Where does the groundwater come from?
The deep aquifer has a strong hydraulic connection to the Columbia River. The deep wells show a clear tidal response and the fluctuation of the static water level inside the well column correlates closely with changes in tide. Isotope analysis is a way to match water chemistry signatures of different water sources and draw inferences about where it is coming from. Although the actual water chemistry is different between the Columbia River and the deep aquifer due to filtration through thick layers sand, silt and gravel, the isotope analysis indicates the deep aquifer is recharged by the Columbia River.
How long will the groundwater supply last?
Our testing indicates there is an abundant supply of water available from the aquifer which will ensure a safe and sustainable water supply for years to come. In the fall of 2009, we constructed and pumped a test production well continuously at a rate of 5.5 million gallons per day for 36 days. While it is typical to pump a test well for only a few days, we pumped for an extended period of time to capture any changes in groundwater quality caused by pumping and confirm the viability of the aquifer as our municipal water supply. Using our network of 17 monitoring wells in and around the Mint Farm, along with sampling from other water sources, we collected and analyzed water quality and flow data. Our test pumping showed very little effect on the aquifer, and that it recharged continuously during our pumping. We are confident the aquifer will easily meet our needs and remain sustainable when we begin pumping 10 to 20 million gallons per day (MGD) from the aquifer.
How do I know the groundwater won’t become contaminated?
An extensive sampling program collected numerous soil and water samples from multiple locations and performed more than 14,500 analytical tests to identify any potential contaminants in the groundwater. In addition to contaminants that are regulated by the State for drinking water, we also tested for non-regulated contaminants, emerging contaminants (pharmaceuticals and personal care products) that may be of concern in the future, and compounds specific to local industry. In all of these tests, naturally occurring iron, manganese and arsenic were the only contaminants detected at levels which warrant treatment.
In addition, a network of monitoring wells (or sentry wells) has been constructed around the perimeter of the Mint Farm and proposed well field. These monitoring wells will become a critical part of a Well Head Protection Program and will be regularly monitored for changes in water quality. They are intended to safeguard the well field by providing early detection of potential contaminant migration, allowing the City several years advance notice to install additional treatment equipment or implement an alternative solution.
While drilling the first 17 shallow and deep monitoring wells, soil samples were collected to confirm that a confining layer exists which is very resistant to water seepage, and that confining layer protects the deep aquifer from potential contamination at the surface. In addition, the deep aquifer is under pressure, which prevents potential shallow contamination from migrating into the deep aquifer. We constructed a full size production well and tested the well by pumping it at 5.5 million gallons per day continuously for 36 days and the pressure in the aquifer dropped only the equivalent of 3-feet (less that 2 psi), confirming that the aquifer will remain under pressure after our plant begins operation. We collected water samples before, during, and after test pumping, specifically looking for indications of migration of potential contaminants, and actually found that the water quality improved slightly during pump testing.
What is in the groundwater?
The groundwater contains small amounts of naturally occurring iron, manganese and arsenic.
Iron and manganese are not considered a risk to human health and federal regulations do not require treatment to remove them from drinking water. Many people take vitamin and mineral supplements containing iron and manganese, and when ingested in small concentrations, both can provide a health benefit. However, at the concentrations found in the Mint Farm aquifer, state regulations do require treatment because iron and manganese cause objectionable aesthetic issues like taste, odor, color and a tendency to stain. The City plans to treat for iron and manganese removal in order to produce high quality drinking water and prevent those types of problems.
The groundwater also contains trace amounts of naturally occurring arsenic. For many years, the drinking water standard for arsenic was 50 parts per billion (ppb). In 2004, regulations tightened the drinking water standard for arsenic from 50 ppb to 10 ppb to lessen people's long-term exposure. The groundwater at the Mint Farm contains approximately 6 ppb of arsenic, roughly one-half the allowable limit. At that concentration, drinking water regulations only require that we notify our customers that arsenic exists above the specified reporting level. Our current water source, the Cowlitz River, also contains arsenic but at lower levels. Although not required, the City plans to treat for further arsenic removal and reduce the arsenic concentration to approximately 2 to 3 ppb.
What will the groundwater taste like?
A pilot study was performed to find out whether the groundwater could be successfully treated to meet and exceed drinking water standards. Conventional filtration using granular media was found to be very effective in treating the groundwater to provide high quality drinking water that is colorless and odorless. A taste test was conducted using bottled water, treated groundwater, and city water from two different locations. While bottled water generally scored the highest, the wide variability of scores for the other three sources demonstrated there was no discernible difference between surface water from the existing water treatment plant and treated groundwater from the Mint Farm.
Will the groundwater stain my laundry and household fixtures?
No. It is not uncommon for groundwater in the Longview-Kelso area to contain some amount of iron and manganese. Left untreated, raw water containing iron and manganese will oxidize when exposed to air (as it leaves the tap) and these minerals will change from a colorless, dissolved form to red-brown (iron) or brownish-black (manganese) particles. If not removed from the water, iron can cause reddish-brown staining of laundry, porcelain, dishes, utensils and glassware. Manganese acts similarly but causes a brownish-black stain. Soaps and detergents do not remove these stains, and use of chlorine bleach can intensify the stains.
The City intends to treat for iron and manganese removal in order to prevent the problems associated with staining and to prevent the build-up of iron and manganese deposits which can collect in pipes, pressure tanks, water heaters and water softeners.
Why not re-build the existing water treatment plant?
The existing water treatment plant on Fisher’s Lane was originally constructed in 1946. Despite upgrades to increase capacity in 1960 and 1980 and a regulatory upgrade in 1998, much of the facility is aged and failing. Several of the concrete structures have deteriorated to the point that is simply not practical to restore those facilities.
Maintenance requirements are increasing and the plant struggles to keep up with demand given frequent equipment and structural failures. Eleven filters failed in the last ten years, including three catastrophic failures in recent years which were declared emergencies by the City Council in order to expedite their repair. While care is being taken to prevent this from happening again, more filter failures are expected and the cost to repair another catastrophic failure is on the order of $140,000. In addition, operational and maintenance problems with the intake structure and intake pumps due to the sediment in the river are ongoing.
If the existing water treatment plant were to be rehabilitated, it would be necessary to keep the plant in operation throughout construction. In order to do that, construction must be phased to maintain plant capacity to meet water demands year-round while making the needed improvements. Three construction phases are necessary, requiring approximately nine years to complete at an estimated project cost of $52.6 Million.
What’s wrong with staying in the Cowlitz River?
The problems with staying in the Cowlitz River are three-fold.
Volcanic debris continues to be washed down the Toutle and Cowlitz Rivers from the eruption of Mt. St. Helens in 1980. In the spring and winter, high turbidity caused by suspended silt and sediment in the water significantly reduces plant capacity. Spring run-off and winter storm events can raise the turbidity in the river above 2,000 Nephelometric Turbidity Units (NTU) for sustained periods of time. This requires reducing the plant output significantly in order to reduce the turbidity to below 5 NTU and meet other drinking water regulations.
In the summer, with the elevation of the river bottom continuing to rise from sediment deposition, sand bars and other sediment deposits threaten to leave the intake dry. In 1986, the U.S. Army Corps of Engineers (USACE) constructed a dam on the Toutle River to capture sediment before it reached the Cowlitz River. In 1998, that structure reached capacity and flow began passing over the spillway, bringing more silt, sand and sediment with it. In 2002, the USACE projected the Cowlitz River bottom would raise 9-feet at the City’s intake structure by 2034. But by 2006, depth measurements taken at the mouth of the Cowlitz showed the river bottom had already filled in roughly 12-feet. In 2005, the City constructed its own 8-foot dam in front of the intake structure to prevent it from being silted in, but the dam was overtopped the very next year. And while the USACE recently completed a dredging project in the lower Cowlitz, funding is not available to dredge far enough upriver to reach our intake structure at River Mile 5.2 and maintain that dredging effort year after year.
Finally, although the City has obtained a dredging permit allowing emergency maintenance dredging to maintain a sump in front of the intake structure and prevent sediment from blocking the intake, the dredging permit requires the intake structure be upgraded to meet current fish code requirements. Currently, the openings size in the screening of the intake structure is too large to prevent recently hatched fish from being entrained, the structure lacks the required fish return to divert entrained fish back out to the river, and the flow velocity at the face of the intake screening is too high, exacerbating the fish entrainment issue. However, we are already experiencing intake screen failures due to the buildup of sediment against the screens. Smaller openings in the screening will prevent coarser sediment from passing through and add to the problem by causing plugging and sediment buildup more quickly.
Why not move the water supply intake to a better location on the Cowlitz River or Columbia River?
The problems in the Cowlitz River with moving sandbars and turbid water are not specific to the location of the intake structure at River Mile 5.2. Moving the location of the intake structure to a wider or deeper section or a bend in the river that historically seems to stay scoured out does not address the larger problem of sediment transport. River training structures such as rock dike fields, submerged pile dikes and Iowa vanes have been suggested as a way to improve water flow but all of these would require extensive modeling evaluation and there is disagreement amongst river experts about whether or not it would work. Rock vanes installed in front of the intake structure in 2005 to promote flushing flows across the face of the intake were buried by sediment within the first year of operation.
The Cowlitz River and Columbia River are federally defined as navigable waterways and fall under the jurisdiction of the U.S. Army Corps of Engineers. Construction in or over the river, excavation or discharge of material into the river, or any work which affects the course, location, condition, or capacity of the river requires approval and permitting from multiple state and federal agencies. The permitting process to construct a new intake structure on the Cowlitz River or Columbia River is expected to be lengthy, difficult and expensive. And to further complicate the situation, NOAA Fisheries is taking a close look at adding Pacific Smelt to the list of Endangered Species in response to a recent petition from the Cowlitz Tribe urging smelt protection in the Columbia River and its tributaries. Salmon and steelhead fish are already listed as endangered species, making the process and conditions of any permit to construct and operate a new intake very complex, if it is possible at all.
Finally, the cost of a relocating the intake to a presumed better location on the Cowlitz River or to the Columbia River, together with rehabilitating the existing water treatment plant, was evaluated early on in the planning process and determined to be not cost effective. In order to avoid similar sedimentation problems at a new intake on the Cowlitz River, the intake would need to be located upstream of the confluence of the Toutle River (the primary source of the sediment). The distance from an intake structure at either location to the water treatment plant on Fisher’s Lane and the need for a river crossing in order to route a raw water main back to the plant make the total project cost prohibitive. In 2007, the cost to install an intake structure upstream on the Cowlitz River and rehabilitate the existing water treatment plant was estimated at $66 Million. And the cost to install a Columbia River intake and rehabilitate the existing water treatment plant was estimated at $72 Million.
How much will the new groundwater supply cost?
Total project costs for the new water plant and groundwater well facilities, including design and construction, are currently estimated at $38.7 million. As with all construction projects, this cost estimate is subject to change if unforeseen events, changed site conditions or other complicating factors impact final design and construction.
When will the new water plant be finished?
In late January 2010, the City Council will decide whether or not to continue developing a new groundwater supply at the Mint Farm, and how quickly to proceed with the project. If approved, final design of the treatment plant will take about 12 months to complete. Construction of the groundwater wells could begin within 5 months and be completed while the treatment plant design is still underway. Construction of the new plant will require about 18 months to complete. The total time required for design and construction is estimated to be about 2½ years. If a new treatment plant is brought online, the existing plant will be de-commissioned, abandoned and eventually demolished.
If the City Council decides to rebuild the existing treatment plant, that project is estimated to take about nine years to complete. Because the existing plant must remain operating at full capacity throughout construction to meet our customers' demand for water, the design process is much more complex and time-consuming. Additional capacity must be built before the existing facilities can be removed from service for rebuilding, and all work must be phased to keep the plant fully operational during construction.
