Clean Water Program

Overall, the GBP monitoring tasks are designed to measure compliance with selenium load levels and to detect impacts due to the GBP. Another overall goal of the Project, as described in Section 1.4.1, is to improve, where possible, the current scientific understanding of selenium fate and transport. The monitoring approach provides the opportunity to increase the general understanding of selenium mass balance within the SLD (Grassland Bypass), Mud and Salt Slough and the San Joaquin River.

Data quality objectives (DQO) for the project are defined in the Quality Assurance Project Plan (QAPP) that accompanies the Monitoring Plan. Each agency has established DQOs for every field and laboratory parameter it is responsible for measuring. Agency DQOs are discussed in detail in the text of the QAPP (Section 2.5), and summarized collectively in Table 3 of that document. Discussion of DQOs includes definitions for the quantitative goals of precision, accuracy and completeness, and the qualitative goals of representativeness and comparability.

The interim GBP is intended to remove unusable water from wetland water supply conveyance channels. The project, by combining drainage flow within the SLD, will provide the opportunity for more focused monitoring which may in turn result in improved management of those flows. The project should allow for better measurement of the selenium load being discharged from the Grassland Basin. Further, the monitoring program will provide data which may elucidate the selenium flux (e.g. in-transit losses) between the water column, biota and sediment.

The Department of Water Resources (DWR) measures flow at a number of stations along the San Joaquin River, including Newman, which is located within the GBP area. The DWR also measures flow in Salt Slough at Lander Avenue. These DWR stations (B00470 and B07375) are at the same location as two proposed primary stations (F and G).

The Monitoring Plan is divided into six sections. Section 1.0 (Introduction) describes the framework of the GBP and summarizes the Project. Section 2.0 (Previous Studies and Other Monitoring Programs) summarizes the past and present data monitoring effort undertaken in the Grassland Subarea. The reader will note that this monitoring plan is designed to utilize on-going monitoring, so as to reduce duplication of effort. Section 3.0 (Monitoring Plan Approach) discusses the objectives of the overall Project and the monitoring plan in particular.

Agricultural subsurface (tile) drainage water from irrigated lands currently enters the Grassland Water District (GWD) from the south, where it is mixed with variable quantities of surface return flows (tailwater) from the Central California Irrigation District (CCID) and the other riparian diverters.  The commingled water flows northward through the GWD in ditches and canals leading to Mud and Salt Sloughs and eventually to the San Joaquin River.  The proposed GBP would intercept this drainage water at a point between Dos Palos and Russell Avenue, south of the GWD, and convey it through th

Historically, no other drainage districts in the area have used the SLD for the conveyance of drainage water. The Grassland Basin Drainers (GBD) discharge drainage water through a more circuitous route, utilizing the wetland water supply channels, Salt Slough and Mud Slough, for disposal of the drainage water to the San Joaquin River upstream of its confluence with the Merced River. Agricultural return flows, including GBP drainage water, dominates the flow in the San Joaquin upstream of the Merced for most months of the year.