{"id":64953,"date":"2007-10-02T21:32:33","date_gmt":"2007-10-02T21:32:33","guid":{"rendered":"https:\/\/zonda-develop.go-vip.net\/concrete-construction\/article\/processing-success_o"},"modified":"2007-10-02T21:32:33","modified_gmt":"2007-10-02T21:32:33","slug":"processing-success_o","status":"publish","type":"post","link":"https:\/\/zonda-develop.go-vip.net\/concrete-construction\/projects\/infrastructure\/processing-success_o\/","title":{"rendered":"Processing Success"},"content":{"rendered":"
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The coastal city of Warrenton, Ore., was at a crossroads in the mid-1990s.<\/p>

Population growth and an overloaded sewer system had overwhelmed the city’s 45-year-old, 25-acre facultative lagoon system, leading to National Pollutant Discharge Elimination System (NPDES) permit violations\u2014just when the city of 4400 residents was placing additional emphasis on conserving and protecting the environment.<\/p>

In 2004, the Oregon Department of Environmental Quality (DEQ) announced it would not approve any sanitary sewer line extensions until the city came into compliance with current NPDES discharge requirements. This essentially halted the city’s growth by keeping sewer lines from being built for new subdivisions as well as new industry.<\/p>

A happy medium had to be found.<\/p>

The solution: Warrenton signed a mutual agreement and order with the DEQ outlining the schedule and steps it would take to study, plan, design, and construct a new wastewater treatment plant that includes three sequencing batch reactor (SBR) basins and 1 mile of outfall pipe into the Columbia River.<\/p>

With these additions, the public works department can prepare for anticipated residential and commercial population growth of 60% over the next 20 years while keeping the environment at the forefront of the city’s social and economic awareness.<\/p>

A Team Approach<\/b> <\/p>

Warrenton officials selected local engineering firm HLB Otak Inc. to complete its plant improvements. When the city and DEQ established the need for a new plant, HLB Otak turned to other design professionals to join the team. Ledby the city of Warrenton, the team consisted of H.R. Esvelt Engineering as design engineer, Richard Sample Engineering for electrical design, Structural Research Co. for structural design, and HLB Otak for site civil engineeringand general oversight-construction management.<\/p>

In February 2005, the city and DEQ began the final plan review for the new plant. Funding for the $7.9 million project came from the Oregon Clean Water State Revolving Fund, which is supported by annual grants from theEPA. The plans for the treatment plant consisted of three concrete-lined SBR basins; new site piping; influent force mains; and an influent, effluent, and operations building.<\/p>

Warrenton officials opted for an environmentally and economically prudent activated sludge process and UV light disinfection system that uses no chemicals, produces no toxic residuals, and has no adverse impact on the environment, the Columbia River, or the multiple fish and marine species nearby.<\/p>

Plant plans included a unique feature that enables operators to reach out to the public and teach the importance of caring for the environment: a 200-gallon aquarium that is continually filled with treated effluent. This aquarium, home to indigenous wildlife such as bass, blue gill, freshwater clams, and a Red Eared Slider turtle, provides a tangible display for the public to learn about the importance of caring for the symbiotic environment.<\/p>

Creative Construction<\/b> <\/p>

Construction started in late 2005. Five months in, a horizontal directional drilling (HDD) company was hired to install the new outfall by boring 80 feet below the Columbia River bottom and horizontally drilling and pushing 4407 linearfeet of pipe from the plant site to the Columbia River.<\/p>

Design engineer firm Cosmopolitan Engineering Group handled this separate contract. Normally, HDD involves creating a bore hole and pulling pipe to anexit hole. However, The HDD Co. Inc., Orangevale, Calif., proposed two changes: forward-drilling the 18-inch bore hole from the land side to under the surface of the Columbia River shipping channel, then pushing a steel pipe with a treated Permalock coating. Once reaching the exit hole, divers wouldbe shuttled by barge to install the 40-foot diffuser. This process created the treatment plant outfall.<\/p>

These innovative construction methods served two purposes. First, pushing rather than pulling the pipe enabled the crew to complete most of the installation from land, thus avoiding interrupting the crucial shipping lanes in theColumbia River. Second, this strategy helped mitigate the effects of the harsh winter weather and water currents, which would make handling the pipe extremely challenging in light of the Oregon Fish and Wildlife Department-enforced in-water work period, which limits construction in the river to four months: Nov. 1 to Feb. 28.<\/p><\/div>

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Treating The Wastewater<\/b>

Warrenton’s previous facultative lagoon system had two 12-acre cells in series. In this method, algae populates the top layer of the water column, using sunlight and producing oxygen. Aerobic bacteria grows in between, and anaerobic bacteria populates the bottom layer to treat the wastewater of organics and nutrients. The wastewater, moved by gravity, then heads through a chlorine contact chamber where it’s disinfected with chlorine gas before beingdischarged into a constructed drainage ditch; it then flows into the Columbia River during low tides.<\/p>

In the new process, the influent building receives incoming wastewater, which is screened and subsequently treated by a grit removal system before being dispersed into one of the three basins. The activated sludge technology uses microorganisms (bacteria) present in the reactors of the SBR basins. Treatment consists of filling, reacting, settling, and decanting. Nitrification and denitrification can occur with alternating aeration and mixing regimens.<\/p>

Within the SBR, the blowers aerate the wastewater through a diffused aeration system, starting the bacteria’s aerobic reaction. These bacteria are retained to maintain sufficient quantities. When the aeration process ceases (i.e., theblowers stop), the biomass settles and a decanter removes treated effluent from the top while the bacteria settle to the bottom. Sludge is then pumped to one of two digesters.<\/p>

The decanted effluent flows to the final process and undergoes UV disinfection. This type of disinfection is user-friendly for operators and prevents the spread of waterborne diseases to downstream users, leaving the environmentfree of any residual effect that can be harmful to humans or aquatic life. Once the effluent is treated through the UV process, it is ready to be discharged through an outfall pipe to the Columbia River.<\/p>

All Systems Go<\/b> <\/p>

The plant began operations June 2006 (though not fully operational until January 2007) and in less than a year, city manager Ed Madere received test results for the plant’s first batches of effluent. Initial laboratory test samplesyielded =4 parts per million (ppm) biochemical oxygen demand test results, =2 ppm total suspended solids, =0.1 ppm nitrogen as ammonia, and =2 fecal coliform. The treated water is also cooler than the ColumbiaRiver, translating into cleaner, safer water than the river itself.<\/p>

In addition, the project had less than 3% in change orders and came in on schedule and under budget on construction-management costs.<\/p>

The advantages of the new wastewater treatment plant include greater flexibility, improved operational reliability, lower investment and recurrent cost, energy savings, and a smaller plant footprint. Warrenton’s facility alsonow has the capability to treat 2.3 mgd with a peak instantaneous flow of 4.7 mgd, depending on how the plant is being operated.<\/p>

Equally important, the new plant illustrates the balance that this coastal community has found between accommodating growth, ensuring the vitality of the environment, and promoting the viability of the local economy. These factors, combined with the site’s scalability to four basins if the growth rate requires it, have positioned Warrenton to meet both today’s desires and tomorrow’s demands.<\/p>

Forrester is a senior engineering technician at HLB Otak, Seaside, Ore.<\/i><\/p>

Articles<\/b> <\/p>