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CITY OF SANTA ANA Well No. 32 Nitrate Mitl9ation and Rehabilitation Study 3.2.2 Blending in Memory Lane Pressure Reducing Facility A second alternative is to blend water at the Memory Lane Pressure Reducing Facility. The ground water pumped by Well No. 32 would be mixed with ground water with lower nitrate levels from the City's easterly wells. The pressure reducing station currently takes water from the City's higher easterly zone and breaks pressure to serve the lower zone west of the 5 Freeway. The City reports that the ground water from the higher zone has a nitrate level of approximately 10 mg/L. In order to maintain a pumping rate of 2,500 gpm from Well No. 32 a flow rate of 6,100 gpm is required in order to achieve half of the MCL. This results in a net flow rate of 8,600 gpm. The existing pipe size is 16- inches in diameter. This flow rate results in a velocity of 13.7 feet per second; higher than what is typically designed for in the industry. A velocity such as this results in increased pumping costs due to higher head loss in the system and can also begin to cause damage to traditional cement and mortar lining systems. In addition, it is also unknown if the City's system has the capacity to send 6,100 gpm from the higher zone to the lower zone. In lieu of pumping 2,500 gpm from Well No. 32, a lower pumping rate may be selected. Using a velocity of 5 feet per second within the existing 16 -inch pipeline, the required flow rate blending ratio between Well No. 32 and the Memory Lane Pressure Reducing Facility is 1,400 gpm and 3,600 gpm respectively to achieve a nitrate level of half of the MCL. This results in the production out of Well No. 32 being reduced by over 40% when blending is required. There is also a concern regarding mixing time at this location. The nearest customer to be served by this blended water is located approximately 100 feet from the pressure reducing facility. Without the benefit of a water model of the City's system, it is recommended that the blending of the waters be agitated through the use of a static mixer installed as part of the piping in order to blend the water. The efficacy of this will need to be further studied. In order to convey the flows to the Memory Lane Pressure Reducing Facility approximately 3,100 feet of new 16 -inch diameter pipeline would need to be constructed as shown on Figure 1. From Well No. 32 the new pipeline would head southerly in Westwood Avenue then east in Memory Lane to the end of Memory Lane alley terminating at the Pressure Reducing Facility. Summarized below are design issues that would need to be addressed in regards to this alignment selection: Memory Lane Alley: Approximately 30 -feet wide Residential area with garage access for many houses. All houses are fronting other streets • Trash collection performed in the alley Existing utilities — 16 -inch water — 30 -inch sewer — Overhead utilities Memory Lane: • Four lanes (two lanes in each direction, transitions to one lane east bound and two lanes west bound at Lowell. Traffic is mostly residential traffic. Raised median with mature trees east of Westwood • Existing utilities — sewer — water — overhead utilities FT0059A0086\9.& in n.,\05 \_We11-32-Nilw, Min,ationT.fl Re,odV)21ax15 1 _2� TETRA TECH