Creating a Solid Foundation for Solar Project Success: Establishing Vegetation Pre-Pile Driving and Phasing for Stabilization
“Without a solid foundation, you will have trouble creating anything of value.”
The rapid establishment of permanent vegetation in a uniform density is the foundation of a solar farm. Vegetation establishment, an often overlooked and undervalued process, will have adverse short and long-term effects on construction and the facility’s operation and maintenance function if not planned and implemented correctly by the general contractors.
Erosion, extended construction schedules, increased budgets, added scopes of work, state and federal interaction, warranty items, and safety concerns are a few of the inherent risks to the project if the seeding process fails to meet the desired intentions. As established, perennial vegetation to a specific density is required in most cases to meet and terminate permitting associated with the National Pollutant Discharge Elimination System (NPDES) and the construction general permit. Contractors adapting to the specific conditions of solar farm construction misleadingly identify this step as reclamation, hence delaying this scope to the end of construction. This one misstep sets in motion an accumulative ripple of financial impacts.
As solar projects continue to increase in size and acreage expanding from roughly 0.25 GW in 2008 to almost 3GW in 2018, the industry has grown tenfold. Common industry size of new solar projects in 2021 currently exceeds 1,000 acres (405 hectares) or more per phase with earth disturbing activities aggressively scheduled to meet the increase in green energy demands and cash-on-delivery expectations of investors.
To meet this demand and requirement of stabilization, the use of larger seeding and farming equipment capable of tackling vast areas efficiently are quickly becoming the standard. Phasing in use of this equipment and using it to its full potential has a limited window of utilization—a window that cannot be reopened once its closed.
Solar photovoltaic (PV) projects that are out of seeding phase can present a unique industry challenge and a significant financial loss through the process of recovery. In the onset of PV installation, the solar infrastructure construction begins with foundation I-beam embedding, which is referred to in the industry as “pile driving.”
The offset rows of I-beams prevent the use of large-scale equipment to seed vegetation and requires the use of less effective and low yielding methods of vegetation establishment. As installation progresses, access issues increase with additional obstacles such as torque tubes, racking and paneling, and other simultaneous construction operations that restrict access.
The high erosion potential associated with lack of stabilization over vastly disturbed areas and ever-worsening ground conditions during construction results in overwhelmed best management practices (BMPs), civil works degradation, discharge events, loss of topsoil, delays in schedule and subsequent stormwater hardships.
When phased properly, seeding operations should follow directly behind final grading or land preparation to establish final stabilization prior to the installation of solar farm infrastructure. Phasing, sequencing activities and seeding directly behind final grading and earth-disturbing activities is not only good practice, and in line with permit language, these techniques comprise a vital window of opportunity with detrimental repercussions if missed.
Planning and Phasing Considerations
During the preplanning phases consider the preconstruction land use. Phasing, BMPs and scheduling are critical to the success of the project. Three primary preconstruction land uses include:
- Range land – Fully vegetated preconstruction.
- Forestland – Fully vegetated preconstruction and fully disturbed areas prior to solar infrastructure construction.
- Agricultural Land (row crop) – Fully disturbed preconstruction and must be seeded preconstruction.
Each of the primary three preconstruction land uses require coordination with the developer, landowner and the engineering, procurement, and construction contractor (EPC). After experience with numerous solar projects across many states, climates, and topographical regions one main difference with solar project construction, as compared to other projects, has become apparent: additional preplanning involvement between the EPC and the engineer of record (EOR) is critical for project success. Typical engineering milestones include: 5%, 30%, 60%, 90% issued for permit and issued for construction (IFC). Depending upon the project the contractor may be required to account for material quantities and cost estimate at the 30% planning milestone. Typically, the 30% plans may not include all the temporary sediment and erosion control BMPs; therefore further discussions with the EOR are recommended. For purposes of this discussion, the bid process and quantity estimation are assumed at 60% plans. The table on the previous page summarizes considerations for the EPC and EOR to discuss for each planning milestone.
Account for Construction Schedule Impacts
The project erosion and sediment control plan and subsequently the EPC’s BMP budget must consider the local weather of the project area and construction duration. The EPC should consult with the EOR regarding known schedule milestones of the project and potential impacts to the phasing of BMP application. Important dates to include are start of construction, temporary seasonal shutdown or winterization, end date of grading and completion of construction. The project schedule and how the schedule correlates with average precipitation and temperatures will present unique challenges or advantages to maintaining existing vegetation, establishing seeding and need to rely on more robust temporary stabilization techniques, such as temporary stabilization with a low “C Factor” and BMPs with a long duration of erosion control effectiveness, when vegetation is not feasible. Furthermore, if a project start date is outside of the typical growing season for cool or warm season grasses or during winter, the need for multiple applications of seeding and stabilization BMPs will need to be addressed and included in the budget.
In some areas, such as Bakersfield in central California, starting a project during the rainy season presents challenges for temporary sediment and runoff control BMPs, but it also presents a seasonal advantage to establish vegetation for preconstruction seeding or for final stabilization of a site area for permit termination. If construction starts during a rainy season, the EPC should anticipate more BMP maintenance as well as additional sediment and runoff controls to maintain compliance.
In other areas, such as Lexington, Kentucky, the rainfall is more evenly dispersed throughout the year. Seasonal temperatures changes could impact BMP applications and the potential for snow and freezing temperatures needs to be considered. Project activity spanning from fall into winter must account for fall temporary stabilization for all non-vegetated areas. The freeze/thaw cycle, snowmelt and rain runoff can result in significant rutting of exposed soils on solar sites. Soils disturbed from non-grading activities must also be stabilized prior to spring and dormant seeded to control runoff during spring rains and establish the vital vegetative cover for successful erosion control.
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About the Experts
Aaron Mlynek, CPESC, CESSWI, CISEC, QSD/P has over 20 years of NPDES compliance experience. He has been part of wind and solar projects in approximately 35 different states. He currently manages NPDES/SWPPP compliance services at Westwood Professional Services, Inc. His primary focus is on corporate quality control and implementing industry standards for services, products, and compliance for Westwood clients nationwide.
Joseph Ridley, CCIS, QSWPPP, CESCL has over 16 years of experience in the renewable energy industry and currently focuses on risk minimization through effective erosion and sediment control planning and phasing for Westwood Professional Services. He specializes in environmental process, permitting, regulations and compliance. His past experience includes working for an Engineering, Procurement and Construction contractor as well as consulting.