The Cupertino Sanitary District (CSD) recently underwent significant equipment upgrades at its lift stations, as well as benefiting from a number of other proactive measures. The district's submersible pumps now operate with a new type of impeller designed to virtually eliminate blockages. These enhancements will allow the district to experience continued reductions in operating costs.
Prior to this upgrade, an emergency crew dispatched to a clogged station typically cost CSD up to $1,000 per incident, which occurred almost monthly at one or more stations, according to Dave E. Ross, P.E., the manager-engineer of the utility.
During the year following the pump retrofit program, the utility saved several thousand dollars by preventing all but one blockage. Additional energy savings are being realized due to the suspended high operating efficiency offered by the new pumps.
CSD serves 52,000 South Bay residents within a 15-sq-mile area approximately 35 miles outside of San Francisco. The 21,000 service connections extend throughout the city of Cupertino and parts of Saratoga, Los Altos, Sunnyvale and unincorporated Santa Clara County.
The system conveys approximately 5 MGD with a combination of gravity lines and pumps to the 143-MGD San Jose/Santa Clara Water Pollution Control Plant.
CSD presents an early example of privatized management of a wastewater utility service. Instead of directly employing administrative, engineering and field labor, the district has contracted since 1956 with Mark Thomas & Company, Inc.--a multidisciplinary engineering and management services firm--for the overall planning, engineering and administration of the operations. Whenever the firm is brought in, Mark Thomas & Company assigns eight, full-time field inspectors and office personnel, including Ross, and contracts out any repair, maintenance or construction projects.
"The arrangement has worked very well here," noted Ross. "The staff is kept to a minimum, the need for major field equipment eliminated, and competitive pricing and productivity seem more assured by contracting out our projects. These have all contributed to reasonable rates as the population increased within the service area."
He is equally proud of the district's environmental compliance record in a state that has some of the nation's toughest regulations. California regulators deal harshly with spills or bypasses, scrutinizing every detail, from the prompt filing of reports to the measures implemented to prevent and correct any incidents.
In addition to penalties imposed on the districts, their management can face personal fines or even jail time where negligence has contributed to violations of the state's environmental protection statutes.
This makes the reliability of the lift stations a high priority for CSD.
During the past 46 years, the district's infrastructure investment has evolved into one million feet of line, ranging from 8 in. to 27 in. interceptors, 14 lift stations, and ongoing technology additions to remotely monitor and effectively manage the operations.
"The more recent investments include GIS technology compatible with that used by the city of Cupertino. This will facilitate joint planning," Ross noted.
The older vitrified clay lines are cleaned of roots on a schedule of six-month or annual intervals. This utility has since adopted polyvinyl chloride plastic pipe (C-900, SDR-26 and SDR-11) to eliminate joints that inevitably invite root intrusions into the clay lines.
Still in the planning stage is a collaborative initiative with the area's many restaurants to regulate grease haulers and stop them from dumping loads into CSD's manholes.
The utility has also become better equipped to provide itself with emergency power. This includes 10 emergency backup generators initially bought as safeguards against potential power outages. Some additional units were added with the concern over Y2K outages and to cope thereafter with the rolling blackouts that plagued California a few years ago.
Four of the six trailer-mounted, 25 KVA units have been wired since then to automatically start during an outage.
"Taking the action a step further, the district plans a redundant pump station with a separate power source as a disaster backup for lift stations located close to major streams," Ross said.
The lift stations were built to overcome the rolling topography that runs perpendicular to the lines to the distant regional treatment plant. The utility began building pumping facilities in 1970 as the city of Cupertino grew concentrically outward into the hills and could no longer operate solely with gravity lines. CSD now has three, 600 to 1500 gpm dry wells; two stations equipped with small, 25 gpm package units; and nine others rated at 50 gpm to 300 gpm.
"The $19,600 N-pump impeller upgrade program involved nine locations in May 2001 and still had effectively prevented any further blockages well over a year after the improvements," Ross said.
Of the nine stations that received the ITT Flygt N-pump impeller upgrades, only one had experienced a blockage by the summer of 2002. The incident involved an older two horsepower unit with little torque to overcome a particularly thick sock.
This problem-prone station had a previous record of clogging every two to three months.
Honored with several engineering awards, the new technology from ITT Flygt benefits from a self-cleaning channel impeller that is innately less susceptible to the fouling that eventually causes blockages. CSD could also experience improved energy efficiency at the stations.
In field tests where recurring blockages had been an issue elsewhere, the ITT Flygt innovation not only eliminated clogging but also is delivering power savings throughout the expected service life period of over 50 years.
ITT Flygt attributes this to the unique design of the semi-open, screw-shaped impeller that maintains unobstructed leading edges of the vanes where fouling normally leads to higher energy usage and clogging.
With the new design, each leading edge of the rotating impeller passes across a sharp stationary relief groove located in the pump suction. The dynamic action shears, cleans and pumps away any rags, stringy materials or solids from the impeller without any loss in hydraulic efficiency.
"In the past, we had to pull the pumps at one of our eight stations at least once a month," Ross explained. "That's not even an issue anymore. We've gained improved reliability and even a safety advantage. Fewer blockages mean less frequent exposure of our employees and contractors to vehicle traffic and three-phase, 230-volt electrical service at the stations."
"These and other maintenance measures are expected to extend the service life of key components within the district's system to perhaps 100 years," Ross concluded.
For further information, phone 203/380-4700.
