The Mariposa Public Utility District (MPUD or District) was established in 1947 under the "Public Utilities Act of 1921", as contained in Sections 15501 through 18055 of the California Public Utilities Code. The District was formed in response to a report and recommendation prepared by the Mariposa County Planning Commission. At issue was the provision of public water and sewer services for the community of Mariposa. The documents which establish the MPUD do not delineate any specific purposes or functions for the District. Under Division 7 of the California Public Utilities Code, a public utility district has the following powers:
1. It can acquire and operate works for supplying the District's inhabitants with light, water, power, heat, transportation, phone or other means of communication, or means for disposition of garbage sewage or refuse.
2. It may purchase and distribute such services and commodities and acquire and operate a fire department, ambulance service, street lighting system, public parks, playgrounds, golf courses, swimming pools, recreation and other public buildings and drainage works including street improvements.
MPUD provides public water and wastewater services to the town of Mariposa. The District currently has 722 water and wastewater service connections and services a population of approximately 2000.
MPUD is an independent district; policy is established by a Board of Directors. Directors meet the first Tuesday of each month at 6:30 PM. Generally, the meetings are held at the MPUD administrative office at 4992 Seventh Street in Mariposa.
MPUD is basically an enterprise district. The Board sets charges for services provided by the District. These charges are collected on a monthly basis for each enterprise fund (water and sewer). The General Manager (also Clerk to the Board) is appointed by the Board and has full charge and control of the construction of the works of the District and their maintenance and operation (PUC 16114).
MPUD WATER SYSTEMS
MPUD has been providing public drinking water services since 1950. The operation and maintenance of the public water systems is financially supported by fixed monthly service charges adopted by Ordinance by the Board of Directors. The last rate change for water was adopted in 2020 and eliminated the five-tier structure for charging commercial water customers and charges a uniform rate for all usage. Commercial customers are charged based on meter size rather than customer category. Residential rates are proposed to be charged based on a new four tier structure. The proposed change is designed to comply with the legal requirements of Proposition 218. The new rate became effective on January 2021 utility bills. The District does administer a special assessment district to secure and retire bonds for the Saxon Creek Water Project. The bonds were sold to the USDA Farmers Home Administration.
Source of Supply
Saxon Creek Water Project (Merced River):
MPUD owns and operates a pump station adjacent to the Merced River near Saxon Creek. The pump station is equipped with two 1,000 horse power pumps expandable to include a third pump. The current capacity of the pump station is 2,400 gallons per minute (gpm), expandable (with the third pump installed) to 3,200 gpm. The entire pump station is constructed under the historic Yosemite railroad bed (now an access road for the BLM recreation areas) approximately 1 mile west of Briceburg. Immediately south of the pump station on the south side of the river, the District operates an electrical substation to access power from the PG&E high voltage Yosemite transmission line accessed by Rancheria Creek Road.
The pump station supplies a 43,000-foot-long, 12" transmission main that extends to a 10" pipeline located at the Stockton Creek dam. At the high elevation point of the pipeline there is a one-million-gallon raw water, steel storage reservoir. The pumps in the river are called on or off based on the operator set point water level in the one-million-gallon reservoir and set point time of day. The water treatment facility draws water directly from the transmission main and the million-gallon reservoir. In addition, and/or as alternative, water can be diverted from the Saxon Creek project pipeline directly to the Stockton Creek Reservoir for storage.
The Saxon Creek water project is a diversion of water from the Merced River in Mariposa County. The project title was derived from the point of diversion being located near the confluence of Saxon Creek and the Merced River. The actual water right for the Saxon Creek project is held by the Merced Irrigation District (MID). In February 1995, the MID water right license #2685 was amended to include the Mariposa Town Planning Area (as it existed during project planning) as an additional place of use and the Saxon Creek pump station as an additional point of diversion. The water right license provides for a maximum diversion of 7 cubic feet per second (cfs) (3,150 gpm) and 5,000-acre feet per year. A significant requirement of the amendment restricts the diversion based on stream flow. “Licensee shall, during the period from January 1 through December 31 by-pass a minimum of 50 cfs in the Merced River at the point of diversion for water intended for delivery to Mariposa Town Planning Area. The total stream flow shall be by-passed whenever it is equal to or less than 50 cfs”. Other permits such as Bureau of Land Management (land use) and California Department of Fish Wildlife (stream alteration) have restrictions and requirements. The 50 cfs limitation is the most significant. Historically, the 50 cfs limitation has been applicable from late August to December during low Sierra snowpack years. The State Water Resources Control Board (SWRCB) has issued curtailment orders on certain water right licenses in June of 2014, April of 2015 and 2016 as a result of extreme drought conditions resulting in shorter term pumping opportunities.
Stockton Creek Reservoir
MPUD owns and operates a 440-acre foot reservoir on Stockton Creek approximately one mile from the town of Mariposa. The Stockton Creek dam was built in 1949/1950. There is a 7,000-foot-long 10" pipeline from the dam to the water treatment facility near town. The District uses Stockton Creek as a primary water source of supply. The watershed above the dam is less than 3500’ elevation. Reservoir recharge is dependent upon rainfall at lower elevations.
The California SWRCB has issued two licenses for diversion and use of Stockton Creek to the MPUD. License #7743 provides for a diversion of 320-acre feet and maximum withdrawal of 245-acre feet per year. License #10582 provides an additional diversion of 108-acre feet with withdrawal of 57-acre feet per year for a total of 428-acre feet diversion and 302-acre feet withdrawal. In the event of low run-off in the Stockton Creek watershed, the District can divert water from the Saxon Creek Water Project to the Stockton Creek Reservoir.
The District currently has four water wells in operation located within the District boundaries. The wells are connected directly to the water distribution system. All wells are equipped with chemical feed equipment that injects chlorine when the wells are operated. The capacity of the four wells is approximately 360 gallons per minute (pumped less than 12 hours per day). Two of the wells supply pressure Zone 3 and two wells pump directly to Zone 1 of the distribution system.
The existing sources of water are adequate for future growth of the District, probably for the next ten to twenty years. Major changes in the town’s growth rate and water quality/water rights requirements could affect the future capacity of these sources.
Stockton Creek Watershed Preserve and Trails
MPUD, in collaboration with the Sierra Nevada Conservancy (SNC) and the Sierra Foothill Conservancy (SFC) acquired 410 acres of land in 2011 adjacent to and upstream of the Stockton Creek Reservoir. In 2019, MPUD acquired land south of the Stockton Creek Dam, adding 360 acres of open space to the preserve. MPUD and SFC have been constructing public use trails and sponsoring fuel reduction projects and organizing tours in the watershed. Over 4 miles of trails and two trail head kiosks are available for public access to the preserve. Over time the project is expected to reduce risk of catastrophic fire, improve water quality and enhance wildlife habitat in the watershed as well as provide public access to hiking and biking trails close to the town of Mariposa.
Water Treatment Facility
The District completed construction of a replacement surface water treatment facility (SWTF) in August of 2013. The design capacity is one million gallons per day. All surface water sources are treated at the SWTF. The SWTF is permitted under the SWRCB Division of Drinking Water. The operations staff is individually certified through the SWRCB Water Treatment Operator Certification Program.
The primary components of the new facility include a clarifier/flocculation tank, membrane filters, granular activated carbon reactors, emergency power generator, chemical feed systems and operations building. The SWTF is required to meet a .1 ntu turbidity standard. The SWTF also provides corrosion control water conditioning to meet the lead and copper drinking water requirements at the customers tap. The facility will enable the District to consistently meet current safe drinking water standards adopted by the USEPA and the SWRCB Drinking Water Program.
Water Distribution System
The water distribution system consists of four pressure zones. Pressure Zone 1 is supplied by a one-million-gallon water storage tank near the SWTF. Pressure Zone 1 includes the downtown area, Bullion Street, Jones Street, Stroming Road, Miller Road, Jessie Street and the Joe Howard Street areas. In 2004-2005 MPUD replaced all of the steel water mains originally installed in 1950-1952 with 17,000 feet of 6", 8", and 10" PVC pipe with ductile iron fittings; fire hydrants and service connections meeting AWWA standards in this pressure zone.
Zones 2 and 4 are supplied from Zone 1. Two pump stations pump from Zone 1, each equipped with two, 250 gpm pumps - one at Jones and Bullion Streets and one near the hospital. These stations pump water to a one-million-gallon water storage tank approximately one mile north of the hospital (pressure Zone 4). Pressure Zones 2 and 4 include Hospital Road, Campbell Tract, Mueller Tract, Smith Road and the east side of Highway 49 North from Smith Road to the Cal Fire facility. The pumps are controlled by a computerized Supervisory Control and Data Acquisition (SCADA) system that communicates by radio signal. The default condition (communication and/or power failure) allows full access for flow from the one-million-gallon tank in Zone 4.
About 80% of the distribution system in Zones 2 and 4 is relatively new and installed according to AWWA standards. The transmission pipeline between the Jones Street pump station and the Hospital pump station is constructed of 6" ductile iron pipe installed in 1952. The one-million-gallon water tank and 12" main in Zone 4 as well of all of Zone 4 are outside of the existing District boundaries to take advantage of elevation for gravity flow from the water tank and future service to the northeast portion of the Mariposa Town Planning Area (MTPA).
Zone 3 is supplied by the two wells near Idle Wheels Mobile Home Park that pump to a 72,000-gallon concrete water storage tank. Zone 2 is connected to Zone 3 via a pressure reducing valve. In the event of system failure or large pressure drop (such as fire flow) in Zone 3, the pressure regulating valve will automatically open allowing water to flow from pressure Zone 2 to Zone 3 which accesses the one-million-gallon tank in Zone 4. Most of the distribution system in Zone 3 was constructed in 1976. The material used was PVC pipe; however, it does not meet American Water Works Association (AWWA) or current MPUD standard specifications. The combined total length of distribution mains is approximately 75,000 feet.
The operations staff is individually certified through the SWRCB Water Distribution Operator Certification Program.
MPUD WASTEWATER SERVICES
The District constructed the first public wastewater collection and treatment facilities in 1958. The operation and maintenance of the public wastewater system is financially supported by fixed monthly service charges adopted by Ordinance by the Board of Directors. The last rate increase for wastewater was adopted in 2020 with yearly incremental increases through July of 2024.
The District completed construction of improvements to the 1984-constructed wastewater treatment facility (WWTF) in 2020. The project included the addition of tertiary treatment and upgrading existing treatment processes to allow the WWTF to meet discharge limitations. The major upgrades included: installation of recirculation system, installation of mixing pumps, new gravity filters, new effluent pump station, new ultra-violet disinfection (replacing chlorine), new biosolids storage area, and rehabilitated headworks and clarifiers. The District was approved by the SWRCB for $9,030,000 in funding, $3,030,000 loan and $6,000,000 grant. In addition to State Revolving Funds, the District contributed $621,000 in general funds to the project. The debt service for the loan portion of the project funding is $131,000 per year, beginning Fiscal Year 2020-2021.
The permitted capacity of the facility is .610 million gallons per day (mgd), average daily flow. The facility is operating at nearly 30-40% of design dry weather flow capacity. The operations staff is individually certified through the SWRCB Wastewater Treatment Operator Certification Program.
The WWTF discharges treated wastewater to Mariposa Creek. The District operates the facility under a National Pollutant Discharge Elimination System (NPDES) permit issued by the California Regional Water Quality Control Board (RWQCB). The NPDES permit is renewed every five years. The most recent renewal was in March of 2021.
Collection mains installed after 1975 have been constructed with PVC pipe. The combined total length of all public wastewater collection mains is 73,000 feet. (separate from the NPDES permit for the treatment facility). All significant sewer collection system overflows are reported through the SWRCB California Integrated Water Quality System (CIWQS). MPUD has implemented a routine collection main cleaning schedule to avoid system failures that may result in a sewer overflow. The wet weather infiltration of storm water into the collection system does result in high flows to the WWTF during significant rain fall events. MPUD staff monitors and repairs failing collection system mains as they are identified.
MPUD operates a water quality laboratory at the WWTF certified under the SWRCB Environmental Laboratory Accreditation Program (ELAP). MPUD is able to perform most of the daily, weekly and monthly water quality monitoring for the public water and wastewater system in the MPUD lab. The operation of the laboratory provides the operations staff to more efficiently monitor water quality and operational parameters for the water and wastewater treatment systems. MPUD has also provided bacteriological and nitrate analysis of drinking water for the Mariposa County Schools and the general public.