United States
Environmental Protection
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ARSENIC IN DRINKING WATER
COMPLIANCE SUCCESS STORIES

Ripon, CA: Pilot Studies Useful for
Treatment Evaluations

Case Study Contact Information

Matt Machado
City Engineer
(209) 599-2108

The City of Ripon, CA completed a pilot study to compare three different treatment
systems for removing arsenic from their groundwater supply.

Lessons Learned

The City of Ripon, CA piloted three different coagulation/filtration systems using ferric
chloride as the coagulant. The pilot study showed that all three systems were capable of
reducing arsenic to acceptable levels and demonstrated high water production efficiency
in the range of 90 to 99 percent based on backwash volume and the number of events.
Using a bidding process, the City awarded a contract to Kinetico, Inc. to install treatment
facilities which are expected to be placed into service in December 2006.

During the pilot study evaluations, the City also identified a sulfur-modified iron test
media that can remove nitrate from water and also can benefit the arsenic treatment
system by providing a source of iron. Iron combines with arsenic and the resulting
compound is removed by filtration. The City is continuing to evaluate this media on a
pilot-scale because several wells have elevated levels of nitrate in addition to arsenic.

System Description

The City of Ripon, California, located 80 miles east of San Francisco, serves
approximately 12,000 residents with an average daily demand of 4.0 MGD. The City has
six wells that are used for potable water.


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Two of the potable supplies, Wells 9 and 10, were found to contain arsenic at
concentrations of 11 to 12 ppb. Both wells also have nitrate levels that exceed the MCL
of 10 mg/L. Water quality and operating data for these wells are summarized below.

Well

System

Date

Production Rate

Max Nitrate

Max Arsenic

No.

Type

Drilled

(gpm)

Cone. (mg/L)

Cone, (ppb)

9

Potable

1989

600

41

12

10

Potable

1993

2,000

27

11

The City of Ripon, CA piloted three different coagulation/filtration systems using ferric
chloride as the coagulant. The pilot study showed that all three systems were capable of
reducing arsenic to acceptable levels and demonstrated high water production efficiency
in the range of 90 to 99 percent based on backwash volume and the number of events.
Using a bidding process, the City awarded a contract to Kinetico, Inc. to install treatment
facilities which are expected to be placed into service in December 2006.

During the pilot study evaluations, the City also identified a sulfur-modified iron test
media that can remove nitrate from water and also can benefit the arsenic treatment
system by providing a source of iron. Iron combines with arsenic and the resulting
compound is removed by filtration. The City is continuing to evaluate this media on a
pilot-scale because several wells have elevated levels of nitrate in addition to arsenic.

Pilot Study Evaluation

The City completed a pilot study to identify the necessary operating conditions for
removing arsenic from Wells 9 and 10 using a coagulation/filtration process with ferric
chloride as the coagulant. Arsenic is removed from the water by co-precipitating the
arsenic with iron onto the filter media as ferric arsenate. The pilot study set-up is shown
in the photo, below. Six objectives were identified for the pilot study:

1.	Demonstrate the ability of the arsenic treatment systems to achieve treated arsenic
goals under dynamic operational conditions.

2.	Validate the optimal coagulant conditions determined at the bench-scale.

3.	Comparatively assess the ability of the filtration systems (granular and ceramic
media and membrane) to remove arsenic.

4.	Establish the water efficiency for each
treatment system.

5.	Evaluate the coagulation and filtration
backwash residuals quantity and quality.

6.	Provide an opportunity for City
personnel to gain experience in
operating the treatment systems.

Three filtration system vendors participated in
the pilot study: Kinetico, Inc.; Layne
Christensen; and Pall Corporation. The Kinetico


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system used pressure filtration with a ceramic media, Macrolite®, which is chemically
inert and uniform in size. The Layne system featured pressure filtration with
LayneOxTM media, a high rate granular media. The Pall system featured membrane
microfiltration using polyvinylidine fluoride (PVDF) hollow fiber membranes with a pore
size of about 0.1 microns.

Three pilot study runs were conducted with ferric chloride dosage rates varying from 2 to
10 mg/L. All three treatment technologies were capable of removing arsenic to levels
below the MCL, and all three demonstrated high water production efficiency in the range
of 90 to 99 percent based on backwash volume and the number of events. Based on pilot
study results, the City decided to use a ferric chloride dosage rate of 7 mg/L. The City has
contracted with Kinetico Inc. to design and build the treatment facilities which are
expected to be put into service by December 2006.

Funding Process

The City received $450,000 in federal funding to offset treatment costs for Well 9. This
funding was provided by a congressional line item appropriation. As part of the funding
process, the City completed detailed documentation on arsenic treatment alternatives and
other project justification. The remaining treatment expenditures were funded through
revenues received from local water customers. No rate increase is anticipated.


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