November 12, 2010 > Water, water... where is it?
Water, water... where is it?
By William Marshak
In the famous poem Rime of the Ancient Mariner by Samuel Taylor Coleridge, an old man who spent his life sailing the oceans relates a tale filled with hope, woe and redemption to a passerby. During his recitation, he speaks of thirst and misery that befell him and his fellow sailors; the famous lines are uttered:
Water, water, everywhere,
And all the boards did shrink;
Water, water, everywhere,
Nor any drop to drink.
Surrounded by a vital substance of life, yet unable to use it was the ultimate irony for these sailors in the late 1700s. This also became a problem for farmers of the Tri-City area in the early 1900s. Demand for water increased and wells began to yield salty (brackish) water from the Bay as it intruded into the natural aquifer beneath the Tri-City area.
Ultimately, this led to creation of the Alameda County Water District (ACWD) with its mission to protect and assure Tri-City residents of safe and adequate resources for current and future use by a growing population. The cycle of water collection and use including watershed and groundwater protection was and remains of paramount importance to ACWD.
In a quest to diversify sources of fresh water, a program was implemented to supplement supplies that arrive through natural means (rivers and groundwater) and pipelines of the State Water Project and Hetch Hetchy. ACWD explored reclamation of brackish water that had intruded into a portion of a natural aquifer called Niles Cone Aquifer. Here, millions of gallons of water are available if cleansed of impurities and unacceptable salt content.
Seawater had, at one time, intruded as far as the Hayward Fault due to excessive pumping. Connections between the upper aquifer (30-100 foot depth) and lower aquifer (several hundred feet) provided seawater access to this semi-isolated area as well. In the upper aquifer, fresh water from Alameda Creek that percolates into the ground at Quarry Lakes helps "push" underground brackish water toward the bay. However, the lower level of brackish water is separated from the bay and cannot move unless it is pumped away.
What is termed the "Aquifer Reclamation Program" addresses this dilemma. ACWD wells connected to Reverse Osmosis (RO) facility reclaim lower aquifer brackish water and make room for fresh water in those spaces. Although brackish water had been pumped from the lower aquifer for decades prior to construction of the desalination plant, the water was discarded through flood control channels. As the idea of desalination took root, severe drought years of the 1970s (the driest year on record was in 1977) provided an impetus to act.
Reverse Osmosis coaxes water to move through a membrane that traps impurities and salts and allows reclamation of brackish water trapped in the lower aquifer for human consumption. Fresh water that percolates from the surface can then replace the brackish water. A desalination facility in Newark using RO became operational in 2003 and recently, ACWD announced that it has doubled its capacity.
According to Assistant General Manager - Engineering Robert Shaver, the original capacity of the desalination plant was about five million gallons per day although practically, the amount of water available though this process was about three and a half million gallons per day. This represented approximately five percent of overall demand.
Over the past several years, Shaver says, "we essentially doubled its capacity." Capacity of the desalination facility is now at twelve and a half million gallons per day - 10 million gallons of "permeate" and two and a half million gallons of "blend around" water from other sources. This creates an additional local high quality water supply which is dependable, cost effective and locally controlled; approximately 10-15 percent of overall supply.
The purity of water that results from RO is based on the degree of filtration used. "Micro" filtration removes bacteria and pathogens. "Ultra" filtration, the technology employed at the Mission San Jose plant, is capable of removing virus size impurities; beyond that is "Nano" filtration. At the Newark facility; the total dissolved solids are reduced to "very low levels" which means that in order to manage taste and introduce some mineral content, it is mixed with water from other sources before delivery to ACWD customers.
Is this a limited supply? Shaver says that the volume of brackish water that can be accessed through ACWD wells is more than sufficient. He notes, "Within the design life of the desalination facility, there is more than enough brackish water to operate this for the foreseeable future."