Land Disposal Program

SWAT Program


Program Background

Program Tasks

Available Documents

In a 1993 Memorandum of Understanding, the State Water Resources Control Board (SWRCB) agreed to submit a comprehensive report on the Solid Waste Assessment Test (SWAT) Program to the California Integrated Waste Management Board (CIWMB). This report summarizes the work completed to date on the SWAT Program, and addresses both the impacts that leakage from solid waste disposal sites (SWDS) may have upon waters of the State and the actions taken to address such leakage.

In 1984, the Legislature passed a law requiring testing of water and air media at all solid waste disposal sites (Chapter 15, Statutes of 1984). In particular regarding water testing, the law added Section 13273 to the Water Code, requiring the SWRCB to rank all solid waste disposal sites in groups of 150 each, according to the threat they may pose to water quality. The law requires the operators of each of the 150 sites in a given rank to submit a water quality "solid waste assessment test" (SWAT) report. In addition, the law requires the Regional Water Quality Control Boards (RWQCBs) to evaluate the reports for adequacy of the monitoring networks. If the monitoring networks are adequate, RWQCBs are to determine whether any hazardous waste has migrated into the water, notify the State Department of Toxic Substances Control (DTSC) and the California Integrated CIWMB of hazardous waste migration, and take appropriate remedial action.

RWQCBs approved a total of 528 reports or exemption questionnaires (for sites with undetermined leak status) in all ranks and waived a total of 16 reports from sites already known to leak. These 544 sites were predominantly from the lower ranks and therefore represented the SWRCB's and the RWQCBs\' estimates of the sites most likely to have leaked hazardous wastes into the waters of the State. Of these 544 sites,

  • 392 sites [72%] were found to have leaked waste constituents from the waste management unit.
    • 33 of the 544 sites [6%] were classified as leaking wastes at concentrations exceeding hazardous levels.
    • 276 of the 544 sites [51%] were determined to be leaking waste constituents above other "regulatory levels".
    • 83 of the 544 site [15%] were determined to be leaking waste constituents above background levels but below any applicable"regulatory levels"
  • 76 of the 544 sites [14%] were not known to be leaking.
  • 76 of the 544 sites [14%] are undetermined with regard to their leakage status, in many cases because background water quality cannot be determined.

Thus, the percentage of sites found through the SWAT Program to be leaking waste constituents outside the limits of the landfill is between 72% (if all 76 "undetermined" sites are actually not leaking) and 86% (if all 76 "undetermined" sites are actually leaking).

Because of slight variations in RWQCBs criteria for determining beneficial uses of waters, the exact number of sites which have impacted beneficial uses has not been determined. Using certain assumptions, we estimate that, disregarding "undetermined" leak status sites, about 70% of the tested sites have impacted beneficial uses.

The results of the SWAT Program have particular bearing on the subject of landfill liner design. Specifically, the SWRCB's requirement to use composite liners (i.e., both clay and plastic as a single liner) for new or expanding municipal solid waste landfills has been controversial. Of the 290 sites for which the SWRCB has chemical constituent data, only 23 (8%) of these sites had even a partial liner. Most of the 23 sites\' liners were clay-only, and none of the sites were completely composite-lined. The leakage results for partial or non-composite liners were similar to leakage results for unlined landfills, i.e. most leaked and some are unknown if they leak. Thus, the SWAT Program results strongly indicate that unlined and clay-lined landfill designs are not effective in preventing leakage.

Over half of the landfills "closed" longer than 30 years leaked in excess of "beneficial uses" criteria. The leakage data do not indicate when during the landfill's "lifetime" it began to leak; however the SWAT data show that landfills tend to leak even if they have not accepted waste for more than thirty years.

Available data indicate no apparent correlation between the percentage of landfills which leaked and any of the different site-specific factors checked, including depth to ground water, average annual precipitation, waste acceptance rate, and rock type. Thus, information collected through the SWAT Program demonstrates that unlined or clay-lined landfills leak, regardless of factors such as climate or site-specific geology.

Corrective actions are either in progress or proposed at many of the leaking landfills. RWQCBs are requiring further investigations at most of the remaining sites in order to determine the full extent of constituent migration prior to implementing corrective action to address the leakage.


SWAT Legislation

In 1984, the Legislature passed a law requiring testing of water and air media at all solid waste disposal sites (Chapter 15, Statutes of 1984) [See Appendix]. The law added Section 13273 to the Water Code, requiring the SWRCB to rank all solid waste disposal sites in groups of 150 each, according to the threat they may pose to water quality. The law requires the operators of each of the 150 sites in a given rank to submit a water quality "solid waste assessment test" (SWAT) report. The SWAT reports for each rank are due in consecutive years. In addition, the law requires the RWQCBs to evaluate the reports for adequacy of the monitoring networks. If the networks are adequate, the RWQCBs are to determine whether any hazardous waste has migrated into the water, notify the DTSC and the CIWMB of hazardous waste migration, and take appropriate remedial action.


For the purpose of this report, the terms listed below are defined as follows:

  • Solid Waste Disposal Site (SWDS): The tract of land which is used or has been used for the disposal of solid waste. Usually referred to as a "landfill".
  • Facility: An area of land which contains one or more SWDS(s). Facility includes areas outside of the SWDS which may be used for other purposes.
  • SWAT Site: A facility which is on the Ranked SWAT List as adopted June 22, 1989.


Site Ranking

During 1985, candidate sites for the SWAT rank list were gathered from several sources. The major sources were:

  1. SWRCB/RWQCB Waste Discharge System database,
  2. California Integrated Waste Management Board listings,
  3. Sites listed in County Solid Waste Management Plans,
  4. Sites listed in California Department of Health Services reports from 1968 and 1973,
  5. Sites listed by the South Coast Air Quality Management District,
  6. An unpublished 1985 inventory by the Los Angeles County Engineer's office, and
  7. Sites recommended by RWQCB staff but otherwise not on an existing list

The SWRCB first adopted a SWAT rank list in December 1985. It was comprised of approximately 1,800 sites ranked according to their expected threat to water quality. RWQCB staff later determined that the original rank list contained some sites that were:

  1. duplicated as another site name on the list,
  2. proposed, but never operated, or
  3. not actually subject to the SWAT legislation, such as wrecking yards, spill sites, and industrial surface impoundments.

The RWQCBs did not require SWAT reports of this third category of sites once they determined that they were not subject to the SWAT legislation.

The rank list was revised in October 1986, December 1986, December 1987 and June 1989 to include additional sites and to delete sites that were determined to not be subject to the SWAT legislation. The current rank list (adopted June 22, 1989) contains 2,242 sites. Landfills constructed after June 1989 are not on the current list. Since the last re-ranking in 1989 and as work continued on the SWAT Program, RWQCBs designated a small number of additional sites on the rank list as not subject to SWAT.

Occasionally, a specific facility may have two or more distinct waste management units, primarily large industrial or military sites. Generally, the entire facility was treated as a single entity, and only one SWAT report was submitted. In a few cases, the waste management units were listed in different ranks, and separate SWAT reports were submitted for the waste management units.

Exemption Questionnaire

The SWAT legislation was amended in 1987 to permit site operators only in Ranks 3 and greater to submit a Solid Waste exemption questionnaire. The questionnaire allowed RWQCBs to exempt an operator of a site from submitting a full SWAT report provided that the following conditions were met: 1) the site capacity was less than 50,000 cubic yards; and 2) hazardous waste had not been discharged to the unit. Small sites in rural counties were typical candidates for exemption. Exemption resulted in no monitoring data being submitted for the SWAT program to determine whether the landfill leaks.

Waiver of SWAT Reports

The SWAT legislation provides that a RWQCB may waive the submittal of a SWAT report if it determines from other information that hazardous wastes are already migrating into the waters of the State. The issuance of a waiver means that the landfill leaks hazardous waste, based on other available data.

Review of SWAT Reports

Under SWAT legislation, RWQCB staff review SWAT reports and decide whether to accept the report as complete or to require the site operator to perform additional work. Initially, the acceptance criteria included the determination that the monitoring network complied with the requirements of Chapter 15, Article 5, thus minimizing the possibility of false leakage indication. In 1993, however, the acceptance criteria were revised such that SWAT reports were approved for sites that showed significant leakage regardless of the monitoring system's completeness. This allowed for quicker approval of reports and for fewer resources to be expended at this stage.
In an effort to expedite a cost-effective review of SWAT reports for facilities in the Department of Defense Environmental Restoration Program (DERP), many SWAT sites at military facilities were reviewed in conjunction with ongoing DERP activities. Funding for these efforts were through the Department of Defense/State Memorandum of Agreement, beginning with Fiscal Year 1991-92.


Law requires RWQCBs to notify DTSC (formerly DHS) whenever: (1) the RWQCB waived the requirement for a SWAT report (i.e., site was known to leak), or (2) a SWAT report finding indicated hazardous waste leakage. In the case of waived sites, actions to address the leakage were generally being implemented with oversight by DTSC. For example, because DTSC monitors many Superfund site cleanups, it is already aware of their hazardous waste leakage status. In the case of federal military facilities, actions at the waived site are being addressed under the Department of Defense Installation Remediation Program.

Follow-up Activities

There is no specific provision in the SWAT legislation for follow-up investigations to determine the magnitude of any identified leak or to design a cleanup program. These tasks are generally undertaken in compliance with requirements in Chapter 15 regulations. RWQCB actions on these matters are prioritized based on the leak's threat to water quality and impact on beneficial uses.

Technical Guidance Manual

In 1988, the SWRCB produced a SWAT Technical Guidance Manual for use by RWQCB staff in reviewing SWAT reports, and by owners/operators in preparing SWAT reports. The manual recommended that the following basic information be in a SWAT report:

  • Description of the disposal site and its history.
  • Thorough description of the site hydrogeology.
  • Rationale for the location and design of all monitoring points.
  • Well logs and sample analysis data.
  • Interpretation of the data relative to hazardous waste leakage.
  • Certification of the preparer's credentials.

The manual emphasized the following:

  1. Initial submittal of a SWAT Proposal or "Workplan" to the RWQCB containing the operator's plans for compliance with the SWAT law.
  2. Establishment of a monitoring network that meets all requirements of California Code of Regulations, Title 23, Division 3, Chapter 15.
  3. Either inclusion of upgradient monitoring points or acceptance of responsibility by the owner/operator for all pollutants detected through downgradient monitoring.
  4. Sampling at least four different times over a year in order to ensure detecting any seasonal discharges.
  5. Analysis of water quality samples for:
    • Volatile Organics (EPA 624)
    • Semi-volatile Organics (EPA 625)
    • ICAP Metals
  6. Quality Control/Quality Assurance of all laboratory chemical analyses.

The SWAT Program focused on ground water monitoring. However, in cases where there was an apparent threat to surface water quality, surface water monitoring points were also to be established.

The SWAT legislation required vadose zone monitoring. RWQCBs often waived this requirement for sites where the waste was very close to or present in the ground water; that is, where little or no vadose zone existed, and where it was assumed that the ground water analysis would show any leakage. In the early part of the Program, RWQCBs often "waived" vadose zone monitoring because of a prevalent lack of understanding of the methods for installation and operation of lysimeters or related means for vadose zone monitoring.

In a few cases, a site was already being addressed as required by SWAT legislation through another program or action by the RWQCB. In those cases, RWQCBs could consider reports submitted for the other program or action to be equivalent to a SWAT report. Examples include submittals of Hydrogeological Assessment Reports (HARs) for compliance with the Toxic Pit Cleanup Act, reports prepared in response to a Cleanup and Abatement Order, or monitoring under the core regulatory waste discharge requirement program for waste discharges to land (Land Disposal)

Available Documents

*To request a document, please email the Land Disposal Program and include your contact information, document title(s), and if you require a converted accessible PDF document.

  • California Wastewater Agency Survey, 91-18CWP, March 1991, Water Resources Control Board, State of California (PDF, 5.41 MB)

  • Report to the Integrated Waste Management Board, 96-1CWP December 1995, WRCB California Environmental Protection Agency (PDF, 3.87 MB)

  • Report to the Legislature 1987-88, Report No. 88-14WQ, Division of Water Quality, SWRCB, January 1989

  • Report to the Legislature 1989-90, 90-20CWP January 1991, Water Resources Control Board, State of California (PDF, 8.64 MB)

  • Solid Waste Assessment Questionnaire & Guidelines (California Water Code Section 13273.1) (PDF, 54 KB)

  • Technical Guidance Manual, Solid Waste Water Quality Assessment Test (SWAT) Proposals and Reports, Solid Waste Disposal Program Hydrogeology Section, Land Disposal Branch, Division of Water Quality, SWRCB, August 1988 (PDF, 2.80 MB)