4.2 HYDROLOGY AND WATER QUALITY

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1 4.2 HYDROLOGY AND WATER QUALITY INTRODUCTION This section provides information regarding hydrology and water quality in the vicinity of the proposed reclaimed water use areas. Following an overview of the regional and existing setting in Section and the relevant federal, state, and local regulations in Section 4.2.3, project-related impacts and recommended mitigation measures are presented in Section As explained in Section 1.0, the discussion and analyses in this SEIR tier from the information and conclusions included within the 2006 City of Hollister Domestic Wastewater System Improvement (DWSI) and San Benito County Water District Recycled Water Project (RWP) EIR (2006 EIR). The 2006 EIR described, in general, what potential environmental effects may be expected from the development of reclaimed water sites and the extension of water distribution pipelines, and how these impacts are to be addressed and/or mitigated. The 2006 EIR anticipated no significant and unavoidable hydrology and water quality impacts resulting from implementation of the DWSI and RWP. Potential impacts to hydrology and water quality were mitigated to less than significant levels through implementation of mitigation measures. This section expands on the hydrology and water quality impacts discussion of the 2006 EIR as it relates specifically to the development of reclaimed water irrigation sites ENVIRONMENTAL SETTING The regional environmental setting for surface water hydrology, groundwater hydrology, and water quality is incorporated by reference from Chapter of the 2006 EIR (refer to Section 1.3 of this EIR). No further discussion on the watershed, regional water quality, regional groundwater levels and quality, or salts in groundwater encompassing the project sites is warranted. Site-specific surface and groundwater hydrology and water quality features are discussed in more detail below under the existing setting. Project Site Setting Site 1 - Hollister Municipal Airport Surface Water The Hollister Municipal Airport area does not contain natural any surface water features such as lakes, ephemeral streams, or creeks. The site consists of previously disturbed agricultural fields, which utilize a channeled drainage system to prevent standing water. Drainage and Flooding The topography of the Hollister Municipal Airport is generally flat. Surface sediments are primarily silt and clay, a composition expected to exhibit slow to moderate rates of water infiltration (USDA, 2007). Runoff is conveyed from the site through the use of swales to channel storm water runoff off and away from the runways. Federal Emergency Management Agency (FEMA) Flood Insurance Rate Maps (FIRMs) locate the Hollister Municipal Airport Site outside 100-year flood areas. AES Hollister Reclaimed Water Project

2 The existing drainage system at the site consists of curbs and gutters designed to direct water run-off from airport runway to adjacent vegetated swales and ditches adjacent that provide detention and percolation of stormwater. Groundwater Existing groundwater levels within the area of Site 1 vary seasonally and range from approximately 10 to 40 feet below ground surface (bgs) (Yates, 2007). Groundwater levels have ranged from approximately 40 to 80 feet bgs from the 1920s through the 1950s (DWR, 2007). A substantial reduction in groundwater levels in the area of Site 1 occurred during the late 1970s and 1980s, when groundwater levels fluctuated from approximately 130 to 220 feet bgs (DWR, 2007). Since that time, as a result of declines in local groundwater pumping and other management actions, groundwater levels in the vicinity of the airport have increased to present levels. Concentrations of total dissolved solids (TDS) in groundwater near the airport range from approximately 800 to 2700 mg/l, with higher values occurring within the shallowest portion of the groundwater table (Yates, 2007). Site 2 - Brookhollow Ranch Surface Water The northern area of Site 2 considered for reclaimed water irrigation (Subarea A) does not contain any major surface water resources, such as creeks, streams, or standing water bodies. Several small ephemeral drainages are located within the southern portion of Subarea A. Several small, ephemeral streams and other drainages are also located within the southern area of Site 2 considered for reclaimed water irrigation (Subarea B), and an approximately 10-acre, ephemeral playa is located directly east, and downhill, of this site. A detailed analysis of the playa and its habitat is contained in Section 4.5. Both sites are adjacent to an engineered stock pond and two reservoirs. Drainage and Flooding Subarea A includes a relatively flat slope from approximately 270 feet near its western border to approximately 190 feet near its eastern border. Topography within Subarea B is more complex and includes foothills ranging from approximately 280 to 550 feet in elevation. Soil texture within Subarea A is generally clayey, and would be expected to have low to moderate infiltration rates. Soil texture within Subarea B is generally loamy and is also anticipated to exhibit low to moderate infiltration rates. Due to the topography and soil associations found at Site 2, storm water collects at the lowest point amongst the hills and pools, including the adjacent reservoirs and stock pond. FEMA FIRMs locate the proposed reclaimed water irrigation areas at the Brookhollow Ranch site outside 100-year flood areas. Groundwater Little groundwater information is available for the northern Brookhollow Ranch site, and none is available for the southern site. Nearby wells suggest that the water table at the northern site is on the order of 100 feet below the ground surface, and groundwater salinity near the water table probably exceeds 2,000 mg/l. At the southern site, nearby springs suggest that the water table may be a few feet to 70 feet AES Hollister Reclaimed Water Project

3 below the ground surface across the area that would be irrigated. The TDS concentration in this area has not been measured. Site 3 - Riverside Park Surface Water The San Benito River flows adjacent to the northeastern side of Riverside Park. A detailed description of the San Benito River, including water quality, is contained within the 2006 EIR. Drainage and Flooding Riverside Park drains north/northeast towards the floodplain of the San Benito River. A majority of the soils on the Riverside Park site have high infiltration rates and corresponding low runoff potential when saturated. Runoff generated onsite flows to the San Benito River. FEMA flood maps locate Riverside Park Site adjacent to the 100-year flood plain. The Riverside Park site is designated Zone AE fringe. This zone represents areas that are within the 1-percent-annual-chance floodplain, but are outside the actual floodway. Groundwater Existing groundwater levels within the area of Riverside Park range from approximately 18 to 30 feet bgs (Yates, 2007). In general, groundwater levels in the area of Riverside Park have increased from lows during the late 1970s and 1980s to their current levels as a result of changes in pumping and management practices within the groundwater basin. Concentration of TDS in the area of Riverside Park is approximately 1000 mg/l (Yates, 2007). Site 4 - Pacific Sod Farm Surface Water The San Benito River flows adjacent to the northern side of Pacific Sod Farm. A detailed description of surface water resources, including water quality, associated with the San Benito River is contained within the 2006 EIR. Drainage and Flooding Topography in the area of the Pacific Sod Farm is generally flat. Surface sediments consist of primarily loamy sand (USDA, 2007), and are therefore expected to exhibit higher rates of infiltration. FEMA flood maps locate the northern portions of the Pacific Sod Farm within the 100-year flood zone. Projected flood heights were not delineated for this portion of the FEMA study. Groundwater Groundwater levels within the area of Site 4 vary seasonally, from approximately 60 to 80 feet bgs (DWR, 2007), while levels immediately underlying the site are typically approximately 10 feet bgs (Yates, 2007). These levels represent a substantial increase in groundwater levels that occurred in the area during the 1970s and 1980s, when groundwater levels ranged from approximately 110 to 85 feet bgs. These changes have resulted primarily from changes in groundwater management practices and pumping AES Hollister Reclaimed Water Project

4 reductions. Concentrations of TDS in groundwater within the area of Pacific Sod Farm range from approximately 950 to 2050 mg/l (Yates, 2007). Site 5 - San Juan Oaks Golf Club Surface Water Surface water within Site 5 is dominated by water features associated with the existing San Juan Oaks Golf Club. These include approximately seven engineered perennial lakes, as well as several modified or created drainages and waterways. Several small ephemeral drainages from the foothills above the golf course also drain onto the golf course area. Drainage and Flooding Topography in the area of the San Juan Oaks Golf Club includes rolling foothills. The golf course itself has less topographical relief than surrounding areas. Surface sediments are primarily clayey in texture and typically exhibit relatively low rates of infiltration. San Juan Oaks Golf Club area is not located within a delineated 100-year flood zone. Groundwater Available groundwater data indicate that levels are approximately 35 feet bgs. TDS ranges from approximately 1100 to 2250 mg/l, with the highest values indicated within upper groundwater levels (Yates, 2007) REGULATORY SETTING A description of the regulatory setting is incorporated by reference from Section the 2006 EIR (refer to Section 1.3). Section of the 2006 EIR provides a description of the following: FEDERAL Clean Water Act (33 USC ): Sections 303, 304, 401 and 402 Antidegradation Policy (40 CFR 131.6) National Flood Insurance Program STATE The Porter-Cologne Water Quality Control Act (Division 7 of the California Water Code) State Water Resources Control Board (SWRCB) and Regional Water Quality Control Board (RWQCB) Central Coasts RWQCB s Antidegradation Policy Central Coasts RWQCB s Basin Plan SWRCB Construction Storm Water General NPDES Permit California Water Code Recycled Water Management Water Recycling Criteria (Title 22, Division 4, Chapter 3) AES Hollister Reclaimed Water Project

5 REGIONAL/LOCAL San Benito County General Plan Open Space and Conservation Element Water Resources Association of San Benito County Groundwater Management Plan City of Hollister General Plan Community Services and Facilities Element\ City of Hollister Urban Area Water and Wastewater Master Plan IMPACT ANALYSIS Groundwater Modeling The groundwater modeling analysis undertaken to assess potential changes in groundwater levels and quality associated with implementation of the proposed project is included in Appendix F of this SEIR. The results of the analysis are divided between the main report and supplemental addendum report. The groundwater level model used is based in MODFLOW and was used to simulate potential changes over 30 years. The simulations utilized data from past hydrologic years (1975 through 2004) at quarterly increments in order to assess future conditions under extremely dry, drought, normal, and extremely wet water years. The MT3DMS model was utilized, in conjunction with MODFLOW, to predict changes in groundwater quality. Vertically, the model is subdivided into five layers, which enables properties within each layer to be varied to represent vertical and lateral changes in sediment type observed within the aquifers in the Hollister area. The Hollister groundwater model is subdivided into 7 regions for the purpose of evaluating impacts of the project on groundwater budgets. These regions are similar to the subbasins that have been used for water budget calculations in the San Benito County Water District s (SBCWD) annual groundwater reports since Seismic faults in the Hollister area influence groundwater flow and were a key feature used to divide the model into regions. The model utilized for this simulation is the same model that was utilized for the 2006 EIR. Modeled Operational Scenarios Modeling compared changes in groundwater level and water quality that would potentially result from the use of reclaimed water for irrigation at the five potential sites. As discussed in Section 3.3, limitations in the amount of water that could be applied at Riverside Park and San Juan Oaks Golf Club would require operation in combination with other land application areas in order to achieve the objective disposal capacity for Phase I of the City s Long Term wastewater Management Plan (LTWMP) of 0.72 MGD. Additionally, reclaimed water deliveries and irrigation scenarios would vary at the airport in the event that adjacent privately owned property is not utilized, and at San Juan Oaks depending on the blend ratios that are utilized. In order to account for this within the groundwater modeling analysis, a series of nine operational scenarios were developed as reasonably foreseeable alternatives for achieving the disposal capacity requirements. The timing and amount of water delivered to each site is based on differences in soil conditions, irrigated area, and water demands of potential crops to be grown at the site. The nine operational scenarios and associated modeling assumptions are presented in Table Within Appendix F, Operational Scenarios A through F are analyzed in the main report and Operational Scenarios G, H and J are analyzed in a supplement to the report prepared as an attachment. AES Hollister Reclaimed Water Project

6 TABLE IRRIGATION SCENARIOS FOR GROUNDWATER MODEL Scenario No-Project: Continued Moratorium No-Project Urbanization Project Scenario A- RWI: Airport (expanded) and Riverside Park Project Scenario B- RWI: San Juan Oaks (with blending) and Sod Farm Project Scenario C- RWI: Riverside Park and Sod Farm Project Scenario D- RWI: Airport (expanded) Project Scenario E- RWI: Sod Farm Description Neither the wastewater or groundwater demineralization projects occur. Building moratorium continues throughout the evaluation period (30 years). A hypothetical scenario in which urbanization occurs but no reclaimed water is used for irrigation at the project sites Riverside Park at maximum rate throughout Phases 1 and 2. Irrigation at Airport site occurs on airport property and adjacent privately owned land. Years 7 and 8 transition from Airport to Offsite Irrigation sites. No irrigation at Airport after Year 8. Begin irrigation at Pacific Sod Farm in Year 3. San Juan Oaks Golf Club irrigation starts in Year 1 and is at maximum sustained rate in Year 3. At San Juan Oaks, reclaimed water is blended with CVP water to achieve a TDS level of 500 mg/l. Riverside Park at maximum rate throughout Phases 1 and 2. Pacific Sod Farm has gradual increase in irrigation during Phase 1. Maximum rate reached in second year of Phase 2. Offsite irrigation starts in second year of Phase 2. Irrigation at Airport site occurs on airport property and adjacent privately owned land. Years 7 and 8 transition from Airport to Offsite irrigation during Phase 1. No irrigation at Airport after Year 8. Pacific Sod Farm has gradual increase in irrigation during Phase 1. Maximum rate reached in second year of Phase 2. LTWMP Phase Riverside Park Pacific Sod Farm Irrigation Area Airport San Juan Oaks Brookhollow Ranch I II I II I II I II I Offsite Irrigation II AES Hollister Reclaimed Water Project

7 Scenario Project Scenario F- RWI: Brookhollow Ranch Project Scenario G- RWI: Airport (reduced) and Riverside Park Project Scenario H- RWI: Airport (reduced) Project Scenario J- RWI: San Juan Oaks (no blending) and Airport (reduced) Description Brookhollow Ranch has gradual increase in irrigation during Phase 1. Maximum rate reached in second year of Phase 2. Offsite irrigation starts in second year of Phase 2. Similar to Project Scenario A however irrigation at Airport site is confined to Airport property and turf grass is the only product irrigated at the airport site (versus turf grass and grass hay). Similar to Project Scenario D however irrigation at Airport site is confined to Airport property and turf grass is the only product irrigated at the airport site (versus turf grass and grass hay). San Juan Oaks receives all reclaimed water until exceeding demand in year 2, and remains at 100% capacity during remainder of Phase 1 and 2. Blending of reclaimed water is not utilized at the gold course under this scenario. Irrigation at Airport site occurs on airport property only and starts in year 2, reaching a maximum rate in Year 6. No irrigation at Airport after Year 8. LTWMP Phase I Riverside Park Pacific Sod Farm Irrigation Area Airport San Juan Oaks Brookhollow Ranch II I Notes: = irrigation during the time period; = irrigation during a portion of the time period. RWI = reclaimed water irrigation. A Scenario I was not identified to avoid confusion with Phase I of the LTWMP. Source: Yates, 2007; AES, II I II I II Offsite Irrigation Land use changes as identified in the Hollister General Plan and associated changes in municipal water use, wastewater generation, agricultural water use, and groundwater use are accounted for within the groundwater analysis. The No Project Scenario assumes that the present building moratorium would continue indefinitely and that current land uses would continue. Therefore, under the No Project Scenario, water and wastewater use is assumed to remain constant, and no part of the proposed project would be implemented. AES Hollister Reclaimed Water Project

8 In order to provide a point of comparison, the No Project: Urbanization Scenario was also analyzed. This scenario considered additional effects of urbanization without the potential effects of the proposed reclaimed water irrigation project. Thus, evaluation of the No Project: Urbanization Scenario enabled identification of changes in groundwater levels and quality that are attributable to the effects of urbanization as compared to the direct effects that would occur from irrigation under the proposed project. It should be noted that the No Project: Urbanization Scenario is not a feasible alternative as the City s current building moratorium would continue without achieving the necessary increase in disposal capacity at the DWTP afforded by implementation of the proposed project. This scenario is utilized only as a point of comparison for the purposes of determining potential groundwater impacts related to the proposed project. Model Input Parameters and Assumptions Physical characteristics of the five potential sites, including soil texture, land use, and depth to groundwater, were included in the modeling analysis. Additional input included existing groundwater levels, salinity, and the amount of water that would be applied to each site on an annual basis over the 30- year period of analysis. The effluent salinity from the DWTP was assumed to decrease from its existing level (1204 mg/l TDS) to 600 mg/l TDS by 2016, when demineralization of groundwater used for domestic supply will be fully implemented. 1 This change would occur with implementation of Phase II of the LTWMP. Once the changes indicated for Phase II occur, it is anticipated that increased demand for recycled water will occur resulting in distribution to areas other than the five sites currently being considered. This substitution is assumed to result in an equal decrease in the amount of CVP water supplying local irrigation water. With the exception of the Hollister Municipal Airport, it is assumed that reclaimed water irrigation would continue throughout Phase I and Phase II of the LTWMP for all of the sites. Reclaimed water irrigation at the airport is assumed to be phased out in 2016 to allow for urbanization of site parcels consistent with General Plan designations and to allow for more beneficial uses of LTWMP Phase II recycled water. Appendix F outlines assumed annual irrigation quantities for each site under each operational scenario. Findings The results of the groundwater modeling analysis for each operational scenario are discussed in detail in Appendix F. Findings are summarized in Table and briefly described below. Groundwater Levels Basin-wide Effects to Groundwater Budgets From a regional perspective, the overall water budget would not be substantially affected by implementation of reclaimed water irrigation. The largest localized impact would be decreased recharge to the Hollister West and San Juan subbasins from percolation at the DWTP and IWTP ponds. Changes in municipal groundwater pumping due to urban growth would also have a concurrent effect on water 1 The target level for recycled water salinity in Phase II is 500 mg/l, but local agreements allow concentrations to occasionally reach a maximum of 700 mg/l. An average of 600 mg/l was conservatively assumed for the modeling analysis. AES Hollister Reclaimed Water Project

9 4.2 Hydrology and Water Quality TABLE SUMMARY OF GROUNDWATER CHANGES 1 FOR THE EVALUATED SCENARIOS Scenario A Scenario B Scenario C Scenario D Scenario E Impact WATER LEVEL EFFECTS (LTWMP Phase I) Site 3 Riverside Park Site 1 Airport (Expanded) Site 4 Pacific Sod Farm Site 5 San Juan Oaks (w/ blending) Site 3 Riverside Park Site 4 Pacific Sod Farm Site 1 Airport (Expanded) Site 4 Pacific Sod Farm Max Increase inlayer 1 (feet) No increase <+0.1 No Increase *Note (LTWMP Phase II) Local municipal pumping increases and decreases in percolation. At north end of airport, irrigation off-set by local municipal pumping increase Decreased on-site well use Minimal change because current CVP water is delivered and groundwater is rarely used. Local municipal pumping increases and decreases in percolation. Decreased on-site well use At north end of airport, irrigation offset by local municipal pumping increase Decreased on-site well use Max Increase in Layer 1 (feet) No increase No increase *Note Local municipal pumping increases and decreases in percolation Although irrigation ceases in Year 17, local agricultural pumping decreases because of urbanization Decreased on-site well use Minimal change because current CVP water is delivered and groundwater is rarely used. Local municipal pumping increases and decreases in IWTP percolation. Decreased on-site well use Although irrigation ceases in Year 17, local agricultural pumping decreases because of urbanization Decreased on-site well use CHANGES IN BASINWIDE SALT LOAD (%) (LTWMP Phase I) (LTWMP Phase II) LOCALIZED SALINITY EFFECTS (LTWMP Phase I) Salinity Trends Steady increase Steady increase Steady increase Steady increase Steady increase Steady increase Steady increase Steady increase Max TDS Change (mg/l) 3 +1, Max TDS Concentration (mg/l) 2,000 2,800 2,100 2,400 2,000 2,100 2,900 2,100 Maximum Off-site Migration (feet) 300 1, < , Number of Impacted Wells (LTWMP Phase II) Salinity Trends Stable 5 Steady decrease Steady decrease 5 Steady decrease Stable 5 Steady decrease 5 Steady decrease Steady decrease 5 Max TDS Change (mg/l) , decreasing to , decreasing to +400 Max TDS Concentration (mg/l) 1,500 2,100-2,400 1,400 2,700 1,500 1,400 2,200 2,500 1,400 Maximum Off-site Migration (feet) 600 5, ,000 5,000 1,000 Number of Impacted Wells AES Hollister Reclaimed Water Project

10 4.2 Hydrology and Water Quality WATER LEVEL EFFECTS (LTWMP Phase I) Impact Site 2a Brookhollow Ranch Subarea A Scenario F Scenario G Scenario H Scenario J Site 2b Brookhollow Ranch Subarea B Site 3 Riverside Park Site 1 Airport (Reduced) Site 1 Airport (Reduced) Site 5 San Juan Oaks (no blending) Site 1 Airport (Reduced) Max Increase in Layer 1 (feet) No increase *Note (LTWMP Phase II) Low permeability Decrease due to increased municipal pumping and decreased IWTP percolation At north end of airport, irrigation off-set by local municipal pumping increase At north end of airport, irrigation off-set by local municipal pumping increase Minimal change because recycled water replaces CVP irrigation of turf At north end of airport, irrigation off-set by local municipal pumping increase Max Increase in Layer 1 (feet) No increase *Note Dependent on climatic conditions Groundwater levels reach ground surface Decrease due to municipal pumping and decreased IWTP percolation Although irrigation ceases in Year 17, local agricultural pumping decreases because of urbanization Although irrigation ceases in Year 17, local agricultural pumping decreases because of urbanization Minimal change because recycled water replaces CVP irrigation of turf Although irrigation ceases in Year 17, local agricultural pumping decreases because of urbanization. CHANGES IN BASINWIDE SALT LOAD (%) (LTWMP Phase I) (LTWMP Phase II) LOCALIZED SALINITY EFFECTS (LTWMP Phase I) Salinity Trends Steady increase Steady increase Steady increase Steady increase Steady increase Steady increase Steady increase Max TDS Change (mg/l) , Max TDS Concentration (mg/l) 3,100 2,500 2,000 2,800 3,000 3,000 2,600 Maximum Off-site Migration (feet) ,000 1,000 <100 1,000 Number of Impacted Wells (LTWMP Phase II) Salinity Trends Steady increase Steady increase Stable 5 Steady decrease 5 Steady decrease Increase approaching equilibrium Steady decrease 5 Max TDS Change (mg/l) , decreasing to , decreasing to decreasing to +100 Max TDS Concentration (mg/l) 4,000 3,200 1,500 2,700 2,700 3,200 2,400 Maximum Off-site Migration (feet) 1, ,000 5, ,000 Number of Impacted Wells Notes 1 Results shown in this table summarize the results of each modeled scenario compared to the No-Project Scenario results. 2 Water-level impacts essentially the same for all model layers unless otherwise noted. 3 Change is relative to No-Project conditions during the same time interval 4 This includes only existing wells identified during the well inventory; other wells may be present 5 Due to the proximity of the San Benito River, flood events after extended droughts dilute and flush salinity from the Riverside Park and Pacific Sod Farm sites. Sources: Yates, 2007; AES AES Hollister Reclaimed Water Project

11 budgets, particularly in the Hollister East and Hollister West subbasins. Increased groundwater recharge in municipal groundwater pumping due to urban growth would also have a concurrent effect on water budgets, particularly in the Hollister East and Hollister West subbasins. Increased groundwater recharge at the project sites is a relatively small amount of water in the context of overall groundwater recharge. At the two sites already irrigated (Pacific Sod Farm and San Juan Oaks Golf Club), recharge would remain constant irrespective of the selected project scenario. Results of the groundwater modeling analysis indicate that the effects of urbanization would have a much larger influence on groundwater budgets than deep percolation of irrigation water at the project sites. In the Hollister East region, for example, demand from municipal water supply wells is projected to increase 14 percent, from 7,069 AFY for the No-Project Scenario to 8,079 AFY in each project scenario. Figure illustrates changes to regional groundwater levels that would occur as a result of anticipated growth and buildout of the City s General Plan under the No Project: Urbanization Scenario. Localized Effects to Groundwater Levels Simulated water levels were less than 8 feet below the ground surface at the north end of the Airport Site during Scenarios A, D, G, H and J as well as the No Project Scenario. These higher groundwater levels occur in areas that are planned for urban development. Groundwater levels shallower than 8 feet below grade are also anticipated at the Pacific Sod Farm (Scenarios B, C, and E), but an existing tile drain system is in place that is designed to prevent any adverse impacts on crop growth. At the Brookhollow Ranch Site, simulated groundwater levels rose above ground level. Figures 4.2-2a-j illustrate localized effects to groundwater levels that would occur as a result of the proposed project under each potential operational scenario for reclaimed water irrigation. The upper plot in each figure indicates the maximum change in groundwater elevations from the No Project conditions that would occur under each operation scenario, and the lower hydrographs show the change in groundwater elevations that are projected to occur over the 30 year simulation period. Groundwater Quality Basin-wide Salt Balance The largest source contributors to salt concentration in the San Benito County part of the Gilroy-Hollister groundwater basin include stream percolation, importation and use of CVP water, and application of gypsum and fertilizers on agricultural soils. Urbanization would affect salt loads from wastewater percolation at the DWTP and IWTP, evaporative concentration of urban irrigation water, and evaporative concentration of irrigation on lands that become urbanized during the simulation period. Figure illustrates the effects of urbanization to regional groundwater salinity levels. These changes would be the same for all of the project scenarios. In addition, each scenario would affect the evaporative concentration of irrigation water at the project sites and at offsite cropland irrigated with recycled water. As shown in Table 4.2-2, under most operational scenarios, the change in basin-wide salt load is projected to decrease slightly during Phase I of the LTWMP, with a more significant decrease anticipated during Phase II. AES Hollister Reclaimed Water Project

12 Localized Effects During Phase I of the LTWMP, salinity levels in groundwater at each of the potential project sites are simulated to increase above the Basin Plan objective of 1,200 mg/l TDS, in part because existing salinity levels at each of the sites, with the exception of Riverside Park, already exceeds this objective. During Phase II of the LTWMP, localized groundwater salinity levels are projected to decrease steadily at each of the sites, with the exception of San Juan Oaks Golf Club and Brookhollow Ranch. In the case of the Pacific Sod Farm site, salinity levels are projected to improve over current conditions under each operational scenario. Localized salinity effects under each operational scenario are described in detail in Appendix F and summarized in Table Figures 4.2-4a-j illustrate localized effects to salinity levels that would occur as a result of the proposed project under each potential operational scenario for reclaimed water irrigation. Contours of changes in shallow groundwater salinity levels after project implementation are shown in the upper plot of each figure, and hydrographs of simulated salinity concentration at indicated locations are shown in the lower portion of each figure. Thresholds of Significance Criteria for determining the significance of impacts to water resources have been developed based on Appendix G of the CEQA Guidelines. An impact to hydrology or water quality would be considered significant if the proposed project: Changes quantity, quality, or rate and direction of flow of groundwater or surface water, either by direct additions or withdrawals or by puncture of an aquitard, sufficient to preclude an intended use. Substantially alters the existing drainage pattern of the site or area or substantially increases the rate or amount of surface runoff in a manner that would result in flooding on- or off-site. Places structures within a 100-year flood hazard area as mapped on a federal flood hazard boundary map, flood insurance rate map, or other flood hazard delineation map. Exposes people or structures to a significant risk of loss, injury, or death involving flooding, including flooding as a result of the failure of a levee or dam. Introduces development that would interfere with the ability of an agency to repair or maintain levees for public safety. Creates or contributes runoff water that would exceed the capacity of existing or planned stormwater drainage systems or provide substantial additional sources of polluted runoff. Violates any water quality standards, waste discharge requirements, or otherwise substantially degrades water quality; Substantially alters the existing drainage pattern of the site or area in a manner that would result in substantial erosion or siltation on- or off-site; or Substantially degrades the existing surface and groundwater quality due to erosion and siltation. Thresholds for groundwater levels and salinity have been developed as guidelines for evaluating the results of groundwater modeling for each project scenario. For purposes of this SEIR, impacts would also be considered if the proposed project would: AES Hollister Reclaimed Water Project

13 Insert Figure AES Hollister Reclaimed Water Project

14 Insert Figure 4.2-2a AES Hollister Reclaimed Water Project

15 Insert Figure 4.2-2b AES Hollister Reclaimed Water Project

16 Insert Figure 4.2-2c AES Hollister Reclaimed Water Project

17 Insert Figure 4.2-2d AES Hollister Reclaimed Water Project

18 Insert Figure 4.2-2e AES Hollister Reclaimed Water Project

19 Insert figure 4.2-2f AES Hollister Reclaimed Water Project

20 Insert Figure 4.2-2g AES Hollister Reclaimed Water Project

21 Insert Figure 4.2-2h AES Hollister Reclaimed Water Project

22 Insert Figure 4.2-2j AES Hollister Reclaimed Water Project

23 Insert figure AES Hollister Reclaimed Water Project

24 Insert Figure 4.2-4a AES Hollister Reclaimed Water Project

25 Insert Figure 4.2-4b AES Hollister Reclaimed Water Project

26 Insert Figure 4.2-4c AES Hollister Reclaimed Water Project

27 Insert Figure 4.2-4d AES Hollister Reclaimed Water Project

28 Insert Figure 4.2-4e AES Hollister Reclaimed Water Project

29 Insert figure 4.2-4f AES Hollister Reclaimed Water Project

30 Insert Figure 4.2-2g AES Hollister Reclaimed Water Project

31 Insert Figure 4.2-2h AES Hollister Reclaimed Water Project

32 Insert Figure 4.2-2j AES Hollister Reclaimed Water Project

33 Result in elevated groundwater levels that would disrupt beneficial use of the project site or affected area. This would occur if the root zone area for agricultural crops were to become saturated as a result of shallow groundwater levels. Result in water levels below historical minimum water levels. Increase the average groundwater salinity near the project sites above the Regional Water Quality Control Boards (RWQCB) goal of 1,200 mg/l for dissolved solids. If existing TDS concentrations exceed the 1,200 mg/l threshold, a change in TDS concentration resulting from implementation of the proposed project would result in a significant impact if it further increased TDS concentrations resulting in a violation of the State Water Resources Control Board s antidegradation policy. Methods and Assumptions Impacts to hydrology and water quality were analyzed based on field surveys of the project sites, groundwater modeling, and published information regarding the water resources of the project area. When impacts to hydrology and water quality resulting from the proposed project would exceed the significance thresholds listed above, mitigation measures have been recommended to reduce impacts to less-than-significant levels. Impacts that were determined to be less than significant in the Initial Study (Appendix B) are not discussed within this SEIR. Mitigation measures identified in the 2006 EIR are assumed to be implemented as a component of the proposed project. The 2006 EIR identified five mitigation measures applicable to development of reclaimed water projects that would reduce potential impacts to hydrology and water. These measures are described in detail in Appendix C and are briefly summarized below: 2006 EIR MM 4.2.4a: Irrigation with reclaimed water would be subject to Waste Discharge Requirements issued by the RWQCB, which would restrict application of reclaimed water to prevent off-site runoff. The City of Hollister shall implement measures required by the CCRWQCB, which could include, but are not necessarily limited to the following measures: 1) No reclaimed water shall be applied to irrigation areas during periods when soils are saturated. Irrigation schedules shall be defined by evapotranspiration rates of crops, available soil moisture, and rainfall. Soil moisture levels shall be monitored by the development of at least four monitoring locations at each sprayfield/irrigation site utilizing tensiometers, electrical resistance blocks, or other measuring devices. 2) Reclaimed water shall not be allowed to escape from the designated use area(s) as surface flow that would either pond and/or enter waters of the State. Irrigation schedules and methods shall be utilized to avoid surface runoff from irrigation sites. Methods shall include the use buffers, berms, and ditches to control runoff. 3) Incidental discharge of recycled water to waters of the State shall be minimized through the use of buffers, berms, and ditches to control runoff. AES Hollister Reclaimed Water Project

34 2006 EIR MM 4.3.2: a) Install three shallow monitoring wells along the down-gradient boundaries of any area irrigated with Phase I recycled water. Areas with blended irrigation water are exempt from this requirement if the TDS concentration and annual irrigation rate meet the following criterion: (TDS) x (IRRIG/6) < 3000 where, TDS = total dissolved solids concentration in the irrigation water (mg/l) IRRIG = annual irrigation application rates (inches). Monitor groundwater salinity in those wells and several nearby down-gradient water supply wells at least semiannually until Monitoring shall be conducted for TDS, sodium, chloride, sulfate. b) Tabulate and interpret the data at least semiannually to determine the extent to which shallow and deep groundwater salinity is being impacted by the increase in irrigation water salinity. Interpretation of data shall project when increased salinity levels would affect existing uses of groundwater. c) For the proposed Hollister Municipal Airport sprayfield, if the TDS, sodium, chloride, or sulfate concentrations in a nearby down-gradient water supply well are projected to increase to a point that it would adversely affect the existing uses of the water, and if the increase in can reasonably be attributed to Phase I recycled water operations based on the monitoring data, then the City of Hollister shall provide an alternative water supply to the well operator. The alternative supply shall have water quality characteristics no worse than the pre-project well water. The alternative supply may consist of wellhead treatment. d) For all other Sprayfields, if the TDS, sodium, chloride, or sulfate concentrations in a nearby down-gradient water supply well are projected to increase to a point that it would adversely affect the existing uses of the water, and if the increase in can reasonably be attributed to Phase I recycled water operations based on the monitoring data, then one or more of the following shall occur: 1) Reduce or discontinue recycled water irrigation. 2) Blend recycled water with CVP or groundwater to reduce salinity of irrigation water. If the TDS, sodium, chloride, or sulfate concentrations in a nearby down-gradient water supply well increase to the point that existing uses of the water are adversely affected, and if the increase can reasonably be attributed to Phase I recycled water operations based on the monitoring data, then the City of Hollister and/or SBCWD shall provide an alternative water supply to the well operator. The alternative supply shall have water quality characteristics no worse than the pre-project well water. The alternative supply may consist of wellhead treatment EIR MM a: The following measures shall be implemented to avoid impacts from the Hollister Municipal Airport sprayfield. (1) Install three monitoring wells along the down-gradient boundaries of the Airport irrigation area. Monitor groundwater levels in those wells at least semiannually until irrigation of the Airport for DWTP effluent disposal purposes ceases. (2) Tabulate and interpret the data at least semiannually to determine the extent to which shallow and deep groundwater levels are being impacted by the increase in irrigation AES Hollister Reclaimed Water Project

35 water. Interpretation of data shall project when increased levels would affect the surrounding area. (3) If groundwater levels in the surrounding area are projected to increase to a point that it would adversely affect the area, and if the increase in levels can reasonably be attributed to irrigation operations based on the monitoring data, then the City shall increase pumping of the municipal supply well located at Fallon Road to offset increases associated with the irrigation of the Airport EIR MM b: The following measures shall be implemented to avoid impacts from the development of other sprayfields. (1) Analysis shall be completed to determine the groundwater elevations at proposed sprayfield locations. If this analysis reasonably concludes that sprayfield operation could increase groundwater elevations to a point that it would adversely affect the area the following measures shall be implemented. (a) Install three monitoring wells along the down-gradient boundaries of the proposed irrigation area. Monitor groundwater levels in those wells at least semiannually until irrigation for DWTP effluent disposal purposes ceases. (b) Tabulate and interpret the data at least semiannually to determine the extent to which shallow and deep groundwater levels are being impacted by the increase in irrigation water. Interpretation of data shall project when increased levels would affect the surrounding area. (c) If groundwater levels in the surrounding area is projected to increase to a point that it would adversely affect the area, and if the increase in levels can reasonably be attributed to irrigation operations based on the monitoring data, then irrigation shall be reduced or discontinued, and/or other measures taken to avoid the adverse impact EIR MM : Comply with the State s NPDES General Permit for Discharges of Storm Water Runoff Associated with Construction Activity. The Central Coast Water Quality Control Board (CCRWQCB) requires that all construction sites have adequate control measures to prevent the discharge of sediment and other pollutants to streams or rivers. To comply with the permit, the City will file a Notice of Intent with the CCRWQCB and prepare a Storm Water Pollution Prevention Plan (SWPPP) prior to construction. A copy of the SWPPP must be current and remain on the project site. Control measures are required prior to and throughout the rainy season. Impact Statements and Mitigation Measures The following discussion outlines the projected impacts anticipated to result from implementation of the City of Hollister Reclaimed Water Irrigation Project as analyzed in this SEIR. Additional mitigation measures or refinements of the 2006 EIR mitigation measures described above have been recommended where appropriate to reduce or minimize the potential for adverse environmental effects. AES Hollister Reclaimed Water Project

36 Short-term Construction Related Effects IMPACT Construction activities associated with the proposed project could result in the contamination of surface water or groundwater. Sites 1-5 Construction of the proposed project would involve excavation and stockpiling of fill on the project sites. During storm or strong wind events, these activities could result in erosion and sediment discharge into the drainage system or tributaries of the San Benito River, and subsequently into the San Benito River itself. Water quality decreases with increased turbidity and increased amounts of total suspended solids, which influences stream ecology and the amount of treatment needed for human consumption. Siltation can damage downstream agriculture by inhibiting or delaying seed emergence and burying small seedlings. It can also contribute to road damage, clog drainage ditches and stream channels, cover fish spawning grounds, and increase silt in reservoirs. In addition, construction equipment and materials have the potential to leak, thereby discharging additional pollutants into stormwater. Construction site pollutants include particulate matter, sediment, oils and greases, concrete, paints, and adhesives. Discharge of these pollutants could result in contamination of area drainages and tributaries to the San Benito River, causing an exceedance of water quality objectives. Because construction and excavation activities associated with the components of the proposed project have the potential to result in soil erosion, siltation, and contamination of stormwater, which could lead to adverse environmental consequences, this is considered a potentially significant impact. Trenching, jack and bore tunneling, and directional drilling during pipeline installation to and within the project sites could occur in areas of shallow groundwater. Areas where groundwater levels are higher than the bottom levels of the trenches and tunnels may require dewatering to facilitate construction. Discharge of groundwater from trenches to drainages and tributaries of the San Benito River could increase soil erosion and silt deposition, decreasing the water quality of receiving surface waters. Furthermore, groundwater within trenches could become entrained with construction contaminants, reducing water quality in receiving surface waters. This impact is considered potentially significant. Previously identified mitigation measures included in the 2006 EIR MM summarized above, and additional mitigation recommended below would reduce significant impacts surface and groundwater resources during construction to less than significant. Less Than Significant with Mitigation. Mitigation Measure 4.2-1a. In the event that trenching, jack and bore tunneling, and directional drilling encounter groundwater, dewatering shall be performed in such a manner as to reduce potential contact with construction materials. Mitigation Measure 4.2-1b. Encountered groundwater shall be disposed of in accordance with the requirements of the NPDES permit for general construction and AES Hollister Reclaimed Water Project

37 applicable regulations. Typical methods of disposal include land application for purposes such as dust suppression, which will not reach surface waters, and disposal at an appropriately permitted facility such as a WWTP. Drainage and Flooding Effects IMPACT The proposed project could result in an alteration of or re-direction of flood flows, potentially exposing people or structures to a significant risk of loss, injury, or death involving flooding. Sites 1-2, 5 Sites 1, 2, and 5 are located outside of FEMA designated flood zone areas. Construction and utilization of these sites would not contribute to flood waters or expose people or structures to risk, loss, injury, or death involving flooding. No Impact. Sites 3 The proposed Riverside Park site is located within the fringe of Zone AE of the floodplain of the San Benito River. Importation of fill could result in increasing the floodplain elevation. In order to determine the potential impact, hydraulic modeling was performed using the HEC- RAS model, the U.S. Army Corps of Engineers one-dimensional open-channel flood model. The results of this analysis are included in Appendix G. The model was used to estimate the 100-year floodplain elevation in the vicinity of Riverside Park of five cross sections of the project site. The model indicated that the existing floodplain elevation is currently below the elevation of Riverside Park within 4 of the 5 cross sections. The fifth cross section identified the flood plain elevation to be 0.6 feet above the lowest elevation of the project site. However, the model only interprets the flood elevation of the main channel and does not take into account the elevated bank adjacent to the project site. According to the model results, the floodplain elevation of the main channel adjacent to the site is feet. The elevation of the bank adjacent to Riverside Park is 269 feet. The results of the modeling indicate the project site is outside the floodplain elevation and that flooding would only occur in conjunction with bank failure. Because the project site was determined to be outside the floodplain elevation, importation of fill would not result in the alteration of the floodplain. Construction and utilization of reclaimed water irrigation at this site would therefore not result in significant alteration or redirection of flood flows. Less than Significant. Site 4 Utilization of the Pacific Sod Farm for irrigation with reclaimed water would result in the application of treated wastewaters within the area of a FEMA-defined 100-year flood zone. Construction of the proposed project at Site 4 would not result in the placement of buildings or fill within the 100 year flood plain. Therefore, construction and utilization of reclaimed water irrigation areas at this sites would not result in significant alteration or redirection of flood flows. The impact would be less than significant. Less than Significant. AES Hollister Reclaimed Water Project