Page 148 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

JWCL344_ch03_061-117.qxd 8/17/10 7:48 PM Page 110

110 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

Negative Raw water
coliform testing

Figure 3.17 Identification of Groundwater Sources Under the Direct Influence of Surface
Water (GWUDI)—Source Screening Phase Methodology

5 years of quarterly monitoring) are designated as not being under the direct influence of
surface water. Disinfected wells are subject to the options of either performing 1 year of
monthly raw water coliform monitoring or moving directly into the detailed evaluation
phase. Any raw water sample that is positive for E. coli would require the system to per-
form a detailed evaluation. Conversely, once 1 year of satisfactory monthly raw water
coliform samples have been obtained, the source can be designated as not being under the
direct influence of surface water, or not-GWUDI.