Microbial Risk Assessment Guide

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Microbial Risk Assessment Guide PDF

MICROBIAL RISK ASSESSMENT GUIDE

- THE RANKING TOOL

Welcome to the Small Water System Surveyuidance. This part of the Microbial Riskssessment Guide will provide helpfulformation for answering system survey

uestions, and assist you in understandingour water system's risk scores.

We suggest that you view the introductionnd print all required survey documentsefore proceeding to the guidance content in

nits 1-7. If you have missed either of theseeps, please click the MENU tab above anden choose the appropriate link below the

Microbial Risk logo. If you are ready for guidance, please click a section below.

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.1 - General Survey Instructionshe Small Water System Survey collectsformation on various water system

omponents. Based on your answers, theanking Tool provides numerical scores forach system component and suggestions

ou may want to consider when trying toinimize potential microbial contaminationsks. The scores can be used to evaluateoth specific (each well or pump station) andeneral components (all water sources or allump stations) of your water system. Theurvey is divided into six parts:

art A requests general information aboute water system, such as population served, number of wells, number of pump stations, etc.ompleting the survey for Part A is the first step in the process of filling out the survey forms

or your water system. If you have viewed the introduction movie and printed your surveyorksheets, then you have already completed this worksheet.

urvey Part B addresses the source(s) of water for your water system. For example, if youvert water from a lake you would answer questions in the survey for "II. Surface Water -ake or Impoundment." Unit 2 provides more specific guidance for Part B.

art C covers treatment facilities associated with your water system. There are separate

urveys for various types of treatment facilities, so you will only address questions for theeatment facilities that are part of your water system. Disinfection and corrosion controlrocesses are included under treatment. Guidance for treatment processes can be found innit 3.

art D consists of questions regarding any pump station or storage tank in your system. If aater source or treatment plant has a pump station, e.g., a pumping system at a well, answeruestions for the pump facilities using Part D. and use Part B. for the well. For moreformation about pumping and storage survey questions, see Unit 4.

art E covers both transmission pipelines and the distribution system. It addresses topicsuch as what type of materials are installed, how the system is maintained, who performsaintenance, etc. See Unit 5 for guidance.

art F involves questions about who monitors your water for microbial safety, how oftenonitoring is performed, and if there have been violations of current standards. If you are

nsure how to answer any of the questions in Survey Part F, refer to Unit 6 of this tutorial.

ou should print and complete a survey for each part of your water system. You can skip a

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urvey type that does not apply to your system. For example, if your system has nostribution system you would not complete the survey for Part E.II.-Distribution System. If you

ave more than one source of water (two wells, well and spring, etc.), three pump stations,c., then fill out an appropriate survey form for each source or facility.

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.2 - The Ranking Toolhe Ranking Tool consists of a series ofnked worksheets within a single workbook.he term "workbook" refers to all worksheets a single file. Think of each worksheet as a

age in a multiple-page workbook. At the

ottom of the Excel screen are labeled tabsor each part of the survey. Think of tabsuch like divider tabs you might see in aorkbook or 3-ring binder. By placing theouse cursor over and left-clicking on the tab you want, the worksheet for that part of the

urvey is opened. In all there are 21 worksheets (tabs) in the workbook file RankingTool.xls.

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.3 - Viewing CommentsWhen you have completed answeringuestions for a part of the survey, and haventered answers to questions in the Rankingool, you can view comments oruggestions that are based on your answers.

s shown in (FIGURE 1) , the right hand sidef the worksheet has a summary of theformation entered into the "Part_A"orksheet (general water systemformation). You can view this information directly on the screen of the computer's monitor,

ut you may not be able to see all of the information due to limitations of the monitor's size.

owever, you can view all of this information by placing the mouse pointer over the "Viewummary" button and left-clicking. This will allow you to see all of the summary or commentsn a worksheet. To return to the answers part of the worksheet, simply left-click on the "Viewnswers" button to return to the left side of the worksheet. In place of the "View Summary"utton, each survey answer worksheet or Part has a "View Comments" button.

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.4 - Navigating Worksheetshe user can switch between worksheets byicking on the appropriate "tab" at theottom of the worksheet screen. To facilitateuicker movement from worksheet toorksheet, a navigation window is provided.

here are two ways to access this window.ne way is to hold down the "Ctrl" key andressing the "h" key (Ctrl + h), or it can beccessed by pointing to and left-clicking one Sheets and Forms button of the Surveyool Bar.

his toolbar should be a small window on topf the worksheet. If the toolbar is not visible, go to the View menu at the top of the Excelcreen, select Toolbars, and select the Customize menu item. In the "Customize" windowick on the Toolbar tab and then make sure there is a check in the box in front of "Surveyools." If not, left-click the box to select the "Survey Tools" toolbar then close the window.

FIGURE 2) indicates the short-cut key combinations to access other control forms (windowsat allow you to easily perform tasks such as clearing all answers on a worksheet).

When the "Select Survey Sheets & Control Forms" window is open, you can select any of theurvey answer sheets or sheets showing results of the survey by left-clicking on the downrow to show all sheets and then left-clicking on the sheet you want to view. This window can

so be used to select four other help windows (control forms) for the Ranking Tool.

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.5 - Clearing Worksheet Answerst any time, the user can clear the answers the current worksheet, a series oforksheets or all worksheets. The "Clear

Worksheet Answers" window can be broughtp using the "Select Survey Sheets &

ontrol Forms" window, or by using the (Ctrla) shortcut. To clear (delete) answers forny survey answer sheet, select the checkox next to the Part you want to clearnswers for and then left-click on the "Clearhecked Items" button. A message box will come up asking if you want to clear all answersn the selected worksheet(s). Left-click on the "Clear ALL Answers" button to clear answersn ALL worksheets, or left-click on the "Cancel" button to close the window.

fter clicking on the "Clear Checked Items" button a question dialogue box will appear askingou if you want to clear answers to checked items. If you click on the "Yes" button, anotheruestion dialogue box will appear asking if you want to clear the answers to a specific answerorksheet. Answers can be cleared while working on any survey answer worksheet by left-icking on the button at the top of that sheet.

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.6 - Checking Percent Valueshe "Check Percent Values" window

FIGURE 3) shows the user the currentum of the percent of annual supply, orercent of all storage, values required the survey forms. Each survey form

or Parts B., C., D., and E.I. require theser to input the percent of annualater supply provided by each facility,r in the case of Part D.II.-Storage, theercent of the total storage volume.hese are the same survey answerheets that provide up to four answerorms for each type of source,eatment or facility they cover. The

ollowing example demonstrates theum of percent values concept.

water system has three waterources: a spring and two wells. Theurvey for each source asks whatercent of the average annual waterupply is provided by each source.irst one must determine the averagennual water supply. For this example the water system produces approximately 200,000allons of water per day (200,000 gallons/day x 365 days/year = 73,000,000 gallons/year or3 million gallons per year). There are several ways to determine the percent of annual supplyrovided by each source:

Based on operator knowledge, the spring supplies 80% of the annual supply and each wellupplies 10%. The total should sum up to 100%. (80% + 10% + 10% = 100%).

If the operator has data on the total gallons of water supplied by each source last year, theercent of annual supply values can be calculated as follows:otal annual water supply = 73,000,000 gallons per yearnnual spring water production = 58,400,000 gallons per yearnnual well production, each well = 7,300,000 gallons per year

ercent of Annual Supply for Spring = 58,400,000 / 73,000,000 x 100 = 80%

ercent of Annual Supply for a Well = 7,300,000 / 73,000,000 x 100 = 10%

at any time the user of the Ranking Tool is unsure as to what the sum of all percentages for

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given "Part" are, the user can bring up the "Check Percent Values" window (Ctrl + k). Beforeewing or printing results for Part B or D, the user should check to make sure all components a particular Part add up to 100, otherwise the numerical scores assigned to each

omponent in the total water system scores will be in error. The Ranking Tool will give you aessage warning you of this condition, if it exists, prior to printing results. In addition to the

Check Percent Values" window, there is an up-to-date box on each survey sheet showing theurrent sum of percent values as shown in (FIGURE 4) .

um of percent values for all of Part C, Part D.I., and Part E.I. do not have to add up to 100.owever, the percent values for a particular Part cannot exceed 100, e.g., the sum of percentf supply for raw water transmission pipelines cannot exceed 100, but could be less than 100the pipe only supplied a fraction of the total supply. The exception to this is Part D.I.,

umping Facilities. Four different types of pumping facilities can be entered:

) Distribution System Pumping (e.g., a booster pump station),2) Wells (vertical turbine or submersible-type pumps),3) Treated water (e.g., pump station at a treatment plant), and4) Raw water (e.g., lake intake pump station).

With the exception of distribution system pumping facilities, the sum of percent values cannotxceed 100% for any one type of pumping facility. For example, the sum of percent for alleated water pumping facilities cannot exceed 100%. However, the sum of percent forstibution system pumping can exceed 100%. You will receive a warning if the sum of

ercent values you enter for a type of pump station, say for wells, exceeds 100%. There is noaximum sum of percent value for distributions system pumping facilities.

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- WATER SOURCE

nit 2 provides guidance material forompleting Part B - Water Source in themall Water System Survey. The Rankingool contains surveys for surface water and

round water source types. A surface waterource is all of the watershed upstream of antake point, including the intake structure. A

round water source includes the facilityesigned to extract water from an aquifer,e aquifer itself and the land areas thatfluence the quality of water in the aquifer.

Well pumps, pump stations, and treatmentcilities are covered in separate surveys.

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.1 - Surface Water: Stream or RiverWater diverted or pumped from a stream or

ver that is open to the atmosphere is aurface water source. Surface water sourcesre vulnerable to a wide variety of microbialontaminants originating from sources such

s wastewater and stormwater discharges toe watershed. Part B.I. questions inquirebout items such as ownership andanagement of land within the watershed,scharges to the waterway upstream of theversion point, and prevalence of native and

omestic animals within the watershed.

Stream or river source identification

ive each surface water source a number, starting at 1. If the water from each source iseated at different treatment facilities, answer "Part C - Treatment" for each facility.

xample: Suppose a water system has intakes on two different streams, North Fork andouth Fork, and the combined water from both sources is treated at one treatment facility.ive the North Fork supply the No. 1 and the South Fork supply the No. 2. Answer a survey

or each intake and its associated watershed. When you fill out Part C for Treatment,esignate the treatment facility as number 1. A treatment facility that treats a third source cane given the number 2.

Source Water Assessment

ource water assessments are an initial survey that indicates the extent of the watershed foris supply source, characteristics of the watershed (such as land uses and ownership), and

n inventory of potential contaminant sources that could reach the surface water.

xamples of contaminant sources are a municipal wastewater discharge, presence of cattler other livestock grazing along stretches of a stream or lake, or numerous septic systemscated near the surface water source.

Source Water Protection Program

source water protection plan uses the information gathered as part of the source waterssessment and develops a management plan for the watershed. The goal of theanagement plan should be to develop agreements and relationships with landowners or

gencies to minimize the potential for pollution of the water supply.

n example would be working with landowners to fence-off a buffer area along streams to

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ntakes on rivers or streams come in many different configurations, but most have some formf screen or bar rack to prevent objects and contaminants from entering the water supply.enerally, fine screens are the best, keeping out fish and other rodents. Fine screens require

ome form of cleaning mechanism or they become easily clogged with debris. Coarsecreens or bar racks are typical, but cannot remove smaller contaminants.

is good practice to control human and animal access to the area around the water intakeructure. Most desirable is a security fence with a locked gate. Less desirable but many timesecessary are fences to prevent livestock or native animals away from the intake site. Postinge area with signs that indicate access is restricted to only authorized personnel can help

revent people from entering the water intake site. Keeping the intake site secure from peoplend animals can help prevent intentional or unintentional contamination of the water supply.

Many times it is evident to water system operators that the location of the intake or its designseverely limiting the ability to divert the best quality water. Moving or reconstructing thetake may improve water quality and reduce treatment costs.

0. Known sources of microbial contamination

When operators of a water system are aware of sources of microbial contamination, effortshould be made to eliminate, minimize or manage those sources. Preventing microbialontaminants from entering the water supply is an important task in the protection of theonsumer from water contamination. This can be particularly important if a situation such as aeatment unit failure should occur.

1. Filtration waivertates and EPA have strict requirements that must be met if a waiver of filtration of surfaceater is to be granted. Extensive watershed protection and management are required if aater source is to meet the requirements for remaining unfiltered.

2. Source treatment

oes this water source receive any form of treatment, including disinfection? (yes/no)

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.2 - Surface Water: Lake or ImpoundmentWater diverted or pumped from a lake,

servoir or other type of impoundment thatopen to the atmosphere is a surface water

ource. Surface water sources areulnerable to a wide variety of microbial

ontaminants originating from sources suchs wastewater and stormwater discharges toe lake or impoundment. Part B.II. questionsquire about items such as ownership andanagement of land within the watershedat supplies water to the lake, discharges ine watershed upstream of the diversion

oint, and location of domestic animals withine watershed.

General

ive each surface water source a number, starting at 1. If the water from each source iseated at different treatment facilities, answer "Part C - Treatment" for each facility.

xample: Suppose a water system has intakes on two different streams, North Fork andouth Fork, and the combined water from both sources is treated at one treatment facility.ive the North Fork supply the No. 1 and the South Fork supply the No. 2. Answer a survey

or each intake and its associated watershed. When you fill out Part C for Treatment,

esignate the treatment facility as number 1. A treatment facility that treats a third source cane given the number 2.

Source Water Assessment

ource water assessments are an initial survey that indicates the extent of the watershed foris supply source, characteristics of the watershed (such as land uses and ownership), and

n inventory of potential contaminant sources that could reach the surface water.

xamples of contaminant sources are a municipal wastewater discharge, presence of cattler other livestock grazing along stretches of a stream or lake, or numerous septic systemscated near the surface water source.


source water protection plan uses the information gathered as part of the source waterssessment and develops a management plan for the watershed. The goal of theanagement plan should be to develop agreements and relationships with landowners or

gencies to minimize the potential for pollution of the water supply.

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n example would be working with landowners to fence-off a buffer area along streams toinimize cattle access to water. Many watersheds are so extensive that only those areas that

ould conceivably contribute contaminants to the water are considered, such as the areaithin a set number of feet of rivers, streams or lakes, and within a certain distance upstreamf the water intake.

Management of land use and activities within the watershedhe geographic extent of the watershed should be identified in the source water assessmentr source water protection plan. When a water system or other governmental agencyanages land use and activities within the area that could influence water quality, it becomesore feasible to monitor and control those land uses or activities that could pose a

ontamination risk to the water supply. Most management plans include setting clear lines ofommunication between the water utility and those that could pose a serious risk ofontamination (e.g., municipal wastewater treatment plant). For example, if a cattle feedlotxisted within the watershed it may be possible to work with the owner to insure proper wastesposal and control of surface water runoff.

Domestic and native animals within watershed

he presence of domestic animals within the watershed can be a source of microbialontaminants under some circumstances. Grazing or confinement of domestic animals woulde of concern if the animals had unlimited access to streams or lakes. Minimizing domesticnimal access to surface water sources can improve water quality in several ways, includingduction of microbial contaminants. Other benefits are protection of stream and lake banks

nd reduced erosion, thus lowering suspended matter in the water.

onfined animal feeding operations (CAFOs) are another potential source of microbialontamination. If surface runoff from a CAFO can reach a stream or lake during a precipitationvent, there is greater risk for contamination of the surface water. Vegetated buffer strips cane effective in reducing microbial transport to a waterway.

ome watersheds support a large population of native animals such as deer or elk. Thereater the number of native animals in the watershed, the greater the risk of microbialontamination. While native animals do not generally pose a great threat, their presencehould be noted as a potential source of microbial contamination.

Human access to and activities practiced within watershed

Many watersheds exist on public lands, such as national forests, and it is not possible totally restrict access to the watershed. There are a large number of activities that can be

racticed within a watershed, many of which are recreational activities such as hiking,amping, boating, swimming, etc. These activities do not generally result in significanticrobial contamination, but should be noted as potential sources unless properly managed

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r supervised. Boating and swimming are commonly practiced on lakes or rivers that supplyrinking water, but those activities can increase the risk for microbial contamination.

atural resource extraction activities are more noted for water quality contaminants other thanicrobial contaminants. However, the mere presence of human activities can be considered ask unless properly managed and supervised.

Upstream wastewater dischargeshe discharge of treated and untreated wastewater to rivers, streams or lakes upstream of arinking water intake can be a major source of microbial contamination. Some towns andties have combined wastewater and stormwater sewers, resulting in overload of the sewerpes during heavy precipitation events and potential discharge of untreated wastewaterrectly to surface water. These discharges are referred to as combined sewer overflows

CSOs). Most wastewater utilities are working to eliminate or treat any CSOs, however theirresence can be a serious threat to a drinking water supply.

Many homes and businesses within any given watershed may rely on individual wastewatersposal systems, primarily septic tanks and drainfields. When located too close to a stream,ver or lake, the effluent from these systems can reach the surface water and possibly result microbial contamination.

he greater the distance from a water intake to an upstream discharge, the less is risk there isf microbial contamination. Dilution and pathogen die-off can occur within a healthy surfaceater source, decreasing the chance of serious contamination of downstream uses.

Upstream stormwater discharges/runoff within watershedtormwater can enter a surface water source as a point discharge or nonpoint discharge.oint discharges are pipes or waterways specifically designed to carry stormwater. Nonpointscharges are those that naturally occur as surface runoff during a precipitation event. Pointscharges arise from stormwater collected in urban, suburban or other developed areas and

onveyed to a nearby waterway or lake. These stormwater discharges can contain microbialontaminants.

onpoint discharges occur naturally during a precipitation event. When the surface runoff isom certain types of land uses, there is greater risk of microbial contamination. Specific landses of concern are land used for disposal of municipal wastewater sludge (solids from theeatment process), liquid municipal wastewater, or animal wastes such as those produced byAFOs. Vegetated buffer strips and/or diversion ditches are required to minimizeontaminated runoff from reaching the surface water.

s with wastewater discharges, the closer a potential contaminant source is to the watertake, the greater the risk for contamination.

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Surface water intake structures

Many lakes or impoundments have variable water quality with depth based on the season ofe year. Therefore, the ability to withdraw water from variable depths within the lake can help

mprove the ultimate quality of water withdrawn from the lake.

ntake structures for lakes of impoundments often are constructed with screens to prevent fish

nd other small animals from being drawn into the water supply. Manual or automaticeaning systems are often required to prevent clogging of the screen. Cleaning systemsenerally improve the quality of the water being withdrawn. Coarse screens may not requireeaning but have the potential to let fish or other small animals enter the water supply.

is good practice to control human and animal access to the area around the water intakeructure. Most desirable is a security fence with a locked gate. Less desirable, but manymes necessary, are fences to keep livestock or native animals away from the intake site.osting the area with signs that indicate access is restricted to only authorized personnel canelp prevent people from entering the water intake site. Keeping the intake site secure fromeople and animals can help prevent intentional or unintentional contamination of the waterupply.

0. Known sources of microbial contamination

When operators of a water system are aware of sources of microbial contamination, effortshould be made to eliminate, minimize or manage those sources. Preventing microbialontaminants from entering the water supply is an important task in the protection of theonsumer from water contamination. This can be particularly important if a situation such as a

eatment unit failure should occur.

1. Filtration waiver States and EPA have strict requirements that must be met if a waiver ofltration of surface water is to be granted. Extensive watershed protection and managemente required if a water source is to meet the requirements for remaining unfiltered.

2. Source Treatment

oes this water source receive any form of treatment? (yes/no)

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.3 - Ground Water: Wells & Drilled, Horizontal Well CollectorsWells are constructed to allow water to berawn from an aquifer located below theround surface. Aquifers are natural geologicormations that are pervious enough to allowater to move within the open pore spaces.

quifers are often composed of sand, gravelnd cobbles, but there are many other typesf materials that can serve as an aquifer.round water is generally less vulnerable toicrobial contaminants than is surface water,

ut there are numerous cases ofroundwater becoming polluted withicrobial contaminants from the ground's

urface. Shallow, unconfined aquifers can beusceptible to contamination from surface pollutants.

art B.III. questions cover both vertical wells (drilled or dug) and horizontal well collectors.orizontal well collectors consist of a central, vertical caisson that extends from the ground

urface to below the ground water table, with horizontally drilled wells located in a radialattern around the caisson. Protection of a well source from contamination requires knowinge area of influence, defined as the surface and subsurface area surrounding a well throughhich surface contaminants are reasonably likely to move toward and reach the well.etermining the area of influence requires experts and will not generally be available unless aource Water Assessment or Source Water Protection Plan (or Wellhead Protection Plan)as been developed for the well. Part B.III. questions inquire about items such as ownershipnd management of land within the area of influence, the characteristics of the aquifer suchs distance to the ground water table, well construction information, and prevalence of septicnk/drainfield systems in the area of the well.

Well source identification

ive each ground water well source a number, starting at the number 1.

xample: Suppose the Main Street well is one of your system's wells, and there is chlorineed equipment at this well. Give the Main Street well the number 1. When you answer Part Dor the pumping facility at this well, designate the pump station as No. 1. When you fill out Part

for treatment at this well, designate the treatment facility as number 1 also.

Type of ground water source

art B. III. should be used only for wells, including horizontal, drilled wells. Horizontal drilledells are those where a central sump or shaft was first constructed, then horizontal collector

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pes were drilled in a radial direction. Horizontal well collectors may be known as "Ranney"ollectors.

Source Water Assessment (Initial examination of area around well where contaminationould exist)

ource water assessments are an initial examination that indicates where the well's area of

fluence lies (the area where any contaminant spill or source could potentially reach the wellithin a short period of time). Potential contaminant sources are inventoried within the areaound the well. The assessment can help identify possible sources of contamination near theell, such as an area where livestock are being raised.

Source Water Protection or Wellhead Protection Program (Detailed management program protect the water quality in this well)

source water protection plan or wellhead protection plan uses the information gathered asart of the source water assessment and presents a management plan for the area offluence and any other area that could potentially contribute to well contamination. Theseans many times involve land use management agreements with landowners to minimize

nd control potential contaminants that could reach the well or the aquifer that supplies theell.

Management of land use and activities within the area of influence

he area of influence should be identified in the source water assessment or source waterrotection plan for this well. If you do not know the area of influence, assume it is all land

ithin 1000 feet of the well (an area of 7.2 acres). When a water system or otherovernmental agency manages land use and activities within the well's area of influence, itay be more feasible to monitor and control any activities that could pose a contaminationsk to the well's water supply aquifer.

Aquifer type

n aquifer is the geologic material (rock, cobbles, sand, gravel, etc.) below the ground surfacehere ground water is found. The following gives a very general definition for confined andnconfined aquifers.

confined aquifer has both top and bottom confining layers. The confining layers are lessermeable and restrict water movement, and can consist of materials such as clays.

n unconfined aquifer has no top confining layer, only a bottom layer that is impermeable toater movement.

confined aquifer can be less vulnerable to nearby contamination compared to annconfined aquifer since it has a top confining or impermeable layer that helps restrict

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ontaminant movement from above. Groundwater under the direct influence of surface waterGWUDISW). A groundwater supply that is under the influence of surface water can usuallye determined by comparing the groundwater quality to that of nearby surface waters that areuspected to be contributing to the groundwater in some way. If the State or EPA hasesignated a ground water source as GWUDISW, then the source (aquifer) is moreulnerable to microbial contamination and appropriate treatment and disinfection is required.

Potential microbial contaminantspreliminary inventory of potential sources of microbial contamination can help assess aell's risk to contamination. There are many possible sources, but the ones listed in theuestionnaire are obvious ones that have greater contamination potential. These sources ofotential contamination should be listed in the source water assessment or source waterrotection plan, if they exist. The closer a potential contaminant source is to the well, thereater the risk for contamination. Many sources may appear innocuous but the numbers ofaterborne disease outbreaks that have been associated with these sources are numerous.

Well construction - below ground

Does this well meet your State's current standards for construction of this type of well ororizontal collector system?

you are certain this well meets all current State regulations for drinking water wellonstruction, then answer Yes to question 2.a. As you answer the questions below you maynd areas where there may be some doubt as to whether or not the well meets all regulationsr standards for well construction.

Type of well

drilling process is used to install most wells. A casing pipe is installed in the well to preventell collapse and block out groundwater areas where the water quality is less desirable. Dugells were generally installed in areas where the groundwater was shallow, near the ground

urface. Shallow wells have a greater potential for contamination.

What is the depth from the ground surface to the static water level (water level when pumpse off)?

n general, the greater the depth to the static water level, less will be the potential forontamination.

Drilled well casing was NOT grouted to a depth of 20-feet or greater

ement or bentonite slurry should have been placed around the well casing to a depth greateran 20 feet by the well driller. The grout prevents movement of water and pollutants from the

round surface along the pipe casing to the groundwater below.

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Well casing pipe (if this is a vertical, drilled well), and

Horizontal well collectors (if it applies to this well) - type of materials used

teel well casing pipe is vulnerable to corrosion. Corroding steel casing pipes can sometimesad to other problems such as growth of iron bacteria or coliform organisms, making itfficult to meet water quality standards.

Well construction - above ground

The well casing should extend above the ground surface to prevent any surface water fromccidentally entering the well and contaminating the water. Many wells have air vent lines fore casing pipe. These lines or pipes should extend above any possible flooding elevation,

nd in a down-turned position, and have a tight-fitting insect screen over the end. The end ofe well should be equipped with a tight, sanitary seal to prevent any contaminant from

ntering the well. Small wells sometimes have a pitless adapter installed. The pitless adapter,

installed correctly, should prevent contaminants from entering the well. Make sure allpening are properly sealed or screened, as appropriate.

Horizontal well collector sumps or central structure generally have access doors in the rooff the sump. Access doors should be installed on a raised curb or other extension to preventntry of surface water. Doors should be of the "shoe-box lid" type, with a tight fit that preventsny water, insects, rodents or dirt from entering the sump. Security locks can preventnauthorized tampering and possible water contamination. Manhole covers are commonlysed for access to sumps or water reservoirs. It is generally difficult to remove manhole-type

overs without contaminating the water below.Runoff and Flooding potential. Wells and well houses should not be vulnerable to surfaceater or floodwater. Flooding of a well house could contaminate the well, particularly if anyent lines or openings terminate at an elevation that would allow water to enter the well viae vent line or opening.

Flooding potential. Wells and well houses should not be vulnerable to surface water oroodwater. Flooding of a well house could contaminate the well, particularly if any vent linesr openings terminate at an elevation that would allow water to enter the well via the vent liner opening.

If a sample tap exists at the well, water samples can easily and safely be obtained to checke quality of water from the well. Frost free hydrants are sometimes used as sample taps, butgeneral these hydrants can allow some backflow of contaminants and should not be used

ithout proper backflow prevention between the hydrant and the main line.

0. Historical microbiological contamination

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When a well has shown microbial contamination in the past, it may be more vulnerable toontinuing contamination, making it necessary to take greater precautions when using waterom the well. A source water assessment could help identify potential contaminant sources.he disinfection system would be more critical for this source if there was knownontamination potential. Many systems are not required to regularly sample their water sourcesome form of treatment is being provided. However, regular source water sampling can

rovide an indication if anything is changing with respect of microbial quality of the source.

1. Treatment of this source

nter a "1" in one of the boxes to indicate whether this water source receives treatment and/ r disinfection.

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.4 - Ground Water: Springs & Infiltration Galleriesprings exist where a water-bearing aquiferas become exposed to the ground surface,lowing ground water to flow from the

quifer and become a surface water source.quifers are natural geologic formations that

e pervious enough to allow water to moveithin the open pore spaces. Aquifers areften composed of sand, gravel and cobbles,ut there are many other types of materialsat can serve as an aquifer such asactured rock or limestone.

round water is generally less vulnerable toicrobial contaminants than is surface water,

ut there are numerous cases of ground water becoming polluted with microbial contaminantsn the ground's surface. Spring water collection systems gather the ground water from thepring prior to the water exiting the aquifer. The shallow nature of most spring water collectionystems makes the spring water collection area susceptible to contamination from surfaceollutants.

art B.IV. questions cover both traditional spring collection facilities as well as infiltrationalleries. Infiltration galleries are generally located in the alluvial material near a surface waterource such as a river; the quality of the water that they collect is usually influenced by theuality of the surface water. Protection of a spring source from contamination requiresnowing the area of influence, the area around the spring where surface contaminants couldotentially reach the spring water at concentrations detrimental to human health. Determininge area of influence requires experts and will not generally be available unless a Source

Water Assessment or Source Water Protection Plan has been developed for the spring. Part.III. questions inquire about items such as ownership and management of land within therea of influence, characteristics of the aquifer, spring water collection system informationuch as materials and surface water barriers, and control of native and domestic animalsound the spring area.

Spring or Infiltration Gallery source identificationive each ground water source a number, starting at number 1. Example: Suppose theottonwood Spring is one of your system's springs, and there is chlorine feed equipment atis spring. Give Cottonwood Spring the number 1 and when you fill out Part C for treatmentthis spring source, designate the treatment facility as number 1. If there is a pump station atis spring, designate it as number 1 also.

Type of ground water source

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art B. IV. should be used only for springs or infiltration galleries not associated with a spring.prings generally consist of spring boxes (a box or manhole-type structure placed over thepring source); buried, perforated or slotted collector pipes; or in some cases both.

nfiltration galleries not associated with a spring generally consist of buried, perforated orotted collector pipe; the water source being associated with groundwater being fed by a

urface water source such as a stream or river.Source Water Assessment

ource water assessments are an initial examination that indicates where the spring orfiltration gallery's area of influence lies (the area where any contaminant spill or source

ould potentially reach the ground water within a short period of time). Potential contaminantources are inventoried within the area around the source.


ource water protection plans use the information gathered as part of the source waterssessment and present a management plan for the area of influence and any other area thatould potentially contribute to ground water contamination. These plans many times involvend use management or agreements with landowners to minimize and control potential

ontaminants that could reach the water source.

Management of land use and activities within the area of influence

he area of influence should be identified in the source water assessment or source waterrotection plan for this ground water source. If you do not know the area of influence, assumeis all land within 1000 feet of the spring or infiltration gallery (an area of 7.2 acres). When aater system or other governmental agency manages land use and activities within the areaf influence it may be more feasible to monitor and control any activities that could pose aontamination risk to the water supply aquifer.

Aquifer type

n aquifer is the geologic material (rock, cobbles, sand, gravel, clay, etc.) below the ground

urface where ground water is found. The following gives a very general definition foronfined and unconfined aquifers.

confined aquifer has both top and bottom confining layers. The confining layers are lessermeable and restrict vertical water movement, and can consist of materials such as clays.

n unconfined aquifer has no top confining layer, only a bottom layer that is impermeable toater movement.

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confined aquifer can be less vulnerable to nearby contamination compared to annconfined aquifer since it has a top confining or impermeable layer that helps restrictontaminant movement from above.

round water under the direct influence (GWUDI) of surface water. A ground water supplyat is under the influence of surface water can usually be determined by comparing the

round water quality to that of nearby surface water suspected to be contributing to the

round water in some way. If the State or EPA has designated a ground water source asWUDI, then the source (aquifer) is more vulnerable to microbial contamination.

Potential microbial contaminants

preliminary inventory of potential sources of microbial contamination can help assess thesk for contamination. There are many possible sources, but the ones listed in theuestionnaire are obvious ones that have greater contamination potential. These sources ofotential contamination should be listed in the source water assessment or source waterrotection plan, if they exist. The closer a potential contaminant source is to the spring orfiltration gallery, generally the greater the risk for contamination.

Protection of area around spring box/spring collector pipes or infiltration gallery collectorpes

pring collection facilities can consist of a simple spring box located over the primary springource, to a series of buried collector pipes that are joined at collector pipe structures (manymes a concrete manhole structure). Infiltration galleries generally include buried collectorpes and structures at pipe junctions.

eep-rooted vegetation can destroy the integrity of collector pipes and spring boxes,creasing the risk of contamination from the surface. Removing vegetation that could becomeproblem is a recurring maintenance task for most spring or infiltration gallery sites.

n many areas a stock fence is required to prevent domestic animals from entering the springte. A fence capable of keeping out native animals may be required for some spring sites. A

ecurity fence with locked gates is desirable to prevent unwanted persons from tamperingith the spring box or collection pipe structures.

iversion of surface runoff from a spring or infiltration gallery site is necessary to preventansport of potential microbial contaminants to the areas around the spring box or buriedollector pipes.

Construction of spring collection facilities

Most spring boxes or collection pipe structures have access doors, a way to access the buriedpes in case cleaning of the pipe is required. For example, if vegetation is not controlledithin the spring site, roots can clog collector pipes, requiring the pipes to be cleaned to

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store system capacity. Access doors should be installed on a raised concrete or metal curbat is capable of keeping rainfall or surface water from entering the structure via the door.ccess doors should close tight and be similar to a shoebox lid in design, having a lip that

xtends down over the opening. Access doors should be capable of preventing rain, insects,odents and dust from entering and contaminating the water source. Vandalism-proof locksre desirable on access doors to prevent unauthorized access to the water source. In theurvey, answer questions regarding access doors for the ones least likely to meet the criteria

dicated above for access doors. For example, if one structure has a shoebox-type lid ande other is a manhole cover with holes, answer the questions assuming manhole covers for

ccess doors.

Many collector pipe structures or spring boxes are concrete manholes with standard manholeovers. It is difficult to remove manhole covers without contaminants from the cover ringlling into the water below. If manhole covers exist, make sure all holes are permanentlyugged and a vandalism-proof security lock exists for the cover.

ny unscreened holes or open joints in a spring box or collector pipe structure can allownwanted animals or insects to enter the water source. General maintenance can prevent anynwanted holes or open joints from developing.

Many spring boxes or structures are equipped with an air vent, typically a pipe extendingpward. Air vents should be covered with a screen and protected to prevent rain or dust fromntering the water supply. The ends of air vent pipes should have a down-turned fitting and beghtly screened to prevent insects from entering the pipe.

o minimize movement of surface contaminants with water that percolates down from the

urface, an impervious liner material can be buried near the surface and over the collectorpes below.

ollector pipes constructed of steel are vulnerable to corrosion. Corroding steel pipes canometimes lead to other problems such as growth of iron bacteria or coliform organisms,aking it difficult to meet water quality standards.

verflow pipes are required for some spring or infiltration gallery systems to prevent waterom flowing out of certain structures. Overflow pipes can be a potential source of

ontamination if not properly constructed. The ends of overflow pipes should not becomeubmerged when an overflow event occurs. If the pipe discharges into a waterway it shoulde above normal and high water levels. Ends of overflow pipes should be tightly screened torevent insects and rodents from entering the pipe, or a tightly closing flap gate should be ate pipe's end.

a sample tap exists at the spring, water samples can easily and safely be obtained to checke water's quality. It may be necessary to install sample taps in pipes that carry the water toe system.

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0. Historical microbiological contamination

When a source has shown microbial contamination in the past, it may be more vulnerable toontinuing contamination, making it necessary to take greater precautions when using waterom the source. A source water assessment could help identify potential contaminant

ources. The disinfection system would be more critical for this source if there was known

ontamination potential. Many systems are not required to regularly sample their water sourcesome form of treatment is being provided. However, regular source water sampling canrovide an indication if anything is changing with respect of microbial quality of the source.

1. Does this water source receive any form of treatment, including disinfection?

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- TREATMENT INFORMATION

nit 3 provides guidance material forompleting Part C - Treatment in the Small

Water System Survey. Treatment processesan be as simple as disinfection or as

omplex as conventional surface watereatment plants. Since many water systemsmploy only disinfection treatment, there areurveys provided for those facilities thatrovide only disinfection of surface water orround water. Separate surveys are providedor facilities that provide filtration or otherpes of treatment for surface water or

round water.

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.1 - Surface Water: Disinfection/Corrosion Control Treatmentisinfection is the treatment processesigned to inactivate (kill) most potentiallyarmful microorganisms present in water.isinfection can be performed by the additionf an oxidizing chemical (chlorine,

ypochlorite, chlorine dioxide, chloramines,r ozone) or by exposing the water to antraviolet (UV) light source.

ll surface water sources must be treatedefore use as drinking water, disinfectioneing the minimum form of treatment thatan be provided. If a surface water sourceceives only disinfection, then the water

ystem must have a Filtration Waiver frome State or U.S. EPA.

o obtain a Filtration Waiver the waterystem must demonstrate that the quality of the surface water is consistently such thatsinfection will result in a safe drinking water supply. Corrosion control treatment typicallycludes the addition of a chemical to reduce the tendency for metals such as iron, copper

nd lead to become soluble in the water.

art C.I. questions inquire about the treatment processes, the redundancy of equipment,

afety features, controls, quality of the water, etc. Questions are also included regarding theresence of potential cross-connections or backflow situations that may occur within theeatment facilities. The questions have been selected based on those components of aeatment system that could potentially allow microbial contamination or components that ifresent can help prevent microbial contamination.

Are disinfection and/or corrosion control the only types of treatment provided for thisurface water supply? (yes/no)

Treatment Facility Identification

ive each water treatment facility a number, starting at 1. The treatment facility number muste the same number as that on the survey worksheet you use. If this facility treats water fromeveral sources, indicate the source numbers that were designated when Part B wasompleted.

xample: Suppose a water system has intakes on three different streams, North Fork (Supplyo. 1), Middle Fork (Supply No. 2), and South Fork (Supply No. 3). The combined watersom the North and South Forks are treated at one treatment facility, and water from the

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Middle Fork is treated at a second treatment facility. Give the treatment facility for the Northnd South Forks the No. 1 and the treatment facility treating water from the Middle Fork theo. 2. Answer a survey for each treatment facility, indicating on the survey the number used

or the sources treated by that facility.

ndicate the number used in Part B for each water source treated by this facility.

Filtration Waivera surface water supply does not have a filtration waiver from the state or EPA, then the

ource requires a greater degree of treatment than disinfection only. Only surface waterources that have a waiver of filtration can be treated using disinfection only. Proactiveatershed protection and management along with a history of very high quality water arequired if a water source is to meet the requirements for remaining unfiltered.

Treated Water Turbidity

tate and EPA regulations require the turbidity of an unfiltered surface water supply be lessan 5.0 NTU. Regulations state that turbidity cannot exceed 5.0 NTU for more than two

vents in 12 months or 5 events in 120 months. Water turbidity is a surrogate indicator foricrobial contamination. In general, low water turbidity indicates less likelihood of

ontamination.

Disinfection - Water Quality

isinfectant concentration (C, mg/L) multiplied by the contact time (T, minutes) gives the term

xT. Disinfectant concentration is dependent upon how much disinfectant is added to theater. For example, if liquid sodium hypochlorite were being used as a disinfectant, C woulde milligrams per liter (mg/L) of free chlorine. T is based on the flow rate of water, the volumef the detention facility, and the effectiveness of the detention facility (ability to prevent short-rcuiting of water through the detention facility). For example, if the water flow rate was 300allons per minute (gpm), the detention facility had a volume of 4000 gallons, and it has beenetermined that the detention facility is only 50% effective, the contact time would be:

water system determines if it is providing adequate disinfection treatment by meeting apecific CxT value based on several water quality factors. CxT values have been developedor common disinfectants like chlorine, chloramines, chlorine dioxide and ozone. CxT valuesre dependent upon 1) type of disinfectant, 2) disinfectant concentration, 3) watermperature, and 4) water pH. Tables are published giving CxT values that must be met by aater supplier. When the water supply is unfiltered, the ability to meet CxT requirements ofe surface water treatment rule is crucial to insuring that microbial contaminants areactivated by the disinfectant. With the exception of ozone, common disinfectants like

hlorine and chloramines do not inactivate Cryptosporidium oocysts at concentrations used inrinking water. CxT values are available in guidance documents found on the EPA's web site

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ttp://www.epa.gov/safewater/regs.html .

ystems that use UV-light disinfection will most likely be required to meet a UV light doseased on disinfection efficiency tests performed before the UV disinfection system is placedto operation. UV dose is defined as the energy of the UV light per unit area, milliwatts per

quare centimeter (mW/cm2) multiplied by the exposure time of the fluid or particle to beeated (seconds). The units for UV dose are therefore mW-s/(cm2). Exposure time is a

unction of flow rate and reactor configuration, i.e., it is the detention time within the UV lightactor. UV dose will have to be monitored, along with several other parameters, to assureat the required dose is provided at all flow rates and water quality conditions. UVsinfection systems will most likely be required to monitor flow rate, UV-light intensity, UV-ght transmittance, water turbidity, and operational UV dose (determined based on the firstour parameters. Since the process is new, many states have yet to develop standards for itsse, control and monitoring. The survey presents a list of possible items that may be requiredor a UV-light facility.

he Ranking Tool relies on disinfectant dose and type to determine a score for this item.enerally the higher the disinfectant dose the better the inactivation of microorganisms. If aater system has very high quality water and can effectively use low disinfectant doses, sayss than 0.5 mg/L free chlorine, the Ranking Tool may give too high a score for this item. Theser of the tool should take this into account when looking at the results of the Ranking Toolodel.

Type of Disinfectant

rimary disinfection is the process used to meet required CxT values. Primary disinfection is

here the disinfectant or disinfecting process inactivates microbes.

econdary disinfection is the process of adding sufficient disinfectant to maintain a residualoncentration in the distribution system. Many facilities use one type of disinfectant forrimary disinfection and another for secondary disinfection. A chlorine-based disinfectantust be provided for secondary disinfection if ozone or ultraviolet (UV) light is used for

rimary disinfection; ozone and UV-light do not provide any residual for protection of water ine distribution system.

hloramines have become popular for use as a secondary disinfectant because they do notact with natural organic matter in water to form disinfection byproducts. Combining freehlorine with ammonia creates chloramines. There is some evidence that chloramines areore effective at controlling biofilm in the distribution system and provide a more stablesidual concentration. However, chloramines are not as effective against pathogens as are

hlorine or chlorine dioxide.

Disinfection - Facilities and Equipment

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isinfection provides the last barrier to possible microbial contamination and is extremelymportant for unfiltered surface water supplies. First and foremost the facilities must haveufficient capacity for meeting required CxT values. This requires having sufficient contactme and being able to feed a sufficient dose of disinfectant.

disinfection facility treating surface water must be capable of providing the right disinfectantose at all times. If the water flow rate changes during the day based on system water

emands, the concentration of disinfectant in the water will also change unless there is aechanism to make the addition of disinfectant proportional to water flow rate. This can beerformed by having a control system that adjusts the rate of disinfectant addition based one flow rate and/or disinfectant concentration as measured by meters or other instruments.he result is more consistent disinfectant concentrations.

V-light disinfection may become popular as a primary disinfection process because it isffective at killing Giardia and Cryptosporidium . Since the process is new, many states haveet to develop standards for its use, control and monitoring. The survey presents a list ofossible items that may be required for a UV-light disinfection facility.

ddition of the disinfectant almost always requires there be power for pumps, controls, etc.oss of power will usually result in water going through the facility without addition of anysinfectant. Some facilities provide a back-up power generator that automatically starts uponss of power. A way to shut-off the treated water flow if a power outage occurs could prevent

mproperly disinfected water from entering the system.

isinfection facilities should be in good operating condition because of their importance toafe drinking water. If equipment is in poor condition and needs replacement or repair, it is the

sponsibility of the operator or manager to work towards correcting the situation. It is alwaysesirable to have a spare unit for critical items such as feed pumps or water supply boosterumps, items that can take a long time to replace or repair.

Disinfection System Monitoring and Alarms

Most small water system disinfection facilities are not manned full time. Thus it is important toave some way for a responsible person to know when a problem has occurred. Alarms at thecility could include visible or audible alarms. Sending an alarm or message to an on-call

erson is very desirable and can be accomplished using telemetry or a simple autodialer unitat is set up to call various phone numbers upon activation of an alarm. When facilities aremote or no one is around most of the time, an alarm system could prevent improperlyeated water from entering the system.

Flow Rate Control

ontrolling flow rate can provide more consistent disinfection of the water. This can bearticularly important if the disinfection system is not automated to feed the disinfectant

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roportional to flow rate. Some small systems find it easier to control flow rate through thecility than to feed a disinfectant proportional to flow rate or residual concentration. Manual

ontrol of the disinfectant dose requires frequent monitoring of the treated water to assure thatater quality changes have not impacted the requirement for the disinfectant. Unfiltered

urface water supplies require very careful monitoring of disinfectant dose.

0. Corrosion Control Treatment

here is evidence that treatment of water for control of corrosion can reduce the number ofositive coliform samples from the distribution system. Addition of a phosphate-basedorrosion inhibitor has been effective when the system contains unlined cast or steel pipe.hese corrosion inhibitors consist of orthophosphate and blended ortho- and poly-hosphates, the latter being more effective with hard water or water with high alkalinity.orrosion control using pH adjustment or silica addition may not be effective in regard toinimizing coliform positive samples.

1. Turbidity Monitoring and Alarms

urface water sources that are unfiltered should (must) be continuously monitored forrbidity. New online turbidimeters have adjustable alarm set points to allow an alarm signal

e sent upon reaching a certain turbidity level (say 4 or 5 NTU for an unfiltered supply).larms at the facility could include visible or audible alarms. Sending an alarm or message to

n on-call person is very desirable and can be accomplished using telemetry or a simpleutodialer unit that is set up to call various phone numbers upon activation of an alarm. Whencilities are remote or no one is around most of the time, an alarm system could prevent

mproperly treated water from entering the system.

2. Cross-connections

ross-connections in a treatment plant can lead to microbial contamination of treated water.he survey lists several possible cross-connections that may exist, repeated below:

Dilution water tanks or carrier water lines for chemical feed unitsDilution water lines that are activated by a float valve (float valves must be located upstreamf a vacuum breaker assembly to prevent possible cross-connection)Safety shower and/or eye wash stationsDrain lines from the air inlet/outlet port of an air release or vacuum breaker valveHose bibs (common point of cross connection unless vacuum breaker used)Permanent or seasonal connections for irrigation

hese and other cross-connections could exist at a treatment plant. Installation of anpproved backflow prevention device is important to protection of the treated water.

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.2 - Surface Water: Filtration/Disinfection/Corrosion ControlMost surface water sources require someorm of filtration in addition to disinfection.he filtration step is included to remove mostotentially harmful pathogens from the waterrior to disinfection. There are numerous

ypes of filtration. Many treatment plantsclude high-rate granular media filtrationapid sand filtration). This form of treatmentvolves the addition of chemical coagulants,pid mixing, slow mixing (flocculation), andany times settling prior to the filtration step.

Many new treatment facilities use a pressurer vacuum-driven membrane system where a man-made membrane is used to "filter-out"armful microorganisms.

art C.II. questions inquire about the treatment processes, the redundancy of equipment,afety features, controls, quality of the treated water, etc. Questions are also includedgarding the presence of potential cross-connections or backflow situations that may occurithin the treatment facilities. The questions have been selected based on those componentsf a treatment system that could potentially allow microbial contamination or components thatpresent can help prevent microbial contamination.

Treatment Facility Information

ive each water treatment facility a number, starting at 1. The treatment facility number muste the same number as that on the survey worksheet you use. If this facility treats water fromeveral sources, indicate the source numbers that were designated when Part B wasompleted.

xample: Suppose a water system has intakes on three different streams, North Fork (Supplyo. 1), Middle Fork (Supply No. 2), and South Fork (Supply No. 3). The combined watersom the North and South Forks are treated at one treatment facility, and water from the

Middle Fork is treated at a second treatment facility. Give the treatment facility for the North

nd South Forks the No. 1 and the treatment facility treating water from the Middle Fork theo. 2. Answer a survey for each treatment facility, indicating on the survey the number usedor the sources that facility treats.

ndicate the number used in Part B for each water source treated by this facility.

Treated Water Turbidity

Water turbidity is a surrogate indicator for microbial contamination. In general, low waterrbidity indicates less likelihood of contamination. It is recommended that filtration treatment

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ants set a turbidity goal that is much more stringent than the 0.3 NTU mandatory standard.turbidity goal of 0.1 NTU or less is typically used. Having a turbidity goal and operating thecility accordingly provides a level of safety for producing quality water.

tate and EPA regulations require the turbidity of a filtered surface water supply be less than3 NTU in greater than 95% of samples taken in a month. This requirement is met byeasuring turbidity of the combined effluent from all filters on a continuous basis, or at least

very 15 minutes. Regulations state that turbidity cannot exceed 1.0 NTU.n addition to measuring turbidity of combined filter effluent, turbidity must be monitoredontinuously (or at least every 15 minutes) for each individual filter. Filter performance muste recorded and submitted with monthly monitoring reports to the state or EPA. If certainrbidity levels are exceeded for a given number of measurements, the treatment plant (thoseat operate or are in charge) must perform work to try and correct any filter deficiencies. Theong Term 1 Enhanced Surface Water Treatment Rule (Federal Register, 40 CFR, Parts 9,41 and 142, National Primary Drinking Water Regulations) outlines the requirements. In

eneral, exceeding 1 NTU in 2 or more consecutive measurements 15 minutes apart willigger a requirement to notify the State.

ontinued problems will lead to specific requirements for correcting the filter operation (seeT1ESWTR).

a turbidimeter should fail and require repair or replacement, you should take grab samplesvery four hours until the unit is back in service. Current rules allow 14 days to resumeontinuous monitoring.

nformation on the LT1ESWTR can be found on the EPA's web site at http://www.epa.gov/ afewater/standards.html .

Disinfection - Water Quality

isinfectant concentration (C, mg/L) multiplied by the contact time (T, minutes) gives the termxT. Disinfectant concentration is dependent upon how much disinfectant is added to theater. For example, if liquid sodium hypochlorite were being used as a disinfectant, C woulde milligrams per liter (mg/L) of free chlorine. T is based on the flow rate of water, the volumef the detention facility, and the effectiveness of the detention facility (ability to prevent short-rcuiting of water through the detention facility). For example, if the water flow rate was 300allons per minute (gpm), the detention facility had a volume of 25,000 gallons, and it haseen determined that the detention facility is only 50% effective, the contact time would be:

water system determines if it is providing adequate disinfection treatment by meeting apecific CxT value based on several water quality factors. CxT values have been developedor common disinfectants like chlorine, chloramines, chlorine dioxide and ozone. CxT valuesre dependent upon 1) type of disinfectant, 2) disinfectant concentration, 3) water

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mperature, and 4) water pH. Tables are published giving CxT values that must be met by aater supplier. The ability to meet CxT requirements of the surface water treatment rules is

rucial to insuring that microbial contaminants are inactivated by the disinfectant. With thexception of ozone, common disinfectants like chlorine and chloramines do not inactivateryptosporidium oocysts at concentrations used in drinking water. CxT values are available inuidance documents found on the EPA's web site http://www.epa.gov/safewater/regs.html .

he Ranking Tool relies on disinfectant dose and type to determine a score for this item.enerally the higher the disinfectant dose the better the inactivation of microorganisms. If aater system has very high quality water and can effectively use low disinfectant doses, sayss than 0.5 mg/L free chlorine, the Ranking Tool may give too high a score for this item. Theser of the tool should take this into account when looking at the results of the Ranking Toolodel.

Type of Disinfectant

rimary disinfection is the process used to meet required CxT values. Primary disinfection ishere the disinfectant or disinfecting process inactivates microbes. Secondary disinfection ise process of adding sufficient disinfectant to maintain a residual concentration in thestribution system. Many facilities use one type of disinfectant for primary disinfection and

nother for secondary disinfection. A chlorine-based disinfectant must be provided forecondary disinfection if ozone or ultraviolet (UV) light is used for primary disinfection; ozonend UV-light do not provide any residual for protection of water in the distribution system.

hloramines have become popular for use as a secondary disinfectant because they do notact with natural organic matter in water to form disinfection byproducts. Combining free

hlorine with ammonia creates chloramines. There is some evidence that chloramines areore effective at controlling biofilm in the distribution system and provide a more stablesidual concentration. However, chloramines are not as effective against pathogens as are

hlorine or chlorine dioxide.

Disinfection - Facilities and Equipment

isinfection provides the last barrier to possible microbial contamination. First and foremoste facilities must have sufficient capacity for meeting required CxT values. This requires

aving sufficient contact time and being able to feed a sufficient dose of disinfectant.disinfection facility treating surface water must be capable of providing the right disinfectant

ose at all times. If the water flow rate changes during the day based on system wateremands, the concentration of disinfectant in the water will also change unless there is aechanism to make addition of disinfectant proportional to water flow rate. This can be

erformed by having a control system that adjusts the rate of disinfectant addition based onow rate and/or disinfectant concentration as measured by meters or other instruments. Thesult is more consistant disinfectant concentrations.

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V-light disinfection may become popular as a primary disinfection process because it isffective at inactivating Giardia and Cryptosporidium . Since the process is new, many statesave yet to develop standards for its use, control and monitoring. The survey presents a list ofossible items that may be required for a UV-light facility.

ddition of the disinfectant almost always requires there be power for pumps, controls, etc.

oss of power can result in water leaving the facility without addition of any disinfectant. Somecilities provide a back-up power generator that automatically starts upon loss of power. Aay to shut-off the treated water flow if a power outage occurs could prevent improperlysinfected water from entering the system.

isinfection facilities should be in good operating condition because of their importance toicrobially safe drinking water. If equipment is in poor condition and needs replacement orpair, it is the responsibility of the operator or manager to work towards correcting thetuation. It is always desirable to have a spare unit for critical items such as feed pumps,ater supply booster pumps, or items that can take a long time to replace or repair.

Disinfection System Monitoring and Alarms

Most small water system disinfection facilities are not manned full time. Thus it is important toave some way for a responsible person to know when a problem has occurred. Alarms at thecility could include visible or audible alarms. Sending an alarm or message to an on-call

erson is very desirable and can be accomplished using telemetry or a simple autodialer unitat is set up to call various phone numbers upon activation of an alarm. When facilities aremote or no one is around much of the time, an alarm system could prevent improperly

eated water from entering the system.

Flow Rate Control

s discussed above under Item 5, controlling flow rate can provide more consistentsinfection of the water. When coagulation and filtration processes are employed, flow control

ecomes critical to proper treatment. Flow control can be particularly important if the chemicaleders or the disinfection system is not automated to be proportional to flow rate. Some small

ystems find it easier to control flow rate through the facility than to feed a chemical orsinfectant proportional to flow rate or residual concentration.

Corrosion Control Treatment

here is evidence that treatment of water for control of corrosion can reduce the number ofositive coliform samples from the distribution system. Addition of a phosphate-basedorrosion inhibitor has been most effective for systems with unlined cast or steel pipe. Theseorrosion inhibitors consist of orthophosphate and blended ortho- and poly-phosphates, thetter being more effective with hard water or water with high alkalinity. Corrosion controlsing pH adjustment or silica addition may not be effective with regard to minimizing coliform

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ositive samples in the distribution system.

Turbidity Monitoring and Alarms

iltered surface water sources must be continuously monitored for turbidity. Turbidity of theombined filter effluent and turbidity of each individual filter must be continuously monitorednd recorded. Exceeding certain turbidity levels can become critical, requiring the facility be

orrected. Most online turbidimeters have adjustable alarm set points to allow an alarm signale sent upon reaching a certain turbidity level (say 0.3 NTU for the combined filter effluent).larms at the facility could include visible or audible alarms. Sending an alarm or message to

n on-call person is very desirable and can be accomplished using telemetry or a simpleutodialer unit that is set up to call various phone numbers upon activation of an alarm. Whencilities are remote or no one is around most of the time, an alarm system could prevent

mproperly treated water from entering the system.

0. Chemical Feed Units

hemical feed units of some type are required at filtration plants. See Item 7 above forformation regarding control of flow rate. Certain treatment plants control the addition of

hemicals based upon different parameters, flow rate being the most common. Sometimeshemical feeders are controlled by signals from turbidimeters, particle counters, or streamingurrent detectors. All of these devices provide some measurement for how well theoagulation/filtration process is performing. Control devices like streaming current detectorsan be important if quality of the water supply can change rapidly and unexpectantly.

1. Rapid Mixing, Flocculation and Settling

he addition of a chemical coagulant and subsequent rapid mixing, flocculation and settlingre three very important treatment processes when granular media filtration is utilized. Rapidixing (high intensity, vigorous mixing) of the chemical coagulant and water should precedee flocculation step. Flocculation refers to the process of slow, gentle mixing of the water and

hemical coagulant to form larger "floc" particles that can be either settled in a sedimentationasin and/or removed more easily in a granular media filter. Sedimentation basins createuiescent conditions to promote settling of the large particles that can form during flocculation.nder no circumstances should granular media filters be operated without addition of a

hemical coagulant.apid mixing of chemical coagulant with the water is an important step in the treatmentrocess for granular media filtration facilities. Rapid mixing generally consists of a motor-riven propeller or turbine or an inline static mix unit. Inline static mix devices consist ofaffles installed inside a pipe to create turbulence and mixing as water passes through. Thetensity of mixing for inline static mixers depends upon flow rate through the unit; thus therelittle control over how well the chemical coagulant is mixed if the flow rate must be varied.ertain types of granular media filtration plants do not use flocculation or sedimentation. Inline

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ltration refers to facilities that do not have any flocculation or sedimentation processes. Thehemical coagulant is mixed with the water using a rapid mix facility followed directly byltration. Direct filtration refers to plants that do have flocculation facilities, but do not haveedimentation basins. Conventional filtration refers to plants that have both flocculation andedimentation.

2. Filtration

Water treatment plants can employ many different types of filtration. These can be generallyrouped into two types: granular-media and membranes. Diatomaceous earth is a third typef filtration. Granular media typically includes one or a combination of garnet, sand, anthracitend granular activated carbon placed to total depths from 20 to 72 inches. Granular medialters can rely on gravity or pressure to move water through the filter. The use of pressure-pe granular media filters is discouraged or prohibited in several States. It is difficult for an

perator to visually inspect the media before, during and after a backwash event for pressurelters. Membranes can remove bacteria and cysts if properly designed and operated. Ineneral, the relative microbial removal capabilities of membrane types are: reverse osmosis>anofiltration> ultratfiltration> microfiltration. Knowing the type of membrane used in a plantan give the operator an idea of its capabilities for removal of bacteria and cysts.

iltration processes require some form of flow rate control if a quality effluent is to beroduced. Knowing and understanding how flow rate through the filters is controlled is crucial

proper operation and maintenance. Improper or faulty flow control should be replaced orpaired. Generally flow control can be a costly item to replace, and sometimes to repair, butabsolutely necessary for proper operation of the filtration process.

ranular media filters require some method for diverting filter effluent to waste immediatelyollowing backwash of the filter. Filter effluent can contain large numbers of bacteria and cystsuring the initial few minutes of operation after backwash or after a filter is re-started. Filterffluent should be sent to waste for the first 10 to 30 minutes of filter operation after aackwash and a short filter-to-waste period is desirable after a filter is re-started following aeriod of inactivity. Facilities without filter to waste capabilities are many times difficult if notmpossible to retrofit.

Measurement of turbidity for each filter's effluent is now mandatory, and was discussed above

nder Item 2. Two additional important parameters, particularly for granular media filters, areead loss across the filter and run time between filter backwash cycles. Head loss across thelter measures how plugged the filter has become since it was last cleaned. In membraneants the influent pressure is monitored to determine if the membrane has become plugged

nd must be cleaned. Based on recent research it is recommended that backwash of granularedia filters be initiated based on head loss or run time. Waiting to backwash a granularedia filter based on an increase in effluent turbidity (break-through) can lead to passage ofryptosporidium oocysts at the end of the filter run.

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3. Filter Waste Backwash Water Recycle

t treatment facilities where waste wash water cannot be discharge or otherwise disposed of,e waste backwash water is recycled to the front end of the treatment plant. The Filterackwash Recycling Rule (Federal Register, June 8, 2001, 40 CFR Parts 9, 141 and 142,ational Primary Drinking Water Regulations, Filter Backwash Recycling Rule, Final Rule)quires recycled filter backwash water, sludge thickener supernatant, and liquids from

ewatering processes be returned to a location such that all processes of a system'sonventional or direct filtration including coagulation, flocculation, sedimentation (conventionalltration only) and filtration, are employed. Recycled waste backwash water can containicrobial contaminants that can reduce the efficiency of the treatment process and lead to

ossible passage of the contaminants to the effluent. If a treatment facility recycles wasteackwash water to a point that does not receive full treatment (to head of plant), then thecycle point must be changed or it must be shown that the current recycle does not in anyay impair treatment.

4. Cross-connections

ross-connections in a treatment plant can lead to microbial contamination of treated water.he survey lists several possible cross-connections that may exist, repeated below:

Dilution water tanks or carrier water lines for chemical feed unitsDilution water lines that are activated by a float valveSafety shower and/or eye wash stationsDrain lines from the air inlet/outlet port of an air release or vacuum breaker valveHose bibs (common point of cross connection unless vacuum breaker used)

Permanent or seasonal connections for irrigation or wash-down of plant areas

hese and other cross-connections could exist at a treatment plant. Installation of anpproved backflow prevention device is important to protection of the treated water.

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.3 - Ground Water: Disinfection/Corrosion Control Treatmentisinfection is the treatment processesigned to inactivate (kill) potentiallyarmful microorganisms present in water.isinfection can be performed by the additionf an oxidizing chemical (chlorine,

ypochlorite, chlorine dioxide, chloramines,r ozone) or by exposing the water to antraviolet (UV) light source. Many, but notl, ground water sources receive disinfectioneatment. Many new treatment facilities nowse or will use UV light disinfection foreating ground water. Corrosion controleatment typically includes the addition of ahemical to reduce the tendency for metalsuch as iron, copper and lead to becomeol

Microbial Risk Assessment Guide

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