Lin S.D. Water and Wastewater Calculations Manual

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Public Water Supply 335

water ingestion. If there is no additional information to consider on

potential cancer risk from drinking water ingestion, chemicals classi-

ﬁed as A or B carcinogens are placed in Category I.

Category II contaminants include those contaminants for which EPA

has determined that there is limited evidence, pharmacokinetics, and

exposure. If there is no additional information to consider on potential

cancer risks from drinking water ingestion, chemicals classiﬁed by the

Agency as Group C carcinogens are placed in Category II. For Category

II contaminants, two approaches are used to set the MCLGs—either

(1) setting the goal based upon noncarcinogenic endpoints (the RfD)

and then applying an additional uncertainty (safety) factor of up to 10

or (2) setting the goals based upon a normal lifetime cancer risk calcu-

lation in the range of 10

⫺5

to 10

⫺6

, using a conservative calculation

model. The ﬁrst approach is generally used. However, the second is

used when valid noncarcinogenicity data are not available and ade-

quate experimental data are available to quantify the cancer risk. EPA

is currently evaluating the approach to establishing MCLGs for

Category II contaminants.

Category III contaminants include those contaminants for which there

is inadequate evidence of carcinogenicity via ingestion. If there is no

additional information to consider, contaminants classiﬁed as Group D

or E carcinogens are placed in Category III. For these contaminants, the

MCLG is established using the RfD approach.

Maximum contamination level or treatment technique. Once the MCLG is

deﬁned, the US EPA sets an enforceable standard. In most cases, it is

as maximum contamination level (MCL). The MCL is the maximum

permissible concentration of a contaminant in water that is delivered

to any user of a public water system. The MCL is set as close to the

MCLG as feasible that the contaminant level may be achieved with the

use of the best available technology, treatment techniques, and other

means of corrections and improvement.

If there is no reliable method that is technically and economically

feasible to measure a contaminant at particularly low levels, a TT (treat-

ment technique) is set rather than an MCL. The TT is an enforceable

procedure or level of technical performance that public water treatment

systems must follow to ensure control of a contaminant.

The US EPA must conduct a cost-beneﬁt analysis, after MCL or TT

is determined. Based on the results of the cost-beneﬁt analysis, the US

EPA may justify any variances and exemptions from standards for some

water utilities.

The SDWA required the US EPA to review each primary standard at

least once every 6 years for revision if needed. The primary standards

went onto effect 6 years after they were ﬁnalized.

336 Chapter 5

4.2 Two major rules updated in 2006

Over the past 8 years, the US EPA has worked collaboratively with

stakeholders to develop regulations that will provide a balance between

the needs to disinfect drinking water and to protect citizens from poten-

tially harmful contaminants. Two of the most recent major rules ﬁnal-

ized and published in 2006 are:

1. The Stage 2 Disinfectants and Disinfection By-products Rule (Stage 2

DBP rule or DBPR, Stage 2).

2. The Long Term 2 Enhanced Surface Water Treatment Rule (LT2 rule

or LT2ESWTR).

More information about the US EPA drinking water regulations can be

found at www.epa.gov/OGWDW/regs.html. This site, developed by the

EPA’s Ofﬁce of Ground Water and Drinking Water, lists current drink-

ing water rules, proposed rules, the code of federal regulations, drink-

ing water standards, and a wealth of other information, such as fact

sheets, guidance manuals, and more. Moorman (2006) summarized infor-

mation below from various EPA documents helping to understand the

immediate requirements and the overall purposes of these two new rules.

Cryptosporidium has caused serious disease outbreak and are resist-

ant to traditional water disinfection practices. Consumption of water

that contains Cryptosporidium can cause gastrointestinal illness that

can be fatal for people with weakened immune systems. In addition,

water chlorination can react with naturally occurring organic matters

to form disinfection by-products (DBPs), which also pose health concerns.

To respond to these new threats, amendments to the SDWA in 1996

require the US EPA to develop rules to balance the risks between

pathogens and DBPs. As the ﬁrst phase of this requirement, the Stage 1

Disinfectants and Disinfection By-products Rule (Stage 1 DBP rule) was

promulgated in December 1998 to reduce exposure to DBPs for customers

of community water systems and nontransient noncommunity systems,

including those serving fewer than 10,000 people, that add a disinfectant

to the drinking water during any part of the treatment process.

The Interim Enhanced Surface Water Treatment Rule (IESWTR) was

also promulgated in December 1998, but this rule was made to improve con-

trol of microbial contaminants, particularly Cryptosporidium, in systems

using surface water, or groundwater under the direct inﬂuence (GWUDI)

of surface water, that serve 10,000 or more persons. As the small-system

counterpart to the IESWTR, the Long Term 1 Enhanced Surface Water

Treatment Rule was ﬁnalized in January 2002 and strengthens control of

microbial contaminants for systems serving fewer than 10,000 people.

The Stage 2 DBP rule. The Stage 2 DBP rule building upon the Stage 1

DBP rule was published in the Federal Register on January 4, 2006. This

Public Water Supply 337

rule is intended to reduce potential cancer and reproductive and devel-

opmental health risks from DBPs in drinking water through more strin-

gent methods for determining compliance.

Requirements. Under the Stage 2 DBP rule, community and nontran-

sient noncommunity water systems that add and/or deliver water that

is treated with a primary or residual disinfectant other than ultravio-

let light must conduct an evaluation of their distribution systems, called

an Initial Distribution System Evaluation (IDSE), to identify locations

with high DBP concentrations. These locations must then be used by the

systems as the sampling sites for Stage 2 DBP rule compliance moni-

toring. The rule requires two steps for the IDSE. First, the system must

develop a plan of how they will approach the IDSE. There are four

options: a very small system waiver, 40/30 certiﬁcation, standard mon-

itoring program (SMP), and system speciﬁc study (SSS). This plan must

be submitted to the state or primary agency with proposed DBP moni-

toring sites. After receiving approval, the system must conduct the IDSE

with 1 year of DBP monitoring if the standard option is used.

Compliance with the MCLs for trihalomethanes (THMs) and ﬁve

haloacetic acids (HAA5) will be calculated as an average at each compli-

ance-monitoring location (instead of as a system-wide average as in pre-

vious rules). This approach is referred to as the locational running

annual average (LRAA).

The Stage 2 DBP rule also establishes operational evaluation levels. A

system that exceeds this level must conduct an operational evaluation

(a review of operational practices) to determine ways to reduce DBP con-

centrations. This provides an early warning of possible future MCL viola-

tions, and allows the system to take proactive steps to remain in compliance.

The Stage 2 DBP rule and the LT2 rule are the second phase of rules

required by the Congress to help balance the risks between pathogens

and DBPs. These rules strengthen protection against microbial con-

taminants, especially Cryptosporidium, and at the same time, reduce

potential health risks of DBPs.

Time frame. The time frame of the Stage 2 DBP rule is a multiyear

process for water systems to determine where higher levels of DBPs occur

in their distribution systems. These locations will become the new DBP

monitoring sites, and corrective action will be taken if DBP levels are

above the MCL. These actions could include small operational changes

up to major facility construction. Depending on system size and the extent

of needed construction, systems will begin the ﬁrst year of compliance

monitoring between 2012 and 2015, and must be in compliance with the

Stage 2 DBP rule MCLs at the end of a full year of monitoring (Table 5.3).

Costs. The Stage 2 DBP rule will result in increased costs to public

water utilities and states. Although the rule applies to nearly 75,000 sys-

tems, only a small portion will be required to make treatment changes.

338 Chapter 5

The average cost of the rule is estimated at $79 million annually (using

a 3% discount rate), according to the US EPA.

The LT2 rule. The LT2 rule was published in the Federal Register on

June 5, 2006. This rule is intended to improve public health by reduc-

ing waterborne outbreaks due to Cryptosporidium and other pathogens

in drinking water.

Requirements. The LT2 rule requires large public water systems (serv-

ing at least 10,000 people) that are supplied by surface water or GWUDI

of surface water to conduct 2 years of monthly sampling for

Cryptosporidium (and E. coli and turbidity for ﬁltered systems). To

reduce the cost of these monitoring, small water systems will monitor

for E. coli for 1 year only because it is less expensive to analyze. The

TABLE 5.3 Timeframes for the Stage 2 DBP Rule and the Long Term 2 Enhanced

Surface Water Treatment Rule

DBPR, Stage 2 Year LT2ESWTR

Proposed rules 2004

2005

Final rules 2006

IDSE

∗

Plan to Primary Agency: ← A – 7/1/06, Crypto sample schedule due

Person served

†

A –10/1/06 ← A – 10/1/06, Monitoring starts

B – 4/1/07 2007 ← B – 1/1/07, Crypto sample schedule due

C – 10/1/07 ← B – 4/1/07, Monitoring starts

D – 4/1/08 2008 ← C – 1/1/08, Crypto sample schedule due

← C – 4/1/08, Monitoring starts

IDSE Report due: A – 1/1/09 2009 ← D – 7/1/09, Crypto sample schedule due

B – 7/1/09 ← D – 10/1/09, Monitoring starts

C – 1/1/10 2010

D – 7/1/10

2011

Stage 2 LRAA starts (80/60 ␮g/L) Additional Cryptosporidium treatment

at sampling site for: required if > 0.75 oocysts/L

2012

A – 4/1/12 ← A – 4/1/12

B – 10/1/12 ← B – 10/1/12

C – 10/1/13 2013 ← C – 10/1/13

2014

D – 10/1/14 ← D – 10/1/14

2015

∗

Other abbreviations—See the text

†

Person served – A: ≥100,000; B: 50,000–99,999; C: 10,000–49,999; D: <10,000

←

Public Water Supply 339

systems will only monitor for Cryptosporidium if their E. coli results

exceed speciﬁed concentrations.

After monitoring is complete, ﬁltered water systems will be classiﬁed

in one of four treatment categories (bins) based on their monitoring

results. The EPA expects the majority of systems to be placed in the

lowest bin, and require no additional treatment. Systems placed in the

higher bins will be required to provide additional treatment to reduce

Cryptosporidium levels. Water systems in the higher bins and systems

that do not ﬁlter their water will choose additional treatment options

from a “microbial toolbox” of treatment and management processes.

Because of contamination risks, the LT2 rule also addresses uncov-

ered ﬁnished water storage facilities, such as reservoirs. The rule

requires systems that store treated water in uncovered facilities to

either cover the facility or treat discharge to inactivate 4-log virus, 3-log

Giardia lamblia, and 2-log Cryptosporidium.

The LT2 rule also establishes disinfection benchmarking, in which sys-

tems are required to review their current level of microbial treatment

before making signiﬁcant changes in disinfection practices. This will

help systems maintain protection against microbial pathogens as they

strive to reduce DBPs under the Stage 2 DBP rule.

Time frame. System-monitoring start dates correspond to system size.

Approximately 3 months before the monitoring start date, systems must

submit a sampling schedule and sampling location description. Systems

serving at least 100,000 people should begin monitoring in October

2006. Those serving 50,000 to 99,000 people will begin monitoring in

April 2007. Systems serving 10,000 to 49,000 people will begin moni-

toring in April 2008. The smallest systems (serving less than 10,000

people) will begin monitoring for E. coli in October 2008. If needed,

additional Cryptosporidium treatment will start in April 2012 through

October 2014 depending on the size of the system (Table 5.3.).

When these 2 years of monitoring are complete and bin classiﬁcation

is determined, systems will have approximately 3 years to implement

any additional treatment requirements. Systems will then conduct a

second round of monitoring 6 years after completing the initial round

to determine if source water conditions have changed signiﬁcantly.

Costs. The LT2 rule also will result in increased costs to public

water utilities and states. The US EPA estimates that the average

annualized present-value costs of the LT2 rule range from $92 to $133

million (using a 3% discount rate). Public water systems will be

responsible for nearly all of the total cost (99%), and states will pick

up the remaining 1%. The LT2 rule will also result in increased costs

for households, with the US EPA estimating an average annual house-

hold cost of $1.67 to $2.59.

340 Chapter 5

Remark. Singer (2006) stated that accordingly, all utilities should

modify their monitoring programs to measure all nine bromine- and

chlorine-containing HAA species. Even though they are only required

(sum of ﬁve HAA) species, they will have a much better understanding

of their system and the interrelationships among source water quality,

treatment practices, and DBP formation if all nine species are measured.

Furthermore, it is that in future versions of the DBP regulations—and

most assuredly, there will be future versions—US EPA will regulate all

nine bromine- and chlorine-containing THMs.

4.3 Compliance with standards

The US EPA has established a maximum contaminant level (MCL) of

drinking water for a number of biological, physical, and chemical (inor-

ganics and organics) parameters, and radioactivity (Table 5.1, National

Primary Drinking Water Regulations). All the primary standards are

based on health effects to the customers, and they are mandatory stan-

dards. The National Secondary Drinking Water Regulations (Table 5.1a)

pertain to those contaminants such as taste, odor, and color and some

chemicals that may adversely affect the aesthetic quality of drinking

water. They are intended as guidelines for the states. The states may

establish higher or lower values as appropriate to their particular cir-

cumstances to adequately protect public health and welfare.

The design engineer should be thoroughly familiar with and integrate

the various regulatory requirements into a water treatment design. In

addition to the federal regulations stated above, the other rules and reg-

ulations pertaining to drinking water are the Surface Water Treatment

Rule (SWTR), the revised Total Coliform Rule, the Lead and Copper

Rule, consumer conﬁdence report, Interim Enhanced SWTR, and the

Groundwater Rule. It is necessary to obtain a permit from the state reg-

ulatory agency. Meetings with the representatives of the necessary reg-

ulatory agencies and related parties are recommended. The state review

of the designs is based on considerations of minimum design require-

ments or standards, local conditions, and good engineering practice and

experience. The most widely used standards are the Recommended

Standards for Water Works promulgated by the Great Lakes-Upper

Mississippi River Board of State Sanitary Engineers (GLUMRB) that

are called the Ten-State Standards. This board includes representatives

from the states of Illinois, Indiana, Iowa, Michigan, Minnesota, Missouri,

New York, Ohio, Pennsylvania, and Wisconsin. Recently, the Province of

Ontario (Canada) has joined the board. Many other states have used iden-

tical or similar versions of the Ten-State Standards.

The operational personnel at the drinking waterworks also have to be

familiar and compliant with the regulations (especially the two rules

updated in 2006) related to the system. They have to take more aggressive

Public Water Supply 341

sive management and technical approaches to produce drinking water

that meets all standards and requirements. For these safeguards to

their water supply, consumers are expected to pay more than the cur-

rent very low price.

Maximum contaminant level goal (MCLG) for water quality is set by the

US Environmental Protection Agency (EPA). For agents in drinking water

not considered to have carcinogenic potential, i.e. no effect levels for

chromic and/or lifetime period of exposure including a margin of safety, are

commonly referred to as reference dosages (RfDs). Reference dosages are

the exposure levels estimated to be without signiﬁcant risk to humans

when received daily over a lifetime. They are traditionally reported as

mg/(kg⋅d). For MCLG purposes, however, no effect level in drinking water

is measured by mg/L which has been in terms of the drinking water equiv-

alent level (DWEL). The DWEL is calculated as (Cotruvo and Vogt, 1990)

(5.13)

where NOAEL ⫽ no observed adverse effect level, mg/(kg⭈d)

(70) ⫽ assumed weight of an adult, kg

UF ⫽ uncertainty factor (usually 10, 100, or 1000)

(2) ⫽ assumed quantity of water consumed by an adult, L/d

When sufﬁcient data is available on the relative contribution from other

sources, i.e. from food and air, the MCLG can be determined as follows:

MCLG ⫽ RfD ⫺ contribution from (food ⫹ air)

In fact, comprehensive data on the contributions from food and air

are generally lacking. Therefore, in this case, MCLG is determined as

MCLG ⫽ DWEL. The drinking water contribution often used in the

absence of speciﬁc data for food and air is 20% of RfD. This effectively

provides an additional safety factor of 5.

Example: The MCLG for nitrate–nitrogen is 10 mg/L. Assume UF ⫽ 100.

What is the “no observed adverse effect level for the drinking water?”

solution: Using Eq. (5.13)

since DWEL ⫽ MCLG ⫽ 10 mg/L

10 mg/L 5

sNOAEL, mg/kg

ddd 3 s70 kgd

100 3 2 L/d

NOAEL 5

2000

5 28.6 smg/skg

ddd

DWEL 5

sNOAELd 3 70

sUFd 3 2

DWEL 5

sNOAELds70d

sUFds2d

342 Chapter 5

4.4 Atrazine

Atrazine is a widely used organic herbicide due to its being inexpensive

compared to other chemicals. Often, excessive applications are used. When

soil and climatic conditions are favorable, atrazine may be transported to

the drinking water sources by runoff or by leaching into groundwater.

Atrazine has been shown to affect offspring of rats and the hearts of

dogs. The US EPA has set the drinking water standard for atrazine con-

centration to 0.003 mg/L (or 3 ␮g/L) to protect the public against the risk

of the adverse health effects. When atrazine or any other herbicide or pes-

ticide is detected in surfacewater or groundwater, it is not meant as a

human health risk. Treated (ﬁnished) water meets the EPA limits with

little or no health risk and is considered safe with respect to atrazine.

Example: The lifetime health advisory level of 0.003 mg/L for atrazine is set

at 1000 times below the amount that causes no adverse health effects in lab-

oratory animals. The no observed adverse effect level is 0.086 mg/(kg ⭈ d). How

is the 0.003 mg/L of atrazine in water derived?

solution: As previous example,

Using Eq. (5.13)

5 Water Treatment Processes

As the raw surface water comes to the treatment plant, physical screening

is the ﬁrst step to remove coarse material and debris. Thereafter, following

the basic treatment process of clariﬁcation, it would include coagulation, ﬂoc-

culation, and sedimentation prior to ﬁltration, then disinfection (mostly by

the use of chlorination). With a good quality source, the conventional treat-

ment processes may be modiﬁed by removing the sedimentation process and

to just have the coagulation and ﬂocculation processes followed by ﬁl-

tration. This treatment process scheme is called direct ﬁltration.

Groundwater is generally better quality; however, it is typically asso-

ciated with high hardness, iron, and manganese content. Aeration or air

stripping is required to remove volatile compounds in groundwater.

Lime softening is also necessary to remove the impurities and recar-

bonation is used to neutralize excess lime and to lower the pH value. Ion

exchange processes can also be employed for the softening of water and

the removal of other impurities, if low in iron, manganese, particulates,

DWEL 5

sNOAELds70d

sUFds2d

s0.086 mg/skg

ddds70 kgd

s1000ds2 L/dd

5 0.003 mg/L

and organics. For a groundwater source high in ion and manganese, but

with acceptable hardness, the aeration process and/or chemical oxida-

tion can be followed by ﬁltration to remove these compounds.

The reverse osmosis process is used to remove chemical constituents

and salts in water. It offers the promise of conversion of saltwater to fresh-

water. Other membrane processes, such as microﬁltration, ultraﬁltration,

nanoﬁlteration, and electrodialysis, are also applied in the water industry.

6 Aeration and Air Stripping

Aeration has been used to remove trace volatile organic compounds

(VOCs) in water either from surface water or groundwater sources. It has

also been employed to transfer a substance, such as oxygen, from air or

a gas phase into water in a process called gas adsorption or oxidation

(to oxidize iron and/or manganese). Aeration also provides the escape of

dissolved gases, such as carbon dioxide and hydrogen sulﬁde.

Air stripping has also been utilized effectively to remove ammonia gas

from wastewater and to remove volatile tastes and other such sub-

stances in water.

The solubility of gases which do not react chemically with the solvent

and the partial pressure of the gases at a given temperature can be

expressed as Henry’s law:

p ⫽ Hx (5.14)

where x ⫽ solubility of a gas in the solution phase

H ⫽ Henry’s constant

p ⫽ partial pressure of a gas over the solution

In terms of the partial pressure, Dalton’s law states that the total pres-

sure (P

) of a mixture of gases is just the sum of the pressures that each

gas (P

) would exert if it were present alone:

(5.15)

Since PV ⫽ nRT

(5.16)

P 5 na

1 n

###

1 n

###

5 P

1 P

###

1 P

Public Water Supply 343

344 Chapter 5

Combining Henry’s law and Dalton’s law, we get

(5.17)

where Y

⫽ mole fraction of ith gas in air

⫽ mole fraction of ith gas in ﬂuid (water)

⫽ Henry’s constant for ith gas

⫽ total pressure, atm

The greater the Henry’s constant, the more easily a compound can be

removed from a solution. Generally, increasing temperature would

increase the partial pressure of a component in the gas phase. The

Henry’s constant and temperature relationship is (James M.

Montgomery Consulting Engineering, 1985; American Society of Civil

Engineers and American Water Works Association, 1990):

(5.18)

where H ⫽ Henry’s constant

∆H ⫽ heat absorbed in evaporation of 1 mole of gas from

solution at constant temperature and pressure, kcal/kmol

R ⫽ universal gas constant ⫽ 1.9872 kcal/kmol ⭈ ⬚k

⫽ 0.082057 atm ⭈ L/mol ⭈ k

T ⫽ temperature, Kelvin

J ⫽ empirical constant

Values of H, ∆H, and J of some gases are given in Table 5.4.

Example 1: At 20°C the partial pressure (saturated) of chloroform CHC1

is 18 mm of mercury in a storage tank. Determine the equilibrium concen-

tration of chloroform in water assuming that gas and liquid phases are ideal.

solution:

Step 1. Determine mole fraction (x) of CHC1

From Table 5.4, at 20°C and a total pressure of 1 atm, the Henry’s constant

for chloroform is

H ⫽ 170 atm

Partial pressure of CHC1

, p, is

p 5

18 mm

760 mm

3 1 atm 5 0.024 atm

logH 5

2⌬H

1 J