SSES

G&D has extensive experience performing sanitary sewer evaluation surveys (SSES), which include the following field inspections services:

1. Manhole and Visual Pipe Inspection
2. Smoke Test Inspection
3. Night-Time Flow Isolation
4. Flow and Rainfall Monitoring (as discussed elsewhere)
5. Cleaning and CCTV inspection
6. Dye Water Test Inspection

Manhole Inspections and Visual Pipe Inspections

G&D frequently performs comprehensive inventories and inspection of manholes for our clients, including internal and visual pipe inspection at manholes to assess the presence and degree of inflow and infiltration problems, the general physical conditions of the system, and any potential maintenance problems. Inspections record the following data:

1. Manhole physical information
2. Pipe Sizes
3. Direction of flow
4. Observations of sewer defects or potential problems

All subsurface manhole components from the frame seal, walls, and manhole bench and trough are inspected. Visual pipe inspection data will include depth and velocity measurements at each line segment, if possible, in addition to detecting line conditions from the manhole. The manhole rim to invert dimension for all connecting lines will be recorded. Digital photographs of unusual conditions will be taken along with inventory information compatible with the Client's GIS system. Video may also be captured in digital format, if requested. Preliminary field maps are corrected as discrepancies are found and delivered to the Client. Flow rates for major sources of I/I in each of the manholes inspected is also estimated.

Smoke Testing

Smoke testing is performed to locate sources of potentially excessive I/I. Smoke testing can identify sources of excessive I/I by simulated wet-weather conditions. Smoke is blown into the system using high pressure smoke blowers that force the smoke to escape through defects in the main line, laterals, and connections from typical sources such as catch basins, downspouts, yard drains, and area drains. Smoke testing is only performed during dry periods to maximize effectiveness of the testing.

Digital photographs are taken of all defects and linked to GIS throughout the project, if requested. Traditionally, smoke defects are illustrated in a hand drawn sketch or map by the field technician. G&D also often ties in smoke defects with geo-reference to aerial photos and sewer lines for ease of data management and defect locating in the field. Detailed information such as type of defect, severity and image of the defect can be easily attached to each location to help the repair crew locate the leak in the field.

Private Source Detection

Smoke testing will identify defects in the private service laterals. Field inspectors will also record "suspect sources" located on private property. Suspect sources are those that do not smoke, but due to the potential of being connected to the sanitary sewer (i.e., yard drains) should be followed up with dyed water testing.

Dye Water Test Inspection

Field technicians conduct dye water testing/flooding to identify direct or in-direct cross connections in the sanitary and storm conveying systems. Inflow sources can be identified and quantified by dye flooding storm sewer sections, stream sections, ditch sections, and ponding areas that may be contributing to inflow. Dye test areas are selected based on results of the smoke testing program. Positive dye tests are quantified for leakage rate. An analysis of the dye test data can also determine possible TV inspection follow-up requirements.

Night-Time Flow Isolation

Night flow isolations measure infiltration in the system. This technique is typically used in areas where flow monitoring indicates an excessive amount of infiltration entering the system. Flow isolations are performed in the early morning hours when the domestic sewage component is minimal. Its purpose is to measure I/I in clusters of line segments. Typically, 1,000 linear feet to 4,000 linear feet in length, a cluster is isolated by using plugs and the isolated flow rate is measured using in-line weir plates or with a flow depth and flow velocity measurement. The resulting measured flow rate is used to balance the infiltration defects observed during television inspection.

Cleaning and CCTV Inspection

Cleaning and CCTV Inspection may be required after completing manhole, flow isolation, and smoke test inspection phases. This field activity is conducted on line segments suspected as entry points for I/I based on collected field data results. Lines that indicate historical maintenance or structural problems are also candidates for TV inspection. If infiltration sources are excessive, based on flow monitoring and night flow isolations, it may be necessary to introduce dyed water into adjacent drainage structures and suspected inflow sources to recreate rainfall simulation conditions.

During CCTV inspection, field technicians, experienced in identifying sewer defects, will observe the television monitor while CCTV is in progress and record data during the inspection using NASSCO codes. Both I/I defects and maintenance defects are recorded. The data is then transferred for analysis and updated for estimates of inflow rates and defects noted from CCTV inspection. The information obtained through CCTV Inspection can be vital to establishing realistic rehabilitation costs. For example, a line segment exhibiting a high inflow rate as a result of 50 feet of collapsed pipe will have a higher rehabilitation cost than a direct stormwater connection with a similar inflow rate.