The Decant Facility - Another GEM Success Story6/10/2009
The Decant Facility located at 11203 NE 76th St. and is a multi-agency facility. It will be used at this time by Clark County, City of Vancouver and WSDOT. Mission Clark County is committed to providing an environmentally sound system for the handling of waste generated from the cleaning of stormwater drainage systems. Clark County has built a decant facility for treatment and safe disposal of stormwater waste.
This facility can be used by all municipalities within Clark County, including the City of Woodland. Introduction A Decant Station is a large concrete pad where maintenance crews can discharge waste material retrieved from storm drain catch basins, drywells and piping systems. Maintenance crews operate what is called a Vactor truck that uses an industrial vacuum pump to pull waste material from clogged drainage systems. The material is vacuumed into a holding tank on the truck for transport and later processing. This waste material consists of dirt, gravel and sediments that have settled out of stormwater in solid form, semi-solid or slurry condition.
The common name for this material is Vactor waste. Vactor waste has been known to contain some petroleum, heavy metals and other contaminates in low concentrations. There are many reasons for contaminates in storm drainage waste. As rain water runs off impervious surfaces, it collects contaminants from the surface. Many of the contaminants adhere to small soil particles and dust located on the surface. This dirt is then transported by stormwater runoff to a drainage system where it settles and collects. Most of the contaminants come from automobiles that expel oils and greases, petroleum, lead, copper, zinc, asbestos and chromium onto the impervious surfaces.
How the Decant Facility works
The Decant Facility is a series of three sloping pads and two holding tanks, that allow the solids to settle while the liquids continue on through an oil water separator to the first holding pond. The material will accumulate in this pond to the depth of approximately two feet until it over flows into the second pond where it resides before testing and/or disposal through the Hazel Dell sanitary sewer system. The water is transported to the Salmon Creek Treatment Plant where it is treated along with household sewage. The two ponds are lined with 24 mil PVC to prevent contamination of the underlining soil. Periodically, County Crews will take the solids off of the concrete sloping pads and store them on an asphalt pad that slopes toward the decant, capturing any excess liquids. The solids will remain there long enough to drain, dry and aerate. The solids are screened, which separates the large rocks out, then the material is sent down a conveyor belt where the garbage is picked out, leaving only natural material. The solids will then be periodically tested and disposed of appropriately. Uses for these solids involve fill on road projects in where they will be covered with an impervious surface such as asphalt. This will keep any material from leaching into the ground. Vactor waste that tests out with low oil hydrocarbons may be placed within public right-of-ways as fill material. No material will impact wet lands, streams or any other bodies of water.
History of Clark County's Decant Facility
The Decant Facility started out to be a joint project between Clark County, WSDOT, City of Camas, City of Washougal and the City of Vancouver in 1994. As these other agencies developed temporary decant facilities, Clark County decided to complete the project within it's own budget. Since the completion of the Decant Facility in May of 1998 there has been a number of public agencies interested in using it. The City of Vancouver, Washington Department of Transportation, City of Camas, and City of Battle Ground are some of the interested parties. There are also several companies that offer Vactor service to private property owners that are interested in using the site, since it offers a safe and effective disposal for Vactor waste. The site was permitted for the disposal of publicly collected waste only. There are no plans at this time to open the site private sector. With the proposed increase in traffic to the facility, road improvements will need to be done before Clark County can let other agencies use the facility. The City of Vancouver and WSDOT are looking to fund the cost of the road frontage improvements. The completion of the facility was in May,1998. Between the completion date and February of 1999, Clark County has never had to dump into sanitary sewer. Through the summer months there is quite a bit of evaporation, eliminating the water in the holding ponds. The Clark County Road Operations Department has been the only one using the facility at this time and has dumped approximately 800 cubic yards of vactor waste.
Regulations Governing Operation of Decant Facility.
The most notable requirements of discharge authorization into Hazel Dell Sewer are:
- Only water collected from the cleaning of storm drains is allowed to be discharged
- Track every discharge by facility user's name and origin of material collected
- Test liquid waste for metal and oil pollutants by a certified laboratory
- Field test liquid waste for settable solids and pH
- Submit a quarterly report on test results and usage to Hazel Dell Sewer Dept.
Working with Hazel Dell Sewer and the Southwest Washington Health Department, Clark County Road Operations Division will be testing for the following substances, and their allowable limits:
Parameter Allowable Limits
Arsenic 4.0 ml/L
Nickel 5.0 ml/L
We recycle everything we take out to the facility. The rocks are picked out and pushed over the bank to refill the pit and the garbage is picked out and taken to the dump, while the grit is used on road projects. We use the Offender Status Crews (OSC) to pick out the garbage, this saves the tax payers money while supplying a beneficial service.