I need to bid on a park that is at the lower part of a hill and needs a drain system put in. Water pools in 50% of the park. The park is 175' x 110', soil is glacier runoff (rocks). The drain pipes can be run out the side of the hill after they are run under the park. I was thinking french drains every 20'. Should they crisscross in a grid pattern or would one running perpendicular to the hill then have runners going down the hill every 20' be correct. After putting in the french drain system I would put about 6" of top soil down and level and grade the park since the developer did not. Rock is about $10 a yard and topsoil $12. Any help would be appreciated.