Planning For The Future With Water Independence Now (WIN)

August 10, 2011  |  Monitoring, Water  |  No Comments

Water Independence Now (WIN)

The Water Independence Now (WIN) program is a series of projects that will fully utilize stormwater and recycled water sources to restore and protect the groundwater resources of the Central and West Coast Basins. In the past, a large percentage of replenishment water came from sources in Northern California and the Colorado River. WIN seeks to completely eliminate this dependence on imported water to ensure the future security of our region by developing local resources to create a locally sustainable groundwater supply.

WIN Projects & Programs

Leo J. Vander Lans Advanced Water Treatment (AWTF) Facility Expansion

The existing Leo J. Vander Lans Advanced Water Treatment Facility began recycled water deliveries to the Alamitos Gap Barrier in 2005. This facility utilizes disinfected tertiary treated effluent from the Long Beach Water Reclamation plant and further treats it to near distilled water quality using advanced microfiltration and reverse osmosis (MF/RO).

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Regional Groundwater Monitoring

Nearly 4 million people in the Central and West Coast Basins depend on groundwater to supply 40% of their water needs. WRD maintains an extensive network of monitoring wells to ensure the safety and quality of this urban supply as part of its Regional Groundwater Monitoring Program.

The Regional Groundwater Monitoring Program consists of a network of nearly 300 monitoring wells at over 50 locations throughout the District. WRD collects nearly 500 water samples from these wells on an annual basis and tests them for over 100 potential pollutants in order to ensure the safety of the water throughout the District.

Rep. Grace Napolitano sponsors bill to fund desalination efforts

July 28, 2011  |  Water  |  No Comments

Rep. Grace Napolitano (D-Calif.) yesterday offered legislation that would fund research into ways to turn sea water into drinkable water.

Napolitano authored H.R. 2664, which would reauthorize the Desalination Act of 1996 and allocate $2 million per year through 2016. That law has funded projects or studies in more than half of the 50 states, Napolitano’s office said. In California, which has been beset by droughts, there have been 38 projects since 1996.

“Desalination is another promising source of water, especially for Western states, and these programs deserve federal support,” Napolitano said in a statement. “If we can continue to perfect the technologies and bring down the cost of producing new water from the ocean, we will have a reliable, drought-proof source of water and a powerful engine for economic growth.

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WRD’s Safe Drinking and Well Profiling Program

July 20, 2011  |  Monitoring  |  No Comments

Today there are over 500 groundwater production wells in the Central and West Coast Basins that deliver water to nearly 4 million people in 43 cities overlying the basins.  Although many of the production wells extract high quality groundwater, some wells require water quality treatment before use due to the slight possibility of human or industrial contamination.

The Water Replenishment District established a Safe Drinking Water Program in 1991 that removes contaminants from groundwater through wellhead treatment.  Untreated water runs through filters and cleaning devices to remove such contaminants before being sent to the distribution system.

To assist water purveyors with their wellhead treatment projects, WRD’s program has provided grants and loans to construct wellhead treatment projects at 19 wells throughout the District.

However, WRD is researching other water quality treatments that are more cost effective than the wellhead treatment system that can be expensive in capital and long-term operational and maintenance costs.

Well Profiling, which has been around for years, is one such technology that shows promise as an alternative or beneficial supplement to wellhead treatment.  The technology determines where the water entering the well is coming from and analyzes the water quality by raising and lowering measurement tools inside the well during pumping and non-pumping conditions.  A water quality profile is then generated to show the flow contributions and water quality information in the well.  If poor water quality is detected in a well zone then that zone can be sealed off so that the well produces higher quality water from the other zones.

Through various case studies, this type of method has proved more cost effective when compared to a full arsenic treatment system.  Check out www.wrd.org for more information on WRD’s Safe Drinking Water Program and Well Profiling Program.

Groundwater Investigations and Water Well Design

July 14, 2011  |  Monitoring, Water  |  No Comments

BOREHOLE GEOPHYSICS FOR GROUNDWATER INVESTIGATIONS AND WATER WELL DESIGN

By: Tony Kirk, Hydrogeologist Email: tkirk@wrd.org

INTRODUCTION

Borehole geophysics is the science of recording measurements of the physical properties of the soil and water in a drilled borehole or well casing. Graphs or logs are generated from the data and are used in various ways to understand the subsurface hydrogeology, to help design water wells, and to address ongoing water supply challenges.

Geophysical logs have been used in these ways for over 100 years largely in the petroleum industry but also in the groundwater field to

supplement traditional data collection methods such as logging soil cuttings and core samples.

Borehole geophysical logging is performed using a tool or sensor suspended on an electric wireline which is raised and lowered within a borehole or well casing from a special spool called a drawworks. Figure 1 shows a cable drawworks mounted in the back of a logging truck. At the drawworks the top of the wireline is connected to logging devices such as a chart recorder or computer with processing software.

BASIC BOREHOLE LOGS

Figure 1 Borehole logging truck with wirleline and drawworks.

water and the drilling fluid. The measurement works best when there is a significant contrast between the two fluids, such as a saline aquifer in a borehole drilled with fresh water mud. In water wells drilled in fresh water aquifers with fresh water drilling mud, there may be little to no contrast on the SP curve.

Resistivity (apparent) is a measure of the electrical resistance or conductance within formations. The resistivity of a formation is affected by its lithology, water quality, and pore geometry. Sand with fresh water will have a higher resistivity than clay with fresh water. Sand with salt water, however, may have a resistivity lower than a fresh water clay since the salt water is highly conductive. Because of the factors influencing resistivity,

the log should not be used on its own to interpret lithology or water quality.

Gamma is a measure of the natural gamma radiation emitted by the formation adjacent to the borehole. The gamma log is affected by the presence of potassium, uranium, and thorium isotopes naturally present in the earth materials. In general, finer grained materials (silts and clays) emit higher levels of gamma radiation than coarser grained materials (sands and gravels), making gamma a useful tool to help determine the lithology of a borehole.

Figure 2 shows a simulated basic geophysical log which might have been collected in the Central and West Coast Basins (CWCB). Generally, resistivity plotting right (increasing), and gamma plotting left (decreasing) indicate permeable aquifer material like fresh watrer sands and gravels indicated by blue layering. Alternatively, resistivity low

The “basic” geophysical logs include spontaneous potential, resistivity, and natural gamma. Individual logs provide limited information by themselves, but when analyzed together with soil cuttings can provide a good interpretation of geologic layers, aquifers, and water quality.

Figure 2

Spontaneous Potential (SP) is a measure of the electrochemical voltage difference between the formation

Basic Borehole Geophysical Log.

and gamma high indicates lower permeability sediments such as silt and clay aquitards shown as tan layers. SP will generally plot similar to gamma, however poor water quality zones are pronounced (yellow layer) while good water quality zones have a muted SP response. The common basic borehole logging tools are shown on Table 1.ADVANCED BOREHOLE LOGS

Transfer of oilfield technology to the water resources field is improving our understanding of the groundwater resources. Beyond the basic logs described above, new logging technology includes techniques to determine porosity and permeability and highly refined versions of the basic logs such as resistivity and gamma. Figure 3 shows some advanced borehole logs used to design and construct a well. Computer processing and analysis of these advanced logs can also produce information on clay mineralogy, grain-size distribution, and hydraulic conductivity. Another advanced borehole log is the Formation Micro-imager which logs geologic structure. Many other specialized geophysical logging tools are available and new ones are being developed. Table 1 lists the common advanced geophysical logging tools used in groundwater investigations and in design of wells.

GROUNDWATER INVESTIGATIONS

Geophysical logs provide continuous vertical records which help with correlation to other locations and input to hydrogeological models. The continuous logs are helpful in generating cross-sections because they can provide subtle details for correlation between boreholes not available from soil samples. Often, borehole logs within a region share a common “signature” which is another correlation technique to match related hydrogelolgic layers or sequences.

WELL DESIGN

Geophysical logs are a powerful tool when designing and constructing monitoring wells and water supply wells. Logs can indicate permeable zones where groundwater flow is substantial and where to place perforated intervals. They can also show poor water quality zones which could be avoided in a production well. Perforations for wells are generally placed where logs indicate greatest permeability and meet desired water quality objectives. For example the blue rectangle plot on Figure 3 shows the greatest continuous free water porosity at depths from 270 to 350 meters based on the combination of logs. This zone might be screened when designing a well.

Advanced borehole geophysical log shows a productive water zone from 270 to 350 meters outlined by the blue rectangle based primarily on calculated hydraulic conductivity (green), supported by high effective porosity (blue), SP, gamma, FMI, Array Induction, and Salinity.

Sources of Information for this Technical Bulletin:

Driscoll, F.W., 1986, Groundwater and Wells, 2nd Edition, Published by Johnson Filtration Systems, Inc.

Heath, Ralph C., Basic Groundwater Hydrology, United States Geological Survey Water Supply Paper 2220, 1987.

Keys, W. Scott, Borehole Geophysics Applied to Ground-Water Investigations, National Groundwater Association, 1989 .

Groundwater Monitoring

February 14, 2011  |  Water  |  No Comments