INTRODUCTION

To further understand, manage, and protect their groundwater resources, Madera County has retained Todd Engineers to assist with groundwater planning. Todd Engineers conducted two concurrent studies: a larger study covering western Madera County and a smaller study covering eastern Madera County (Figure 1). The western study involved the preparation of an AB3030 Groundwater Management Plan that documented groundwater conditions in the alluvial basins of the San Joaquin valley portion of the County (approximately 507,746 acres). The Final Draft AB3030 Groundwater Management Plan was submitted to the County in January 2002. This Technical Memorandum summarizes the study in eastern Madera County (approximately 866,334 acres) including the foothill and mountain regions east of the alluvial groundwater basins (Figure 1).

Objectives

The primary purpose of this study was to document existing data and identify key regional groundwater issues associated with existing and future groundwater development in eastern Madera County. Specific objectives of this study were:

1) Compile and summarize existing data relating to hydrogeology and groundwater conditions

2) Conduct preliminary analyses of available data with a focus on water demands, groundwater quantity, and groundwater quality

3) Provide recommendations regarding additional data collection and groundwater management measures.

Data Sources

Primary data sources and available information compiled for this Technical Memorandum are summarized below:

· Madera County Engineering – data from county water systems including inspection reports, pumping data, limited well construction data, and system status summaries

· Madera County Environmental Health – water systems list, small system inspection reports, and water quality data

· California Department of Health Services (DHS), Drinking Water Division – information on private systems including inspection reports, limited well construction data, and water quality data

· California Department of Water Resources (DWR) – published documents and data on geology, hydrogeology, precipitation, surface water, reservoirs, evaporation and more than 4,609 Water Well Driller’s Reports (driller’s logs) with information on water well location, drilling methods, geology, construction, testing, water levels, and well yields.

· Private Water Systems including Broadview Terrace Mutual Water Company, Hillview Water Company, Cascadel Water Company, Yosemite Springs Park Utility Company, Yosemite Forks, and Cedar Valley – production data, system information, limited well location and construction information, and limited water quality data

· U. S. Geological Survey (USGS) – published and unpublished documents and data on hydrogeology, geology, and streamflow.

Documents and data sets are listed in the References section at the end of this Technical Memorandum.

REGIONAL SETTING

Madera County covers more than 1.3 million acres in the geographic center of California. The western third consists of a relatively flat-lying portion of the San Joaquin valley overlying alluvial groundwater basins. The eastern two-thirds of the County consist of the foothills and mountains of the Sierra Nevada and are defined as the Study Area in this Technical Memorandum (Figure 1). Groundwater conditions in eastern Madera County are significantly more complex than in the alluvial basins to the west. In eastern Madera County, groundwater occurs predominantly in undefined fracture systems of granitic and metamorphic bedrock. A review of the regional setting including topography, land use, geology, soils, precipitation, surface water, and evapotranspiration provides the background for developing a conceptual hydrogeologic model of groundwater conditions in the area. This is an important first step in managing water resources in eastern Madera County.

Topography and Land Use

Ground surface elevations in eastern Madera County range from 300 feet above mean sea level (MSL) at the base of the foothills to over 13,000 feet MSL at the crest of the Sierra Nevada in the east. The region is characterized by a variety of topographic features from gently rolling hills to steep mountains.

The foothills region is used for grazing, irrigated pasture, animal husbandry, small towns, and rural development. Most of the development in eastern Madera County has occurred in the foothill region with elevations ranging from 300 to 3,500 feet MSL. Cultivated agriculture including vineyards and orchards has recently increased in the area due to advances in agriculture technology. Relatively significant areas of commercial and residential development are located near the unincorporated communities of Oakhurst (2000 population of 2,868), Raymond, Ahwahnee, Coarsegold Highlands - Indian Lakes, and Yosemite Springs Park (California Department of Conservation, 2000). Other communities are located at Yosemite Forks, Sunset Ridge, and Quartz Ridge (California Department of Conservation, 2000). Tourism and recreation are also important land uses in the foothills. For example, the economy of the Bass Lake area is dependent on the recreation industry (Madera County, 1995).

The Madera County Important Farmland Map of 1998 identifies agricultural and other land uses in the foothill region up to and including Oakhurst (but not including Bass Lake) (California Department of Conservation, 2000). Most of this area is categorized as suitable for grazing, although only a minor portion is currently used for grazing. A small area near Ahwahnee is designated prime farmland and farmland of local importance. Another area of prime farmland and farmland of statewide importance is located just downstream of Millerton Lake.

The Madera County General Plan includes four area-specific plans in the foothill region including North Fork Study Area Plan (1979), O’Neals Study Area Plan (1980), Oakhurst-Ahwahnee Area Plan (1980), and the Coarsegold Community Plan (1982) (Madera County, 1995). Although these plans were adopted in the late 1970s and early 1980s, they are still generally followed for land use and development. A consistent theme in each plan is to maintain a rural setting. Urban development is limited to existing communities and minimum lot sizes are usually recommended for both urban and rural development (Madera County, 1995).

The predominant land uses in the mountain region are tourism, recreation, and natural resources such as timber. Forests under federal ownership cover more than one-third of the County and include portions of the Sierra and Inyo National Forests and Yosemite National Park. Timberlands of pine and fir forests cover approximately 400,000 acres and support a wood products industry in the foothills, especially near the community of North Fork.

Geology

More than 250 million years ago in the Paleozoic Era, thick marine sediments and volcaniclastics were deposited in the area of the present-day Sierra Nevada. These sediments were extensively folded and faulted during a mountain-building event known as the Nevadan orogeny, which began in early Jurassic time (about 200 million years ago). The mountain-building process resulted from collision of two crustal units of the earth, known as plates, that brought metamorphic rocks onto the continent. The mountain belt produced by the orogeny was extensively intruded by granitic batholiths during Cretaceous time, resulting in the granitic bedrock that outcrops in eastern Madera County today (Norris and Webb, 1990).

The granitic and metamorphic bedrock underlie the entire Study Area as shown by the geologic map on Figure 2 (Bateman, 1992). Major rock types and some common map unit names are identified on Figure 2; the reader is referred to Bateman (1992) for more complete descriptions of map units. The granitic bedrock is predominantly composed of tonalite and granodiorite, and is Cretaceous in age (designated in map unit names on Figure 2 by “K”). The major areas of development in the foothills (Oakhurst, Ahwahnee, Bass Lake) are underlain by the Bass Lake Tonalite, a gray, medium-grained tonalite with hornblende and biotite. Metamorphic rocks, including schist, greenstone, phyllite, quartzite, and metagabbro are generally older than the granitic rocks (Triassic and Jurassic) and outcrop in the foothill region predominantly along a northwest-southeast band southwest of Bass Lake. Metamorphic rocks are also present in the mountain region of Madera County, especially in the vicinity of Iron Mountain (Bateman, 1992) (Figure 2). Alluvium is limited to small areas in major valleys.

Fractures and joints are present in the bedrock units, but are likely more extensive and interconnected within the upper few hundred feet. Fractures typically decrease in number and size with depth, as noted by USGS investigators working in the Wawona area of Mariposa and Madera counties (Borchers, 1996). The extent of weathering and decomposition of granitic rocks varies from none to approximately 100 feet below ground surface. Weathering of metamorphic rocks appears limited to the upper 50 feet (Bateman, 1992; DWR, 1966; Ressell and Cebull, 1977; Strand, 1967).

Soils

Soils of the Madera County uplands are subdivided into five broad associations, or groupings of different soils that occur together geographically. The five upland soil associations in Madera County generally occur in bands with increasing elevation from the lower foothills to the lower mountains as summarized below:

*Soil Association*	*Elevation*
*Daulton-Whiterock*	500 to 1,000 feet, MSL
*Ahwahnee-Vista*	500 to 1,500 feet, MSL
*Ahwahnee-Auberry*	1,500 to 2,800 feet, MSL
*Coarsegold-Trabuco*	1,500 to 3,500 feet, MSL
*Holland-Tollhouse*	2,800 to 3,500 feet, MSL

Soils in mountain areas above approximately 3,500 feet, MSL were only mapped at a reconnaissance level and not included on soil survey maps. Soil associations differ in water holding capacity, permeability, and potential for groundwater recharge. Each of the five associations is described briefly in the following paragraphs, based on the Madera Area Soil Survey (USDA, 1962).

Daulton-Whiterock Association. These soils occur in a five-mile wide discontinuous band along the lower foothills between elevations 500 and 1,000 feet MSL. The soils are developed on slate and schist in hilly topography with slopes varying widely from 8 to 45 percent. Both soils are notable for rock outcrops known as “graveyard” or “tombstone” schist. The Daulton soils are relatively extensive (about 30,300 acres), while the Whiterock soils are very limited in extent (664 acres). The Daulton and Whiterock soils are relatively coarse (loam, fine sandy loam, rocky fine sandy loam) with moderate to rapid infiltration. However, the soils are thin with low water holding capacity, which limits the opportunity for retention of rainfall and subsequent percolation to the water table. The representative profile for the Daulton soil is only 17 inches thick, while that of the Whiterock soil is only 8 inches.

Ahwahnee-Vista Association. The Ahwahnee-Vista Association dominates the foothills, accounting for nearly 192,800 acres over a 10- to 15-mile wide band between 500 and 1,500 feet MSL. Both the Ahwahnee and Vista soils are developed on decomposing granite. The Ahwahnee soils are mapped together with Auberry and Vista soils. The Ahwahnee and Vista soils occur on a wide range of slopes varying from 8 to 75 percent. The Ahwahnee soils generally are deep (48 to 60 inches) with thinner profiles occurring on the steeper slopes. The soils range in texture from coarse sandy loams to very rocky coarse sandy loams on steeper slopes, where the soils are marked by extensive bedrock outcrops. Given the coarse texture of the Ahwahnee soils, they are likely permeable. The thicker profiles also provide moderate water holding capacity, providing temporary storage and thereby increasing the potential for water to percolate downward toward the water table.

The closely associated Vista soils generally occur in the lower foothills and on relatively gentle (3 to 8 percent) slopes. The Vista soils are coarse textured (coarse sandy loam), but thinner than the Ahwahnee soils with depth to bedrock of about 36 inches. The Vista soils also are relatively permeable and have moderate water holding capacity.

Ahwahnee-Auberry Association. This association (covering nearly 52,500 acres) occurs on the higher foothills in a discontinuous band between elevations 1,500 and 2,800 feet MSL. The Ahwahnee and Auberry soils occur on a wide range of slopes (8 to 75 percent). As described for the Ahwahnee-Vista Association, the Ahwahnee soils generally are deep, except on steeper slopes, and consist of coarse sandy loams to very rocky coarse sandy loams. Given their coarse texture and relatively thick profile, Ahwahnee soils are relatively significant to groundwater recharge in upland areas. The Auberry and Ahwahnee soils are similar, but the Auberry soils have finer-textured subsoils. While the representative Ahwahnee soil is a coarse sandy loam throughout the profile, the representative Auberry soil consists of a surficial sandy loam overlying with lower zones including sandy loam, gritty loam, sandy clay loam, and sandy loam zones. Accordingly, while internal drainage in the Ahwahnee soil is rapid, that of the Auberry soil is medium to moderately slow.

Coarsegold-Trabuco Association. This soil association occurs in the foothills between elevations 1,500 and 3,500 feet MSL, similar to but slightly higher than the Ahwahnee-Auberry Association. The Coarsegold-Trabuco Association includes reddish soils developed on metasedimentary and intrusive igneous rocks. The Coarsegold soils predominate in the association (about 37,300 acres) and occur on rolling topography with 8 to 75 percent slopes and rock outcrops on the steeper slopes. The Coarsegold soils include loams and rocky loams on the steeper slopes. The loam soils generally are more than 34 inches thick, with the representative profile including a surficial loam and subsoil clay loam to a depth of 38 inches over disintegrating schist bedrock. The soil has moderate water holding capacity, but internal drainage is moderately slow, given the relatively fine-textured subsoil zones.

The geographically-limited Trabuco soils (2,320 acres) consist of rocky loam and loam soils with depths ranging from a few inches to more than six feet. The representative profile of the Trabuco rocky loam includes surficial loam over gravelly clay loam and a hard clay subsoil. As a result, these soils have slow internal drainage.

Holland-Tollhouse Association. The Holland-Tollhouse soils occur between elevations 2,800 and 3,500 feet MSL and have developed on coarse-grained granitic bedrock. The more extensive Holland soils (about 18,000 acres) occur in the high foothills with slopes ranging from 15 to 45 percent. These soils are sandy loams and rocky sandy loams with sandy clay loam subsoil. The soils are relatively deep; the representative profile for the Holland sandy loam extends downward to disintegrating granite at 58 inches. The Holland soils have moderate soil water holding capacity, but moderately slow internal drainage.

The Tollhouse soils occur over about 3,300 acres in the lower mountains. These soils occur on steep slopes (30 to 75 percent), are relatively thin (3 to 36 inches to bedrock), and marked by bedrock outcrops. The soils are rocky coarse sandy loams characterized by very rapid runoff and rapid internal drainage. These characteristics limit the significance of the Tollhouse soils with regard to recharge of groundwater.

Precipitation

Precipitation in eastern Madera County occurs as rainfall and snow, with the proportion as snow being greater at higher elevations. Above approximately 4,000 feet MSL, precipitation occurs primarily as snow. The general geographic distribution of average annual rainfall across the Study Area is shown on Figure 3 (DWR, 1966, 1975). Average annual rainfall amounts range from a low of 14 inches at the base of the foothills (near the Madera Canal) to more than 70 inches in the mountains. Much of the residential development in the foothills has occurred in the area with precipitation ranging from 20 to 40 inches per year.

Precipitation data for the foothill region were obtained for two representative stations: North Fork RS and Crane Valley PH (Figure 3). Annual precipitation amounts from water years 1970 through 2001 are illustrated on Figure 4. As shown on the figure, data are incomplete for 1980 and 1981 at both stations and 1997-2001 at the Crane Valley PH station. Available data indicate an average rainfall of 33.2 inches at the North Fork station (elevation 2,630 feet MSL) and 39.9 inches at the Crane Valley station (elevation 3,400 feet MSL) (Figure 4). More than 87 percent of the annual precipitation at these stations occurs between the months of November and April. These recent precipitation data show good agreement with historical average annual precipitation data for other eastern Madera County stations provided by DWR (1966).

Precipitation in the upper foothill/lower mountain regions is three to four times greater than the average annual precipitation of 11 inches at the City of Madera (elevation 270 feet MSL). The increase in precipitation with elevation is quantified on the following graph. This relationship allows estimation of average annual precipitation based on elevation throughout eastern Madera County up to an elevation of approximately 4,000 feet MSL.

Surface Water

Runoff from rainfall and snowmelt feed river drainages and reservoirs in eastern Madera County. Most of the county is drained by the San Joaquin River and its tributaries (Figure 5). The San Joaquin River forms most of the southern boundary of Madera County, and ultimately serves as the discharge point for runoff from more than 90 percent of the county (including the Fresno River and Chowchilla River basins). Less than 10 percent of precipitation and streamflow originating in Madera County drains out of the county to another river system. This occurs in the northwestern portion of the county where surface water drains westward into the Merced River system (Figure 5). The Fresno River basin drains much of the central county. The Chowchilla River basin drains a narrow portion of the western foothill region (Figure 5). Both of these rivers ultimately discharge to the San Joaquin River in western Madera and Merced counties.

Major reservoirs in the lower portion of the foothills include Millerton Lake on the San Joaquin River, Hensley Lake on the Fresno River, and Eastman Reservoir on the Chowchilla River. Major reservoirs at higher elevations include Bass Lake on the Willow Creek tributary to the San Joaquin River and Mammoth Pool Reservoir on the upper San Joaquin River (Figure 5). Many small lakes and reservoirs are also present, particularly at higher elevations. Major areas of development are present within the upper Fresno River drainage (Oakhurst) and the Willow Creek tributary to the San Joaquin River (Bass Lake area).

Streamflow data collected by the USGS for eastern Madera County are compiled on Table 1. Data summarized on the table include the streamflow gage station, gage elevation, drainage area, and mean annual streamflow for the period of record. Approximate average annual precipitation was estimated for each drainage area based on precipitation data from Figure 3. Streamflow is also presented as a percentage of precipitation in each drainage area. Assuming that precipitation is the main contribution to streamflow in the upland areas, this provides an estimate of the portion of precipitation that is attributable to runoff and perhaps unavailable for groundwater recharge. Although these estimates vary, percentages shown on Table 1 indicate that streamflow typically accounts for 20 to 30 percent of the average annual precipitation over the drainage area (Table 1).

Evapotranspiration

Evaporation from open water surfaces and evapotranspiration from soil/vegetation can represent a significant part of the overall water budget. These amounts vary throughout the Study Area with changes in climate factors such as temperature, wind, and humidity. The maximum amount of evaporation that could occur under average climate conditions if sufficient water is available is referred to as evaporative demand. The geographic distribution of average annual evaporative demand as measured by DWR (1975) for eastern Madera County is shown on Figure 3. Evaporative demand ranges from less than 40 inches per year to more than 60 inches per year with the highest demand in the southern and northern portions of the study area (Figure 3).

Evaporative losses from surface reservoirs can be relatively large because the water surface is continually exposed to evaporation. To estimate this amount, evaporation for the five largest reservoirs in the foothills was calculated. Using a computation of daily lake evaporation for Millerton Lake from DWR for the period of April 2000 to July 2001, an estimated 4.15 feet of water evaporated from the lake surface over one year. This estimate presumably accounted for daily weather conditions and lake surface area and resulted in an annual average lake evaporation of 20,120 acre feet per year (AFY). Using DWR pan evaporation data and correcting for an appropriate lake coefficient of 0.7, evaporation amounts from the other reservoirs were estimated in a similar manner. Surface areas were estimated from topographic maps, which tend to show lakes at full capacity. No evaporation data were available for Eastman Lake, but based on a water surface elevation similar to Millerton and Hensley Lakes, 5.0 feet per year of lake evaporation were assumed. Evaporation estimates are summarized on the following table.

Reservoir	Surface *Area*	*Est. Annual* Evaporation	*Evaporation as a Percentage* *of Watershed Precipitation*
*Millerton Lake*	4,850 acres	20,120 AFY	< 1 percent
*Eastman Lake*	1,750 acres	8,750 AFY	2.8 percent
*Hensley Lake*	1,550 acres	7,950 AFY	2.3 percent
*Bass Lake*	1,150 acres	3,335 AFY	2.7 percent
*Mammoth Pool*	1,000 acres	2,300 AFY	< 1 percent
*TOTAL*	10,300 acres	42,455 AFY

As shown on the table above, more than 42,000 AFY of water is lost to evaporation from the largest surface water reservoirs. Although Bass Lake and Mammoth Pool are almost as large as Hensley Lake, evaporation is much less because of the lower evaporative demand. Reservoir evaporation is also shown on the table as a percentage of precipitation in the drainage area. Depending on the size of the watershed, reservoir evaporation can account for more than 2.5 percent of precipitation amounts. Because of Millerton Lake and Mammoth Pool’s very large drainage area, computed lake evaporation accounts for less than one percent of total estimated precipitation.

Water is also lost from evapotranspiration, the combined effect of evaporation from soils and transpiration from vegetation. The potential evapotranspiration (PET) throughout eastern Madera County can be estimated by applying an appropriate coefficient (approximately 0.8) to the evaporative demand on Figure 3. The estimated PET in the Study Area ranges from 40 inches/year in the Oakhurst/Bass Lake area to 52 inches/year along the Madera Canal (DWR, 1974). The actual evapotranspiration (AET) depends on the availability of soil moisture throughout the year.

GROUNDWATER OCCURRENCE

A conceptual hydrogeologic model provides the overall framework for groundwater occurrence, levels, flow and storage in a given region. Because hydrogeologic data are currently limited in eastern Madera County, the simplest and most likely conceptual model for the area is presented, based on available site-specific and regional data.

Groundwater likely occurs in the fractured bedrock under unconfined and semi-confined conditions as shown by the conceptual diagram on Figure 6. The assumption of an unconfined aquifer derives from the fact that bedrock fractures, permeability, and specific yield typically decrease with depth. Although the likelihood of intercepting a productive and extensive fracture system decreases with depth, details of the fracture systems are unknown. Some bedrock areas are relatively unfractured, even near the surface, and may not yield sufficient water to wells (Figure 6).

Fractured bedrock aquifers would be recharged at the surface, especially in areas where shallow alluvium overlies extensively fractured or weathered bedrock. Rates of recharge would depend on such factors as slope and amount of water available for recharge in the watershed.

The fact that water levels rise in wells above the screened zones has been used by other investigators to suggest confined aquifers. Rather than evidence of confinement, this is likely the result of vertical gradients in a low permeability, unconfined system. In general, it is unlikely that regional confined aquifers with usable groundwater exist, as this would require the following:

· a continuous unfractured rock layer relatively close to the surface, acting as a confining layer

· an underlying zone that is extensively fractured at depth

· a regional connection of the deep fracture system with upland recharge areas.

This layering seems unlikely on a regional basis and not as probable as groundwater wells tapping a regional shallow fracture system that decreases with depth. A confined aquifer system would require substantial field data to justify proposing it as the conceptual model for eastern Madera County.

Groundwater Levels

Groundwater levels throughout the foothill and mountain region can be expected to vary significantly depending on location, with relatively shallow depths to the water table in valley areas and greater depths to the water table beneath upland areas as shown on the schematic profile on Figure 7. Water levels recorded in wells in the foothills or mountains may not reflect the depth of the water table due to strong vertical gradients (downward in upland locations and upward in valley locations). Flowing wells in valley areas are likely due to greater heads at depth caused by upward gradients in unconfined aquifer systems. Thus, the water level in a deep valley well typically rises above the water table in an unconfined bedrock aquifer. Conversely, the water level in an upland well is typically below the water table due to downward gradients causing lower heads with depth

Water level data were generally unavailable for this study. Although water levels are sometimes measured for county water systems, data are not systematically recorded or available in non-archived files. DHS staff indicated that some water level data may be available for some of the large water systems in their public files, but are in storage and difficult to access. Because of this general lack of water level data and difficulty in obtaining the limited data, groundwater level contour maps and hydrographs could not be constructed for the foothill and mountain areas. A review of driller’s logs in the Oakhurst and Bass Lake areas (Township 7 South, Ranges 21 and 22 East) indicate static depths to water that average approximately 54 feet with a range of 15 to 127 feet (average well depth of 395 feet).

In most cases where both the first occurrence of groundwater and static water levels are reported, the static water levels are shallower. This is typical in low permeability settings, where it can take a considerable amount of time (sometimes days, weeks, or even months) for water to seep into the borehole or well and reach a stabilized static water level condition. In fact, the heat generated at the drill bit and slow rate of seepage due to low permeability may give the appearance of a dry hole during drilling, when in fact, the borehole may be below an unconfined water table. For these so-called “dry holes” drilled below the regional water table, water would likely seep into the borehole if open for a sufficient amount of time. However, wells with very low seepage rates would also have lower permeability (fewer fractures) and ultimately lower well yields (Figure 6).

Groundwater Flow

Groundwater flow in an unconfined aquifer in mountainous terrain typically mimics the topography, such that the water table is a subdued replica of the topographic profile. Elevation differences of the land surface provide the topographic drive mechanism for movement of unconfined groundwater in the bedrock flow system. Recharge accumulating from higher elevations discharges at lower elevations as shown by the flowlines on Figure 7. This groundwater recharge maintains the continual flow of groundwater through the system (Domenico and Schwartz, 1990).

Mountainous regions tend to be characterized by flow systems on various scales, ranging from local to regional. Regional flow systems may involve deep circulation of groundwater, whereas local groundwater flow systems would typically be limited to shallow circulation (Domenico and Schwartz, 1990). The greatest amount of groundwater flow would occur within the local/shallow flow system. Topographic divides and major stream valleys tend to be the locations of groundwater divides, at least for the local flow system as shown by the flowlines on Figure 7. Given this flow system, surface water divides are often used in defining a groundwater basin and designating an appropriate unit for a water balance.

Groundwater Storage

Groundwater storage in the fractured bedrock aquifer of eastern Madera County is expected to be relatively small. Specific yield values for fractured rock are typically in the range of 0.1 to 3 percent, with decreasing values with depth. A typical average value of specific yield in the upper 1,000 feet of saturated fractured rock may be on the order of 1 percent. Using this value to quantify storage beneath one square mile (640 acres), the upper 1,000 feet of saturated bedrock would have an estimated groundwater storage of 6,400 AF. Assuming that specific yield decreases significantly with depth, most useable groundwater in storage likely occurs in the upper 300 feet of saturated bedrock, thus reducing the storage estimate to 1,920 AF over one square mile.

GROUNDWATER USE

Groundwater is the main source of water supply in eastern Madera County. Surface water in streams, reservoirs, or springs, is used to supplement the groundwater supply in some areas. Water systems range from large systems with more than 200 connections to single domestic wells. Madera County operates 15 community water systems in eastern Madera County as Maintenance Districts or Service Areas. Of these 15 systems, only one (Indian Lakes) is considered a large system (more than 200 connections) and permitted by the Department of Health Services. The 14 small systems are permitted by the Madera County Environmental Health Department. Four additional large water systems, Hillview/Goldside (Hillview Water Company), Oakhurst/Sierra Lakes (Hillview Water Company), Yosemite Lakes Park (Yosemite Spring Park Utility Company), and Bass Lake (Bass Lake Water Company), are operated by private companies. Production data were collected from all of the county-operated systems, the four largest private systems, and six additional private systems that provide drinking water to foothill communities. The locations of the 15 county-operated systems and the 10 private systems are shown on Figure 8, and a summary of these water systems is provided in Table 2. Combined, these 25 water systems provide more than 10,000 persons with water supply. Average annual production is more than 2,600 AFY, most of which is provided by groundwater as discussed below (Table 2).

County Water Systems

Of the 15 county-operated community water systems, 13 rely solely on groundwater for their water supply. As shown on Table 2, the systems serve an average of 596 AFY to approximately 969 connections, but may need to expand capacity as future development occurs. Almost one-half of the systems either have current water shortage problems or have reported being close to capacity. Peak demands require several systems to operate close to their full capacity as illustrated by the Peak Demand/Capacity ratio shown on Table 2. The higher this ratio, the more likely the system has water shortage problems unless surface storage can be used to supplement well production for peak demands. County-operated systems with documented concerns about current or future capacity include Hidden Lakes, Indian Lakes, Mountain Ranches, Lakeshore, Marina View, and Teaford. Demand at Miami Creek Knolls exceeds system capacity but additional supply is available through an intertie to Dillon Estates (Table 2, Figure 8). In addition, more than 500 parcels in the county-operated water system service area are vacant. Many of the systems do not appear to have sufficient capacity to support full build-out.

A data summary of the wells used by county and private systems is included as Table 3. As shown in the table, many details on well construction and yield are unavailable in current files. Additional well details may exist in archived records for each district. The County may wish to further research well detail information and record other helpful information such as specific capacity data and static water levels. A brief summary of each of the county-operated systems is provided in the following sections.

Hidden Lakes MD 1 - This district, located on Millerton Lake, uses lake water for their water supply. The district serves water to 33 homes and contains approximately 170 vacant parcels. Two pumps in the lake provide raw water to a 60 gallons per minute (gpm) surface water treatment plant built in 1986. Treated water goes to a 135,000 gallon storage tank for delivery to customers. Water demand exceeds supply during peak use in summer months. Currently, residents are alerted to low supply conditions and try to conserve water during these times. It has been noted that the distribution mains are in very poor condition and will eventually need to be replaced (Madera County Special Districts, no date; Beck, April 18, 2001). Sewage disposal is through individual septic tanks (Madera County, April 11, 2000).

Mountain Ranches MD 5 - This district is located on Road 400 above Hensley Lake. The district serves water to 15 homes and has 34 vacant parcels. The source of water is two bedrock wells, located 20 feet apart at the corner of Road 400 and Mountain Ranch Drive. The older well, installed in 1964, was originally drilled to 360 feet and deepened in 1992 to 600 feet. The well produces approximately 12 gpm. This well was supplemented with a new well installed in 1998 to a depth of 1,007 feet. At the time of drilling, an airlift test indicated that the well could yield 28 gpm, but current production is approximately 13 gpm. Current combined production from the two wells is estimated at 25 gpm. Groundwater is stored in a 20,000-gallon storage tank for delivery to customers. Since it is necessary to pump both wells in summer to keep up with current demands, additional development will likely cause water shortages. Water quality issues include slightly elevated concentrations of fluoride. Fluoride concentrations are 1 part per million (ppm) in the older well and 2 to 3 ppm in the newer well, resulting in a blended supply at or near the flouride maximum contaminant level (MCL) of 2 ppm. The nearest septic system is 150 feet from the wells (Madera County Special Districts, undated; Beck, April 18, 2001; Madera County, June 17, 1999).

Lakeshore MD 6 - The Lakeshore Water and Sewer District is located on Road 274 along the north shore of Bass Lake. Water is supplied to 46 homes and the district has 3 vacant parcels. Water is supplied from two bedrock wells located north of Road 274 and approximately 50 feet from a stream. The main well, designated the Lower Well, is 450 feet deep and produces 35 to 40 gpm. The Upper Well produces 10 gpm, but depth and construction details are not available. Combined production is estimated at 46 gpm. Groundwater is pumped to three storage tanks with a combined capacity of 105,000 gallons. Currently, the water supply is about equal to peak summer demands. With respect to water quality, groundwater exceeds maximum contaminant levels for arsenic and uranium. Sewer service and treatment is provided for 42 homes. Aeration capacity is often exceeded on major holidays when the population of the area increases. The nearest septic system is approximately 2,500 feet from the wells (Madera County Special Districts, undated; Beck, April 18, 2001; Madera County, July 27, 1998).

Marina View MD 7 - The district is located on the north shore of Bass Lake along Road 274. The district supplies water to 71 homes and has 21 vacant parcels. The water system includes two wells with a combined production capacity of 57 gpm according to one report (Beck, April 18, 2001). A previous report indicated a combined production capacity of 43 gpm for the two wells (Madera County, no date). These reported production capacities are considerably less than the combined well yields of 170 gpm reported on the two driller’s logs (Madera County, May 25, 2001). The wells are located on the northeast corner of Road 274 and Marina View Way about 30 feet apart, and 50 feet from a stream. The main well, designated the Lower Well, is 570 feet deep after deepening in 1979, and the Upper Well (sometimes referred to as Wishing Well) is 202 feet deep. Groundwater is stored in two tanks with a combined capacity of 95,000 gallons. Well capacity meets peak summer demands, but an increase in demand would likely exceed capacity. Groundwater quality concerns include uranium, which exceeds the maximum level for drinking water. Sewer service is provided to 71 homes with no current problems, but the treatment plant is old and may need to be replaced in the future. The nearest septic system is approximately 2,500 feet away (Madera County Special Districts, undated; Beck, April 18, 2001; Madera County, May 25, 2001).

North Fork MD 8 - This district serves water to the town of North Fork and the U.S. Forest Service complex. The district has 49 residential connections, 9 commercial connections having 27.56 equivalent dwelling units (EDUs), and 22 standby connections. The water system has one well, designated the Library well, pumping 240 gpm into a 200,000-gallon storage tank. The well was drilled in 1994 to a depth of 520 feet. An additional existing well, known as the North Fork Center Well, is currently inactive but available for future use. Water shortages have not been an issue for this district. Sewer service is also provided by the district to the town of North Fork, North Fork School, and the US Forest Service Complex. (Madera County Special Districts, undated; Beck, April 18, 2001; Madera County, January 7, 1998).

Teaford MD 24 - This district is located near Road 223 at Teaford Saddle between North Fork and Oakhurst at an elevation of 3,700 feet MSL. Water service is provided to an area with 56 homes and 16 vacant parcels. The water system consists of three bedrock wells producing at a combined rate of approximately 37 gpm. Water is pumped into a 125,000-gallon tank for storage. Well #1 is the main well producing 30 gpm on Teaford Poyah Road on the south side of Finegold creek. Well #2 is 500 feet west of Well #1 on the north side of the creek and produces 13 gpm. Well #3 is on the east side of Finegold Creek Road across Road 221 and produces 7 to 8 gpm. Water supply just barely keeps pace with peak summer demands. Sewer service is currently provided to 51 homes. No septic system is located within 500 feet of the wells (Beck, April 18, 2001; Madera County, November 13, 1996a).

Sunset Ridge MD 40-A - The district is located near Road 417 at Sunset Ridge Road East and Sunset Ridge Road West at a topographic elevation of 1,500 feet. Water is served to a subdivision with a total of 26 build-out connections, 16 of which are currently developed. The water system includes two wells pumping a combined 73 gpm, and two storage tanks with a combined 12,000 gallon capacity. Well #1 is 680 feet deep and produced 100 gpm during the driller’s airlift test and 53 gpm during a 72 hour pumping test. Well #2 is 550 feet deep and produced 30 gpm during the driller’s airlift test. Groundwater contains elevated iron and manganese levels that have caused complaints of dirty water. No water shortages have been reported. The homes have onsite septic systems, but no septic system is located within 150 feet of a well (Beck, April 18, 2001; Madera County, October 22, 1997a).

Still Meadow MD 42 - The district is located at Road 426 and Meadow View Drive. The water system is located above Oakhurst at a topographic elevation of 3,000 feet MSL. Water is served to 25 homes and includes 12 vacant parcels (Beck, April 18, 2001). The water source includes two bedrock wells: Well #4 is 405 feet deep and produced 50 gpm on an airlift test; Well #6 is 430 feet deep and produces an estimated 35 gpm (Madera County November 13, 1996b). Actual combined production from the two wells is reported at 55 gpm (Beck, April 18, 2001). Groundwater is pumped to two storage tanks with combined capacity of 50,000 gallons. Future build-out may require additional water supply. Problems with radiological water quality have been reported for at least one of the wells. Houses have septic systems but none within 200 feet of the two wells (Madera County, November 13, 1996b).

Miami Creek Knolls MD 43 - The district is located on Lauri Lane at Highway 49 near Ahwahnee at an elevation of 2,500 feet MSL. The water system has three active wells with a combined production capacity of 15 gpm, and a 13,000-gallon storage tank. The water source includes four bedrock wells. Well #4 is 439 feet deep and produces 5 gpm according to airlift tests. Well #1 produces 1 gpm, but specific well construction and production information were unavailable for wells #2 and #3. Supplemental water is received as needed from District 60, and thus no water shortages occur. However, water shortages were a problem prior to hook-up with MD 60. The distribution system is old and in very poor condition. Water is served to 26 homes and includes 6 vacant lots. Houses have septic systems, but none within 150 feet of wells ((Beck, April 18, 2001; Madera County, May 29, 1997).

Ahwahnee Country Club and Miami Creek Estates MD 46 - The district serves water to 37 homes and one commercial connection using 4 EDUs and has 69 vacant parcels. The water system includes six wells with combined production of 184 gpm, and two storage tanks with combined capacity of 185,000 gallons. The wells include the following:

ACC Well #1 produced 68 gpm during a 72 hour pumping test

ACC Well #2 produced 80 gpm during a 72 hour pumping test

ACC Well #3 produced 90 gpm during a 72 hour pumping test

MCE Well #1 produced 31 gpm during a drillers airlift test

MCE Well #2 produced 9 gpm during a drillers airlift test

MCE Well #3 produced 2 gpm during a drillers airlift test

No water shortages have been reported. Uranium concentrations in the water are near or exceeding the MCL. The homes in the area have onsite septic systems, but none located within 150 feet of the wells (Beck, April 18, 2001; Madera County, October 22, 1997b).

Sierra Highlands MD 58 - The district is located at Road 223 and Road 236 in the mountains at a topographic elevation of 3,500 MSL. The district serves 20 homes with 8 vacant parcels. The water system has one active well producing 86 gpm and a 60,000-gallon storage tank. No water shortages have been reported, and one additional well is available if needed. The water source consists of two bedrock wells installed in 1990. Well #1 was drilled to a depth of 705 feet and serves as a backup source. A 1991 pumping test lasted 72 hours and produced 44.5 gpm. Well #4 was drilled to a depth of 380 feet, and a 72-hour pumping test produced 93.4 gpm. Houses have septic systems but none are within 150 feet of wells (Beck, April 23, 2001; Madera County, November 23, 1998).

Dillon Estates MD 60

The district is located near Highway 49 and Sunrise Drive at a topographic elevation of 2,000 feet MSL. Water is supplied to 33 homes and 5 vacant lots, and to District 43 on an as-needed basis. The water system consists of two wells with combined production of 105 gpm, and a 64,000-gallon storage tank (Beck, April 18, 2001). The water source is two bedrock wells. Well #1 was drilled in 1990 to depth of 900 feet and produces 55 gpm based on 72 hour pumping test. Well #2 is 140 feet deep and produces 15 gpm based on 72-hour pumping test (Madera County, June 26, 1997). The reason for the discrepancy in production capacity (105 gpm versus 70 gpm) between the two references cited above is unknown. However, no water shortages have been reported. Houses have septic systems but none within 150 feet of wells (Madera County, June 26, 1997; Beck, April 18, 2001).

Quartz Mountain MD 73 - The district is located on Quartz Mountain Road near Road 417 behind Indian Lakes Subdivision in the Coarsegold area. Water is served to 64 homes and 72 vacant parcels. The water system includes four wells with combined production of 170 gpm, and a 125,000-gallon storage tank (Beck, April 18, 2001). The four bedrock wells had a combined flow of 189 gpm when tested in 1999. Well #1 (Willow Pond #1) is located near Willow Pond Land and Willow Pond Road, and pumps 23 gpm for a limited pumping time. Well #2 (Willow Pond #2) is located on Willow Pond Road just before Willow Pond Lane and produces 58 gpm. Well #3 (Quartz Mtn. #1 or Ridge Well #1) is located on Quartz Ridge Road near Long View lane and produces 51 gpm, but has iron and sulfur problems. Well #4 (Quartz Mtn. #2 or Ridge Well #2) is located on Long View Land East near Long View Lane, and was installed in 1994 or 1995 to a depth of 400 feet; it is artesian, has iron problems, and produces 58 gpm. No water shortages have been reported, but it is noted that water shortages may occur with total build-out. Water quality issues include high levels of iron and manganese. Houses have septic systems but none within 150 feet of community wells (Madera County, April 7, 1999; Beck, April 18, 2001).

Indian Lakes SA 1 - The district is located at Road 417 and Delaware in the Coarsegold area. The water system includes five wells with combined production of 600 gpm and a 750,000-gallon storage tank. The district serves water to 403 homes and 110 vacant parcels (Beck, April 18, 2001). The water system includes six bedrock wells of which four (or five) are active and producing 500-600 gpm. The estimated maximum demand rate is 449 gpm. Well #1 was drilled in 1966 to a depth of 375 feet, and produces 100-140 gpm. Well #2 was drilled in 1966 to a depth of 325 feet, and deepened to 450 feet with no additional water production; the well is planned to be abandoned. Well #3 was drilled in 1966 to 285 feet and later deepened to 405 feet, and produces approximately 55 gpm. Well #4 was drilled in 1979 to 375 feet and produces 50-65 gpm; and is near a natural drainage. Well #5 was drilled in 1988 to 370 feet, and the pump capacity is 150 or 375 gpm but the ability of the well to maintain these rates is unknown. Well #6 was drilled in 1999 and is not yet online (California DHS, October 10, 2000). These wells are not closer than 100 feet to sewage disposal. Due to water shortages and dirty water complaints, major improvements have been made including an iron/manganese treatment plant and the drilling of Well #6 (Beck, April 18, 2001).

Bass Lake - Wishon Cove SA 2 - Bass Lake Service Areas 2B and 2C are located on Road 222 on south shore of Bass Lake at an elevation of 3,335 feet MSL. Water is served to 32 homes and three commercial connections (43 active and 6 standby EDUs). The water system consists of two submersible 50 gpm pumps in Bass Lake that supply a treatment plant capable of processing 100 gpm. Treated water is stored in a 60,000-gallon storage tank. Water shortages have not generally been a concern. Wells were originally installed but not used due to arsenic, uranium, iron, and manganese levels exceeding MCLs. The fuel oxygenate, methyl tertiary-butyl ether (MTBE), occurs in raw lake water at concentrations of approximately 25 ppb and is sometimes present at lower levels in treated water. Sewage disposal is via a community sewer system. (Beck, April 18, 2001; Madera County, September 19, 2000).

Private Water Systems

Hillview Water Company is the largest private water provider in eastern Madera County, accounting for almost 1,500 AFY of groundwater. They operate four separate water systems from Raymond to Coarsegold to the Oakhurst area (their largest system) (Table 2, Figure 8). The second largest system is operated by Yosemite Spring Park Utility (also referred to as Yosemite Lakes Park or YLP) located in the central foothill region southwest of Coarsegold (Figure 8). They provide 734 AFY to water users in three local service areas. With the exception of Cedar Valley, which relies on Hackney Springs for its supply, all of the systems rely on groundwater wells. Three systems (Bass Lake Water District, Cascadel Water Company, and Yosemite Forks) supplement their groundwater supply with surface water from streams and springs. A brief summary follows for these and the other private and county-operated systems listed on Tables 2 and 3 and shown on Figure 8.

Broadview Terrace Mutual Water Company - Broadview Terrace is located in Oakhurst at an elevation of 2,500 feet. This water system serves 163 residential connections, two small apartment buildings, and the Fresno Flats historical museum. The system sources include seven bedrock wells and a connection to the Hillview water company. However, the Hillview source is not currently used due to its own water supply and uranium concentration problems. The current active production of the seven wells is estimated to be 181.5 gpm. Well 1 produces 15 gpm, Well 2 is 300 feet deep and produces 15 gpm, Well 3 is 233 feet deep and produces 15 gpm, Well #4 is 200 feet deep and produces 10 to 15 gpm, Well 5 is 900 feet deep and not used due to high uranium levels, Well 6 is 210 feet deep and produces 1.5 gpm, and Well 7 is 525 feet deep and produces 125 gpm. Two storage tanks of 45,000 and 50,000 gallon capacity are used. Uranium concentrations are a concern with Well 7 having a level of 329 pC/l. Homes have on-site septic systems (Madera County, April 24, 2000).

Raymond Water System (Hillview Water Company) - The Raymond Water system serves a small area between Hensley Lake and Eastman Reservoir. The service area includes 74 connections and a population of 207. The Raymond water system has five active bedrock well sources that produce a combined 55 to 60 gpm. However, recorded production of the wells at the time of inspection was 32 gpm. A summary of the active and inactive sources is provided in Table 3. The water storage system consists of five 25,000-gallon storage tanks. It appears that peak summer demands may equal or exceed well production capacity. Water quality concerns include elevated (but within state standards) nitrate levels at active Wells 5 and 8, and inactive wells 6 and 9 (California DHS, March 9, 2001).

Hillview-Goldside Water System (Hillview Water Company) - Water service is provided to residences in the Hillview, Goldside, Goldside Estates, and Fresno River Estates subdivisions. There are 267 residential service connections with a population of 801. This water system has 10 bedrock wells of which five are active (Table 3). Peak hour water demand of 162 gpm is not met by the active well production capacity of 129 gpm, but is met with inclusion of storage. Two water storage tanks have capacities of 408,000 and 105,000 gallons. Water quality concerns include elevated chloride and total dissolved solids (TDS) at Goldside Well No. 4 and elevated nitrate at Goldside Well No. 1 (California DHS, June 13, 2001).

Coarsegold Highlands Water System (Hillview Water Company) - The water system serves residences in the Coarsegold Highlands subdivision with 22 residential connections and a population of 62. The water source is one active bedrock well with a pumping capacity of 37 gpm. A second well has been drilled and may be brought on-line in the future. The current production capacity is sufficient to meet the estimated peak hour demand of 21.6 gpm. Water is stored in a 30,000-gallon storage tank. An occasional exceedance of the manganese standard has been reported (California DHS, April 19, 2001).

Oakhurst - Sierra Lakes Water System (Hillview Water Company) - This water system serves the majority of residences and businesses in the Oakhurst area, and has 922 connections serving a population of 2,582. The total number of dwelling units and spaces served by the system is estimated to be 1,266. The sources consist of nine active bedrock wells with a combined production reported to be 700 to 800 gpm (Table 3). Iron and manganese treatment is required for most of the wells, and gross alpha, uranium, and TDS concentrations exceed the standard at some wells. Water is stored in 18 tanks with a combined capacity of 902,500 gallons (California DHS, November 30, 1999).

Yosemite Springs Park Utility Company (YLP) - The service area is located in the Fresno River drainage between Hensley Lake and Oakhurst. The water system has an estimated 1,450 connections serving a population of 3,400. The current water supply is derived from 14 active wells (summarized in Table 3) and stored in nine tanks. There are also several inactive and abandoned wells. The combined water production capacity of 14 wells is estimated at 1,215 gpm. This capacity is sufficient to meet maximum day (1,042 gpm) but not peak hour (1,563 gpm) water demands. The available storage tanks do allow the system to meet peak hour demands. Residents have individual septic systems or leach field disposal systems (California DHS, May 8, 2001).

Bass Lake Water Company - The water system consists of 787 residential connections and 27 commercial connections serving a permanent population of 700 and a seasonal population of 3,000. Water sources include surface water and groundwater. Surface water is obtained from Willow Creek, which drains a 20,000-acre watershed. Surface water goes to a treatment plant with a design capacity of 400 gpm. During peak summer months the treatment plant operates at or above its design capacity. Groundwater is supplied by three active wells producing a combined 103 gpm based on three day pumping tests (see Table 3). An elevated iron concentration exceeding the secondary MCL was reported for one of the active wells. A fourth well is designated as a standby source, and produces 100 gpm of high uranium water. Three additional wells were being evaluated in 1995 for possible inclusion in the water system (California DHS, June 7, 1995).

Cascadel Water Company - This water system of over 130 connections is located at an elevation of 3,500 feet MSL along Cascadel Drive east of the community of North Fork. The four sources of water include three wells and one spring. Historical spring flows range from a low of five gpm during the drought to over 100 gpm. The spring was originally the main source of water, but was not able to meet Title 22 requirements for bacteriological quality and had high turbidity after rain events. It was considered to be under the influence of surface water as defined by the surface water treatment rule. Recent renovations to the spring appear to have solved the problems and it is considered a potable source, although it is still closely monitored. The spring may be under the influence of surface water as turbidity spikes occur after rain events; however, the turbidity also may be related to decomposed granite. A 24-hour pumping test of Wells 1 (500 feet deep) and 1A produced 57 gpm combined, and Well 2 is 550 feet deep and produces 25 gpm. Assuming an average spring flow of 50 gpm and well capacity of 82 gpm provides 132 gpm capacity for the system, or about 1 gpm per connection. No water outages have been reported.

Reservoir 1 was installed in 1995. It consists of two tanks of 45,500-gallon capacity each, and collects water from the spring and Well 1. Reservoir 2 consists of three 15,000-gallon capacity tanks, and collects water from Well 2. Homes use septic systems, but none within 300 feet of any well and none within 1,000 feet of the spring (Madera County, July 14, 2000).

Yosemite Forks - This water system serves 114 homes. The three sources of water are Hackney springs in Cedar Valley and two bedrock wells. The springs are described in the Cedar Valley section below and are estimated to produce 45 gpm. Well 1 was drilled in 1985 to 286 feet and produces 45 gpm based on drillers lift test. Well 2 was drilled in 1996 to a depth of 500 feet and produced 55 gpm from a drillers lift test. Water storage includes a 44,000-gallon below ground tank. The wells are not within 150 feet of any septic system (Madera County, June 6, 1997).

Cedar Valley - This water system is located along Highway 41 north of Oakhurst, and serves a subdivision of small lots with onsite septic systems. The water source is Hackney springs. There have been recent problems with positive bacteria tests and failure to sample for bacteria. Hackney springs are located in a meadow northeast of the subdivision. The springs were initially developed several decades ago. Spring water flows to a 4,000 gallon below ground storage tank, water is pumped up to a 1,500 gallon storage tank for gravity feed to Cedar Valley customers. Overflow water goes to Yosemite Forks 120,000-gallon storage tank. No septic system is within 300 feet of spring, but a horse pasture is 200 feet from spring (Madera County, May 5, 1999).

Additional Small Community Systems

In addition to the 25 water systems discussed above, approximately 20 additional small community water systems also provide water supply to customers in the foothill region (Table 4). These water systems include mutually-owned water companies and typically provide water to well-defined areas such as a mobile home park. Although water demand is unknown for these small systems, water use based on population has been estimated. Using a small water system factor estimated from the 15 county-operated systems, these additional community and small state water systems likely provide about 934 AFY of groundwater.

Non-Community Water Systems and Domestic Use

Additional water use in eastern Madera County includes the non-community water systems and individual wells. The non-community water systems include commercial locations such as gasoline stations, mini-marts, restaurants, churches, or schools that are not tied into another system. Often these facilities have one well and a variable or seasonal population. Groundwater use by these systems has not been quantified. There are approximately 69 such non-community water systems in eastern Madera County (Madera County, March 31, 2001).

Many individuals in rural developments rely on individual groundwater wells for water supply as indicated by names on Water Well Driller’s Reports (driller’s logs). There are 4,609 logs for wells drilled in eastern Madera County that were obtained from DWR files. Although the logs may be a relatively reliable estimate of the number of wells drilled in eastern Madera County for a certain period of time, they may not reflect the number of currently active wells used for domestic purposes. Limitations of using driller’s logs to estimate current domestic production include:

· wells may be shared by several households;

· wells may be abandoned;

· wells may have been tied into a community water system;

· wells may be used for non-potable uses only;

· logs may not be filed for every well;

· DWR files did not include wells drilled 1999 or 2000 when logs were copied.

Recognizing these limitations, the 4,609 driller’s logs remain the only practical data for estimating domestic use of groundwater. Approximately 109 wells are estimated to be associated with the community water systems, where water demand is estimated separately. If a water demand factor of 0.5 AFY (typical factor often used to estimate a household’s water demand) is assigned to the 4,500 remaining driller’s logs (4,609 less 109), an additional water demand of 2,250 AFY is calculated. The uncertainty in this estimate from driller’s logs is unknown, given the limitations outlined above.

Water Demand

Current annual production for the County Maintenance Districts, selected Private Water Systems, and other small community water systems is tabulated on Tables 2 and 4 and summarized below:

County Water Systems 596 AFY

Larger Private Water Systems 2,023 AFY

Additional Community Water Systems 934 AFY

Domestic Water Wells 2,250 AFY

Total 5,803 AFY

Recognizing the limitations of these estimates, especially the estimation of domestic water use, total water demand in eastern is estimated at 5,803 AFY.

Driller’s logs are a good indication of the relative density of water wells that have been drilled in eastern Madera County. Driller’s logs were tabulated by townships and plotted with patterns representing concentrations of wells (Figure 9). As shown on the figure, most of the wells have been drilled in the foothill region with the majority occurring in the Fresno River basin near and south of Oakhurst including T7S/R21E, T8S/R20E, and T8S/R21E. Collectively, these three townships contain approximately 2,222 wells, almost one-half of all wells drilled in eastern Madera County. Other areas of concentrated wells include T7S/R22E (Bass Lake), T8S/R23E (North Fork), and T6S/R21E (Ahwahnee/Yosemite Forks), with each township containing more than 300 wells as tabulated below.

Townships with more than 300 wells:

Oakhurst area (7S/21E) 1,114 logs,

Coarsegold area (T8S/R21E) 603 logs

along the Fresno River (T8S/R20E) 505 logs

Yosemite Forks area (T6S/R21E) 444 logs

Bass Lake area (T7S/R22E) 378 logs

TOTAL 3,349 logs

These six townships represent roughly 18 percent (6 of 33 townships) of the Study Area, yet contain 73 percent of the wells drilled in eastern Madera County.

Groundwater use is most concentrated in the Oakhurst area as indicated by water system production on Table 2 and the large number of wells drilled as shown on Figure 9. The Upper Fresno River drainage, including this Oakhurst area, covers approximately 116 square miles (74,000 acres) upstream of Potter Ridge, or approximately nine percent of the total foothill/mountain area of Madera County (866,334 acres) (Figure 5). The water demand in this drainage area is met by nine of the water systems included on Table 2 with annual production as follows:

Oakhurst/Sierra Lakes 622 AFY

Broadview Terrace Mutual Water 46 AFY

Still Meadow MD 42 21 AFY

Hillview/Goldside 100 AFY

Miami Creek Knolls MD 43 17 AFY

Dillon Estates MD 60 16 AFY

Ahwahnee Country Club MD 46 19 AFY

Yosemite Forks 58 AFY

Cedar Valley 74 AFY

Total 973 AFY

In addition to these systems, there are approximately 1,900 driller’s logs in the DWR files for this area. Again, applying a water demand factor of 0.5 AFY per well (950 AFY) and adding in the above production data, approximately 1,923 AFY is estimated as water demand in the Upper Fresno River drainage area. This is approximately 33 percent of the total water demand in eastern Madera County over less than 10 percent of the area.

GROUNDWATER QUANTITY

Well Yields

Driller’s logs in the Oakhurst and Bass Lake areas (1,492 logs in two townships) were examined for data on construction, water levels, and well yields. More than 98 percent of the driller’s logs reported well yields, all of which were estimated using airlift methodology. There are inherent problems in using airlift methods rather than more conventional pumping tests to estimate well yields because exact drawdown and discharge data are rarely known. As mentioned previously, for the few wells with both airlift data and pumping data, yields from the airlift methods are noticeably larger. With these limitations in mind, well yields estimated by airlift methods ranged from less than 2 gpm to more than 50 gpm and averaged 22 gpm with a median yield of 8.5 gpm. The number of wells associated with various well yields are shown below.

More than one half of wells had yields of 10 gpm or less and 86 percent of wells had yields of 40 gpm or less. Well yields in most fractured bedrock aquifers are typically in the range of 1 to 50 gpm on a long-term sustained basis (Borchers, 1996; DWR, October 1990b; Page et al., 1984).

Estimates of well yields may not reflect sustainable pumping rates in a well, and as such, well yields presented above may be misleading with respect to water availability. To better estimate actual well yields from airlift yield estimates, Todd Engineers examined data from another bedrock area where well yields from 17 wells were estimated using both airlift methods and pumping tests of long duration. The results of the analysis are tabulated in Table 5. Average and median well yields from airlift methods were measured at 24 and 10 gpm, respectively. Comparable well yields from these same wells using pumping test data were 12 and 8 gpm, respectively. Data indicate that airlift estimates were close to pumping test estimates when the well yields were 10 gpm or less. However, for airlift-measured yields greater than 10 gpm, actual yields were determined to be about 50 percent lower. These data suggest that airlift-measured well yields exceeding 10 gpm for bedrock wells are likely higher pumping rates than can be sustained and should be verified with long-duration constant rate pumping tests conducted under the supervision of a hydrogeologist. This is especially true when the stated well yield for a particular well is critical to meeting water demands.

This observation is further substantiated when comparing well yield data from eastern Madera County water systems that provide well yields measured from both airlift methods and pumping tests. Table 6 shows well estimates from ten such wells. For nine out of the ten wells, airlift well yield estimates are higher than pumping test or production rates. Although Table 6 does not factor in variables such as possible declining yields over time, data suggest that airlift-measured yields are much higher than actual production capacities, often more than double.

Water Balance

A preliminary watershed-based water balance approach is discussed in this section as a first step in assessing the capacity for additional development of groundwater supplies from bedrock areas. Whereas the assessment of well yields provides general guidelines for the number of wells that may be necessary for a given local water demand, a water balance is helpful to evaluate the overall capacity of a given area to support existing uses and potential future water demands. Given the limited data available for this assessment, a qualitative approach is put forth with a focus on groundwater recharge.

A water balance examines change in groundwater storage by quantifying and subtracting outflows from inflows. Groundwater inflow in the eastern portion of Madera County is primarily limited to percolation of a portion of precipitation, referred to as groundwater recharge. Groundwater outflow could include discharge to streams and springs, groundwater pumping, evapotranspiration, phreatophyte use, and groundwater throughflow to the alluvial basin. If groundwater outflows consistently exceed groundwater inflows (as may occur when groundwater pumping becomes excessive), a continuous decline in groundwater storage results.

Estimating groundwater recharge is key in determining the perennial water yield from a drainage basin. Perennial yield for a groundwater basin is the rate water can be withdrawn on an average annual basis without producing an undesired result, such as declining water levels or water quality (Todd, 1980). DWR (1966) estimated that average annual recharge in the Oakhurst area is approximately five percent of average annual precipitation of 36 inches, or 1.8 inches. The basis for this estimate is not provided.

To evaluate groundwater recharge, a simple computer model was employed. The modeling approach uses a U.S. Environmental Protection model code, Hydrologic Evaluation of Landfill Performance (HELP) (Schroeder, Lloyd, Zappi and Aziz, September, 1994; and Schroeder, Dozier, Zappi, McEnroe, Sjostrom and Peyton, September, 1994). Although originally designed to calculate water balances specifically for landfills, the model is commonly being used for calculation of groundwater recharge in a variety of geologic and environmental settings. Several model runs were made to examine the percentages of runoff, evapotranspiration, and groundwater recharge that may occur in the foothills. Although the HELP model accounts for most aspects of the water balance, it does not account for phreatophyte water use and reservoir lake evaporation. For the purposes of these estimates, phreatophyte water use was assumed to be five percent of the total water balance and reduces available groundwater recharge accordingly. Reservoir lake evaporation was calculated separately and deducted from total runoff.

The modeling approach assumed a three layered vadose zone with a three foot thick upper soil layer, an intermediate three foot thick highly weathered bedrock/soil layer, and a 50 foot thick fractured bedrock layer down to the water table. Simulations were conducted to represent both the upper foothill area (Oakhurst/Bass Lake region) and the lower foothill area (Raymond area). Results are summarized in Table 7. Evapotranspiration for all model runs was based on monthly climate data at the Fresno station, resulting in more evapotranspiration than actually occurs at foothill elevations. Thus, results are conservative because the higher evapotranspiration amounts reduce streamflow and groundwater recharge in the model.

Results for the Oakhurst/Bass Lake region indicate that groundwater recharge in areas with steep slopes (e.g., 30 percent) would be in the range of 8 to 12 percent of the precipitation based on the inputs used. Evapotranspiration was typically on the order of 36 to 41 percent and runoff to streamflow (including runoff and lateral drainage) was approximately 43 to 48 percent in steep slope areas (Table 7). Streamflow consists of both surface runoff and lateral drainage (interflow) along the top of the fractured bedrock layer. The modeled runoff range of 25 to 47 percent for the Oakhurst/Bass Lake areas agrees reasonably well with the streamflow results in Table 1.

Areas with relatively flat slopes (e.g., 5 percent) had groundwater recharge in the range of 15 to 26 percent, evapotranspiration of 41 to 43 percent, and streamflow from 25 to 39 percent. Results for a model run in the lower foothill region (Raymond area) is also included on Table 7. Results indicate a net groundwater recharge of approximately 13 percent, with evapotranspiration of 70 percent, and streamflow of 12 percent.

These model simulations are intended to be another means of examining the overall water balance, and are not necessarily intended to be the sole or primary method of water balance determination. The model results are best used in conjunction with other methods to provide a range of values for various components of the water balance.

Based on modeling analyses and DWR estimates, a representative and conservative value for net groundwater recharge is approximately 10 percent of precipitation. Based on an area of 512,000 acres (800 miles squared) for the foothill region in Madera County, average groundwater recharge of 10 percent per year, and an average foothill region annual rainfall of 25 inches per year, the total groundwater recharge in the region amounts to approximately 107,000 AFY.

Although current water demand in the overall Madera County foothill region (5,803 AFY) amounts to only slightly more than five percent of groundwater recharge, most of the groundwater recharge occurs in portions of the county that do not contribute to the areas of groundwater use. For example, the Oakhurst urban area (Township 7 South, Range 21 East, Sections 10 to 15) covers six square miles (3,840 acres) with estimated water demands of 815 AFY. The estimated groundwater recharge for 3,840 acres is 1,250 AFY. Thus, water demands are estimated to be more than 65 percent of groundwater recharge in this area.

GROUNDWATER QUALITY

Inorganic and limited organic water quality data were compiled from Madera County Environmental Health, Madera County Engineering, DHS, and private water systems in eastern Madera County. These data are summarized in Tables 8 and 9 and on water quality plots (Trilinear Diagrams) in Appendix A. Inorganic groundwater quality and constituents of concern are discussed in the following sections.

Inorganic Water Quality

Water quality reports are provided annually to customers of the county-operated water systems. Although general in nature, these reports provide summary water quality data for the production wells and surface water sources. Annual reports for 1999 were compiled and summarized on Table 8. Using total dissolved solids (TDS) as an overall indicator of inorganic water quality, groundwater quality appears to be of good quality with some exceptions. TDS concentrations in groundwater average 226 ppm, well below the maximum limit of 1,000 ppm recommended for drinking water. The two surface water sources (MD1 and SA2B/2C) had TDS levels of approximately 40 ppm, less than the more mineralized groundwater. None of the county water systems appears to be impacted by the highly saline groundwater encountered in some foothill wells as reported by Mack and Schmidt (1981). However, some water quality problems do occur in the county systems including elevated concentrations of total coliform bacteria (MD6, MD7, MD42, SA1), gross alpha/uranium (MD6, MD7, MD46), arsenic (MD6), iron (MD73, SA1), and manganese (MD8, MD40, MD58, MD73, SA1). Elevated iron and manganese concentrations may be due to elevated turbidity in the sample and may not reflect actual groundwater concentrations.

Groundwater quality data were obtained for the private water systems of Hillview (Raymond, Goldside, Oakhurst, and Coarsegold), Bass Lake Water District, and Yosemite Springs, Cedar Valley, Yosemite Forks, Broadview Terrace, and Cascadel. Most of the data were provided by DHS and supplemented with data provided by the system operator. These data sets generally include analytical results for inorganic constituents for sampling events over the last 10 years (1990 through 2000). A summary of these data is provided in Table 9.

Similar to summary data on Table 8, TDS concentrations for the private systems on Table 9 are in the 100 ppm to 300 ppm range for most of the groundwater samples and generally below 100 ppm for surface water samples. However, elevated TDS levels exist in several wells of three Hillview Water Company systems including Oakhurst/Sierra Lakes, Raymond, and Hillview/Goldside. Each of these systems has at least one well with recent (1999) TDS concentrations exceeding the 1,000 ppm maximum limit recommended for drinking water. Although these levels do not generally present health concerns, a more mineralized taste may be associated with these groundwater samples. Perhaps more importantly, the limited data suggest an increase in TDS concentrations and worsening water quality over time. This increase in TDS appears to correlate to an increase in sodium (Na) and chloride (Cl) (Table 9). Although well construction and water quality data are limited, the increases do not appear to be directly related to depth; increases are noted in both shallow (less than 300 feet deep) and deep (deeper than 600 feet) wells. Because water level data were difficult to obtain, the correlation of water quality change and water levels could not be assessed. The source of the increase in TDS and sodium chloride over time in selected wells is unknown and will require additional investigation.

Recent (1999 or 2000) groundwater quality data were also obtained for county-operated water systems from Madera County Environmental Health. A summary of these data is also included in Table 9. TDS levels in county water system data from Environmental Health agree relatively well with the summary from the annual reports (Table 8) and range from 100 to 300 ppm.

To illustrate general groundwater quality in selected systems, data on Table 9 were plotted on water quality diagrams, referred to as Piper or Trilinear Diagrams. These are standardized plots that summarize the inorganic water chemistry graphically to illustrate different geochemical types of water (Hem, 1989). These plots are provided as Appendix A. Concentrations of major anions and cations in the water are converted to appropriate units and plotted on the two outer triangles. These points are moved along the graph lines to a summary point on the middle diamond. Points on the middle diamond are used to categorize different water types. The size of the circle around each plotted water sample indicates the concentration of TDS as measured on the TDS scale provided on the upper left. Appendix A contains summary plots for the following water systems:

Oakhurst/Sierra Lakes A-1

Raymond A-2

Yosemite Spring Park A-3

Bass Lake A-4

Indian Lakes A-5

Also provided is a plot of water quality data from the Hillview/Goldside Well No. 4 that illustrates the increasing chloride and TDS over time discussed above (Appendix A, page A-6).

Several observations can be made from the Trilinear Diagrams in Appendix A. Most of the groundwater samples indicate a strong predominance of the bicarbonate anion and a slight predominance of calcium among cations, indicating a calcium-bicarbonate water type. However, there is wide variability in groundwater chemistry within this water type, especially in the sources of Oakhurst/Sierra Lakes (Appendix A, A-1). As shown on page A-1 of Appendix A, samples are not clustered together (which would indicate similar water chemistry); rather, samples are scattered throughout the lower portion of the middle diamond, indicating highly variable water chemistry. The elevated chloride concentrations in the Ditton wells are shown by the sample cluster in the upper right portion of the diamond with large circles indicating TDS levels above 1,000 ppm. As shown on page A-2, groundwater and spring water samples are more tightly clustered on the Trilinear diagram for the Raymond system, with the spring sample plotting close to several wells in the central left portion of the diamond, indicating very similar water quality. A groundwater sample from Well No. 5 is the exception, plotting toward the top of the diamond and indicating higher TDS concentrations (A-2). As shown on page A-3, groundwater data from the Yosemite Spring Park Utility Company is clustered in a similar area to the groundwater samples in the Raymond system, again, indicating similar groundwater geochemistry. Groundwater samples shown on page A-4 from the Bass Lake Water Company also show calcium-bicarbonate water similar to other systems. However, the sample from Willow Creek has a higher percentage of chloride anions as shown by the sample plotting more to the center of the trilinear diamond, indicating different water chemistry than the local groundwater (A-4). As seen on page A-5, groundwater samples from Indian Lakes are tightly clustered, indicating a calcium-magnesium bicarbonate water that is similar in all wells. The increasing chloride and TDS concentrations in the Goldside No. 4 well discussed in detail above is illustrated on the Trilinear Diagram on page A-6 of Appendix A. As shown on page A-6, chloride and TDS concentrations increased steadily in samples taken in 1985, 1992, 1996, and 1999.

Inorganic water quality in the foothill region appears variable from area to area and often from source to source within a system. Variability in the groundwater geochemistry may be related to varying interconnection within fracture systems, varying mineral composition of the aquifer, and varying residence times of water in the groundwater system. In some cases, man-related sources such as septic tanks or commercial/industrial contaminants may be influencing groundwater chemistry.

Constituents of Concern

As discussed above, inorganic constituents of concern include uranium, arsenic, iron, and manganese. Although naturally occurring and typically related to the granitic rocks of the Sierra Nevada, elevated concentrations of gross alpha uranium and arsenic have rendered some sources of supply non-potable (Table 8). Elevated concentrations of iron and manganese seem to correlate to elevated turbidity in the sample and may indicate iron and manganese that are in soil/rock particles in the sample and not actually dissolved in the water. If not in solution, the iron and manganese concentrations reported on Tables 8 and 9 are higher than actual levels in drinking water and may not pose a problem.

Although nitrate data were not compiled for many of the water systems, numerous septic systems in eastern Madera County suggest that this is likely a chemical of concern in some areas. Water quality analyses in western Madera County noted septic systems and sewage percolation ponds as a possible source of elevated nitrates in wells. Data from the Miami Creek Knolls water system (MD43) indicate elevated nitrate levels up to 43 ppm in one well, close to the maximum contaminant level of 45 ppm.

Increasing development in the foothills has brought increasing risk for man-related contamination of the groundwater supply. For example, Yosemite Springs Park Utility Company had to curtail use of one well because of contamination from MTBE, an oxygenate recently added to automobile gasoline. MTBE has also been detected in Bass Lake. Monitoring of water systems in eastern Madera County is generally excellent for coliform bacteria and general minerals. However, analyses of additional constituents may need to be added to monitoring programs to protect the groundwater supply from increasing development.

CONCLUSIONS AND RECOMMENDATIONS

The overall water balance and current water demands in the foothill region suggest that a sufficient quantity of water is available on a regional basis to meet current demands and support some future development. However, the concentration of foothill development (such as Oakhurst) in the upland portion of a relatively small watershed, , is causing water demands to become a significant portion of estimated groundwater recharge. Planning for future development needs to examine the hydrologic conditions on a localized watershed and subwatershed basis in order to ensure an adequate water supply for local and downstream uses.

Well yields in most fractured bedrock aquifers are typically in the range of 1 to 50 gpm on a long-term sustained basis. Several wells in the Madera County foothill region are reported to have well yields in excess of 50 gpm, but the long-term viability of this production is not known. Often several wells are drilled to find a well with an adequate yield. This practice may distort well yield reports since wells with insufficient yield are abandoned and are not accounted for in the water system inspection reports. Wells located near streams may also indicate a higher yield since local recharge may be enhanced.

Based on a detailed review of 1,492 of 4,609 well log records in the foothill region, the median well yield is 8.5 gpm and average well yield is 22 gpm. These well yields are based on drillers airlift tests and actual production may be lower. In terms of future development, caution should be used in assigning well yields to determine the amount of water available from a given well. In particular, bedrock well yields in excess of 10 to 20 gpm (and especially greater than 50 gpm) should be evaluated in more detail by means of 72-hour pumping tests with a consistent and constant pumping rate. Generation and analysis of a time versus drawdown curve by a qualified hydrogeologist from properly- conducted pumping tests are the best means of assigning a sustainable well yield.

Groundwater quality in the foothill region is generally good in terms of inorganic constituents with typical groundwater TDS values ranging from 100 to 300 ppm. However, certain wells have encountered very high TDS levels with an increasing trend over time; the cause of this increase is unknown. Other significant groundwater quality problems at some wells include high levels of uranium, fluoride, and arsenic. Water treatment and/or blending is used to address various water quality problems. It should be noted that the potential for future development in some areas could be limited by water quality problems, and each new development proposal should be evaluated within a watershed framework.

Challenges exist to additional groundwater development with respect to quantity and quality. To adequately evaluate water resources in eastern Madera County the following minimum steps should be taken:

1) Establish a water level monitoring program that incorporates selected key wells. Both static water level (non-pumping) and pumping water levels should be collected. Water level data should be collected on at least a quarterly basis, but monthly water levels are preferable. All historical water level data should be compiled and analyzed with respect to the data collected on well yield, pumping, and groundwater quality.

2) Conduct a detailed water balance on the watersheds containing the most development, including the Fresno River and the Willow Creek watersheds. Detailed streamflow, pumping, spring discharge, precipitation, and evaporation should be evaluated to determine likely areas and amounts of groundwater recharge and change in groundwater storage. These evaluations would assist in determining a perennial yield for the watersheds.

3) Evaluate well yields for new water uses with 72-hour pumping tests conducted at a constant rate, including collection of several hours of recovery data. Tests should be conducted and analyzed by a qualified hydrogeologist.

4) Evaluate the adequacy of water quality monitoring in the foothill area considering septic systems and commercial/industrial development. Conduct additional studies and sampling of high TDS production wells to further evaluate the cause of high TDS levels that show an increasing trend over time.

5) Consider adopting a county ordinance (similar to Monterey County) that requires new development proposals to include a detailed hydrogeologic study of the watershed prior to permit approval. Primary components of each study should include assessment of the existing and proposed water demands, well yields, the water balance, and water quality.

6) Conduct a detailed and field-oriented study of aquifers in the highly developed watersheds that incorporates some elements of the USGS study in nearby Wawona.

REFERENCES

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Beck, Joe, Special Districts Emergency Preparedness Status, memorandum to Mike Kirn, County Engineer, April 18, 2001.

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California Department of Health Services, Drinking Water Field Operations Branch, Annual Inspection of Madera County Service Area No. 1, Indian Lakes Estates Water System No. 2010011, Madera County, October 10, 2000.

California Department of Health Services, Drinking Water Field Operations Branch, Annual Inspection of Hillview-Goldside Water System, Hillview Water Company Water System No. 2010014, Madera County, June 13, 2001.

California Department of Health Services, Drinking Water Field Operations Branch, Annual Inspection of Raymond Water System, Hillview Water Company Water System No. 2010012, Madera County, March 9, 2001.

California Department of Health Services, Drinking Water Field Operations Branch, Annual Inspection of Coarsegold Highlands Water System, Hillview Water Company Water System No. 2010013, Madera County, April 19, 2001.

California Department of Health Services, Drinking Water Field Operations Branch, Annual Inspection Hillview Oakhurst – Sierra Lakes Water System No. 2010007, November 30, 1999.

California Department of Health Services, Drinking Water Field Operations Branch, Annual Inspection Bass Lake Water Company, June 7, 1995.

California Department of Health Services, Drinking Water Field Operations Branch, Yosemite Springs Park Utility Company, Annual Water System Inspection, System No. 2010005, Madera County, May 8, 2001.

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California Department of Water Resources (DWR), San Joaquin District, Hard-Rock Wells in the Sierra Nevada, October 1990b.

Domenico, P.A., and F.W. Schwartz, Physical and Chemical Hydrogeology, John Wiley & Sons, New York, 1990.

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Draft Technical Memorandum

March 2002

Emeryville, CA

TABLE OF CONTENTS

INTRODUCTION................................................................................................................. 1

Objectives................................................................................................................... 1

Data Sources............................................................................................................... 1 ...............................................................................................................................................

List of Figures

Appendices

A. Water Quality Plots