Collection System
 
Each city within the District owns and operates its own system of sewage collection lines. In general, city lines are smaller and serve individual subdivisions. The smaller city lines discharge into larger District-owned lines.

The District’s collection system consists of approximately 100 miles of sewer line with approximately 1,570 system manholes. The sizes of pipes range from 8 inches in diameter to 84 inches in diameter. The majority of the lines are constructed of reinforced concrete pipe. The oldest lines in the District’s system were constructed in the mid 1940’s. 


                        TV Van
Flow characteristics in the collection system vary throughout the day and differ from weekday to weekend. There are two peak flow periods during each day, one in the late morning and one in the evening. These peaks correspond with higher water usage during the early morning and evening. Although the higher discharges originate in the early morning, the higher flows are not received at the plant until the late morning and midday because of the time it takes to travel the distance from its point of origin to the treatment plant. It takes more than 10 hours for flow to reach the treatment plant from the most remote areas of the District.

District personnel perform an inspection of each manhole in the system every six months. Any signs of deterioration, odor, corrosion, obstruction of flow, and other abnormalities are reported so that action can be taken to maintain the system operating efficiently and with a minimal risk of problems.

The lines are routinely flushed and televised to  minimize the accumulation of sediment that can

 
                             Flusher Truck                       
contribute to odors and corrosion and to inspect for cracking, infiltration, deterioration, root intrusion, grease build-up, or other conditions that would indicate needed repair or maintenance. A video tape recording is made of the televised inspection for filing and future reference. Specialized equipment is used to perform the flushing, cleaning, and televising of the lines. Each year approximately 130,000 feet of pipe are flushed and televised. This rate of production allows the entire system to be flushed and inspected once every four years.

All lines, regardless of their size, are designed to create minimum flow velocities of 2 feet per second when flowing full. The flow velocity is important because it is what keeps solids from settling and accumulating in the pipe. Properly designed, constructed, and maintained lines generally have service lives of 50 years and longer.

Note to contractors

For your convenience the District is providing sample drawings of the following items;

   NDSD Notice to Contractors (pdf)
   Standard Service Connection (pdf)
   Standard Manhole Connection (pdf)
   Manhole Standards

© North Davis Sewer District 2006