PracticeVideosBlogFlashcardsEspañol

Free exam prep

New Jersey Water/Wastewater Operator

Practice QuestionsStudy GuideFlashcards

13.1 Sampling Procedures, Chain of Custody & QA/QC

Key Takeaways

  • Grab samples are mandatory for transient, volatile, or biological parameters (pH, DO, temperature, chlorine residual, coliform bacteria, VOCs, oil & grease) that alter rapidly in a composite sampler.
  • Composite sampling (flow-proportional vs. time-proportional) provides a representative 24-hour characterization of fluctuating waste streams for BOD5, COD, TSS, total phosphorus, ammonia, and metals.
  • Potable sampling lines must be flushed for 2 to 3 pipe volumes after removing aerators and screens; microbiological samples require sterile containers containing sodium thiosulfate (Na2S2O3) to neutralize chlorine.
  • Strict chemical preservation and holding times (EPA / Standard Methods / NJDEP OQA) govern legal validity: coliforms require chilling (<10°C DW, max 30 hr; <6°C WW, max 8 hr); BOD5 requires cooling ≤6°C (max 48 hr); TSS requires cooling ≤6°C (max 7 days); nutrients require H2SO4 to pH <2 (max 28 days); metals require HNO3 to pH <2 (max 6 months).
  • Quality assurance protocols ensure legal defensibility via unbroken Chain of Custody (COC), trip and field blanks, laboratory duplicates (Relative Percent Difference ≤20%), matrix spikes (% Recovery), and clear distinction between MDL and PQL.
Last updated: September 2026

13.1 Sampling Procedures, Chain of Custody & QA/QC

Core Function: Analytical laboratory data is only as reliable as the sample collected. Even the most sophisticated spectroscopic or microbiological instrumentation cannot correct for an unrepresentative, contaminated, improperly preserved, or degraded sample. Licensed New Jersey water and wastewater operators must master standardized sampling collection mechanics, preservation chemistry, maximum allowable holding times, legal Chain of Custody (COC) documentation, and quality assurance/quality control (QA/QC) validation.

1. Grab Samples vs. Composite Samples

Environmental monitoring data under the Safe Drinking Water Act (SDWA) and the New Jersey Pollutant Discharge Elimination System (NJPDES) requires strict adherence to designated sampling types based on physical stability and analytical chemistry.

                               SAMPLING METHODOLOGY SELECTION
                                              │
             ┌────────────────────────────────┴────────────────────────────────┐
             ▼                                                                 ▼
     [ Grab Sampling ]                                               [ Composite Sampling ]
     - Discrete, instantaneous snapshot                              - Pooled collection over 24 hours
     - For unstable / volatile parameters                            - Representative for daily loading
     - Required: pH, DO, Temp, Cl2, VOCs,                            - Methods: Flow-Proportional (preferred)
       Coliforms, Oil & Grease, Sulfide                                or Time-Proportional
                                                                     - Used for: BOD5, COD, TSS, Nutrients,
                                                                       Metals, Cyanide (flow-composited)

Fundamental Characteristics & Comparison

+------------------------+---------------------------------------+---------------------------------------+
| Operational Parameter  | Grab Sample                           | Composite Sample                      |
+------------------------+---------------------------------------+---------------------------------------+
| Definition             | An individual, discrete sample volume | A series of sample aliquots collected |
|                        | collected at a specific location and  | over an extended period (typically 24 |
|                        | precise point in time.                | hours) combined into one container.   |
+------------------------+---------------------------------------+---------------------------------------+
| Primary Purpose        | Identifies instantaneous water quality| Quantifies average water quality and  |
|                        | conditions, extreme peak loading, or  | total mass pollutant loading (lb/day) |
|                        | batch discharge slug events.          | across operational diurnal cycles.    |
+------------------------+---------------------------------------+---------------------------------------+
| Mandatory Parameters   | pH, Dissolved Oxygen (DO), Temperature| 5-day Biochemical Oxygen Demand (BOD5)|
| (Never Composite)      | Total & Free Chlorine Residual, VOCs, | Chemical Oxygen Demand (COD), Total   |
|                        | Coliform Bacteria, Oil & Grease.      | Suspended Solids (TSS), Total Metals. |
+------------------------+---------------------------------------+---------------------------------------+
| Sampling Limitations   | Misses cyclical diurnal peaks and     | Blurs short-duration toxic spikes;    |
|                        | off-shift shock loads if taken once.  | chemical reactions can occur in jug.  |
+------------------------+---------------------------------------+---------------------------------------+

Parameters Strictly Restricted to Grab Sampling

Operators must never composite the following parameters due to physical, chemical, or biological volatility:

  1. pH & Temperature: pH shifts within 15 minutes due to carbon dioxide ($CO_2$) absorption or off-gassing, shifting the carbonate equilibrium; temperature equilibrates rapidly to ambient sampler conditions.
  2. Dissolved Oxygen (DO): Continues biological respiration or atmospheric re-aeration within the collection vessel.
  3. Chlorine Residual (Free & Combined): Decomposes rapidly via photochemical exposure, oxidation of organics, and auto-decomposition.
  4. Microbiological Indicators (Total Coliform, E. coli, Enterococci): Bacteria reproduce, die off, or adhere to sampler tubing and container walls during extended holding.
  5. Volatile Organic Compounds (VOCs): Purge and volatilize into the air headspace or are stripped by vacuum peristaltic sampler pumps.
  6. Oil and Grease (HEM): Heavy hydrocarbons adhere permanently to peristaltic sampler tubing, suction lines, and container surfaces, preventing quantitative transfer.

Composite Sampling Mechanics: Flow-Proportional vs. Time-Proportional

  • Flow-Proportional Composite (Mandatory for Diurnal Variations): Sample aliquots reflect changes in stream flow rate. This is achieved in one of two ways:
    • Constant Time / Variable Volume: Aliquots are drawn at uniform time increments (e.g., every 15 minutes), with the volume collected directly proportional to instantaneous effluent flow.
    • Constant Volume / Variable Time: A fixed aliquot volume (e.g., 100 mL) is drawn each time an integrated flow meter records a pre-set increment of total volume (e.g., every 50,000 gallons).
    • Mass Loading Formula: True daily mass discharge ($L$ in lb/day) can only be calculated accurately with flow-proportional composites: L=Flow (MGD)×Concentration (mg/L)×8.34L = \text{Flow (MGD)} \times \text{Concentration (mg/L)} \times 8.34
  • Time-Proportional Composite: Aliquots of identical volume are collected at fixed, uniform time intervals (e.g., 200 mL every 60 minutes over 24 hours). This method is legally valid only when flow rates vary by less than 15% throughout the entire monitoring cycle.

2. Sample Collection Procedures & Container Selection

Proper sample collection eliminates external contamination and prevents sample-container chemical reactions.

                    POTABLE WATER TAP SAMPLING PROTOCOL
  ┌─────────────────────────┐     ┌─────────────────────────┐     ┌─────────────────────────┐
  │   1. Inspect & Clean    │ ──► │  2. High-Flow Flushing  │ ──► │  3. Controlled Capture  │
  │ - Remove aerators/hoses │     │ - Flush cold water line │     │ - Throttle to smooth,   │
  │ - Avoid swivel/hot taps │     │   for 2 to 3 pipe vols  │     │   laminar stream        │
  │ - Sanitize tap spout    │     │ - Check temp stability  │     │ - Zero splashing/rinse  │
  └─────────────────────────┘     └─────────────────────────┘     └─────────────────────────┘

Tap Sampling Guidelines for Potable Water

  1. Avoid Inappropriate Faucets: Never sample from drinking water taps fitted with aerators, charcoal/sediment filters, hose bibbs, or swivel spouts (leaking packing glands harbor biofilm). Select a rigid, non-threaded cold water tap served directly from the distribution main.
  2. Aerator Removal & Disinfection: Unscrew external aerators, screens, or splash fittings. Swab or spray the interior and exterior of the faucet nozzle with a 5.25% sodium hypochlorite (bleach) solution or 70% isopropyl alcohol, allowing 2 minutes of contact time.
  3. Line Flushing: Open the cold water tap fully and flush for 2 to 3 pipe volumes (typically 3 to 5 minutes) until the water reaches a constant, stable temperature. This ensures that the water sampled represents the water main rather than stagnant interior plumbing.
  4. Sample Capture: Throttle the flow to a smooth, non-splashing laminar stream about the thickness of a pencil. Fill the container leaving a 1-inch headspace (except for VOCs) to facilitate mixing prior to analysis. Never rinse a pre-preserved bottle.

Container Types & Material Compatibility

+-----------------------+-----------------------------+---------------------------------------------+
| Container Material    | Target Analytes             | Scientific Rationale & Limitations          |
+-----------------------+-----------------------------+---------------------------------------------+
| High-Density          | Inorganics, general wet     | Non-reactive, non-leaching, rugged;         |
| Polyethylene (HDPE)   | chemistry (TSS, TDS, SO4,   | prevents trace metal adsorption. Never use  |
| or Polypropylene      | Cl, alkalinity), metals.    | for organics or VOCs (organic absorption).  |
+-----------------------+-----------------------------+---------------------------------------------+
| Borosilicate Glass    | Semi-volatile organics,     | Inert, zero organic solvent leaching;       |
| (Clear)               | pesticides, PCBs, oil and   | baked at 400°C to eliminate trace carbon.   |
|                       | grease, extractables.       | Fragile; trace metals can leach from glass. |
+-----------------------+-----------------------------+---------------------------------------------+
| Amber Glass           | Light-sensitive organic     | Blocks UV and visible light penetration,    |
|                       | compounds (PAHs, phenolics, | preventing photochemical decomposition and  |
|                       | nitrosamines, chlorinated). | photodegradation during transport.          |
+-----------------------+-----------------------------+---------------------------------------------+
| Sterile Polystyrene / | Total Coliform, Fecal       | Radiation-sterilized or autoclaved;         |
| Polypropylene with    | Coliform, E. coli,          | pre-dosed with 10 mg sodium thiosulfate     |
| Na2S2O3 Tablet        | Enterococci.                | tablet to neutralize chlorine residuals.    |
+-----------------------+-----------------------------+---------------------------------------------+
| 40-mL Glass VOA Vials | Volatile Organic Compounds  | Zero headspace required; Teflon-faced       |
| with Septum Caps      | (VOCs, THMs, purgeables).   | silicone septum prevents VOC gas migration. |
+-----------------------+-----------------------------+---------------------------------------------+

Sodium Thiosulfate Neutralization Chemistry

When collecting microbiological compliance samples from disinfected water (potable mains or treated effluent), the container must contain sodium thiosulfate ($Na_2S_2O_3$). In drinking water testing, a 10 mg tablet or 100 mg/L powder neutralizes up to 5 mg/L of residual free and combined chlorine immediately upon contact:

Na2S2O3+4Cl2+5H2O→2NaHSO4+8HClNa_2S_2O_3 + 4 Cl_2 + 5 H_2O \rightarrow 2 NaHSO_4 + 8 HCl

Without sodium thiosulfate, residual chlorine continues killing bacteria inside the container during the transit period, yielding a false-negative coliform test that masks bacteriological contamination in the distribution network.

3. Chemical Preservation & Maximum Holding Times

Preservation arrests biological activity, hydrolytic degradation, precipitation, and adsorption onto container walls. Holding times reflect the maximum duration permissible between sample collection and laboratory extraction or analysis under EPA 40 CFR Part 136, Standard Methods, and NJDEP Office of Quality Assurance (OQA) regulations (N.J.A.C. 7:18).

+----------------------+--------------------+-----------------------------+--------------+-----------------------+
| Analytical Parameter | Container Type     | Chemical Preservative       | Storage Temp | Maximum Holding Time  |
+----------------------+--------------------+-----------------------------+--------------+-----------------------+
| Coliform Bacteria    | Sterile plastic or | Sodium thiosulfate          | Cool < 10°C  | **30 Hours**          |
| (Drinking Water)     | glass (120 mL)     | ($Na_2S_2O_3$, 10 mg)       | (Do not freez| (SDWA Compliance)     |
+----------------------+--------------------+-----------------------------+--------------+-----------------------+
| Coliform Bacteria    | Sterile plastic or | Sodium thiosulfate          | Cool < 6°C   | **8 Hours**           |
| (Wastewater / Effl)  | glass (120 mL)     | ($Na_2S_2O_3$, 10 mg)       | (Wet ice)    | (6 hr transit + 2 lab)|
+----------------------+--------------------+-----------------------------+--------------+-----------------------+
| Biochemical Oxygen   | Plastic (HDPE) or  | None permitted              | Cool ≤ 6°C   | **48 Hours**          |
| Demand (BOD5 / CBOD5)| ungreased glass    | (Never acidify!)            | (Wet ice)    |                       |
+----------------------+--------------------+-----------------------------+--------------+-----------------------+
| Total Suspended      | Plastic (HDPE) or  | None permitted              | Cool ≤ 6°C   | **7 Days**            |
| Solids (TSS / TDS)   | glass              |                             |              |                       |
+----------------------+--------------------+-----------------------------+--------------+-----------------------+
| Ammonia-Nitrogen     | Plastic (HDPE) or  | Sulfuric acid ($H_2SO_4$)   | Cool ≤ 6°C   | **28 Days**           |
| ($NH_3\text{-N}$)    | glass              | to $pH < 2$                 |              |                       |
+----------------------+--------------------+-----------------------------+--------------+-----------------------+
| Total Phosphorus     | Plastic (HDPE) or  | Sulfuric acid ($H_2SO_4$)   | Cool ≤ 6°C   | **28 Days**           |
| ($TP$)               | acid-washed glass  | to $pH < 2$                 |              |                       |
+----------------------+--------------------+-----------------------------+--------------+-----------------------+
| Nitrate ($NO_3\text{-| Plastic (HDPE) or  | None (Unacidified)          | Cool ≤ 6°C   | **48 Hours**          |
| N}$) - Separate      | glass              | (Acid converts NO2 to NO3)  |              |                       |
+----------------------+--------------------+-----------------------------+--------------+-----------------------+
| Nitrate + Nitrite    | Plastic (HDPE) or  | Sulfuric acid ($H_2SO_4$)   | Cool ≤ 6°C   | **28 Days**           |
| (Combined)           | glass              | to $pH < 2$                 |              |                       |
+----------------------+--------------------+-----------------------------+--------------+-----------------------+
| Metals (Total - Al,  | Plastic (HDPE) or  | Concentrated nitric acid    | Ambient or   | **6 Months**          |
| Fe, Pb, Cu, Zn, etc.)| fluoropolymer      | ($HNO_3$) to $pH < 2$       | Cool ≤ 6°C   | (180 Days)            |
+----------------------+--------------------+-----------------------------+--------------+-----------------------+
| Mercury (Total - Hg) | Borosilicate glass | Concentrated nitric acid    | Cool ≤ 6°C   | **28 Days**           |
|                      | or Teflon          | ($HNO_3$) to $pH < 2$       |              |                       |
+----------------------+--------------------+-----------------------------+--------------+-----------------------+
| Volatile Organics    | 40-mL glass VOA    | Hydrochloric acid ($HCl$)   | Cool ≤ 6°C   | **14 Days**           |
| (VOCs / Trihalometh) | vials with septum  | to $pH < 2$, zero headspace | (Wet ice)    | (7 days if unpreserved|
+----------------------+--------------------+-----------------------------+--------------+-----------------------+
| Oil & Grease (HEM)   | 1-Liter wide-mouth | Sulfuric ($H_2SO_4$) or     | Cool ≤ 6°C   | **28 Days**           |
|                      | glass bottle       | Hydrochloric ($HCl$) to < 2 |              | (Separate grab only!) |
+----------------------+--------------------+-----------------------------+--------------+-----------------------+

The Acidification Trap: Never add nitric acid ($HNO_3$) to nutrient samples, and never add sulfuric acid ($H_2SO_4$) to metals samples! Sulfuric acid precipitates barium and lead as insoluble sulfates ($BaSO_4, PbSO_4$), removing them from solution. Nitric acid acts as a powerful oxidant that oxidizes ammonia and organic nitrogen, invalidating nutrient profiles.

4. Chain of Custody (COC) Legal Documentation

Compliance data submitted to the NJDEP constitutes legal evidence. In any enforcement proceeding, civil litigation, or administrative penalty hearing, analytical results are inadmissible unless backed by an unbroken, legally defensible Chain of Custody (COC).

                    LEGAL CHAIN OF CUSTODY (COC) CONTINUUM
  ┌─────────────────────┐     ┌─────────────────────┐     ┌─────────────────────┐
  │ 1. Field Collection │ ──► │  2. Secure Transit  │ ──► │ 3. Lab Receipt/Log  │
  │ - Sample ID, Date/  │     │ - Tamper-evident    │     │ - Check temp cooler │
  │   Time, Preservative│     │   custody seals     │     │   (≤ 6°C wet ice)   │
  │ - Relinquished by   │     │ - Locked cooler or  │     │ - Verify integrity, │
  │   Sampler Signature │     │   courier tracking  │     │   Relinquish/Receive│
  └─────────────────────┘     └─────────────────────┘     └─────────────────────┘

The Legal Definition of "Custody"

Under federal and New Jersey administrative standards, a sample is officially in an individual's legal custody if:

  1. It is in the individual's physical possession;
  2. It is in the individual's view, after being in physical possession;
  3. It was in the individual's physical possession and then secured in a locked area to prevent tampering;
  4. It is placed in a designated, secured container sealed with a tamper-evident custody seal such that opening the container breaks the seal.

Mandatory COC Form Elements

A complete Chain of Custody record must accompany every sample cooler and contain:

  • Unique sample identification code (matching bottle labels exactly).
  • Sample matrix (e.g., raw surface water, finished drinking water, activated sludge MLSS, final effluent).
  • Sampling point location (e.g., Well #4 Raw Tap, Outfall 001A).
  • Date and exact military time of collection (e.g., 2026-09-08 09:45).
  • Sample type: Discrete Grab or 24-Hour Composite.
  • Preservatives used (e.g., $HNO_3, H_2SO_4, Na_2S_2O_3$, or unpreserved on ice).
  • Specific analytical test methods requested (e.g., EPA 200.8, SM 5210 B, EPA 180.1).
  • Signatures of all individuals relinquishing and receiving the sample, with matching dates and timestamps.
  • Cooler internal temperature upon arrival at the certified laboratory (measured via a dedicated temperature blank vial, required to be $\le 6^\circ\text{C}$ on wet ice, but not frozen).

5. Laboratory QA/QC Protocols & Statistical Control

Quality Assurance (QA) refers to the comprehensive management framework (operating procedures, certifications, training), whereas Quality Control (QC) represents the specific technical operations and statistical checks conducted to ensure that data is precise, accurate, and defensible.

+-----------------------+---------------------------------------+---------------------------------------+
| QC Quality Indicator  | Operational Preparation Protocol      | Analytical Purpose & Standard Limits  |
+-----------------------+---------------------------------------+---------------------------------------+
| Trip Blank            | Laboratory reagent water filled in    | Assesses cross-contamination of VOCs  |
|                       | lab, sealed, travels with cooler,     | during transit, handling, or storage; |
|                       | never opened in the field.            | must be below detection limit (< MDL).|
+-----------------------+---------------------------------------+---------------------------------------+
| Field Blank           | Reagent water poured into empty       | Quantifies atmospheric deposition or  |
| (Ambient Blank)       | sample container in the field at the  | environmental airborne contamination  |
|                       | sampling location during collection.  | present at the sampling site.         |
+-----------------------+---------------------------------------+---------------------------------------+
| Equipment Blank       | Reagent water flushed through clean   | Verifies field decontamination and    |
| (Rinsate Blank)       | sampling apparatus (pumps, dippers,   | cleaning protocols of non-dedicated   |
|                       | tubing) after field washing.          | sampling hardware (< MDL).            |
+-----------------------+---------------------------------------+---------------------------------------+
| Method Blank          | Analyte-free laboratory water taken   | Identifies background contamination   |
| (Reagent Blank)       | through all analytical steps, reagents| introduced by laboratory reagents,    |
|                       | acids, and digestion cycles in lab.   | glassware, or analytical extraction.  |
+-----------------------+---------------------------------------+---------------------------------------+
| Field Duplicate       | Second independent sample collected   | Measures combined field sampling      |
|                       | at the same tap/outfall immediately   | precision, repeatability, and site    |
|                       | following the primary sample.         | spatial/temporal variability.         |
+-----------------------+---------------------------------------+---------------------------------------+
| Laboratory Duplicate  | Single environmental sample split into| Measures pure laboratory analytical   |
|                       | two identical aliquots and analyzed   | precision and instrument measurement  |
|                       | independently in the laboratory.      | repeatability (Target: RPD ≤ 20%).    |
+-----------------------+---------------------------------------+---------------------------------------+
| Matrix Spike (MS) /   | Known concentration of target analyte | Evaluates matrix interferences,       |
| Matrix Spike Dup (MSD)| spiked into environmental sample.     | chemical suppression, and method      |
|                       |                                       | accuracy (% Recovery: 80% - 120%).    |
+-----------------------+---------------------------------------+---------------------------------------+

Relative Percent Difference (RPD) Formula

Analytical precision between duplicate samples is quantified using the Relative Percent Difference (RPD):

RPD=∣D1−D2∣(D1+D22)×100\text{RPD} = \frac{|D_1 - D_2|}{\left( \frac{D_1 + D_2}{2} \right)} \times 100

  • Where $D_1$ is the first sample concentration and $D_2$ is the duplicate sample concentration.
  • Standard Acceptance Criteria: For aqueous samples, the RPD must be $\le 20%$. An RPD exceeding 20% indicates sampling heterogeneity, balance error, poor mixing, or instrument instability.

Matrix Spike Percent Recovery Formula

Matrix interferences (high salinity, dissolved organics, suspended solids) can chemically bind the analyte or suppress detection. Accuracy is evaluated via Matrix Spike Percent Recovery (%R):

%R=SSR−SRSA×100\%R = \frac{\text{SSR} - \text{SR}}{\text{SA}} \times 100

  • Where $\text{SSR}$ = Spiked Sample Result, $\text{SR}$ = Unspiked Sample Result (native background), and $\text{SA}$ = Spike Added concentration.
  • Standard Acceptance Criteria: Recovery must typically fall within 80% to 120% (or 70% to 130% for challenging matrices).

MDL vs. PQL (Reporting Limit)

  0 ───┬───────────────────────────────┬───────────────────────────────► Concentration
       │                               │
       ▼                               ▼
     [ MDL ]                         [ PQL / RL ]
     - Method Detection Limit        - Practical Quantitation Limit
     - 99% confidence analyte > 0    - Reliable quantitative measurement
     - Qualitative, NOT quantitative - Typically 3x to 5x MDL
     - Values here are "Estimated"   - Enforceable regulatory compliance limit
  • Method Detection Limit (MDL): The minimum concentration of a substance that can be identified, measured, and reported with 99% statistical confidence that the analyte concentration is greater than zero ($MDL = t \times S$). It is determined by analyzing seven replicate spikes at 1 to 5 times the estimated detection level. Results between the MDL and PQL are flagged as "J-values" (estimated concentrations).
  • Practical Quantitation Limit (PQL) / Reporting Limit (RL): The lowest concentration that can be reliably achieved within specified limits of precision and accuracy during routine laboratory operating conditions. The PQL is typically 3 to 5 times higher than the MDL. Compliance with NJDEP discharge permits and drinking water Maximum Contaminant Levels (MCLs) is legally evaluated at or above the PQL.

6. Practical Operational Scenarios & Exam Traps

Practical Operational Scenario

A certified New Jersey wastewater plant operator conducts a morning audit of compliance samples collected by an automated 24-hour composite sampler for weekly NJPDES reporting. Upon opening the sampler cabinet, the operator notes that the internal thermometer reads 11.8°C because the ice pack melted during a heatwave. The composite container holds 8 liters of pooled final effluent intended for BOD5, TSS, and ammonia testing.

  • Diagnostic Investigation:
    1. The operator checks regulatory preservation limits: composite samples for BOD5, TSS, and ammonia must be maintained at $\le 6^\circ\text{C}$ on wet ice throughout the entire 24-hour collection period.
    2. At 11.8°C, bacterial biodegradation of soluble organic matter continued inside the unchilled jug for hours, artificially suppressing final BOD5 and hydrolyzing organic nitrogen to ammonia.
    3. If these samples are logged and sent to the certified contract laboratory, the lab must flag the temperature exceedance on the COC, rendering the results legally invalid and subjecting the utility to NJDEP violation notices for failure to monitor.
  • Immediate Remediation Protocol:
    1. The operator voids the composite sample and notes the equipment thermal failure in the facility logbook.
    2. The operator repairs the sampler refrigeration compressor, loads fresh ice, verifies that the internal cabinet holds $\le 4^\circ\text{C}$, and initiates an immediate replacement 24-hour composite collection to ensure compliant monthly data reporting.

Critical Exam Traps

  • Trap 1: Microbiological Sample Bottle Rinsing. Never rinse a bacteriological sample container before filling! Rinsing washes away the sodium thiosulfate tablet, leaving chlorine unneutralized and invalidating the test.
  • Trap 2: Holding Time for BOD5 vs. TSS. Operators frequently mix these up: BOD5 holding time is 48 hours, while TSS holding time is 7 days. Both require chilling to $\le 6^\circ\text{C}$ with zero chemical preservatives.
  • Trap 3: Acidifying BOD5 Samples. Adding acid ($H_2SO_4$) to a BOD5 sample to "preserve" it will instantly destroy the viable microbial population, resulting in zero oxygen depletion and total test failure. Acid is used for nutrients (ammonia, phosphorus), never BOD5.
  • Trap 4: Nitrite Preservation. Sulfuric acid must NOT be added to samples specifically targeted for separate Nitrite ($NO_2\text{-N}$) analysis; the acid accelerates the conversion of nitrite to nitrate, invalidating the test. Nitrite samples must remain unacidified and tested within 48 hours at $\le 6^\circ\text{C}$.
Test Your Knowledge

A New Jersey wastewater utility operator is preparing a sampling schedule for compliance monitoring under their New Jersey Pollutant Discharge Elimination System (NJPDES) permit. Which group of analytical parameters MUST be collected strictly as discrete grab samples rather than through an automated 24-hour composite sampler?

A
B
C
D
Test Your Knowledge

An environmental technician collects compliance monitoring samples from a potable distribution system and a wastewater treatment plant outfall. According to EPA Part 136 and NJDEP Office of Quality Assurance (OQA) regulations, which preservation protocol and maximum allowable holding time combination is legally compliant?

A
B
C
D
Test Your Knowledge

As part of internal laboratory quality assurance, an operator runs duplicate compliance tests for effluent Total Suspended Solids (TSS). Sample Duplicate 1 yields a result of 18.0 mg/L, and Sample Duplicate 2 yields a result of 22.0 mg/L. What is the Relative Percent Difference (RPD) between these duplicate measurements, and does it satisfy the typical standard laboratory quality control acceptance limit of 20%?

A
B
C
D
Up Next

13.2 Drinking Water Laboratory Testing

Continue learning