Water System Design Manual, December 2009
Document source : www.doh.wa.gov
Water System Design Manual
December 2009
Page 71
7.2.3 Groundwater Under the Direct Influence of Surface Water
Groundwater under the direct influence of surface water (GWI) is any water beneath the surface
of the ground with:
1.
Significant occurrence of insects or other macroorganisms, algae or large diameter
pathogens such as Giardia lamblia, or
2.
Significant and relatively rapid shifts in water characteristics such as turbidity,
temperature, conductivity, or pH, which closely correlate to climatological or surface
water conditions (WAC 246-290-010).
Purveyors with sources confirmed to be GWI must comply with the filtration and disinfection
requirements for surface water sources (WAC 246-290, Part 6).
Purveyors must evaluate all potential GWI sources to determine if additional treatment is
necessary (WAC 246-290-640). Potential GWI sources include:
·
Wells that withdraw water from less than 50 feet below the ground surface and are
located within 200 feet of surface water.
·
Infiltration galleries.
·
Ranney wells.
·
Springs.
DOH will not approve a new potential GWI source before a proper evaluation. Figure 7-1, at the
end of this chapter outlines the evaluation process for potential GWI sources.
Potential GWI sources not confirmed to be GWI are not required to meet the treatment
requirements for surface water sources. However, potential GWI sources that are in hydraulic
connection with surface water must provide adequate disinfection prior to distribution (WAC
246-290-640(4)). Additional guidance on evaluating potential GWI sources is available from
references at the end of this chapter (WSDOH 2003a; WSDOH 2003b).
7.2.4 Blending Dissimilar Waters
Water systems must review how proposed projects could potentially affect water quality (WAC
246-290-110(4)(d)). Blending a new source with existing sources or replacing existing sources
with new ones can create water quality problems in the distribution system (Taylor et al. 2005;
Kippin et al. 2001). For example, iron or manganese can precipitate when surface water with
higher dissolved oxygen levels is blended with groundwater. Water systems must specifically
address how a new source will affect compliance with the Lead and Copper Rule (40 CFR
141.90).
Summary :
Water System Design Manual December 2009 Page 71 7.2.3 Groundwater Under the Direct Influence of Surface Water Groundwater under the direct influence of surface water (GWI) is any water beneath the surface of the ground with: 1. Potential GWI sources include: · Wells that withdraw water from less than 50 feet below the ground surface and are located within 200 feet of surface water.
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