Manhole Distance / Actual vs On Map
A new manhole has been installed 500 ft from an existing manhole. On a map the scale is 1 inch equals 50 ft., what is the distance between the manholes on the map?
Given the scale 1 inch equals 50 ft, divide the actual distance by the representative distance from the scale.
Distance (inches) = (500ft) / (50 ft) = 10 inches
The distance between two manholes on a map is ¾ of an inch. The scale for the map is 1 inch equals 200 ft. What is the actual distance between the manholes?
Distance (ft) = (3) / (4) = 0.75
0.75 x 200 ft = 150 ft
Population Equivalent Estimates
Population equivalents that are used to calculate hydraulic and organic loadings for domestic wastewater treatment if actual operating information is not available are as follows:
BOD5 = 0.17 lbs./capita/day (NOTE: CAPITA IS THE SAME AS PERSON)
TSS = 0.20 lbs./capita/day
Phosphorus = 0.0048 lbs/capita/day
Flow = 100 gallons/capita/day
Estimate the population served if a treatment plant is processing 0.885 MGD.
The number of people can be determined by dividing the flow by the population equivalent. Change MGD into gpd.
# of people served = (885,000 gal/day) / (100 gal/day/person) = 8,850 people
Total Suspended Solids and Total Solids
The term total solids refers to matter suspended or dissolved in water or wastewater, and is related to both specific conductance and turbidity. Total Solids includes both total suspended solids, the portion of total solids retained by a filter and total dissolved solids, the portion that passes through a filter.
A certain level of these minerals in water is necessary for aquatic life. Changes in total dissolved solids concentrations can be harmful because the density of the water determines the flow of water into and out of an organism’s cells. Total suspended solids are the solids captured on the special filter when performing the TSS test, as specified by Standard Methods for the Examination of Water and Wastewater. TSS can include a wide variety of material, such as silt, decaying plant and animal matter, industrial wastes, and sewage. High concentrations of suspended solids can cause many problems for stream health and aquatic life.
Suspended solids are capable of settling out of the water column onto the bottom when velocities are low. They include silt, clay, plankton, organic wastes, and inorganic precipitates such as those from acid mine drainage. Approximately 70 percent of the suspended solids and 40 percent of the dissolved solids are organic in nature. This leaves 30 percent of the suspended and 60 percent of the dissolved solids that are inorganic. These solids are made up of minerals, such as carbonate, sulfate, phosphate, nitrate, calcium, magnesium, sodium, grit, and others. Some of these minerals may be removed through chemical precipitation. High TSS causes less dissolved oxygen to be released into the water. If light is completely blocked from bottom dwelling plants, the plants will stop producing oxygen and will die. Low dissolved oxygen can lead to fish kills. High TSS can also cause an increase in surface water temperature, because the suspended particles absorb heat from sunlight. This can cause dissolved oxygen levels to fall even further (because warmer waters can hold less DO), and can harm aquatic life in many other ways, as discussed in the temperature section. High TSS in a water body can often mean higher concentrations of bacteria, nutrients, pesticides, and metals in the water. These pollutants may attach to sediment particles. High TSS can cause problems because the solids may clog or scour pipes and machinery. Some types of wastewaters, such as noncontact cooling water, are naturally low in suspended solids and do not require treatment.
Suspended solids interfere with effective drinking water treatment. High sediment loads interfere with coagulation, filtration, and disinfection. More chlorine is required to effectively disinfect turbid water. They also cause problems for industrial users. Suspended sediments also interfere with recreational use and aesthetic enjoyment of water. A positive effect of the presence of suspended solids in water is that toxic chemicals such as pesticides and metals tend to adsorb to them or become complexed with them which make the toxic less available to be absorbed by living organisms.