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major raw-water supply canals(the Delta-Mendota Canal or the California Aqueduct)would be affected by project area drainage. Additionally,local groundwater levels would remain unaffected by the project, as any dewatering necessary for foundation construction would not infringe upon the existing phreatic surface. In the future,it is recognized that area watercourses will continue to be subject to increased discharges resulting from .- encroaching development and associated infrastructure improvement projects.Most natural watercourses serve as receiving waters for stormwater as either direct channeled inflow(via storm drainage)or unchanneled diffuse flow. Each stream exists in a delicate balance of longitudinal profile,carrying capacity,and entrainment load based largely on the characteristics and nature of the draining upland watershed.Where these watershed characteristics change,so too will the hydrodynamics of the flow regime. ` The primary causes for concern are related to the increased flooding potential(resulting from the increased total runoff quantity and maximum peak flows)as well as the erosive potential that these higher flows may impart to the existing natural streambed and banks. State regulations provide protections(e.g.,NPDES permits and Storm Water Pollution Prevention Plans)and standard industry construction BMPs as the best means of protecting against adverse changes in stream hydrology, channel form, and erosion caused by construction practices. Projects with the potential to alter natural drainage flows typically undertake studies (e.g.,Drainage Master Plans) and,where appropriate, seek permits and other authorizations to safeguard against adverse hydrological or drainage impacts. It is anticipated that this level of compliance and adherence to industry good-management practices will continue in the future.Accordingly,the future cumulative impact on area drainages would likely not be damaging to existing streams and rivers in the region. The proposed project would result in a total increase in impervious surface area, capable of generating direct overland flow, from 15%to 47%(representing an approximate 30%or 300-cubic-feet-per-second increase in potential maximum flows under the 100-year probabilistic stone event).Hydrologically, an increase of this magnitude with a 100-year return period could be considerable, depending on the base flows of the receiving waters(e.g.,Mountain House Creek or Old River).Regardless,if the BMPs and other provisions specified in the MHMP provide also for the protection of the downstream reaches of the receiving waters (and not just the stormwater drainages),then it is unlikely that this project would adversely contribute to the future cumulative condition of the region's natural drainages. The proposed project would provide storm drain infrastructure in general compliance with the drainage infrastructure programmed by the MHMP,the Mountain House Master Drainage Plan,and the MHCIP.Both the ., existing and proposed storm drain infrastructure would have adequate capacity to serve the proposed project along with the stormwater runoff to be generated by the balance of the Mountain House community(see Section 4.7, "Drainage").Furthermore,the proposed project would implement all BMPs required by these plans to reduce ` erosion and sedimentation and ensure proper maintenance of the drainage infrastructure. Therefore,the proposed project would contribute a less-than-considerable demand for drainage infrastructure and would contribute less- than-considerable erosion and sedimentation. A less-than-significant cumulative impact would occur. 6.3.7 WATER QUALITY It is accepted that the water quality of the primary natural waterways in the project area as well as much of the Sacramento and San Joaquin Valleys have degraded over the years.The causes are many: long-standing agricultural practices,urban encroachment,industrial development,transportation vehicular exhaust,use of chemical pesticides/fertilizers,etc.Although agricultural lands are diminishing along with the farmland-generated waste discharges that end up in local receiving waters,these lands are being incrementally replaced by urban, commercial,and industrial land uses, each with their own set of new water quality risks. Although direct discharges to receiving waters(through the monitoring and regulation of direct dischargers)can be controlled with varying degrees of success, it is virtually impossible to gauge and control indirect or diffuse College Park at Mountain House Specific Plan III Draft EIR EDAW San Joaquin County 6-9 Cumulative Impacts