Golfers who show up at the Ala Wai Golf Course expecting to use the driving range are being turned away as a result of a lengthy project to improve stormwater drainage on the site.

The project, originally expected to run through the end of the year, is required under the Environmental Protection Agency’s National Pollutant Discharge Elimination System laws that apply to all larger properties where water is allowed to flow into waterways.

Work on the project actually began in mid-December last year and initial plans called for construction to be done this December. But the contractor is ahead of schedule and is forecasting a July 29 completion, city officials said. Work takes place from 7 a.m. to 3:30 p.m. weekdays and neighbors are being warned of construction noise.

City officials said the $1.3 million project is being assisted by money from the EPA Clean Water State Revolving Fund, which is administered locally by the state Health Department.

About 75,000 people use the driving range annually, which averages to about 200 people a day. Assuming a 10-month closure time, the project will cause about $400,000 in lost revenues, city spokesman Jesse Broder Van Dyke said.

With the exception of the closure of the parking lot fronting the driving range, the rest of the golf course facility is not affected. Ala Wai is considered the busiest golf course in the state, and some believe the nation.

When the driving range project is completed, users will see a recontoured facility that’s fully grassed and irrigated to allow most rain and other water runoff to percolate into the ground instead of flowing directly into the Ala Wai, according Eduardo Manglallan, deputy director for the city Department of Facility Maintenance.

The plan calls for seashore paspalum grass to be planted throughout the 306,331-square-foot driving range, on top of 5,000 cubic yards of topsoil and nearly 1,900 cubic yards of “soil amendments” comprising a mixture that includes granulite bio-recyclable solid pellets generated at the city’s Sand Island Wastewater Treatment Plant.

Once the driving range improvements are completed, the city will begin a related NPDES project to reconstruct and repave the golf course parking lot, including the access road from Kapahulu Avenue.

The project will feature vegetated drainage swale that will capture and filter water runoff before it enters the canal, Manglallan said. That yearlong project is expected to cost $3 million, which will be paid for out of the same revolving fund that’s providing money for the driving range improvements.

The parking lot project is expected to have a “manageable impact” to visitors to the facility, city officials said.

The proposed fiscal 2017 capital improvements budget includes similar NPDES projects at Makalena and West Loch golf courses.