Quality Assurance and Quality Control of Water Quality Data
DEC's Division of Water (DOW) is committed to transparency and standardization of data that reflects the quality of New York's waters. The methods used to generate and analyze water quality data must be reproducible and correct. Consistency in the collection of data allows DOW to compare water quality data across time periods and/or locations, determine patterns, and understand water quality issues. To ensure the scientific integrity of its work, DOW requires water quality data and information it uses include a description of quality.
Data quality is described with measures known as Data Quality Indicators (DQIs). DQIs are used to define the minimum data requirements needed to meet project goals. These requirements are described before work begins in a standard written document, known as a Quality Assurance Project Plan (QAPP). After the completion of work, a Data Usability Assessment Report (DUAR) is written to describe how these minimum requirements were met.
Examples of DQIs are:
- Precision: How close are multiple measurements from the same location?
- Accuracy: How close is an observed measurement to a known value?
- Bias: Are there underlying factors (e.g., sample collection method) leading to a consistent misrepresentation of results?
- Sensitivity: Does a measurement method (e.g., laboratory analysis) provide the resolution or level of detail necessary to meet project goals?
- Comparability: Can data collected at multiple locations be compared to one another?
- Representativeness: Does the collected data correctly portray the characteristics of interest (e.g., the ambient water quality of a lake)?
- Completeness: Was enough valid data (data determined to meet other DQI project requirements) available to meet project goals?
For more information on DQIs, please see Table 3, in EPA's Guidance for Quality Assurance Project Plans (EPA QA/G-5). DQIs provide DOW with the necessary Quality Assurance (QA) information to determine how to use data appropriately and responsibly.
QA has a positive impact on all elements of DOW's waterwheel (Figure 1 below). The waterwheel represents how DOW programs work together to protect water quality in New York. QA ensures that this cycle can be completed efficiently and effectively. The DOW Quality Assurance Management Plan (PDF) describes the QA roles, responsibilities, and procedures within this cycle. DOW's requirements for QA are included below.
Environmental Data Requirements
The data and information DOW uses to implement its regulatory programs must adhere to the following requirements:
- QAPP based on guidance provided by the EPA Guidance for Quality Assurance Project Plans (QA/G-5 May 2006). The fulfillment of the data verification, validation, and usability component of the QAPP is to be documented in a Data Usability Assessment Report (DUAR).
- Adhere to approved test procedure methodologies defined in 40 CFR Part 136, as appropriate.
- Use laboratories certified by the New York State Department of Health (DOH) under the Environmental Laboratory Approval Program (ELAP) pursuant to Section 502 of the NYS Public Health Law. This requirement does not apply to specific parameters where DOH ELAP has not issued a certificate for the specific parameter.
QAPPs, DUARs, and SOPs
- Quality Assurance Project Plan (QAPP): a document created prior to the start of work that outlines the who, what, where, when, why, and how of the project.
- Data Usability Assessment Report (DUAR): a document created at the end of a project to describe how well the QAPP was followed and if data met the quality control requirements defined in the QAPP.
- Standard Operating Procedures (SOP): a document that details the step-by-step process of an activity. For example, how to calibrate and use a multi-parameter probe. They can be useful to reference when filling out a QAPP.