Summary of California's Water Reuse Guideline or Regulation for Impoundments

This page is part of the EPA’s REUSExplorer tool, which summarizes the different state level regulations or guidelines for water reuse for a variety of sources and end-uses.
The source water for this summary is Treated Municipal Wastewater.

On this page:

Technical basis
History of microbial benchmarks in California
History of key treatment requirements in California
Water reuse for impoundments approved for use in California
Water reuse treatment category for impoundments
Additional context and definitions
Water reuse for impoundments specifications (table)
Upcoming state law or policy
References
Disclaimer

This page is a summary of the state’s water reuse law or policy and is provided for informational purposes only. Please always refer to the state for the most accurate and updated information.

In California, water reused for include nonrestricted recreational impoundments for primary contact recreation, restricted recreational impoundments for certain activities and publicly accessible impoundments at fish hatcheries. The source of water is specified by the state as municipal wastewater. The write-up uses state terms when discussing sources or uses of water that may differ from the Regulations and End-Use Specifications Explorer's (REUSExplorer's) terms.

Technical basis

California allows the use of recycled municipal wastewater for impoundments including nonrestricted recreational impoundments and restricted recreational impoundments (Cal. Code Regs. tit. 22). All applicable provisions of the Clean Water Act (CWA) (33 U.S.C. §§ 1251 et seq.), including its implementing regulations, must be met in addition to any state water quality standards. California specifies the types of body contact and recreational activities permitted in each impoundment and each type of impoundment varies in the permitted level of body contact and recreational activities. California requires a higher level of treatment and more stringent performance standards when primary contact recreation is permitted. The technical basis for developing the specifications and/or removals of microbial contaminants, chemicals and other relevant indicators is summarized by Olivieri et al. (2014). Olivieri et al. (2014) conducted a quantitative microbial risk assessment (QMRA) and reported that when assuming full tertiary treatment, the annual median risk of infection for enteric viruses, Cryptosporidium parvum and Giardia lamblia and Escherichia coli O157:H7 ranges from 10^-8 to 10^-4 based on the assumption of daily exposure.

Classes of recycled wastewater differ by both their treatment requirements and microbial specifications (Cal. Code Regs. tit. 22).

Disinfected secondary 2.2 recycled water requires that total coliform bacteria must not exceed 23 MPN/100 mL in more than one sample in any 30-day period and requires a 7-day median concentration of total coliform bacteria of ≤2.2 most probable number (MPN)/100 mL.
Disinfected tertiary recycled water requires a 7-day median concentration of total coliform bacteria of ≤2.2 MPN/100 mL and requirement of ≤23 MPN/ 100 mL in more than one sample in any 30-day period. Additionally, it requires turbidity of ≤2 NTU in the filter effluent and a 5-log removal of F-specific bacteriophage MS-2 or poliovirus.

History of microbial benchmarks in California

Total coliform standard of 2.2 most probable number (MPN)/100 mL represents the non-detect threshold in a standard MPN test and is not based on a formal risk assessment, but rather on experience and the knowledge that accepted treatment processes can effectively reduce pathogen numbers (National Research Council, 1996). Historically, a concentration of total coliform bacteria of ≤2.2 MPN/100 mL served as the drinking water standard in California (NWRI, 2012). Drinking water meeting this criterion was categorized as “pathogen free” in the absence of quantification methods for viruses (NWRI, 2012).
Total coliform standard of 23 MPN/ 100 mL was established in 1968 as an indicator that a disinfection process was operating effectively for oxidized (but not filtered) wastewater.
Total coliform standard of 240 MPN/100 mL was established in 1978 to assure a robust disinfection process and avoid brief lapses in treatment.
The 5-log reduction in virus requirement is based on a correlation to a total coliform reduction to ≤ 2.2 MPN/100 mL in Pomona’s tertiary effluent. The 1977 Pomona Virus Study evaluated a range of operational treatment conditions across pilot treatment trains using seeded poliovirus I (Sanitation Districts of Los Angeles County, 1977). The CT requirement specified in the Water Recycling Criteria (NWRI, 2012) of 450 mg-min/L is based on the Pomona Virus Study, which used combined chlorine and a modal contact time of about 90 minutes. The study determined a CT of 450 mg-min/L met the coliform standard of 2.2 MPN/100 mL and simultaneously reduced the seeded virus level by 5-logs.

History of key treatment requirements in California

In addition to the above microbial water quality standards, the treatment for the highest end uses involving food crop and landscape irrigation were based on current drinking water standards because the exposures were considered similar. The degree of treatment and levels of disinfection specified are commensurate with the expected level of public exposure to the treated wastewater.

Oxidation of wastewater is required to assure an acceptable minimal quality of recycled water and to have a recycled water that is more uniform in quality than primary effluent and with a lower ammonia and organic content to assure reliable disinfection of the water (NWRI, 2012).
Coagulation is required based on studies carried out by the US Public Health Service at the Robert A. Taft Sanitary Engineering Center, which demonstrated that the use of chemical coagulants with media filtration is the most effective and practical method of removing viruses and suspended material that may contain viruses from the water being treated (NWRI, 2012).
Filtration is necessary to assure physical removal of the agglomerated material which may contain virus particles and other particulates that could shield virus from disinfectants in the recycled water. A turbidity limit of 10 NTU was originally established in 1968 to assure the filtration process is functioning properly (NWRI, 2012). The turbidity limit was lowered in 1975 (average of 2 NTU and not to exceed 5 NTU more than 5 percent of the time during any 24-hour period) to assure that the filtration process produces a water quality that enables the downstream disinfection process to be effective and reliable. Subsequent adjustments of the turbidity standard were made to establish achievable limits, taking into account the capabilities of a filtration technology and requirements of the disinfection process. Specific maximum turbidity limits were established in 2000 to assure that filters would not be operated at the high rates which result in breakthrough of solids (NWRI, 2012).
Chlorine disinfection: The regulations require a minimum chlorine concentration versus time (generally referred to as CT values) of 450 based on a minimum 90-minute contact time. These requirements are based on the Department of Public Health’s (Department, now DDW) experience with several demonstration projects (including the 1977 report on the Pomona Virus Study) where these concentrations and detention times were shown to be effective in inactivating viruses and on operational testing data submitted by the Los Angeles County Sanitation Districts (Sanitation Districts of Los Angeles County, 1977). Based on these data, CDPH published a policy statement (Policy Statement for Wastewater Reclamation Plants with Direct Filtration) that required a chlorine residual of at least 5 mg/L after a modal contact time of at least 90 minutes (NWRI, 2012), which resulted in a minimum allowable CT of 450 mg-min/L. The CT and modal contact time requirements were incorporated into the 2000 revision of the 1978 criteria, which as originally only based on coliform inactivation (NWRI, 2012).
Alternative disinfection: The regulations also allow an alternative disinfection method if it is demonstrated to be capable of removing or inactivating viruses to a level of 1/100,000 (5 logs) of the initial concentration. The demonstration of a 5-log reduction or use of the specified CT values were determined by the Department to be necessary to assure effective and reliable removal and inactivation of enteric viruses for those uses where the public exposure to the recycled water is high (NWRI, 2012).

Water reuse for impoundments for use in California

Cal. Code Regs. tit. 22 defines the following approved water reuse for impoundments:

Nonrestricted recreational impoundments for primary contact recreation (Disinfected tertiary)
Restricted recreational impoundments for fishing, boating or other non-body contact activities (Disinfected secondary-2.2)
Any publicly accessible impoundments at fish hatcheries (Disinfected secondary-2.2)

Water reuse treatment category for impoundments

The various classes of recycled water treatment are defined by their respective treatment requirements and applicable performance standards.

For disinfected tertiary recycled water, the treatment requirements are filtration and disinfection via chlorine disinfection or another disinfection process, that when combined with filtration, achieves a 5-log inactivation or removal of culturable F-specific bacteriophage MS-2, poliovirus or a similar virus. In the disinfected effluent, the median concentration of total coliforms cannot exceed 2.2 MPN/100 mL, cannot exceed 23 MPN/100 mL in more than one sample in any 30-day period and cannot exceed 240 MPN/100 mL in a single sample.
For disinfected secondary-2.2 recycled water, the treatment requirements are secondary treatment with oxidation and disinfection. The water must meet a 7-day median concentration of ≤2.2 MPN/100 mL of total coliform bacteria with a 30-day median concentration of ≤23 MPN/100 mL with a single sample maximum of ≤240 MPN/100 mL.

Additional context and definitions

In California, recycled municipal wastewater is defined as “recycled water that is the effluent from the treatment of wastewater of municipal origin” (California 2015). A nonrestricted recreational impoundment is defined as “an impoundment of recycled water, in which no limitations are imposed on body-contact water recreational activities.” A restricted recreational impoundment is defined as “an impoundment of recycled water in which recreation is limited to fishing, boating, and other non-body-contact water recreational activities.”

No impoundment of disinfected tertiary or secondary-2.2 recycled water may occur within 100 feet of a domestic water supply well.

All use areas where recycled municipal wastewater is used that are accessible to the public must have signs posted that include the wording “RECYCLED WATER – DO NOT DRINK” and display the international “Do Not Drink” symbol (Cal. Code Regs. tit. 22). No physical connection is allowed to exist between a recycled water system and a potable water system (except as allowed under Section 7604 of Title 17). The portions of the recycled water in areas accessed by the general public (except for cemeteries) must not include any hose bibs and must use quick couplers that differ from those used on the potable water system. Dual plumbed systems are approved for use in California and are defined as “a system that utilizes separate piping systems for recycled water and potable water within a facility” and the recycled water is used to either serve plumbing outlets (excluding fire protection systems) within a building or for outdoor landscape irrigation at individual residences (Cal. Code Regs. tit. 22). Only a “recycled water agency” is allowed to deliver recycled water to a dual plumbed facility.

Water reuse for impoundments specifications

Summary of California's Water Reuse for Impoundments Specifications

Recycled Water Class/Category (Approved Uses)	Source Water Type	Water Quality Parameter	Specification	Sampling/Monitoring Requirements (Frequency of monitoring; site/ location of sample; quantification methods)^*
Disinfected tertiary (nonrestricted recreational impoundments)	Domestic wastewater	Turbidity	≤2 NTU (filter effluent turbidity) ≤10 NTU (single sample maximum) Influent turbidity should not exceed 5 NTU for over 15 minutes	Continuous monitoring
		Total coliform (with conventional treatment)^a	≤2.2 MPN/100 mL (7-day median) ≤23 MPN/100 mL (does not exceed in more than one sample in 30-day period) ≤240 MPN/100 mL (single sample maximum)	At least once daily
		CT^b (with conventional treatment)^a	≥450 milligram-minutes/L	Must be maintained at all times with a modal contact time of at least 90 minutes, based on peak dry weather design flow
		F-specific bacteriophage MS-2 or polio virus^c,d (with conventional treatment)^a	5-log removal	Must be demonstrated after filtration and disinfection
Disinfected secondary-2.2 (Restricted recreational impoundments; Publicly accessible impoundments at fish hatcheries)	Domestic wastewater	Total coliform	≤2.2 MPN/100 mL (7-day median) ≤23 MPN/100 mL (does not exceed in more than one sample in 30-day period)	At least once daily

Source= Cal. Code Regs. tit. 22

* Information about sampling and monitoring requirements such as frequency, site and quantification methods not specifically listed in the table was not explicitly specified in the State-specific regulations.

^a Conventional treatment is defined as “a treatment chain that utilizes a sedimentation unit process between the coagulation and filtration processes and produces an effluent that meets the definition for disinfected tertiary recycled water” (Cal. Code Regs. tit. 22). Treatment for Giardia, enteric viruses and Cryptosporidium in place of conventional treatment must consist of a treatment train of at least three separate treatment processes. No treatment may be credited with more than 6-log reduction for any pathogen, except for underground retention of recycled municipal wastewater that meets additional criteria. For each pathogen, at least three processes must be credited with ≥1.0-log reduction.

^b The CT is the product of total chlorine residual and modal contact time measured at the same point (Cal. Code Regs. tit. 22). This only applies if chlorine was used for disinfection.

^c This only applies if a disinfection process other than chlorination was used.

^d A virus that is at least as resistant to disinfection as polio virus may be used for the purposes of the demonstration.

Upcoming state law or policy

No upcoming reuse regulations related to impoundments were found for California.

References

Clean Water Act, 33 U.S.C. §§ 1251 et seq.

Olivieri, A. W., Seto, E., Cooper, R. C., Cahn, M. D., Colford, J., Crook, J., Debroux, J.-F., Mandrell, R., Suslow, T., Tchobanoglous, G., Hultquist, R. A., Spath, D. P., & Mosher, J. J. (2014). Risk-Based Review of California’s Water-Recycling Criteria for Agricultural Irrigation. Journal of Environmental Engineering, 140(6), 04014015.

Water Recycling Criteria, Cal. Code Regs. tit. 22.

Disclaimers

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