Water Quality Criteria and Treatment-Session 4

Nephelometric Turbidity Unit (NTU)

A measure of the clarity of water. Turbidity in excess of 5 NTU is just noticeable to the average person.

Turbidity

A measure of the cloudiness of the water.

Highlights of 1996 SDWA ammendments

Drinking water state revolving loan fund est'd to help PWS's finance projects to comply with SDWA Contaminant selection process for regulation based on health risk, occurrence, costs/benefits Est'd schedule for Crypto, DBPs, Arsenic, Radon Provisions for systems' capacity to comply, source water assessment, operator certification/training, CCRs, etc.

water qulity reporting

Exceedences reportable to local Department of Health DOH determines need for additional sampling, boil water alerts, system shutdowns, and informs public as appropriate Sampling frequency depends on chemicals

Funding for Drinking water security

$160M authorized for FY2002 to provide financial assistance to CWS's to meet above requirements FY2003-06: $10's of millions authorized each year for VA's (small & medium-size systems), state water security coordinators to assess water security, training, etc.

Statistics on Public Water Systems

159,000 privately/publicly owned systems are subject to Federal drinking water regulations 52,838 are community water systems 18,650 are non-transient, non-community water systems 84,740 are transient non-community water systems

Safe Drinking Water Act

Federal legislation designed to ensure safe drinking water as provided by public water systems -Enacted in 1974, amended in 1986 and 1996 -Federal-state structure established where states and tribes may be delegated primary enforcement and implementation authority by the USEPA

Settled water turbidity performance goals

If raw water intake >10 NTU, <2 NTU 95% of time If raw water intake ≤10 NTU, <1 NTU 95% of time

Maximum Residual Disinfectant Level Goal (MRDLG):

Level of a drinking water disinfectant below which there is no known or expected risk to health. MRDLGs don't reflect benefits of the disinfectant use to control microbial contamination.

Direct filtration

Avoids sedimentation stage Requires high-quality source water with constant flow and low turbidity

Treatment Technique

A required process intended to reduce the level of a contaminant in drinking water.

Conventional coagulation-flocculation-sedimentation

Addition of coagulant to source water to form "flocs" Solids settle out in a sedimentation basin

Dissolved air flotation

Addition of coagulant, followed by flocculation Instead of using sedimentation, pressurized air bubbles force them to the water surface where particles can be skimmed off

White Plains, NY Water Supply Source

All water is purchased from NYC DEP, through Westchester County Water District No. 1; drawn from the Kensico Reservoir (unfiltered) Two surface reservoirs (70 MG and 125 MG capacities); three wells (150,000-200,000 gpd) removed from service in 2009 -Expected to return to service in 2016 through use of new filtration plant Emergency interconnection to Delaware Aqueduct in Yonkers

Small water systems issues

CWS's serving <3,300 persons: Are 84% (44,000) of the 52,800 CWS's Represent 9% of U.S. population Major problems: -Deteriorated infrastructure -Lack of access to capital -Limited customer and rate base -Inadequate rates -Diseconomies of scale -Limited managerial and technical capabilities

Packaged filtration

Chemical addition, flocculation, sedimentation, and filtration all housed in one unit Often used for small CWS's, recreational areas, construction sites, etc

White Plains, NY Water Supply Service Area

City of White Plains: 9.8 sq. miles, population ~57,000 160 miles of water mains, >10,000 metered accounts 2.8 billion gallons produced in 2014 (~7.65 MGD) 8.27 MGD treated and pumped into distribution system $1.87 per 100 ft3 (748 gal) of water; average annual bill = $212

Bioterrorism Preparedness Act of 2002 amended SDWA to require CWS's to:

Conduct vulnerability assessments Prepare emergency response plans Review methods that terrorists could use to disrupt provision of safe water supplies and review methods to prevent, detect, and respond to disruptions

Affordability issues and compliance

Criteria to determine affordability of technology Provision of grants for small system compliance assistance

Filtration Performance Goals

Filtered water turbidity <0.1 NTU 95% of time, with max of 0.30 NTU Max backwash recovery period of 15 min. Max filtered water measurement of <10 particles/mL

Cartridge filtration

Good for small systems with low-turbidity influent

Maximum Contaminant Level goal (MCLG)

Level of contaminant in drinking water below which there is no known or expected risk to health. Allow for a margin of safety. (associated with no health effects) Considers sensitive sub-populations. Generally set at 0. (infants, elderly, immunosuppressent) Based only on health effects (not treatment cost, ability to detect), so may not be feasible for systems to meet) After established, USEPA sets an enforceable standard

Disinfection by products continued- Chlorite (ClO2-)

MCL = 1 mg/L, MCLG = 0.8 mg/L Hemolytic anemia Control of treatment processes to reduce disinfectant demand/levels

Disinfection by products continued- Bromate (BrO3)

MCL = 10 g/L, MCLG = 0 g/L Gastrointestinal, kidney, and hearing effects Formed during ozonation

Major issues heading into 109th Congress

MTBE, perchlorate, lead Cost and complexity of drinking water standards and ability of systems (esp. small ones) to comply Drinking water state revolving fund established in 2006, but the $837.5M provided falls far short

exemptions from EPA

May be temporarily granted by State or USEPA if a system cannot comply on time Ex.: 2-year extensions to meet arsenic standard

Disinfection by products continued- Haloacetic acids (HAA5)

Monobromoacetic acid, dibromoacetic acid, monochloroacetic acid, dichloroacetic acid, and trichloroacetic acid MCL = 60 g/L Nervous system and liver effects

Chlorine

Most widely used technology for water and wastewater treatment Primary disinfection: achieves desired level of microorganism kill or inactivation Secondary disinfection: maintains a disinfectant residual in the finished water that prevents microorganism regrowth Pros: Powerful against bacteria, viruses, Giardia Low cost, low maintenance Cons: Forms carcinogenic disinfection byproducts Not effective against Cryptosporidium Safety concerns with transportation and handling

Slow Sand Filtration

No coagulation and (usually) no sedimentation step

Factors affecting the sedimentation process

Particle size, distribution, shape, density, charge Area, time, velocity of water injection Water temperature, contents Sedimentation basin design and hydraulics

Activated Carbon

Powdered, Granular ... high surface areas (1g>500m2)

Disinfection

Process to remove microbial contamination from drinking water prior to distribution Chlorine Cl2 gas, ClO2, NaOCl, Ca(ClO)2 Advanced Processes UV Light, Ozone

Sedimentation

Process where solid particles settle to bottom of a large clarifier or sedimentation basin Sludge in tank scraped to sump for drainage.

Water Quality Reporting parameters

Regulated Contaminants -Arsenic, barium, chromium, fluoride, nitrate, mercury, selenium, lead Radioactive Contaminants -Alpha emitters; combined Ra-226/228 -Unregulated Chemical Contaminants Sodium, sulfate Contaminants Subject to an Action Level -Lead, copper Disinfection Byproducts -Free chlorine residual, trihalomethanes, haloacetic acids (HAA5) Microbial Contaminants -Total coliform bacteria; fecal coliform, E. coli

Filtration

Removal of particulate matter, turbidity and pathogens from drinking water by passing water through a permeable fabric or porous bed of materials

Filter Backwashing

Reversal of water flow to wash out accumulated debris and particles Use water from clear well, storage tank or distribution system When to backwash indicated by turbidity and pressure loss Filter bed expansion considerations (15-20%) Backwash water considerations Reversal of water flow to wash out accumulated debris and particles Use water from clear well, storage tank or distribution system When to backwash indicated by turbidity and pressure loss Filter bed expansion considerations (15-20%) Backwash water considerations

Diatomaceous Earth

Soft fine-grained deposits formed from skeletal remains of diatoms ... more or less replaced by activated carbon

Physical and chemical processes involved in the filtration process

Straining, adhesion/adsorption Biological processes break down algae, bacteria, organic matter

Action Level

The concentration of a contaminant which, if exceeded, triggers treatment or other requirements which a water system must follow

Membrane filtration

Typically used for desalination applications Microfiltration (0.1 m), Ultrafiltration (0.01m)

Maximum Contaminant Level (MCL)

The highest level of a contaminant that is allowed in drinking water. MCLs are set as close to the MCLGs as is feasible using the best technology or other means available, taking cost into consideration

Maximum Residual Disinfectant Level (MRDL):

The highest level of a disinfectant allowed in drinking water. There is convincing evidence that addition of a disinfectant is necessary for control of microbial contaminants.

Disinfection Byproducts

Total Trihalomethanes (TTHM): -Trichloromethane (chloroform): CHCl3 -Dibromochloromethane: CHClBr2 -Bromodichloromethane: CHCl2Br -Tribromomethane (bromoform): CHBr3 -MCL (TTHM) = 80 g/L -Removal of precursors via enhanced coagulation/ optimization of filtration process ... decreasing pH (to 4-5), increase feed rate of coagulants, use of ferric coagulants instead of alum, use of reverse osmosis Group B carcinogen

Flocculation

Usually a two- or three-stage process Pretreatment chemical is added Iron or aluminum salts Mixture is stirred to encourage particulates to induce tiny suspended particles to aggregate to form larger and more easily removable clots, or "flocs" Last stage - water agitation is slower and consistent so as to not break up particles Followed by sedimentation process to allow particles to settle out by gravity into a sludge-like material

Variances

When issuing a regulation, USEPA must identify technologies that meet the standard and are affordable for systems serving <10,000 persons Variance technologies can be identified that don't necessarily meet the standard but does protect public health States may grant a variance to a system serving <3,300 persons if it can't afford to comply with a rule (via treatment, alternative source, other restructuring) Affordable compliance technologies are available for all drinking water regulations Concern about D/DBP, arsenic, and radium rules, though ...