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Table 17
BORON CONTENT FOR IRRIGATION WATER-/
from Ayers, R. S. and Branson, R. L. (1974).
Boron Content (mg/l) Remarks
<0.5 Satisfactory for all crops
0.5 - 1.0 Satisfactory for most crops; sensitive crops may show leaf injury but yields may not be affected.
1.0 - 2.0 Satisfactory for semitolerant crops. Sensitive crops usually show reduced yield and vigor.
2.0 - 10.0 Only tolerant crops produce satisfactory yields.
West of Dry Creek, Well No. lON/lOW-27D2 was drilled into a mass of Jura-Cretaceous ultramafic rock. The presence of 13.36 mg/1 of boron is typical of ground water affected by water contained in an ultramafic mass. Wells in the southern parts of Petaluma and Sonoma Valleys contain excessive boron due to the presence of sea water which has intruded the water-bearing materials. Wells tapping thermal waters, such as those at Boyes Springs, also yield water containing excessive boron. In these instances, boron is attributed to juvenile water rising along fault zones and commingling with percolating ground water.
A few wells, such as No. 8N/9WlORl, tap the Glen Ellen Formation and do not appear to be located along any mapped fault trace. The presence of boron in this well may be due to ground water percolating laterally through old soil horizons containing large quantities of the highly soluble boron salts.
Hazardous quantities of boron in shallow wells such as No. lON/9W18R1, which is 14 feet (4 meters) deep, are probably due to direct infiltration of surface water containing large concentrations of boron. Table 19 presents boron concentrations in surface water available for recharge. Boron concentrations are highest during periods of low flows and, conversely, are lowest during periods of high winter runoff. Moreover, some streams draining areas of thermal springs, such as Big Sulfur Creek which drains The Geysers area, contribute significant quantities of boron to the Russian River system.
Table l9
BORON CONCENTRATIONS IN SURFACE WATER AVAILABLE FOR RECHARGE
Stream : Sampling Station: Discharge : Boron Concentration
: Location : (cfs) (cumec): (mg/l )
Russian River 8N/lOW-32C 20,800 589 2 Oo 883
9N/9W-22H 14,500 410.7
228 6.5
0.17
0.93
Unnamed Creek Tributary 9N/9W-20H 10 0.3 0.58
to Dry Creek
Warm Springs Creek lON/lOW-18 - - 0.10
- - 2.8
Dry Creek lON/llW-11 - - 0.53
Big Sulfur Creek ll N/ll W-5 8 O. 2 0. 51
Sodium Hazard
Water with a relatively high concentration of sodium ion will tend to deflocculate, or "puddle", soils and form a hard crust after irrigating; hence, it results in adverse effects on filth, permeability, and infiltration. The degree of sodium hazard in ground water is determined by its Adjusted Sodium Adsorption Ratio (ASAR). This ratio is computed by the following formula:
ASAR = Na+[ 1 + (8.4 - pHc)]/ (Ca++ + Mg++)1/2
where the values of the mineral constituents are reported in milliequivalents per liter (me/l) and the quantity pHc is determined from the values shown on Table 20. The concept of the ASAR is similar to that of the Sodium Adsorption Ratio, with the addition of the effects by carbonate and bicarbonate ions. The ASAR evaluates the tendency of irrigation water to dissolve lime from the soil (when pHc values are above 8.4) or precipitate lime from irrigation water when the pHc value is below 8.4.
A rough determination of sodium hazard can be ascertained by relating the ASAR value and the specific conductance of the water as measured in micromhos. This relationship is presented on Table 21. Ideally, water intended for agricultural use should have only a minimum concentration of sodium ions and consequently a larger amount of calcium and magnesium ions. This is just the opposite of the ideal water intended for domestic use.
Sodium is the dominant cation in much of the ground water in Sonoma County. Excessive amounts of this ion may cause a significant decrease in the permeability of agricultural soils receiving irrigation water. The presence of excessive amounts of sodium ion in ground water is due to the phenomenon of cation exchange as the water percolates through clay-rich sediments. Ground water containing calcium ion reacts with the clays according to the formula:
2 NaX + Ca++ = CaX2 + 2 Na+
where X represents a unit of exchange capacity in the solid phase material. Calcium ion becomes adsorbed by the clay minerals in exchange for sodium ion, which is released to the ground water. The analysis from Well No. 6N/7W-17E1 on Table 22 is typical of ground water that has undergone this cation exchange.
One measure of the salinity hazard in agricultural water is its electrical conductivity. Plants sensitive to salinity are those which require a specific conductance of less than 250 micromhos; plants in this group include berries, fruit trees, and clover. Moderately tolerant crops are those which can tolerate water with specific conductances of up to 750 micromhos; plants in this group include grapes and most vegetables and forage crops. Tolerant crops are those which can use water with conductivities greater than 750 micromhos; these include asparagus and hay.
The salinity of domestic water supplies is measured by the content of chloride ion. In this case, the California Administrative Code recommends that the maximum concentration of chloride ion in drinking water be 250 mg/1. Water containing more than 250 of chloride ion usually has a noticeably salty taste. None the major water purveyors deliver water containing chloride excess of 250 mg/1.
Saline ground water found in Sonoma County is attributable to a number of different sources. In alluvial areas adjacent to bodies of salt water, such as the lower Russian River Valley, lower Petaluma Valley, and Bodega Bay area, salt water wedges have moved inland along the basal portions of freshwater aquifers, causing sea water intrusion. The analysis from Well No. 7N/llW-16 shows a chloride concentration of 2,920 mg/1 on Table 23, a condition that is indicative of wells which tap intruded aquifers. The distance inland that the salt water wedge extends depends on the amount of pumpage from the aquifer and the amount of fresh water that is available locally to repel the intrusion. Areas of sea water intrusion are shown on Figure 21. Almost all wells in these intruded areas produce sodium-magnesium chloride water of questionable suitability.
Sodium chloride water also is reported from some wells tapping the Petaluma Formation, as well as from a few other formations of marine origin. Nine inland wells yield sodium chloride water; analyses from selected wells of this group are presented on Table 23. The source of the chloride ion has not been determined for most of these wells; those located close to marine sediments presumably derive their chloride concentration from those sediments.
The presence of excessive iron and manganese in ground water is reported to be fairly widespread throughout Sonoma County. Both of these impurities can impart a metallic taste to water or to food prepared with such water. The metallic impurities may also stain fixtures, fabrics, and utensils. Soaps and detergents cannot remove such stains, and bleaches serve only to intensify them. After a prolonged time, the iron and manganese deposits which build up in pressure tanks, water heaters, and pipes reduce the available quantity and pressure of the water supply .
In the past, many mineral analyses of water from wells did not include these two constituents because of difficulties in preparing samples so that the two minerals would not precipitate before analysis. Hence, only a few analyses show iron in excess of the 0.3 mg/1 recommended limit or manganese in excess of the 0.5 mg/1 recommended limit. Wells producing water above the recommended limits are shown on Figure 21.
The California Administrative Code provides for limits in the amount of iron and manganese in drinking water. The limits are for esthetic and taste reasons, and excessive iron and manganese do not constitute a serious detriment to the purity of drinking water. Excessive amounts of iron in water combine with oxygen
from the air to form a reddish-brown insoluble precipitate which resembles rust. Manganese acts in a similar manner, but forms a brownish-black precipitate.
Under certain conditions dissolved iron and oxygen in the water promote the growth of iron bacteria. The result is a slimy, rust- colored mass which clings to the interior walls of tanks and pipes. These bacteria can also impart an unpleasant taste and odor to the water and discolor fabrics.
Iron and manganese can be removed from water supplies by a combination of chlorination and fine filtration. The chlorine oxidizes the iron and manganese to form insoluble precipitates and kills any iron bacteria present. The filter then removes the iron and manganese precipitates, leaving the water clear and potable.
Iron is one of the most abundant mineral constituents of rocks and soils. In sandstones, iron oxide, carbonate, and hydroxide are often present in the cementing material in appreciable percentages. Iron also is present as oxide, carbonate, and sulfide in shales. In addition to solution from natural sources, iron also may be added to ground water from its contact with well casing, pump parts, piping, storage tanks, and other iron objects which come in contact with the water. Suspended sediment in surface waters also may contain iron.
Iron occurs in water at two levels of oxidation, either as bivalent ferrous ion (Fe++) or as trivalent ferric ion (Fe+++). The chemical behavior of the two forms is somewhat different, although both may be present in the same solution under certain circumstances. Under reducing conditions, iron in natural ground water will tend to be in the ferrous state. Ferrous salts, however, are unstable in the presence of oxygen or air. They are changed to the ferric state through oxidation when natural water containing both ferrous and bicarbonate ions comes in contact with air. In this situation, insoluble ferric hydroxide precipitates and carbon dioxide gas is liberated according to the following formula:
4Fe++ + 8HC03- +2H20 + O2 -> 4Fe (OH)3 + 8CO2
Sedimentary rocks frequently contain manganese oxides and hydroxides. These constituents have been concentrated through the removal of more soluble minerals and frequently are found in association with iron oxides. There also is a tendency for manganese to accumulate in soils that are formed from rock weathering. This condition is true whether the soils are present- day or whether they are old soil horizons that now are buried.
Manganese found in ground water is probably most often the result of solution of manganese from soils and sediments aided by bacteria Like iron, manganese occurs in more than one state of oxidation. The oxidation states of manganese in ground water are the bivalent, Mn++, and quadrivalent, Mn+4, states. Manganese can also occur in more highly oxidized states (Mn+6 and Mn+7), but it is not normally encountered in these forms in natural water. Under reducing conditions, manganese can be taken into solution in ground water containing carbon dioxide in a manner analogous to iron. In the quadrivalent form as manganic hydroxide, Mn(OH)4, manganese is nearly insoluble, and it is carried in colloidal suspension in a manner similar to ferric hydroxide. Thus, like iron, when ground water containing both manganous and bicarbonate ions comes in contact with air, an insoluble manganic hydroxide precipitates and carbon dioxide is liberated according to the following formula:
2Mn + 4HCO3- + 2H2O + O2 -> 2Mn (OH)4 + 4CO2
In some parts of California, water rich in iron and manganese occurs near the bottoms of various individual aquifers. Because iron and manganese are relatively heavy, they tend to settle in an aquifer until they are concentrated just above a lower clay member. Hence, water drawn from a well perforated near the bottom of an aquifer would tend to have greater concentrations of iron and manganese than another well perforated at a higher zone in the same aquifer.
Hem (1959) reported on a number of studies of nitrate in water supplies. These studies linked nitrate in ground water to methemoglobinemia, or cyanosis, in infants whose feeding formulas are mixed with these waters. Waters containing an excessive amount of nitrate ion may also contain nitrite ion in excess of 1 mg/1, which according the the U. S. Environmental Protection Agency (1973) is even more hazardous to infants.
Nitrate compounds in ground water frequently may be attributed to pollution from surface sources such as septic tanks or livestock areas. Because of this situation, sanitary seals in water wells used for domestic purposes are mandatory. Analyses of ground water in Sonoma County indicate that nine wells yield ground water containing nitrate ion in excess of the California Administrative Code recommended limit of 45 mg/1 (10 mg/1 expressed as nitrogen); the locations of the wells are shown on Figure 21.
The amount of total dissolved solids in water indicates the total mineralization of the water. All excellent quality water contains less than 500 mg/1 total dissolved solids. Water containing an excessive amount of total dissolved solids may also be expected to exhibit other water quality hazards, usually excess chloride ion. Ground water in Sonoma County ranges in total dissolved solids from a low of 129 mg/1 at Well No. llN/lOW-33Gl, which produces an excellent quality calcium bicarbonate water from terrace materials, to a high of 4,301 mg/1 at Well No. 5N/7W-24B1, which produces an unacceptable quality water that has been affected by sea water intrusion. Areas of excessive total dissoved solids are shown on Figure 22.
Ground water containing calcium and magnesium salts is divided into two general hardness classifications: carbonate and noncarbonate. Carbonate hardness becomes apparent after water has been heated. Heating reconstitutes the soluble calcium and magnesium bicarbonates into precipitates of insoluble carbonates. The precipitates adhere to heated surfaces, such as the inside of water heaters and hot water pipes, and ultimately cause a reduction in the capacity of the fixture. Noncarbonate hardness is not affected by heat, as it is principally caused by the presence of calcium sulfate. Both forms of hardness reduce the cleansing ability of many soaps and detergents.
Water softening is a process for the removal of the hardness-forming mineral constituents in water. Most domestic water softeners are of the ion-exchange type. In this process, the calcium and magnesium ions are adsorbed by an ion-exchange material in exchange for sodium ions. The resulting water then is relatively rich in sodium ion and is termed "soft".
Hardness of ground water is the major domestic and municipal water quality hazard in Sonoma County. Ground water in the county ranges from very soft to extremely hard. Three hardness ranges are depicted on Figure 21: Soft waters are those with a hardness of less than 100 mg/1; moderately hard waters are those with a hardness range of from 101 to 200 mg/1; and hard waters are those which have a hardness in excess of 200 mg/1.
Extremes of ground water hardness are illustrated by the analysis of very soft water from Well No. 5N/6W-30D1, which has a total hardness of 8 mg/1. In contrast, the analyses from Well No. 4N/6W-33R1 indicate that this is a very hard water; the total hardness is 1,970 mg/1 and the noncarbonate hardness is 1,500 mg/1.
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