Executive Summary: Draft Combined 2018/2020 Integrated Report


Section 305(b) of the Clean Water Act (CWA) requires states to submit a biennial report to the Environmental Protection Agency (EPA) on the quality of their waters.

Section 303(d) of the CWA requires states to submit a list of waterbodies that do not meet the state’s water quality standards as part of the IR. This list guides the state’s development of water quality improvement plans (Total Maximum Daily Load plans or TMDLs) for impaired waterbodies to bring them into compliance with water quality standards and their beneficial uses.

The IR supports DWQ’s commitment to protecting and improving the water quality of Utah’s rivers, streams, and lakes by providing critical information and thorough analyses of water quality conditions, waterbody impairments, statewide trends, and emerging issues. DWQ uses these data to identify areas with impairments and prioritize projects, TMDLs, and best management practices (BMPs) to improve and enhance water quality in affected areas.


The Draft Combined 2018/2019 IR assessed 913 assessment units (AUs), over 82.5 thousand miles of flowing surface waters of the state and canals, and nearly 1.5 million lake, reservoir, and pond acres. The water quality assessment data cover the period between October 1, 2010, and September 30, 2018, and include updates from previous reports. The data used in the report were collected by DWQ, 12 agencies, and numerous public and private stakeholder groups and individuals.


The State of Utah sets water quality standards that support designated beneficial uses for rivers, lakes, and streams. These designations protect water quality for different uses, including drinking water, recreation, aquatic life, and agriculture. Waterbodies are protected for several combinations of beneficial uses, such as recreation and aquatic life.

Data Collection

The IR uses water quality data collected by DWQ and a range of public and private entities to determine whether assessed waterbodies in the state meet water quality standards and support their designated beneficial uses. Data submitted or obtained by DWQ during the IR data compilation process are integrated into DWQ’s assessments and subject to DWQ’s data management and quality assurance and quality control (QA/QC) processes. Datasets may include laboratory results for water chemistry sampling for conventional (e.g., temperature) and toxic (e.g., metals) parameters, monitoring data specific to lakes, reservoirs, ponds, or flowing surface waters, potential causes of impairments, and macroinvertebrate surveys.

DWQ combines data from individual monitoring sites into a larger spatial scale or Assessment Unit (AU). The Division collects all readily available and credible water quality data for each AU and prepares the data for assessment. Data are assessed according to specific conventional and toxic parameters against beneficial use criteria established in state regulations. DWQ uses these data to categorize the state’s assessment units to determine if they meet their designated beneficial uses.

The state uses five EPA-approved categories in its assessment determinations:

  • Category 1: All beneficial uses attained.
  • Category 2: Some beneficial uses attained but there are insufficient data to determine if all beneficial uses are supported.
  • Category 3: Insufficient or no data to make a determination.
  • Category 4: Impaired for one or more beneficial uses. Does not require the development of a TMDL because one has already been completed (4A), uses are expected to be attained within a reasonable timeframe (4B), or the impairment is not caused by a pollutant (4C).
  • Category 5: Impaired for one or more beneficial uses by a pollutant. Requires the development of a TMDL.

Waters determined to be impaired are placed on the state’s 303(d) list and prioritized for TMDL development. The TMDLs calculate the pollution reduction levels needed to support designated beneficial uses and meet water quality standards. Once a TMDL is completed and approved by EPA, the assessment unit covered under the TMDL is transferred from Category 5 (impaired) to Category 4A (approved TMDL in place).


DWQ reviews the data submitted during the IR process to determine whether assessment units identified as impaired in previous IRs are now meeting their designated beneficial uses. If DWQ finds during its assessment that waterbodies previously listed as impaired are now meeting water quality standards, it provides a list of the sites proposed for removal from Category 5 and the 303(d) list in the report. DWQ can delist a previously impaired parameter, waterbody, or segment within a waterbody that is currently meeting water quality standards if it can demonstrate good cause to stakeholders and EPA. Good cause includes one or more of the following:

  • The impairment was resolved through the implementation of nonpoint source projects and/or revised effluent limits.
  • Revised water quality standards and/or beneficial uses put the waterbody into attainment of those standards and/or uses.
  • A new listing method consistent with state water quality standards and classifications and federal listing requirements changed the previous listing.
  • New data led to a reassessment that demonstrated that applicable standards and uses are being met.
  • Flaws in the original analysis led to an incorrect listing.
  • Improved modeling applications demonstrated that applicable standards and uses are being met.

AU Resegmentations

When site-specific assessments within a single AU conflict, DWQ may determine that it is appropriate to re-segment (i.e., “split”) an existing AU polygon into two or more new AUs rather than aggregate those conflicting assessments into a single AU scale category. AUs where water quality criterion exceedances are clearly isolated to a relatively small, hydrologically distinct portion of the larger AU may be re-segmented to more accurately reflect that variation in water quality. This results in a higher resolution and overall more accurate assessment. DWQ does not consider it appropriate to re-segment an AU when exceedances are observed in multiple locations throughout an AU, or where impaired sites are not hydrologically distinct from unimpaired portions of the AU.

Public Comment

DWQ engages its stakeholders early in the process as part of its ongoing commitment to work with the public to safeguard human health and protect and enhance Utah’s waters. Communities and others affected by the decisions under CWA 305(b) and 303(d) are asked to participate in the IR process during three public involvement opportunities before the Division submits the IR to EPA.

Public Comment on 305(b) and 303(d) Decisions

DWQ provides another formal public notification at the end of the IR report process that requests comments on AU placement in the five categories. DWQ responds to the comments in a summary document. The Division can revise the IR based on public feedback. Public comments and DWQ’s response are then submitted to EPA along with the 305(b) report and 303(d) listing decisions.

Public Comment on Assessment Methods

DWQ held a public comment period on the 303(d) Assessment Methods from November 7, 2018, to December 21, 2018, to solicit public input on the assessment methods for the Combined 2018/2020 IR. DWQ received comments from eight different individuals and groups for a combined total of approximately 215 unique comments. DWQ’s Response to Comments, as well as the comments submitted, can be found on Utah’s Integrated Report page.

Publicly Submitted Data Notification

DWQ issues a formal public notification during each IR cycle through website postings and listservs, requesting data and information that can be used for the assessment. Whenever possible, DWQ tries to obtain all data and information with sufficient time to compile the information during odd-numbered years. This provides the Division with adequate time to obtain clarification where necessary and ensures that outside sources of information are used to the greatest extent possible for IR assessments. The Combined 2018/2020 IR Call for Data ran for 60 days from May 21, 2019, to July 20, 2019. Data submitters registered on the DWQ Call for Data website and were provided detailed instructions on how to submit data accurately and effectively to EPA’s Water Quality Exchange.


DWQ compiled all existing and readily available data and conducted designated beneficial use assessments to determine which waters in the state are supporting or not supporting these uses. The figures, charts, and graphs offer a view of the state’s total waterbody miles and acreage, and areas and water quality parameters assessed.

Map Instructions

Click the assessment unit polygons for draft assessment information. Hover over the layers button to turn on and off assessment category polygons. The “Reset View” button will set the map to its original bounds around the state of Utah. Use the “Search” box to look up assessment units by name or assessment unit ID.

Data Reviewed

  • Number of data records downloaded from EPA’s Water Quality Portal: 1.36 million
  • Number of data records that passed screening and data preparation checks for assessment: 432,280
  • Number of data records rejected during the secondary review process: 35,281
  • Number of data records in the core assessment dataset for the period of record following screening, secondary review, and daily aggregation: 348,003
  • Number of unique assessments by site, use, parameter, and criterion: 61,388

Assessment Totals (Flowing Surface Waters of the State, Canals, Lakes, Reservoirs, and Ponds)

  • Total AUs reported on: 913
  • Total AUs fully supporting (Category 1): 80
  • Total AUs partially supporting (Category 2): 133
  • Total AUs with insufficient data (Category 3): 321
  • Total AUs with a plan in place (Category 4): 32
  • Total AUs impaired (Category 5): 347

Flowing Surface Waters of the State and Canals

  • Total assessment units (AUIDs) reported on: 771
  • Total miles reported on: 82,339
  • Total monitoring locations assessed and reported on during the period of record: 1,929

Impairment counts by parameter category for the State’s flowing surface waters and canals.

Lake, Reservoir, and Pond Assessments


  • Total AUs reported on: 142
  • Total acres reported on: 1.46 million

Impaired parameters

Impairment counts by parameter category for the State’s lakes and reservoirs.


Priority Waters

The CWA requires the development of total maximum daily load (TMDL) plans for all impaired waterbodies on the 303(d) List but recognizes the limitations in data, time, and staff resources to accomplish this task. Taking these limitations into account, the CWA requires states to prioritize where they will dedicate resources toward TMDL development. DWQ prioritizes impairments or risks to human and ecological health as described in the Division of Water Quality’s (DWQ) 303(d) vision document (2.3 MB). These priorities focus on the protection and restoration of waters designated for culinary, recreational, and aquatic wildlife uses.

For more info on priority waters and the schedule for TMDL development, contact the Watershed Protection Section.