Laboratory Flashcards
What is a Maximum Residual Disinfectant Level (MRDL)?
Maximum measurement of disinfection allowed in order to prevent disinfection by-products
What is the MRDL for Chlorine, Chloramines, and Ozone?
Chlorine = 4.0 mg/L Chloramines = 4.0 mg/L Ozone = 0.0 mg/L
What is the MRDL for Fluoride?
- 0 mg/L (Primary)
2. 0 mg/L (Secondary)
What is Modeling in relation to fluoride?
Drinking water with too much fluoride causes brown stains on teeth
What is the target fluoride range and optimum level?
Range - 0.6 mg/L - 0.8 mg/L
Optimum - 0.7 mg/L
How often must the water be tested for fluoride?
Once a day at representative sites
How often must samples be sent to the state lab for fluoride analysis?
One sample per month taken from a representative location in the distribution system and submitted to the state laboratory of hygiene. The sample submitted to the state laboratory of hygiene shall be a portion of a split sample so that the operator can determine the fluoride concentration with the operator’s equipment and compare it to the state laboratory results. The fluoride concentration obtained by the operator shall be noted on the data sheet prior to submission to the state laboratory.
Describe the sample container requirements for collecting fluoride samples
Glass/Plastic - State will send you bottle.
Rinse initially with distilled water
then rinse with sample water
What lab test is the chemical DPD used to detect?
DPD = N,N-diethyl-p-phenylenediamine
Chlorine & Chloramines
What lab test is the chemical SPADNS used to detect?
SPADNS = 4,5 Dihydroxyl-3-(p-Sulfophenylazo)-2,7-Naphthalene-Disulfonic Acid Trisodium Salt
Fluoride
What is the specific ion test used for?
calibrate to detect specific ion…. probably need more info this is vague
Describe the free chlorine residual test utilizing the DPD method
Calibrate (Zero Out) Add DPD reagent to bottle(powder) Add sample Shake Test with pocket unit (is this a small spectrophotometer?)
Darker pink = more chlorine
Wavelength will identify Cl2 (530 nm)
Describe the Fluoride procedure test utilizing the SPADNS method
Absorbs fluoride and becomes a LIGHTER shade of red (opposite Cl2)
Compare to known fl- sample using a spectrophotometer.
Fl- = 580 nm
Temp of SPADNS, Temp of Sample, Temp of known sample should all be the same
What is the correct way to read a meniscus?
Concave = Water meniscus Convex = Mercury meniscus
Describe how to run a pH test
First add 7 buffer
Then add either 4 or 10 buffer depending on where you think the pH falls (this is called bracketing)
4 buffer if its between 0-7
10 buffer if its between 7-14
When and Where are the samples taken to determine trihalomethanes (THMs) and haloacetic acids (HAA5s)?
When - At the warmest water time of the year (August/September)
Where - At the site of the highest recorded THM and highest HAA5 site (if its the same site, use second highest for HAA5
What is the MCL for THMs (trihalomethanes) and HAA5s (haloacetic acids) ?
THMs = 80 ppb HAA5s = 60 ppb
What are the 5 methods used to determine the stability of water with respect to calcium carbonate saturation?
- Langalier Index (LI)
- Baylis Curve
- Ryznar Stability Index (RSI)
- Caldwell Lawrence
- AWWA Standards
What (5) factors effect the Langalier Index and what does a positive/negative result indicate?
- Calcium Hardness
- Alkalinity
- Temperature
- pH
- TDS (Total Dissolved Solids)
Positive = Scale Forming Negative = Corrosive (0 --> -2 only slightly corrosive; -3 and below corrosive)
Describe the Baylis Curve and what areas above/below curve indicate?
pH v.s. Alkalinity (water stability)
stable water does not dissolve nor deposit calcium carbonate
Above curve = scale forming
Below curve = corrosive
Describe coliform and pathogenic bacteria
Coliform = indicator, not harmful itself, found in intestines of humans/animals
Pathogenic = Harmful ex: Salmonella (Typhoid), Shigella (Dysentary), Vibriocome (Cholera); Cryptosporidium (parasite); Giardia Cyst (parasite)
Also harmful - Viruses
Describe the MCL for coliform bacteria
Present - POSITIVE
Absent - NEGATIVE
No more than 1/40 or 5% of samples can be positive
If positive for fecal coliform with repeat sample, must have boil order
How is the minimum number of routine monthly bacteriological samples of community water systems determined?
Proportional to population (according to table in NR809)
Some limits because Milwaukee, can’t do 500 samples
Describe a good bacteriological sampling program
Aseptic - clean
Representative - flowing, fresh, not dead end
Varying times - not taken at same time every month
Acceptable faucets - don’t allow stuff to grow on them
What is an ideal sampling point for bacteriological sample sites?
- Smooth faucet?? (Does this mean smooth flow??) maybe smooth nose faucet?
- Sanitary location
- Representative (Allow water to flow for a few seconds to get an accurate sample) I think. or representative location idk
What types of faucets are NOT ideal for sampling?
- Swing faucet (like a kitchen sink) because it has “o” ring that will melt when heated with torch
- Aerated
- Threaded
- Screened
- Garden Hoses
- Bubblers
- Slop Sinks
What are the sample container requirements used in collecting bacteriological samples taken from a CHLORINATED DISTRIBUTION SYSTEM?
Sterilized, 100 mL, contains sodium thiosulfate (aka Thio)
What are the sample container requirements used in collecting bacteriological samples taken from a NON-CHLORINATED DISTRIBUTION SYSTEM?
Only needs to be sterilized
What is the holding time for bacteriological samples?
Must get to lab in 24 hours
Max life of sample is 30 hours (6 hours to test)
How are bacteriological samples stored when they cannot be used immediately?
In a fridge 40-50 degrees Fahrenheit or 4-10 degrees Celsius.
Cannot freeze or get too hot
What labs in Wisconsin where bacteriological samples can be analzyed?
Some have their own CERTIFIED labs that have been approved by the Department of Health (Milwaukee)
Otherwise the State Lab of Hygiene for smaller communities
What is the procedure when a sample has been deemed unsafe? (presence of bacteria)
Three repeat samples
- Retake same sample
- Take sample upstream within 5 service connections
- Take sample downstream within 5 service connections
Must be within 48 hours… or maybe 24?
If connected to a well, take a “triggered” sample of that well - only one time
How many bacteriological samples have to be taken after a reservoir has been cleaned/repaired before it is put back in service?
one initial Bacti, and one 24 hours later
If it has at least 0.10ppm Cl2 in it, it can be put BIS before 2nd bacti
What are the AWWA standards for placing Pipes and Tanks back in service after repairs?
C650??
C651 - Pipes - Disinfect with minimum of 50 ppm for 24 hours
C652 - Tanks - Same as Pipes OR 200 ppm for 2 hours, then overflow until it gets to 2 ppm. Then BIS
