Arsenic Case Study - POU Reverse Osmosis

Black Canyon City, Arizona

Black Canyon City is a unique community considering POU reverse osmosis as a means to meet the safe drinking water act requirements for arsenic. The city water municipality has an average arsenic concentration of 12 to 15 ppb and consists of approximately 700 service connections, including single family households, multi-family dwellings, mobile home parks, RV parks and schools. The Black Canyon community obtains its water from three separate, non mixing well sites. The water is pumped directly from these three well sites to the service connections, each sight has a small chlorinator hooked up inline to chlorinate the water. Chlorine levels however are not high enough to have detectible free chlorine at the service connections. Point of use reverse osmosis is being considered in Black Canyon City based upon these three separate non mixing wells and the cost for centralized water treatment is tripled as three separate systems would need to be installed.

An initial meeting was held at the Black Canton City Water Improvement District office, and included members of the Black Canyon City Water Improvement District, ADEQ and Watts Premier. This initial meeting was used to discuss the overview of a pilot project, cost, time frame, number of individuals, and the overall goals.

In brief, 20 reverse osmosis units, all NSF Certified for arsenic V removal (300 ppb), were installed in to volunteer dwellings where specific water and operational parameters are evaluated over an eight month period. Monitored water characteristics include: arsenic, alkalinity, bacteria, total chlorine, free chlorine, fluoride, hardness, inlet pressure, iron, manganese, pH, TDS and temperature. The testing matrix that has been put together will evaluate; pre and post filtration concentrations, as well as the difference between ADEQ wet lab test results and Hach on site quick test kits.

Water parameters will be evaluated every other month over an eight month period and charted. During the study, the home owners will be provided a total of three surveys to complete regarding the installation, use and feel of the reverse osmosis unit. A second meeting was held at the Black Canyon City Water Improvement District monthly board meeting. Participants at this meeting were the water district board, community individuals, ADEQ and Watts Premier. ADEQ and Watts Premier spoke briefly about arsenic, the EPA requirements, and the pilot project. During the meeting, the Water Board agreed to proceed with a reverse osmosis pilot project for the community.

Following this meeting, an advertisement was placed in two local papers requesting 20 volunteers for the project. At the next water district board meeting, it was announced that they had the 20 volunteer's necessary, and they were ready to move in to the installation phase.

Black Canyon City Water Improvement District decided for the pilot project to use a local installer recommended by Watts Premier. However the water district commented that they would formally bond the plumber in they move forward with a complete POU RO install. Initial calling and scheduling for the installations was conducted by the Black Canyon City Water Improvement District. Additionally, members from the water district accompanied the installers to the installation sites. This was an important element of the program for two reasons, for directions to the homeowners as well as gaining access to the home. The homeowners knowing the water district staff were very receptive to the group entering the homes to install and gather water samples.

The RO units used for this project were the new Watts Premier WP-5 Manifold systems . These systems are equipped with three pre filters, one 5 micron sediment and two 5 micron carbon blocks. Following the prefiltres is the 25 GPD RO membrane, three gallon holding tank and a final 10 inch in-line polishing filter. These systems carry NSF International Certification for the reduction of arsenic, barium, cadmium, copper, cyst, hexavalent chromium, fluoride, lead, radium 226/228, selenium, TDS, trivalent chromium and turbidity. Service connections that had inlet pressure less than 40 psi were equipped with a booster pump.

Instillation was completed in a day and a half with the assistance of Aqua Science, a local Phoenix Arizona dealer. On average it took 20 to 30 minutes to install the RO, however there was an additional 20 minutes on average where we spoke to the homeowners about the project and answered questions that they had about the project, as well as other plumbing and kitchen appliance concerns. In some instances we assisted with some simple housekeeping tasks such as replacing clock batteries or moving furniture around. Some of the homeowners had refridgerator with water dispensers and automatic ice makers, which in some instances were hooked up to the RO as well. All participants were left with a project overview hand out and the first of the three surveys. The project overview handout was put together in order to provide background information about regulations, arsenic, reverse osmosis and the schedule of the project. In conversations with the homeowners, this was an important part of the program as nearly all of the homeowners reviewed the hand out and felt better informed and more a part of the project. Additionally, the document provided directions and telephone numbers in the event of an emergency, which provided reasutrance to the homeowner on the operation and maintenance of the project.

One week following the installation of the RO's, ADEQ and Watts Premier returned to the sites of installation in order to test the water. At this time the initial set of survey's were also collected. Two methods were used for water analysis. First there was onsite testing through the use of Hach test kits. These test kits were able to test for arsenic, alkalinity, total and free chlorine, hardness, iron, pH and TDS. Samples were also obtained through the ADEQ for wet lab analysis. The teat parameters for the wet lab analysis included all of those mentioned above, and also included bacteria, fluoride and manganese.

Black Canyon City Water Characteristics

Survey Results

Further updates, results and survey results will be posted as they are received. The Black Canyon City project is estimated to be completed in between September and October 2004.