1.1 Water Quality Standards, CWA & SDWA

Water Quality Standards, CWA & SDWA

Environmental engineers must navigate a complex framework of federal regulations designed to protect both the natural environment and human health. The two primary statutes governing water quality in the United States are the Clean Water Act (CWA) and the Safe Drinking Water Act (SDWA). Understanding their distinct scopes, regulatory mechanisms, and quantitative standards is critical for the PE Environmental exam.

The Clean Water Act (CWA)

The CWA, originally enacted as the Federal Water Pollution Control Act of 1972, establishes the basic structure for regulating discharges of pollutants into the waters of the United States and regulating quality standards for surface waters.

NPDES Permitting Program

Section 402 of the CWA introduces the National Pollutant Discharge Elimination System (NPDES). Under this program, it is unlawful to discharge any pollutant from a point source into navigable waters without a permit.

• Point Sources include pipes, ditches, and municipal wastewater treatment plants.
• Permit Limits are typically based on Technology-Based Effluent Limitations (TBELs) or Water Quality-Based Effluent Limitations (WQBELs), whichever is more stringent.

Water Quality Standards (WQS) and TMDLs

When technology-based limits are insufficient to meet the water quality standards of the receiving waterbody, Section 303(d) of the CWA comes into play.

• WQS consist of designated uses (e.g., recreation, aquatic life), water quality criteria (numeric or narrative), and an antidegradation policy.
• TMDL (Total Maximum Daily Load) is the calculation of the maximum amount of a pollutant that a waterbody can receive and still safely meet WQS.

The TMDL equation is typically expressed as: $TMDL = \sum WLA + \sum LA + MOS$ Where:

• $WLA$ = Wasteload Allocations (point sources)
• $LA$ = Load Allocations (nonpoint sources and background)
• $MOS$ = Margin of Safety

Section 404 and 401

• Section 404 regulates the discharge of dredged or fill material into waters of the United States, including wetlands. The US Army Corps of Engineers (USACE) administers this program with EPA oversight.
• Section 401 requires that any federal applicant for a permit to conduct an activity that may result in a discharge to navigable waters must provide a certification from the state that the discharge will comply with applicable state WQS.

The Safe Drinking Water Act (SDWA)

Passed in 1974, the SDWA focuses on all waters actually or potentially designed for drinking use, whether from above ground or underground sources. It authorizes the EPA to establish minimum standards to protect tap water and requires all owners or operators of public water systems to comply with these primary (health-related) standards.

Primary vs. Secondary Standards

• National Primary Drinking Water Regulations (NPDWRs): Legally enforceable standards that apply to public water systems. They protect public health by limiting the levels of specific contaminants. These take the form of Maximum Contaminant Levels (MCLs) or Treatment Techniques (TT).
• National Secondary Drinking Water Regulations (NSDWRs): Non-enforceable guidelines regulating contaminants that may cause cosmetic effects (e.g., skin or tooth discoloration) or aesthetic effects (e.g., taste, odor, or color). These are represented by Secondary Maximum Contaminant Levels (SMCLs).

MCLGs and MCLs

• Maximum Contaminant Level Goal (MCLG): The level of a contaminant in drinking water below which there is no known or expected risk to health. MCLGs are non-enforceable public health goals. For known carcinogens, the MCLG is set at zero.
• Maximum Contaminant Level (MCL): The highest level of a contaminant that is allowed in drinking water. MCLs are enforceable standards set as close to MCLGs as feasible using the best available treatment technology and taking cost into consideration.

Treatment Techniques (TT) and Action Levels

For some contaminants, it is not economically or technologically feasible to measure their concentration. In such cases, the EPA establishes a Treatment Technique (TT), a required process intended to reduce the level of a contaminant in drinking water.

• Lead and Copper Rule (LCR): Lead and copper are regulated via an Action Level rather than an MCL. The Action Level is the concentration of a contaminant which, if exceeded, triggers treatment or other requirements that a water system must follow. The Action Level for Lead is 0.015 mg/L (15 ppb) and for Copper is 1.3 mg/L.

Unregulated Contaminant Monitoring Rule (UCMR)

The SDWA requires the EPA to issue a new list of up to 30 unregulated contaminants to be monitored by public water systems every five years. The UCMR provides occurrence data for contaminants that are suspected to be present in drinking water but do not yet have health-based standards.

Quantitative Standards Reference

Engineers must be intimately familiar with both the legal mechanisms and the specific numeric limits that govern municipal water and wastewater treatment system design. Failure to comply with an NPDES permit can result in severe fines, while failure to meet SDWA standards can endanger community health.