MAGNOLIA RANCH SPECIFIC PLAN

Transcription

1 TECHNICAL MEMORANDUM DOMESTIC WATER MAGNOLIA RANCH SPECIFIC PLAN Prepared by: MHM Incorporated 1204 E Street, P.O. Box B Marysville, California August 21, 2012

2 Domestic Water Technical Memorandum Page Introduction 1.0 Water Distribution and Supply As part of the Magnolia Ranch Specific Plan Area (MRSPA), a domestic water system is required to provide water to the proposed residential development. The project will include the construction of numerous new domestic water wells, storage tanks and a looped trunk line system. This planning effort will be undertaken to ensure water system capacity for existing and future customers. The supply and maintenance will be provided by most likely Olivehurst Public Utilities District (OPUD). OPUD uses ground water sources to provide domestic water. Overall the domestic water system for the Magnolia Ranch project will be a standalone system capable of serving the project without outside water sources. All the improvements will become the property of OPUD. This memorandum will be followed by a more detailed technical analysis report. All of the improvements will be constructed in accordance with District (OPUD) and Yuba County Standards. The improvements will be constructed and financed by the developer as part of the development roadway improvements. No certificates of occupancy shall be granted until all necessary improvements have been constructed and are operational Goals of the Analysis This Pre-Design Analysis has been prepared for use as an aid in determining new water infrastructure. The intent of this analysis is to review and to assess existing information and to determine possible infrastructure improvements. The goals of the analysis are as follows: Collect and review existing infrastructure Determine the geometric and hydraulic design parameters Prepare design calculations and schematic design Prepare Conceptual Design 1.30 Design Criteria The design of a domestic water system depends on many factors, some of which can be measured with a fair degree of precision and others which rely upon engineering judgment. This section of the report discusses the parameters required to design a domestic water system acceptable to OPUD and the MRSPA. The project must be both technically and economically feasible. A domestic water system has six major elements as follows: 1. A source or sources of supply. The source will be underground (wells) regardless of the service provider. Storage tanks are used to insure an adequate supply for emergencies or when maintenance on a well is required.

3 Domestic Water Technical Memorandum Page 2 2. A means of testing the purity of the water and treating it as necessary to assure its potability. 3. Water mains to interconnect the sources of supply and the storage tanks, and to connect them with the local distribution systems enabling the local distribution networks to draw from alternative sources when necessary. 4. Local lines to distribute the water to individual customers, and meters to measure the amount of water used by them. These lines must be sufficiently large to provide fire flows. It is important that these local lines provide "loop" circulation to provide continuous flow. 5. A system of hydrants to be used by the Fire Departments. 6. A management, operating, and maintenance group. The emphasis of this pre-design analysis is element number 3. Elements 4 and 5 will be provided internally as part of the MRSPA Development and the remaining elements will be provided by OPUD General Design Considerations Numerous design considerations had to be made to properly produce a conceptual design. These design considerations will assure that the project meets current engineering standards and the approval of OPUD. The design criteria and considerations are as follows: 1. Easements. All proposed facilities will have a dedicated easement provided for future operation and maintenance or the infrastructure will be located within existing County right-of-way. The dedicated easement will be based on the following criteria: WIDTH = Trench depth + pipe diameter + two feet, or 15 feet, whichever is greater. In most cases, the proposed facilities will be located in County roadways, the above criteria refers to areas not located in County roadways. 2. Water Demand. The water demand requirements will be a combination of demand rate for each land use type plus the corresponding fire flows. Table No. 1.1 reveals the domestic water demand rates and fire flow conditions for each use proposed. The projected population was based on: The average density (dwelling units per acre for each residential land use classification). Land Use Types shown in the MRSPA. Average household size of 2.67 people per dwelling unit. Age Restricted average household size of 1.80 people per dwelling unit.

4 Domestic Water Technical Memorandum Page 3 Table No. 1.1 Maximum Day Water Demand Rates Land Use Demand Rate / Acre Fire Flow Very Low Density Residential 4.0 gpm (1.0 gpm/edu) 1,750 gpm Aged Restricted Low Density Residential 4.5 gpm (0.8 gpm/edu) 2,000 gpm Low Density Residential 5.0 gpm (1.0 gpm/edu) 2,000 gpm Medium Density Residential 7.0 gpm (1.0 gpm/edu) 2,500 gpm High Density Residential 20.0 gpm (1.0 gpm/edu) 3,000 gpm Neighborhood Commercial 8.0 gpm 3,000 gpm* Schools 8.0 gpm 4,000 gpm* Park 10.0 gpm n/a * Based on automatic sprinkler system. All distribution lines will be capable of 50 psi minimum, 20 psi residual with fire flow. The Magnolia Ranch Specific Plan Area is comprised of approximately 123 very low density residential units, 2,210 low density residential units, 540 aged restricted low density residential units, 240 medium density residential units, acres of High Density Residential, acres of commercial/business park, acres of school, and acres of park. The design scenarios are shown in Table No. 1.2 Table No Design Scenario(s) Design Scenario Phase 1 (1,721 lots) + Fire Complete construction w/ Phase 1 + Fire Design Flow (Max Day plus Fire) 3,000 gpm 10,000 gpm 3. Storage. Water storage to meet fire flow and peak hour demand requirements will be necessary. Water storage will equalize supply and demand in the long term and will furnish water during emergencies, such as fires and loss of water supply. The capacity of the storage tanks depends upon the flow variation expected in the system. In order to equalize the rate, when use is less than average, the excess must be stored for use when the rate is higher than average. Additional storage beyond this requirement is required to provide fire protection. 4. Hydraulic Design Criteria. The following criteria shall be followed for all hydraulic computations and the conceptual design: a. The Hazen Williams equation will be used to analyze the hydraulic grade line. The

5 Domestic Water Technical Memorandum Page 4 Hazen Williams value to be used in the computation will be 150. b. Velocities at maximum flow, including fire flow, will be limited to eight (8) feet per second. c. The minimum pressure at the point of delivery will be a normal static pressure of 60 to 75 lb/in 2. The distribution line within the Magnolia Ranch Specific Plan Area will be capable of 50 psi minimum with 20 psi residual with fire flow. 5. Air-vacuum and air-relief valves. Air-vacuum and air relief valves will be used to permit release of air which accumulates in the pipeline and to prevent negative pressures from building up when the lines are drained. Valves will be located at high points throughout the system. Air release valves will be considered on long ascending, descending, and horizontal reaches to alleviate constructing air pockets from forming in the pipeline. 6. Pressure Reducing/Regulating Valves. Pressure reducing/regulating valves will be provided automatically to reduce the pressure on the downstream side to any desired level. They function by using the upstream pressure to throttle the flow through an opening similar to that in a globe valve. The throttling valve will close (or open) until the downstream pressure reaches the preset value. 7. Backflow Preventers. Backflow Preventers will be provided to prevent contamination of water supplies by transient unfavorable pressure gradients which might otherwise cause reversal of flow. They will be either double-check values or reduced-positivepressure values. The former close when flow reverses, and the latter when the pressure drops, thus providing an additional margin of safety. The type used depends upon the application and the risk to the general public. 8. Fitting and Valve Standards. All required fittings and valves shall be placed into the water distribution system according to the California Waterworks Standards, California Health and Safety Code, California Administrative Code Title 22, the EPA, and OPUD Standards. This includes gate valve clusters at each intersection for the partial system isolation, air vacuum/release valves, check valves, backflow prevention devices, meter valves, water meter, sample ports, etc Geometric Layout The geometric layout of the system was based on the Magnolia Ranch Specific Plan. With a few isolated exceptions, the water mains have been located within the road right-of-ways. Figure No. 1.1 shows the conceptual layout of the domestic water system Hydraulic Analysis No hydraulic analysis was conducted as part of this study. A more detailed study is currently being completed.

6

7 Domestic Water Technical Memorandum Page Pipe Selection The type of pipe used for the closed conduit will meet the requirements of OPUD and Yuba County. We have provided three different pipe alternatives, which we feel will meet the requirements of the design. The pipes are as follow: 1. High Density Polyethylene (HDPE) Pipe. The pipe shall be 100 psi (DR17) minimum and conform to the requirements of AWWA C906. All joints and fittings shall be by the butt fusion method. All fittings shall conform to AWWA C906 requirements. 2. Ductile-Iron Pipe (DIP). The pipe shall be Class 250 minimum and conform to the requirements of AWWA C151 for ductile-iron pipe. The fittings shall conform to AWWA C110 for cost iron fittings and C111 for rubber gasket joints. All flanged fittings shall conform to AWWA C Polyvinyl (PVC) Pipe. The pipe shall be 165 psi (SDR25) PVC 1120 ASTM D 1784 (12454-B) minimum and conform to the requirements of AWWA C905 or AWWA C900. The polyvinyl chloride pipe joints shall be rubber rings conforming to ASTM F477 and have joint meeting or exceeding the requirements of ASTM D A forth pipe is also considered on a limited scale to be used for locations where bore and jacking is required. The pipe is as follows: 4. Welded Steel Pipe (ST). The pipe shall be ten (10) gauge minimum and conform to the requirements of AWWA Designation: C 200; ASTM Designation: A 53, Grade B; API Specification 5L, Grade B; API Specification 5LX, Grade X42. The field welding shall be performed in accordance with the specifications of AWWA Designation: C Protection of Water Quality Although the water produced from wells by OPUD meets stringent quality standards as it leaves the source, it may deteriorate as it passes through the distribution system. Organic materials may pass through the walls of plastic pipe and metals may dissolve from pipe or solder. Additionally, autotrophic bacteria can grow within the pipes using carbonate and bicarbonate ion alkalinity of the water as the sole carbon source. The organic matter produced by this growth can then support other microbial life and result in taste, odor, and color problems. The system will be designed to prevent this from occurring. Systems can use five primary operation procedures to maintain water quality: (1) minimize bulk water detention time, (2) maintain positive pressure, (3) control the direction and velocity of the bulk water, (4) maintain a disinfectant residual in the distribution, and (5) prevent cross-connections and backflow. Backflow preventers will be used to prevent backflow at required cross-connections.

8 Domestic Water Technical Memorandum Page Summary and Recommendations The intent of this technical memorandum was to provide the broad overview of the domestic water system prior to a more detailed study being completed. The construction of the domestic water system is required to provide a reliable potable water system and fire protection system for the construction and development of the Magnolia Ranch Specific Plan Area. Figure No. 2.1 provides a conceptual layout of the system loop trunk lines, wells and tanks. Again a more detailed study will be developed to address the onsite and offsite in more detail, including sizing of all facilities in order to meet the domestic and fire needs of the complete community.