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82 4. SALINE WATER INTAKES AND PRETREATMENT
For comparison, concentrate from RO plants with open intakes would typically have DO concentration of 5e8 mg/L, which is adequate for disposal to a surface water body (ocean, brackish lake, or river) without reaeration. Therefore, the use of this type of intake is not likely to pose a challenge to the marine environment surrounding the outfall in terms of DO level in the discharge and pretreatment of the discharge prior to its release will not be needed.
4.2.6 Subsurface IntakesdEnvironmental Impacts and Mitigation Measures
Subsurface intakes are considered a low-impact technology in terms of impingement and entrainment. However, to date, there are no studies that document the actual level of entrain- ment reduction that can be achieved by this type of intakes.
Because subsurface intakes naturally filter the collected saline water through the granular formations of the aquifer in which they operate, using this type of intakes minimizes entrain- ment of aquatic organisms. The saline source water collected by this type of intake typically does not require mechanical screening and, therefore, subsurface intakes do not cause impingement impacts on the aquatic organisms in the area of the intake.
Subsurface intakes could have a number of environmental impacts, such as loss of coastal habitat during construction, and visual and aesthetic impacts, as well as it could affect nearby coastal wetlands depending upon the intake method of construction and design. The environ- mental impacts and mitigation measures of such intake wells are discussed in greater detail in the following publicationd Voutchkov (2013).
4.2.7 Construction Costs of Subsurface Intakes
Table 4.1 provides a summary of the construction costs for the types of subsurface intakes presented in the previous sections. As seen from this table, vertical wells are usually less costly than any other type of subsurface intakes, which is one of the main reasons why ver- tical well intakes are used most commonly for small desalination plants. Infiltration galleries
TABLE 4.1 Construction Costs of Subsurface Intakes
Subsurface Intake Type
Vertical wells
Horizontal Ranney wells
HDD wells (i.e., Neodren)
Infiltration galleries
Typical Production Capacity (Yield) of Individual Well (ML/day)
0.1e3.5 0.5e20
0.1e5.0 0.1e50
Construction Cost of Individual Well (US$ million)
0.3e2.5 0.8e6.4
0.4e1.8 0.9e42.0