Small Municipal Separate Storm Sewer System (MS4)
On 28 December 2017, Central Valley Water Board staff received a complaint of ongoing illegal discharge of wastewater from an unknown source into the storm water system and subsequently into Mule Creek. In response, Central Valley Water Board staff inspected MCSP on 4 January 2018 and collected samples. The results indicated that the discharge exhibited the characteristics of domestic and industrial wastewater, and exceeded several applicable regulatory limits, resulting in the issuance of a Water Code Section 13267 Order (13267 Order) on 14 February 2018. As part of the 13267 Order, CDCR completed monitoring and an investigation of the storm water and sanitary sewer systems to determine the source of the waste. It determined that both systems had numerous defects allowing liquid to infiltrate and ex-filtrate and that groundwater was mounded beneath MCSP as a result. CDCR’s Investigation Findings Report and Central Valley Water Board Staff’s Review Memo for that report are linked below.
During the investigation, Central Valley Water Board staff determined that the storm water system at MCSP may pose a threat to water quality and storm water discharges from MCSP should be regulated under the Small MS4 General Permit. On 8 February 2019 the Central Valley Water Board adopted Resolution R5-2019-0006 designating MCSP as a Non-Traditional MS4, and on 10 April 2019 MCSP was designated as a Regulated Small MS4 by the State Water Resources Control Board (State Water Board). The Small MS4 General Permit requires CDCR to develop and implement a storm water control program for MCSP to reduce the discharge of pollutants from its MS4 to Mule Creek and ensure compliance with applicable water quality requirements.
Due to potential water quality impacts to Mule Creek while the MCSP storm water control program is being fully developed and implemented, and to ensure compliance with the Small MS4 General Permit requirements, the Central Valley Water Board determined that an interim monitoring and reporting program is necessary to monitor MS4 discharges from MCSP to Mule Creek. The Central Valley Water Board issued a 13383 Order to perform monitoring and reporting on 6 August 2020. The 13383 Order was initially updated on 16 December 2020, followed by an additional update on 30 November 2021.
On 18 February 2021, the Central Valley Water Board approved Settlement Agreement and Stipulation for Entry of Administrative Civil Liability and Administrative Civil Liability Order (Stipulated Order), Order No R5-2021-0001 regarding the unpermitted discharge of co-mingled storm water and wastewater to Mule Creek from the MCSP MS4. The scope of the Stipulated Order only included discharges occurring between the discovery of waste constituents in the discharge by Central Valley Water Board staff on 18 January 2018 and 10 April 2019, which is when MCSP enrolled in the Small MS4 General Permit. As part of the Stipulated Order, CDCR agreed to defer funds from the penalty amount to the following Enhanced Compliance Actions (ECAs): a Landscape Irrigation System Replacement Project to repair broken landscape irrigation pipes that are contributing to excessive dry weather flows into the MS4 and a microbiological study (Microbial Study) performed by the Southern California Coastal Water Research Project. The Landscape Irrigation System Replacement Project is expected to be completed in March 2025. The Microbial Study is complete but unfortunately was not performed with EPA-certified methods and was mostly inconclusive, although human biomarkers were detected in Mule Creek.
|Strategy to Return to Compliance
Insufficient flow and composition data to determine threat to water quality and public health posed by the discharges to Mule Creek from the MS4
|The updated 13383 Order requires the collection of monitoring data needed to determine the threat to water quality and public health posed by MS4 discharge. The Small MS4 General Permit requires CDCR to address any illicit discharges occurring to the system once they are found.
|Discharges from the MS4 have been occurring during long periods of dry weather
|As part of the 2021 Stipulated Order, CDCR is required to repair the landscape irrigation system. In addition, Central Valley Water Board staff reviewed CDCR’s Non-Storm Water Discharge Report and determined that the irrigation runoff from defects in the irrigation system does not meet the Small MS4 General Permit’s definition of incidental runoff. As required by the Small MS4 General Permit, CDCR submitted a Non-Storm Water Discharge Elimination Plan (NSWDE Plan) to eliminate the non-storm water runoff. This NSWDE Plan is currently under Central Valley Water Board staff review.
|The Stormwater System Investigation Findings Report (Report) detailed numerous defects and locations of infiltration in the MS4 system
|The Report concluded that there are defects in the sanitary sewer and irrigation systems and MS4. For Non-traditional MS4s, the Small MS4 General Order requires that illicit discharges into MS4 be corrected once the source is identified.
- 14 February 2018 13267 Order (will provide document, is not currently online)
- 1 November 2019 Stormwater Investigation Findings Report (will provide document, is not currently online)
- 7 December 2020 Stormwater Investigation Findings Report Review Memo (will provide document, is not currently online)
- 18 February 2021 Settlement Agreement Administrative Civil Liability Order R5-2021-0001
- 18 February 2021 Board Presentation for ACL Adoption (will provide document, is not currently online)
- Historical data of the Discharge to Mule Creek collected under the 13267 Order (will provide document, is not currently online)
- All MS4 monitoring reports are available to the public via the Stormwater Multiple Application and Report Tracking System (SMARTS):