FAQs Master List

A wastewater collection system is the network of pipes, manholes, pump stations, and related structures that convey sewage from homes, businesses, and industry to a treatment plant.​

A sanitary sewer carries only wastewater (sewage) and no stormwater. A storm sewer carries rain and snowmelt runoff, while a combined sewer conveys both sewage and stormwater in the same pipe.​

A CSO is a discharge of a mixture of stormwater and untreated wastewater that occurs when the capacity of a combined sewer system is exceeded during wet weather.​

An SSO is a discharge of raw or partially treated sewage from a separate sanitary sewer system before it reaches the treatment plant, often due to blockages, equipment failure, or overloading.

Stormwater runoff is rain or snowmelt that flows over land surfaces, streets, and roofs instead of soaking into the ground, often entering storm drains and sewers.​

Level is the depth or height of water above a reference point (such as the invert of the pipe or the channel bottom), often used with a known relationship to calculate flow.

Flow monitoring data are time-series records of depth, velocity, flow rate, and sometimes rainfall, collected to analyze system performance, I&I, and capacity.

A scattergraph is a plot of measured depth versus velocity from a flow monitor that helps evaluate data quality, sensor performance, and hydraulic behavior such as surcharge or backwater.

Real-time monitoring is the continuous collection and transmission of sensor data with minimal delay, enabling near-instant visibility into sewer conditions and faster response.

Real-time control uses live data and automated controls (such as gates, pumps, or valves) to actively manage flows and storage in the sewer system to reduce overflows and optimize capacity.​

In wastewater monitoring, DaaS refers to turnkey programs where a provider supplies equipment, installs and maintains it, collects and validates data, and delivers results and reports to the utility.​

• The d/D ratio is the ratio of flow depth (d) in the pipe to the internal pipe diameter (D) for gravity sewers.​
• It is a standard hydraulic performance indicator used to assess remaining capacity and identify potentially undersized or overloaded pipes.​

• Many design standards limit dry-weather d/D to about 0.5 for small sewers (≤ 15 in) and 0.75 for larger sewers to ensure reserve capacity and ventilation.
• Peak or wet-weather design is often limited to d/D between about 0.7 and 0.83; for example some agencies require d/D ≤ 0.7–0.83 at peak flow to avoid chronic surcharge.

• In circular pipes, velocity at partial flow can exceed the full-flow velocity, with maximum velocity typically occurring around d/D ≈ 0.8.
• Discharge is not maximized at exactly full flow; for circular sections, maximum discharge usually occurs at about d/D ≈ 0.95.

• High d/D values indicate low residual capacity; agencies flag pipes with high d/D and low reserve capacity for further evaluation or upgrades.
• Sustained high d/D (near or above 1.0) implies surcharging, raising risks of basement backups, manhole overflows, and structural or infiltration/inflow problems.

• Brief, infrequent wet-weather events may be allowed to approach d/D ≈ 1.0, but many guidelines still recommend that even wet-weather d/D not routinely exceed 1.0.
• Existing systems with high d/D are commonly monitored, modeled, and prioritized for capacity relief projects rather than immediately replaced, especially in trunk sewers.

Flow rate is the volume of water or wastewater passing a reference point in a specific period of time, typically expressed in liters per second, gallons per minute, or cubic feet per second.​

Open-channel flow is water movement in a conduit that is not completely full and has a free surface exposed to the atmosphere, such as most gravity sewers and ditches.​

Closed-channel flow occurs when a pipe runs full under pressure, such as in a force main or pressurized water line, where flow is usually measured with in-line meters.​

A diurnal pattern is the repeatable daily variation in sewer flow caused by human activity, such as morning and evening peaks and lower nighttime flows.​

It varies. Ideally, this task should be performed during the initial planning stages of an I/I study. From a practical standpoint, whoever has control of the GIS data should be the one to perform this important task. The municipality often has the best access to the GIS data and is best positioned to correct any GIS errors identified in the process. However, from a contractual standpoint, this task is sometimes assigned to a consulting engineer or to a flow service provider.

An I/I study needs sufficient data to characterize both dry weather and wet weather performance at each flow monitor location, and in the United States and Canada, it is often the number of storm events that drive the length of the study period. Statistically, the more storm events the better, and practically, we look for 6 to 12 storm events where a meaningful wet weather response is observed in the sewers. For this reason, a minimum 90-day study period is often needed.

Gravity sewers typically need to have flow depths less than full pipe for sensors to be properly installed, maintained, or removed. However, once installed they can measure flow depth and velocity in both non-surcharged and surcharged conditions.

Once suitable locations are identified and flow monitors have been properly installed, routine data review is used to make sure that flow monitors are working correctly. At ADS, we use both automated reviews and human reviews for this purpose. The urban sewer environment is quite dynamic and can be quite hostile at times. As such, we remain on alert for changing hydraulic conditions and/or problems with monitoring equipment that may arise. Problems that are found quickly can often be resolved quickly, and that is our goal. Periodic field confirmations are also a routine practice and ensure that the measurements made by the monitors are reasonable.

Years ago, there was a significant difference, as permanent flow monitors were connected to a telephone line and temporary monitors required a manual cable connection to retrieve data. With mobile communication technology available today, there is much less of a distinction between a permanent and temporary flow monitor. Whether permanent or temporary, you want to find a location with suitable hydraulic conditions that is easy to access, easy to maintain, and has minimal safety concerns.

The nature of the hydraulic conditions at a given location are the primary driver of the technology selected with the purpose of the data being a secondary concern. With that said, what kind of hydraulic conditions are often of most concern during infiltration and inflow studies Wet weather events where surcharge conditions occur are often of most concern, and this will require measuring flows during transitions into and out of surcharge conditions. For these scenarios, we recommend a suite of flow depth and velocity sensors, where the sensors are installed inside a pipe as opposed to flow depth and velocity sensors installed in the manhole over the manhole channel.

This rule-of-thumb works as follows: If you have a monitor basin with typical residential and commercial development you can expect to see dry weather flows on the order of 5 gallons per day per linear foot of sewer. If you notice flow rates that are dramatically different, you should look for an explanation. Are the flow monitor data correct Is the basin size information correct Is the basin boundary properly delineated This rule-of-thumb serves as a useful gut check .

Empirical data suggests that the ideal basin size is around 10,000 LF of sewer, with a goal of maximizing granularity to minimize follow-on condition assessments such as manhole inspection, smoke testing, and closed-circuit television (CCTV) inspection. Smaller basins sizes are generally better than larger basin sizes, but it is important to remember that whatever the basin size, it is preferable to keep basin size as consistent as possible across the study area for better apples-to-apples comparisons.

Yes. ADS flow monitoring services, including data approval in PRISM, are governed by written procedures that are part of our quality assurance and quality control program which is certified under ISO 9001: 2015 standards.

Product design takes this into account, and materials that are used should be compatible with these environments.

Nighttime flow isolations can be effective in the extreme upper reaches of the sewer system. However, the most useful nighttime flow isolations are the ones where no flow is observed, as you can automatically rule out these stretches of sewer from further evaluation and not have to worry about the accuracy of the weir measurement. As you go a little further downstream, micro-monitoring then becomes an option, but results from micro-monitoring are perhaps best used in a qualitative rather than a quantitative manner.

If a consistent level of bias is detected in the data, it can be adjusted accordingly during data review and approval. We also can correct individual outliers and estimate their correct values from surrounding data and observed hydraulic patterns. Outliers can adversely affect engineering metrics and calculations, and they are reviewed and corrected whenever possible. We often refer to these processes as Data Review, Data Editing, and Data Approval.

Assuming that locations with suitable hydraulic conditions are used and that the flow monitors have been properly installed, diligence is required to assure data quality over the full monitoring period. Routine data review is one key aspect. You must keep track of the ƒ pulseƒ  of the data. At ADS, we use both automated reviews and human reviews for this purpose. The urban sewer environment is quite dynamic and can be quite hostile at times. As such, we remain on alert for changing hydraulic conditions and/or problems with monitoring equipment that may arise. Problems that are found quickly can often be resolved quickly, and that is our goal. Periodic field confirmations are also a routine practice and ensure that the measurements made by the monitors are reasonable.

The number of discrete rainfall events that you extract from a continuous time series of rainfall data is inversely proportional to the specified minimum inter-event time. If you use a smaller value for the minimum inter-event time, you will have a larger number of smaller rainfall events. If you use a larger value, you will have a smaller number of larger rainfall events. In terms of an I/I study, you seek to match rainfall with a flow response in the sewer. Therefore, think of the minimum inter-event time as a default value, not as an ideal value. As you review the I/I responses, you will find cases where the default values work out just fine, and you will find other cases where individual adjustments need to be made. Combining two adjacent rainfall events into one larger event is a common example. Use a reasonable default setting to do most of the work for you, then apply your engineering judgement to adjust other Rainfall Events as needed.

Yes. ADS offers SLiiCERƒ › ƒ a web-based infiltration and inflow analysis application. We have a version that has been available for many years and have recently released a new Cloud-based version that integrates with PRISM.

The ADS ECHO can help you judge the timing of I/I by observing the quickness of the flow response and the rate at which the system recovers. ECHOs can also be used to indicate if the system becomes surcharged. However, if the sewer moves into backwater or is restricted in any way the resulting depth increase will be incorrectly interpreted as an I/I response. Also, converting flow depth data to flow rate data using the Manning Equation in the invert channel in a manhole is not reliable above 1/3 or 1/2 pipe depth (spillover to manhole bench). Because of these two issues the data from level monitors are not generally reliable for quantifying RDII or used as devices to subtract upstream flow from downstream flow.

When determining sewer basin and sub-basin areas for an I/I analysis, do you typically use the entire acreage of the sub-basin, or do you subtract out undeveloped areas, native growth areas, critical areas, etc. for a better comparison of I/I rates between sub-basins.

The primary, independent recommendation for rain gauge density in the United States is from the American Society of Civil Engineers (ASCE) and the Water Environment Federation (WEF). They recommend a rain gauge density of one rain gauge for every 5 to 10 square miles. There are some finer points to consider with rain gauge density when it comes to topography and perhaps the design storm of interest, but Step 1 is having a rain gauge network with a density that meets ASCE and WEF guidelines.

Most I/I studies look to quantify rainfall entering a sewer system as I/I. As a result, frozen precipitation events that occur during an I/I study are often ignored. Keep in mind that the most intrusive effects of I/I on a sewer system result from rainfall, not snowfall. Some municipalities in colder climates have an interest in this, but the analysis is not straight-forward and can be problematic.

A double mass analysis is one method to compare cumulative rainfall from various rain gauges where consistency between rain gauges is deemed an indicator of proper operation. Keep in mind that a double-mass analysis is generally intended for use evaluating data over long time periods, not individual rainfall events. For example, you could look at cumulative rainfall over a rolling 12-month period. Based on past literature reviews, rain gauges are considered to pass the double-mass analysis if they are within ñ20% of reference or within ñ20% of each other.

The answer depends on the type of sewer. For storm sewers, specified rainfall return frequencies are used to provide various levels of service and are often specified in local storm sewer design requirements. For combined sewers, specified rainfall return frequencies are often used as well and are derived from combined sewer overflow (CSO) discharge permit requirements. For sanitary sewers, there are no specified requirements. This topic has been discussed on-and-off for years within the industry and between municipalities and regulators, but no consensus has emerged. However, it makes sense to establish a level of service for sanitary sewer systems and use that as a basis to benchmark performance over time and plan system improvements with the desired level of service in mind.

Think of the minimum Rainfall Threshold as a default value to automatically identify rainfall events, not as an ideal value. As a rule-of-thumb, we often do not evaluate a rainfall event for I/I if the rainfall total is less than 0.5 inches. However, there is not a particular rainfall total that is universally accepted as a significant wet weather event in the context of I/I. Rather, it is the response of the sewer system to a given rainfall amount that determines if a rainfall event is significant or not. This amount can vary from one sewer system to another and can even vary within different parts of the same sewer system.

The National Oceanic and Atmospheric Administration (NOAA) and USGS both maintain networks of rain gauges across the United States, and data from them are available for public use. Our recommendation is that you can use them to supplement your own rainfall monitor network when they are available but do your homework and use some caution. Also, never rely on them as your sole source of rainfall data. Before you consider using one, first Investigate data availability. We have seen some of these rain gauges where data is intermittent and not always available for the time periods needed. Second, investigate the sample rate reported by the rain gauge. Some locations only report daily totals or hourly totals. A sample rate of 5-minutes is preferred for most I/I studies and related hydraulic modeling applications.

We call this situation a flow imbalance, and this is indeed a problem. This first thing to do is evaluate the data from each flow monitor. Were both monitors installed where you think they are installed Are both flow monitors configured with the correct pipe shape and pipe height Is the silt value correct These are some of the obvious things to check. You also need to evaluate the site hydraulic conditions. Are hydraulic conditions optimal at one location and not the other If so, be more suspicious about the location with less-than-ideal conditions. If you find that the monitor data appears in good shape, recheck the mapping and verify that the correct flow schematic is used. If that checks out, you may have to do some field work to further validate the actual connectivity and determine if the maps are accurate or not. Sometimes, a simple error is found, and the problem is easily resolved. Other times, the answer is not as obvious and may require cooperation from the utility, the consulting engineer, and the flow service provider to resolve.

Yes. ADS flow monitoring services, including data approval in PRISM, are governed by written procedures that are part of our quality assurance and quality control program which is certified under ISO 9001: 2015 standards.

A flow monitor is an instrument installed in a pipe or channel to measure flow rate and related parameters like depth and velocity over time.​

A level monitor is a device that continuously measures water depth in a sewer, manhole, or tank, often used to provide early warning of blockages and overflows.

An ultrasonic level sensor emits sound pulses toward the water surface and measures the time it takes for the echo to return, converting this distance into water level.​

A submerged pressure transducer is a sensor placed under water that converts the pressure exerted by the water column into a level reading.

A magnetic flow meter uses a magnetic field and electrodes to measure the voltage induced as conductive fluid flows through the meter, which is proportional to velocity and used to compute flow.​

A weir or flume is a hydraulic structure installed in open-channel flow that creates a known relationship between water level and flow rate, allowing indirect flow measurement.

An ultrasonic level sensor measures only distance to the liquid surface, converting that to depth, while an ultrasonic flow sensor uses ultrasound to derive flow velocity (often with transit‑time or Doppler methods) and then computes volumetric flow. In open channels, a level sensor is often paired with a separate velocity or area‑velocity sensor, whereas ultrasonic flow meters for full pipes directly calculate flow from velocity and known pipe area.​

An area‑velocity sensor measures both water depth and velocity at a point in an open channel or sewer, and multiplies the cross‑sectional area (from depth and geometry) by the velocity to calculate flow. These sensors typically use ultrasonic or electromagnetic methods for velocity and ultrasonic or pressure methods for depth, making them popular for portable sewer flow studies and permanent open‑channel sites.​

A radar level sensor emits microwave (radio) pulses toward the liquid surface and measures the time of the reflected signal to determine distance and level. In harsh wastewater sites with heavy foam, vapors, or temperature swings, radar is often chosen instead of ultrasonic because it is less affected by these conditions.​

Hydrostatic (submersible pressure) sensors are used where non contact sensors struggle, such as deep wet wells, narrow chambers, or locations with strong turbulence, steam, or obstructions. They sit in the liquid and convert water pressure into level, providing robust measurement but they need to be protected from debris and regularly inspected.

Mag meters generate a magnetic field and measure the voltage induced as conductive fluid flows through, while ultrasonic meters use sound waves and either transit‑time or Doppler principles. Mag meters are widely used on full, pressurized pipes with conductive liquids (e.g., force mains), whereas ultrasonic meters can be clamp‑on, inline, or open‑channel and are often chosen where non‑intrusive or retrofittable installations are needed.​

Yes, some modern open channel sensors combine non contact radar for velocity with ultrasonic or other methods for level, providing area velocity measurements without contacting the wastewater. These systems are designed for challenging locations with high solids, shallow flows, or corrosive conditions where traditional in pipe AV sensors are hard to maintain.

Hydraulic capacity is the maximum flow that a sewer, manhole, or facility can convey without causing unacceptable surcharging, flooding, or structural stress.

A bottleneck is a location where limited pipe size, slope, or condition restricts flow, causing upstream levels or surcharging to increase during higher flows.​

Surcharge occurs when the water level in a gravity sewer rises above the pipe crown, meaning the pipe is running full and pressurized, often during wet weather or downstream restrictions.

A hotspot is a location prone to problems such as blockages, high I&I, or frequent overflows, which often receives targeted monitoring or maintenance.​

Asset criticality reflects how important an asset is to system performance, safety, and compliance, often driving which locations receive more monitoring, inspection, and rehabilitation.​

The URL is: https://www.adsprism.com .

Yes. Go to http://www.adsenv.com/video-library.

You will get the best user experience viewing PRISM with Google Chrome or Firefox .

Yes. If you have the appropriate user permission, click on USERS under the ADMIN tab. Then choose the Add New User icon in the lower left.

Yes, in the PRISM login area, enter your User Name and click on Forgot Password. You will be prompted to enter your User Name or an Email address. Click the I'm not a robot and answer the question; then click RESET.

Yes. You can set a customer as your Favorite so that each time you log in to PRISM that customer will be the one to display. To do this, choose your user name from the upper right corner of the PRISM window and then User Preferences . Select the customer you wish to be your Favorite . Click the star to save this as your favorite customer; a gold star indicates the favorite customer; a hollow star indicates that the customer is not the favorite.

Yes. Select the Action in the bottom left-hand corner of the Map ( Home page). Select the Add Location icon.

Yes. Select the Action in the bottom left-hand corner of the Map ( Home page). Select the Add Composite Location icon.

The Data Communication tile displays the number of locations that had no data collection (by polling or data delivery) within the last 24 hours.

Once KML layers are uploaded to a project, a new Layers icon is available on the right side of the Map under the Legend icon.

Yes. Click on the graph link on the Alarms Widget , the alarm thresholds now display.

Yes, click on the Alarms Tile to open the Alarm Widget. Click on the Filter and select the type of Alarm, Date and Location of interest. The historical alarm information will display in the widget.

Yes. The KML feature must be turned on for the given project. KML files (3MB or less) can be uploaded to the project. Contact the ADS Customer Support Center for assistance.

If you have the appropriate user permissions, select the Customer Editor icon to the right of the Customer drop-down list. Then choose the Add New Customer icon in the lower right.

Yes. Units of measure selection are available through the Customer Editor located to the right of the Customer drop-down list. Select the appropriate customer and Edit. The Units drop-down list on the Edit Customer window includes three choices: US Standard MGD (reports depth in inches, velocity in feet per second and flow rate in MGD; US Standard CFS (reports depth in inches, velocity in feet per second and flow rate in CFS) and Metric (reports depth in millimeters, velocity in meters per second and flow rate in liters per second).

Yes. Time can be displayed in either a 12-hour or 24-hour format. Choose Customer Editor icon located to the right of the Customer drop-down list. Select the appropriate customer and Edit. Choose the desired time format from the Time Format drop-down.

Yes, there is a Date Format setting and the project can be set to that Year/Month/Date preference.

Yes. In the upper right corner of the Locations Dashboard, open the Setting panel (three vertical dots) and set the Scattergraph Annotations on for Invert Scatter Axis

Yes. You can create graphs with multiple locations in the Custom Dashboard.

The ability to save templates is recognized as needed and will be available in PRISM in the near future.

No. At this time a user cannot change the entity colors.

No, not at this time. Each location graph must be printed individually.

Yes. In the upper right corner of the Locations Dashboard, open the Settings panel (three vertical dots) and set the Scattergraph Annotations on for Iso-Q lines and Pipe Overlay.

Yes. In the upper right corner of the Locations Dashboard, open the Settings panel (three vertical dots) and set the Hydrograph Annotations on for Rain on Top.

Yes. There are selection buttons for 1 day, 1 week, 1 month at the top of each graph OR you can manually drag the slider below the hydrograph.

Yes. That way the new location will not populate its data into the old location.

Yes. Choose the on-demand Collect button from the Location Properties card on the HOME screen; enter the Start and End Dates for your collect period.

Yes. PRISM supports the activation of ADS ECHOƒ › and RainAlert III monitors. Open the Location Properties screen for the monitor you wish to activate and select the Activate icon.

You can access graphical data from the Home page through the Location Properties page. Select a location through the mapƒ s Search Location option or by choosing the map icon. Once the Location Properties page displays, select the graph symbol located at the bottom of the page to open the Location Dashboard .

When the Is Active option is set to Yes , the associated location is considered active in PRISM. Active locations can be included in scheduled data collects. If Is Active is set to No , the location is removed from any scheduled collect and will only display in the interface if you choose the Display All Locations icon (located in the upper right corner of PRISM, to the left of your user name).

Import a csv data file from ADS Profile or Q start XML to fill in the data gap or back-collect the data through the Location Properties Card .

If you activate an ADS TRITON+ , ECHO or RainAlert III monitor using ADS Q start 1.9 or higher, an .xml file is generated in the location folder. Use this file to import into PRISM.

The Uptime Report values are based on the data availability from the previous calendar day for UNIDEPTH, VELOCITY and Qcontinuity.

Click on the location name on the Data Summary Report . A new screen will open showing minimums, maximums, averages and flow total for the past seven days. You can use the filter icon next to DOWNLOAD to define a new time period to view or change the data entities displayed in the report.

The Daily Summary Report reports the previous daysƒ Maximum, Minimum and Average depth and velocity data and the previous daysƒ Maximum, Minimum, Average flow rate and the Total Flow volume.

Yes. There is a SAVE SETTINGS feature. Give your Settings information a name. When you want to use it again, simply select Load Settings the next time you EXPORT.

Yes. There are now 2 File Types to choose in the Export Location feature.

Yes. Multiple rain gauges can be exported to a single Excel data file. Choose EXCEL as the File Type and Single File.

There are three categories of files you can upload to PRISM: Files , Location and Data . Select Files to import a document, for example site reports, location pictures, Microsoft Word or Excel documents. Select Location to import a location xml file from Q start XML . Select Data to import a csv data file in the ADS file format.

Yes. The file must be less than 20 MB in size.

No. There is no limit to the number of files a user can store at this time.

All PRISM exported data files are placed in a folder named dataExports in the Vault .

No. PRISM supports the import of .xml location files only.

To import a new or updated location xml file, you must first upload the file using the Vault > UPLOAD > Location feature. Second locate the imported file and select Import to add the file to the PRISM database.