AU740218B2 - Stormwater dispersing chambers - Google Patents

Description

Our Ref:7518930 P/00/011 Regulation 3:2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): Address for Service: Infiltrator Systems, Inc.

4 Business Park Road PO Box 768 Old Saybrook Connecticut 06475 United States of America DAVIES COLLISON CAVE Patent Trade Mark Attorneys Level 10, 10 Barrack Street SYDNEY NSW 2000 Stormwater dispersing chambers Invention Title: The following statement is a full description of this invention, including the best method of performing it known to me:- 5020 S1VR4MWER DISPESIIM CHAMBERS DESCRIPT ION The present invention relates to means for dispersing liquids in gjranular materials'; more particuiarly7, to systems for dispersing storm wdaters within soil of the earth.

In urban and industrial developmeont, enqineers often provide Tor kia.,4li', the volumes of rainwater which tall upon the earth. firom time. to t--ime. Traditionally, large seorm sewers, with or without surface detention k~pasins, have been used. However, there are adverse environmental effects from such.'They include the costs of land used for detention basins, lake and stream pollution and erosion due to storm sewer runoff, and lowering of Local water tables when water is diverted from percolating into tha earth.

:Consequently, it is desirable to direct storm water into the earth.

This has been done, such as by using large gravel or crushed stone filled T-rertches, with ar-d without perforated pipes running through the stone.

Stone filled systems are inefficient in that the stoeo occupies a substantial part of the trench void, thus limiting the ability of the system to handle large surge volumes associated with heavy storms. And b~oth the stone and the perforated pipe are susceptible to clogging by dlebris carried by water.

*Arch shaped molded plastic leaching chambers, especially those sold under the Infiltrator brand name, and having design features like those shown in various patents mentioned herein, have met wide commercial success in the USA, especially for dispersing the waters associated with domestic I8930se.doc.29 Augum 2001 -2sewage systems. Such leaching chambers have also been used in receiving storm waters, detaining them for regulated flow, and for dispensing them beneath the surface of the earth. Typically, the chambers are laid side by side in parallel rows. They rest on and are surrounded by gravel or crushed stone. While such installations provide greater void volume than the stone trench systems, and have been in many instances satisfactory, further improvements are desirable as indicated just below.

Subsurface storm water systems using known technology can take up large surface areas, since a normal design criterion is that the system be able to handle and store for gradual dispersal of a large volume of rainwater. Thus, where land is expensive it is very desirable to maximise various aims. Among those aims are First, the volumetric storage capacity of the system on a unit land surface area basis should be maximised. Second, the system should be adapted to resist the loads imposed by other uses of the surface of the land, most commonly for motor vehicle parking or driving. Third, the system should be resistant to clogging and degradation caused by sand, dirt and other debris which may be carried along with the water. And, of course, the system should be economic, durable and maintainable.

According to one aspect of the present invention there is provided a chamber for 20 dispersing liquid when buried beneath soil, of the type wherein the chamber has an arch :o shaped cross section defining a hollow chamber interior, a base, opposing inward sloping sidewalls having substantially spaced apart sidewall upper ends, each sidewall running from the base to a curving arch shape top which connects said sidewall upper ends, and corrugations comprised of peaks and valleys running up the opposing sidewalls of the 0 25 chamber and transverse to the length of the chamber, the improvement which comprises: "i the chamber having a cross section aspect ratio of at least about 0.7 to 1, where aspect ratio is the ratio between the chamber height and chamber width measured at the base.

According to another aspect of the present invention there is provided a chamber for dispersing liquid when buried beneath soil, of the type wherein the chamber has an arch shaped cross section defining a hollow chamber interior, a top, a base, opposing sidewalls P:IWpDoCs~dys\spmiea775l8930rpedc..9 Augus 2001 -2Arunning from the base to the top, and corrugations comprised of peaks and valleys running up the opposing sidewalls of the chamber and transverse to the length of the chamber, the improvement which comprises: the chamber having inward sloping sidewalls with a sidewall angle with the vertical plane of less than about 15 degrees; and, the chamber having a cross section aspect ratio of at least about 0.7 to 1, where aspect ratio is the ratio between the chamber height and chamber width measured at the base.

Preferably, the chamber has inward sloping sidewalls with a sidewall angle with the vertical plane of less than about 15 degrees, more preferably about 6 to 9 degrees.

Further, preferably, at least one of the peaks and valleys of the sidewall has an arcuate shape, as measured in a plane parallel to the base of the chamber.

*o P~fefblya subsurface stormwater systemu is comprised of chambers running paxallel to one another, with the space between any palr of chambers be,ng spanned by a bridge cover resting on Lmposts of the chambers. Preferably, the im~posts are tower than the' e-levation of the highest part of the top of the chamnber. The system is typically laid on a flat bed of stone or the like, and covered over. wimh.

mail or the like. The syratem has means for enabling flow of storu".ater between a chamber anid the space, such as perforations in a chambe= midewall. Water is preferably flowed first into the space bertween any chamber pair, and then Into the chambers, tc disperse or leach into the stone or sail at- the chamber bases.

:In preferred practice of the invention: Chambers have a height to width aspect- rar.io of 0.8:1 or more, and naidewail, angles with the ertical plane of less than 15 degrees, to provide strength and load carrying abIlity to the system. Chamber walls are arcuate, or bowed, aLs viewed in a horizontal cross section plane, to increase sidewall and system strength. The bridge covers are arched, and the h ighest ,part of th'e r-op of the bridge cover arch is at about the same elevation as the highest points of the chamabers. And, base flanges of adjacent chambers abut or interlock no defiLne the pitch of the chambers, thereby def ining the centert-o-Lcenter and impoat-to-imposz spacings of the chambers, -ahlle protecting the material at the bottom of the space from erosion due to liquid falling into the space, when the flanges are continuous along the length of the chamber bases.

The means for enabling flow between the space and the *adjacent.chambers is preferably perforations in the sidewalls of the chambers. More preferably, the perforations are only located at an elevation higher than~ aoccumuluates in a cavity at thie bottom of' the apace, and then flows into the chambers, thereby induacing some of dirt' and debris in the w.'ater to settle out in the cavity.

Further, -in the pref erred practice of -the invention: The enids of t--he chambers, am well as the ends of the spaces between adjacent: chambers, are cloibed by endplates. Pipes fit openings in the endplates of the spaces, to deliver storinwater to the chambere ass embly. Xt Ls.

intended that debris accumulate in the space and thus, in another aspect of the invention, means, such as a pipe with perforations, Le laid at the bottom of then space. Water flowed through the pip%- is usmed to agitate and suspend the debris, which then preferably flows out the same pipe to a discharge point, such as a sump- **The invention efficiently receives, stores, and disperses; storat :waters, and it in particularly strong. The chambers are economical, 4durable, ef ficiently. shipped and easily installed.

3FIg. I is a perspective end view of part of a stormwater. chamber, with a cover bridge, and. with an adjacent chamber shown in phantom.

Pig. 2 is an and view of a pair of adjacent chambers buried within soil, having a cover bridge spanning the space between them.

Fig. 3 is a perspective view of the ends of an array of parallel lying =hambers having endplates, showing how stormwater is delivered by jpipes to the spaces between the chambers.

Fax f rom: 10/88/88 03:04 Fig. 4 is a horizontal plane cross section of part of the-sidewall of the chamber of Fig. 1, -showing the arcuate shape..of the sidewall.

Fig. 5 shows how the ends of chambers mate with a strong joint, when put together as a string of chambers.

Fig. 6 shows an endplate for one of the spaces between a chamber pair.

Fig. 7 shows in vertical transverse plane section how an impost has a buttress to better retain an arch shape bridge cover in place.

Fig. 8 shows a non-corrugated chamber with a relatively flat top and a lintel type bridge cover.

Fig. 9 shows in end view a system where a bridge covers is supported on.

the very tops of the adjacent chambers, the chamber base flanges intefrock, and there are internal struts to strengthen the cover.

Fig. 10 shows in perspective cross section part of the peak section of chamber 20 of Fig. 1, revealing internal strengthening ribs.

Be. Fig. 11 shows an end 'cross section of the space between.two chambers where debris and a conduit lie at the bottom of the space.

Fig. 12 shows an longitudinal cross section of the space shown in Fig. 11, together with th6 conduits which enable. water to be Introduced into the space and the resultant suspended debris to be removed by gravity flow to a Dum'p.

The stormwater chambers of the Invention have many structural and material characteristics like molded plastic leaching chambers known in the prior art. Reference should be made to U.S. Patents No. 4,759,661, No.

5,401,116 and No. 5,401,459, having common ownership, and inventorship in part, the disclosures of which are hereby incorporated by reference.

Stormwater chambers of the present invention are preferably fabricated by gas-assisted injection molding of predominantly high density polyethylene, anid have plastic f low chinnelp, which also. aid strength, in accord witch Pat. No- 5,401,459 and the general art. Other plastic material and process conmbinations may be employed.

Typically, an array of chambers, sometimes called a "system", is Listalled by digging a hole in the earth and creating within it an emeentjially planar surface of gravel or crushed stone. The chambers are mated erid-to-end in-parallel rows and laid on the gravel surface. Afterthe system is inetalled in accord with the description below, It in covered w.,ith suitable soil. The following preferred embodiments of the invention acwe largely described in terms of two adjacent chambers, being illustrative of: a large system comprised of mavy parallel rowas of chambers.

An end fragment of a preferred chamber 20 is shown in Fig. 1, along w~ith a bridge covet SO and a portion of a like adjacent chamber 20A, in phantom. Fig. 2 shows the chamber 20 in end view .and paired w;Lth chamber and part of a larger array, as they appear installed on a gravel bed aind covered over with gravel or soil. Referring to both Figures, the otiamber 2'0 has an arch shape cross section and is corrugated, with alternating peaks 24 and valleys 26 running up the opposing sidewall. 28 anid across the top of the arch shape cross section. Peaks and valleys aLxe connect-ed by webs 35. The highest point of the top has a height h and t~le base has a nominal width w. Stiffeninag webs, such as ribs 32, are used on the exterior and interior of the chamber, for additional strengthening, am generally taught by the )prior art. When using the gas assisted ~Injection molding process some of the ribs and other chamnber parts will be desirably hollow. The chamber 20 has a base 22 with flanges 30 extending laterally outward, for supporting the chamber and resisting vertical loads, arid for t-hu other purposes described below. Ribs 31 strengthen the base fElange.

6 Pre ferred* ch ambers have ad arch shaped. cross section and are about 2.2 m~ long, 86 cm wide and 76 cm" high. They are designed to nest, one within the other, for easy shipping. Familiar commercial leaching chamzbers of the type described in the aforementioned patents and others commercially known kiave comparatively low aspect ration in the range 0.36 to 0.65. where aspect ratio of height h to nominal base width w. Width w is measured b~atween the opposiig outermost (peak) parts of -the videwalls9, where they Lintersect the base; and this dimension is nominally; the same as thas width wpeasured between the outermost edges of the flanges 30 in most c:KaAsbrs, =mince moat chambers do not have exceptionally wide flanges- In the invention, the aspect ratio is. high, preferably greater than.

0-7:1, more preferably about 1:1. Table I compares the dimensions and akapect ratios of prior art with the present invention. 'the high aspect ratio invention chambers are generally useful for 1liaching without using t-he bridge covers feature, as prior art chambers are. The invention ahambers provide superior strength and improved liquid disperal at the n Ldewall relative to the base. They are especially suited for arid soils, anid reduce the surface area of land which must be utilized for-.a given dlomestic sewage leaching capacity. A1n array of parallel chambers can be b~uried within crushed stone for stormwater dispersal.

The preferred high aspect ratio chamzber- ha. aidewalls 28 runntag upwardly at a nominal angle, measured from the vertical plane, in the range <of 6.3 to 8.7 degrees. Because, as described herein, sidewalls are arcuate iLn the horizontal plane, the nominal sidewall angle Is determined from the khypothetical Inclined plane which rests on the tops of the. peaks, or in the bases of the arcuate valleys, as the case may be, as they run vertically up 1te sidewall. And, while current comxnerciAl practice is mostly to make the aldewalls essentially straight when viewed in end cross section. some .7 4comnexcial cbamber sidewalls -have a curved arch shape when viewed in end Cirosp section. For such, tlje'sidewall angle plane might be taken as A. best :Eit, or in limiting cases, there.is, no Ascertainable aidewall angle in the =context of this aspect of the present invention. The most. pref erred Ta.-ble 1. Typical/nominal paranetere of leaching chambers.

chamber Produact Sidewall (degree)

W

-inch---- Aspect Ratio h/u

IMS

C330 SD I

BVII

Pat.

ISIS

Isla no. 5,441, 363' No. 5,087,151 13 30.S 10- 11 12 712 12 16 33 33.3 34 52 20w 34 34 1l.5* 34 34 34 74.9 0.36 75 0.54 84 0.39 90 0.64 0.50 77 0-32 76 0.35 0.65 90 0.35 75 0.35 75 0.47 Typical Invention 30 30 87 0.99 Legend: W width, the maxiipum wall-to-wall sPacing at the plane h maximum height of a chamber peak measured from plane I. length =arbitrary units from scaling of patent drawing *0-no data.

of chamber base of base =kiamber of the present invention has an essentlially straight sidewall, viewed in cross sectional plane, with an angle of 8 degrees from the -vaertieal. This incline compares to prior art chamber sidewall angles of :f rom 15 to 22 degrees. The sidewalls of the invention are thus more nearly %rwrtical. In the generality of the invention chambrs wi'll have a nominal midewall angle of lean than -15 degrees, preferably in the range S-14 deggrees, more preferably about 7-9 degrees, as measured from the vertical longitudinal plane of the chamber. The combination of both higher aspect iratio and lessner sidewall angle, compared to leaching chambers heretofore Limed in storm water systems, provides superior strength and increases the l-oad which the brIdge cover and thus the system can bear.

TAO opposing 3iderwalls 28 of the chamber 20 have 'perforations 29 in the p: form of about 3.2 cm diameter holes. They are located in either or both the rallyr, and peaks of the sidewalls. The lowermost perforation is at- an emlevation* of about 38 cm, from the base f or reasons described below.'- To ]provids stiffness and buckling resistance,,the peak and valley corrugations car the sidewalls, are arcuateo preferably bowed outwardly (concave side '0009, facing the chamber interior) with radii of* about S. 3 Inch, an viewed in the off* hiorizontal cross section plane of the chamber, and an illustrated by the mid-elevation horizontal plane cross section of chamber sidewall in Fig. 4- 6 Sewhen chambers are buried in the earth, the outermost sidewalls of the system will of course not have bridge covers. The perforations in any such sidewalls are either plugged or covered with a fabric to prevent intrusion o~f the covering earth.

Referring again to Fig. I. and 2, the top of the chamber 20 has peaks and valleys which are continuations of peaks and valleys of the opposing oidewalls; the top comprises nominal segments of a circular arch-. imzposts 34, in the form of flat ledges, are molded into the chamber at the upper ezid of the sidewall, where the curved arch segments of the top of the ehaaber atart, to receive a: bridge cover 50 as detA~led below. In other iernbodiznentn, the imuposts may be located higher -up, on the top, or- lower 4down the sidewall.

As in the cited prior art patents, chambers have mating ends -and are =c~nnected one to the other to form strings; and, the mating ends overlap agmd interlock as illustrated by the fragments of mating chambera 208 and 21 ±rjn F ig. 5. (The end joint interlocking features are omitted fro~m Fig.. 1 focr clarity.) Fig. S shows how the end of chamber 21, overlaps the f lange Vportion 40 of the end of the chamber 205; And, typical leg 42 overlaps oe*o c~framber 21 at the joint, to streng-then the connection, in accord withi the principles taught; by U.S. Pat. No. S,401,116 and other prior art.

rLkewiue, the briLdge c overs, which typically axe half the length of the chamber, are preferably provided With ends which overlap to prevent 0.0 infiltratilon of soil, and they may also be interlocked with each other to 00.. increas vertical load resistance.

0 'Strings of chambers are installed side by side, running In jiarallel iro'.'s, at predetermined spacing. Preferably, the chamaber-to-chamber spacing 0 0 0 La determined b'y buttiLng the flanges 30, 30A of adjacent chamber=, as shown 0* iLn Figs. 2~ and 2. The shape and spacing of the sJidewalls of the abuxting oooos:chambers defines the width of the space 36 therebetween and the spacing of the impost.. when in place, a corrugated arch shape bridge cover 50 rests iapcn and Is supported by the imposts of adjacent parallel chambers. The bridge cover fits and laps onto the impost surfaces in a way designed to Aprevent passage of soil or gravel into the space between the chambers from above. M~ost simply, the bridge cover is molded in one piece without perforatilon. and Is impermeable to soil or water.

Fig. 1 illueitratep -how the preferred impost is continuous, with a portion running along the top of typical web 35 connecting a peak rcorrugation with a valley corrugation..- In the preferred embodiment, the i.apost is a ledge and the bridge cover outer edge runs continuously along the ledge. Within the generality of the inventi.on, an impost is a reature of the chamber exterior surface which is adapted to receive and Locate a bridge cover and provide vertical support. Preferably, it provides remiatance to lateral motion 'when. cooperating with the bridge cover featurea'wherie it contacts the Impost. Alternative kinds of iisposts may comprise such integral features as Ylats, ridges, pi, bosses, c-avitias auid holes in the chamber wail. For such alternatives the bridge cover will have appropriate mating feature.

:Fig. 10 shows how the Impost 34 and general structure in vicinity of.

t ehe peak corrugation 2 4 in strengthened by ribs 50, 62 running lengthwi.se_ along the chamber and smaller gusset ribs -84 under the impost running bietween the top of t-he web and the underside of the impost.

Fig. 9 shows *an- unperforated arch shape molded bridge cover resting an impost surfaces 75 ait the tops of adjacent perforated-wall chambers 72.

Vertical fins 74 running lengthwise along the chamber top define the Inner edge. of the opposing imposts on the chamber top, and restrain the bridge covers from lateral. motion, anm discumnd below.

Preferably, as showyn in Fig. 2, the very top of the arch of the bridge cover is at the same elevation am the very top of the arches of the chambers, to provide a relatively even surface and maximize system storage capacity for a given depth of system. Ina the generality Of 'the invention, the top of the bridge cover way be either higher or lower than the tops of the chamber arches.

When an arch shape bridge cover rests on the imposts and vertical loads are applied, nuph as from a motor vehicle passing across the earth I

V'.

ajbove, -an arch shape coxeC bridge will tend to flatten out and expand in w;jdth. Thu s, the edge of the cover bridge will tend to move, laterally, itc bear against the curved rising part of the. chamber top, so the mot ion~ Will be resisd to a degree.' Even better resistance to lateral deflectIon isz obtained when a protrusion, such as buttress. 58 is molded Into the =ctaber'adjaceflt the impost, ao shown i.n Fig., 7. See also fins 74 inl Fig.

Alternative Lateral restraint means, such as, screws or pins may also be emsployed, provided there is accomodation for slight relative mtibn of the lparts under changes in vertical load, to avoid lo6cal failure of thie plastic icbaxnber or bridge cover material. In alternative embodiments, the bridge coover malt have molded plastic tabs or pin. that engage mating features. in :vicin'ity 'of the Imposts. In st-ill other embodiments,. Additional structural members, integral or separate from the bridge vover, may improve vertical 00strength of the brIage cover. For instance, strut -mesmbers may extend vwertically from the bottomumost of the space between the chambers, or struts 7 6 may angle up from, the. chamber walls, as shown In Fig. 9.

A chamber embodying the invention principles may have amooth rxather than corrugated sidewalls and top, as shown for chamber 60O in Fig.

6.and, bridge covers may have cross section shapes other than the.

preferred arch shape. For instance, a lintel type bridge cover 62 is shown 00: In Fig. 8, where the lintel cross section is molded as a simple truss.

aind, while the bridge cover Is ordinarily unperforated and Impermeable, in some instances small perforations may be present to better enable any liquid above the system to percolate into it.

to the preferred embodiment, the width of the bridge cover the length of span from one impost to another) is a bit less than the width of the bases of the chambers on which the bridge cover rests, or the center-to-center distance between the chambers. In other embodiments, the bridge cover may be equal to or wider than either such.

Chambers may have varioUs Arch shape cross sections, including those wbich are rectangular, trapezoid, triangular, etc. Chambers may be molded w.,th integral closed ends, but preferably they have. open ends.- The eands of strings of chambers are typically closed by end plates 52 which fir.

iato the chamber end openings as shown In Fig. 3. Endplates are held in place by detente, screws or the. like. Bridge cover endplatee 54 having isimilar construction and function close of f the ends of the spaces 36 beatween adjacent chaibers. As w.ith' the chambers, the bridge cover 4er4plateB may be made integral, but preferably they are separate pieces.

OV'. Preferably, the bridge cover endplates have ports or openings 55. to :riceive pipes 56 carrying storaswater from catch basins to the chamber system. See Pigs. 3 and 6. Alternately, the bridge covers may have to=p openings, so Ithe stormwater is delivered vertically downward into the mpaces. Thus, water Ls preferably flowed to the chamber system by entering *hxough the space endplates and falling to thu bottom of spaces 36 betwreen the chamers. While water is preferably iniroduced by flowing it -directly into' Ithe spaces, it may be alternatively delivered into the chambers. or both.

It s not necessary that every space or chamber, an the case may be, have cirect delivery of storm water.

As mentioned, perforations 29 in the chamber sidewall Preferably are a clistance above the base, to create a cavity or pocket 31 at the bottom of ispace 36, near the chamber base where liquid introduced through openings will accumiulate before flowing through the perforations into the Interior of the chambers. See the arrows Indicating liquid flow in Fig. 2. Such construction enables a significant portion of the dirt and other debris carried by the water to settle out at the region or cavity 31 at the bottomn of the space 36 when the water is storm water is piped into the space.

Preferably, the chamber base flanges 30, 30A abut. to Set the centerto-center di.mension which fits the bridge covers, and they are continuous itic cover the soil at the bottom 'of the space 36 and protect it f roma beIng eroded by incoming water, or by auctioning away of debris if such means. is ewsployed. Abutting chamber f langes may be overlapped or engaged one with..

t:2ze cther along their lengths to l.imit lateral chamber movemnt and ensure positive locating, as illustrated for the flange connection 78 in Fig. 9.

Generally, flangea can be discontinuous, and irregular in lazeral dimension while serving the chamber apacinj funfction. When f laingems are not carstrucied to set chamber spacing, other built Ln gaging means, manual measuring, or other fixturing w~ay be used to achieve the spacing w.hich f its :the bri.dge co~rers.

The 'Chamber sidewall perforations preferably have a total area sufficient to enable good fluid flow or communication between r-he chambers and the spaces therebetween, relative to the size and capacity of the inlet pipe and chambers. Perforatione. -other than rousid holes may be used, such as slots. In the generality of the invent-ion, other means for connecting t-he chamber with the space than sidewall perforations may be used. For imicample, the parts of the system may be connected by external pilping; orc, when the settling cavity feature in the space is not required, the means may comprise cutocuts at the base flange.

Fig- 11 and 12 show how debris removal in conveniently enabled by a ]perforated pipe 90 laid in the bottom of the space 110 created by chambers 82, 84 and bridge cover 86. Settled out debris 99 is shown as ilt Wrould accustulate in the cavity at the bottom of the space. Thle pipe has a multiplicity of longitudinally spaced apart and downward facing holes 92.

To remove the debris a flexible, hose having a jet nozile is lowered down the channel 94, typically another pipe connected to pipe 90, so that it ipaea along the. lengrth of pipe 90 within the chabr to the desire eoctent. Pressur~ized water Issulng froma the nozzle flows through the holes 9;2, to agitate and temiporarily suspend the debris in the water in the cavity. When pressurized water flow is ceased, or-moved -to a. suff icientlyr distant point along the pipe, debris-laden water f lows out the pipe aIown the diversion channel 96 and into the sup 98. From there Lt may be iremnoved up access channel.100, typically, a .larger diameter pipe or shaft Xr% an alternate emboIment, the line 90 may be used only for agitating and a separate pipe or channel may be used for flowing the debris away.: *Throughou .t this' specification and the claims which follow,' unless the context requires otherwise, the word "comprise", and variations such as "comprises" or "comprisig ilb understood to imply' i ilb the 'inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

CThe reference to any prior. art in this specification is not, and should inot be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

Claims (9)

1. A chamber for dispersing liquid when buried beneath soil, of the type wherein the chamber has an arch shaped cross section defining a hollow chamber interior, a base, opposing inward sloping sidewalls having substantially spaced apart sidewall upper ends, each sidewall running from the base to a curving arch shape top which connects said sidewall upper ends, and corrugations comprised of peaks and valleys running up the opposing sidewalls of the chamber and transverse to the length of the chamber, the improvement which comprises: the chamber having a cross section aspect ratio of at least about 0.7 to 1, where aspect ratio is the ratio between the chamber height and chamber width measured at the base.

2. The improved chamber of claim 1, wherein said cross section aspect ratio is at least about 0.8 to 1.

3. The improved chamber of claim 2, wherein said cross section aspect ratio is about 1:1.

4. The improved chamber of claim 1, 2 or 3 wherein the chamber has inward sloping 20 sidewalls with a sidewall angle with the vertical plane of less than about 15 degrees.

5. The improved chamber of claim 4 wherein the sidewall angle is about 6 to 9 degrees. 25

6. The improved chamber of claim 4 wherein at least one of the peaks and valleys of the sidewall has an arcuate shape, as measured in a plane parallel to the base of the chamber.

7. A chamber for dispersing liquid when buried beneath soil, of the type wherein the chamber has an arch shaped cross section defining a hollow chamber interior, a top, a base, opposing sidewalls running from the base to the top, and corrugations comprised of peaks PA\WPD0CS\dys~rspec\7530spe doc-29 Agum 2001 -17- and valleys running up the opposing sidewalls of the chamber and transverse to the length of the chamber, the improvement which comprises: the chamber having inward sloping sidewalls with a sidewall angle with the vertical plane of less than about 15 degrees; and, the chamber having a cross section aspect ratio of at least about 0.7 to 1, where aspect ratio is the ratio between the chamber height and chamber width measured at the base.

8. The improved chamber of claim 7 wherein the sidewall angle is about 6 to 9 degrees.

9. A chamber for dispersing liquid substantially as hereinbefore described with reference to the accompanying drawings. Dated this 29" day of August, 2001 INFILTRATOR SYSTEMS, INC. By Its Patent Attorneys DAVIES COLLISON CAVE *ooo o 000o