Flooding Is Always a Threat for a Riverside RV Park

Securing the replacement wastewater system for California’s River Bend RV park was a major design challenge
Flooding Is Always a Threat for a Riverside RV Park
The AdvanTex (Orenco Systems) units at the River Bend RV park in Forestville, California, were placed at grade. Even though the Russian River is at the park’s edge and tends to flood, lids on the AdvanTex units are tight enough to prevent infiltration. During construction, the river flooded twice, and water was high enough to lap at the edge of the tanks.

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Located in the heart of California wine country, the River Bend RV park needed a new wastewater system to serve 50 recreational vehicle sites. But, the park is also on the shore of the Russian River, which empties into the Pacific Ocean. That means the property is prone to flooding.

After 10 years, the previous system was failing. The old leach lines had collapsed.

“It sounded to me as if those alluvial soils — sand and silt — migrated into those drainfield trenches,” says Peter Lescure, principal civil engineer of Lescure Engineers Inc. in Santa Rosa. His firm was hired to design the new system.

The owner had land intended for the repair system, but as they did the survey work, Lescure and his staff found the property’s boundaries were not as clear as the owner thought. They took another look at the RV park property and realized there was just enough space on a high point, next to the road, for a wastewater system using Orenco Systems AdvanTex AX100 modules.

Pumps and dripline

Wastewater enters the system at a receiving station, a 2,000-gallon concrete tank near the river and at a lower elevation on the property. Then, wastewater is pumped uphill through 250 feet of 1 1/2-inch Schedule 40 force main by a pair of Orenco PFEF4011-B pumps. On the uphill end are three 2,000-gallon, concrete septic tanks connected in series and placed on high ground next to the public road that runs past the park. The last tank in the series is equipped with an Orenco effluent filter.

Water flows by gravity through the septic tanks and into a pair of 2,000-gallon, concrete dosing tanks. A pair of Orenco PF500712CV-10 pumps doses one AdvanTex AX100 unit. Effluent from the tanks is split, with 80 percent going back to the dosing tanks and the other 20 percent flowing to a pair of 2,000-gallon pump tanks.

Three Orenco UV units are placed at the inlet of the dosing tank. A pair of Orenco PF100511CV-20-FC pumps moves water to the dripfield.

The dripfield is 1,710 linear feet of Geoflow, but the tubing is divided into three zones. Each zone is further subdivided into four sections of varying width. Width depended on what would fit the space because each section is placed between the RV parking pads. These pads are on high ground in the park, above the river’s usual floodplain. A HydroTech hydraulic distribution valve splits the flow to the three drip zones.

Near those zones is an area of land that could accommodate another 1,630 linear feet of dripline for future reserve to augment the primary field if it becomes stressed. This is also where the failed leachfield of the previous system was located. Lescure believes the fine, cohesionless alluvial soils migrated into the drain rock and leach line pipes of the old field and prevented effluent from entering.

The aeration fan for the AdvanTex units is located above grade — and above the river’s flood level — on a platform that was already in place. It’s where utility power enters the property and where the main switch panel for the park is located. The Orenco control panel running the system is on the same platform.

Orenco risers and lids were used throughout the project. Concrete tanks for the project were made by Selvage Concrete Products of Santa Rosa.

Ready for floods

The reality of flooding along the Russian River also caused Lescure to look at other potential problems. The system lies within the 10-year floodplain.

“You need an air intake for the AX100, so I put on a Wager air vent that is designed to block water from flowing in. I knew about it because of a water system I designed for a flood zone a couple of years ago, and I used the same vent on the well there,” he says.

The site flooded twice during construction. The recirculation tank for the AdvanTex unit is typically only one-quarter to one-third full, so it can float. The dosing tanks for the drip system are also typically less than one-quarter full. Those tanks were covered with 12-inch-thick, anti-flotation concrete slabs located at grade.

“We left the AX100 sitting totally above grade in this case. Its lid is fairly watertight. The water might rise 2 or 3 feet above it in a heavy flood. In the floods we had during installation, water lapped at the edge of the AX units,” he says. The AX100 is bolted to a 12-inch-thick, anti-flotation concrete slab located at grade.

Originally Lescure designed the system with fiberglass tanks, but there was a delay in obtaining those and the equipment to handle them, so the owner opted to use concrete tanks that were immediately available.

Lescure and his staff laid out the dripline sections, and allowed installer Carl Van Dyke & Associates the flexibility to lay some of the dripline a bit closer. Whether lines are 24 inches on center or 23 doesn’t matter much in the end, Lescure says. And Carl Van Dyke had to compress the line spacing in one spot where there were some trees the owner did not want to lose.
Water from the driplines irrigates turf. “I don’t know what he has in there — it’s like Bermuda grass — but the owner says it grows like crazy,” Lescure says.


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