Page 102 - Water Engineering Hydraulics, Distribution and Treatment

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Chapter 3
Water Sources: Groundwater
Box 1: Screening Criteria
There has been a biological waterborne disease
•
outbreak associated with the source
•
There has been a chemical contaminant incident
in the source that was thought to have originated
from the surface water
The source is a spring, infiltration gallery,
•
crib intake, dug well, or shallow horizontal
collector
•
Rapid fluctuations in source output, well water
level, and/or chlorine demand (particularly when
associated with runoff events)
• The source is located in a carbonate aquifer
• The source is within 200 feet (61 m) of surface
water in a fractured bedrock setting with < 100 feet Any true
(30.5 m) of casing Source selected
for further review
None true
Both true
Box 2: Screening Criteria
• The source is located 200 feet (61 m) or less
from a surface-water body or recharge boundary
• The source has 50 feet (15.2 m) or less of casing
E. coli
One true
positive
Both untrue
Is well
disinfected?
No Yes
Not GWUDI (with waiver Choose
and good history) one
Figure 3.17 Identification of
groundwater sources under the direct
Negative Raw water influence of surface water (GWUDI)—
coliform testing source screening phase methodology.
biological waterborne disease outbreak has been associated are met, the source is selected for further review under the
with the source; (b) a chemical contaminant incident has box “Source selected for further review.” If neither of these
occurred in the source that was thought to have originated conditions is met, the source is designated as not being under
from the surface water; (c) the source is a spring, infiltration the direct influence of surface water, or not-GWUDI. When
gallery, crib intake, dug well, or shallow horizontal collec- only one of the criteria in Box 2 of Fig. 3.17 is met, the next
tor; (d) rapid fluctuations have been noted in the source out- step in the GWUDI determination is dependent on whether or
put, well water level, and/or chlorine demand (particularly not the water source is currently disinfected. Undisinfected
when associated with runoff events); (e) the source is located wells that have met the criteria for a disinfection waiver and
in a carbonate aquifer; and (f) the source is within 200 ft have an adequate coliform monitoring history (typically 5
(60 m) of surface water in a fractured bedrock setting with years of quarterly monitoring) are designated as not being
<100 ft(30 m) of casing. If none of these criteria are met, then under the direct influence of surface water. Disinfected wells
the screening process continues in Box 2 of Fig. 3.17. If any are subject to the options of either performing 1 year of
of these criteria is met, then the screening process continues monthly raw water coliform monitoring or moving directly
to the box “Source selected for further review.” into the detailed evaluation phase. Any raw water sample that
The criteria in Box 2 of Fig. 3.17 ask if the source is is positive for E. coli would require the system to perform a
located within 200 ft (60 m) of surface water, and/or if the detailed evaluation. Conversely, once 1 year of satisfactory
well has 50 ft (15 m) or less of casing. When both criteria monthly raw water coliform samples have been obtained,