SU0004916 - Laserfiche WebLink

Home Browse Search

OLD RIVER Old River flows from east to west and into the Sacramento—San Joaquin Delta. Old River borders the northern boundary of the MHMP,approximately 4.8 miles north of the College Park site(see Figure 3-2 in Chapter 3, "Project Description').As described above,Mountain House Creek drains to the southern levee of Old River in the northern portion of the MHMP area north of Byron Road,and ponds there until pumped into Old River. Stormwater runoff generated in and flowing through the MHMP area, including the College Park site, is planned to be conveyed to Mountain House Creek,and subsequently Old River,under the adopted Mountain House Drainage Master Drainage Plan Update(PACE 2003). — EXISTING AND PLANNED MHMP STORM-DRAIN SYSTEM The Mountain House Drainage Plan Update(PACE 2003)was adopted by the MHCSD in 2003 and sets forth the drainage plan for the MHMP area,including for the College Park project site which is located in the upstream (southerly)portion of the MHMP area.The drainage plan identifies a planned storm-drain system to provide _ conveyance for all on-and off-site runoff to Old River as a terminal drain.The planned system incorporates trunk storm-drain lines, secondary storm-drain lines,major open channels,and water-quality basins(MHCSD 2003). Trimark(the Specific Plans I and R developer)has already constructed many components of the planned storm-drain system, including the downstream north—south trunk storm drains m Central Parkway,DeAnza Boulevard,and Mountain House Parkway,as well as Water-Quality Basin No. 1 (WQBI)located at the northwest corner of the Byron Road and Mountain Home Parkway intersection,and has sized this infrastructure to serve the ultimate buildout of the Mountain House community(including development of the College Park site).Trimark has completed the downstream components of the MHC1P,and is developing the upstream components. Per the Mountain House Stormwater Master Drainage Plan Update(MHCSD 2003)and the proposed Specific Plan III 1 Amendment to the Stormwater Master Plan Update(MacKay&Somps 2004),extension of the trunk storm drains southward to the College Park project site,expansion of WQBI,completion of the upstream components of the MHCIP,and development of an on-site storm-drain system,would all be required to provide storm-drain service to the College Park project.According to the College Park engineer,interim on-site detention could potentially allow for some development at the College Park project site before completion of the on-and off-site storm-drain facilities (MacKay&Somps 2004). _ The three north—south trunk storm drains in Central Parkway,DeAnza Boulevard, and Mountain House Parkway serve the developed portions of Specific Plan I. These trunk storm drains discharge to Mountain House Creek, with urban runoff currently diverted to WQB I before discharge or run through smaller water-quality facilities associated with Specific Plan I before being discharged to the creek.The southerly extent of these storm-drain facilities is shown in Figure 3-12 in Chapter 3,"Project Description." EXISTING DRAINAGE CONDITIONS AT THE PROJECT SITE The College Park project site is currently served by agricultural drainage ditches and some drainage pipes or — culverts at street crossings.Drainage is from the south and southwest toward the north and northeast. Runoff water from four drainage watersheds located upstream(south and southwest)of the College Park project site is funneled into culverts under Interstate 205 (1-205)and the Delta—Mendota Canal and onto the project site. The runoff from these off-site drainage watersheds is considered"clean"water because the runoff is generated from undeveloped lands or is treated before entry to the project site.The culverts focus"clean"drainage water from the drainage watersheds to the project site at the southern and southwestern boundaries.The runoff flows over the site toward the north as sheet flow and eventually drains to Mountain House Creek,where it ponds along the southern levee of Old River until it is pumped into Old River by agricultural pumps.Runoff is seasonal and results primarily from precipitation during late fall,winter, and early spring. Oft-site drainage courses would EDAW College Park at Mountain House Specific Plan III Draft EIR Drainage 4.7.2 San Joaquin County