SPEAKING OUT
Figure 1. Conceptual well schematic for the alternative treatment process.
IN 2014, THE CALIFORNIA DEPART-ment
of Public Health (CDPH) promul-gated
the first Cr6-specific drinking water
maximum contaminant level (MCL). Re-jecting
repeated requests to include a rea-sonable
compliance period, CDPH pro-vided
just six months for water agencies
to begin determining their compliance
with the new regulation. With dozens of
water sources expected to be impacted by
naturally occurring Cr6 found in Coach-ella
Valley groundwater, CVWD initiated
research on best available technologies
soon after the draft MCL was released.
CVWD simultaneously pursued a legis-lative
fix to obtain a suitable compliance
period but faced stiff opposition. Using
available information on existing tech-nology,
difficult decisions were made to
develop treatment facility designs and
begin the environmental review process
to construct dozens of ion exchange treat-ment
facilities.
On September 27, 2016, CVWD learned
that there might be a better Cr6 treatment
technology when Dr. Chad Seidel shared
preliminary results from an ongoing re-search
project in Watsonville, CA. Seven
days later, a research team led by Dr. Nicole
Blute was in CVWD’s laboratory perform-ing
bench-scale tests of this alternative treat-ment
technology using local groundwater.
The process uses low doses of stannous
30 SOURCE winter 2017
chloride, an approved corrosion inhibitor
for drinking water systems, to reduce Cr6
to trivalent chromium (Cr3) and form parti-cles
comprised of stannous and chromium
that are removed by particle filters.
An optional five-year compliance pe-riod
in U.S. Environmental Protection
Agency (USEPA) drinking water regula-tions
for contaminants that do not repre-sent
urgent threats to public health was
included in the 1996 amendments to the
Safe Drinking Water Act. Promulgation of
an MCL for a drinking water contaminant
is the most important driver for innova-tive
research used to refine and optimize
existing water treatment technologies or
develop better technologies capable of
meeting the MCL. Besides providing time
to perform these studies, the compliance
period is needed for water agencies to
identify and pilot test treatment technol-ogies,
review the environmental impacts
of the technology, ensure the technology
is compatible with the water distribu-tion
system, identify and obtain project
funding and ultimately design and install
the selected technology. Skipping any of
these steps to meet impractical compli-ance
dates can result in water treatment
systems that do not work, are too costly to
operate, or have unintended consequenc-es
that may be more harmful than serving
the water without additional treatment or
do not use new technology developed af-ter
rule promulgation.
USEPA’s 2001 revision to the arsenic
drinking water MCL illustrates the ben-efits
of a reasonable compliance period.
Few water agencies installed activated
alumina treatment identified by USEPA
as the most likely best available tech-nology
for removing arsenic. By 2003,
research spawned by the agency’s arse-nic
rule resulted in better technologies,
including many types of adsorption me-dia,
ion exchange, and coagulation filtra-tion
processes. Had USEPA not provided
the five-year compliance period, many
water agencies would have been forced
to make decisions based on the limited
treatment knowledge that existed when
the draft arsenic rule was written, likely
resulting in the widespread use of less op-timal
treatment technologies. Some water
agencies that made treatment decisions
before these new technologies matured,
or which skipped the pilot test process,
ended up with treatment systems that
were ineffective or too costly to operate
because they were not selected based on
their water quality conditions or waste
management requirements.
CVWD’s OSCAR
The results of CVWD’s bench test of stan-nous
chloride-assisted Cr6 removal provid-
Cr6 Revisited: Coachella Valley
Goes Back to the Drawing Board
By Steve Bigley
SOURCE Fall 2016 featured an article on the Coachella Valley Water District’s (CVWD) approach to meeting
California’s new hexavalent chromium (Cr6) MCL. With over 30 percent of its wells impacted, it is important
for the district to get it right. Research results on an alternative technology reported after CVWD green lighted
its $228 million ion exchange treatment project caused it to halt construction and undertake pilot testing of
the alternative technology.