METHODS TO REDUCE OR AVOIDTHERMAL IMPACTS TO SURFACE WATERA MANUAL FOR SMALL MUNICIPALWASTEWATER TREATMENT PLANTSPrepared bySkillings Connolly, Inc.5016 Lacey Blvd SE, Lacey, WA 98503Prepared forWashington Department of EcologyWater Quality ProgramJune 2007Ecology Publication # 07-10-088
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TABLE OF CONTENTS1.0Introduction.126.96.36.199.0Why Temperature Is Important.188.8.131.52.42.53.0Purpose.1Need .2Organization of Report .2Water.3Temperature and Aquatic Habitat.3Regulatory Background .4Washington’s Temperature Water Quality Standards .5Sources of Additional Information .7Overview of Approaches to Reduce Thermal Impacts to Receiving Waters .83.1 Unique Solutions.83.2 Multiple Approaches.83.3 Method Categories .93.4 Cost Considerations .103.5 Sources of Additional Information .104.0Cooling Effluent While It Is Still Influent .184.108.40.206Public Awareness and Education.11Pretreatment of Heat Loads .12In-Plant Modifications to Cool Effluent .155.1 Clarifier Covers.165.2 Disinfection Alternatives .186.0Discharging from the Treatment sonal Storage .21Move Discharge Location.23Multiple Port Diffusers .25Effluent Blending.28Land Application .31Unlined Ponds or Lagoons.34Infiltration Trenches.36Rapid Infiltration.38Exfiltration Gallery .41Hyporheic Injection and Floodplain Channel Restoration.43Constructed Wetlands .46Wastewater Reclamation and Reuse.49i
7.0Direct Cooling of Effluent .5220.127.116.11.47.57.6Riparian Shading.56Cooling Ponds.60Spray Cooling .63Cooling Towers.66Chillers.69Geothermal Heat Exchanger .72Appendix: Fresh Water Designated Uses and Criteria, WAC 173-201A-200.77ii
METHODS TO REDUCE OR AVOID THERMAL IMPACTS TO SURFACE WATER1.0 INTRODUCTION1.1 PURPOSE. The purpose of this manual is to provide the reader with an overview of methodsto reduce or eliminate thermal impacts from municipal wastewater treatment plant discharges tosurface water. If you are in some way involved with municipal wastewater treatment—as a plantoperator, engineer, public works director, city council member, environmental advocate, orinterested citizen, you may find this information of interest. The information provided is intended toassist decision makers in the first step of consideration and selection of effluent management optionsthat may be most applicable to a particular situation.This report does not address much in the way of engineering detail, and is not intended to substitutefor the analysis and advice of a wastewater engineer. The selection of one method from severaloptions will necessarily include a detailed review of equipment and cost analysis. This step of theselection process should be accomplished by an engineer who is familiar with treatment plantdesign, processes, and equipment. The analysis should include up-front capital costs as well asoperation and maintenance costs over the plant’s operating horizon or other logical planning period.The ultimate goal of this document and theWater Quality Program that initiated it is tohelp our streams maintain appropriatetemperature ranges to support their nativeand natural animals and plants, particularlyfish that spawn, migrate, or live in coldwater.This report is provided to you through theWashington Department of Ecology(Ecology). Any opinions expressed hereinor references to specific manufacturers,vendors, or equipment do not represent anysort of endorsement by the Department, norany regulatory requirement or guidance.References to equipment or manufacturersare provided as examples only, and are notbased on a review or analysis of similarequipment or manufacturers.City of Yelm wastewater treatment plantSource: Skillings Connolly, Inc.Water Quality staff at Ecology can provide additional assistance regarding temperature criteria andwater quality standards, discharge permitting, total maximum daily load (TMDL) analysis, andfinancial assistance for municipal projects. An organization chart for the Water Quality Programand staff contacts by subject are available on Ecology’s website s.1
METHODS TO REDUCE OR AVOID THERMAL IMPACTS TO SURFACE WATER1.2 NEED. In November 2006, the Washington Department of Ecology adopted temperaturecriteria in the surface water quality standards, found at Chapter 173-201A, WashingtonAdministrative Code (WAC). The temperature criteria limit the allowable temperature increase ofthe receiving water due to human caused impacts, including point source discharges. Ecology staffrecognized that implementation of the new temperature criteria could impact municipal wastewatertreatment plants if the effluent discharges were shown, through temperature modeling, to exceed theallowable temperature increment. In that event, municipalities would need to find ways either toreduce the temperature of the treatment plant effluent before discharge to the receiving water, or findanother discharge mechanism that would reduce or eliminate the thermal impact of the plant’seffluent. As municipal budgets are typically already overstretched, there was a clear need to identifyapproaches that could be implemented relatively inexpensively.1.3 ORGANIZATION OF REPORT. This manual outlines a number of different approaches inan attempt to satisfy this need as well as to provide general comparative information for themethods. Section 2.0 discusses why receiving water temperature is important and how thermalloading impacts aquatic habitat. Section 3.0 provides an overview of the types of cooling methodsdescribed, the potential for using multiple approaches, and a brief discussion of the issue of cost.Approaches to limiting the heat content of wastewater before it reaches the treatment plant areaddressed in Section 4.0. Modifications that could be made to the treatment plant itself to keep thewastewater from warming during the treatment process are addressed in Section 5.0. Alternativedischarge methods are discussed in Section 6.0. Direct cooling methods are described in Section7.0.2
METHODS TO REDUCE OR AVOID THERMAL IMPACTS TO SURFACE WATER2.0 WHY TEMPERATURE IS IMPORTANT2.1 WATER. Water is unquestionably the essential ingredient of life on this planet. Water is alsoa finite resource. As global population grows and the demand for food, fuel, electricity, industry,housing, and recreation increases, water becomes increasingly more valuable and precious.Management of this resource to ensure adequate water supplies for all of its uses is becoming yearby-year more difficult. Part of this difficulty is ensuring that water bodies are not contaminated bypoint and non-point discharges, and that the water quality remains sufficient to support the usesrequired of each stream, river, and lake.Improvements in wastewater treatment in the U.S. over thepast 100 years have helped reduce contamination of freshwater and marine water with biological and chemicalconstituents. We now have over 50 years of evidence thattoxic chemicals from industrial practices can have devastatingeffects on wildlife, fish, and human health. Increasingunderstanding of aquatic habitats, particularly in studiesrelated to endangered species, has shown that it is not justchemical or biological pollutants that can impair species healthand survival rates. Physical properties such as temperatureand dissolved oxygen are also very important to aquaticorganisms.2.2 TEMPERATURE AND AQUATIC HABITAT.Great blue heronPacific Northwest salmonids are cold-blooded. TheirSource: Skillings Connolly, Inc.distribution, health, and survival depend on the temperature ofthe water in which they live. Certain activities in the life of a salmonid are triggered by watertemperature, such as cooler river water temperatures in the fall which signal the time for upstreammigration. To some degree, fish can tolerate the seasonal swings in temperature and the moredramatic variations in climatic conditions that push temperatures outside the optimal range.However, there is a clear connection between rising temperatures in many Northwest streams andreductions in salmonid populations in the same areas. Numerous studies since 1985 havedocumented declines in Oregon and Washington salmonid populations where temperature wasidentified as a contributing factor. (1)Human activities have caused increases in stream water temperature in a number of ways. Thefollowing list summarizes activities that contribute to increasing the thermal input to the river,reducing the amount of groundwater that serves to moderate stream temperatures, or reducing thecapacity of a river to absorb heat. (1) Urban development, timber harvest, land clearing for agricultural purposes, and livestock grazinghave removed streamside vegetation that provides shade over rivers and streams. When the waterreceives direct sunlight, it is warmed.3
METHODS TO REDUCE OR AVOID THERMAL IMPACTS TO SURFACE WATER Stream bank erosion and sedimentation loading in the stream, also caused by removal ofstreamside vegetation, increases the solar heat transfer in the stream. Erosion causes the streambanks to widen and the streambed to become shallower. Water discharges from a variety of sources can add heat to the stream. These sources includestormwater runoff, industrial discharges, wastewater treatment plant effluent, and irrigation returnflows. Withdrawal of excessive quantities of water from a river can significantly impact its capacity toabsorb heat. The smaller volume of water remaining instream will heat more quickly and dissipateheat from a warm discharge less effectively. Reshaping a river for flood control, urban development, or agricultural purposes can alsocontribute to impairment of a river’s natural ability to moderate temperatures. Straightening,channeling, diking, and dam construction can reduce the flow of groundwater through naturalflood channels and through the hyporheic zone, where groundwater flows under and through theriverbed. Dams and reservoirs create different temperature patterns within the river system. (1)2.3 REGULATORY BACKGROUND. Washington’s adoption of temperature water qualitystandards in November 2006 was preceded by EPA Region 10’s development of guidance on thissame topic. The guidance document, EPA Region 10 Guidance for Pacific Northwest State andTribal Temperature Water Quality Standards, is