DDW-2024-009305

June 13, 2024
Michael Goodman
Mt. Tabby Springs Subdivision
2729 Durban Road
Sandy, UT 84093
Subject:MPA Result Notification, Mt. Tabby Spring (WS001);
Mt. Tabby Springs Subdivision, System #07009, File #14956
Dear Michael Goodman:
The Division of Drinking Water (Division) suspected Mt. Tabby Spring (identified as WS001 in
the Division’s database) to be under the direct influence of surface water (UDI) based on multiple
Total Coliform positive (TC+) samples taken from the source and within the distribution system.
Therefore, an initial Microscopic Particulate Analysis (MPA) sample was collected from Mt.
Tabby Spring (WS001) on May 25, 2024. . The sample scored 0, which indicates a low risk for
being UDI. On this basis, Mt. Tabby Spring (WS001) is not considered to be UDI at this time.
The Division can re-evaluate this source at any time if there are circumstances that affect its
susceptibility to surface water influence. For information about UDI and MPA sampling, see the
attached UDI Definition and Possible Causes.
If you have any questions regarding this letter, please contact Sarah Page at [phone] or
Brian Pattee at [phone].
Sincerely,
Mark Berger
Monitoring and Standards Section Manager
195 North 1950 West • Salt Lake City, UT
Mailing Address: P.O. Box 144830 • Salt Lake City, UT 84114-4830
Telephone [phone] • Fax [phone] • T.D.D. [phone]
www.deq.utah.gov
Printed on 100% recycled paper
Michael Goodman
Page 2 of 3
June 13,2024
Enclosure:Laboratory Report of MPA Sample Taken on May 25,2024
cc:Cindy Austreng,Tri-County Health Department,[e-mail]
Michael Goodman,Mt.Tabby Springs Subdivision,[e-mail]
Division of Drinking Water VSA Team,[e-mail]
Nathan Hall,P.E.,DEQ Tri-County District,[e-mail]
UDI Definition and Possible Causes
A groundwater source that is Under the Direct Influence of surface water (UDI)is vulnerable to
contamination by pathogens found in surface water.This vulnerability could be because the
sub-surface formation is not sufficiently filtering water as the water percolates through the
formation or because the groundwater collection infrastructure is poorly constructed and allows
surface water to directly contaminate the groundwater.The Division of Drinking Water ’s protocol
determines and classifies a groundwater source as UDI based on one or more of the following
factors:
1.Physical evidence of source deficiencies that allow,or have the potential to allow,surface
water contamination of the source
2.MPA sampling results indicating surface water influence:
a.One high-risk MPA sample result
b.Two consecutive moderate-risk MPA sample results
c.Inconclusive MPA sample results,such as alternating low-risk and moderate-risk
results,along with other water quality data or observations of the source that
indicate potential contamination by surface water
3.Water quality data indicating contamination by surface water,for example,Escherichia
coli positive source sample results not caused by physical deficiencies,detection of
Cryptosporidium or Giardia in the source water,etc.
An MPA test (Item #2)consists of running the source water through a spiral-wound filter for a
period of time.Particles collected by the filter are extracted in a laboratory,examined under a
microscope,and identified.Particles that are expected to be found only above ground or in surface
water indicate a risk of surface water contamination.Such indicators include chlorophyll-bearing
algae,parts of flying insects,plant debris,Cryptosporidium,Giardia lamblia,etc.Some of these
indicators are not pathogens,but their presence in the source water means the source water is
susceptible to contamination by pathogens found in surface water.
An MPA sample is rated as having a low,moderate,or high risk of UDI if the score is 0-9,10–19,
or 20 and above,respectively.When basing the classification of a groundwater source on MPA
results,the Division protocol classifies a source as UDI if any MPA sample is high risk or if any
two MPA samples are moderate risk or above.
The path that surface water takes as it flows to a groundwater source can and usually does vary
with season and hydrogeological conditions.It is common for the flow path to be directly
influenced by surface water under some conditions,such as during a high surface runoff during
spring,but not to be directly influenced under others.So a surface-water-influenced water source
may have MPA sample results of various risk levels,depending on the timing of the sampling.A
true groundwater source that is not under the direct influence of surface water will always have
only low-risk MPA results.