Mocho Subbasin facts for kids
The Mocho Subbasin is the biggest underground water area in the Livermore Valley watershed. This watershed is a region where all the water drains into one main river or lake. The Mocho Subbasin is located in Northern California.
This underground water area has borders. To the west, it's next to the Livermore Fault Zone. To the east, it's next to the Tesla Fault. A fault is a crack in the Earth's crust. Some underground water can flow across these faults. However, the water flow is not continuous deep down. It stops below 50 feet (about 15 meters) across the Tesla Fault. It also stops south of the Arroyo Mocho channel across the Livermore Fault.
Rivers and streams on the surface in this area include Arroyo Valle and Arroyo Seco.
Understanding the Underground Water Layers
To the north, the Mocho Subbasin touches the Tassajara Formation. This is a type of rock layer. No underground water moves between these two areas.
Underground water in the Mocho Subbasin generally flows from the southeast to the northwest or north. This matches how the land slopes. It also matches the slope of the water table. The water table is the top level of the underground water.
Shallow underground water, which is not held in a confined space, is found close to the surface. It can be within 25 feet (about 7.6 meters) of the ground. Deeper water is held in confined spaces. This water is found at different depths. It can be from 75 feet (about 23 meters) to 150 feet (about 46 meters) below the surface.
Water Quality in the Subbasin
The quality of the water in the Mocho Subbasin is generally good. This is true for things like sodium bicarbonate and magnesium bicarbonate.
However, there is a concern about the water quality. The amount of total dissolved solids (TDS) is increasing. TDS means all the tiny bits of minerals and salts dissolved in the water. If this trend continues, the water might not be safe to drink by 2020. This is because more people are living in the Livermore-Amador Valley. More people can lead to more salts getting into the underground water.
Geology and Fault Lines
This underground water area is near the Greenville Fault. This fault is part of the Diablo Range. The Greenville Fault is known for having earthquakes.
In fact, a part of the Greenville Fault is named after this area. It's called the Arroyo Mocho Segment. This segment is the second one from north to south. Scientists believe the Arroyo Mocho Segment is older and more developed. Other parts, like the Marsh Creek-Greenville Segment, are newer.
