Virgin Valley Water District Arsenic Treatment Plants
BACKGROUND
Edward Bunker was a member of the Mormon Battalion and a missionary to England. He led a company of handcart pioneers across the plains and founded Bunkerville in 1877. The Town, 9 miles south of Mesquite, is reached from I-15 or from Mesquite on state Route 170. Both Mesquite and Bunkerville are located on the Virgin River which runs from southwestern Utah across northwestern Arizona to Clark County and empties into Lake Mead.
Bunkerville was a Mormon settlement, formed around a sort of "pioneer communism." The tiny Town was owned by one and all. It consisted of a community dining hall and six houses walled with adobe, and holding the entire Town's inhabitants. Bunkerville maintains a separate identity from its younger, but much larger, neighbor of Mesquite. One can cruise the tidy little Town's streets to spot several pioneer-era residences and other buildings from earlier times among the more modern construction. Bunkerville is a sleepy little agricultural town and still has a very rural flavor, with gardens on residential lots and fields of alfalfa.
The Virgin Valley Water District (VVWD) was created by the Nevada State Legislature during the 1993 legislative session and signed into law on May 10, 1993. The District initially served the Mesquite area, but has since been expanded to include Bunkerville.
The current source of drinking water supplied by VVWD is from groundwater and is specifically produced from the Muddy Creek aquifer, which is hydraulically separated from sediments associated with the Virgin River flood plain. Ground water from the Muddy Creek aquifer contains varying concentrations of arsenic. The USEPA lowered the arsenic standard in January 2006 from 50 µg/L to 10 µg/L. The arsenic concentration in the drinking water supplied by VVWD exceeds the new arsenic standard. Studies to evaluate treatment alternatives for arsenic were completed in September 2002 and pilot testing of the arsenic treatment methodologies was completed in 2004. In September 2006, the State Environmental Commission granted the VVWD an exemption from the arsenic compliance requirement until January 23, 2009.
PROJECT DESCRIPTION
 The VVWD made plans to construct 5 separate arsenic removal plants (click on the map image to the right to open a larger version of the map in a new window). Three of the plants would be located within the Mesquite Water System and two within the Bunkerville area. All of the plants would use coagulation/filtration technology with chemical addition to remove arsenic from the groundwater. The plants were designed after a nine month pilot process.
The total cost of the three arsenic removal plants in the Mesquite area (Sites 27, 26 and 32) was originally estimated to be $10.2M, with 75% of that total covered by a grant from the Army Corps of Engineers. The remaining 25% was funded by the VVWD with the aid of $1.7M in SRF loan funds.
The other two arsenic removal plants (Sites 29 and 31) were located in the Bunkerville area. The original total cost of these two arsenic removal plants was estimated to be approximately $5.3M. The VVWD applied for a grant under the AB 198 program to assist with the arsenic treatment system project. The grant was originally approved by the Board for Financing Water Projects on January 27, 2005, for $2,000,137.16 (30.41% of the total eligible project cost of $6,577,235). The scope of the project included the installation of two arsenic removal plants, a 2 million gallon Scenic Reservoir, and 8,500 feet of 12-inch pipeline from the Scenic Reservoir to the White Rocks pressure reducing valve. The USEPA funded 55% of this project through an EPA STAG grant. The remaining 45% is funded by the VVWD with the aid of the $2M in AB-198 grant funds, approximately $590,000 of which was applied to the new Scenic tank and transmission line leaving approximately $1.41 million for the arsenic treatment facilities in Bunkerville.
The design changes in the waste discharge from the backwash operation increased the estimated project cost for the two Bunkerville treatment plants as both required concrete-lined drying basins for the sludge and recycling of the backwash water. VVWD opened bids on all 5 of the arsenic plants in June 2007. Two bids were received with the lowest bid exceeding the engineer's estimate by about $9 million. The high prevailing wage in the area and busy construction schedules for most firms led to significantly higher construction bids than originally anticipated.
The VVWD directed their engineers to modify some of the design features of the plants in order to reduce costs and chose to re-bid the project with the modified design hoping to get increased bidding competition. The project was re-bid in September 2007, and the low bidder at $22,945,000.00 was MMC, Inc., a division of New Com, Inc. of North Las Vegas, Nevada. They specialize in water and wastewater treatment facilities. The project was awarded in September 2007 and was planned for completion by May 2009.
With the higher than anticipated project bids, the VVWD used its remaining bonding capacity to secure funds to get the project started. After the new project costs were known, the VVWD sought further funding from the EPA and was able to secure $260,000 for Sites 29 and 31. The VVWD provided a letter from its financial consultant discussing the inability to afford additional bonds in the near future. This essentially prevented the VVWD from obtaining additional funding in loans from the SRF. Funds currently in the capital reserve account were primarily earmarked to cover the cost overruns due to changes in discharge requirements for this project. The Board approved an additional $1.2M in AB-198 grant funding for the Bunkerville sites at its meeting in June 2008 with the condition that the VVWD raise the water rates to conform to the Board's policy on reasonable water rates.
PROJECT STATUS
The Scenic Reservoir and distribution main connection were completed in 2007. The new coagulation-filtration arsenic treatment facilities for the high arsenic wells in Bunkerville were redesigned to include concrete lined drying beds to handle the sludge from the backwash basin.
The coagulation/filtration process takes place in vertical steel pressure filters with dual media filter beds. Sodium hypochlorite is added as an oxidant and disinfectant and ferric chloride is added as a coagulant to the raw water prior to filtration. After filtration, sodium hypochorite is added once again for disinfection and sodium hydroxide is added to adjust the pH of the finished water.
 The design firm, Bowen Collins and Associates, provided project management and inspection. Monthly progress reports were received for all 5 sites. All sites employ the same coagulation-filtration with chemical addition technology for arsenic removal. Sites 29, 31, and 32 required concrete lined drying beds with recirculation of the backwash water. Sites 27 and 28 were permitted to dispose of the sludge into the sanitary sewer with the backwash water being recycled to the headworks of the plants.
The Board for Financing Water Projects made a visit to the construction sites in December 2008. The treatment facilities at Sites 29 and 31 were essentially complete in July 2009. The schematic of the project is courtesy of Bowen Collins & Associates, Inc. Click on the schematic above to enlarge - note that it will open in a new window as a pdf file.
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