United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-89/050 Mar. 1990
Project Summary
Point-of-Use Treatment of
Drinking Water in
San Ysidro, NM
Karen Raborn Rogers
This study was conducted to deter-
mine whether point-of-use (POU)
reverse osmosis (RO) units could
satisfactorily function in lieu of cen-
tral treatment to remove arsenic and
fluoride from the drinking water
supply of San Ysidro, NM. POU treat-
ment was evaluated for removal
efficiency, cost, and management
effectiveness.
Seventy-eight under-the-sink model
RO units were Installed in private
homes, and 72 were monitored for
about 18 mo to evaluate operational
and maintenance data for POU treat-
ment
This Project Summary was devel-
oped by EPA's Risk Reduction Engi-
neering Laboratory, Cincinnati, OH, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
The Village of San Ysidro is a small
rural community of approximately 200
people located in the north central part of
the State of New Mexico approximately
45 mi (72 km) north of Albuquerque.
Leedshill-Herkenhoff, Inc. (Engineers and
Architects), was initially retained by the
Village in June 1982 to evaluate San
Ysidro's water supply system. The Vil-
lage was having problems meeting water
demands and was also out of compliance
with the National Interim Primary Drinking
Water Regulations for arsenic and fluo-
ride. Feasibility studies were to be per-
formed to determine whether economical
improvements to the system could be
recommended—improvements that would
solve both San Ysidro's water quantity
and quality inadequacies.
The Village has had a long history of
water supply problems including low
water pressure, no water at all, and
quality problems including taste, color,
clarity, and odor in addition to arsenic
and fluoride contamination and sporadic
coliform violations. The water supply
source is an infiltration gallery that pro-
duces an average of 27,000 gpd in the
winter and 36,000 gpd in the summer
from the groundwater. The Village uses
an average of 30,000 gpd, which equates
to about 150 gpd per person. This con-
sumption rate pushed the production
limits of the gallery.
The local groundwater contains leach-
ate from geothermal activity in the area's
abundant mineral deposits and is there-
fore high in mineral content. At the time
of the study, the groundwater exceeded
the recommended standards and/or
maximum contaminant levels (MCL's) for
arsenic, fluoride, iron, manganese, chlo-
ride, and total dissolved solids. The con-
taminants of concern in the Village water
supply were arsenic V and III and fluoride
which exceeded the MCL's by three to
four times. Table 1 shows a typical
analysis of the water in the infiltration
gallery. A University of Houston study
indicated that the arsenic present in the
San Ysidro water supply averaged 35%
as As III.
A variance from the Safe Drinking
Water Act (SDWA) for arsenic and
fluoride was granted to the Village while
U.S. Environmental Protection Agency
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(EPA) sponsored research was done (Dr.
Dennis Clifford of the University of
Houston, Texas) to determine an eco-
nomical and effective solution to the
contaminant problem. The treatment
technologies studied were activated
alumina and RO. Central and POU treat-
ment were considered.
Table 1. Analysis of Filtration Gallery
Water in San Ysidro
Analyte
Analytical Results
As
Cd
Cr
Pb
"9
Ca
Alkalinity
Cl
Hardness
Fe
Mg
Mn
pH
S04
N03 as N
F
Na
TDS
0.075
< 0,008
<0.02
<0.001
<0.01
86.4
447
88
272
0.06
13.6
0.05
778
30
0.1
1.6
135
914
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mgIL
mg/L
mg/L
mg/L
units
mg/L
mg/L
mg/L
mg/L
mg/L
Central treatment of the entire water
supply was not considered feasible for
many reasons. Firstly, a disposal problem
exists with both the arsenic-contaminated
wastes from activated alumina regen-
eration and the reject brine from an RO
system. Secondly, the capital costs and
the operation and maintenance costs of
central treatment were determined to be
higher than POU treatment. And, lastly,
central treatment was considered too
complicated to be efficiently operated by
a community the size of San Ysidro. The
results of the study indicated the best
solution to be POU treatment with RO
units.
Procedures
System and Contractor
Selection
A notification letter was sent to each
water customer, and a public hearing was
held on December 18, 1985, in which the
cooperative agreement between the
Village and the EPA was brought before
the villagers to explain the water quality
problem and to discuss the procedures
needed to have the RO POU devices
installed, maintained, and tested during
the study period. The Village passed an
ordinance requiring the installation of an
RO system in each water customer's
home if the home had indoor plumbing.
The ordinance was deemed necessary
because POU treatment could not be
considered a viable alternative to central
treatment for a public water system
unless the utility furnished safe drinking
water to each water customer. Each
water customer also had to sign a per-
mission form to allow the Village to install
the unit in their home and to allow access
to the unit for testing and maintenance.
The permission form was necessary be-
cause an ordinance could not give the
Village the authority to enter a person's
house (only an individual can grant per-
mission to the Village to enter his home).
A Request for Proposal was prepared
in which contractors were asked to
prepare competitive bid proposals for
furnishing approximately 80 RO units,
including installation and 14 mo of unit
maintenance, to the Village of San Ysidro.
The RO units were required to be
under-the-sink models capable of pro-
ducing a minimum of 5 gal of drinking
water per day with a storage capacity of
3 gal (Figure 1). The system pressure
range was given as 40 to 60 psi maxi-
mum, with a minimum pressure of 20 psi.
The units were required to reduce the
contaminants to below the established
MCL's as shown in Table 2.
The contractor was required to perform
service checks and preventive mainte-
nance on each unit every other month as
well as repairs to maintain the units
operational during an initial 14-mo period.
Maximum time allowed for service calls
was 3 working days. The contractor was
required to cover the costs of any house-
hold damages resulting from malfunction
of the RO units during the service period.
Based on the above criteria, each
bidder was required to submit prices for
a per unit purchase price, a per unit
installation price, and a per unit monthly
service charge. Each bidder was also re-
quired to furnish manufacturer's data
covering typical installation instructions,
construction details, and operating in-
structions.
Four bid proposals were received and
evaluated by Leedshill-Herkenhoff, the
EPA Project Officer, and a representative
of the State of New Mexico Environ-
mental Improvement Division. The pro-
posals were evaluated on nine factors
(Table 3), and associated weights, as
described in the Request for Proposal,
were given each factor.
The selected proposal was submitted
by Southwest Water Conditioning (a
Culligan* representative in Albuque
The price per unit for purchase,
lation, and monthly service was $2
$35.50, and $8.60, respectively. Th
posal also included an RO test IT
on each unit that consisted of an
total dissolved solids (TDS) meter.
Within the first 4 mo of the proje
RO units were installed, and 5 more
added by the end of the project p
Of the 78 units installed, however
72 were actually available for testin;
regular basis. At three homes, tot;
meters were also installed on the
line to the RO units to measur
amount of water used by the systen
Data Collection
The RO units were operatec
monitored for an 18-mo period.
samples were scheduled to be col
every other month for arsenic
fluoride analyses. In addition, the
were to be sampled every 4 to 6 t
chloride, iron, and manganese. Be
of various restrictions, only 40 unit;
analyzed for total coliforms. Each r
an average of 31 units were sampl
arsenic and fluoride; of these, 15
also sampled for chloride, iron
manganese and 10 for total coliforrr
Results
Water Usage
The average water use by th
systems recorded at the three f
with totalizing meters varied from
17.0 gpd (Table 4). Water use
because of the size of the familie
their use of the RO-treated water. P
water production (recovery) by tt
system depends on inlet water pr
and TDS but ranges from 20% to c
the total flow into the unit at 50 p
less than 1,500 ppm TDS.
Operational Problems
The initial 14-mo maintenance a
signed with Southwest Water (
tioning was extended to 20 mo
contractor could train a Village em
to perform routine RO system (
and maintenance.
Operational problems were re<
during the study. Within the first
six RO modules were replaced <
installations required service bees
"Mention of trade names or commercial pn
does not constitute endorsement or r
mendation for use
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Legend
Tap Connection to Existing Water Line
Pre-filter
@ Carbon Filter
^y Reverse Osmosis Unit
^) Storage Tank
^y Carbon Post-filter
\7j Faucet with Built-in Air Gap for Drain Line
^y Existing Sink
^y Drain Connection to Existing Sink Drain
gure 1. Typical under the sink reverse osmosis unit.
\tile 2. RO Requirements for Contaminant
Reduction
Contaminant-mg/L
Contaminant
From
To
ron
Manganese
Chloride
:luoride
Ursemc V & III
'otal Dissolved Solids
2.0
0.2
325.0
5.2
0.2
1000.0
0.3
0.05
250.0
1.8
0.05
500.0
leaks, IDS monitor problems, or water
flow problems. A summary of service
calls performed during the 20-mo
service period is shown in Table 5.
Because a few RO-treated water
samples tested positive for coliform and
the central water system did not test
positive during the sampling period, an
extensive investigation was conducted to
determine the cause. During the investi-
gation, all RO units were found to have
been installed with the RO drain con-
nected directly to the kitchen sink drain
(without an air gap). Because every
home in San Ysidro has a septic tank,
the cross-connection between the RO
dram line and disposal line was strongly
suspected to be causing the positive
coliform tests. The installer modified all
systems to eliminate the cross-
connection by providing an air gap
between the discharge line and drain
line. After the air-gap problem was
corrected, no more positive coliform
tests were obtained. Only a few months
of samples were taken after the change,
however, and therefore the air-gap
problem could not be positively iden-
tified as the source of the problem.
Chemical Contaminant Removal
The RO units effectively removed
arsenic and fluoride from the water. The
RO units also effectively removed chlo-
ride, iron, manganese, and TDS, but did
not quite meet the removal rates stated
in the manufacturer's cause of the
number and concentration of literature.
This was probably because of the
contaminants in the water supply. Table
6 shows average removal percentage for
each of the contaminants during the
project period.
Because of the high costs of arsenic
and fluoride analyses, conductivity
measurements were evaluated as a
substitute for arsenic and fluoride tests.
An analysis of the arsenic, fluoride and
conductivity data showed a rule of
thumb could be established whereby a
conductivity measurement of less than
600 micromohs/cm would maintain less
than 0.03 mg/L of arsenic and less than
1.0 mg/L of fluoride.
Bacteria Samples
Over a 13-mo period, 131 water
samples were collected from 40 RO unit
special taps for coliform analysis by
membrane filter technique. Nine of these
tests were positive for coliforms. In ad-
dition, 10 tests showed non-coliform
counts from 11 to too-numerous-to-count
(TNTC). Of the microbiological tests, 15
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Table 3. Factors and Weights for Proposal Evaluation
Table 6. Contaminant Removal by RO Systems
Factor
Weight
1. Construction of Unit
2. History of Similar Installations
3. Proposal Completeness
4. Removal Efficiencies (including amount
of water wasted by treatment)
5. Maintenance Record
6. Ease of Maintenance
7. Maintenance Service Contract
8. Price of Units and Installation Cost
9. Maintenance Service Contract Costs
Total
Contaminant
Arsenic
Fluoride
Chloride
Iron
Manganese
TDS +
Average
Influent
(mg/L)
0.059
2.7
91
0.58
0.09
780
Average
Effluent
(mg/L)
0.008
0.339
14.59
0.019
0.012
93
%
Removal
86
87
84
97
87
88
% Remo\>
(Manufactui
Data)
68/96'
82
94
-
97
94
* 68% removal of Arsenic III, 96% removal of Arsenic V.
*As tested by contractor's service technicians on routine checks
Table 4. Water Usage by RO Units
Family
r
2 +
3*
Family
Size
6
2
5
Average
Flow (god)
8.5
14.2
17.0
Maximum
Flow (gpd)
13.3
20.0
30.0
" Water used for cooking only.
* Water used for cooking and drinking.
* Water used for all purposes.
Table 5. Service Calls by Types for 20-Month Period
Type
Number
Comments
Leak
TDS Monitor
Flow Problem
Routine Check
Other
Routine Check-
No One home
38
11
217
150
122
8% of leaks were not from the RO
unit.
All calls regarding red light of
monitor. 3 calls required a part
replacement, others required
adjustments only.
2 of reported flow problems were
due to low system pressure (25
psi).
25% of routine checks resulted in
repair or adjustment of unit not
identified by customer.
Other customer complaints
included taste or odor problems,
broken faucet handles, noisy air
gaps, and reinstallations.
This is 36% of the total routine
checks attempted. The actual
percentage is probably higher
since some "not at home" calls
were unrecorded.
Total
412'
"Average number of calls per month = 412/20 = 20.6.
Number of calls required by contract = 33 to 35.
Contract required checks on each installed unit every other month.
Number installed varied over contract period.
of the 131 samples from the RO ui
showed some evidence of bacte
contamination.
Five water samples were collected fr
sink taps, and three of these tested I
high noncoliform counts. None of thi
samples tested positive for coliforms
did any of the community's chlorina
water supply samples test positive
coliform during the study. The carl
prefilter in the RO unit removes chlorint
protect the polyamide RO membrane.
An extensive investigation was m«
into the coliform problem. A gene
description of the investigation and
action taken to correct the problem
given in the previous section on Opt
tional Problems.
Regulations and Compliance
When the project started, the VilU
passed an ordinance requiring each w<
customer to have an RO unit, if the ho
had indoor plumbing. Also, each w<
customer had to sign a permission forn
allow the Village personnel access to tl
home to install, test, and maintain the
unit. At the end of the project,
ordinance was modified to deal w
several problems and situations t
developed during the project. The r
ordinance required "commercial users'
provide water treatment to meet
drinking water standards and allowed
Village to sample their water. The Villa
therefore, maintained complete con
over the residential systems and tra
ferred all responsibility for providing s
drinking water to the commercial us
The ordinance also provided some latiti
to the commercial user in selecting
most economical treatment method.
The new ordinance required that
residential RO units continue to be own
maintained, and monitored by the Villa
but made certain requirements of
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individual water customer. The ordinance
prohibits tampering with the RO unit in
any way and requires a weekly check for
leaks and operation of the IDS test
switch. Also, the user is required to pro-
tect the unit from freezing and standing
dry.
The new ordinance also addressed two
liability issues. The Village assumed lia-
bility for damages to the users home
caused by the RO unit, with limitations.
The user is held liable for damages if the
user did not perform the maintenance
check, tampered with the unit, or allowed
the membrane to be destroyed because
of temperature (freezing) or drying out.
Cost
Cost data and information were col-
ected on the replacement parts, mainte-
nance, bookkeeping, analytical tests, and
nsurance. These data indicated that a
nonthly service charge of $7 would be
necessary to cover the costs. If the cost
Df the unit was included in the monthly
;harge, the surcharge would be $12 to
15, which is about half of the $30 to $40
jstimated cost of central treatment for
he Village. The actual cost of treated
water based on an average RO produc-
ion of 7 gpd is, however, $0.06 per gal
is compared to less than $0.01 per gal
or central treatment.
yublic Acceptance
A survey of the users (80 forms) was
:onducted at the end of the project.
Twenty-five responses representing 73
residents were returned. Approximately
85% of the responses indicated they
were pleased with the RO units, which
was about the same as results from a
house-to-house survey.
The majority of the negative comments
dealt with the quantity of water produced
and the water pressure from the unit's
faucet. Thirty-eight percent were not
pleased with the quantity, and all of these
comments were from families of four or
more persons. Of the responses, 64%
indicated a willingness to pay $5 to $10
per mo for continued use of the RO units,
20% were willing to pay more than $10
per mo, and 16% were unwilling to pay
anything at all.
Conclusions and
Recommendations
The following conclusions were drawn
as a result of the San Ysidro study:
POU treatment of drinking water is an
effective, economical, reliable, and viable
alternative to central treatment in a small
community like San Ysidro to remove
arsenic as well as other contaminants.
Adopting a POU treatment system in a
small community requires more care than
does a central treatment system relative
to time-keeping to monitor the individual
systems.
POU systems require special regula-
tions regarding customer responsibilities,
water utility responsibilities, and the re-
quirement of installation of the devices in
each home obtaining water from the
utility.
POU systems require special consider-
ations from regulatory agencies to deter-
mine appropriate methods for record
keeping, monitoring, and testing fre-
quencies that may differ from existing
regulations.
The RO units with polyamide mem-
branes installed in San Ysidro resulted in
the following removal percentages, bring-
ing all of the contaminant levels well
below the MCL's: arsenic (total) - 86%;
fluoride - 87%; TDS - 88%; chloride -
84%; iron - 97%; and manganese - 87%.
The cost to the customer of POU
treatment per month ($7) in San Ysidro is
less than half of the estimated cost of
central treatment ($30 to $40 per mo).
The cost per gal of treated water, how-
ever, is over three time? that of central
treatment, since central treatment treats
the entire water supply and the POU
device treats a small fraction of the
supply.
Total usage of water through the RO
units, including consumption, averaged
from 8.5 to 17.0 gpd. The units were
designed to produce 5 to 8 gal of treated
water.
The full report was submitted in ful-
fillment of Cooperative Agreement CR-
812499 by Leedshill-Herkenhoff, Inc.,
under the sponsorship of the U.S. Envi-
ronmental Protection Agency.
-------
Karen Raborn Rogers is with Leedshill-Herkenhoff, Inc., Albuquerque, NM 87103.
Kim R Fox is the EPA Project Officer (see below).
The complete report, entitled "Point-of-Use Treatment of Drinking Water in San
Ysidro, NM," (Order No. PB 90-108 838/AS; Cost: $17.00. subject to change) will
be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S2-89/050
US.OFFICIAL MAIL*
{J.S.POSTAR '
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