Minimizing Environmental Impact During Creek Culvert Rehabilitation – Wildlife and Water Quality Safeguarded

Lafayette, CO – The City of Orinda, California sits within the Diablo Mountain Range just nine miles east of Oakland, California. Local roads wind through the rolling hills next to many main streams that run through the mountain range. These tributaries empty into the Pablo Reservoir and the Upper San Leandro Reservoir.

These seasonal streams are environmentally sensitive for local aquatic life and drinking water derived from the reservoirs. Many large culverts were installed in the 1940s and 50s to take these streams under the roads, which are now showing signs of fatigue and some with their inverts completely corroded.

The City recognised the corrosion as an issue and called on Walnut Creek-based HDR, Inc to evaluate which trenchless technology would be a feasible repair option. HDR considered slip lining, cured in place pipe and spray applied geopolymer mortar.

Geopolymer mortar was selected based on its ability to minimize environmental impact. It was identified as having the least impact to surrounding area as well as delivering the ability to reinstate flow through the culvert immediately after installation. It also maintained the hydraulic capacity of the rehabilitated culverts and had a lower overall cost of installation.

The City required a permit from the California Regional Water Board for the project and the work could occur only during the non-rainy season. The permit required ecotoxicity data on the selected material, to determine the time required before the stream could start flowing through the culvert after rehabilitation.

The contractor chosen to complete the rehabilitation was National Plant Service, a Carylon Company with the chosen material being GeoSpray 61 by GeoTree Solutions. The decision was made based on the material holding ‘Acute Toxicity of Effluents and Receiving Water to Freshwater and Marine Organisms, 5th Edition’. This indicated that flow could be reinstated after only two to four hours of curing. GeoSpray 61 is also NSF 61 certified for drinking water standards and has a high flexure strength, which meant the installed thickness of the material could be reduced, compared to other materials and systems on the market.

In preparation for the rehabilitation work, a diversion was put in place which would run the summer creek flow through a gravity flow bypass pipe without the use of a pumping system, which could negatively affect aquatic life. The bypass did not change the flow of the creek up and down stream during the rehabilitation, did not increase turbidity or increase erosion from the discharge of the bypass pipe. The bypass was installed directly through the pipe being rehabilitated which allowed for the gravity flow to occur. The city hired LSA from Point Richmond, California to have a wildlife biologist on site to verify that the bypass and the installation of the GeoSpray 61 was not affecting wildlife.

National Plant Service Manager Danial Solano said “A temporary dam was installed using gravel filled geotextile bags and plastic. This directed the water from the upstream side of the culvert into the bypass pipe. The bypass pipe exited the culvert and drained into the creek downstream.”

The project consisted of three culverts at different locations within City of Orinda that each sat on different tributaries. One was a 72 inch by 110 inch acm arch culvert, the other two were cmp culverts measuring 66 inch and 60 inch. All mixing and pumping operations were carried out on a spill control pad within a tarp tent to minimize dust release. A disposal container sat next to the mixing area for the cleaning of hoses that conveyed the material into the culvert to the spray head applying the material.

GeoTree Solutions engineers calculated the thickness required to adequately line the culverts. The thickness applied was 1.5 inches for the 60-inch and 66-inch diameter pipe and 1.75 inches for the 72-inch x 110-inch arch culvert. The invert was partial deteriorated in two of the culverts. These required filling
with GeoSpray 61 to eliminate water movement under the pipe which could cause issues later. Again, GeoSpray 61 was used to eliminate any ecotoxicity issues with stream. All the geopolymer was hand sprayed with the finial ½ inch thickness of the structural rehabilitation spin casted.

The construction equipment, which measured 10ft by 75ft, was stagged along the street to ensure it did not affect traffic flow. For the arch culvert the equipment was along the side of a residence driveway but access was still possible. Work could be carried out between 8:00 am and 4:00 pm to eliminate disruption to the residences. Each culvert from mobilization to completion took just five days.