7.1. Planning Stage - Part 03

Mi, 09/19/2012 - 18:36 -- klm-admin

Site short list:

After feasibility studies are completed, a short list of two sites is developed and detailed technical investigations are carried out. Reasons for limiting detailed work to two sites are testing and surveying costs.

  • Obtain site map from municipality, or draw one.
  • Soil analysis (kind of soil, profile/structure, permeability 'kf-factor', presence of large and small rocks & frequency of occurrence)
  • Water analysis (nutrient load, toxic persistent substances)
  • Existing wastewater and rainwater collection system, including piping & treatment facilities
  • Where does wastewater come from?
  • Where is it collected?
  • How does collection system work?
  • Groundwater level
  • Possible infiltration of collection system by groundwater, rainwater & sand
  • Site microclimate - rainfall differences from regional climate
  • Sources for wastewater contamination by toxic substances such as oil (back-yard repair shops etc.)
  • Site slope
  • Gravity-fed water flow: are pumps required
  • Elevation of site compared to wastewater sources
  • Hourly flow rates of water sources in liters per second over 3 days
  • Meeting with local community association to undertake survey
  • Undertaking community survey
  • Detailed analysis of legal status of the land

Preliminary Site Clearance:

  • It may be necessary to clear  possible sites of wild growth to determine elevations and water flow.
  • It may also be necessary to dig test canals to determine water flow patterns, plus drain the area.
  • If this is necessary it is essential to preserve large trees and topsoil. The sites should be disturbed as little as possible at this stage.

Determining volume of water flow:

Physical flow is estimated by:

  • placing a container of known volume  (20 or 100 liters) in the path of total water flow.
  • measuring the time it takes to fill the container with the total water flow exiting the wastewater outlet.
  • a sample calculation:
    - 30 seconds to fill a 20 liter container
    - equals flow rate of 40 liters per minute
    - equals flow rate of 2.4 cu. m. per hour
    - equals flow rate of 53 cu. m. per day
  • this process should be repeated every hour from as early in the morning until as late at night as possible, e.g. 0500 to 2300 hrs on three different days including at least one rainy day.
  • the maximum, minimum and average flow rates are then calculated.

The final site choice is largely a subjective decision based on:

  • perception of the level of community co-operation
  • comparative favorability of technical conditions
  • cost and legal factors for the site

Community co-operation is an equally important factor as other conditions. After site choice occurs, design and construction pre-planning begin.

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