4. 1 Arsenic Results Based on Well Construction
Due to the changing Drinking Water Standard, wells were categorized based on the results being less
than 50 (the old standard) or less than 10 (the new standard). Since the standard was 50 ppb when the
study began and when the original well drilling guidance went into effect, it was deemed necessary to
determine how successful the wells would be under the previous standard of 50 ppb and the current
standard of 10 ppb. The following tables compare the effectiveness of each type of well construction
under each standard. These tables are categorized by maximum value; since this is a health issue, it
made more sense to use maximum values rather than averages for this table.
Table II: Effectiveness of wells meeting standards based on well construction
Arsenic Level        Wells Not Constructed     Wells Constructed
According to Guidance    According to Guidance
<10 ppb                10(43.5%)                18(43.9%)
10- 49 ppb               10(43.5%)               20(48.8%)
>50 ppb                 3(13%)                   3 (7.3%)
Table II illustrates the effectiveness of wells based on whether or not the well was constructed
according to guidance. There is essentially (statistically) no difference in the success rate of the wells
meeting the current standard whether the guidance was followed or not (43.9% compared to 43.5%
success rate, respectively). However, it should be noted that the wells that followed the guidance
would have had a slightly better success rate if the standard had remained 50 ppb. Wells constructed
according to guidance would have had a success rate of 92.7% compared to 87% for those that did not,
indicating that even if the standard had remained at 50 ppb, the '80-foot' guidance would likely not
have been adequate.
To determine if there is a difference between the success rates of wells that did follow guidance based
on the type of well, the wells were further compared based on the three different types of wells that did
follow guidance, as seen in Table III.
Original and replacement wells tended to have a greater success rate than reconstructed wells based on
the current standard of 10 ppb. Since there are a limited number of wells in each category, it is difficult
to know if they would continue to have a greater success rate over a larger sampling set. If the standard

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