such that it impacts the alluvial aquifer or sensitive ecological areas.

Manage the resource so that only the sustainable amount of groundwater is extracted.

Avalon Canyon receives all freshwater inflow as precipitation. Water imported from the Middle Creek watershed supplies the town of Avalon and is separate from groundwater in Avalon Canyon.

Groundwater and surface water are not entering from other basins and the hydraulic divide between groundwater basins is effectively defined by the topographical (watershed) divide.

Annual precipitation at Avalon (e.g., Pleasure Pier weather station) is very similar to precipitation throughout Avalon Canyon.

Most of the precipitation that falls in the Canyon evaporates into the atmosphere or is intercepted by plants and transpired back into the atmosphere.

Water in the soil flows downward under partially saturated flow conditions. At depths below the root zone, this water flows under saturated conditions and into the alluvial and bedrock aquifers to become groundwater recharge.

The soil depth on sloping (upland) topography is generally only a few feet thick. At the Canyon bottom the alluvium can be over 100 feet thick.

The alluvial terrace south of the golf course was deposited when the ocean level was higher than today. The water storage potential of these deposits is unknown.

Below the soil layers is predominantly quartz diorite bedrock. The shallow bedrock is weathered and fractured with a moderately low permeability and storativity. The relationship of fracture density and depth is undefined in Avalon Canyon. However, the outcrops of bedrock demonstrate that they are well fractured with fractures spaced less than a foot apart.

Avalon Canyon and the side canyons are very linear indicating they are located on large bedrock fractures. These areas are more heavily fractured than the surrounding areas and tend to topographically collect groundwater and provide areas of higher bedrock permeability.

The steep topographic slopes and lower bedrock hydraulic conductivity at depth tends to keep most groundwater flow at relatively shallow depths.

The Tunnel Spring is an example of a perched spring where groundwater reaches land surface because of a low permeability layer below the soil. The water level in the bedrock at the adjacent Golf Links well is about 84 ft below the elevation of Tunnel Spring discharge. The difference in water level elevation of the spring and the bedrock aquifer demonstrates that the spring flow is decoupled from the bedrock aquifer.

Beneath the stream channels there are coarse sediments and fractured bedrock that can transmit significant amounts of groundwater.

The unconsolidated sediments (alluvium) in the valley bottom are very permeable at depths just above the bedrock.

Current groundwater pumping extracts water from the alluvium that is hydraulically connected to the bedrock aquifer; the strength of this connection is undefined.