Forgotten Facilities: The City of Pasadena Tri-City Sewage Treatment Plant – Part 1

Nicholas Pinhey, CWEA History Committee, History, Resource Recovery, Technology and Innovation

“Forgotten Facilities” The City of Pasadena Tri-City Sewage Treatment Plant

Note: this is a first part of a series on the City of Pasadena’s Tri-City treatment plant and the CSWA.  Part I provides the background on how the plant was developed.  Part II will provide information on the CSWA conference tours, the plant-of-the-year award, and  technical presentations related to the Tri-City treatment plant.

The history of the City of Pasadena’s Tri-City wastewater (sewage) treatment plant is closely tied to the early history of CWEA, from the Association’s founding in 1928 until 1948, when the plant was decommissioned and the Tri-City system connected to the Sanitation Districts of Los Angeles County (LACSD) system. 

As the Chair of the CWEA History Committee, I first became aware of the City of Pasadena’s “sewage treatment works” while researching the development of wastewater collection and treatment in California during the 19th and 20th centuries.  Later, while reviewing early Association documents, I noted technical papers, conference tours, citations and articles about the City of Pasadena’s sewage treatment plant. In fact, numerous articles and papers about the Pasadena plant were published in the California Sewage Works Association Journal, the Federation’s Sewage Works Journal, the Engineering News-Record and a variety of municipal journals, construction periodicals and public health journals from the first half of the 20th century.  These articles and papers intrigued me because I was not aware that the City of Pasadena and its Tri-City partners had operated a wastewater treatment plant – I had assumed the Pasadena/South Pasadena/Alhambra wastewater systems were always served by the LACSD treatment facilities.  I was also intrigued by the fact that the City of Pasadena’s Tri-City sewage treatment plant was CWEA’s (CSWA’s) second plant of the year (1930), two of the plant staff were charter members and leaders of CSWA (1928) and that the plant superintendent (William Allen) served as CSWA president in 1932.  Finally, film footage of the 1930 CSWA conference tour of the Pasadena Tri-City plant “sealed the deal” for me – it was time to find out more about this somewhat “forgotten facility” and its relationship to the CSWA.




A Brief History of the City of Pasadena’s Sewage Treatment Works
The “Sewer Farm” Years, 1887 to 1914

Understanding of the background history of the “modern” (1924-1948) Pasadena Tri-City sewage treatment plant is helpful because it illustrates of many of the issues and problems that were faced by many growing communities in California during the early 20th century. 

In 1887, the City of Pasadena purchased 320 acres of land southwest of the City (now the site of the City of Alhambra’s Almansor Park) to establish a “sewer farm” and utilize “broad irrigation” to treat sewage (Figure 1.)1. In 1892, after five years of construction, the City of Pasadena’s sewage collection system was connected to the sewer farm and an additional 200 acres of land were added to the farm expand the farm operation.  Initially 60 acres of the sewer farm were planted in English Walnuts (later expanded to 114 acres of walnuts) and 50 acres were planted in orange trees (Figure 2.). The balance of the Pasadena sewer farm acreage was used to grow alfalfa, barley, wheat, hay and pumpkins, with alfalfa being the main crop.2

During the first years of its operation, the City of Pasadena sewer farm was relatively isolated and had few operational problems – overall, the sewer farm was characterized as successful in the journal articles and sewage treatment textbooks of the early 1900’s.  However, the development of neighboring orange groves and residences, particularly in Alhambra to the west and northwest and San Gabriel to the east, soon began to encroach on the Pasadena sewer farm.3 The encroaching development became problematic for the sewer farm as it was difficult to avoid creating odors while farming alfalfa because it was impossible to cultivate between the applications of raw sewage for irrigation.  In the early 1900’s, the City began to receive odor complaints about the sewer farm.  In response, the City of Pasadena installed a 2 million gallon septic tank on the outfall line (Garfield Avenue outfall) to the sewer farm in 1910 to pretreat sewage prior to irrigation.4, 5  A sludge disposal line from the new septic tank to San Pasqual Wash was also installed in 1910.6

Figure 3. Imhoff Tank (background) and Sludge Draw-off Basin at Pasadena Sewer Farm, 1917 (Pasadena Public Library Collection)

Figure 3. Imhoff Tank (background) and Sludge Draw-off Basin at Pasadena Sewer Farm, 1917
(Pasadena Public Library Collection)


A second outfall (the Allen Avenue outfall) to the sewer farm was constructed in 1913 to accommodate growth in Pasadena.  An Imhoff tank for treatment prior to irrigation was also constructed at the end of the second outfall along with another sludge disposal line to San Pasqual Wash (Figure 3.). The Imhoff tank was sized to treat the sewage of 2,500 people and its effluent was applied to the northeastern 40 acres of the sewer farm. This was initially found to be a satisfactory alternative to the land application of raw sewage.7

The improvements at the Pasadena sewer farm, while judged to be satisfactory by some observers, did not totally eliminate the odor complaints about the sewer farm operations.  Additionally, the disposal of sludge to San Pasqual Wash created problems and the State Board of Health received its first complaint about this practice and its negative impact on a neighboring dairy farm in 1913.8  Complaints about the sewer farm operations increased and in 1914 the City of Pasadena Commissioners, anticipating legal action against the City, decided it was time to take action.9

Moving Quickly to Find a Solution to the Sewage Problem 1914-1916

Report of the Board of Engineers Sewage DisposalThe Cities of Pasadena, Alhambra and South Pasadena decided the best long-term course of action for solving the future sewage treatment needs their growing cities, as well as addressing the ongoing encroachment of growth and development near the Pasadena sewer farm, would be the development of a regional treatment and disposal facility at a new location.  The idea of regional sewage treatment and disposal came up when the City of South Pasadena completed its sewer collection system improvements in 1914 and requested permission to connect to the City of Pasadena’s Garfield Avenue outfall for treatment and disposal at the Pasadena sewer farm.  The outfall had been constructed with excess capacity and could serve South Pasadena and also portions of Alhambra. The outfall pipeline passed through the City of Alhambra and, per the sewer agreement between Alhambra and Pasadena, Alhambra was also required to approve South Pasadena’s request to connect.10 Discussions between the three cities resulted in a contract between the Cities of Pasadena, Alhambra and South Pasadena to find a joint solution for the long-term treatment and disposal of sewage. The three cities executed the joint contract in December 1914 and a board of engineers, consisting of the city engineers for the three cities, was appointed the following month for the purpose of developing a recommended plan for the regional treatment and disposal of sewage.11

The board of engineers approached the problem in three steps; first they identified and analyzed the available treatment process alternatives and second, they identified and analyzed the effluent disposal alternatives. The recommended treatment process alternative and disposal alternative were then used to develop the recommended plan.  In summary, the board of engineers report identified the following alternatives:


  • Imhoff tanks (with sprinkling filters and secondary clarification)
  • Broad irrigation
  • Intermittent sand filtration
  • Contact beds
  • Activated sludge

Effluent Disposal

  • Outfall to the ocean
  • Discharge into the Rio Hondo River
  • Agricultural irrigation combined with disposal to a wash

The costs of construction, operations and maintenance, plus the future costs for expansion (based on growth projections over a 40 year period) for each alternative were taken into consideration during the analyses by the board of engineers.  Amazingly, the board of engineers study and report was completed in 14 months and included preliminary plans, designs, estimates of costs and a recommended cost-sharing arrangement between the three cities.

After careful consideration of the alternatives, the board of engineers recommended that the sewage from the three cities be treated by the “tried and true” process of using Imhoff tanks, sprinkling filters and secondary clarifiers (a typical treatment process for the era) and that the effluent be used for agricultural irrigation and discharged to a wash when not needed for crops. Chlorination (gas or hypochlorite) was recommended by the board for effluent disinfection.12

It should be noted that in 1916 activated sludge was a relatively new treatment process in the U.S. (the first activated sludge plant in California was constructed at Folsom State Prison in 1917).13  The new activated sludge process, while viewed by the board of engineers as impressive in terms of treatment effectiveness, was considered to be too costly due to the need for more operational oversight and increased electrical energy costs when compared to other alternatives. The board of engineers also considered using activated sludge to be a risk due to the uncertainties associated with the new process (such as the impact of winter temperatures on treatment efficiency).14  


Figure 4. Imhoff Tanks and Sprinkling Filter Plan for Reppeto Ranch Site, 1916

Figure 4. Imhoff Tanks and Sprinkling Filter Plan for Reppeto Ranch Site, 1916

The board of engineers also recommended that 1,000 acres of land south of the City of Pasadena sewer farm be purchased to implement the recommended treatment and disposal plan.

Per the board of engineer’s recommendation, the Tri-City partners approved the purchase of 600 acres of land identified by the board of engineers and known as the Reppeto Ranch. The ranch was located south of the existing Pasadena sewer farm and north of Whittier Boulevard (approximately 1.5 miles south of the City of Alhambra’s city limit in 1916). The Reppeto Ranch land acquisition process was actually completed prior to the publication of the board of engineers report due to the need to secure the land and move quickly towards a solution. It was felt that the additional 400 acres needed to accommodate projected growth could be acquired by the Tri-City partners at a later date.


Not in my Backyard!

The Tri-City partners applied for a permit from the State Board of Health for the proposed Imhoff tank/sprinkling filter treatment plant in May 1916. Immediately, the residents in the vicinity the Reppeto Ranch organized to oppose the proposed treatment plant and the residents in the unincorporated areas of Montebello and Ramona Acres incorporated into the City of Monterey Park in November 1916 (an early example of “NIBYism”). The newly formed City of Monterey Park quickly passed an ordinance prohibiting sewage treatment facilities within the City limits.15  This ordinance effectively defeated the proposal to build the new plant as the majority of the ranch land for the proposed Tri-City sewage treatment plant was within the corporate limits of the new City of Monterey Park.

As part of the opposition to the proposed treatment plant at the Reppeto Ranch, the residents in the area also presented the Los Angeles County Board of Supervisors with an affidavit that stated that odors from a modern sewage treatment plant “were known to kill” within a range of “4 miles” from the plant.  This information on the “toxicity” of odors was said to be related to the operation of the Atlanta Georgia treatment plant which used an Imhoff tank/sprinkling filter treatment process similar to what the Tri-City board of engineers had proposed.16

In 1916, partly to counter the allegations of toxic odors, T.D. Allin, Pasadena’s Commissioner of Public Works, and R.V. Orbison, Pasadena’s City Engineer, embarked on a seven week trip in across the United States to inspect major municipal sewage treatment plants and review the latest sewage treatment technologies.  The municipal treatment plants they visited included those serving the cities of Chicago, Boston, Houston, Atlanta, Baltimore, Philadelphia Cleveland, Rochester, Milwaukee, and several more.17  Allin and Orbison’s findings debunked the “toxic odors” allegations, but more significantly, the activated sludge facilities they visited impressed the two with its flexibility and treatment efficiency when compared to Imhoff tanks and sprinkling filters – they found it “was getter better results than any other process known.”18 It was this favorable impression of the activated sludge process that influenced the next steps in finding a solution to the Tri-City partner’s sewage treatment and disposal problem.



“Back to the Drawing Board”
Finding a Second Solution to a Growing Problem 1917-1924

The 1917-1924 period was not an easy time for the City of Pasadena and its partners.   Increased flows and loadings to the Pasadena sewer farm due to growth led to numerous complaints that were filed with the State Board of Health.  Additionally, the City of San Marino connected to the Pasadena system during this period, thus contributing more loading to the Pasadena sewer farm. Complaints were filed regarding problems with sludge discharges from the sewer farm, odors, raw sewage run-off into surface waters and raw sewage ponding both on and off of the farm site.  A 1920 State Board of Health investigation showed there were more homes in the vicinity the Pasadena sewer farm than any other sewer farm in California, which, no doubt, increased the volume of complaints during this period.19 The Tri-City partners were faced with a situation that required immediate attention.

When it came to finding a second solution to the sewage problem, the Tri-City partners were left with very few alternatives due to the elimination of the Reppeto Ranch as the preferred treatment and disposal site.  An ocean outfall was not feasible for multiple reasons and attempting to locate another plant site south of the three cities was virtually impossible.  Legal action to overturn the Monterey Park ordinance was considered, but discarded.20 One alternative that appeared to be the most attractive was to continue using the Pasadena sewer farm site as the sewer collection systems for the three cities were already “plumbed” to the site and the sewer farm had existing operating permits for on-site disposal.  The scenario of reusing the existing sewer farm included using “highly treated” effluent for irrigation on the farm and discharging excess treated effluent to the Rio Hondo River.21 The key to the successful continued use of the existing site would be finding a treatment and disposal process that would not create nuisance conditions for the sewer farm’s neighbors and be economical to operate.

The Tri-City partners began testing both activated sludge and sprinkling filters at the sewer farm in 1917 (after the defeat of the Reppeto Ranch project) to determine if these technologies could eliminate or reduce the odor and sludge handling issues.  A 50,000 gpd activated sludge pilot plant was constructed under the direction of the City of Pasadena’s City Engineer to test the process.  The pilot plant aeration tank was 20 feet by 9 feet and 10 feet deep with two partitions that created a 60 foot long continuous channel. Two settling tanks were also constructed along with a re-aeration tank (Figures 5 & 6).  The aeration tank was equipped with 21 “Filtros” plate diffusers and the re-aeration tank was equipped with 4 Filtros diffusers and air was supplied by a turbine blower (Figure 8). The tests were conducted using both fill and draw initially and continuous flow after the activated sludge was established.22 A grit chamber and “rag picker” were designed by the City of Pasadena’s Assistant City Engineer and constructed to improve the process, however, while the rag picker was very successful, the solids settling in the grit chamber would become septic (even with multiple daily cleanings) and the chamber was eventually filled with concrete (Figure 9)23.

The pilot testing indicated that activated sludge would be the most promising treatment process alternative. The initial tests produced a 99 percent reduction in sewage strength and the construction cost for full-scale plant (3 MGD) was estimated to be half the cost of an Imhoff tank/sprinkling filter plant of the same capacity.24

In 1919, the City of Pasadena constructed a second activated sludge pilot plant designed by the L.C. Trent Engineering Company of Los Angeles to test a refinement of the conventional activated sludge process (Figure 10).  This “Trent Process” activated sludge pilot plant was larger than the earlier pilot plant using three aeration tanks and one settling tank. The Trent process, which utilized a unique aeration and pump recirculation system, was found to be “too erratic”, was “not stable” and required “too close attention”, especially “when compared with the old (pilot) plant”. It was also determined that the older activated sludge pilot plant produced a better quality effluent.25

Interestingly, the City of Pasadena assessment of the Trent Process was most likely accurate.  A Trent Process activated sludge plant constructed by the City of Turlock in 1921 and was found to be failing by the State Board of Health in 1924 due to the lack of operational oversight. The State Board of Health subsequently revoked the City of Turlock’s permit to operate the plant and the Trent Process treatment plant was replaced by the City.26

Based on the 1917 pilot plant test results, conventional activated sludge was the process selected for the new Tri-City sewage treatment plant, along with the proposal to discharge treated disinfected effluent to the Rio Hondo and also use it for irrigating the existing sewer farm site. With this determination made, the City of Pasadena moved ahead quickly with the plant design and financing.  The formal application to construct the Tri-City sewage treatment plant on the Pasadena sewer farm property was submitted the State Board of Health on October 3, 1922.  The permit was granted by the Board on November 4, 1922 and construction of the new plant was started by the City of Pasadena on November 16, 1922.  The new 3 MGD Tri-City sewage treatment plant was completed and placed into operation on January 4, 1924 – just 13.5 months after the start of construction.27

Sewage Treatment Plant

The completion of the Tri-City plant in 1924 was the start of modern regional municipal wastewater treatment and disposal for the area (the LACSD activated sludge plant was completed and placed into operation in 1928).28 The Tri-City plant start-up was not easy, mostly due to the newness of the process and the unfamiliarity of designers, equipment suppliers and operators with activated sludge.  The issues faced by the plant operations and maintenance staff during the start-up became the topic of one of the first CSWA published technical papers and conference presentations.  Part II of this series will present the details of the operations of the “new” treatment plant.

Continue reading about the TriCounties treatment plant in part 2 >

  1. Wood, J.W., Pasadena Historical and Personal, (Pasadena: Wood, 1917) 497-498.
  2. Wood, 497-498.
  3. Ibid.
  4. Goudey R.F., In the Matter of the Application of the City of Pasadena to Construct Sewage Works Serving the Cities of Pasadena, South Pasadena, Alhambra and San Marino, Findings and Opinion (CA State Board of Health, 1925) 6.
  5. Wood, 1917, 498.
  6. Goudey, 1925, 6-7.
  7. Goudey, 1925, 7.
  8. Ibid.
  9. Wood, 1917, 498.
  10. Allen, William, Historical Background, 1940
  11. Goudey, 1925, 7-8.
  12. Report of the Board of Engineers, Sewage Disposal, to the Cities of Pasadena South Pasadena and Alhambra, Los Angeles County California (1916), 15.
  1. Report of the Board of Engineers (1916), 16.
  2. California Sewage Plants are Neglected (Engineering News-Record, December 13, 1917) 1127.
  3. Orbison, R.V. and Allin, T.D., How other Cities in the United States are Disposing of Their Sewage (San Francisco, Pacific Municipalities, 1917) 62.
  4. Orbison, 1917, 61-74.
  5. Orbison, 1917, 74.
  6. Goudey, 1925, 13.
  7. Goudey, 1925, 10.
  8. Goudey
  9. Orbison, R.V., The Activated Sludge Experiments at Pasadena, Cal. (Engineering and Contracting, January 8, 1918) 36-37.
  10. Orbison
  11. Orbison
  12. Orbison, R.V., The Trent Activated Sludge Devices at Pasadena (Engineering News-Record, December 30, 1920) 1286-1287.
  13. Turlock cites
  14. Goudey
  15. Rawn AM