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installed along portions of the site perimeter to provide proper slope for utilities or to provide adequately sized flat area in the rear yards. Staff finds the proposed grading to be minor and generally acceptable. Staff is recommending a few relatively modest changes which it believes would enhance the overall project. First, staff recommends that short (up to approximately 2.7- foot tall) retaining walls be installed along the rear property lines of Lots 10-13 and 16-17 in order to eliminate the 2:1 slope bank in the rear yards and to maximize the flat, usable space. Second, Lots 32-40, 44-51, and 78 would have up to a 3.5-foot tall retaining wall along the rear property lines. A seven-foot tall precast wall would be located on top of this retaining wall, resulting in up to a 10.5-foot tall wall as viewed from the residences where there could be a 10- foot rear yard setback to the home. Staff feels that a 10.5-foot tall wall would be overbearing on these properties. Since the seven-foot wall height is not required for noise mitigation at this location, staff is recommending that the soundwall either be lowered in height or be designed with openings in the upper portions of the wall. Conditions of approval address these items. Drainaee Plan In order to reduce stormwater runoff and pollutants from the site, drainage from the roofs and lot surface drainage would be conveyed to and treated by grassy swales between the homes and sidewalk/street. Bioretention and landscape-treatment areas would be located in the common open space areas. The project would also include an underground storage basin in order to match pre-project runoff from the site. These are types of stormwater runoff measures that are strongly supported by the Regional Water Quality Control Board and local agencies like Pleasanton implementing the urban clean water runoff program. Drainage from most of the private roads would be conveyed to media filtration vaults (i.e., oil/water separators) below the roadway. Staff notes that media filtration units are no longer a preferred stormwater treatment measure by the Regional Water Quality Control Board and local agencies implementing the urban clean water runoff program as they require regular maintenance and do not provide an effective means to treat both the quantity and quality of stormwater runoff from a site. Therefore, staff recommends that the applicant utilize an alternative storm water treatment for the roads and that its design be shown on the tentative map plans. Geotechnical Study A Zone 71ake (formerly Hanson Aggregates quarry) is located to the north and northeast. The top of the bank of the lake is approximately 85 feet from the northern perimeter of the project site. The lake's southern slope bank is steeply sloped (roughly 1.5:1 to 2:1). Portions of the slope bank are unstable and Zone 7 is working with the former owner to repair it. A geotechnical investigation was prepared by Cornerstone Earth Group to evaluate the physical and engineering properties of the subsurface soils and prepare recommendations for site work PUD-74 Page -13 - June 25, 2008