Assessing Samples, Sampling Sites and Sampling Protocols
Some of the common items that should be evaluated at the sample site(s) include:
- Cleanliness and suitability of the sample tap and sink,
- Potential for hot water to enter the sample through the tap, and
- Conditions that may have changed at the sample site since the last sample collection, such as new uses for the sink as janitorial cleanup area, dirt accumulation near the faucet or installation of a point-of-use device on the faucet.
- In addition to sample tap contamination, it is possible that elements of the sampling protocol that were not followed closely could result in contamination of the sample. Elements of the sampling protocol that systems should follow may include:
- Removal of the tap aerator,
- Adequate flushing of the tap prior to sample collection,
- Proper storage and preparation of the sampling container,
- Correct sample collection technique, including elimination of splashing water from sink and the sampler touching the inside of the sample bottle,
- Correct storage, preservation and handling of sample(s) during transport to laboratory, including items such as cleanliness of coolers and use of watertight bottles during transport (to prevent leakage), and
- Compliance with holding time and temperature requirements, including items such as maintenance of ice packs.
Assessing the Distribution System Area Near the Positive Samples
A Level 1 assessment of the distribution system should include the collection and review of available data. The data to be reviewed includes operational data and information on the physical condition of distribution system components. The area of the distribution system that should be evaluated depends on the system configuration along with the extent of coliform positive samples.
The operational data elements should be reviewed by all systems, regardless of size or type. The available data and accessibility of electronic data may vary by system size and type.
Larger systems may have electronic databases from which to extract pertinent information including:
- Distribution system and treatment plant process data from SCADA systems for pumping, storage and pressure data,
- Water quality measurements from laboratory information management systems (LIMS) or external laboratory reporting systems,
- Customer complaint and water usage data from customer service information systems (CSIS),
- Data on operations and repairs in the distribution system from maintenance management information systems (MMIS),
- Recent and historical information from main break databases,
- Pipe material and condition information from asset management databases,
- Hydrant testing and fire-fighting from fire department information, and
- Activities performed from operations logs.
For smaller systems, much of the data sources listed above may not be electronic and would thus involve additional effort by the system to compile the data as part of the assessment.
Water Quality Data
As part of any assessment, the assessor should compile and evaluate water quality data. This data would include parameters collected in the distribution system and at the source or treatment plant. The parameters to be evaluated will likely vary by system type, treatment process used and other operational practices but may include the items outlined below:
|Water Quality Parameter||Location of Sample Collection|
|Disinfectant residual concentration||Throughout the distribution system, including total coliform sampling sites as specified in the sample siting plan|
|At storage tanks throughout the distribution system|
|At the entrance to the distribution system at each source|
|Disinfection by-products (DBPs)||At approved monitoring locations in the distribution system|
|Total coliforms and E. coli||All distribution system sampling sites, including those for repeat, additional routine and special purpose samples (like those associated with recent main installation or repair)|
|Entrance to the distribution system at each source|
|Heterotrophic plate count (HTP)||All distribution system sampling sites for total coliforms|
|Nitrite and nitrate (systems using chloramine)||Distribution system sites with low disinfectant residual|
Operational Activities and Unusual Events
Along with water quality measurements, it is important to understand the extent of activities occurring in the water system that may have resulted in total coliform-positive samples. Compilation of operational activity data may require consultation with different departments within the water system and with external agencies. The types of activities and events to be noted would include those that might result in distribution system contamination, including:
- Pipe breaks and associated repairs,
- Events resulting in a loss of pressure (e.g., power failures),
- Flushing and hydrant testing,
- Construction activity that impacts water pipes,
- Unusually high (or low) demands that might alter typical flow patterns, including temporary connections for construction and firefighting,
- Break-ins and vandalism at system facilities,
- Treatment process upsets,
- Weather events, and
- Source water changes.
Once a list of distribution system activities and events has been compiled, this list can be compared to historical records to determine if any activities or events could have led to the distribution system contamination. Any suspect operational activities or events should be further investigated and documented on the assessment form.
Assessing Distribution System Components
The objective of the Level 1 Assessment is to help determine if a particular distribution system component has a sanitary defect that would require correction or if distribution system events could have contributed to the positive coliform samples.
The assessor should focus first on the area of the distribution system closest to the positive coliform samples. Operator knowledge or the results of a flow path analysis or hydraulic model can be used to determine the area(s) likely to be associated with a given sample site. For example, if the positive sample is located within a defined pressure zone, the entry point to the zone and related facilities should be assessed before moving the assessment to other more remote zones. Once the immediate area has been examined, the assessor can continue to evaluate the areas of the distribution system farther from the positive coliform samples.
The assessor should evaluate distribution system facilities to determine whether infrastructure and equipment are operational and in good repair. The evaluation should include elements such as:
|Component||Typical Items to Evaluate|
|Pump stations||Proper operation of pumps and valves|
|Recent losses of power|
|Recent losses of pressure|
|Proper operation of surge control appurtenances|
|Distribution system pressure||Maintenance of adequate pressure|
|Air-relief / Air-vacuum valves||Proper operation of valves|
|Valve vault free of standing water and debris|
|Fire hydrants||Proper operation of shut-off valves|
|Leaks at connection to lateral piping|
|Flushing assemblies/Blow-offs||Proper operation of valves|
|Leaks at connection to piping|
|Pipes||Recent main breaks|
|Recent installation of new mains or construction activity|
|Distribution system isolation valves||Recent operation resulting in breakage|
Assessing Storage Facilities
Storage facilities, or tanks, have been linked to microbial contamination events and therefore are an important component to assess when responding to positive coliform samples (Clark et al. 1996). Microbial contamination can enter storage facilities either through system water or external tank breaches. If contamination is introduced through system water (i.e., transported to the storage facility or tank from a different contamination site), microbes can remain viable and possibly multiply within the tank water and sediments.
Review of the most recent tank inspection reports, review of operation and maintenance records and operator interviews should provide valuable information for the assessment. If a thorough inspection of the storage facility or tank has not been completed in the recommended timeframe for that facility (usually every three to five years), the system should consider whether a professional cleaning and inspection is appropriate as part of the Level 1 assessment. For systems that use hydropneumatic tanks and/or bladder tanks, these tanks should be maintained and inspected according to manufacturer recommendations. A Level 1 assessment should include review and inspection of maintenance records for these types of tanks.
If warranted, the assessor could also examine historical disinfectant residual data for the tank and its vicinity and collect additional samples for disinfectant residual and/or total coliforms. Depending on the record review and results of additional monitoring, an on-site inspection may be appropriate. The assessment should initially be focused on the storage facilities that supply the area near the total coliform-positive sample, with evaluation of other more remote facilities as a next step.
|Storage Tank||Typical Items to Evaluate|
|Access hatches||Signs of vandalism or forced entry|
|Ability of hatch to seal tightly when closed|
|Rust, holes or other breaches|
|Vents||Signs of vandalism or forced entry|
|Absence of screen; holes or other breaches in screens|
|Rust, holes or other breaches in vent piping and penetration through tank wall|
|Overflow piping||Rust, holes or other breaches in piping and penetration through tank wall|
|Absence of screens; holes or other breaches in screens|
|Control valves||Correct operation of level control valves. altitude valves and related appurtenances|
|Tank exterior||Signs of deterioration, rust or other breaches|
|Tank interior||Integrity of lining material|
|Presence and extent of floating material and sediment within tank; existence of microbes within sediment|
|Presence of dead animals|
|Disinfectant residual||Level of disinfectant in tank, ideally at different tank levels|
Assessing the Treatment Facilities
For a PWS operating a treatment plant, even if the only treatment is a chlorinator at a well, assessment of the proper operation of the treatment process is important to determine if a plant upset could be the source of the microbial contamination resulting in positive coliform samples.
As part of a Level 1 assessment, the assessor should review the treatment process data and records. When reviewing the treatment data and records, particular attention should be paid to disinfection processes and turbidity removal, as these processes are responsible for the majority of microbial inactivation. For disinfection processes, data records regarding the disinfectant feed systems and resulting disinfectant concentration should be evaluated to ensure that proper dosing has taken place and desired residuals are maintained. For turbidity removal, data and records regarding coagulation/sedimentation and filtration processes should be evaluated to ensure that microbial contaminants could not have entered the distribution system along with a spike in turbidity. Power outages and other events that disrupt normal operations should also be considered. Depending on the results of the data and records reviews, additional monitoring or site visits may be appropriate.
Types of data elements that could be reviewed as part of a Level 1 assessment include:
|Treatment Facility Element||Typical Items to Evaluate|
|Equipment (pumps, mixing units, settling units, pipes, valves, chemical feed units, filters)||Status of equipment -operational and maintained in accordance with the treatment plant Operation and Maintenance procedures|
|Recent installations or repairs|
|Treatment Process||Introduction of new sources or changes in the source water|
|Recent changes in the treatment process|
|Interruptions in treatment – lapses in chemical feed or proper mixing|
|Turbidity measurements at all appropriate locations in the treatment process (source, settled water, pre- and post-filtration, finished water, etc.)|
|Disinfectant residual measurements and C x T (concentration x time) calculation|
|Flow rates at each plant process|
Assessing the Source Water
The source water can include wells, springs and surface water. Changes in source water, extreme weather events and introduction of new sources can all be possible causes of microbial contamination. The source water should be evaluated using historical data and system records to determine if the source water has contributed to the coliform positive samples. Additional monitoring and site visits may be appropriate based on the results of the evaluation of the data and records.
For systems served by a well (or wells), the integrity of the well and proper operation of the well system should be verified to ensure that contamination could not have entered the distribution system from the well. The assessor should pay particular attention to potential pathways that would allow the entrance of surface water, soil, animals or other foreign matter into the well. Well inspection records and operation and maintenance records should be reviewed and weather events should be considered if runoff could have affected the well. The well should be constructed to prevent the accumulation of surface water around the well head and prevent inundation during periods of flooding or increased runoff. Some typical items that should be evaluated for wells include:
|Well Element||Typical Items to Evaluate|
|Well house I enclosure||Signs of vandalism or forced entry|
|Unsanitary conditions like the presence of rodents or other animals|
|Well cap I Well seal||Tightness of well cap and seals. presence of gaps or openings|
|Well vent||Vent properly screened, angled to be self-draining and has sufficient|
|Well casing||Holes, breaks, corrosion or deformation in casing and welds|
|Annular grout seal||Missing, sunken, bridged or channeled grout surrounding the well|
|Pump and pump assembly||Attached to casing with no unprotected openings and has watertight|
|Pitless adapter||Integrity of pitless adapter connection|
|Inundation||Signs of inundation by floodwater or runoff; depressions around wellhead|
For systems served by a spring (or springs), the assessment should verify the sanitary condition and proper operation of the spring and associated piping. Typical items the assessor should evaluate for a spring source include:
- Condition of the spring development,
- Impacts from surface water runoff and weather conditions,
- The physical condition of the spring box,
- Impacts from vandalism or forced entry to determine if holes or other breaches could have occurred that would allow for the introduction of microbial contaminants,
- Signs of inundation, including deposits of soil or soil erosion, and
- Signs of small animals, slugs, bugs, etc., in the spring box.
Surface water sources can be impacted by extreme weather events that can influence the influent water quality to the treatment plant. Atypical events may impede the ability of the treatment process to perform as desired and may allow for the introduction of microbial contaminants into the distribution system. Heavy rainfall and rapid snowmelt can carry large soil loads into surface water sources, thereby increasing turbidity and baseline microbial contaminant concentrations. Similarly, flooding can alter the raw water quality and require treatment changes to achieve good finished water quality. For systems that have multiple surface water sources, a change from one source to another could trigger a treatment upset that might result in microbial contamination entering the distribution system. In performing the Level 1 assessment, the assessor should obtain and review the source water data to determine if atypical surface water quality could have impacted the treatment process.
Large systems may want to determine whether the contamination is widespread or localized in the distribution system. If the total coliform-positive samples that triggered the assessment are clustered in one part of the system, the assessor may want to target the assessment to specific sections of the distribution system or facilities. It may not be practical or necessary to conduct an assessment of the entire distribution system. Looking at historical data may also help determine if the problem is episodic or chronic. Knowing so would help determine the type of corrective action the system has to take to address the problem.
Systems with Limited Or No Distribution System
For small systems, it might be the case that they do not have any treatment process or an extensive distribution system. In this case, the Level 1 assessment will only focus on those elements that are present in the system such as the source water (e.g., wells) and the limited distribution system. For non-community water systems (NCWSs) that have their own source water and do not supply water beyond their premises (typical examples are schools and churches), then an assessment of the pipes inside the building (what is typically considered premise plumbing) is required. Typically in a community water system (CWS), premise plumbing is beyond the control of the PWS. However, in the case of NCWSs, the premise plumbing may be part of the system and if so, must also be included as part of the assessment. One thing the assessor might look for is the presence of cross connections. The majority of backflow events resulting from unprotected cross connections occur in premise plumbing (USEPA 2001b).
Wholesale and Consecutive Systems
For PWSs that purchase water from another system, also known as consecutive systems, the source water can be considered to be the connection(s) from the wholesale (seller) system. During a Level 1 assessment, a review of the records related to the connection (e.g., flows, pressures, water quality parameters if measured) should be performed.
It is also recommended that the consecutive PWS contact the wholesale system to coordinate assessment efforts. The possibility exists that a contamination event occurred in the wholesale system upstream of the connection and that the contamination has migrated to the consecutive system.