Well Schooled on Los Osos

By D. CAMERON RIPLEY

As a student, I have the luxury of reading wastewater engineering textbooks and using them as sound and conservative engineering information without allowing politics to influence the outcome. In commenting on the Los Osos wastewater treatment dilemma, I want to focus on the facts.
    In March 2007, the latest textbook on water reuse issues, technologies, and applications was released. The title of the textbook is “Water Reuse.” Dana Ripley’s design (STEP collection/treatment/storage/reuse) for a wastewater treatment system for housing developments and small communities is published in the textbook, the same design he is proposing for Los Osos. 
    The collection systems portion of the book describes gravity collection as having a high installation cost and “issues with nonwatertight joints and damaged sections result in potentially high volumes of inflow and infiltration, or exfiltration…which may result in groundwater or surface water contamination.” In the same paragraph, it comments on STEP collection by saying “flexible plastic piping is much less likely to leak…and can be installed easily by directional drilling that results in minimal disturbance to property and roads.”
    “Water Reuse” was authored by the top wastewater professionals in the world, including Prof. George Tchobanoglous. “Water Reuse” is considered the bible for wastewater management systems by engineers and will be a valuable textbook for undergraduate and graduate students in the field of environmental engineering. 
    Also cited numerous times in “Water Reuse” is Bahman Sheikh, a consultant on the Ripley Pacific Team, who is world renowned as a water reuse specialist. Dr. Sheikh was the lead in the first large-scale study designed to investigate the health risks and other effects of irrigation with reclaimed water on food crops that included raw-eaten vegetables. The study was conducted in Monterey County, which is under the same RWQCB jurisdiction as Los Osos. Similar to Los Osos, Monterey County’s intensive groundwater withdrawal resulted in depletion of groundwater levels and seawater intrusion. Dr. Sheikh’s research work for the Monterey Regional Water Pollution Control Agency is considered a milestone for water reuse projects and studies.
    In the textbook, “Small and Decentralized Wastewater Management Systems,” also co-authored by Prof. Tchobanoglous, gravity collection is regarded as an obsolete technology in the “not-so-distant future.”  The textbook was published nine years ago.  The name “gravity collection” creates a large popular misconception that the collection system is all gravity under all conditions. Gravity collection, especially in topographic conditions similar to those in Los Osos, requires lift stations that have pumps lifting sewage to a high point and then gravity feeding it to a lower point in elevation. This process is expected to be repeated about 20 times in Los Osos, if gravity collection is finally selected. These lift stations are extremely energy-intensive compared to the many small pumps used in STEP collection.
    At the Water Environment Federation Technical Exhibition Conference (WEFTEC) in October 2006, Metcalf & Eddy Inc. engineers presented their evaluation document on membrane bioreactor (MBR) technology. The title of the evaluation is “Energy Usage & Control at a MBR Facility.” The engineers consider MBR treatment use on facilities of 15 mgd and more. The community of Los Osos requires a treatment facility suited for 1 mgd. The evaluation continued to say, “as utility agencies consider MBR treatment, they may tend to overlook its high energy requirements for its obvious benefits. MBR facilities require a high commitment of energy, and are often the most energy-intensive biological treatment process.”
    Broderson leach fields continue to be a topic of discussion for the TAC meetings I attend. The vendor intending to manufacture the plastic chambers for the Broderson leach field did so for another community in Wyoming with about the same size effluent disposal site. According to the vendor, the basic footprint is the same for both. Different soil characteristics change the way plastic chambers are installed, within a limited range of the application flow rates. So, the same amount of treated effluent would be applied to about the same effective width and length of soil area. Under design specifications, the vendor cited the flow rate as 45,000 gpd for the Wyoming leach field. The Tri-W/MBR/Broderson design intended 810,000 gpd. Even at half the flow, 405,000 gpd far exceeds what is specified. The Broderson design relied on an unrealistically high infiltration rate due to the use of the 1981, “EPA Process Design Manual for Land Treatment of Municipal Wastewater.” The EPA 1980 or EPA 2002 manuals for application rate determinations for either leach fields or infiltrator chambers are the necessary manuals required to assess the proper infiltration rate.
    There were more, other than those stated above, practical reasons for why the Tri-W project was halted. There were major engineering errors in the design of the system. Just to name a few; it did not account for a reverse osmosis component required to meet discharge requirements (DHS, Title 22), it did not account for cement in construction costs, and the final project report was not stamped by a licensed engineer.
    I cannot speak on behalf of Los Osos citizens for the last 30 years, but I can for the last five. My experience with Los Osos citizens has been intriguing. They are a knowledgeable and well-educated community that deserves an affordable and sustainable wastewater treatment system.