Here is the problem. Just when you would most like to be laying on top of it on a blanket in the Seattle late summer sun, that’s when the new grass of Cal Anderson Park will grow best. You’ll need to take your blanket elsewhere.

This August, Seattle Parks plans to begin a process to repair a central section of Cal Anderson where poor soil and drainage have conspired to create dead patches in the lawn in dry months and soppy wet puddles the other 11 months of the year (ha ha). The situation with the soil conditions is so poor that those tufty patches you see throughout the park — that’s not grass. That’s some form of rush — a plant normally found in marshy wetlands.

The Seattle Parks official overseeing the grass repair project said the root of the problem is the soil Seattle Public Utilities chose in the construction of the park on the lid atop the now buried Lincoln Reservoir. “The soil is not well suited to drainage and park use,” said Randy Robinson, senior landscape architect for Parks.

“There’s an intricate relationship,” Robinson said of Parks and SPU. “The good news is that SPU and Parks are working more closely. We still have a couple of these to build.”

Last summer, SPU found itself in a re-do situation with two other lidded city reservoirs as leaks were discovered and an expensive repair process undertaken.

For Cal Anderson, the solution is a $250,000 project to repair the conditions in a 3/4-acre area of the park where Robinson says the grass has struggled since the summer the park was completed in 2005. Robinson said Parks has been complaining about the screw-up for years. SPU is now on the hook for the project budget.

According to a Parks document describing the project, the plan is for a 3/4-acre swath of the northeast section of the park — and a portion of 11th ave parking to be used for construction vehicles and stagin — to be fenced off starting in August. The contractor who wins the job will then carefully remove three to five inches of topsoil while not damaging the sensitive reservoir lid. New drainage trenches will be created and a new layer of sand-based top soil and soil conditioner will be layered over it all. By September, Robinson said, the new grass will be planted and, if everything goes as planned, later in fall the fences will be adjusted and the park pathways reopened.

The grass area will remain fenced through next spring. By summer 2011, if the repairs have worked and the grass is growing, Cal Anderson should be back to its full glory, Robinson said.

In the meantime, there will still be plenty of places to put down your blanket in the park — including Teletubby Hill. Robinson said grass is doing just fine up there.