Kaibigan ng Kaunlaran at Kalikasan (KKK)

Kaibigan ng Kaunlaran at Kalikasan (KKK)

Friends of Progress and the Environment

Updated Water Quality Guidelines (WQG) and General Effluent Standards (GES)

The DENR Administrative Order 2016-08 of 24 May 2016 prescribed revised and new WQG and GES which could impact on the operations of existing facilities and on new investments involving industrial plants

Among the salient points of the DAO are:


1.0 Effluent standards for hazardous/toxic substances, such as (for illustration purposes):


Selected Water Quality Guidelines for Secondary Parameters-Organics

2.0 Revocation of previous exemption to small volumetric discharges with the former following provision:


Previous per DAO 35.

"The effluent standards apply to industrial manufacturing plants and municipal treatment plants discharging more than thirty (3) cubic meters per day."


3.0 Revised WQG on Temperatures of surface water as stipulated below


Water Quality Guidelines (Selected) for Primary Parameters

Notes in the Administrative Order on the Guidelines for Temperature:


– The natural background temperature as determined by EMB shall prevail if the temperature is lower or higher than the WQG; provided that the maximum increase is only up to 10 percent and that it will not cause any risk to human health and the environment.

The above is of particular interest and concern to facilities which use surface water e.g. sea water for cooling purposes in a “önce-through” system whereby the abstracted water is returned to the water body at elevated temperature.

Among the points of current discussions are:

There are some ambiguities in the above particularly in reference to ..."the natural background temperature in relationto the WQG" arising from the given temperature ranges which vary by more than 10 % and the clarifying statement.."will not cause any risk to the environment"… On the "risk to the environment" the challenge is how a facility which is still in the planning stage could ascertain the absence of this risk.


The previous guidelines for temperature effects are contained in the concept of "mixing zone" which was then defined in DENR Administrative Order No. 35 as follows:

"'Mixing Zone' is the place where the effluent discharge froma point source mixes with a receiving body of water. The area or extent of the zone shall be determined by the discharger and approved by the Department on a case-to-case basis."


Mixing Zone Requirements.The following general conditions shall govern the location and extent of the mixing zone:


  1. No mixing zone or combination of mixing zones shall be allowed to significantly impair any of the designated uses of the receiving body of water.
  2. A mixing zone shall not include an existing drinking water supply intake if such mixing zone would significantly impair the purposes for which the supply is utilized.
  3. A mixing zone for rivers, streams, etc., shall not create a barrier to the free migration of fish and aquatic life.
  4. A mixing zone shall not include a nursery area of indigenous aquatic life nor include any area designated by the Department of Environment and Natural Resources for shellfish harvesting, tourist zones and national marine parks and reserves, coral reef parks and reserves and declared as such by the appropriate government agency.
  5. In general, the length of the mixing zone or plume in rivers or similar waterways shall be as short as possible and its width shall be preferably not more than one-half of the width of the waterway.
  6. In discharging hot effluents from power plants, mineral ore milling and similar generators of large volume of liquid wastes the permissible size of the mixing zone shall be determined through modeling taking into consideration the size, hydraulic and hydrological data of the receiving body of water and the design and siting of the wastewater outfall.

US EPA Regulations


The US EPA recognizes the use of mixing zone(Ref: National Service Center for Environmental Publications (NSCEP) under the title "Compilation of EPA Mixing Zone Documents" 2006). Its definition of mixing zone

Mixing Zone Definition


Acording to EPA's Technical Support Document for Water Quality-based Toxics Control (TSD) (USEPA, 1991), "a mixing zone is an area where an effluent discharge undergoes initial dilution and is extended to cover the secondary mixing in the ambient waterbody. A mixing zone is an allocated impact zone where water quality criteria can be exceeded as long as acutely toxic conditions are presented." ( Water quality criteria must be met at the edge of a mixing zone.)


Mixing zones are designed to be protective of human health, aquatic habitat and the water body as a whole.


Additionally, the State of Oregon Department of Environmental Quality recognizes "best practicable treatment" in itsRegulatory Mixing Zone Internal Management Directive


Part One: Allocating Regulatory Mixing Zones May 2012


State requirement for highest and best practicable treatment


OAR 340-041-0007(1) requires highest and best practicable treatment and/or control of wastes, activities, and flows to maintain the overall water quality at the highest possible levels and deleterious factors (e.g., temperature, toxics) at the lowest possible levels. While this is evaluated on a case-by-case basis, and additional state or federal regulations may apply, the department generally uses EPA technology-based effluent limitations to make this evaluation.

Under the NPDES (National Pollutant Discharge Elimination System of the USEPA) permitting authorities allow an allocated impact zone for dischargers—an area near the outfall where higher pollutant concentrations, temperatures, or suspended solids are allowed before water quality standards must be met. Permit conditions are established through mixing zone analysis that considers the size, position within the receiving stream, constituents of concern, dilution capabilities, and sensitive ecological communities.

Mixing zone analyses allow dischargers to confidently evaluate receiving water effects based on different discharge/treatment scenarios, defining the appropriate balance between water quality protection and necessary level of treatment.

Application of the Mixing Zone Concept to Projects Still to be Implemented/Constructed


Internationally-accepted numerical methods are available and readily applicable to make a scientific determination as to whether a discharge of water at elevated temperatures will in fact create adverse impacts on the water environment in an area called "mixing zone".


The presence or absence of significant marine species in this zone can readily be established. Upon the determination of the temperature profile in the zone it can determined if adverse impacts will in fact occur.

An Illustration of the Mixing Zone concept as determined by numerical modeling for a facility which is yet to be implemented is provided below:

The cooling water return to the sea at an elevated temperature at the outfall is predicted to result in a mixing zone shown in the Figure below. From this map are seen that only a small area (zone) in the sea will experience temperature increase of less than 31 deg C while the greater portion of the mixing zone will experience an increase of less than 28.5 deg C versus an ambient of 28.5 deg C.

Factors affecting the mixing zone are : volumetric flow rate of the water discharged, temperature at point of discharge, depth of the discharge point, below the sea suface, wind velocities and direction, bathymetry of the sea at the point of water discharge.


Ultimately, the test of"not causing any risk to the environment"is made by making a survey of marine species within the mixing zone that may be exposed to risks.

Map Showing the Thermal Mixing "Zone"


4.0 Remedies for Clarifications or Revisions


In principle, the Administrative Order provides room for requests for modifications in the WQG and GES, as stipulated below:

Download: New DENR DAO on General Effluent Standards

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